Photoniques 116

N°116 

LIGHT AND APPLICATIONS 

LABWORK 

EXPERIMENT 

BACK TO BASICS 

BUYER'S GUIDE 

The Newton 

experiment revisited 

 

The first detection 

of the CMB 

The geometric phase 

made simple 

Nonlinear crystals for 

frequency conversion 

FOCUS ON 

OPTICAL 

MATERIALS 

• Halide perovskites for photonic applications 

• Lithium niobate on insulator from classical 

to quantum photonic devices 

• Narrow band gap nanocrystals for infrared 

cost-effective optoelectronics 

France/EU : 19 € Rest of the World : 25 €

Editorial 

Photoniques is published 

by the French Physical Society. 

La Société Française de Physique 

est une association loi 1901 

reconnue d’utilité publique par 

décret du 15 janvier 1881 

et déclarée en préfecture de Paris. 

https://www.sfpnet.fr/ 

33 rue Croulebarbe, 

75013 Paris, France 

Tel.: +33(0)1 44 08 67 10 

CPPAP : 0124 W 93286 

ISSN : 1629-4475, e-ISSN : 2269-8418 

www.photoniques.com 

The contents of Photoniques 

are elaborated under 

the scientific supervision 

of the French Optical Society. 

2 avenue Augustin Fresnel 

91127 Palaiseau Cedex, France 

Florence HADDOUCHE 

Secretary General Générale of the SFO 

florence.haddouche@institutoptique.fr 

Publishing Director 

Jean-Paul Duraud, General Secretary 

of the French Physical Society 

Editorial Staff 

Editor-in-Chief 

Nicolas Bonod 

nicolas.bonod@edpsciences.org 

Journal Manager 

Florence Anglézio 

florence.anglezio@edpsciences.org 

Editorial secretariat and layout 

Agence la Chamade 

https://agencelachamade.com/ 

Editorial board 

Pierre Baudoz (Observatoire de Paris), 

Marie-Begoña Lebrun - (Phasics), 

Benoît Cluzel - (Université de Bourgogne), 

Émilie Colin (Lumibird), Sara Ducci 

(Université de Paris), Céline Fiorini- 

Debuisschert (CEA), Riad Haidar (Onera), 

Patrice Le Boudec (IDIL Fibres Optiques), 

Christian Merry (Laser Components), 

François Piuzzi (Société Française de 

Physique), Marie-Claire Schanne-Klein 

(École polytechnique), Christophe 

Simon-Boisson (Thales LAS France), 

Ivan Testart (Photonics France). 

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Routage STAMP (95) 

Light, Matter and Entanglement 

Optics and material science 

share a long history of advances 

and development. 

The 2022 International Year of Glass 

reminded us how the development 

of glass over the different centuries 

has allowed optics and photonics to 

explore novel horizons. And the story 

is not over: this new century has seen 

a soaring rise of novel materials and 

an acceleration in discoveries. Low 

dimensional materials, perovskites, 

phase change materials, quantum 

dots, to cite only a few, have opened 

fresh research domains and attracted a 

keen and growing interest from a wide 

scientific community. Besides these 

novel materials, many efforts have 

been made to push forward the limits 

on the control of optical materials at 

the nanoscale. Integration, tunability, 

linear and/or non-linear properties 

and efficiencies, toxicity and affordability 

are key elements for developing 

novel optical materials. The long story 

of entanglement between optics and 

materials is far from waning and the 

last decade has even seen a tremendous 

acceleration of outcomes in this 

exciting and multidisciplinary field of 

research. The second quantum revolution, 

green photonics, the growing 

needs in energy saving and efficiency 

along with the demand for cost effective 

nanostructured optical components 

will no doubt motivate major 

advances in optical materials. 

Quantum entanglement has aroused 

the interest of the best physicists of 

the 20 th century and is at the core of 

NICOLAS BONOD 

Editor-in-Chief 

the second quantum revolution. The 

2022 Nobel Prize in physics awarded 

to John F. Clauser, Alain Aspect and 

Anton Zeilinger “for experiments 

with entangled photons, establishing 

the violation of Bell inequalities and 

pioneering quantum information 

science” is wonderful news for the 

optics and photonics community. 

Let me congratulate the three Nobel 

Laureates for this incredible recognition. 

It is striking to see that what 

started as an epistemological discussion 

between Bohr and Einstein 

eventually resulted in one of the major 

scientific breakthroughs of the 

20 th century. This shows also how 

fundamental questions can motivate 

developments in terms of instrumentation 

and material science and lead, 

a few decades later, to ground-breaking 

applications. 

In this international issue, we present 

a zoom article on photonics in 

Lithuania. This article shows how 

Lithuania has been building a very 

solid economy based on optics and 

laser technologies. The laser and 

photonics industry has experienced 

fast economic growth over the last 

few years and envisages, as an ultimate 

goal, reaching an impressive 

5% of the country’s GDP in 2030. Other 

European countries have recently invested 

heavily in the photonics sector, 

both in industry and education, and 

we will be pleased to publish zoom 

articles on these countries in the 

upcoming issues, because photonics 

is worth it! 

Photoniques 116 I www.photoniques.com 01

Table of contents 

www.photoniques.com N° 116 

03 NEWS 

Highlights & news 

from our 8 partners! 

NEWS 

03 SFO foreword 

04 Partner news 

14 Crosswords 

15 Research news 

23 The Nobel Prize in Physics 2022 

ZOOM 

26 Photonics in Lithuania 

LABWORK 

32 Frustrated total internal reflection: 

the Newton experiment revisited 

54 

Narrow band gap 

nanocrystals for infrared 


58 


made simple 

PIONEERING EXPERIMENT 

38 The first detection of the CMB that opened 

a new field in Cosmology 

FOCUS 

Optical Materials 

42 Halide perovskites for photonic applications 

48 Lithium niobate on insulator from classical 

to quantum photonic devices 

54 Narrow band gap nanocrystals for infrared 



58 The geometric phase made simple 

BUYER’S GUIDE 

64 Nonlinear crystals for frequency conversion 

PRODUCTS 

69 New products in optics and photonics 

Advertisers 

2B Lighting .......................................... 65 

Accumold ............................................ 39 

APE Gmbh ........................................... 59 

Ardop .................................................... 67 

Comsol ................................................. 61 

Edmund Optics .......................... IV e cov 

Eksma Optics ..................................... 31 

EPIC ....................................................... 13 

FC Equipments .................................. 35 

Idil .......................................................... 53 

Imagine Optic ..................................... 63 

Laser 2000 ........................................... 15 

Laser Components ........................... 57 

Light Conversion ............................... 27 

Lumibird .............................................. 45 

MKS ................................................ II e cov 

Optoman.............................................. 29 

Opton Laser......................................... 33 

Oxxius ................................................... 17 

Phasics ................................................. 41 

Photonics France .............................. 09 

Scientec ............................................... 49 

Silentsys .............................................. 55 

Sill Optics ............................................ 47 

Spectrogon ......................................... 23 

Spectros ............................................... 21 

SPIE Photonex ................................... 19 

Sutter Instrument ............................. 43 

Wavetel / Aragon ............................... 25 

Wavetel / Yokogawa ......................... 37 

Zurich Instruments ........................... 51 

Image copyright (cover): © iStockPhoto

SFO foreword 

ARIEL LEVENSON 

President of the French Optical Society 

“United in diversity” - “Unie dans la diversité” * 

A further stage in the SFO-EOS partnership ! 

This Editorial had been completed when I learned 

with great joy that the 2022 Nobel Prize in Physics 

had been awarded to Alain Aspect, jointly with John 

F. Clauser and Anton Zeilinger. But I immediately asked 

myself what more I could add to the many superlatives 

that were already being written about these three great 

pioneers of quantum optics. But in the context of my role 

as President of the SFO, my role was clear, and this was to 

speak of the many activities of Alain Aspect that may perhaps 

be less well-known to an international readership. 

In particular, Alain has always been a tremendous supporter 

of the SFO, and participated from its creation in 

our COLOQ Club including serving as its President. In 

addition, he has tirelessly made himself available to any 

request from the SFO, including as a conference speaker, 

a panel member, as a member of a prize jury, and as a 

trusted advisor and mentor to SFO members at all their 

career stages! Thus beyond my own warmest congratulations, 

let me add an enormous thank you to Alain on 

behalf of the French optical community! 

In his first interview after the award of the Nobel Prize, 

Alain declared "It is important that scientists maintain 

their international community when the world is not 

doing so well and nationalism is installed in many countries". 

This is exactly the central message of this editorial! 

I am extremely proud to announce that the European 

Optical Society (EOS) and our Société Française d’Optique, 

the French branch and co-founder of the EOS, are strengthening 

their mutual cooperation with the ambition of 

further contributing to the construction and consolidation 

of the European coherence in optics and photonics. 

Beyond the obvious importance for our academic and 

industrial communities of conducting exchanges and 

sharing good practices at the European level, current 

events sadly remind us of the vital need for the scientific 

community to contribute to society at large in order 

to improve international understanding, and to work 

towards peace. 

Among other ongoing actions in this context, I am 

very happy to announce that the next EOS congress, 

EOSAM 2023, will be held in Dijon, France from 

11-15 September 2023. The venue will be the Dijon 

Convention Center, the same place that so successfully 

hosted our own OPTIQUE Dijon 2021 congress with its 660 

participants and its 43 industrial stands. Let’s do better 

for 2023! The EOS and the SFO will share the organization 

of EOSAM 2023, under the guidance of Chairs Patricia 

Segonds, the new president of the EOS, Emiliano Discrovi, 

the new incoming president of the EOS, Guy Millot, the 

Chairman of OPTIQUE Dijon 2021, and Bertrand Kibler 

who is a well-known and very active member of SFO. The 

program (under construction) will be as varied as our 

European optical community, covering a large spectrum 

of hot topics in photonics. 

We are counting on the strong mobilization of the 

European optical community - on your mobilization - 

to make EOSAM 2023 in Dijon a fantastic event for 

scientific exchange and intense academic and industrial 

networking… 

Finally, I would like to take the opportunity of this issue’s 

focus on Lithuanian optics to remember our dear colleague 

Algis Petras Piskarskas who passed away on 11 June. Algis 

was one of the most prominent Lithuanian physicists, 

pioneering the concept and the first experimental demonstration 

of Optical Parametric Chirped-Pulse Amplification, 

a technique at the heart of high power ultrafast laser technology. 

His passing is a great loss for European science. 

Photoniquement vôtre 

Ariel Levenson 

Directeur de recherche CNRS 

Président de la SFO 

* EU motto: It signifies how Europeans have come together, in the form of the EU, to work for peace and prosperity, while at the same time being enriched by 

the continent's many different cultures, traditions and languages. 


NEWS 

www.sfoptique.org 

OPTIQUE Nice 2022, a great success 

The French optical community 

mobilization was strong and 

all the echoes clearly point to the 

pleasure to be together as well 

as to the amazing quality of the 

technical and scientific program. 

We are incredibly proud that our 

colleague Alain Aspect, Nobel 

Prize in Physics 2022, participated 

to the whole Congress, and were 

fascinated by his Plenary lecture, introduced 

by the Congress Chair Sébastien 

Tanzilli, on Nonlocality : from concepts 

to applications. 

The SFO warmely thanks also all the 

Plenary speakers: Sophie Brasselet, 

Jean Dalibard, Frédérique De Fornel, 

Rémi Carminati, Jérôme Faist, Philippe 

Goldner, Sophie Kazamias, Aurélie Jullien 

and Philip Russell as well as Tutorials 

speakers: Jean-Jacques Greffet, Yannick 

De Wilde, Vincent Jacques, Emmanuel 

Beaurepaire, Clément Courde and 

Pernelle Bernardi. 

The videos of these talks are available 

at www.sfoptique.fr 

The next great meeting will be 

OPTIQUE Normandie 2024 in Rouen. 

See you all then. 

OPTIQUE Nice 2022 

in few figures 

✓ 635 Attendees 

✓ 48 Stands of compagnies 

in the ecosystem of optics 

and French photonics 

✓ 10 Stands for educational 

teaching 

✓ 184 Posters 

✓ 247 Talk 

✓ 07H40 Hours of plenary session 

✓ 82H20 Hours of specific sessions 

in parallel 

✓ 4 Prizes awarded 

AGENDA 

General Assembly of SFO, 

SFO members meetings 

20 October 2022 - 10 am to 12 pm 

All members of the SFO are invited to 

vote and participate 

in this general assembly. 

WAVINAIRE the third edition 

Light control in complex media 

december 15, 2022 at 1:30 pm 

JNOG 2023 

SFO Colloque - JNOG Club 

INL, Lyon, France 

July 5 - 7, 2023 

Optomechanics 

& Nanophononics 

Chamonix Mont Blanc Valley, France 

April 17 - 28, 2023 

LIDAR summer school SFO 

International Thematic School 

Haute Provence, OHP, France 

June 11 - 16, 2023 

Waves in complex media 

Chamonix Mont Blanc Valley, France 

September 17 - 29, 2023 

Save the dates and follow us 

on https://www.sfoptique.org/ 

INTERNATIONAL THEMATIC SCHOOL 

OPTOMECHANICS & NANOPHONONICS 

April 17-28, 2023 - Les Houches Physics School, Chamonix Mont Blanc Valley, France 

Attending a thematic school is a unique opportunity to learn, share and connect with 

top leaders in the field. The school is designed for students and researchers using optical 

methods and for physicists participating in their development. 

Application deadline (short motivation letter + CV): November 22, 2023 

www.sfoptique.fr 

The study of the interaction between photons and phonons is a rapidly developing research 

field. Initially, it emerged to answer fundamental questions about thermal properties, 

nanomechanics, and quantum measurements. These questions constitute today the basis 

for new studies feeding fundamental and technological challenges. 

This school aims to overview this interdisciplinary field by treating quantum concepts and 

effects, simulation, sensors, metrology, and ultra-sensitive detection among other fundamental 

effects and applications. 

04 www.photoniques.com I Photoniques 116

www.minalogic.com 

NEWS 

Grenoble, the heart 

of quantum technologies 

For one week, the city hummed to the rhythm of quantum, with 3 events 

that led to very lively exchanges and showed that, in Grenoble, quantum 

technologies are a No.1 priority. 

• The first “Hackathon 

by Minalogic” was 

held on October 1 st 

and 2 nd , 2022. It was 

a competition that 

brought together the 

entire value chain of 

quantum computing 

and demonstrated 

its ability to work 

on real use cases 

provided by industrial 

partners. 

• The “Panorama of quantum technologies” day was hosted by Minalogic on 

October 4 th . During this day of talks and networking, nearly 80 people gathered 

to discuss this topic involving major challenges. 

• The “QuantAlps Days 2022” were held on October 5 th and 6 th , two days that brought 

together Grenoble’s quantum researchers. 

The success of these events shows that Grenoble has everything going for it to 

now be a major contributor in quantum technologies. 

FRENCH PHOTONICS DAYS 2022: 

A MUCH-ANTICIPATED EVENT IN SAINT-ÉTIENNE 

Held in Saint-Étienne on 

October 20 th and 21 st , this 

year’s 4 th French Photonics 

Days, certified under the Saint- 

Etienne Manufacturing Biennale, 

brought together some 150 people 

working on photonics technologies 

throughout France. This was a prime 

occasion to highlight the actions 

and investments taking place in 

the Auvergne-Rhône-Alpes region 

in photonics, and to showcase the contributions of local industries. 

On a more technical level, the topics presented were: the revolution in free-form optics, 

photonics and surfaces, and new LEDs and OLEDs for lighting and displays. Training 

and strategy of the photonics sector were also topics discussed during these two days. 

The event was co-sponsored by Minalogic, Photonics France, SupOptique Alumni and 

the Cluster Lumière, with support from the Metropolitan Area of Saint-Étienne and the 

Auvergne-Rhône-Alpes region. 

For more information about the event: http://frenchphotonicsdays.fr/ 

Startup Fundraising: 

Scintil Photonics and 

Prophesee in the spotlight 

Two deeptech photonic start-ups, 

members of Minalogic, have particularly 

distinguished themselves by carrying out 

major fundraising: 

• Scintil Photonics, a supplier of advanced 

silicon photonic integrated circuits with 

monolithically integrated lasers and optical 

amplifiers, has completed its second 

round of investment, for a total amount of 

€ 15M. This additional funding will enable 

the company to accelerate CMOS-based 

industrialization and global commercialization 

of its III-V Augmented Silicon 

Photonic ICs for optical interconnects. 

• Prophesee closed in September 2022 a 

€50 million C series round with new investment 

from Prosperity7 fund, to drive 

commercialization of revolutionary neuromorphic 

vision technology. With this 

investment round, Prophesee becomes 

EU’s most well-funded fabless semiconductor 

startup, having raised a total 

of $127 million since its founding in 2014. 

Prophesee’s neuromorphic sensors can be 

tested on the technological platform of the 

Institute for Technological Research (IRT) 

System Lab, of which Minalogic is a partner. 

UP-COMING 

EVENTS 

The Photonics Online Meetings, 

November 22, 2022, 

to be held remotely 

Photonics West 2023, 

in San Francisco, 

January 28th - February 2nd 

Laser World of Photonics 2023, 

in Munich, June 27 - 30 

Florent Bouvier 

Minalogic Photonic / 

Optics Manager 

Tel.: +33 (0)6 35 03 98 52 

florent.bouvier@minalogic.com 


PARTNER NEWS 

NEWS 

www.photonics-bretagne.com 

In Brief 

OFS - Photonics Bretagne held a booth 

at OFS, the International Conference 

on Optical Fibre Sensors, in Alexandria 

(USA) and presented a poster. Visitors 

were introduced to the whole range of 

its specialty optical fibres, metal coated 

fibres, and developments on draw 

tower Bragg gratings. 

SPACE - Photonics Bretagne exhibited 

on Innôzh’s booth at SPACE – the 

International Exhibition for Animal 

Breeding – in Rennes (France). It 

highlighted photonics technologies for 

applications in the agricultural sector. 

Thanks to a Photonics Tour, Diafir, HTDS, 

Wavetel, ENSSAT, Tematys, and CEA 

Tech Bretagne also met companies that 

propose photonics-based innovations. 

ECOC - Photonics Bretagne and IDIL 

presented at ECOC, the European 

Conference on Optical Communication 

(Basel-Switzerland), a pioneer low latency 

hollow-core cable to save nanoseconds 

in high-speed trading application. 

Photon Lines - Funded by the European 

project S3Food, Photon Lines has developed 

a high-speed hyperspectral 

camera. HS2I, now eyeSMART, facilitates 

the detection of pathogens in production 

in the agri-food industry. 

Cailabs – The Deeptech is now positioned 

as one of the first private companies in 

Europe to offer industrial optical ground 

stations, including one to be delivered 

within a year to the Swedish Space 

Corporation (SSC). These ground stations 

enable reliable and high throughput 

communication, thanks to the unique 

atmospheric turbulence compensation 

component (TILBA-ATMO by Cailabs). 

Meet European Partners 

Thanks to Photonics4Industry 

Photonics4Industry (P4I) is a European 

project which strengthens the links 

between 5 European photonics clusters: 

VITP/Toolas (Lithuania – project lead), 

Photonics Bretagne, Photonics Austria, 

Photonics BW and Photonics Finland. P4I 

aims to create exchange opportunities 

between photonics companies, to help 

the technological and commercial development 

of photonics SMEs, and to share 

the know-how and services of the clusters. 

Photonics Bretagne is responsible 

for the implementation of the European 

pilot project ClusterXchange which offers 

financial support to organize short 

exchange stays in order to better connect 

European industrial ecosystems. So, if 

you are interested to meet potential 

European partners, Photonics Bretagne 

can organize study visits for you. 

Contact: Gwenaëlle Lefeuvre, PhD, 

glefeuvre@photonics-bretagne.com 

Outcome of the Interreg STEPHANIE Project: 

Two Bi-Regional Projects Launched! 

The Interreg Europe STEPHANIE project, finishing at the 

end of the year, resulted in the setting-up of a bi-regional 

call between Wallonia and Brittany with two accepted 

projects in the last months: CAFCA and RIBLETS. The 

CAFCA 1 project aims to develop a new generation of fibre 

sensors based on Fiber Bragg gratings, by offering a complete solution for measuring variations 

in temperature and stresses in composite structures for applications such as aeronautics, space 

and boats. The partners of the project met in October to take stock of each partner’s progress, 

to define the actions to come, and to visit Photonics Bretagne and IDIL Fibres Optiques. The 

objective of the 2 nd project RIBLETS 2 is to develop a modular laser platform for the manufacture 

of Riblets on composite structures, which allows a better aerodynamics and subsequent fuel/ 

CO 2 saving on different type of vehicles. A successful outcome of the STEPHANIE project that 

strengthened the ties between Wallonia and Brittany and pave the way to collaborations with 

other regions using the same scheme. Don’t hesitate to contact us if you are interested. 

1 

Budget 1.9M€ co-funded by the Walloon and Brittany regions; Partners: Photonics Bretagne, Pixel sur Mer, 

IDIL Fibres Optiques, JD’C Innovation, Open Engineering and Multitel. 

2 

Budget 2.32M€ co-funded by the Walloon and Brittany regions, Rennes Métropole and Lannion Trégor 

Communauté; Partners: Photonics Bretagne, Cailabs, Multitel, Lasea and GDTech. 

AGENDA 

Photonics West, 

January 31- February 2, 2023 

San Francisco (United States) 

Photonics PhD Days 

January 19-20, 2023, Lannion (France) 

2 NEW TALENTS AT PHOTONICS BRETAGNE 

Gwenaëlle 

LEFEUVRE, PhD 

Business 

Development Manager 

Julie HOLSTEING 

Administrative 

& Financial 

Manager 


PARTNER NEWS 

www.institutoptique.fr 

NEWS 

Recruting a student 

of Institut d'Optique Graduate 

School for a internship 

Internships play an essential role in the training of engineering students 

at Institut d'Optique Graduate School (IOGS). They complement the theoretical 

and experimental education acquired, as much on the scientific 

and technical aspects as on the soft skills aspects of the engineering profession. 

The internships take place at the end of each of the three years of 

the curriculum. 

• The end-of-first-year internship, which is optional, allows students to discover 

the professional world. It lasts between 1 and 2 months. This period can also 

be used for linguistic and cultural immersion in a foreign country. 

• The end-of-second year internship, which is compulsory, is of a scientific 

or technological nature. It puts into practice the knowledge and 

know-how acquired during a year that includes many specialization 

courses. It can be carried out in a company or a laboratory. It lasts at 

least 14 weeks (May-August). 

• The end-of-third-year internship is the high point of the engineering curriculum, 

with the writing of a thesis and its presentation to a jury. It can 

also validate the internship of the 2 nd year of a Master's degree. Carried out 

in a company or laboratory, the end-of-studies internship lasts at least 18 

weeks (March-August). 

One of the two compulsory internships must be carried out in a company. This 

gives all students the opportunity to observe the organizational processes of a 

company and to put themselves in the position of junior engineers. The type 

of companies is very broad, ranging from start-ups (Effilux, DAMAE Medical, 

GreenerWave...) to large groups (General Electric, L'Oréal, Mitsubishi, EY, 

Apple, Airbus, Valeo, Essilor, Thalès, Safran...). 

Approximately 75% of the students do a fundamental or applied research internship 

in an industrial or public laboratory (University or research center). 

This type of internship, which allows students to discover the world of scientific 

research, can lead to a doctoral thesis, a path that attracts one-third of 

students each year. 

In order to complete their linguistic and cultural training, while immersed 

in an international professional environment, all students completing their 

studies in France do one of the two mandatory internships abroad. There are 

35 countries in which internships have taken place, in Europe, North America, 

South America, Africa, Asia, Oceania, and even Antarctica! Engineering training 

at the Institute of Optics is a real "business card" that opens many doors 

around the world. 

To know more about internship : 

Prof. Arnaud Dubois, 

arnaud.dubois@universite-paris-saclay.fr 

Internship offers can be posted here: 

https://www.institutoptique.fr/entreprises-et-innovation/ 

recruter-un-stagiaire-deposer-une-offre-de-stage 

The Continuing Education 

Department offers specific 

training courses, adapted to 

your needs and advises you 

in your technical and 

pedagogical choices. 

This can include : 

• Reproducing a course from 

the catalogue in our premises or 

in the client's premises 

• Adapting one or more courses from the 

catalogue to your requirements 

• Creating new training courses including, 

for example, themes not represented 

in the catalogue. 

These courses can be given in French or 

English (depending on the course). 

For more information, you can contact the 

Continuing Education Department at the 

following address: fc@institutoptique.fr 

or visit our website: fc.institutoptique.fr 

AGENDA 

SC10 - Acquisition, perception 

and image processing 

22/11/2022 to 25/11/2022 

EF1 - Optics without calculation 

06/12/2022 to 08/12/2022 

CO1 - Optical design with Zemax®- 

OpticStudio - Introduction 

06/12/2022 to 09/12/2022 

SC13 - Low light level vision 

and photon counting imaging 

12/12/2022 to 14/12/2022 

CO2VIS - Optical design with 

Zemax®-OpticStudio - Advanced 

12/12/2022 to 14/12/2022 

SC8 - Holography: from measurements 

to 3D display 

12/12/2022 to 15/12/2022 

SC2- Optical manufacturing 

and optical metrology 

08/03/2023 to 10/03/2023 

EF2 - Basics of optics 

14/03/2023 to 17/03/2023 and 28/03/2023 

to 31/03/2023 

CO6 - Design of optical systems 

based on off-the-shelf components 

with Zemax® 

22/03/03/2023 to 23/03/2023 and 

05/04/2023 to 06/04/2023 


PARTNER NEWS 

NEWS 

www.photonics-france.org 

AGENDA 

Photonics Online 

Meetings 

Online, 22 November 2022 

Photonics west 

France Pavilion, 

28 January – 2 February 2023, 

San-Francisco 

Photonics west 


28 January – 2 February 2023, 

San-Francisco 

Business meeting 

Photonics for Telecom, 

21 March 2023, Paris 

Business meeting 

Photonics Materials, 

11 May 2023, Paris 

Laser world of photonics 


27-30 June 2023, Munich 

NEW MEMBERS 

Welcome to our new 

members : Cailabs, 

Lavoix, Chauvin- 

Arnoux Spectralys, 

TE Connectivity 

Photonics Online Meetings: 

the 5 th edition is almost here! 

The 5 th edition of Photonics Online 

Meetings, a European wide virtual 

business event dedicated 

to photonics technologies, will be 

held on 22 November 2022. 

L’Oréal, Safran Electronics & 

Defense, Dassault Aviation, Bonduelle, 

Hologarde, CEA, Huawei, 

Vodafone, Bouygues Telecom, Onet 

Technologies, Saint-Gobain, Valeo 

and many other major key buyers 

have already joined the event. 

Photonics Online Meetings aims to bring together major contractors and suppliers of 

photonics technologies and services. An exceptional arrangement of pre-scheduled and 

relevant meetings between technology suppliers and contractors will make this day a 

unique event during which partnerships and business opportunities are woven. In addition, 

a rich program of plenary conferences, demonstrations and technical presentations 

led by experts will form pattern of the event. 

FOR FURTHER INFORMATION AND REGISTRATION: 

www.onlinemeetings.photonics-france.org 

REPORT ON THE 4 TH EDITION 

OF THE FRENCH PHOTONICS DAYS 

IN SAINT-ETIENNE, FRANCE 

TO CONTACT 

PHOTONICS FRANCE 

contact@photonics-france.org 

www.photonics-france.org 

Photonics France, SupOptique Alumni, 

Minalogic and Cluster Lumière, in 

partnership with Manutech Sleight 

and the Institut d'Optique G.S. and with 

the support of Métropole Saint-Étienne, 

co-organized the 4 th edition of the French 

Photonics Days on October 20 and 21 in 

Saint-Etienne, in Auvergne-Rhône-Alpes region in France. This year' s event, which has been was 

held under the theme of "Photonics for Display, Lighting and Manufacturing". The event brought 

together more than 160 participants. 

Sessions on new freeform optics aimed at the regional manufacturing industry, laser-made optical 

surfaces presenting the leading technologies developed by local players, and new LEDs and OLEDs 

for design and display based on technologies developed at LETI and local companies highlighted 

the region's know-how. A session was also dedicated to training with the aim of promoting local 

training (IOGS, Manutech Sleight, Télécom Saint-Etienne) while raising awareness of the growing 

need for recruitment in the sector and the crying lack of technical staff in photonics. 

French photonics industry is a fast-growing field with world-class skills and know-how. The 

Auvergne-Rhône-Alpes region is no exception. The region has one of the most innovative ecosystems 

in France in the fields of optics and photonics. It is home to several hundred companies, 

start-ups, technology transfer platforms and research organizations in this sector, and ranks 

second in terms of R&D, with 25% of national photonics activity. 


NEWS 

www.pole-optitec.com 

EUROPEAN CLUSTERS CONFERENCE 

IN PRAGUE 

On September 26 and 27, 2022, the 

Optitec cluster took part in the 

European Clusters Conference in 

Prague. Ukraine was particularly honored 

in this session. During the presentations and 

the conferences, synergies and supporting actions 

were dully encouraged to help Ukrainian 

clusters to be pillars of the coming rebuilding 

phase of the country. 

This conference was above all an opportunity 

to meet the European strategic clusters 

and to discuss together the various 

synergies that could bring together the 

interests of the clusters within their projects. 

This was, for example, an opportunity 

for the Optitec and SAFE clusters to 

get closer to the Techtera and Systematic 

clusters to identify possible joint actions 

for the Kets4DualUse2.0 and EU Alliance 

projects for their mission in Canada. 

Moreover, it was a privileged occasion 

to meet more than 20 other representatives 

for French clusters (AFPC) during a 

fruitful and friendly networking dinner. In 

this matter, it was the occasion for some 

KETs4DualUse2.0 partners to meet and 

to promote the activities of the project 

such as Stéphanie Renaud (OPTITEC) and 

Adeline Gleizal (Safe) in the picture below. 

This conference was also the place to 

share experiences on support for externationalisation 

such as for example the 

return of Ségolène Leloutre, coordinator 

of the Global Cosmetics cluster project, on 

the actions of the project and the issues 

of the externationalisation of SMEs (How 

to support them, motivate them, inform 

them, improve efficiency and relevance 

and prepare them for externationalisation 

actions...). These lessons-learnt are highly 

valuable for all actions to better support 

SMEs such as the KETs4DualUse2.0 project 

coordinated by OPTITEC. 

Finally, it was also the opportunity to better 

know the clusters that could become 

potential partners and that share the same 

values in Europe and particularly this year, 

in Ukraine. 

From October 4 th to October 6 th was held the 30 th Vision Fair 

in Stuttgart Germany 

VISION 2022 recorded a total number of 

6,505 trade visitors. This made the world's 

leading trade fair again the center of 

the machine vision industry. 

Overall, visitors from 60 countries were 

registered. The strongest presence was 

from Italy, Switzerland, the Netherlands, 

France, Austria, Belgium, Poland, Spain 

and the UK, VISION was also able to welcome 

a larger trade audience from South 

Korea, Japan and the USA. 

A total of 378 exhibiting companies 

– 60 per cent of which came from abroad – 

presented the wide range of machine 

vision solutions across three days 

Two full halls were dedicated to the industrial 

vision, a globally unique spectrum 

of products and services from 

sensors to processor, cables to camera, 

software, AI to lighting was displayed. 

World-leading exhibitors (manufacturers, 

distributors, startups, universities…) were 

on hand to unveil the latest systems and 

components. Vision was the place to have, 

in no time, an overview of key technologies 

related to Industry 4.0 and automated 

processes. This also offered plenty of 

examples of real-world scenarios to find 

out what machine vision offers for different 

industries. 

Optitec had the pleasure to organize 

the French Pavilion "Choose France" in 

the middle of it. 100 m² dedicated to the 

state-of-the-art vision solutions madein-France. 

6 companies from different 

regions (Occitanie, PACA, AURA and 

IdF) demonstrated their products and 

know-how on photonic solutions. This 

spread from chipset component level 

with Pyxalis (leader of low light vision) to 

Blaxtair with its 3D/2D cameras coupled 

with their AI solution; to multi-spectral 

cameras with Silios, Hyperspectral 

cameras with First Light Imaging; confocal 

measurement sensors of Stil-Marposs 

and camera/ Vision solutions of Twiga. 

This was an opportunity, on top of 

meetings with customers/partners, to 

benchmark the photonic industry in several 

aspects, and also to attend the Industrial 

Vision Days forum. This technology forum 

is considered to be the largest and busiest 

presentation forum with public debates 

about image processing around the world. 

The Pavilion France and Vision were 

really a connection from France to the 

world of vision. 

We are looking forward to the next 

Vision fair in October 2024 to showcase 

your innovations. 

AGENDA 

Photonics West 

31 January-2 February 202 

Find the providers of the best 

solutions, components, instruments, 

and system support from around 

the world 

https://spie.org/conferences-andexhibitions/photonics-west 


PARTNER NEWS 

https://nano-phot.utt.fr/ 

NEWS 

The Graduate School NANO-PHOT (nano-phot.utt) 

coordinated by the University of Technology of 

Troyes (UTT), offers a 5-year Master + PhD training 

of excellence on the use of light at the nanometer 

scale. The educational program relies on worldclass 

research laboratories. 

The leading laboratory (L2n, l2n.utt.fr) located at 

UTT, Troyes, was presented in photoniques N°113. 

Here we present a focus on the 6 partner laboratories 

of the University of Reims. They provide graduate 

school students with many opportunities in a wide 

range of applications of nano-optics. In particular, 

many internships at M1 and M2 levels and PhD 

projects are proposed, allowing the construction of 

personalized routes, adapted to the sensitivity and 

personal development projects of each students. 

The University of Reims Champagne- 

Ardenne (www.univ-reims.fr) is 

developing its scientific project 

around four poles of excellence: 

• Agrosciences, Environment, 

Biotechnologies and Bioeconomics, 

• Health, 

• Digital and Engineering Sciences, 

• Humanities and Social Sciences. 

Early partner of the Nano’phot 

graduate school, the Nanosciences 

Research Laboratory 

(www.univ-reims.fr/lrn) has 

developed a strong expertise 

in near-field instrumentation 

and nanotechnology. Research 

projects cover a wide range 

of applications, from optoelectronics to sensors and biomedical 

applications. 

The Fractionation of Agroresources 

and Environment (FARE 

www6.nancy.inrae.fr/fare) joint 

research unit between INRAE and 

URCA studies both the processes 

of deconstruction of lignocellulosic 

biomass for use as various bioproducts 

and the biodegradation 

of organic matter in soils in order 

to better understand biogeochemical cycles and carbon storage. 

At the heart of the 

Reims Health 

center made up 

of the University 

Hospital and 

the Faculties 

of Medicine, 

Pharmacy and 

Dentistry, the 

BIOSPECT laboratory (www.univ-reims.fr/biospect) 

uses molecular optical imaging techniques, more specifically 

vibrational spectroscopy, to analyze biological 

samples (cells, tissues, biofluids) and identify spectroscopic 

markers for diagnostic clinical applications. 

The Institute of Thermics, 

Mechanics and Materials 

(ithemm.univ-reims.fr) has a 

large fleet of scientific instruments supporting its 

research in multiscale thermophysical characterizations 

and analyzes of materials and processes, in 

close collaboration with the LASMIS laboratory of 

the UTT. 

UMR Ineris Environmental 

Stress and Biomonitoring 

of Aquatic Environments 

(www.univ-reims.fr/sebio) 

performs its research in the field of aquatic ecotoxicology 

on the effects of environmental stress. Its objectives 

are to understand the biological responses of aquatic 

organisms as well as to develop and qualify biomonitoring 

tools in the continuum of water masses, from 

continental ecosystems to estuarine and coastal transitional 

waters. 

The UMR CNRS 7369 MEDyC 

(www.univ-reims.fr/medyc) is 

widely recognized in the field 

of extracellular matrix (ECM) 

biology. The MEDyC research project is interdisciplinary 

and aims at developing original approaches 

and methodologies at the interface between physics, 

biology and bioinformatics, to decipher the molecular 

mechanisms supporting cell-ECM interactions. 

MEDyC identifies new pharmacological targets and 

molecules of high therapeutic potential for a ECMtargeted 

pharmacology as well as new tools for diagnosis 

and prognosis 


PARTNER NEWS 

NEWS 

www.alpha-rlh.com 

The internationalisation 

of Euroclusters 

During the European Cluster 

Conference 2022 that took place on 26- 

27 September in Prague, ALPHA-RLH 

participated in a side event that gathered 

representatives from European 

clusters who have been awarded 

grants by the EU programmes supporting 

European Cluster Partnerships as 

well as Euroclusters. 

Isabelle Tovena Pécault, Director 

Europe & International, and Martina 

Bacova, Project adviser, EISMEA, led 

a discussion group on Euroclusters 

internationalisation. The objective 

of this workshop was to share good 

practices, find synergies between the 

participants, deepen the collaboration 

between the consortia, highlight the 

importance of internationalisation 

strategy for SMEs and provide them 

key resources and knowledge. 

UPCOMING 

INTERNATIONAL 

EVENTS 

Smart City Expo 

World Congress 

November 15-17, 2022 

in Barcelona (Spain) 

Photonics West 2023 

January 31 – February 2, 2023 

in San Francisco (USA) 

IoT Solutions World Congress 

January 31 - February 2, 2023 

in Barcelona (Spain) 

ALPHA-RLH EXTENDS ITS JAPAN MISSION 

TO SOUTH KOREA AND SINGAPORE 

ALPHA-RLH has been established in Japan since March 2022. Romain Montini, 

the cluster's Delegate, is based in Tokyo in the offices of the French Chamber 

of Commerce and Industry in Japan (CCI France Japan). Since September 2022, 

this mission has been extended to South Korea and Singapore. 

Concerning Singapore, ALPHA-RLH has been selected 

to participate to an EU-Singapore Matchmaking event in 

October 18th to 19th, which was a good start! 

Romain Montini supports the members, facilitates their 

access to the Japanese, South Korean and Singaporean 

markets, and allows them: 

• To build their network with relevant economic actors (suppliers, partners, distributors...) 

• To develop their exports to these promising markets, facilitate and accelerate their innovation 

projects 

• To be represented on different events directly related to their activity (trade fairs/forums) 

• To adapt their products leaflets to the targeted country. 

Would you like to develop your business to these markets, to get started on an R&D or innovation 

project, to benefit from personalized business support? You are looking for partners? 

For more information, please contact Romain Montini: r.montini@alpha-rlh.com 

The success story 

of the European PIMAP projects 

The European PIMAP Partnership 

project led by ALPHA-RLH was selected 

in 2018 in the framework of the 

« Clusters Go International » call. Its 

objective was to develop economic 

activity and boost innovative SMEs' 

growth at international level for 

photonics industry applications. 

In 2020, PIMAP led to the strand 2 PIMAP+ gathering 6 clusters to strengthen 

cross-sectoral cooperation in the fields of photonics, advanced manufacturing, 

metalworking and aerospace industry. PIMAP+ has facilitated 

access for SMEs to international markets: USA, Canada, China and Japan. 

The project ended in July 2022 with successful results (4 business missions, 4 Memoranda 

of Understanding, 15 events, 30 inter-cluster meetings, 90 beneficiary SMEs) and was 

one of the three nominees for the 2022 Award for the best European partnership. 

Following the end of the PIMAP+ project, ALPHA RLH continues its role as coordinator 

of a new European project with PIMAP4Sustainability. This new project has been officially 

launched on Friday 30 September 2022 during a meeting gathering all partners. 

The objective of this new PIMAP strand is to support the resilience of European 

photonics SMEs through two funding mechanisms : a support mechanism for innovative 

projects that will allow SMEs to obtain a grant of up to 60 k€ and an additional 

mechanism to support the training of SMEs (10 k€) on their green transition 

or internationalisation. 

The next coming steps for the consortium will be to define the scope and framework 

of the open calls and the modalities for obtaining the grants. 


RESEARCH NEWS 

CROSSWORDS 

ON OPTICAL MATERIALS 

By Philippe ADAM 

11 13 15 17 

1 

12 19 21 

2 3 

5 16 

6 

 

 

 

 

 

 

 

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14 18 20 

 

 

4 

 

SOLUTION ON 

PHOTONIQUES.COM 

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10 

 

1 With Macromolecules 

2 Highly efficient electro-optical medium 

for nonlinear effects 

3 Microelectromechanical systems 

4 Diamagnetic III-V semiconductor 

5 Can be quasi or not, a very interesting material 

for photonics and non-linear optics 

6 Technique to arrange matter at atomic 

or molecular level to get new properties 

7 Glasses with very high IR transparency 

8 Quantum box to quantify energy levels 

9 Hard chemical synthetic material 

10 Color associated with sustainability 

11 Type I, II, III or even Fibonacci heterostructure 

12 Resonant interaction between light and metals 

13 Used in beam for etchning at nanoscale 

14 Organic display technology 

15 Polycristalline optically transparent materials 

16 Carbon soccer ball 

17 Optically driven MEMS 

18 Materials with unique mechanical, optical, thermal, 

and electrochemical properties 

19 Semiconductor for diodes, FETs, ICs ... 

20 Laser emitting by its surface 

21 Physicist, pioneer in the field of photonic crystals 


RESEARCH NEWS 

Greenberger-Horne-Zeilinger 

state generation with an all-optical 

programmable qubit memory 

Large entangled states of light containing 

many photons, like Greenberger- 

Horne-Zeilinger (GHZ) states, are the 

key resource that enable networked quantum 

communication and advanced photonic 

quantum computation applications. 

The fundamental understanding of these 

states in theory and experiment was honoured 

with the Nobel Prize in physics 2022 

by the Royal Swedish Academy of science. 

However, in order to successfully apply entangled 

states for real world applications, 

states of bigger and bigger size must be 

reliably generated in the lab. 

This, however, remains an unsolved 

challenge for the quantum community as 

established generation methods rely on interfering 

entangled photon pairs from multiple 

probabilistic sources. The consequential 

exponential drop in generation rates for increasing 

sizes of the target quantum state 

limits scalability and prevents the practical 

usage for profitable quantum technologies. 

On the path towards overcoming the 

scalability challenge, researchers from 

Paderborn University together with colleagues 

from Ulm University demonstrate 

an active feed-forward scheme in combination 

with multiplexing strategies which 

is compatible with prevalent photon 

pair sources. 

At the heart of the design lies an all-optical 

polarization qubit quantum memory which 

can be dynamically programmed by a feedforward 

signal: Upon detection of one photon, 

its pair partner is stored in the memory 

until the generation of the next pair. The 

recording of one partner photon switches 

the operation mode of the programmable 

memory via feed-forward and activates the 

interference between the newly generated 

and the stored photon. By repeating this 

step, the size of the multi-photon entangled 

state is incrementally increased. 

This method leads to an exponential enhancement 

of the generation rates compared to 

prevalent sources without fidelity drawback 

bringing into reach practical system sizes 

and rates for photonic quantum computation 

applications. 

REFERENCE 

E. Meyer-Scott, N. Prasannan, I. Dhand, 

C. Eigner, V. Quiring, S. Barkhofen, B. Brecht, 

M. B. Plenio, and C. Silberhorn, “Scalable 

Generation of Multiphoton Entangled States 

by Active Feed-Forward and Multiplexing” 

Phys. Rev. Lett. 129, 150501 (2022). 

https://doi.org/10.1103/PhysRevLett.129.150501 


RESEARCH NEWS 

A numerical tool to explore the impressive visual 

appearances of macroscopic nanostructured objects 

Nature offers us beautiful visual appearances. The most resplendent 

of them, from the iridescence created by opals 

and some butterfly wings to the vividly colored appearance 

of some birds and fruits, often come from interference effects 

created by nanostructures. Inspired by nature, a wide variety of 

"structural colors" have been artificially reproduced by structuring 

matter at the nanoscale. Color is, however, only one out of the 

many attributes of visual appearance. Gloss and haze, for instance, 

are as important as color for our perception of objects, which additionally 

depends on the object shape and lighting environment. 

These aspects have largely been neglected so far in the extensive 

literature on appearance design with nanostructured materials. 

An interdisciplinary team of researchers at LP2N (CNRS / Institut d’Optique 

Graduate School / Université de Bordeaux) and INRIA Bordeaux 

Sud-Ouest in Talence has now developed a multiscale modelling 

platform merging electromagnetic simulations, multiple scattering 

theory and computer graphics to predict the visual appearance of 

macroscopic objects nanostructured on their surface. The numerical 

tool generates physico-realistic synthetic images of arbitrary objects 

(e.g., a car) covered by disordered metasurfaces (e.g., a random assembly 

of metallic particles on a layered substrate) in arbitrary environments 

(e.g., in front of the Uffizi gallery in Florence). Importantly, 

it unveils the potential of these nanostructures to create impressive 

visual effects at the macroscale, such as an unusual iridescence that 

appears to glide on an object as the observer turns around it. One of 

these visual effects was demonstrated experimentally on a centimetre-scale 

sample, fabricated at LAAS-CNRS micro and nanotechnologies 

platform, a member of the french RENATECH network. 

The modelling platform may find use in several branches of visual 

appearance design, such as for metasurface-based augmented reality 

devices, anti-counterfeiting security features, luxury goods... 

REFERENCE 

K. Vynck, R. Pacanowski. A. Agreda, A. Dufay, X. Granier, and P. Lalanne, 

“The visual appearances of disordered optical metasurfaces”, Nat. Mater. 21, 

1035-1041 (2022). https://doi.org/10.1038/s41563-022-01255-9 

INKJET-PRINTED BRAGG MIRRORS 

Bragg mirrors (also known as dielectric 

mirrors) are multilayer interference 

thin film devices that 

selectively reflect optical bands of interest. 

Such mirrors exist in numerous optical 

and photonic systems such as Raman and 

fluorescence microscopes, imaging systems, 

and laser systems. Due to the nature 

of the multilayer interference, the optical 

performance, in terms of the stop band 

and the center wavelength, is susceptible 

to individual and overall layer thickness. 

For this reason, the Bragg mirrors are 

typically fabricated by technologies like 

ion-assisted deposition, thermal and electron 

beam evaporation, and atomic layer 

deposition. For high-precision coatings, 

all methods are relatively slow and require 

high vacuum, resulting in high capex. 

A research team led by Professor Uli 

Lemmer at Light Technology Institute, 

Karlsruhe Institute of Technology, managed 

to fabricate Bragg mirrors using a 

desktop inkjet printer in ambient conditions. 

The central reflecting wavelength 

of the mirrors can be accurately defined 

in a resolution of 1 nm by simply controlling 

the printing parameters. In addition, 

an ultra-high reflectance of > 99% was 

achieved in purely inkjet-printed Bragg 

mirrors. The drop-on-demand property of 

inkjet printing endows the printed dielectric 

stacks with a high degree of freedom 

in lateral patterning, showing a large potential 

for integrating Bragg-mirror-arrays 

in various optical and photonic systems. 

Furthermore, in-ambient printing gives 

more feasibility in large-area manufacturing. 

The developed approach, therefore, 

enables additive manufacturing for 

various applications ranging from microscale 

photonic elements to enhanced 

functionality and aesthetics in large-area 

displays and solar technologies. 

REFERENCE 

Q. Zhang, Q. Jin, A. Mertens, C. Rainer, R. Huber, 

J. Fessler, G. Hernandez-Sosa, U. Lemmer, 

“Fabrication of Bragg Mirrors by Multilayer 

Inkjet Printing,” Advanced Materials 34, 

2201348 (2022). 


RESEARCH NEWS 

ELECTROACTIVE POLYMERS 

ENABLE REFLECTIVE COLORS TUNEABLE 

THROUGHOUT THE VISIBLE 

Actively tuneable structural colours preferentially 

reflect a portion of the visible spectrum to form dynamic 

colours without any backlight illumination. 

They could enable next generation of e-labels and e-readers 

in colour, with advantages of low power consumption, 

good eye comfort and high visibility even in bright sunlight. 

However, their active control throughout the full visible 

spectrum has been a major challenge, in particular combined 

with good brightness. 

A research group at Linköping University, Sweden, demonstrated 

that conducting polymers can be used as electroactive 

component to tune the reflective structural colour of an optical 

cavity. Conducting polymers can be reversibly doped and 

undoped electrochemically, as is commonly used to modify 

their electronic and optical properties. This redox tuning 

is also associated with swelling/deswelling of the polymer 

film, opening for electrochemical thickness control. The 

team at Linköping University designed a metal-conducting 

polymer-metal optical nanocavity with reflective structural 

colours controlled by the thickness of the polymeric spacer. 

They further demonstrated full reversible colour change in 

the entire visible by redox tuning of the conducting polymer 

at low operating voltages. Remarkably, the tuneable hybrid 

optical nanocavity produced high peak reflectance with 

similar values for all the colours, thanks to the adoption of 

a low bandgap conducting polymer with low absorption 

in the visible. While further studies are needed to improve 

stability and uniformity, this is a step towards a fully tuneable 

mono-pixel in the visible and proof of the capability 

of conducting polymers as electrically controlled optical 

actuators. The findings may be extended to other types of 

structural colours and photonic structures, such as actively 

addressable metasurfaces. 

REFERENCE 

S. Rossi, O. Olsson, S. Chen, R. Shanker, D. Banerjee, A. Dahlin, 

M. P. Jonsson, “Dynamically Tuneable Reflective Structural 

Coloration with Electroactive Conducting Polymer Nanocavities,” 

Adv. Mater. 33, 2105004 (2021). 

https://doi.org/10.1002/adma.202105004 


RESEARCH NEWS 

TEMPORAL SHRINKING OF OPTICAL DATA PACKETS 

Today’s world is witnessing an exponential growth of optical 

data. Dealing with such a massive amount of information 

requires innovative approaches for stretching or 

compressing optical waveforms, beyond the bandwidth limitations 

inherent to conventional electro-optical systems. To this 

aim, photonic platforms exploiting ultrafast nonlinear phenomena, 

such as four-wave mixing interactions, have been shown 

to provide access to extremely large functionality bandwidths. 

In particular, the temporal magnification of light-waves based 

on the time-lens concept has been successfully implemented 

to outperform electronics and has enabled the observation 

of intricate dynamics previously inaccessible. However, the 

converse process — the temporal compression of arbitrary lightwaves 

— still remains a challenging functionality that has been 

largely unexploited so far. 

To overcome this fundamental issue, a team of researchers 

in France and New Zealand (at ICB CNRS laboratory in Dijon 

and The University of Auckland) have just reported in Nature 

Photonics, a novel technique enabling the temporal compression 

of arbitrary optical waveforms with compression factors 

up to 4 orders of magnitude, far ahead of any results reported so 

far. This technique was theoretically proposed by Russian scientist 

Andrey Starodumov in 1996, but never previously achieved 

in laboratory. In their experiments, Fatome and co-workers 

successfully demonstrate Starodumov’s compression scheme 

using a counter‐propagating degenerate four-photon interaction 

occurring in birefringent optical fibres. They report extreme 

temporal compression of optical waveforms by factors 

Temporal compression of an optical data packet through a nonlinear 

focusing mirror created by a counter-propagating readout pulse. 

ranging from 4,350 to 13,000, including non-trivial on-demand 

time-reversal capability. This approach is scalable and offers 

great promise for ultrafast arbitrary optical waveform generation 

and related applications. 

REFERENCE 

N. Berti, S. Coen, M. Erkintalo, and J. Fatome, "Extreme waveform 

compression with a nonlinear temporal focusing mirror,” 

Nat. Photon. In press (2022). 

https://doi.org/10.1038/s41566-022-01072-1 

Crédit: Loïc Brunot 

Unipolar quantum optoelectronics 

for high-speed free-space optics in the mid-infrared 

Free-space optics (FSO) offer an attractive 

alternative for transmitting 

high-bandwidth data when fibre 

optics is neither practical nor feasible. 

This technology has emerged as a strong 

candidate with a large potential of applications 

from everyday life broadband internet 

to satellite links. The availability of 

high-quality transmitters and detectors 

operating in the near-infrared window 

makes the 1.55-micron optical wavelength 

a natural choice for free-space 

optics systems. Nevertheless, the mid-infrared 

region in particular between 8-12 

microns can also be considered especially 

because of its superior transmission 

performances through inclement 

atmospheric phenomena, such as fog, 

clouds and dust. 

In a recent work, a research team at Institut 

Polytechnique de Paris together with researchers 

from Ecole Normale Supérieure 

in France, made substantial progress in FSO 

communications using unipolar quantum 

optoelectronic (UQO) devices. In the experiment, 

the output of a quantum cascade laser 

was modulated by a stark effect external 

modulator and passed through a Herriott 

cell to simulate a light path with an effective 

length of over 30 m. Two different detectors, 

namely a quantum well infrared photodetector 

and a quantum cascade detector 

were tested in the receiver side. As reported 

in Advanced Photonics, they achieved low 

bit error rates even at high speeds, showcasing 

the potential of this technology for 

long-range communication links. This work 

marks a key step towards the realization of 

high-speed FSO telecommunication links 

that are resistant to weather conditions by 

adopting UQO devices. Further developments 

in the integration of UQO devices 

can help to bring high-speed Internet to 

challenging locations. 

REFERENCE 

P. Didier, H. Dely, T. Bonazzi, O. Spitz, E. Awwad, 

É. Rodriguez, A. Vasanelli, C. Sirtori, and 

F. Grillot, “High-capacity free-space optical 

link in the midinfrared thermal atmospheric 

windows using unipolar quantum devices,” 

Adv. Photonics 4, 056004 (2022) 


RESEARCH NEWS 

Capturing the light 

perfectly 

Most substances in the world around us absorb some 

light, but even media that appear black typically 

absorb light only imperfectly. In a new article, now 

published in Science [1], the groups of Ori Katz (Jerusalem) 

and Stefan Rotter (Vienna) demonstrate how even a weakly 

absorbing medium can be turned into a perfect absorber. 

Animals that prey at night, need to make efficient use of the 

little bit of light that is available to them. To do this, they have 

a reflecting layer behind their weakly absorbing retina, that 

recycles the light by passing it through the retina a second time. 

This reflecting layer is the reason, in fact, why cats’ eyes appear 

bright green or yellow at night when you shine at them with a 

flashlight. The interesting question addressed in the new work 

by Katz et al. is how to improve this light-recycling process up to 

the point where light is absorbed perfectly even by a thin film 

that would usually absorb light only very weakly. 

First, the scientists use a second reflecting mirror to form a resonator 

around the weakly absorbing film. While it has already 

been shown earlier that perfect absorption can be reached at 

the condition of “critical coupling”, this condition could so far be 

satisfied only for a specific incoming light beam or “mode”. By 

placing inside their resonator a self-imaging set of two focusing 

lenses, the authors manage to critically couple several thousand 

modes in parallel, creating a device which is the time-reversed 

version of a degenerate cavity anti-laser: a degenerate cavity 

‘anti-laser”. This multi-mode interference effect prevents even 

time-varying speckle patterns from escaping the resonator so 

that the light passes through the weak absorber as many times 

as necessary to be fully absorbed. 

REFERENCE 

Y. Slobodkin, G. Weinberg, H. Hörner, K. Pichler, S. Rotter, 

and O. Katz, “Massively degenerate coherent perfect absorber 

for arbitrary wavefronts,” Science 377, 995 (2022) 

Image below shows the experimental set up. 

© Omri Haim, The Hebrew University of Jerusalem. 


RESEARCH NEWS 

Petabit-per-second data transmission using chip source 

As the global internet traffic continues to grow, so does 

the total power consumption requirements for the interconnecting 

fibre optical backbone. A common way to 

increase the throughput of an optical fibre is to encode data in 

several different wavelengths of light, known as wavelength division 

multiplexing (WDM) which are then all transmitted simultaneously. 

Using optical frequency combs as sources for WDM 

allows for a tighter packing of the data channels compared to 

traditional sources compromised of arrays of lasers. This is due 

to the intrinsic property of the equidistant frequency lines of the 

comb which eliminates the need for spectral buffers ordinarily 

required when using arrays of independent lasers. This increases 

the spectral efficiency of the communication channels but also 

allows for a single light source to replace dozens (or hundreds) of 

lasers, potentially leading to an improvement in the total energy 

efficiency. Researchers at the Technical university of Denmark 

have together with Chalmers University of Technology fabricated 

and implemented a photonic chip which is capable of producing 

a broadband frequency comb using third order nonlinear interactions 

in silicon nitride. The chip is pumped by a single continuous 

wave laser and produces 224 usable comb lines at different 

wavelengths. The comb lines have enough optical power to each 

support 37 spatially independent data streams, which when sent 

through a special 37-core fibre, allowed researchers to transmit 

1.84 Petabit/s, or twice the average global internet bandwidth, 

over a distance of 7.9 km. 

The researchers also developed a theoretical model revealing 

that the scalable potential for these devices could possibly reach 

beyond 100 Petabit/s. 

REFERENCE 

A. A. Jørgensen et al. "Petabit-per-second data transmission using 

a chip-scale microcomb ring resonator source". Nat Photonics 16, 798– 

802 (2022). Link to the freely accessible version: https://rdcu.be/cXXCf 

Credit: Julian Curry Robinson-Tait 

ARTIFICIAL-INTELLIGENCE-POWERED RECORD-BREAKING 

ALL-IN-ONE MINIATURE SPECTROMETERS 

Traditionally, spectrometers rely 

on bulky components to filter and 

disperse light. Modern approaches 

simplify these components but still 

On-chip spectrometer on a fingertip 

suffer from limited resolution and bandwidth 

to shrink footprints. Additionally, 

traditional spectrometers are heavy and 

take up extraordinary amounts of space, 

which limits their applications in portable 

and mobile devices. 

An international research team led by 

researchers at Aalto University has developed 

a miniaturized spectrometer 

that breaks all current resolution records 

and does so in a much smaller package. 

A new chip puts photonic information at 

our fingertips by replacing optical and 

mechanical hardware with the combination 

of AI algorithm and electrical tuning 

of the sensor's spectral response, which 

enables portable, low-cost, high-performance 

on-chip-spectrometers. They 

eliminate the need for detector arrays, 

dispersive components, and filters. 

The result is an all-in-one spectrometer 

thousands of times smaller than current 

commercial systems. At the same 

time, it offers performance comparable 

to benchtop systems. This spectrometer-on-chip 

could be incorporated into 

instruments like drones, mobile phones, 

and lab-on-a-chip platforms, which can 

carry out several experiments in a single 

integrated circuit. It could open up the 

future for the next generation of smartphone 

cameras that evolve into hyperspectral 

cameras that conventional color 

cameras cannot do. 

REFERENCE 

Hoon Hahn Yoon et al. "Miniaturized 

spectrometers with a tunable van der Waals 

junction" Science 378, 296 (2022). 

DOI: 10.1126/science.add8544 


RESEARCH NEWS 

CREATING 3D PARTS IN THE BLINK OF AN EYE 

USING LIGHT-SHEET 3D MICROPRINTING 

Since the presentation of the first 3D 

printer, numerous types of plastic 

3D printers rely on photopolymerization, 

i.e., the local hardening of a liquid 

photoresin triggered by light. Still, 

these 3D printers have only found their 

way into mass-production for few applications. 

In comparison with traditional 

formative methods like injection molding, 

the fabrication time per part in 3D 

printing is long, ranging from minutes 

to hours. Aiming to speed up the fabrication 

time, new 3D printing approaches 

with increased voxel printing rates have 

emerged. One of them is light-sheet 3D 

printing, which was first presented in 

2019 by researchers from the Karlsruhe 

Institute of Technology, Germany. 

In light-sheet 3D printing, a special liquid 

photoresin is exposed simultaneously 

to light of two different colors. The key 

ingredient of the special photoresin is 

the photoinitiator. After absorption of a 

blue photon, the photoinitiator molecule 

is excited to a triplet state. However, in 

contrast to ordinary photoresins, the 

chemical hardening reaction is triggered 

only upon absorption of a second, 

red photon. To achieve the desired high 

printing rates, a photoinitiator having a 

short triplet-state lifetime is required. In 

screening and characterization experiments, 

the researchers identified a compound 

with a lifetime of less than 100 µs. 

In their light-sheet 3D printer, slices of a 3D 

object are projected by a blue laser-diode 

beam. A red-colored light-sheet-shaped 

beam intersects the focal plane of the blue 

projection, triggering the chemical hardening 

reaction. In their Nature Photonics 

publication, the researchers present 3D 

printed microstructures, which are printed 

in a fraction of a second. The demonstrated 

voxel printing rate is 7×10 6 voxels/s and the 

voxel volume is less than 1 µm³. 

REFERENCE 

V. Hahn, P. Rietz, F. Hermann, P. Müller et al., 

“Light-sheet 3D microprinting via two-colour 

two-step absorption,” Nature Photonics 16, 

784 (2022) 


RESEARCH NEWS 

Single-crystal perovskite optical fiber 

Due to their very high efficiency in transporting electric 

charges from light, perovskites are known as the next 

generation material for solar panels and LED displays. 

In particular, single-crystal organometallic halide perovskites 

possess attractive optoelectronic properties and therefore are 

suitable fiber-optic platform in high-speed all-fiber optoelectronics. 

They have direct bandgap, low defect densities, promising 

optoelectronic and nonlinear optical properties. Their optical 

fiber form is therefore attractive and could be an all-round candidate 

in high-speed all-fiber optoelectronics, where light can 

be generated, modulated and detected within an optical fiber. 

Single-crystal organometallic perovskite optical fibers have not 

been reported before due to the challenge of one-directional 

single-crystal growth in solution. Scientists have therefore 

been seeking to make single-crystal perovskite optical fibres 

that can bring this high efficiency to fibre optics. A team at 

Queen Mary University of London now has invented a solution-processed 

single-crystal fiber fabrication method and 

has reported the first single-crystal organometallic perovskite 

optical fibers with controllable diameters and lengths. Their 

perovskite optical fibre consists of just one piece of a perovskite 

crystal, has a core width as low as 50 μm (the size 

of a human hair) and are very flexible – they can be bent to 

a radius of 3.5 mm 

In line with their predictions, due to the single-crystal quality, 

their fibres proved to have good stability over several months, 

and a small transmission loss – lower than 0.7dB/cm sufficient 

for making optical devices. They have great flexibility (can 

be bent to a radius as small as 3.5 mm), and larger photocurrent 

values than those of a polycrystalline counterpart 

(the polycrystalline MAPbBr3 milliwire photodetector with 

similar length). 

REFERENCE 

Y. Zhou, M. A. Parkes, J. Zhang, Y. Wang, M. Ruddlesden, H. H. Fielding, 

and L. Su. “Single-crystal organometallic perovskite optical 

fibers.” Science Advances 8, eabq8629 (2022) 

https://www.science.org/doi/10.1126/sciadv.abq8629 

LASER HEATING FOR LIFE AT HIGH TEMPERATURE 

Life on Earth exists over a significantly 

large temperature range. 

Thermophilic micro-organisms, living 

close to volcanos or black smokers at 

the bottom of the ocean, can thrive in the 

range of 50 to 121°C. Understanding how 

evolution managed to deal with such extreme 

conditions can have important applications 

in science. For instance, the study of 

the thermophilic bacteria Thermus aquaticus 

is at the origin of the conception of the 

now famous PCR test (polymerase chain 

reaction), which relies of thermal cycling to 

rapidly make millions of copies of a specific 

DNA sample. 

While efficient protocols have been developed 

to culture thermophiles in laboratory 

vessels, observing them alive with 

a micrometric spatial resolution remains 

a challenge because optical microscopes 

cannot be heated much above typically 

60°C. 

A team of physicists from the Institut Fresnel 

(CNRS, Aix-Marseille University), in collaboration 

with biologists from the Institute for 

Integrative Biology of the Cell (Paris-Saclay 

University) and the Institut Pasteur (Paris), 

demonstrated the activation of thermophilic 

micro-organisms under the field of 

view of a microscope by local laser heating 

of gold nanoparticles. Life until 80°C could 

be evidenced, where bacteria and archaea 

have been observed to divide, swim, sporulate 

and germinate. This work benefited 

from the use of an optical wavefront microscopy 

technique, capable of measuring 

both the microscale temperature profile, 

and the biomass of individual growing 

cells. This work provides the biomicroscopy 

community with a simple approach 

to observe thermophiles alive, and better 

understand how their live, grow and interact 

with each other. 

REFERENCE 

C. Molinaro, M. Bénéfice, A. Gorlas, V. Da Cunha, 

H. M. L. Robert, R. Catchpole, L. Gallais, P. Forterre, 

G. Baffou, “Life at high temperature observed 

in vitro upon laser heating of gold nanoparticles,” 

Nat. Commun. 13, 5342 (2022) 

https://www.nature.com/articles/ 

s41467-022-33074-6 


THE NOBEL PRIZE IN PHYSICS 2022 

A Nobel prize 

for Alain Aspect, John Clauser and Anton Zeilinger 

Jean DALIBARD, Sylvain GIGAN* 

Laboratoire Kastler-Brossel, CNRS, ENS, Collège de France, Sorbonne Université, Paris, France 

* sylvain.gigan@lkb.ens.fr 

The Nobel committee announced on October 4 th that Alain Aspect, John Clauser and Anton Zeilinger 

were awarded the Nobel prize “for experiments with entangled photons, establishing the violation of 

Bell inequalities and pioneering quantum information science” [1]. In this article, we want to put the 

Nobel Prize in perspective, and replace the three laureates’ contribution in their historical context. 

https://doi.org/10.1051/photon/202211623 

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits 

unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 

The development of Quantum 

Physics during the 20 th century 

is certainly one of the most 

extraordinary intellectual adventures 

of mankind. This theory has 

deeply modified our conception of 

the world, and it has had in parallel 

a strong impact on our life with its 

numerous applications: transistors, 

lasers, integrated circuits. One cornerstone 

of quantum science is the 

concept of photons, introduced in 

1905 (see [2]) and one of the most 

prominent features of the quantum 

formalism is entanglement (a term 

coined by Schrödinger). Einstein, 

Podolsky and Rosen pointed out its 

subtle and paradoxical character in 

a celebrated paper. They used this 

notion to demonstrate the conflict 

between quantum mechanics and 

a realistic local theory of the physical 

world. Moreover, to the question 

“Can a quantum-mechanical 

description of physical reality be 

considered complete?” the answer 

of Einstein and co-authors was negative, 

and their conclusion was 

incompatible with the “orthodox” 

point of view, advocated in particular 

by N. Bohr. This conflict between 

Einstein and Bohr lasted until the 

end of their lives; it remained a philosophical 

question until the work 

of J.S. Bell in 1964. Bell proved that 

the correlations between any pair of 

physical quantities, when calculated 

within a realistic local theory, are 

constrained by a specific inequality, 

which can be violated by quantum 

mechanics. From this moment, the 

above-mentioned conflict was no 

longer a matter of taste, but it became 

a quantitative question that 

could be settled experimentally. 



This is when John Clauser enters 

into the story : first, as a graduate 

student at Columbia University, when 

he found a modified version of Bell’s 

theorem with an inequality that can 

be applied to practical experiments 

(using pairs of entangled photons 

and measurement over various polarizations), 

then in 1972 when he 

performed with Stuart Freedman at 

the University of Berkeley the first experiment 

that conclusively showed 

a violation of Bell’s inequality by 

more than 5 standard deviations [3]. 

This experiment, which was using a 

lamp to excite the atoms (pre-laser 

era!) was a tour-de-force with a data 

acquisition time of 200 hours. The result 

of Clauser was later confirmed 

with a similar experiment by Fry and 

Thompson in 1976. 

In the meantime, starting in 1974, 

Alain Aspect engaged in a program 

in which the independence between 

the polarization measurements on 

each photon of the pair was enforced 

by a relativistic argument. In these 

experiments realized at Institut d’Optique 

in Orsay, the setting of each polarizer 

was changing rapidly in time, 

so that there was no possibility that 

an information about this setting is 

exchanged between the two detection 

channels: The choice of the measurement 

basis for the photons polarization 

was done well after the pair 

of entangled photons was created 

and the locality condition, which 

is an essential hypothesis of Bell's 

theorem, becomes a consequence 

of Einstein’s causality that prevents 

any faster-than-light influence. This 

resulted in the publication in 1982 of 

Figure 1: Concept of the Bell Inequality violation 

experiment designed by Aspect: a source of 

entangled photons (center) distributes each 

photon of the pair to four detectors (left and 

right), where fast switches enable measurements 

over different sets of polarizations. 

two key articles [4], to which one of 

us (JD) was lucky to be associated, 

together with Philippe Grangier and 

with Gérard Roger -a skilful engineer. 

Anton Zeilinger realized in 

Innsbruck in 1997 the first quantum 

teleportation experiment, followed 

in 1998 by the third key experiment 

on Bell inequality violations with 

photons, by using ultrafast and random 

settings of the analyzers, thus 

enforcing so-called “strict Einstein 

locality conditions” [5]. As a postdoc 

in Vienna, where the group of Anton 

Zeilinger moved in the early 2000, 

Figure 2: At a conference honoring the 

memory of Alfred Kastler in 1985, photo of 

A. Messiah, A. Aspect and J. Bell, discussing. 

©Laboratoire Kastler-Brossel. 

one of us (SG) was at one of the epicenters 

of this revolution, and witnessed 

the vitality of the field, and the 

breadth of its application, spanning 

also well beyond optics, to atoms, 

superconductors and mechanical 

systems. Although very little doubts 

remain about local realism, the quest 

to experimentally close all potential 

loopholes continued, and remains 

to date an important topic, both as 

a fundamental subject, but also of 

practical importance, as pointed out 

by Alain Aspect in his 2015 perspective 

paper [6]. 

Beyond their crucial contributions 

for which the prize was awarded, 

one can also stress the importance 

and diversity of the three Laureates’s 

other contributions to quantum 

science, for instance for Alain Aspect, 

the Bose-Einstein condensation of 

Helium or the Anderson localization 

of Atoms, to name just two salient 

examples. Another lasting legacy 

is the many outstanding PhD students 

and postdoctoral researchers 

that they formed over decades, and 

who continue to dynamize the field. 

The impact of the findings of these 

three physicists over our vision of 

the world is tremendous and it goes 

actually far beyond the Physics community. 

Philosophers and epistemologists 

have now incorporated all 

these results in their own works and 

concepts. The hope of Einstein for a 

local and realistic description of the 

physical world has failed, and quantum 

mechanics is in perfect agreement 

with experimental results on 



this matter. The results of Aspect, Clauser and Zeilinger 

are now at the core of several modern textbooks in quantum 

mechanics. 

These seminal works crowned by the Nobel prize did not remain 

limited to closing a philosophical debate or to textbooks, 

but were rapidly followed by a stream of applications of entanglement, 

and to the birth of a blooming field, quantum 

information processing, that spans from teleportation, to 

quantum cryptography, to quantum computing. All these 

feats rely heavily, at their core, on the phenomenon of quantum 

entanglement and on non-locality. Quantum information 

processing is now a very active field worldwide, involving 

thousands of groups, and poised to revolutionize the way we 

communicate and compute. Quantum communications, be 

it on deployed fibered networks spanning across countries 

(and enabled by meshes of “quantum repeaters”), or along 

free-space link through satellites, are already a reality for unconditionally-secure 

cryptography. Quantum computing has 

recently demonstrated over different platforms the so-called 

“quantum advantage”: its capacity to perform some specific 

calculations with an exponential speedup over conventional 

computers. While a large-scale universal quantum computer 

remains years away, the world is already getting prepared for 

the “post-quantum” era, where quantum technologies may 

render several of our current approaches to information processing 

obsolete.For example, it is reasonable to expect that 

quantum simulators could soon be used to solve currently 

intractable problems in chemistry and physics, with crucial 

applications such as the design of new drug molecules. 

It remains a humbling lesson to witness how such a profound 

technological and societal change may stems from 

sheer curiosity-driven research : from the deep philosophical 

considerations of the founders of quantum mechanics, 

later formalized by John Bell into measurable quantities, 

and ultimately to the experiments imagined by Alain 

Aspect, John Clauser and Anton Zeilinger. 

REFERENCES 

[1] Demonstrations of quantum entanglement earn the 2022 Nobel 

Prize in Physics, Physics Today (2022) 

[2] A. Zeilinger et al., Nature 433, 230 (2005) 

[3] S.J. Freedman and J.F. Clauser, Phys. Rev. Lett. 28, 938 (1972). 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.28.938 

[4] A. Aspect, J. Dalibard, and G. Roger, Phys. Rev. Lett. 49, 1804 

(1982). A. Aspect, P. Grangier, and G. Roger, Phys. Rev. Lett. 49, 

91 (1982) 

[5] G. Weihs, T. Jennewein, C. Simon, H. Weinfurter, A. Zeilinger, 

Phys. Rev. Lett. 81, 5039 (1998). D. Bouwmeester, J. W. Pan, K. Mattle, 

M. Eibl, H. Weinfurter, A. Zeilinger, Nature 390, 575 (1997) 

[6] A. Aspect, Physics 8, 123. (2015) 

SOME KEY ARTICLES RECENTLY PUBLISHED IN PHOTONIQUES: 

C. Fabre, Photoniques 107, 55 (2021) 

B. Vest et L. Jacubowiez, Photoniques 113, 26 (2022) 

SEE ALSO: 

T. Van Der Sar, T. H. Taminiau and R. Hanson, Photoniques 107, 

44 (2021) 


ZOOM 

Lithuania 

Photonics in Lithuania 

Laser technologies are one of Lithuania's 

strongest and most intensive value-added 

industrial sectors. Since its beginning in 

fundamental research nearly 60 years ago, it has 

grown into a fully self-sustaining ecosystem, 

providing optics, ultrashort pulse lasers, laser 

technologies and systems to the global market. 

© Go Vilnius. Panorama at night. Neris river 


Gediminas Račiukaitis and Petras Balkevičius 

Gediminas Račiukaitis 1, * and Petras Balkevičius 2 

1 

President of the Lithuanian Laser Association, head 

of Department of Laser Technologies, FTMC - Center 

for Physical Sciences and Technology, Savanoriu ave. 231, 

LT-02300 Vilnius, Lithuania 

2 

Executive Director of the Lithuanian Laser Association, 

Mokslininkų str. 11 LT-08412, Vilnius, Lithuania 

*g.raciukaitis@ftmc.lt 

History of lasers in Lithuania 

Laser research activities started six decades ago when the 

first students were sent to Moscow to learn non-linear optics 

and laser physics in 1962. Laser applications started in 

1966 for semiconductor research, while in 1983, the first 

commercial company EKSMA was established to produce 

picosecond lasers. 

Most of the fundamental research in the laser field was 

directed by prof. Algis Piskarskas, a founding father of 

Lithuanian laser science. Activities at Vilnius University and 

the former Institute of Physics resulted in a significant number 

of disruptive innovations and commercial products, 

such as the optical parametric chirped pulse amplification 

(OPCPA) technology proposed in 1992 by researchers at 

Vilnius University and described by the Nobel committee 

as an ‘important offspring’ of the chirped parametric amplification, 

for which Gérard Mourou and Donna Strickland 

were awarded the Nobel Prize in 2018. 

Scientific laser 

The scientific laser market is a historically strong point 

for the Lithuanian laser industry. Due to the impressive 

scientific expertise of researchers and engineers in new, 

beyond-the-state-of-the-art product developments, 95 out 

of the world’s top 100 universities are using lasers made in 

Lithuania. In addition, the “seal of excellence” is approved 

by applying the laser product, made in our country, 

in CERN, NASA, DESY, SLAC, ELI and other world-class 

facilities. 

ELI-ALPS in Szeged, Hungary - one of the three pillars 

of the Extreme Light Infrastructure intended to deepen 

knowledge in fundamental physics on the attosecond 

timescale. The use of novel concepts overcame current 

technological limitations in laser intensity upscaling. The 

main technological backbone of ELI-ALPS is the SYLOS 

laser which employs OPCPA technology and operates at 

few-cycle to sub-cycle laser pulses. The SYLOS laser has 

been designed and manufactured by a consortium of two 

Lithuanian companies – Ekspla and Light Conversion. 

The two biggest Lithuanian laser companies have pooled 

their knowledge and technologies together and created the 

biggest laser among the fastest – and therefore the fastestamong 

the biggest. Achievements have been selected as a 

finalist for the Berthold Leibinger Innovationspreis in 2018. 

Recently, the third generation SYLOS 3 laser is in assembly. 

The system has been upgraded to produce an even shorter 

pulse duration:

Lithuania 

ZOOM 

single shot or low-frequency regime, SYLOS 3 will be running 

at a 1 kHz repetition rate”, mentioned Kestutis Jasiūnas, CEO 

of Ekspla. Today OPCPA is the leading method for generating 

high-intensity laser radiation as it prevails compared to conventional 

(Ti: Sapphire laser-based) femtosecond technology in 

terms of pumping efficiency, contrast, bandwidth, and as a 

consequence, the degree of control of the generated radiation. 

“Despite being complex, the system will ensure exceptional stability”, 

– added Martynas Barkauskas, CEO of Light Conversion; 

– “SYLOS 3 will deliver ~120 mJ pulses with ≤ 250 mrad CEP 

stability and energy stability ≤ 1%.” 

Lasers for Industry 

Laser physics and applications coexist all the time in parallel 

in Lithuania. That is an active dipole which charges the whole 

laser community to new discoveries and laser application areas. 

Long-term, well-established relations among companies and 

researchers at universities and research institutions evident the 

critical mass required to gain new markets and applications. 

The last decade was marked by intensive penetration into the 

industrial laser market, where nearly half of the total sales are 

currently taking place. This segment is presented not only by 

reliable 24/7 ultrashort pulse laser sources as industrial tools 

for delicate material processing. Solid expertise and a group 

of companies and researchers have been accumulated in the 

field of laser microfabrication with ultrashort pulse lasers. The 

output is laser processing technologies and systems applied in 

electronic, consumables, automotive or bio-medical industries. 

Laser machines are a promising market for our products. 

The main issue for an even stronger presence in the industrial 

market is the lack of large end-users in the country. Therefore, 

laser companies and the Lithuania Laser Association intensively 

work to expose our visibility in global markets. Laser and 

photonics products are exported to more than 80 countries, 

with leading high-tech ones USA, Germany and Japan as well as 

the “world’s factory” China since the main manufacturing facilities 

for consumables and electronics are still working here. We 

are rediscovering the leading manufacturing markets (South 

Korea, Taiwan, …). 

The impressive growth of the laser industry by 16.2% CAGR 

is continuing from 2009 through 2021, and expansion of the 

community to more than 60 companies took place, mainly by 

spin-offs from research laboratories, broadening the spectrum 

of laser products and applications. Today, the Lithuanian laser 

sector presents roughly 200 M€ industry providing more than 

1400 highly skilled jobs at a value-added per employee that is 

more than three times larger than the national average. 

Close to 20 Lithuanian companies are active members of 

EPIC – European Photonics Industry Consortium. EPIC Annual 

General Assembly took place in Vilnius in April 2022, one of the 

first events after the pandemic. Delegates were welcomed by 

the Prime Minister of Lithuania Ms Ingrida Šimonytė. That was 

an excellent opportunity to show our achievements and search 

for new partners, customers or investors. The companies successfully 

raise external funding for business scale-up 


ZOOM 

Lithuania 

OPTOMAN is focused on Ion-Beam Sputtering (IBS) technology 

which provides the highest possible accuracy, repeatability 

and quality of optical coatings. Low GDD ultrafast mirrors 

are designed to handle high peak power at reflectance greater 

than 99.8%. This makes these mirrors ideal for femtosecond 

laser systems, like the Ti: Sapphire, where pulse broadening is 

a concern. Mirrors optimised for high-power pulsed and CW lasers, 

exhibit LIDT as high as 80 J/cm 2 @(1064 nm, 10 ns, S-on-1). 

Ekspla: FemtoLux30 - gold honoree at the 2022 Laser Focus 

World Innovators Awards 

and new product development. LITEK and TOOLas clusters 

are part of the laser and photonics ecosystem, accelerating of 

new companies and promoting photonics-related solutions for 

industry digitalisation. 

Key competencies of Lithuanian laser 

and photonics companies 

• Reliable 24/7 ultrashort pulse lasers for industry; 

• High-intensity TW and PW class laser systems; 

• Tunable wavelength laser devices (OPO, OPA); 

• Optical components and systems; 

• Opto-mechanics; 

• Optical coatings; 

• High-power electronics; 

• Laser technologies for material processing; 

• Equipment for laser processing; 

• Laser-based services; 

• Nonlinear laser spectroscopy; 

• Optical and quantum communication; 

• Optical measurements; 

• Laser systems for medical diagnostics and therapy. 

Lasers 

LIGHT CONVERSION – the world leader in femtosecond lasers 

and OPO - has officially opened an 11,200 sq. m unit at its headquarters 

in Vilnius this year, expanding into a total area of about 

18,000 sq. m. The state-of-the-art building houses research and 

development and vertically integrated laser production: CNC 

machines, micro-optics, electronics and clean rooms for final 

product assembly. A cutting-edge intralogistics system will be 

used to handle components between production steps. The expansion 

will boost the production volume to meet the growing 

demand for femtosecond lasers, wavelength-tunable sources, 

and medical systems. 

For the third year in a row, Light Conversion is honoured 

in the Laser Focus World Innovation Awards. The gold honoree 

in 2022 was awarded to HARPIA-TG - a transient grating 

spectrometer for carrier diffusion coefficient and lifetime 

measurements received. It operates as a non-invasive and 

non-destructive pump-probe spectrometer exciting the specimens 

with a periodical laser interference field, creating 

the transient grating – spatial refractive index modulation. 

Relaxation of the grating provides information on carrier 

diffusion. The latest model of femtosecond lasers PHAROS, 

PHAROS-UP, offers a sub-100 fs output without the need for 

external compression. It was awarded a silver honoree this year. 

Light Conversion: Dr Kipras Redeckas next to HARPIA 

transient grating spectrometer that received Gold Honoree 

in Laser Focus World Innovation Awards 2022 

The latest news from our companies 

Optical coatings and components 

EKSMA OPTICS just moved into a new facility with a total area 

of 7,300 sq. m with the most advanced climate control system. 

Expanded manufacturing area includes >1,000 sq. m of 

cleanroom dedicated to laser optics manufacturing and optical 

systems assembling processes. Investments are made in new 

production equipment for laser-grade spherical and aspherical 

lenses, dielectric coatings deposition equipment for laser optics 

and crystals and quality control. The company is now able to 

make not only aspherical but also free-shape optics. 

ALTECHNA has fully accumulated Altechna Coating and 

is moving to a new 3,100 sq. m facility. They are executing a 

€6.6 M investment plan to acquire technology equipment and 

manufacturing infrastructure. The new capabilities will enable 

the company to scale up with demand and create a competitive 

advantage in technology and cost for customers. 


Lithuania 

ZOOM 

ADVERTORIAL 

New Eksma Optics facility 

The laser expands the capabilities in micromachining applications 

as well as scientific applications such as spectroscopy 

and high-energy physics. 

EKSPLA is entering the market with a new class femtosecond 

laser with a flexible pulse burst operation. FemtoLux 30 laser 

from Ekspla, was recognised as a gold honoree in the industrial 

laser systems category at the 2022 Laser Focus World Innovators 

Awards. The new femtosecond laser employs an innovative 

cooling system and sets new reliability standards among industrial 

femtosecond lasers. The FemtoLux 30 uses an innovative 

Direct Refrigerant Cooling method, which provides the highest 

heat transfer rates, high-temperature stability, small size and 

low weight. The FemtoLux 30 femtosecond laser has a tunable 

pulse duration from 11.20 J/cm 2 @ 355 nm, 6 ns, 10 3 –on–1 

• > 0.484 J/cm 2 @ 343 nm, 300 fs, 10 7 –on–1 

ANTI-REFLECTIVE COATINGS: 

• > 40 J/cm 2 @ 1064 nm, 10 ns, 10 3 –on–1 

• > 12.66 J/cm 2 @ 355 nm, 6 ns, 10 3 –on–1 

POLARIZING COATINGS: 

• > 18.7 J/cm 2 @ 1064 nm, 10 ns, 10 3 –on–1 

About OPTOMAN: 

Born in 2017 in Vilnius, Lithuania, OPTOMAN is a coatings 

SuperHero, who designs, develops and manufactures 

advanced, high accuracy and repeatability IBS thin 

film coatings. By digging deep into each application, 

OPTOMAN provides custom, application-optimized 

optics for academia and industry. 

Get in touch with OPTOMAN at info@optoman.com 

With great laser power comes great responsibility 

for coaters! 


ZOOM 

Lithuania 

Femtosecond laser testing at Light Conversion 

Holes drilled in glass wafer for interposer 

by Workshop of Photonics 

Laser technologies 

The integrated value chain from components to laser machines 

with technologies is another peculiarity of the Lithuanian 

laser community. A group of companies AKONEER (former 

ELAS), EVANA TECHNOLOGIES, FEMTIKA, WORKSHOP OF 

PHOTONICS, together with researchers at Vilnius University 

and FTMC develop technologies for microfabrication utilising 

advances provided by ultrashort pulses lasers: from 

laser-based service to complete laser machines for a factory 

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LABWORK 

Frustrated total internal reflection 

Frustrated total internal reflection: 

the Newton experiment revisited 

/////////////////////////////////////////////////////////////////////////////////////////////////// 

Benoit CLUZEL*, Frédérique DE FORNEL 

Laboratoire Interdisciplinaire Carnot de Bourgogne UMR CNRS 6303, Université de Bourgogne Franche-Comté, 

9 avenue Alain Savary, 21078 DIJON - FRANCE 

* benoit.cluzel@u-bourgogne.fr 


This is an Open Access article distributed under the terms of the 

Creative Commons Attribution License (http://creativecommons. 

org/licenses/by/4.0), which permits unrestricted use, distribution, 

and reproduction in any medium, provided the original work is 

properly cited. 

Three centuries ago, Isaac Newton reported the 

experimental observation of the tunnelling of a light ray 

between two prisms separated by a small gap once one of 

them was shinned in total internal reflection. This article 

describes a modern revisit of this seminal Newton’s 

experiment, generally known as the Frustrated Total 

Internal Reflection. This experiment was created in the 

framework of a series of lectures about near-field optics 

and nanophotonics for Master students. During a 4h lab 

work session, the students are running the experiment 

to evidence and quantify the evanescent wave on top of 

a glass prism once illuminated above the critical angle. 

Any bachelor student who studies 

optics and electromagnetism 

at University knows that 

illuminating a prism under total internal 

reflection results in the generation 

of an evanescent wave on top 

of it. Near field optics, which refers 

to the research field on evanescent 

waves and their related applications, 

has grown amazingly since 30 years 

thanks to the rapid progress of nanotechnologies. 

Primarily restricted to 

the applications in subwavelength 

imaging by scanning probe microscopy 

in the late 90s and earlier in 

evanescent couplers for waveguide 

optics, evanescent waves have widely 

spread to the field of nanophotonics 

and plasmonics where they contribute 

to create the original properties of artificial 

optical materials such as metamaterials, 

metasurfaces or photonic 

crystals. Nowadays, numbers of active 

and passive optical systems are taking 

benefits of these evanescent waves 

such as for fingerprint recognition, 

tactile screens and promising cutting 

edge new technologies for AR/VR vision 

which will reach the market in a 

near future. 

The first direct description of an 

optical experiment involving an 

evanescent wave is attributed to 

Isaac Newton in his seminal book 

“Opticks: or, a treatise of the reflections, 

refractions, inflections and colours of 

light” [1]. In this so-called “Frustrated” 

[2] Total Internal Reflection (FTIR) 

experiment, Newton considered two 

glass prisms brought together so that 

they do not fully touch, one of them 

being illuminated under total internal 

reflection and he wrote in Book 

3: “For the Light which falls upon the 

farther surface of the first Glass where 

the Interval between the Glasses is not 

above the ten hundred thousandth Part 

of an Inch (2.54µm), will go through that 

Surface, and through the Air or Vacuum 

between the Glasses, and enter into the 

second Glass”. The theoretical background 

to explain this phenomenon 

was missing when Newton did these 

observations and it has been explored 

later on both experimentally and theoretically 

by Fresnel and many others. 

More details on attempts and advances 

on this subject throughout history 

are available in an article written 

by E. Hall [2] in 1902 which provides 

references to related works in the 

XVIII th and XIX th centuries, and also 

in a review paper by Zhu and coworkers 

[3] in 1986 which makes the link 

to the XX th century. Because FTIR appears 

for very small distances 


LABWORK 


Figure 1. a) Cover of Isaac Newton’s book. 4 th edition 1730. b) Illustration of the total internal reflection 

between a prism and air for an incident angle larger than the critical angle. c) Illustration of the 

frustrated total internal reflection by bringing a second prism in the near-field of the first one. 

d) s- and p- polarizations of the incident field. 

between the prisms, addressing it experimentally 

and achieving a quantitative 

relationship between the 

prisms distance and the overall transmitted 

light has been a longstanding 

challenge. The experiment described 

hereafter provides such a relationship 

under various illumination conditions 

(polarization, wavelength) in a friendly-user 

setup that has been used by 

more than two hundred students over 

the past 10 years. 

The Newton 

experiment 

as a labwork for 

Master students 

In the framework of our lectures to 

the Master students at Université 

Bourgogne Franche-Comté (International 

Master on Physics, Photonics 

and Nanotechnologies), we created 

10 years ago a set of turn-key experiments 

illustrating some important 

Figure 2. a) Picture of the turn-key setup for evidencing the frustrated total internal reflection. 

b) Schematic drawing of the experiment. c) Picture of the two prisms with the high radius 

of curvature lens glued on top of. d) Smartphone picture of the operating experiment once 

it is shinned with a bright white light. In this situation the two prisms are touching together. 

effects arising in Near-field Optics 

and Nanophotonics and the revisited 

Newton experiment described in 

this article is one of them. All the elements 

of this experimental setup are 

available commercially and we have 

intentionally limited the cost of each 

of them to achieve a setup with a reasonable 

price of less than 5,000 €. As 

shown in Figure 2, it consists of an 

optical bench mounted on a damped 

breadboard and including a set of 

two prisms mimicking the Newton 

experiment. The optical source for 

illumination consists of a blackbody 

lamp coupled to a multimode fiber 

which is free-space collimated 

into a large beam to create a pseudo 

plane wave around the optical 

axis. The source is filtered spectrally 

with a band-pass colored filter 

around 633nm and is linearly polarized 

to set the illumination to s- or 

p-polarization (see Figure 1 d). The 

first prism is a right-angle prism to 

achieve a total internal reflection at 

θ i =45° on its outer face. The second 

prism is also a right-angle prism. 

It is mounted in front of the first 

one and its accurate positioning is 

controlled by a piezoelectric stage. 

To bypass the tricky task to align the 



LABWORK 

Figure 3 . Experimental measurements and theoretical predictions of the Frustrated Total Internal 

Reflection for a) a p-polarized and b) a s-polarized illumination at λ=633nm. 

The transmitted intensity is plotted versus the distance between the two prisms. The approach 

(circles) and the retraction (crosses) of the second prism are separated in the experimental graphs 

to highlight the hysteresis of the piezoelectric effect used for positioning the second prism. 

parallelism between the faces of the two 

prims facing each other, we used a plano-convex 

lens glued (with an optical 

UV glue!) on the inner face of the second 

prism (Figure 2c). In this configuration, 

the top of the convex face defines the 

contact point between the two prisms. 

As the radius of curvature of the lens 

is very large (400mm) compared to the 

characteristic distance between prisms 

at which FTIR occurs (

LABWORK Frustrated total internal reflection 

These FTIR experiments can be described 

analytically from Fresnel relations 

which connect the incident, 

reflected and transmitted amplitudes 

of the different fields at both sides 

of the interfaces between the two 

prisms and the gap medium (air). The 

complete algebraic manipulations giving 

the analytical relations for FTIR 

are described for a general case in 

[4], and, in our situation depicted in 

Figure 1c) where the two prisms have 

the same refractive index n 1 and are 

separated by air (n 2 = 1), the transmission 

of a monochromatic planewave 

is reduced to : 

T = 1/(asinh 2 ρ + 1) 

— 

with ρ = (2πd/λ) √n 2 1 sin 2 θi - 1 

and 

a = a s = [(n 2 1 – 1)/2n 1] 2 {1/[cos 2 θ i (n- 

2 

1 sin 2 θ i – 1)]} for s- polarization, 

a = a p = a s [(n 2 1 + 1)sin 2 θ i – 1] 2 

for p-polarization, 

This theoretical transmission under 

FTIR conditions for both polarizations 

is shown together with the 

experimental results in Figure 3. 

A relatively good quantitative agreement 

is achieved despite the uncertainties 

related to the piezoelectric 

stage motion. In this version of the 

setup, it is worthnoting that such 

an agreement is only achieved for a 

narrow colored filter with a central 

wavelength matching the factory 

EVANESCENT WAVE GENERATION UNDER TOTAL INTERNAL 

REFLECTION ILLUMINATION 

Once the illumination of an interface between two dielectric media is carried out by a monochromatic plane wave with 

a wavelength λ, the relationship between the angle of incidence θ i , and the angle of refraction, θ t , is given by the momentum 

conservation of the wavevectors component parallel to the interface. Hence, using the expression k 2 t,x + kt,y 2 + kt,z 2 = k 2 t = ( 

— 

2π 

n 2 

λ ) 2 , 

the transmitted wavevector is: 

 

k → t = k 

k t,x = 

2π 

— n λ 

2 sinθ t = — 

2π 

n λ 

1 sinθ i = k i,x 

t,y = 0 

k t,z = — 

2π √ — n 2 

λ 

2 – n 2 1sin 2 θ i 

Figure a) Reflection and transmission at an optical interface for an oblique incidence below the critical angle. 

Figure b) Surface wave generation for an oblique incidence above the critical angle. 

For any incident wave with θ smaller than the critical angle θ c = sin ( n –1 2 

n 

— 

1 

), this provides the well-known Snell Descartes law 

n 1 sinθ i = n 2 sinθ t between the incident and the transmitted waves. For higher angles of incidence, k t,z becomes imaginary since 

the argument of the square root is negative, and is written as k t,z = jK̴ with K̴ = — 2π √ — n 2 

λ 

1sin 2 θ i – n 2 2 . For an incident plane wave 

E → i,s (for s-polarized light here), the electric field in the second medium is E t,s (x → , z, t) = t.E i,s exp[ j(ωt – k t,x )].exp(–K̴ z)e → y with t 

the Fresnel complex transmittance. Hence, in the second medium, the transmitted wave is a surface wave which decays 

exponentially along z with a penetration depth d p = 1/K̴ while it propagates along x. 


LABWORK 

alignment wavelength of the fiber collimator (633 nm here). 

Indeed, changing the filter wavelength without changing 

the collimator accordingly results in a slight divergence of 

the incident beam. Thus, it introduces an additional uncertainty 

on the angle of incidence which rapidly moves 

the experimental measurement away from the theoretical 

calculations. In other versions of the setup, for instance 

using lasers with different wavelengths, this artefact vanishes 

but we decided to keep it as it is for pedagogic reasons 

and to motivate discussions with the Master students at the 

end of the labwork. 

Conclusion 

We have presented in this paper a modern revisit to 

Newton's frustrated total internal reflection experiment. 

The setup described here is a turnkey automated experiment 

that provides a quantitative measurement of the 

evanescent wave excited at the top of a glass prism during 

total internal reflection illumination. As part of the 

courses on Near-field optics and Nanophotonics, more 

than 200 Master students from the EIPHI Graduate School 

in Bourgogne Franche-Comté have been carrying out this 

experiment in a 4-hours labwork for the past 10 years. They 

perform the experiment themselves, compare their results 

with the theory in a report in which they also provide their 

own observations and comments. This experiment is the 

first of a series of four other home-made labworks developed 

to illustrate some key features in nanophotonics, 

including surface plasmon resonance, microfibre pulling 

and evanescent coupling to whispering gallery mode resonators, 

optical trapping of nanoparticles and absorption 

molecular spectroscopy. All these experiments are 

available as pedagogical resources on the SMARTLIGHT 

platform at the Laboratoire Interdisciplinaire Carnot de 

Bourgogne (France). 

Acknowledgements 

This work benefited from the facilities of the SMARTLIGHT platform 

(EQUIPEX+ contract "ANR-21-ESRE-0040") and has been supported 

by the EIPHI Graduate School (contract “ANR-17-EURE-0002”) and 

Région Bourgogne Franche-Comté. 

REFERENCES 

[1] I. Newton, Opticks: or, a treatise of the reflections, 

refractions, inflexions and colours of light, Book 2, Part1, 

Obs. 1, 2 & 8; Book 3, Queries 29, 4 th edition, London (1730) 

[2] P.J. Leurgans and A.F. Turner, J. Opt. Soc. Am 37, 983 (1947) 

[3] E. E. Hall, Phys. Rev. 15, 73 (1902) 

[4] S. Zhu, A.W. Yu, D. Hawley, and R. Roy, Am. J. Phys. 54, 

601 (1986) 



The first detection of the CMB 

THE FIRST DETECTION OF THE CMB 

THAT OPENED A NEW FIELD 

IN COSMOLOGY 

/////////////////////////////////////////////////////////////////////////////////////////////////// 

Bruno MAFFEI 1, *, Paolo DE BERNARDIS 2 , Nabila AGHANIM 1 , Samantha STEVER 1,3 

1 

Institut d’Astrophysique Spatiale, CNRS/Université Paris-Saclay, Orsay, France 

2 

Dipartimento di Fisica, Università di Roma, La Sapienza, Rome, Italy 

3 

Department of Physics, Okayama University, Okayama, Japan 

* bruno.maffei@universite-paris-saclay.fr 

Holmdel antenna used by Penzias and Wilson 

for the first detection of the CMB emission 

[credit NASA pictures] 

The Cosmic Microwave Background, the oldest signal 

that can be seen in the sky, is the direct proof that our 

Universe was extremely dense and hot several billion 

years ago. The first experimental detection of this fossil 

radiation has been performed in 1964 and has since 

then become a powerful tool to probe the formation 

and evolution of the Universe. Observations of this 

extremely faint signal pushes the boundaries of many 

technological developments notably in the fields of 

optics, detection and cryogenics for space applications. 


This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted 

use, distribution, and reproduction in any medium, provided the original work is properly cited. 

THE COSMIC MICROWAVE 

BACKGROUND AND ITS FIRST 

DETECTION 

Recycling part of a previous experiment 

in order to perform observations 

of our Galaxy with an antenna operating 

at a wavelength of approximatively 

7 cm, radio astronomers Arno Penzias 

and Robert Wilson had to face the 

presence of a background signal that 

they could not explain when pointing 

their antenna in any direction in the 

sky. After checking for any possible 

source of noise in their instrument or 

from the surroundings, as any good 

scientist would do, this background 

signal implied an astrophysical 

emission that they could not interpret 

immediately. Looking for theoretical 

explanations, they found out 

that some other physicists had earlier 

predicted such an emission, termed 

the Cosmic Microwave Background 

(CMB). Some debates exist still about 

whom first, amongst Alpher and 

Herman, Friedmann, Lemaître, or 

Gamov, alongside Robert Dicke who 

tried to measure such a signal. For this 

first detection of the CMB, Penzias and 

Wilson were awarded the 1978 Nobel 

Prize in Physics. 

The farther we probe our Universe in 

terms of distance, the further we see 

in time, due to the time that light with 

finite speed takes to reach the observer. 

The CMB emission is the most 

direct evidence of the existence of the 

so-called Big Bang, which happened 

about 14 billion years ago when the 

Universe was extremely hot and dense. 

Immediately after the Big Bang the 

Universe began cooling down, but for 

about 380,000 years it was still too hot 

for charged particles to combine to 

form neutral atoms. Therefore, during 

that period, the Universe consisted of 

a plasma strongly coupled to photons 

for which the mean free path was small 

and therefore travelling little distance, 

resulting in a totally opaque medium 

in thermal equilibrium. When the 




temperature dropped below 3000 K, 

recombination of charged particles occurred, 

forming atoms and leading to 

matter and radiation decoupling when 

photons were then free to travel. This 

transition created the surface of last 

scattering radiating like a pure blackbody 

at 3000 K, which is seen nowadays 

as an isotropic blackbody emission at 

2.7 K due to the redshift effect. 

THE CMB AS A NEW TOOL 

FOR OBSERVATIONAL COSMOLOGY 

This very faint CMB emission follows 

Planck’s law at T=2.7 K and peaks today 

at a frequency of about 150 GHz (2 mm 

wavelength). Any other emission from 

the sky, from the surroundings, or from 

the instrument itself (being usually 

warm) could, and will, be stronger 

in this region of the electromagnetic 

spectrum (microwave) than the CMB 

signal. Cooling down the instrument, 

and in particular its receiver to reduce 

noise and therefore gain sensitivity, 

is required. Penzias and Wilson were 

able to perform the first detection at a 

Figure 1. Blackbody spectrum (T=2.725 K) of the 

CMB as measured by the space mission COBE- 

FIRAS [2,3]. Crosses are data point with error bars too 

small to be visible. [Credit from NASA]. 

wavelength of 7.35 cm (not even the 

peak frequency of the CMB) due to 

the fact that the radio receiver that they 

were using at the end of their antenna 

was making use of a switch comparing 

the signal from the antenna to a termination 

cooled at a temperature of 4 K, 

using a tank of liquid helium [1]. 

A full sky-map of the CMB emission 

in which the surrounding noise contamination 

can be mostly removed 

can only be achieved from a space 

platform. The second milestone in 

CMB exploration was achieved in 

the early 1990’s with NASA’s COBE 

satellite [2]. Amongst its outstanding 

results, leading to the award of the 

2006 Nobel Prize in Physics to John C. 

Mather and George F. Smoot, COBE 

not only provided the first low-resolution 

CMB map over the full sky, but 

realised also the first (and still only) 

spectroscopic measurement showing 

a perfect fit to a blackbody emission 

spectrum (Fig. 1) with a temperature of 

T= 2.725 ± 0.001 K [3]. To do so, COBE 

spectrometer was cooled down to 1.6 K 

using superfluid helium. 

Once COBE’s sky maps were “cleaned” 

from instrumental noise and other astrophysical 

sources, which are seen 

as contaminants from a CMB perspective, 

the resulting maps revealed 

that the CMB temperature was not 

constant across the sky. Most 




prominently, a temperature variation 

of ± 0.0035 K was revealed in opposite 

direction in the sky. This dipole 

effect is due to a differential redshift 

(Doppler effect) due to the Galaxy 

moving with respect to the CMB at 

a speed of about 600 km/s. Once this 

effect is removed, we are left with 

temperature variations that are called 

anisotropies. Indeed, like a theatre 

curtain preventing spectators from 

seeing what is happening backstage, 

shapes and intensity of movements 

of this curtain might indicate what is 

happening beyond it. Similarly, we 

cannot see past this surface of last 

scattering as the Universe was opaque 

during that era. However, density 

inhomogeneities in the primordial 

plasma, prior to recombination, that 

then led to the formation of structures 

(e.g. galaxies, clusters of galaxies) 

that we now know, have created CMB 

temperature inhomogeneities across 

the sky. 

This opened a brand-new area of 

observational and experimental 

Cosmology, as theory shows that the 

study of these anisotropies both in intensity 

and polarisation is a unique tool 

to probe the formation and evolution 

of the Universe as well as its geometry 

and its content through an accurate 

determination and constraints of the 

various cosmological constants. 

However, to detect these temperature 

anisotropies with a reasonable signal-tonoise 

ratio, stringent constraints were 

put on the instruments to be used. At 

least an order of magnitude in sensitivity 

had to be gained with respect to 

COBE, together with a need for much 

higher spatial resolution, as COBE’s 

7-degree resolution was far too coarse to 

measure the expected spatial variations 

at angular scales smaller than 1 degree. 

Accurate control of the instrument is 

also required in order to reduce some 

spurious signals (systematic effects). 

Moreover, with such a faint target signal, 

any other astrophysical emissions, 

referred as foregrounds, must also be 

measured and fitted with high precision 

in order to be subtracted from the data. 

This leads to the need of a large spectral 

range, typically from 30 to 800 GHz. 

The balloon-borne project BOOMERanG 

was the first experiment, after COBE, to 

measure the CMB anisotropies over a 

large portion of the sky with sufficient 

accuracy to perform the first measurement 

of the temperature anisotropy 

power spectrum. From these results 

released in 2000, a crucial conclusion 

was drawn at that time: the constant 

setting the curvature of the Universe is 

equal to 1, and we are therefore living 

in a flat Universe [4], meaning that our 

Universe would continue to expand at 

the same rate as today. However, since 

then independent measurements with 

supernovae, have shown that the expansion 

rate is increasing due to what 

is called Dark Energy. 

Other projects (MAXIMA, DASI, and 

NASA WMAP space mission) confirmed 

and improved our knowledge of 

the CMB with the ESA-led third generation 

space mission Planck, launched in 

2009, being the latest major milestone. 

The Planck mission [5] consisted of 

two instruments at the focus of a 1.5 m 

diameter off-axis telescope. The Low 

Frequency Instrument (LFI) was using 

radiometers cooled to 20 K operating 

between 30 and 70 GHz. The High 

Frequency Instrument (HFI) used 

bolometers operating between 90 and 

900 GHz, the most sensitive detectors 

in this frequency range at that time, 

cooled to 0.1 K (for the first time in 

space). Together with careful design 

and calibration of the instruments, in 




particular the optics for which the telescope 

beams were measured with a dynamic 

range better than 80 dB, temperature 

variation measurements of a few μK per 

pixel were reached, allowing for a science 

legacy which has not been surpassed so 

far [6]. Amongst its many results, notably in 

the determination of the parameters of the 

ΛCDM model of our Universe, we can cite 

that the Hubble constant has been measured 

as H 0 = 67.36 ± 0.54 km s −1 Mpc −1 and 

the age of the Universe is 13.797± 0.023 Gyr. 

We can also cite the determination of the 

parameter n s = 0.9649 ± 0.042, called the 

spectral index of the initial perturbations, 

which confirms the existence of an inflationary 

phase that stretched the tiny quantum 

fluctuations into the seeds of galaxies and 

large-scale structures. 

TOWARDS THE FUTURE 

We have continuously seen that each 

time major results (some not foreseen) 

are achieved, cosmologists will have new 

theories to be proven experimentally. 

Theory predicts two types of polarisation 

for the CMB anisotropies: E-modes and 

B-modes. The Planck mission was not originally 

designed for extremely accurate 

measurements of the CMB polarisation, 

Figure 2. 

CMB temperature 

anisotropies sky map 

reconstructed from 

the 9 frequency maps 

measured during the 

Planck mission lifetime 

[Credit ESA and the 

Planck collaboration]. 

even if its results on the E-mode power 

spectrum reconstruction are unbeaten 

still. Measurement of the B-modes, 

amongst all implications in our understanding 

of the evolution of the early Universe, 

will allow for the detection of primordial 

gravitational waves (before the creation of 

the CMB) and the phase of inflation (exponential 

expansion of the Universe just after 

the Big Bang). However, this measurement 

would require an increase in sensitivity of 

about two orders of magnitude with respect 

to the Planck mission. Planck-HFI 

bolometers operated at 0.1 K were already 

photon noise limited (i.e. not limited by the 

detector sensitivity). Therefore, improvement 

of the overall sensitivity can only 

happen through the multiplication of the 

number of detectors (from a few tens to several 

thousands) while improving still the 

performance of each component so that 

the measurement is not limited by instrument 

systematics. Needless to say, this represents 

an incredible technical challenge 

on which many institutes are working. 

Several ground-based and balloon projects 

are being planned and developed, with the 

new Japan-led LiteBIRD project being potentially 

the fourth generation CMB space 

mission. The race is on… 

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ADVERTORIAL 

REFERENCES 

[1] A.A. Penzias, R.W. Wilson, Astrophys. J. Letters 142, 419 (1965) 

[2] N.W Boggess, J.C. Mather et al., ApJ 397, 420 (1992) 

[3] D.J. Fixsen, J.C. Mather, ApJ 581, 817 (2002) 

[4] P. de Bernardis et al., Nature 404, 955 (2000) 

[5] J.A. Tauber et al., Astron. Astrophys. 520, id.A1, 22 (2010) 

[6] The Planck collaboration, Astron. Astrophys. 641, id.A1, 56 (2020) 

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FOCUS 


HALIDE PEROVSKITES 

FOR PHOTONIC APPLICATIONS 

/////////////////////////////////////////////////////////////////////////////////////////////////// 

M. CHAMARRO 1, * , C. R. MAYER 2 , T. PAUPORTÉ 3 , E. DROUARD 4 , H.-S. NGUYEN 4 , C. SEASSAL 4 , S. C. BOEHME 5,6 , 

M. V. KOVALENKO 5,6 , E. DELEPORTE 2, * 

1 

Sorbonne Université, CNRS, Institut des NanoSciences de Paris, 4 place Jussieu, F-75005 Paris, France 

2 

Université Paris-Saclay, ENS Paris-Saclay, CentraleSupélec, CNRS, LuMIn (UMR 9024), 91190 Gif-sur-Yvette, France 

3 

Institut de Recherche de Chimie Paris, ChimieParisTech, PSL University, CNRS, 11 rue P. et M. Curie, F-75005 Paris, France 

4 

Univ. Lyon, École Centrale de Lyon, CNRS, INSA Lyon, Université Claude Bernard Lyon 1, CPE Lyon, INL, UMR5270, 69130 Ecully, France 

5 

Department of Chemistry and Applied Biosciences, Institute of Inorganic Chemistry, ETH Zürich, 8093, Zürich, Switzerland 

6 

Laboratory for Thin Films and Photovoltaics, Empa−Swiss Federal Laboratories for Materials Science and Technology, 

8600, Dübendorf, Switzerland 

* Emmanuelle.Deleporte@ens-paris-saclay.fr; maria.chamarro@insp.jussieu.fr 

Halide perovskites are a new class of semiconductors 

showing an incredible set of physical properties wellsuited 

for a large range of opto-electronic applications. 

These physical properties can be easily tuned and adapted 

to the intended application by modifying the composition 

and the size of the material. Additionally, these materials 

are solution-processed at low temperature and ambient 

pressure, and contain earth-abundant elements. However, 

some important challenges remain: the presence of lead 

and the stability. In this paper, we present some outlines of 

these materials in several fields of opto-electronics, i. e. photovoltaics and light-emitting 

devices, such as LEDs, single-photon sources, lasers, and photonics. 

https://doi.org/10.1051/photon/202216042 

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, 

distribution, and reproduction in any medium, provided the original work is properly cited. 

ABX 3 perovskites constitute 

the oldest families of crystals 

described by crystallography: 

the calcium 

titanate CaTiO 3 was named 

a “perovskite” by the 

German mineralogist Gustav Rose around 

1839 in honor of the Russian mineralogist 

Lev Alexeïevich Perovski. Since then, all 

compounds with ABX 3 stoichiometry are 

called perovskites. Since 2009, the family 

of the halide perovskites is at the origin of a 

dazzling success in the field of photovoltaics 

shortly followed by outstanding results in 

the field of optoelectronic technologies: for 

this family, A is an organic (inorganic) monovalent 

cation such as methylammonium, 

formamidinium, (Cesium), B is a divalent 

metal usually lead, and X is a halogen such 

as I, Br or Cl (figure 1). 

A phenomenal enthusiasm of the international 

community has followed the first 

encouraging results [1] to optimize the material 

itself and the perovskite-based devices 

and to understand the physical properties 

of this new class of semiconductors. Very 

rapidly, it appeared that halide perovskites 

have an impressive number of advantages 

which explain their success story [2]: an appropriate 

and adjustable bandgap which 



FOCUS 

can be easily tuned from the IR to the blue 

region of the electromagnetic spectrum 

by changing the halogen and allowing optimization 

of photon collection combined 

with a high absorption coefficient due to 

the direct nature of the bandgap (in the 

range of 10 4 to 10 5 cm -1 ); large diffusion 

lengths (comparable to the ones in silicon) 

due to a long lifetime of the charge 

carriers; a surprising “defect tolerance”, 

i.e. the electronically benign nature of the 

most common point defects (vacancies 

and interstitials) with only shallow trap 

states close to the valence and conduction 

bands, favoring detrapping of carriers 

at room temperature and, hence, small 

non-radiative recombination rates; and 

finally, a large tunability of the exciton 

binding energy allowing to choose the 

optimal composition depending on the 

targeted application. 

A remarkable advantage of the halide 

perovskites is the fact that they are synthesized 

in solution, under ambient to 

mildly elevated temperature and atmospheric 

pressure conditions, compatible 

with large surface deposition techniques 

and leading to lower production costs 

compared to silicon and other inorganic 

semiconductors. In addition to all these 

advantages, this family of compounds 

presents an exceptional chemical versatility, 

that is to say that it is possible to tune 

the physical properties by changing the 

material composition: as already mentioned 

changing the halogen ion or the 

divalent metal allows to tune the bandgap 

and, as another example, changing the 

organic cation or the synthesis procedure 

allows to tune the dimensionality of the 

density of states (3D: bulk, 2D: quantum 

wells, 1D: quantum wires, 0D: quantum 

dots) and then the excitonic and transport 

properties. 

Thanks to this flexibility, the halide 

perovskites are not only efficient for 

photovoltaic applications, but also for 

other photonic ones. After presenting 

some outlines in the photovoltaic field, 

we will develop their various applications 

in the field of light emitting devices: 

LEDs, single photon sources, lasers, 

and photonics. 

PHOTOVOLTAICS 

The interest of the scientific community 

in halide perovskites for optoelectronics 

was triggered by the surprising performances 

achieved in 2012 by solid-state solar 

cells employing this material as a solar 

light absorber. After more than a decade 

of continuous improvement, the 

Figure 1. Schematic crystal structure of CH 3 NH 3 PbX 3 . Ionic bonds exist between the 

lead atoms and the X – ions, thus forming inorganic PbX 6 

4– 

octahedra, characteristic of the 

perovskite structure. These octahedrons touch each other at their vertex to form a 3D 

network. The CH 3 NH 3 

+ 

cation is placed on the interstitial sites between the octahedra. 


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record power conversion efficiency 

(PCE) of a perovskite solar cell (PSC) is 

now achieving 25.7%. It is close to the 

record PCE of the mature crystalline 

silicon technology which appeared 

in the 1950’s. The use of halide perovskite 

materials with small exciton 

binding energy facilitates the separation 

of electrons and holes after the 

absorption of solar photons. PSC requires 

asymmetric selective contacts 

for the collection of the charge carriers 

photogenerated in the absorber 

layer: the holes are collected by 

a specific p-type layer (HTL) which 

transports holes and blocks electrons 

while, at the opposite end of the cell, 

the electrons are transported by a 

specific n-type layer (ETL) which also 

blocks holes (fig 2). Various architectures 

have been developed depending 

on the position of these layers in the 

stack and on their morphology: direct 

mesoscopic, triple-mesoscopic, direct 

planar and inverted planar. 

Progress in PCE has been driven 

by multiple means such as chemistry 

and interface layers engineering [3]. 

Figure 2. 

Scheme of a perovskite solar cell 

structure and functioning principle. 

The perovskite chemical composition 

is important. The A, B, X components 

can be modulated to increase the stability 

and adjust the optical bandgap. 

The composition of the precursor solution, 

including the use of additives 

and the employed organic solvent, is 

Colloidal metal-halide perovskite nanocrystals (NCs), 

also called "quantum dots", are recently developed 

nanoscale versions of their intriguing parent bulk 

semiconductors. Like other colloidal semiconductor 

(e.g. Cd or Pb chalcogenide) NCs, these perovskite NCs 

consist of a small inorganic core (typically between 

4 nm and 50 nm in size) capped with organic ligands 

(see schematic). While the size and composition 

of the NC core determine the degree of quantum 

(size and dielectric) confinement, providing the 

synthetic chemist a convenient handle to fine-tune 

e.g. the bandgap, exciton binding energy, and (non-) 

radiative rates, the ligands fulfill a multitude of roles: 

first, the ligand tail maintains colloidal stability in 

various solvents, enabling access to a large range 

of solution-processing approaches for sample handling and device fabrication; second, the ligand head groups provide 

electronic passivation of the semiconductor core, yielding trap-free semiconductors with near-unity PL quantum yields; 

and third, the ligand length and coverage can be utilized to control the self-assembly of NCs into NC superlattices, or 

the separation to a neighboring charge/energy donor or acceptor. In the few years since their first colloidal synthesis 

[5], perovskite NCs have already turned into a commercial product (https://avantama.com/), and have demonstrated 

ultra-narrow PL at room temperature, low lasing thresholds, as well as bright and coherent single-photon emission at 

cryogenic temperatures [6]. Given that many researchers and companies are still joining this young and exciting field, the 

next breakthrough in fundamental science and/or applications is likely just around the corner. 

Schematic: Colloidal APbX 3 perovskite nanocrystals are comprised of a size- and composition-tunable perovskite core 

capped by organic ligands, hereby offering a multitude of synthetically very accessible control knobs to engineer structural 

and optical properties for a range of solution-processed optoelectronic devices. The photograph is adapted with permission 

from Nano Lett. 15-6, 3692 (2015). Copyright 2015 American Chemical Society. The TEM image is reprinted with 

permission from ACS Cent. Sci. 7-1, 135 (2021). Copyright 2020 American Chemical Society. 



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very important to control the final properties of the layer 

(homogeneity, crystallinity, defect density…). The various 

steps of the preparation of the perovskite layer, including 

an antisolvent dripping step, the deposition speed, the annealing 

temperature, and its duration, have been studied 

and optimized for reaching high performance. The targeted 

final morphology is a monolithic structure in which each 

perovskite grain of the polycrystalline layer is contacted by 

the ETL on one side and by the HTL on the other side. The 

interfaces between these layers have been the subject of 

chemical treatment for energy band level adjustment and 

defect passivation because defects are at the origin of charge 

recombination and performance losses. Due to the mild temperature 

used for the layer annealing, PSCs can be prepared 

on lightweight low-cost plastic substrates compatible with a 

roll-to-roll process for large-scale production. 

The stability concern has led to important research on the 

reduction of the dimensionality of the perovskites and on the 

preparation of 2D/3D perovskite mixtures. Perovskite can be 

integrated into tandem solar cells to increase their maximum 

theoretical PCE limit. Rather low bandgap perovskites are 

prepared by mixing Pb and Sn B-cation while the bandgap 

is increased by partly substituting I for Br. Full-perovskite 

double-junction solar cells achieve a maximum PCE above 

26.4%. Perovskite solar cells are not only a competitor to 

silicon but, also, an ancillary technology since perovskite 

can provide the top cell with a bandgap larger and complementary 

to that of crystalline silicon in tandem devices. This 

research direction has raised a large amount of effort and 

funds in recent years. The current record efficiency is 31.3%. 

LEDs 

The recent technological developments in various application 

areas such as automotive, smartphones, TV, or flexible 

screens revealed some limitations of the widely used inorganic 

semiconductors. Therefore, the community has moved 

towards alternative technologies that also consider 

the materials' availability. Among the candidates, organic 

electronics is a suitable way to achieve new devices. It is 

particularly true for optoelectronic components. However, 

the all-organic approach does not provide the same performance 

as purely inorganic semiconductors due to the 

moderate transport properties of the charge carriers in 

these materials. In this context, halide perovskites are relevant 

materials, especially the low dimensional ones (2D, 

1D, 0D) which present stronger excitonic effects than the 

bulk [4]. In particular, perovskite nanocrystals (NCs, see 

inset), respond well to the technological need for easily 

exploitable semiconductors, synthesized with facile and 

cheap processes, as conformable as the all-organic, with 

performances equivalent to classical semiconductors [5]. 

Perovskite-based NCs are a viable Cd-free alternative for display 

applications. The main advantages of perovskite-based 

NCs are their facile and low-cost synthesis, high photoluminescence 

(PL) quantum yields between 50% and 


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90% at room temperature in the 

range 2,2 eV - 2,8 eV, wide wavelength 

tunability by using size confinement 

effects or halide exchange reactions, 

ultra-narrow band emission in the 

range of tens of meV at room temperature 

and RoHS (Restriction of hazardous 

substances in electrical and 

electronic equipment) compliance 

(despite the lead content). So, compared 

to current-generation OLED 

screens, a perovskite LED display 

would provide cleaner colors and potentially 

be much brighter and more 

energy-efficient. These materials 

could then be used in a large range 

of displays and lighting to create improved 

aesthetics and lower energy 

consumption. To address these kinds 

of technological needs in optoelectronic 

performance conformabilities, 

future studies will be centered 

on the control of these NCs in terms 

of composition, shape, and size on 

macroscopic volumes. However, 

challenges remain, including improving 

the stability and longevity 

of perovskite LEDs and reducing 

or replacing the use of lead in the 

nanocrystals to comply with more 

stringent safety standards. 

SINGLE-PHOTON SOURCES 

Halide perovskites have also made 

inroads into another area less known 

to the general public but from which 

we can hope for very interesting future 

applications. This is the field of 

quantum optics and quantum information. 

Indeed, from the first synthesis 

of NCs it has been shown that 

the emission of an isolated perovskite 

NC was carried out photon by photon. 

That is a property specific to two-level 

systems or atomic systems that 

also appears under some conditions 

on individual three-dimensional 

quantum confined semiconductors. 

It is also very desired in quantum 

cryptography to design single-photon 

sources because as opposed 

to attenuated coherent sources, a 

single-photon source allows an improvement 

in performance in terms 

of maximum reachable distance for 

Figure 3. a) Scheme of a Hanbury-Brown and 

Twiss experiment: a photon stream is incident 

in a beam splitter, D 1 and D 2 are single-photon 

counting detectors, the correlator gives g 2 (τ), 

the conditional probability of detecting a 

second photon at time t + τ in detector D 2 , given 

the detection of a photon at t from detector D 1 . 

b) g 2 (τ ) ideal curve. 

a given security level. 

Quantum-cryptography protocols 

are based on the coding of quantum 

states (e.g., the polarization of 

a single photon) and the sharing 

between two interlocutors of a secret 

key in the form of a random series via 

a quantum channel (e.g. an optical fiber). 

The laws of quantum mechanics 

ensure the ability of the two interlocutors 

to detect the presence of a spy 

on the transmission line. Moreover, 

the quantum interferences between 

states of one photon can also be applied 

to make photonic logic gates 

to be inserted in future quantum 

computers. 

Whatever the application of the 

single-photon sources, the main 

characteristics of these sources are 

as follows: 

• Ideally, such source should emit one 

and only one photon for each trigger 

signal in a defined mode of the electromagnetic 

field. As already seen in 

Section LEDs, perovskite NCs show 

a highly efficient PL at room temperature. 

That is combined with a reduced 

intermittence or “blinking” 

of the single-photon emission due 

to the fluctuant electrostatic environment 

of NCs. 

• Ideal single-photon sources show 

statistics characterized by a second-order 

correlation function at 

zero time g 2 (0)=0. This function characterizes 

the probability to detect 

another photon at the same time 

that one photon was previously detected 

at t = 0 in a Hanbury-Brown 

and Twiss experiment (Figure 3). For 

CsPbI 3 nanocrystals, g 2 (0) values as 

low as 0.02 have been reported [7]; 

• A high repetition rate (tens of MHz 

at room temperature). 

• Easy and reliable use. The stability 

of NCs against moisture or irradiation 

with intense light needs to 

be improved. 

• Finally, a good collection efficiency. 

As in the case of LEDs, efficient 

collection of the emitted light, 

mostly trapped by total internal 

reflection in the material, is a 

true challenge. 

LASERS/PHOTONICS 

The former sections highlighted 

and illustrated the key advantages 

of halide perovskites for the 

next generations of photonic and 

opto-electronic devices. However, 

advanced photon control is necessary 

to further control their performance 

and to integrate advanced 

functionalities. In particular, tight 

control of the spectral, spatial and 

angular properties of the emitted 

light can be achieved through the 

integration of wavelength scale 

structures like periodic gratings, 

metasurfaces, or other kind of nanophotonic 

patterns. This is generally 

achieved by a direct patterning 

of the halide perovskite layer, using 

processes inspired by nanoimprint 

or hot embossing. Such an advanced 

photonic control could lead to major 

breakthroughs in devices like LEDs 

or single photon sources, where 



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managing the radiation pattern can 

be of prime importance. Using such 

properties, light-emitting devices can 

exhibit characteristics suited to applications 

like visible light communication 

(VLC). Integrating such nanopatterns 

can also assist light trapping in photovoltaic 

solar cells, both in the case of 

single junction solar cell and tandem 

devices [8]. 

Additionally, advanced photon 

control is necessary to reach regimes 

like laser emission or strong coupling. 

To reach this goal, it is necessary to 

integrate wavelength-scale photonic 

patterns to constitute the needed optical 

resonator. During these past years, 

low threshold laser emission was demonstrated 

under optical pumping 

in simple structures including periodic 

grating (1D or 2D), metasurfaces, 

or related patterns. Considering the 

very high optical gain available in such 

media, laser emission could even be 

achieved in single nanostructures, simultaneously 

providing the optical gain 

and the cavity. Beyond these important 

demonstrations, a key challenge is to 

reach laser emission under electrical 

injection, which could be achievable 

thanks to strategies circumventing the 

Joule heating, electric field-induced 

quenching, charge injection imbalance 

and Auger recombination. 

CONCLUSION 

In summary, hybrid halide perovskites 

are a new class of semiconductors 

showing an incredible set of physical 

properties, which are rarely united in the 

same material. These physical properties 

can be easily tuned and adapted to the 

intended application by modifying the 

composition of the material. Additionally, 

these materials are solution-processed, 

with soft conditions of temperature and 

pressure, and contain earth-abundant 

components. However, some important 

challenges remain to be solved for this 

class of materials: the presence of lead 

and the so far limited operational stability 

against environmental parameters such 

as humidity and intense light. If the presence 

of lead can presumably be treated 

by implementing recyclability if necessary, 

the stability remains a major problem 

as the device stability is, at present, not 

yet sufficient for commercialization, even 

if tremendous progress has been made in 

the past few years. Some efforts are still 

needed, the solution to this problem will 

probably come from the major advantage 

of this class of materials: its chemical 

flexibility. 

Acknowledgments 

The authors thank the Think Tank HPERO: 

Groupement de Recherche du CNRS “Halide 

Perovskites”, https://www.gdr-hpero.cnrs.fr/ 

REFERENCES 

[1] A. Kojima, K. Teshima, Y. Shirai, T .Miyasaka, Journal of the American Chemical 

Society 131, 6050 (2009) ; H.-S. Kim, C.R. Lee, J.H. Im et al., Sci. Rep. 2, 591 (2012) ; 

M.M. Lee, J. Teuscher, T. Miyasaka et al., Science 338, 643 (2012) 

[2] J. Even, L. Pedesseau, C. Katan et al., J. Phys. Chem. C 119, 10161 (2015) 

[3] D. Zheng, T. Zhu, Y. Yan, Th. Pauporté, Adv. Energy Mater. 12, 2103618 (2022) 

[4] A. Ghribi, R. Ben Aich, K. Boujdaria et al., Nanomaterials 11, 3054, (2021) ; 

K. Gauthron, J.-S. Lauret et al., Optics Express 18, 5912, (2010) 

[5] L. Protesescu, S. Yakunin, M. I. Bodnarchuk et al., Nano Lett. 15, 3692 (2015) 

[6] G. Raino, N. Yazdani, S.C. Boehme et al., Nature Commun. 13, 2587 (2022) ; 

S. Yakunin, L. Protesescu, F. Krieg et al., Nature Commun. 6, 8056 (2015) ; 

H. Utzat, W. Sun, A. E. K. Kaplan et al., Science 363, 1068-10 (2019) 

[7] C. Zhu, M. Marczak, L. Feld et al., Nano Lett. 22, 3751 (2022) 

[8] F. Berry, R. Mermet-Lyaudoz, J. M. Cuevas Davila et al., Adv. En. Mat. 12, 

2200505 (2022) 


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LITHIUM NIOBATE 

ON INSULATOR 

FROM CLASSICAL TO QUANTUM 

PHOTONIC DEVICES 

/////////////////////////////////////////////////////////////////////////////////////////////////// 

Andreas MAEDER, Helena WEIGAND and Rachel GRANGE* 

ETH Zurich, Department of Physics, Institute for Quantum Electronics, Optical Nanomaterial Group, Zurich, Switzerland 

*grange@phys.ethz.ch 

Integrated photonics is becoming more and more 

multifunctional thanks to the recent availability 

of an established material, lithium niobate, as thin 

films of less than 1 micron thickness. Overcoming key 

fabrication challenges has put this platform on its way 

to achieve scalability. Here, we show the performances 

of integrated and free space devices such as electrooptic 

modulators and active metasurfaces. Finally, we 

mention possible roles of lithium niobate on insulator 

in quantum photonics. 


Who could have 

guessed the 

great evolution 

of lithium 

niobate in applied 

research, 

a bulk material already extensively 

used in telecommunications and lasers? 

This time, it made a sensational 

appearance in integrated optics 

thanks to two technological developments: 

thin film fabrication at wafer 

scale and nanolithography beyond 

the typical semiconductor processes. 

The pressing necessity to reduce 

power consumption and footprints 

in the data transport industry either 

in submarine fibres or data centre 

networks was a breeding ground for 

innovative integrated solutions with 

more functionalities. 

Lithium niobate (LiNbO 3 ) is a 

synthetic crystal, transparent from 

the ultraviolet to the mid-infrared, 

that lacks inversion symmetry and 

displays ferroelectricity, the Pockels 

effect, the piezoelectric effect, photoelasticity 

and nonlinear optical 

polarizability. It is only in the early 

2000’s that lithium niobate was fabricated 

on a thin film platform and less 

than 10 years ago that it was made 

commercially available as lithium 

niobate on an insulator (LNOI) [1]. 

Similar to the silicon-on-insulator 

(SOI) platform, the combination of a 

high refractive index material (n > 2) and 

a thickness of less than 1 μm, bonded to 

an insulator layer, increases the optical 

mode confinement with waveguide 

cross-sections. As illustrated in Fig. 1, 

waveguides with cross-sectional areas 

less 1 μm 2 waveguide can be fabricated 

by electron-beam lithography in thin 

film lithium niobate, which allows for 

much stronger light confinement than 

in waveguides generated by e.g. titanium 

indiffusion or micromechanical 

processes [2]. 

A broad portfolio of optical devices 

has been created in the SOI platform, 



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Figure 1. Cross-sections of typical waveguides for bulk (left) and thin film (right) lithium 

niobate. The color bar shows the intensity of the propagating optical mode. Its mode 

volume is reduced by one order of magnitude for ridge waveguides as compared to 

indiffused waveguides. 

from on chip lasers to optical modulators 

and waveguide-integrated photodetectors. 

Silicon nitride is also worth mentioning 

since it has low propagation losses and 

a wider transparency range than silicon. 

These two thin-film platforms offer high 

mode confinements where the waveguide 

dispersion can overcome the normal 

material dispersion by engineering the 

device parameters. However, silicon and 

silicon nitride do not exhibit second-order 

nonlinearities, thus only few nonlinear optical 

effects such as self-phase modulation, 

third-harmonic generation, or four-wave 

mixing can be exploited. Besides the fabrication 

of photonic integrated 

Figure 2. Typical steps required to fabricate a LNOI integrated circuit. Ion slicing 

(i) - (iii) is used to produce lithium niobate-on-insulator wafers. Thin films are patterned 

using electron-beam lithography (iv) and dry etching (v). If required, subsequent 

lithography steps are used to add metallization layers (vi) for electrodes. 

Finally, the patterned chip has to be cleaned to get the final integrated circuit (vi). 


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Figure 3. An example of a lithium niobate-on-insulator photonic chip with various functionalities 

showing the fabrication capabilities with inset scanning electron microscope images. 

circuits in lithium niobate thin film, we 

will mention free space applications 

using lithium niobate as a metasurface 

for electro-optic modulation and quantum 

light sources. 

NANO-FABRICATION 

Crucially, the miniaturization of 

lithium niobate waveguides was enabled 

by the ion slicing process described 

in Fig. 2. By implanting helium 

ions into the crystal matrix of lithium 

niobate at a depth controlled by the 

ion energy, thin layers of lithium niobate 

can be split-off. To make these 

layers usable, the implanted lithium 

niobate wafer is bonded to a substrate. 

Different kinds of substrates 

such as silicon, quartz or sapphire, 

and possibly an insulation layer, can 

be used depending on the application. 

These thin film wafers are commercially 

available and serve as base 

for further nanofabrication. 

The nano-structuring is based on 

similar approaches as for silicon or 

silicon nitride waveguides as described 

in Fig. 2. However, lithium niobate 

is a notoriously hard material to 

etch, and thus requires specialized 

tools and processes. First, the desired 

waveguide circuit is patterned 

into a photosensitive resist using 

an electron beam, which allows 

features sizes smaller than 1 μm. The 

patterned chip is then etched using 

argon ions in an inductively coupled 

plasma etching tool. To exploit the 

electro-optical properties of lithium 

niobate (see box "Electro-optic effect"), 

metal electrodes are routinely 

ELECTRO-OPTIC EFFECT 

added by patterning a resist and 

then depositing metal via chemical 

vapor deposition. 

Using this fabrication process, 

many different structures can be 

realized. Fig. 3 shows scanning electron 

microscope images of several 

components used to build a photonic 

integrated circuit showing the capabilities 

of the fabrication methods. 

The high precision of electron beam 

lithography enables fabrication of 

crossing waveguides and narrow 

gaps (down to 200 nm) which are 

crucial for general routing, grating 

couplers and integrated microresonator 

coupling. Recently, Joule 

heaters made of platinum with gold 

contacts deposited next to an optical 

waveguide were achieved and allow 

for a fine tuning of the properties 

of a photonic chip without additional 

fabrication [3]. Lastly, electron 

beam lithography also enables fabrication 

of metal nanowires with 

feature sizes below 100 nm. Such 

strips can be used as scatterers to 

probe the optical field inside 

The linear electro-optic effect present in materials with high second-order 

nonlinearities is a response to an externally applied electric field. Due to this field, 

the refractive index of the material changes by an amount Δn, leading to a change 

of the phase light traveling in the material accumulates. Notably this phase change 

Δϕ depends both on the orientation of the applied electric field and the polarization 

of light. In the case of integrated lithium niobate devices, the electric field is typically 

introduced by placing gold electrodes in close proximity to waveguides. In lithium 

niobate-on-insulator, higher electric fields can be achieved due to the reduction 

of the electrode gap as compared to waveguides in bulk lithium niobate. 

Furthermore, for ridge waveguides the electric field is better aligned to the 

extraordinary crystal axis, whereas for buried waveguides in bulk lithium 

niobate there are always components in multiple directions. 


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Figure 4. Lithium Niobate Devices. a) False-colored electron microscope image of a Bragg 

grating modulator. b) Wavelength dependent transmission of Bragg modulator showing the 

characteristic stopband. c) Eye diagram of a 100 GBit/s signal transmitted by the modulator. 

d) Sketch of lithium niobate pillars arranged into a periodic array to form a metasurface. 

e) Sketch of a LN metasurface composed of pillars, which, by applying a voltage, modulates 

a transmitted laser beam. f) Optical image of a fabricated set of metasurfaces with changing 

radii and periods, where the colors directly show the different resonance wavelengths. 

(Adapted from Pohl et al. IEEE Photonics Technology Letters 33(2), 85 (2021), and Weigand 

et al. ACS Photonics 8(10), 3004 (2021)) 

waveguides. This concept was exploited 

in monolithically integrated 

spectrometers [4]. The effort to scale 

the fabrication of the substrate and 

of devices to commercially relevant 

amount experiences a major push in 

Europe currently [5]. 

ELECTRO-OPTIC DEVICES 

Due to the electro-optic effect (see 

box "Electro-optic effect") lithium 

niobate is primarily used for active, 

tunable or reconfigurable 

devices. Today, electro-optic modulators 

using bulk lithium niobate 

are available in many research labs, 

telecommunication networks, or 

satellites. With the miniaturization 

of integrated circuits enabled by 

electron-beam fabrication, smaller 

and more efficient devices can be 

realized with lithium niobate-on-insulator. 

Typical low power consumption 

electro-optic modulators use a 

Mach-Zehnder interferometer [6]. 

For an even smaller footprint, single 

waveguides with an integrated Bragg 

grating, shown in Fig. 4(a), was realised. 

It features a stopband with 

sharp slopes (see Fig. 4(b)), which 

can be shifted by applying an electric 

field. At suitable wavelengths (points 

B or C in Fig. 4(b)), the transmitted 

light is either fully transmitted or 

fully blocked depending on the applied 

electric field. This principle 

is used to translate an electronic 

stream of bits into the optical domain, 

where it can be transmitted 

through optical fibres. Fig. 4(c) 

shows a characteristic eye diagram 

of a 100 GBit/s signal showing high 

quality data transmission through an 

optical fibre. 

Besides integrated photonics, 

thin film lithium niobate is also 

suited for free space applications 

such as electro-optic metasurfaces 

(Fig. 4 d-f), which provide a tool to 

modulate light that passes perpendicular 

through the surface, hence 

circumventing the problem of 

coupling light to the tiny cross-section 

of a waveguide. Metasurfaces 

consist of a periodic 2-dimensional 

array of nanoscale resonators and 

can be scaled to an arbitrary size 

(see Fig. 4d). The small resonators 

can serve mainly two purposes. The 

first idea is to engineer the phase 

of the transmitted light spatially 

and therefore replacing a plethora 

of optical elements for wavefront 

shaping such as lenses or beam deflectors 

with a thin-film alternative. 

The second purpose is to confine 

the light inside the structured material 

and therefore enhance the 

light-matter-interaction. Boosting 

e.g. the frequency conversion for 

second-harmonic-generation or 

spontaneous parametric down 

conversion is especially useful 

since phase matching is not 



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occurring in sub-wavelength interaction lengths, hence 

avoiding the need of periodic poling of the lithium niobate. 

This efficiency boost opens the path towards active 

flat optical devices exploiting the Pockels effect for faster 

pixel switching than spatial light modulators based on 

liquid crystals. Recently we showed that by structuring 

nanoscale pillars in a lithium niobate thin-film, a precisely 

chosen resonance can increase the modulation 

efficiency by a factor of 80 compared to an unpatterned 

thin-film (see Fig. 4(e)) [8]. The modulation voltage was 

kept below 10V, having therefore a comparable power 

consumption to the integrated modulators. Even though 

the modulation amplitude is still far from the optimized 

integrated photonics counterpart, this work shows the potential 

of combining metastructures with nonlinear thinfilms 

like lithium niobate without the need for packaging 

since it all happens in free space (see Fig. 4(f)). 

A FUTURE IN QUANTUM OPTICS 

We have highlighted the development of nano-fabrication 

methods for patterning lithium niobate films and how it 

has led to a fast development of miniaturized devices for 

integrated circuit and compact free space optics. In light 

of the ever-increasing demand for small scale solutions 

for quantum technology, lithium niobate-on-insulator 

is very promising as classical integrated high dynamic 

range modulator for atom traps, or as entangled on-chip 

photon sources through spontaneous parametric down 

conversion [7]. Compared to silicon photonics and other 

semiconductor materials, lithium niobate does not suffer 

from two-photon absorption, which limits the efficiency of 

logical quantum gates. Therefore, the story of this material 

is about to open a new chapter. 

REFERENCES 

[1] P. Rabiei and P. Gunter, Appl. Phys. Lett. 85, 4603 (2004) 

[2] N. Courjal, F. Behague, V. Pêcheur et al., 

Photoniques 98, 34 (2019) 

[3] A. Maeder, F. Kaufmann, D. Pohl, J. Kellner, 

and R. Grange, Opt. Lett. 47, 4375(2022) 

[4] D. Pohl, M. Reig Escalé, M. Madi et al., Nature 

Photonics 14, 24 (2020) 

[5]European consortium to develop and mature LNOI PIC 

platform, www.project-elena.eu 

[6] D. I. Zhu, L. Shao, M. Yu et al., Adv. Opt. Photon. 13, 

242 (2021) 

[7] T. Santiago-Cruz, A. Fedotova, V. Sultanov et al., 

Nano Lett. 21, 4423 (2021) 

[8] H. Weigand, V. Vogler-Neuling et al., ACS Photonics 8, 

3004 (2021) 


FOCUS 


NARROW BAND GAP 

NANOCRYSTALS FOR 

INFRARED COST-EFFECTIVE 

OPTOELECTRONICS 

/////////////////////////////////////////////////////////////////////////////////////////////////// 

Emmanuel LHUILLIER 1, * 

1 

Sorbonne Université, CNRS, Institut des NanoSciences de Paris, INSP, F-75005 Paris, France. 

*el@insp.upmc.fr 


This is an Open Access article distributed under the terms of 

the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), 

which permits unrestricted 

use, distribution, and reproduction in any medium, provided 

the original work is properly cited. 

Infrared optoelectronics is driven by epitaxially grown 

semiconductors and the introduction of alternative 

materials is often viewed with some suspicion until the 

newcomer has demonstrated a high degree of viability. 

Infrared nanocrystals have certainly reached this 

degree of maturity switching from the demonstration 

of absorption by chemists to their integration into 

increasingly complex systems. Here, we review some of 

the recent developments relative to the integration of 

nanocrystal devices in the 1-5 µm range. 

The spectral properties 

of a semiconductor are 

mostly driven by the 

band gap energy. Thus, 

the most obvious strategy 

to achieve spectral 

tunability is to alloy two semiconductors 

to obtain intermediate properties. 

However, this approach tends to be limited 

by metallurgic considerations 

and in particular the difference in 

lattice parameter. Since the late 70’s, 

quantum confinement appears as an 

alternative approach to increase the 

band gap of a semiconductor. When 

the size of a semiconductor is reduced 

below its Bohr radius (7 nm in CdSe 

and around 40 nm in HgTe), its optical 

properties start to deviate from the 

bulk material and the band gap energy 

is increased (i.e. the spectrum blue 

shifts), see Figure 1b. Such quantum 

confined semiconductors are now 

widely spread. For exemple, semiconductor 

quantum wells are used in 

TV remotes and the quantum cascade 

laser is certainly one of the greatest 

outputs of quantum engineering. 

Initially this strategy has been applied 

to semiconductor thin films and quantum 

dots obtained through high vacuum 

epitaxial growth. However, this 

approach quickly reached its limits in 

terms of volume production and thus 

alternative growth methods for such 

quantum confined semiconductors 

have been developed using chemical 

approaches. Since the early 90s, it has 

become possible to grow semiconductor 

nanoparticles (the so-called nanocrystals 

or colloidal quantum dots) in 

solution from a basic glassware setup 

as depicted in Figure 1a. Using wide 

band gap materials such as CdSe or 

InP the whole visible spectrum can be 

covered, see Figure 1c. 

Over time the colloidal synthesis has 

gained maturity and which has allowed 

to grow a broader range of materials, to 

achieve atomic scale control of the size 

and also to synthetize colloidal heterostructures. 

By growing core shell structures, 

the wave functions are pushed 

away from the surface where surface 

traps prevent radiative recombination. 

This has led the growth of nanoparticles 

with a high photoluminescence quantum 

yield that are now integrated as green and 

red sources for display. 

While early efforts have mostly been 

focused on the visible spectral range, a 

significant effort has been later dedicated 

to narrower band gap materials (PbS or 

HgTe). The first motivation for infrared 

absorbing nanocrystals was their use as 

optimal absorbers for solar cells. However, 



FOCUS 

Figure 1. a. Schematic of a setup dedicated to nanocrystal synthesis. b. Schematic band 

structure of a semiconductor highlighting that the finite particle size makes the central 

part of the energy diagram unavailable and thus increases the optical band gap compared 

to the bulk material. c. Image of a pipette coated with nanocrystals of various sizes. 

over the recent years, these materials 

have been strongly challenged by the 

emergence of perovskite materials which 

offer higher power conversion efficiency 

thanks to the defect tolerance of their 

electronic structure. On the other hand, 

the perovskite band gap remains large preventing 

the use of these materials for truly 

infrared applications. HgTe for example 

offers an exceptionally large spectral tunability 

since its band gap can be tuned from 

1 to 100 µm, as shown in Figure 2. This exceptional 

spectral tunability together with 

a reduced fabrication cost make narrower 

band gap materials promising candidates 

for the design of infrared optoelectronic 

devices. Indeed, infrared optoelectronics 

suffers from a low production volume 

which makes the cost of devices generally 

prohibitive. A short-wave infrared camera 

easily costs 10 k€ and its mid infrared counterpart 

almost 10 times more. In addition, 

organic electronics, due to the strong vibration 

between the excitons and the lattice 

vibration, is ineffective above 1 µm. Thus, 

narrow band gap nanocrystals, with few 

emerging 2D materials (black phosphor, 

graphene, PtSe 2 ), generate interest as 

possible alternatives to traditional III-V 

and II-VI semiconductors usually used in 

this spectral window. This paper reviews 

some of the recent development relative 

to the integration of infrared nanocrystals 

as a new active material for optoelectronic 

devices dedicated to the detection and 

emission of light. 

EXPECTED CONTENTS 

Because they appear broadly tunable in 

the infrared range and their absorption is 

robust (i.e. weakly affected by photobleaching), 

infrared nanocrystals are natural 

candidates to be used as photodetectors. 

In this case a conductive film must be fabricated. 

Grown nanocrystals are usually 

capped with long capping ligands. The latter 

ensure the colloidal stability of the particle 

but also ensure the electronic surface 

passivation of the surface dangling bond. 

However, these long ligands (alkyl chain 

with 12 to 18 carbons typically) are insulating 

by nature so a nanoparticle 

Figure 2. Absorbance spectra for HgTe nanocrystals of various sizes. The confined size ranges 

from 1.2 nm for the highest energy curve to above 100 nm for the lowest energy spectrum. 


FOCUS 


Figure 3. a. Schematic of an infrared diode stack coupled to a light resonator 

which role is to enhance the absorption of a thin film. b. Spectrum of the diode 

stack with and without the light resonator. Figure is adapted with permission 

Advanced Optical Materials 9, 2002066. Copyright {2021} John Wiley and Sons. 

array is neither conductive nor photoconductive 

without post synthesis 

treatment. Much of the effort dedicated 

to the integration of colloidal 

nanocrystals into devices has actually 

focused on the modification 

of the surface chemistry to make it 

compatible with charge conduction. 

During the ligand exchange step, the 

initial ligands are replaced by short 

ones in order to increase interparticle 

coupling. Macroscopically this 

leads to an increase in the carrier 

mobility which starts from very low 

values (


FOCUS 

Figure 5. a. Schematic of a light emitting diode stack with emission at around 2 µm. 

b. Electroluminescence and photoluminescence spectra from HgTe nanocrystals. 

The inset is an infrared image of the LED under operation. Figure is adapted from with 

permission Nature Photonics 16, 38. Copyright {2022} Nature springer. 

movies can now be reported in the near 

and short-wave infrared, see Figure 4b. 

The promise of infrared nanocrystals 

is not limited to light absorption for photodetection 

and they can also be interesting 

light sources at telecom wavelength 

and beyond. While the first mass market 

application was their use as down converters 

for display, a large effort has also been 

dedicated to the design of an electrically 

excited light emitting device based on 

QLED. Compared to the strategy where the 

nanocrystals are optically excited the electrical 

excitation may offer a higher contrast 

and reduce electrical consumption, which 

might be an important step toward their 

integration into smartphone display. In the 

infrared, the light emission remains largely 

dominated by III-V epitaxially grown semiconductors. 

Quantum wells based on III-V 

heterostructures are massively used at telecom 

wavelength as a powerful source compatible 

with fast modulation. Above 4 µm, 

the quantum cascade laser is also now a 

well-established source. In the middle 

from 1.5 to 4 µm, there is a technological 

gap where only emerging technologies are 

currently available and where nanocrystals 

can also be used as an infrared photon 

source. Pushing the electroluminescence 

(EL) of nanocrystals in this spectral range 

remains nevertheless challenging due to 

the strong near field coupling between the 

exciton and the vibration of the capping 

ligands. Such coupling tends to quench 

the luminescence, making the ligand exchange 

procedure even more important. 

An example of a light emitting diode with 

an emission above 2 µm is schematized in 

Figure 5a and its operation is imaged using 

an infrared camera in the inset of Figure 

5b. It should be noted that the emission 

is not just blackbody radiation due to the 

passing of current in the stack and that the 

EL spectrum indeed matches the photoluminescence 

signal, see Figure 5b. 

CONCLUSION 

Infrared nanocrystals have made tremendous 

progress in recent years enabling 

their integration into increasingly complex 

devices including photonic structures, focal 

plane arrays and light emitting diodes. 

Future efforts should focus on increasing 

thermal stability to make the material fully 

compatible with traditional semiconductor 

processing. Further understanding of the 

material electronic structure and its transport 

properties will also be required to enable 

the design of complex structures. 

REFERENCES 

[1] C. Gréboval et al, Chem Rev 121, 

3627 (2021) 

[2] M. Chen et al, Advanced Science 8, 

2101560 (2021) 

[3] A. Chu et al, ACS Photonics 6, 

2553 (2019) 

[4] C. Gréboval et al, Nanoscale 14, 

9359 (2022) 

[5] J. Qu et al, Nature Phot. 16, 38 (2022) 



THE GEOMETRIC PHASE MADE SIMPLE 

THE GEOMETRIC PHASE 

MADE SIMPLE 

///////////////////////////////////////////////////////////////// 

Miguel A. ALONSO 1,2,* , Mark R. DENNIS 3 

1 

Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, 13397 Marseille, France 

2 

The Institute of Optics, University of Rochester, Rochester NY 14627, USA 

3 

School of Physics and Astronomy, University of Birmingham, Birmingham B152TT, UK 

*miguel.alonso@fresnel.fr 

We give a simple description of the Pancharatnam-Berry 

geometric phase and some of its applications in optics. 

Geometric phases are a universal phenomenon, but we focus 

here on the case of geometric phases caused by changes in 

polarization. The geometric origin of this phase is explained 

by analogy with the motion of an imaginary creature living on 

a small planet, inspired by Saint-Exupéry’s “The Little Prince”. 





is a universal phenomenon 

that 

appears in many 

areas across wave 

physics. It was first 

discovered within 

the context of optics in 1956 by 

S. Pancharatnam [1] as a net phase 

difference between two beams which 

have undergone different sequences 

of polarization, depending only on 

these sequences. A few decades later, 

Berry [2,3] recognized this phenomenon’s 

universality and underlying 

geometric nature, which goes well 

beyond electromagnetic waves. In 

optics and photonics, geometric 

phases have attracted significant 

attention and found many practical 

applications. While extensive reviews 

exist (for example [4]), the goal of this 

short article is to provide a simple 

description of the Pancharatnam- 

Berry (PB) phase for optical polarization 

and explain why it is so useful 

in applications such as wavefront 

shaping. As one learns in any basic 

course in optics, a propagating optical 

beam is described by its intensity 

and phase, the latter being accumulated 

proportionally to the beam’s 

optical path length. In addition, a 

light beam has “internal” degrees 

of freedom such as polarization, 

which can also change as the beam 

propagates. Such evolution can lead 

to an extra contribution to the phase 

unrelated to the overall optical path 

length. This phase is called “geometric” 

because it is directly related to 

the geometry in the natural abstract 

space that best describes the internal 

degrees of freedom in question. 

CURVED SPACES, 

PARALLEL TRANSPORT, 

AND THE LITTLE PRINCE 

The phenomenon of the geometric 

phase requires that the space 

that describes the internal degrees 

of freedom be curved, and that the 

evolution over such space follows 

the rules of what is known as parallel 

transport. Let us explain the basic 

concept of parallel transport by imagining 

an episode inspired by Saint- 

Exupéry’s Le Petit Prince: 

On his way back from the Sahara 

to his planet (Asteroid B-612), the little 

prince stopped by another small 

planet (Asteroid PB-56-84), inhabited 

only by a strange creature, Par-Tra. 




Figure 1. 

Par-Tra’s 

manoeuvre 

to turn towards 

the little prince: 

starting from the 

position at the top, 

facing left, Par-Tra 

first walks sideways 

(down) along 

a geodesic to the 

antipodal point 

(bottom), and then 

along another 

geodesic (left) facing 

forward, 

back to her initial 

position, where the 

final orientation 

of her head is shown 

in dotted lines. 

Par-Tra had a round body, and her many 

tiny legs could only move radially, making 

her perfectly capable of walking in 

any direction but completely unable to 

turn. When the prince arrived, he accidentally 

stood behind Par-Tra. To face 

him, Par-Tra did what she always did in 

order to turn: walk sideways to the opposite 

side of the planet, and then straight 

ahead back to her starting point. 

In this analogy, the curved space is 

the planet’s surface, and Par-Tra’s movement 

restrictions correspond (as her 

name suggests) to parallel transport—her 

only means of turning is by moving on a 

closed path on the curved surface. The 

angle of rotation (in radians) between 

Par-Tra’s initial and final orientation 

coincides precisely with the solid angle 

(in steradians) enclosed by her trajectory 

(in the illustration, approximately −π). 

Note that the rules of parallel transport 

are not unique to wave phenomena or 

imaginary creatures: they also explain 

mechanical effects such as the precession 

of Foucault’s pendulum, or the fact 

that when one rolls a rubber ball over 

a flat surface in a circular motion, each 

turn makes the ball turn proportionally 

to the solid angle enclosed by the path 

of the contact points with the surface. 

POLARIZATION 

AND THE POINCARÉ SPHERE 

For a paraxial monochromatic optical 

beam (e.g. a collimated laser), the electric 

field vector at any point traces an 

elliptical path. The global size of this ellipse 

depends on the intensity, and the 

specific position of the electric field at 

a given time depends on the phase. The 

remaining, purely geometric properties 

of the ellipse, namely its orientation and 

ellipticity, constitute the state of polarization 

of the field. These are characterized 

respectively by i) the angle ψ between the 

horizontal coordinate axis and the ellipse’s 

major axis, and ii) the angle χ subtended 

by a minor semi-axis from one of 

the vertices, whose magnitude encodes 

ellipticity and whose sign determines the 

handedness with which the electric field 

traces the ellipse. 

Rotating the ellipse by half a turn (that 

is, turning ψ through π) brings it back to 

its initial state. Similarly, the angle χ takes 

values between ±π/4. For the extreme 

values 2χ = ±π/2, the ellipse becomes a 

circle, and ψ becomes irrelevant. These 

geometric properties make 2ψ and 2χ 

reminiscent of the longitude and latitude 

angles on a sphere: their ranges are 

the same, and longitude becomes 




irrelevant when we are at the North 

or South poles. Therefore, each state 

of polarization, determined by ψ 

and χ, can be represented by a point 

with coordinates 2ψ and 2χ over a 

unit sphere, known as the Poincaré 

sphere, shown in Fig.2. In other 

words, the natural abstract space for 

representing polarization is a sphere, 

as is also confirmed by the fact that 

the visibility of the intensity fringes 

resulting from the interference 

of two nearly parallel beams with 

different polarizations and equal intensities 

can be fully determined by 

the angular separation between the 

two corresponding points over the 

Poincaré sphere. Three other aspects 

of polarization that are important to 

understand geometric phases are the 

following: i) two orthogonal polarizations 

correspond to a pair of antipodal 

points on the Poincaré sphere, ii) any 

state of polarization can be expressed 

as a complex linear superposition of 

any two orthogonal polarizations, 

and iii) the angle between any two 

linear polarizations is half the angle 

between their corresponding points 

on the Poincaré sphere. 

How can we change the polarization 

of a beam? Two main types of 

optical element are often used: 

The first corresponds to polarizers, 

which only transmit a given polarization 

component and eliminate the 

orthogonal component (by absorption 

or reflection). In the Poincaré 

Figure 2. The Poincaré sphere parametrizing 

states of elliptic polarization. 

sphere representation, polarizers 

take any initial point (corresponding 

to the beam’s initial polarization) and 

transport it to the point representing 

the transmitted polarization, which 

is always the same regardless of the 

initial polarization. The trajectory for 

this type of projection corresponds to 

the shortest geodesic path joining the 

initial and final points as represented 

in Fig.3, as this is the path that results 

from gradually attenuating the 

orthogonal polarization. This geodesic 

projection automatically follows 

the rules of parallel transport. 

The second type of element corresponds 

to wave retarders, such 

as the waveplates used routinely in 

optical setups. These elements are 

typically almost transparent, and 

hence their action does not rely on 

eliminating a polarization component; 

instead they introduce a phase 

difference δ between two preferred 

orthogonal polarizations. That is, 

these two eigenpolarizations experience 

different refractive indices, 

so one travels faster than the other 

and accumulates a smaller phase. On 

the Poincaré sphere, the action of a 

wave retarder corresponds to a rigid 

rotation by an angle δ around the axis 

joining the two eigenpolarizations, as 

represented in Fig. 3. 

PANCHARATNAM-BERRY PHASE 

By using a sequence of optical elements 

like those just discussed, the 

polarization of the beam can be made 

to trace a path over the surface of the 

Poincaré sphere. Imagine a situation 

in which the final polarization is the 

same as the initial one, so that the 

path is closed. What we learn from 

Par-Tra’s story is that a sequence of 

displacements results in a rotation 

by an angle equal to the enclosed 

solid angle. In the small-planet analogy, 

this rotation can be observed by 

looking at the change of orientation 

of Par-Tra’s head. In the optical 

Figure 3. Left: Polarizers carry all states of polarization to a single polarization 

state here horizontal linear) along red geodesics. Right: Retarders rotate the points 

on the sphere by angle about an axis given by two orthogonal polarizations 

(here horizontal and vertical linear). 




case, on the other hand, polarization 

is represented by a zero-size point 

over the sphere with no discernible 

feature. Nevertheless, it turns out 

that there is a measurable analogue 

of the angle of orientation of Par-Tra’s 

head. To see this, consider the case in 

which the initial/final polarization is 

circular and is represented by a point 

at one of the poles. A rigid rotation 

of the sphere by Φ leaves this point 

unchanged. However, this initial polarization 

state, c, can be expressed 

as a linear superposition of two 

orthogonal states, such as the two 

horizontal and vertical linear polarizations 

h and V, according to c = (h ± 

iV)/√ – 2. While the point for c remains 

at the north pole, the points initially 

representing h and V rotate by 

an angle Φ, and the corresponding 

polarization directions in physical 

space rotate by Φ/2. The final state 

would then be [(hcosΦ/2 + VsinΦ/2) 

± i(VcosΦ/2 − hsinΦ/2)]/√ – 2 = c exp(+ – iΦ/2). 

This last global phase factor, the 

geometric phase, is the measurable 

quantity that reveals that a rotation 

of the point about its axis took place. 

As mentioned earlier, the geodesic 

paths resulting from using polarizers 

automatically satisfy parallel 

transport. However, the same is not 

necessarily true for the circular paths 

resulting from the rotations enacted 

by wave retarders. To visualize this 

fact, let us go back to Asteroid PB-56- 

84, and imagine that the little prince 

and Par-Tra go for a stroll around 

the only tree in the small planet (the 

axis of their rotational displacement). 

They both follow circular paths (of 

different radii in the figure only for 

illustration purposes) around the 

tree. The little prince walks always 

facing the forward motion direction, 

but Par-Tra’s physiology constrains 

her to gradually rotate at an angle 

different from that of the path. After 

completing one full circle, the prince 

has the same orientation as he did at 

the beginning, but Par-Tra’s orientation 

changes by an angle equal 

to the solid angle enclosed by her 

path. Only had they chosen to walk 

along the geodesic normal to the 

tree, would their translational and 

rotational motions have coincided. 

The rotations enacted by a phase 

retarder correspond to the rigid rotational 

motion of the little prince, 

and not to the parallel transport of 

Par-Tra. This can be seen by the fact 

that a “full-wave plate” (e.g. the cascade 

of two parallel half-wave plates), 

corresponding to a full circular path 

around the axis of rotation, does not 

write different phases on different 

polarizations, even though the paths 

over the Poincaré sphere enclose 

different solid angles. That is, if a 

closed path includes non-geodesic 

segments resulting from using wave 

retarders, the corresponding phase 

is not necessarily equal to half the 

enclosed solid angle (although other 

geometric interpretations are possible). 

Therefore, to enact a clean geometric 

phase with wave retarders, the 

displacement must be around great 

circles (geodesics). That is, the polarization 

entering a wave retarder must 

correspond to a point that is at π/2 

over the Poincaré sphere from both 

eigenpolarizations. For birefringent 

waveplates, with linear eigenpolarizations 

(i.e. on the Poincaré sphere 

equator), maximal geometric phase 

Figure 4. 

Par-Tra 

and the 

little prince 

going for a 

stroll around 

the tree. 

control can be enacted if the initial 

polarization is circular (i.e. at one of 

the poles). 

WAVEFRONT SHAPING WITH 

GEOMETRIC PHASE ELEMENTS 

Consider a half-wave plate (δ = π), 

whose linear fast eigenpolarization 

is at an angle γ from the horizontal 

axis. Illuminating this element with 

circular polarization (corresponding 

to the north pole), the path over the 

Poincaré sphere will be a meridian 

ending at the south pole (circular polarization 

with the opposite handedness), 

regardless of γ. However, the 

phase difference between two such 

paths corresponding to two values 

of γ, namely γ 1 and γ 2 , will equal 

one half the solid angle enclosed by 

them. Since the two meridians are 

at an angle 2(γ 2 −γ 1 ), the solid angle is 

4(γ 2 −γ 1 ) and the phase difference is 

simply ±2(γ 2 −γ 1 ), the sign depending 

on the conventions being used. That 

is, the phase of each emerging circularly 

polarized beam is (to within an 

additive constant) ±2γ. 

Modern technologies such as liquid 

crystals or metasurfaces allow 

the creation of birefringent optical 

elements where the eigenpolarization 

orientation can be tailored to 




change from point to point in any desired 

way for a range of applications. 

These devices allow writing arbitrary 

phase profiles on a wavefront. In the 

case of liquid-crystal-based devices, 

these phases can be turned on and off 

through appropriate electric control, something 

that is useful in applications 

such as beam steering. Note that the alternative 

to using geometric phase is to 

use dynamic phase, enacted through an 

increase in optical path length based on 

refractive index and element thickness, 

as is the case with standard lenses, 

prisms, and phase gratings. A very 

attractive feature of geometric phase 

elements is that they naturally incorporate 

the periodicity of the phase in 

the periodicity of the eigenpolarization 

angle. This allows, for example, creating 

optical elements (known as Q-plates) 

that can induce a vortex on the wavefront 

without requiring a discontinuity 

in the element’s surface (as is the case 

in a spiral phase plate), making the resulting 

element more robust to chromatic 

changes. 

OTHER GEOMETRIC PHASES 

Geometric phases are not restricted to 

optics, and there are many analogies 

in other quantum phenomena. For instance, 

the spin of an electron, represented 

on the Bloch sphere, acquires a 

phase evolving through closed paths, 

precisely as on the Poincaré sphere. 

Other systems have more complicated 

parameter spaces whose curvature 

takes more complicated distributions 

than the constant value on a sphere, 

and although the final phase might 

not reduce to a simple enclosed area 

or solid angle, the underlying principle 

is the same. Even in optics there are 

other realizations corresponding to 

different abstract spaces. One case is 

that of a specific family of structured 

beams, where the beam structure can 

be represented as a point on a sphere, 

and rotations of this sphere can be 

enacted with simple combinations of 

cylindrical lenses. Another one that 

involves polarization is the so-called 

(spin) redirection phase: imagine an 

optical fibre carrying a single mode 

with circular polarization. If the fibre 

is bent in 3D so that the local direction 

of propagation changes, a geometric 

phase is acquired that equals the solid 

angle enclosed by the local normalized 

direction vector over the sphere 

of possible directions. It turns out that 

the redirection phase and the standard 

PB phase can be unified through an appropriate 

3D formalism [5]. 

CONCLUSION 

As their name suggests, geometric phases 

arise from the inherent geometry of the 

space that naturally describes a property 

of a wave field. If the laws of parallel 

transport apply, a series of displacements 

in this space enact a rotation if the space 

is curved; if Par-Tra’s planet were flat (or a 

very large sphere), she would be doomed 

to always look in the same direction. The 

fact that the natural space that describes 

polarization (and propagation direction) 

is a sphere leads to a particularly simple 

connection between the rotation (and 

hence the phase) and the enclosed solid 

angle, and to simple ways to control the 

phase of a beam through the local orientation 

of a half-wave retarder. 

REFERENCES 

[1] S. Pancharatnam, Proc. Indian Acad. Sci. A 44, 247 (1956) 

[2] M.V. Berry, Proc. R. Soc. A 392, 45 (1984) 

[3] M.V. Berry, Curr. Sci. 67, 220 (1994) 

[4] E. Cohen et al., Nat. Rev. Phys. 1, 437 (2019) 

[5] K.Y. Bliokh, M.A. Alonso, M.R. Dennis, Rep. Prog. Phys. 82, 122401 (2019) 


BUYER'S GUIDE 

Nonlinear crystals 

NONLINEAR CRYSTALS 

FOR FREQUENCY CONVERSION 

/////////////////////////////////////////////////////////////////////////////////////////////////// 

Patricia SEGONDS 1, *, Benoit BOULANGER 1 and Peter SCHUNEMANN 2 

1 

Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 25 Av. des Martyrs, 38000 Grenoble, France 

2 

BAE Systems, MER15-1813, P.O. Box 868, Nashua, NH 03061-0868, USA 

*patricia.segonds@neel.cnrs.fr 

Crystals can convert wavelengths emitted by lasers 

using a second-order process. They allow light to be 

generated with smaller or higher wavelengths than 

those of the input beam. The issue is to select the 

nonlinear crystal having the best conversion efficiency 

at the targeted wavelengths, which requires a high 

non-linearity and suited transparency range as well 

as phase-matching conditions. 




There is an ongoing 

need for sources 

able to emit a 

coherent radiation 

from the ultra-violet 

up to the far 

infrared range, but 

requested wavelengths are not always 

provided by commercial lasers. In 

this case, the best alternative is to use 

nonlinear light-matter interactions 

in a bulk crystal. These interactions 

can be described by using the dual 

nature of light. 

QUANTUM PICTURE 

Nonlinear optics can be seen as processes 

based on fusion or splitting of 

photons. The effects that are mainly 

considered involve three photons, 

which corresponds to second-order 

nonlinear interactions as shown in 

Figs. 1 and 2. The horizontal continuous 

lines depict the matter energy 

levels and the dashed lines correspond 

Figure 1: Quantum picture for fusion: 

left SFG and right SHG 

to the energy levels of the electromagnetic 

field. In the case of fusion, 

two incident photons with energy 

quanta ħω 1 and ħω 2 , give birth to a higher 

energy photon at ħω 3 = ħω 1 + ħω 2 

according to the energy conservation 

(see Fig. 1 left where ω 1 ≤ ω 2 < ω 3 ). The 

probability of occurrence of this elementary 

process is maximal when 

the photon momentum conservation 

is achieved, i.e. ħk → 3 = ħk → 1 + ħk → 2 

where the k → i (i = 1, 2, 3) are the 

wave vectors. Fusion corresponds 

to the second-order sum-frequency 


Nonlinear crystals BUYER'S GUIDE 

generation (SFG), which is then an 

up-conversion process. If the two incident 

photons have the same quantum 

energy ħω, then a photon of twice a quantum 

energy ħ(2ω) is generated, which 

is called second-harmonic generation 

(SHG) (see Fig. 1 right). 

The spontaneous splitting of one incident 

photon with a quantum energy 

ħω 3 into two photons with energy quanta 

ħω 1 and ħω 2 is shown in Fig 2 left. It 

is the direct reverse process of fusion 

so that it fulfils the same photon energy 

and momentum conservation relations. 

Usually, the photon at ħω 3 is called the 

pump, and the generated photons at ħω 2 

and ħω 1 the signal and idler, respectively. 

This elementary process is also called 

spontaneous parametric down conversion 

(SPDC). The splitting of one incident 

photon at ħω 3 , can also be stimulated by 

a photon at ħω 1 or ħω 2 (see for example 

Fig. 2 right): it corresponds to both optical 

parametric amplification (OPA) of the 

stimulating photon at ħω 2 and to difference 

frequencies generation (DFG) at 

ħω 1 = ħω 3 – ħω 2 which corresponds to 

a “new” photon. When ħω 2 = ħω 3 , DFG 

is called optical rectification (OR). In 

realistic situations, there is a cascading 

of SPDC and OPA/DFG, which is called 

Optical Parametric Generation (OPG). 

And when the nonlinear crystal is inserted 

in a resonant cavity, we have an 

Optical Parametric Oscillation (OPO) [1]. 

Using wavelengths, it comes λ 3 < λ 2 ≤ λ 1 

fulfilling 1 — 

λ1 

+ 1 — 

λ2 

= 1 — 

λ3 

. 

WAVES PICTURE 

From the waves point of view, the incident 

light electric field gives birth to a 

matter induced polarization P → that radiates 

a light electric field E → becoming 

a source of excitation for the volume of 

adjacent matter, and so on. For frequency 

conversion processes, the interest is 

the spectral distribution of the radiated 

electric fields E → (ω i ) where i = 1, 2 or 3. 

They are determined from solving the 

equation of propagation of matter using a 

perturbative approach where the matter 

induced polarization P → (ω i ) is expanded as 

a Taylor power series of the excitation 

electric field. The first-order is the socalled 

linear induced polarization P →(1) 

(ω i ): it is radiated at the same circular 

frequency ω i as the excitating electric 

field E → (ω i ) by involving the first-order 

electric susceptibility χ (1) (ω i ) of the crystal. 

χ (1) (ω i ) is a second-rank polar tensor 

described by a diagonal 3×3 matrix 

when it is expressed in the dielectric 

frame (x, y, z): the three coefficients 

allow to define the three principal refractive 

indices n x (ω i ), n y (ω i ) and n z (ω i ). 

The higher orders of P → (ω i ) correspond 

to the nonlinear matter induced polarization. 

We will limit our purpose to 

the second-order induced polarization 

P →(2) (ω i ), corresponding to three-wave interactions 

governed by the second-order 

electric susceptibility χ (2) (ω i ) of the crystal. 

In the case of SFG (ω 3 = ω 1 + ω 2 ) for 

example, the exciting electric fields E → (ω 1 ) 

and E → (ω 2 ) give rise to the nonlinear induced 

polarization P →(2) (ω 3 = ω 1 + ω 2 ) that 

radiates an electric field at E → (ω 3 ) [1]. 

χ (2) (ω i ) is a third-rank polar tensor described 

by a 3×9 matrix, or by a 3×6 matrix 

when using a contracted notation. 

Note also that the writing convention 

d (2) (ω i ) = 1 – 2 

χ (2) (ω i ) is often used. The number 

of non-zero coefficients of the χ (2) 

tensor depends on the point group of 

the crystal [1]. In this frame work, it is 

important to notice that the only point 

groups allowing non-zero χ (2) coefficients 

are necessary non-centrosymmetric. 

Then a centrosymmetric crystal 

prohibits any second-order frequency 

conversion process. Let’s go back to the 

example of SFG. The goal is to have a 

constructive interference between the 

nonlinear polarization P →(2) (ω 3 = ω 1 + ω 2 ) 

and its radiated electric field E → (ω 3 ). That 

can be achieved if ∆k → = k → 3 – (k → 1 + k → 2) = 0 → , 

which is called the phase-matching (PM) 

relation and corresponds to the photon 

momentum conservation mentioned 

above. In that case, the energy generated 

at the circular frequency ω 3 grows continuously 

over the crystal length, which is 

of prime interest for applications since 

very high energy conversion efficiencies 

close to 100% can be reached [2]. When 

∆k → = k → 3 – (k → 1 + k → 2) ≠ 0 → , the interference 

between P →(2) (ω 3 = ω 1 + ω 2 ) and E → (ω 3 ) is 

destructive so that the generated energy 

oscillates with a spatial period L c = π/|∆ → k| 

that defines the parametric 


BUYER'S GUIDE 


coherent length ranging typically 

between 1 μm and 100 μm. However, 

an alternative is the technique of 

quasi-phase-matching (QPM) that 

allows the phase-mismatch ∆ → k ≠ 0 → to 

be compensated by the periodic modulation 

of the sign of the non-linearity 

over a period equal to 2 times L c . 

This configuration is that achieved in 

ppKTP, ppLN or OPGaAs [3]. Another 

condition to perform an efficient 

conversion efficiency is to find a 

crystal with a high non-linearity. In 

the equations, it appears at the level 

of the so-called effective coefficient 

χ eff which depends on the coefficients 

of the χ (2) tensor and the directions of 

the light electric fields E → (ω 1 ), E → (ω 2 ) 

and E → (ω 3 ), each corresponding to two 

Eigen polarization directions E →+ (ω i ) 

and E →– (ω i ) associated with the considered 

direction of propagation [1]. 

These Eigen modes are connected 

to the index surface described in the 

next section. 

Figure 2: Quantum picture for 

spontaneous and stimulated splitting: 

Left is SPDC and right is OPA &DFG 

optical class and the same relations 

of order apply according to its sign, 

knowing that there are two independent 

principal refractive indices: 

n x (λ i ) = n y (λ i ), called the ordinary principal 

index n o (λ i ), and n z (λ i ) which is 

the extraordinary principal index 

written n e (λ i ) . Cubic crystals belong 

to the isotropic optical class where 

n x (λ i ) = n y (λ i ) = n z (λ i ). The magnitude 

of the principal refractive indices 

increases when the wavelength decreases, 

which is well described by 

the Sellmeier equation [1]. Such a 

Figure 3: Index surface of a positive 

biaxial crystal at a given wavelength 

using the convention n x < n y < n z [5]. 

behavior is classically determined by 

using the prism technique or from 

the interpolation of phase-matching 

curves recorded by using the sphere 

method for example [4]. Given a wavelength, 

refractive indices have an 

angular distribution depicted in the 

dielectric frame by the index surface. 

It is a surface with inside and outside 

sheets labeled (-) and (+) respectively. 

For a given direction of propagation, 

their distance from the origin corresponds 

to the refractive index n – and n + , 

(n + – n – ) being called the birefringence. 

Figure 3 shows the index surface of a 

positive biaxial crystal. The two sheets 

are associated to two possible linear 

Eigen modes of the light electric field 

E →– (ω i ) and E →+ (ω i ). The orientation of 

these two Eigen modes is a function 

of the direction of propagation which 

is an important issue to consider for 

calculating the value of the effective 

coefficient χ eff [1]. 

LINEAR CRYSTAL OPTICS 

Crystals are cut oriented with the highest 

precision (up to 0.01°) in their 

crystallographic frame (a, b, c) by 

using X-rays diffraction techniques. 

Then it is mandatory to determine the 

relative orientation between the crystallographic 

frame and the dielectric 

frame in which all optical properties 

are described. Orthorhombic, monoclinic 

and triclinic crystals belong 

to the biaxial optical class: when the 

principal refractive indices verify 

n x (λ i ) < n y (λ i ) < n z (λ i ), the crystal is 

called a positive biaxial crystal; the 

relation of order is the reverse in 

the case of a negative biaxial crystal. 

Tetragonal, hexagonal and trigonal 

crystals belong to the uniaxial 


Nonlinear crystals BUYER'S GUIDE 

PHASE-MATCHING CONDITIONS 

For colinear interactions, the angular 

distribution of PM directions is found 

by solving: 

∆k = 2π n± (λ 3 , θ PM , φ PM ) 

—– 

λ 3 

– n± (λ 2 , θ PM , φ PM ) 

—– – n± (λ 1 , θ PM , φ PM ) 

— 

λ 2 λ 1 

– = 0 

(θ PM , φ PM ) are the PM angles of spherical 

coordinates, expressed in the dielectric 

frame. In that case, one speaks of 

Birefringence Phase-Matching (BPM). 

It is easy to write the corresponding 

code, but there exists also the commercial 

code SNLO [6]. Such a calculation is 

mandatory before selecting a nonlinear 

crystal especially when the three interacting 

wavelengths are not classically used. 

Otherwise they are already provided by 

several compagnies for non-resonant 

second-order processes widely used in 

devices, as for example SHG of a commercial 

laser emitting at λ ω = 1.064 µm 

to generate λ 2ω = 0.532 µm. It is necessary 

to have principal refractive indices 

that must have been determined with an 

accuracy better than 10 -4 to be able to calculate 

the BPM angles with an accuracy 

better that 1°. There are three possible 

combinations of refractive indices leading 

to the three BPM types [1]: 

type I [n – (λ 3 ), n + (λ 1 ), n + (λ 2 )], 

type II [n – (λ 3 ), n – (λ 1 ), n + (λ 2 )], 

type III [n – (λ 3 ), n + (λ 1 ), n – (λ 2 )]. 

To these three types are associated three 

different configurations of Eigen modes 

polarization that it is important to know 

in order to be able to calculate the effective 

coefficient χ eff as mentioned in the 

previous section. It is then necessary to 

properly polarize the incident beams. 

Note that BPM directions are associated 

to spectral, angular and thermal acceptances 

[1]. 

COMMERCIAL 

NONLINEAR CRYSTALS 

Several commercial nonlinear crystals 

cut as slabs with very high optical quality 

and more or less large dimensions 

can be purchased to convert wavelengths 

emitted by commercial lasers from 

BPM or QPM second-order processes. 

The main suppliers are given in the 

table below. They can even provide PM 

conditions as a function of temperature. 

Take care of maximal values of incoming 

energies for not reaching the crystal optical 

damage threshold and Fresnel losses 

reducing conversion efficiencies. Losses 

can be decreased by a coating but the 

optical damage threshold might decrease 

too. When commercial nonlinear crystals 

do not correspond to your request, 

this article and references provide all 

elements to calculate BPM and QPM 

conditions and the associated conversion 

efficiencies as well as the spectral, angular 

and thermal acceptances. 

REFERENCES 

[1] B. Boulanger, J. Zyss, Non-linear Optical properties, Chapter 1.7 in International 

Tables for Crystallography, Vol. D: Physical Properties of Crystals, A. Authier Ed., 

International Union of Crystallography, Kluwer Academic Publisher, Dordrecht, 

Netherlands, 181 (2013). 

[2] A. Kokh, N. Kononova, G. Mennerat, P. Villeval, S. Durst, D.Lupinski, V.Vlezko, K.Kokha, 

J. Cryst. Growth 312, 1774 (2010) 

[3] V. O. Smolski, S. Vasilyev, P. G. Schunemann, S. B. Mirov, and K. L. Vodopyanov, 

Opt. Lett. 40, 2906 (2015) 

[4] F. Guo, E. Boursier, P. Segonds, A. Peña, J. Debray, V. Badikov, V. Panyutin, D. Badikov, 

V. Petrov, B. Boulanger, Opt. Lett. 47, 842 (2022). 

[5] Y. Petit, S. Joly, P. Segonds, B. Boulanger, Laser Photonics Rev. 7, 1 (2013) 

[6] SNLO from https://as-photonics.com/products/snlo/ 


BUYER'S GUIDE 


COMPANY WEBSITE MANUFACTURER 

OR DISTRIBUTOR 

MAIN BULK NONLINEAR CRYSTALS 

FOR SALE 

ALPHALAS 

https://www.alphalas.com/products/ 

laser-components/nonlinear-crystals.html 

Custom Manufacturer 

LBO, BBO, BiBO, KTP & ppKTP 

ARDOP 

https://www.ardop.com/details-cristaux 

+non+lineaires-54.html 

Distributor 

BBO, LBO, KDP, DKDP, KTP, KTA, AGS, 

AGSe, AgSe 

ARTIFEX 

https://artifex-engineering.com/optics/ 

crystals/ 

Distributor 

BBO, KTP, LBO, LN 

BAE SYSTEMS 

https://www.baesystems.com/en/ 

product/nonlinear-crystal-technologies 


ZGP, CSP, ppGaAs, ppGaP 

BLUEBEAM 

http://www.bbotech.com/product.php 

?cid=55 


BBO, LBO, KTP, KTA, BiBO, LN 

CASIX 

https://www.casix.com/en/productList. 

html?TypeID=13966 


BBO, LBO, KTP 

CASTECH 

https://www.castech.com/product/ 

NLO-Crystals-33 

Stock & 


LBO, BBO, BiBO, CLBO, KTP, RTP, 

KTA, LN, MgO:LN, KDP, DKDP, LilO3 

COVESION https://covesion.com/en/ Stock & 


MgO:ppLN 

CRISTAL LASER https://www.cristal-laser.com/ Custom Manufacturer LBO, KTP, KTA, RTP 

CRYSTECH http://www.crystech.com/product/8/ Custom Manufacturer KTP, KTA, BBO, BiBO, LN 

CRYSTRO 

https://www.tggcrystal.com/supplier-nonlinear_crystals-434498.html 

Distributor 

KTP, LBO, BBO, LN 

EDMUND OPTICS 

https://www.edmundoptics.com/f/ 

nonlinear-crystals/39487/ 

Distributor 

BBO, LBO 

EKSMA OPTICS 

https://eksmaoptics.com/ 

nonlinear-and-laser-crystals/ 

nonlinear-crystals/ 


BBO, LBO, KDP, DKDP, KTP, CLBO, 

KTA, AGS, AGSe, AgSe, ZGP, LiO3, LN 

FOCTECK 

https://www.foctek.net/Products/ 

list-93.html 


BBO, KTP, LN 

GAMDAN OPTICS https://www.gamdan.com/ Stock & 


LBO, BBO, KTP 

GWU https://gwu-lasertechnik.de/crystals/ Distributor BBO, LBO, KTP, KTA, BiBO, CLBO, 

RTP, MgO:LN, DKDP, KDP, LiIO3 

INNOWIT 

https://www.innowit.com/en/ 

cate-1929.html 

Distributor 

KTP, KTA, KDP, DKDP, LBO, BBO, RTP 

LASERTON 

https://laserton.com/index.php 

?m=content&c=index&a=lists&catid=36 


BBO, KTP, DKDP, LN, LBO, KTA, RTP 

OPTOAXIS 

http://www.optoaxis.com/ 

NLO-Crystals.html 


LN, BBO, LBO, DKDP, KTP 

PRINCETON SCIENTIFIC 

https://princetonscientific.com/ 

materials/nlo-crystals/ 


KTP, KTA, KDP, BBO, LN, MgO:LN, LT 

RAICOL CRYSTALS https://raicol.com/ Stock Manufacturer KTP, ppKTP, BBO, RTP, LBO 

RAINBOW PHOTONICS http://www.rainbowphotonics.com/ Stock Manufacturer DAST, DSTMS, OH1, KNbO3 

SHALOM EO 

https://www.shalomeo.com/ 

Laser-Crystals-and-Components/ 

Nonlinear-Crystals 

Stock & 


BBO, DKDP, KTP, LBO, BiBO, ZGP, 

KTA, LilO3, LN, MgO:LN, RTP, YCOB 


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