Mathias FINK - Institut d'études scientifiques de Cargèse (IESC)

Pr. Hui Cao
Light transport through random media : physics and application
The first part is the fundamental study of light transport through disordered photonic waveguides.
We have observed position-dependent diffusion by probing light propagating inside a quasi-twodimensional
random system from the third dimension. The system size and shape are designed to
enhance the interference of scattered waves so that the diffusion coefficient is modified appreciably.
We also use dissipation to control the effective system size, and tune the value of diffusion
coefficient via the interplay of localization and dissipation. This work demonstrates the possibility
of utilizing the geometry of a random system or the dissipation to manipulate wave diffusion.
The second part is the application of random media to spectrograph. We have designed and
fabricated an on-chip spectrometer based on random arrays of scatterers. The speckle patterns are
recorded and used to reconstruct the input spectra after the spectral-spatial mapping is calibrated.
Multiple scattering of light increases the effective optical path length, facilitating the spectral
decorrelation of speckle. It allows us to dramatically reduce the device size without sacrificing
spectral resolution. To reduce the insertion loss, we incorporate certain degree of order to the
random spectrometer. We have also used the speckle generated by a multimode optical fiber to
recover the input spectra. This fiber spectrometer gives high-resolution and has low-loss. A
wavelength resolution of 8 pm is achieved with a 20 meter long fiber and a broadband operation
covering the visible spectrum is obtained with 1.5 nm resolution using a 2cm long fiber.
Pr. Georg Maret
Transition to Anderson localization of light in three dimensions
Georg Maret, Wolfgang Bührer, Tilo Sperling and Christof Aegerter
We report experiments on the time resolved transmission of multiple scattered light in strongly
turbid three dimensional media composed of high index (titania) nanoparticles. At small values of
kl*, with wave vector k and transport mean free path l*, and at long times the total transmission is
delayed [1] and the width of the intensity profile at the backside of the sample saturates [2]. These
deviations from diffusive transport which cannot be accounted for by absorption indicate a
transition to 3D Anderson localization. Data for samples with different thickness and turbidity
provide a direct determination of their localization length as function of kl* and allow to determine
the critical value kl*c of the transition. We also discuss the spectral and power dependence of the
transmission which reveal the presence of nonlinear effects [3].
[1] M. Störzer, P. Gross, C.M. Aegerter and G. Maret, Phys.Rev.Lett. 96, 063904 (2006).
[2] T. Sperling, W. Bührer, C.M. Aegerter and G. Maret, Nature Photonics, 7, 48-52 (2013)
[3] W. Bührer et.al. to be published
Pr. David A.B. Miller
How to design any linear optical component and how to avoid it ?
Any linear optical structure or device can be readily understood mathematically, but we have not
known historically how to design any such device. For example, current challenging practical
devices include efficient arbitrary spatial mode splitters and converters for multimode fiber and
advanced free-space communications, especially avoiding any avoid fundamental power splitting
loss. Here we show the first complete constructive method for design of an arbitrary linear optical
device. In the spirit of a universal machine, this proves any linear optical device is possible in
principle. We propose practical approaches for spatial devices. Finally, we show how all such
actual design work can be avoided completely in systems that can configure themselves without