WAVES AND VIBRATIONS IN INHOMOGENEOUS STRUCTURES ...

emoved and the spectra changed drastically when nearly all the details were removed. In
general the transmission level in the upper arm of the Y-splitter was more affected than in the
lower arm. Furthermore, we observed that absence of the small details in the splitter region
did not lead to improvement of the transmission in the pass bands. Hence, the small details in
the design do not contribute significantly in scattered losses of the Y-splitter. From the above
observations and comments, we infer that these small details play an important role in the
optimized structure and that they cannot be removed without hampering the performance of
the splitter in spite of their negligible size.
The good agreement between the calculated spectra of the designed structure and the
optical measurements on the fabricated structure confirms that the NIL fabrication of the
challenging nanophotonic TO design has been successful. It should be noted though that the
crosstalk is less suppressed in the fabricated structure, illustrating that there still is room for
improvement in the fabrication process.
Finally, it is remarked that the TO compact wavelength splitter functions as designed,
namely as a fairly efficient and coarse high-pass/low-pass wavelength filter.
NORMALISED TRANSMISSION (dB)
0
-5
-10
-15
-20
Upper arm :
Measured
3D FDTD
-25
Lower arm :
Measured
-30
1340 1380 1420
3D FDTD
1460 1500 1540 1580 1620
WAVELENGTH (nm)
Fig. 3. (Left) The original TO design. Light enters the component from the left side and is split
into the two arms dependent on the wavelength. (Middle) SEM image of the fabricated splitter
using NIL. (Right) Normalized measured transmission below the cut-off wavelength for quasi-
TE polarized light from the two output arms. Also shown are 3D FDTD calculations for the
transmission through the output arms of the originally designed structure. The 3D FDTD
calculations have been blue-shifted by 0.5% in wavelength to match the experimental
wavelength scale.
5. Conclusions
We have used NIL to fabricate SOI-based nanophotonic structures with feature sizes down
below 30 nm. The NIL fabricated devices perform comparably to the direct EBL defined
devices and the obtained results are in good agreement with 3D FDTD calculations. Thus, we
have demonstrated the feasibility of NIL as a cost-efficient fabrication technique for siliconbased
nanophotonics.
Acknowledgments
This project was supported in parts by the European network of excellence Epixnet, the
Danish Research Council for Technology and Production Sciences via the PIPE project, and
by the New Energy and Industrial Technology Development Organization (NEDO) via the
Japanese Industrial Technology Research Area. The partial support of the EC-funded project
NaPa (Contract no. NMP4-CT-2003-500120) is gratefully acknowledged. OS and JSJ
received support from the Eurohorcs/ESF European Young Investigator Award (EURYI)
through the grant “Synthesis and topology optimization of optomechanical systems”. Finally,
the authors would like to thank Peixiong Shi, Danchip, DTU, for his technical assistance.
#76773 - $15.00 USD Received 6 November 2006; revised 18 January 2007; accepted 19 January 2007
(C) 2007 OSA 5 February 2007 / Vol. 15, No. 3 / OPTICS EXPRESS 1266