Grating couplers in silicon-on-insulator: The role of photonic guided resonances on lineshape and bandwidth

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Passoni, M.
Gerace, Dario
Carroll, Lee
Andreani, L. C.
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Most grating couplers for silicon photonics are designed to match the approximately 10 μm mode-field diameter (MFD) of single-mode telecom fibres. In this letter, we analyse grating-coupler designs in the Silicon-on-Insulator (SOI) platform in a wide range of MFDs (4–100 μm) and related footprints, to give a physical understanding of the trends in efficiency and lineshape of the corresponding coupling spectra. We show that large-footprint grating couplers have an intrinsic Lorentzian lineshape that is determined by the quasi-guided photonic modes (or guided resonances) of the corresponding photonic crystal slab, while small-footprint grating couplers have a Gaussian lineshape resulting from the k-space broadening of the incident mode. The crossover between the two regimes is characterized by Voigt lineshapes. Multi-objective particle-swarm optimisation of selected small-footprint apodized grating-couplers is then used to locate the “Pareto fronts;” along which the highest coupling efficiency is achieved for a given bandwidth. This approach identifies several high-efficiency 220 nm SOI grating coupler designs with 1 dB bandwidths exceeding 100 nm. Such grating couplers are ideally suited for broadband photonic applications, such as wavelength-division multiplexing and environmental sensing, and are compatible with commercially available ultra-high numerical aperture fibres.
Diffraction gratings , Photonics , Photonic crystals , Silicon , Etching
Passoni, M., Gerace, D., Carroll, L. and Andreani, L. C. (2017) 'Grating couplers in silicon-on-insulator: The role of photonic guided resonances on lineshape and bandwidth', Applied Physics Letters, 110(4), pp. 041107. doi:10.1063/1.4974992
© 2017, AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Appl. Phys. Lett. 110, 041107 (2017) and may be found at