1 March 2006 Monolithically integrated graded-index waveguide input couplers for silicon-photonics
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Abstract
A monolithically integrated asymmetric graded index (GRIN) waveguide structure for coupling light into high index contrast waveguides is described. When analyzed in terms of its waveguide modes, the GRIN coupler is shown to be a multimode interference (MMI) device. The design parameters and tolerances are calculated for quadratic index profile and uniform index amorphous silicon (a-Si) GRIN couplers optimized for coupling light into silicon-on-insulator waveguides. Calculations of coupling efficiencies into 0.5 μm SOI waveguides show that asymmetric GRIN couplers operate over a very wide wavelength range with low polarization dependence, and fabrication requires lithographic resolution of only ±1 μm. Experimental results are presented for a 3 μm thick single layer a-Si coupler integrated with a 0.8 μm SOI waveguide. The measured variation of coupling efficiency with coupler length is in agreement with theory, with an optimal coupling length of 15 μm.
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S. Janz, S. Janz, A. Delage, A. Delage, B. Lamontagne, B. Lamontagne, A. Bogdanov, A. Bogdanov, D. Dalacu, D. Dalacu, D.-X. Xu, D.-X. Xu, K.P. Yap, K.P. Yap, } "Monolithically integrated graded-index waveguide input couplers for silicon-photonics", Proc. SPIE 6125, Silicon Photonics, 61250M (1 March 2006); doi: 10.1117/12.648750; https://doi.org/10.1117/12.648750
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