Comparative Study of Uniform and Nonuniform Grating Couplers for Optimized Fiber Coupling to Silicon Waveguides

다국어 초록 (Multilingual Abstract)

We have investigated the ultimate limits of nonuniform grating couplers (NGCs) for optimized fibercoupling to silicon waveguides, compared to uniform grating couplers (UGCs). Simple grating couplerschemes, which can be fabricated in etching steps of the conventional complementary metal-oxidesemiconductor (CMOS) process on silicon-on-insulator (SOI) wafers without forming any additional overlaystructure, have been simulated numerically and demonstrated experimentally. Optimum values of the gratingperiod, fill factor, and groove number for ultimate coupling efficiency of the NGCs are determined fromfinite-difference time-domain (FDTD) simulation, and confirmed with experimentally demonstrated devicesby comparison to those for the UGCs. Our simulated results indicate that maximum coupling efficiencyof NGCs is possible when the minimum pattern size is below 50 nm, but the experimental value for themaximum coupling efficiency is limited by the attainable fabrication tolerance in a practical device process.

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