Shallow-grating coupler with optimized anti-reflection coating for high-efficiency optical output into multimode fiber

摘要

We present an optimized design of a shallow grating coupler in a silicon-on-insulator (SOI) wafer with a quadruple anti-reflection coating (ARC) of multiple layers of SiO_2 and SiO_xN_y for coupling to a multimode fiber. The ARC is designed to generate sufficient destructive interference for downward emission while maintaining constructive interference for upward emission. We confirm numerically that the upward directionality of the grating is as high as -0.58 dB. Because the grating is shallow and the ARC is away from the SOI core layer, the back reflection along the input waveguide can be suppressed to -27 dB.