Polarization-independent waveguide grating coupler using an optimized polysilicon overlay

We propose and validate a new, to the best of our knowledge, approach to designing a polarization-independent waveguide grating coupler, using an optimized polysilicon overlay on a silicon grating structure. Simulations predicted coupling efficiencies of about −3.6 dB and −3.5 dB for TE and TM polarizations, respectively. The devices were fabricated using photolithography in a multi-project wafer fabrication service by a commercial foundry and have measured coupling losses of −3.96 dB for TE polarization and −3.93 dB for TM polarization.