Ultra-low-loss polarization-splitting grating coupler based on inverse-design

A polarization-splitting grating coupler (PSGC) is a key component for silicon photonic integrated circuits (PICs), which achieves light coupling from/to a fiber for both polarizations. We propose a high-performance PSGC designed by an inverse design method. The PSGC is designed to be able to be fabricated through a single etching step with outstanding fabrication tolerance. Experimental results indicate a peak insertion loss (IL) of -1.05 dB and a polarization-dependent loss (PDL) of 0.04 dB at 1534.7 nm, which are the lowest on current 220nm-silicon on insulator (SOI) platforms, to the best of our knowledge. Additionally, the 1-dB bandwidths of IL and PDL are 48 nm and 68 nm respectively. It is worth mentioning that the PSGC works under 0 degrees injection of fiber, which reduces packaging costs.