Polarization insensitive 1D grating coupler based on a zero-birefringence subwavelength corelet waveguide

Grating coupler devices provide efficient, foundry-compatible vertical fiber-to-chip coupling solutions in integrated photonic platforms. However, standard grating coupler designs are highly polarization sensitive, which hinders their adoption. We present a new type of 1D polarization insensitive grating coupler (PIGC) that is based on a zero-birefringence subwavelength "corelet" waveguide. We demonstrate a PIGC for coupling in the telecommunications O-band in a 45 nm-node monolithic SOI CMOS electronic-photonics platform, with measured insertion losses of 6.7 and 6.1 dB to transverse-electric and transverse-magnetic polarizations respectively, and a ±1 dB polarization dependent loss bandwidth of 73 nm.