Ultra-Compact Sub-Wavelength Grating Polarization Splitter-Rotator for Silicon-on-Insulator Platform

We designed and fabricated a polarization splitter-rotator (PSR) on a silicon-on-insulator (SOI) platform based on an asymmetric directional coupler. The asymmetric directional coupler consists of a regular strip waveguide and a sub-wavelength grating (SWG) waveguide. The SWG waveguide used in the design provides the freedom to engineer the dispersion properties of the supermodes, which allow the design to be fabrication tolerant to the waveguide width variations. A measured peak polarization conversion efficiency of −0.3 dB and crosstalks below −10 dB were achieved. The designed SWG PSR has a compact size of 35
${\mu} \text{m} \times 5\,{\mu} \text{m}$
.