A Monolithic Polarization Controller and Tracking Loop for Optical Interconnect Demonstrated on a 90 nm Silicon CMOS-Photonic Platform

We report, to the best of our knowledge, the first monolithically-integrated silicon CMOS-photonic co-designed polarization tracking circuit implemented in a 90 nm CMOS SOI process. The Polarization Splitter and Rotator (PSR) decompose the optical input into TE and TM component and rotate the TM component to TE mode. The directional couplers combine the two TE components from PSR into single optical output. The thermal phase shifters on the optical path maximize the final optical output. A feedback loop implemented with monitoring photodetector, current mode ADC and Finite State Machine (FSM), control the current mode DACs to adjust the current input of thermal phase shifter. The circuit tracks randomized polarization rotation across the Poincaré sphere, maximizes TE-mode optical power, and experimentally achieves a BER of $10^{-11}$ with 10 Gb/s PAM-2 modulation.