Large-Scale Thermo-Optic Phase Shifter Array with Feedback Photodiodes

V. Gurses, R. Fatemi, A. Khachaturian, A. Hajimiri

Thermo-optic phase shifters (TOPS) are ubiquitously used in large-scale photonic integrated circuits for phase modulation and correction because of their low loss and small form factor [1]. In high-density integration of TOPS, when each TOPS is directly addressed, the number of electrical connections and electrical driver complexity scale rapidly, becoming a limiting factor of scalability [2, 3]. Furthermore, high-density TOPS arrays suffer from thermal crosstalk [4], making precise phase modulation for high-density systems challenging. To overcome these challenges, we introduce a folded row-column architecture for TOPS arrays with a row-column MZI and photodiode (PD) array to acquire real-time feedback information for thermal crosstalk correction and calibration. We realize a 288-element TOPS array with a 256-element PD array and implement a matrix inversion-based thermal
crosstalk correction algorithm.With a thermal excitation model, we also compare pulse amplitude modulation (PAM) and pulse width modulation (PWM) driving schemes of TOPS arrays and investigate their scaling limits.