Comprehensive adaptive tuning of silicon RF photonic filters

RF photonic filters are capable of achieving very high selectivity and dynamic tuning over multi-GHz ranges. This paper presents a mm-wave silicon photonic fourth-order tunable elliptic digital filter designed in the optical domain with ring-resonator-based all-pass filter (APF) unit cells. Inclusion of tunable phase shifters and Mach-Zehnder interferometer (MZI) couplers in the filter's rings and front-end provides comprehensive tuning to compensate for variations in ring resonance frequency, coupling ratio, and phase mismatches. A monitor-based adaptive tuning algorithm is proposed to calibrate the optical filter response with high accuracy.