Automatic Monitor-Based Tuning of Reconfigurable Silicon Photonic APF-Based Pole/Zero Filters

Reconfigurable photonic filters are promising candidates to meet the requirements of future microwave communication systems. However, sensitivity to process and temperature variations necessitates an automatic calibration solution to enable robust operation. This paper demonstrates fully automatic tuning of silicon photonic all-pass filter (APF)-based pole/zero filters using a monitor-based tuning method that calibrates the initial response by controlling each pole and zero individually via microheaters. The proposed tuning approach calibrates severely degraded initial responses to the designed elliptic filter shapes and allows us for automatic bandwidth and center-frequency reconfiguration of these filters. This algorithm is demonstrated on second- and fourth-order filters fabricated in a standard silicon photonics foundry process. After the initial calibration, only 300 ms is required to reconfigure a filter to a different center frequency. Thermal crosstalk between the microheaters is investigated, with substrate thinning demonstrated to suppress this effect and reduce filter calibration to less than half of the original thick substrate times. This fully automatic tuning approach opens the possibility of employing silicon photonic filters in real communication systems.