On-Chip Fully Reconfigurable Microwave Photonic Flat-Top Filter

We propose and experimentally demonstrate an on-chip fully reconfigurable microwave photonic flat-top filter based on cascaded ultrahigh-Q silicon racetrack micro-ring resonators (MRRs). The microwave photonic filter (MPF) is realized based on phase modulation to intensity modulation conversion, which maps the spectral response of the cascaded MRRs in the optical domain to the one of the resulted microwave filter in the electrical domain. To enable filter frequency tunability, two independent micro-heaters are placed on top of the two MRRs. By controlling the direct current (DC) voltage applied to the micro-heaters, a flat-top MPF is produced, whose center frequency and bandwidth can be flexibly tuned. A silicon-based ultrahigh-Q cascaded MRRs chip is designed, fabricated and evaluated. With the use of the chip, a flat-top MPF is experimentally demonstrated. The experimental results show that the MPF has a tunable center frequency from 4 to 24 GHz and a tunable bandwidth from 225 to 405 MHz. Thanks to its strong reconfigurability, the proposed integrated microwave photonic flat-top filter is promising to be widely used in multi-function microwave photonic signal processing systems.