Compact Notch Microwave Photonic Filters Using On-Chip Integrated Microring Resonators

We propose and experimentally demonstrate a compact notch microwave photonic filter (MPF) using two integrated microring resonators (MRRs) on a single silicon-on-insulator (SOI) chip. The free spectral ranges (FSRs) of two cascaded MRRs are 160 GHz and 165 GHz, respectively. Due to the vernier effect, the transmission spectrum of cascaded MRRs is a series of bimodal distribution whose interval is an arithmetic sequence. By locating the laser wavelength at the middle of different bimodal intervals and fine tuning it properly, both central frequency and bandwidth of the notch MPF can be tunable. In the experiment, the tunability of central frequency and 3-dB bandwidth are demonstrated from 2.5 GHz to 17.5 GHz and from 6 GHz to 9.5 GHz, respectively. The best rejection ratio of the notch filter is larger than 40 dB. This approach will allow the implementation of low-cost, very compact, and integrated notch MPFs in a silicon chip.