Microwave photonic notch filter with a tunable frequency and a bandwidth based on gas absorption

We propose and demonstrate a high-performance microwave photonic notch filter (MPNF) based on gas absorption with favorable tunability and a high rejection ratio. In the demonstration experiments, acetylene gas is used to selectively absorb the single sideband produced by phase modulation, and correspondingly to suppress the generated microwave signal. The filter center frequency and bandwidth can be separately tuned by changing the carrier laser frequency and gas pressure. The proposed MPNF achieves a continuously tunable frequency from 2-20 GHz and a 10-dB bandwidth from 0.44-5.89 GHz with a high rejection ratio over 60 dB, which is expected to exceed 100 dB in theory, showing great potential for various applications such as advanced communication and radar.