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Continuously Tunable Microwave Photonic Filter by Using Optical Frequency Comb Based on a Recirculating Frequency Shifter

In this paper, a continuously tunable microwave photonic filter (MPF) with optical frequency comb generated by recirculating frequency shifter (RFS) based on an IQ modular is proposed and experimentally demonstrated. The optical comb generated by the proposed scheme possess good flatness and high optical signal to noise ratio. Optical frequency comb with 63 comb lines can be obtained by RFS based on the single-sideband recirculating frequency shifter (SSB-RFS) scheme, by employing the optical filter with bandwidth of 10 nm and the modulation microwave signal with the frequency of 20 GHz. In addition, the modulation depth of the stable optical frequency comb exceeds 15dB, and the flatness fluctuation of optical frequency is less than 3dB. MPF with narrow bandwidth passbands has been implemented by taking the generated optical frequency comb as the optical source together with a dispersive medium. By changing the frequency of the modulation signal, the number and wavelength interval of optical frequency comb can be changed. As a result, the free spectrum range (FSR) and bandwidth of the MPF can be tuned and in our experiment the central frequencies of two passbans of the MPF has been tuned linearly from 7.38 GHz to 11.30 GHz, and 14.65 GHz to 19.53 GHz, respectively. © 2020 The Author(s)