Fast Tunable Photonic Single-Bandpass RF Filter With Multiple Arbitrary Switching Flat-Top Passbands

A fast tunable single-bandpass photonic radiofrequency filter (PRF) with multiple arbitrary switching flat-top passbands is proposed and experimentally demonstrated. The PRF is comprised of a narrow, flat-top optical filter based on a fiber Bragg grating with multiple phase shifts, and a high-speed wavelength switch module by incorporating an optical carrier-suppressed single-sideband modulation unit and a direct digital synthesizer. The combination of the single flat-top passband and the high-speed digital controlled wavelength switch in the optical domain enables us to achieve a fast and arbitrarily tunable single passband in the microwave domain. In the experiments, the proposed PRF shows a single flat-top passband with a 3-dB bandwidth of 740 MHz, a rectangular shape factor around 2.27, and an out-of-band rejection ratio greater than 41 dB. In the application demonstrations, the multitone or single-tone continuous-wave RF signals with different frequency components are applied to the PRF and then the desired components or waveforms are temporally separated and successfully recovered, verifying the multiple switching passbands with arbitrarily manipulated center frequencies and numbers over the frequency range from 0 to 12 GHz at a switching speed as fast as 1.73 ns.