Frequency- and Notch-Depth-Tunable Single-Notch Microwave Photonic Filter

A single-notch microwave photonic filter with tunable frequency and tunable notch depth is proposed and experimentally demonstrated. In the proposed filter, two phase-modulated optical signals at two different wavelengths are generated at a phase modulator. One phase-modulated signal is filtered by a phase-shifted fiber Bragg grating with an ultra-narrow notch to remove the upper sideband. The other phase-modulated signal is filtered by a wideband optical bandpass filter to remove the lower sideband. Since the remaining lower and upper sidebands in the two optical signals are out of phase, the combination of the beat signals at a photodetector will lead to the cancelation of the detected microwave signals, to generate an ultranarrow notch. An experiment is performed. A single-notch microwave photonic filter with a 3-dB bandwidth of ~180 MHz, a tunable frequency from 1.5 to 6.6 GHz, and a tunable notch depth from 0 to 42 dB is experimentally demonstrated.