A tunable microwave photonic bandpass filter with high mainlobe-to-sidelobe ratio (MSR) based on a phase modulator and a dispersive device is proposed. The multi-tap characteristics of the filter are realized by slicing a broadband source using a Mach-Zehnder interferometer (MZI) which results in a high MSR of 25 dB. The tunability of the filter is realized by an optical variable delay line (OVDL) in one arm of the MZI, which changes the wavelength spacing of the sliced broadband source and results in a tunable free spectrum range (FSR) of the filter. The central frequency of the bandpass filter is tunable from 10.7 GHz to 27 GHz by changing the wavelength spacing from 0.145 nm to 0.054 nm.
Multi-π-phase-shifted fiber Bragg gratings and π-phase-shifted sampled fiber Bragg gratings(SFBGs) with dual wavelength filtering properties are compared.Results show that both of these gratings have the dual wavelength reflective spectra.However,the side lobe of the reflective spectrum of π-phase-shifted SFBGs is lower than that of multi-π-phaseshifted gratings.By adjusting the duty cycle in the range of 0.66-0.80,the filtering properties of π-phase-shifted SFBGs are optimized,and the side lobe suppression ratio(SLSR) is the lowest when the duty cycle is 0.75.The application of the π-phase-shifted SFBGs in the dual-wavelength laser is also demonstrated.
