Performance-improved microwave photonic single-passband filter using birefringence of phase-shifted fiber Bragg grating

A novel microwave photonic single-passband filter with an improved out-of-band rejection and an extended frequency tuning range is proposed and demonstrated, which is achieved by using birefringence of a phase-shifted fiber Bragg grating (PSFBG). If two polarization states of two phase-modulated signals with opposite modulation indices from a polarization modulator (PolM) are controlled to be aligned with two principal axes of the polarization-maintaining PSFBG (PM-PSFBG), respectively, two single-passband or two single-notch filters with slight frequency interval are achieved, depending on the position of the optical carrier relative to the notches of the PM-PSFBG. Through subtraction of the two filters, the out-of-band rejection is significantly improved, and the frequency tuning range is greatly extended. Analytical simulations are performed using an established theoretical model, which are verified by an experiment.