Flat-top Microwave Photonic Bandpass Filter with Tunable Bandwidth Based on SBS and FWM

We propose and demonstrate a flat-top microwave photonic bandpass filter (MPBF) with tunable bandwidth based on stimulated Brillouin scattering (SBS) and four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). The flat-top passband is obtained through subtraction effect between the two anti-phase microwave passbands generated by SBS and FWM, respectively. By adjusting the polarization states of the pump light and the optical signal injected into the SOA, the efficiency of FWM changes and the full width at half maxima bandwidth of the passband can be adjusted from 18 MHz to 52 MHz. During the bandwidth adjusting, the amplitude of the ripple within the passband is less than 0.5 dB.