Widely Tunable Single-Passband Microwave Photonic Filter Based on DFB-SOA-Assisted Optical Carrier Recovery

A widely tunable single-passband microwave photonic filter (MPF) based on a distributed-feedback semiconductor optical amplifier (DFB-SOA) is proposed and experimentally demonstrated in this paper. The fundamental principle is to recover the suppressed optical carrier from a passband optical filter by the wavelength-selective amplification via a DFB-SOA. A microwave signal is then generated by beating the recovered optical carrier with the phase-modulated lower sideband, and thus, an MPF is achieved with the shape of the passband optical filter that is mapped from the optical domain to the electrical domain. By tuning the central wavelength of the passband optical filter, a single-passband MPF with a frequency tuning range from 5 to 35 GHz is obtained. The 3-dB bandwidth and the out-of-band suppression ratio are measured to be 4 GHz and 20 dB, respectively. In addition, the tunability of the MPF that is dependent on the driven current of the DFB-SOA is also experimentally investigated.