title: Flat-top bandpass microwave photonic filter with tunable bandwidth and center frequency based on a Fabry-Pérot semiconductor optical amplifier.
abstract: We propose a flat-top bandpass microwave photonic filter (MPF) with flexible tunability of the bandwidth and center frequency based on optical nonlinearities in a Fabry-Pérot semiconductor optical amplifier (FP-SOA). Phase-inverted modulation induced by cross-gain modulation (XGM) and optical spectral broadening induced by self-phase modulation (SPM) are exploited to achieve flat-top and bandwidth tuning, respectively. Wideband and continuous tuning of the center frequency is achieved by altering the bias current of the FP-SOA. Experimental results demonstrate a flat-top single-passband MPF with its center frequency tunable from 6.0 to 18.3 GHz by adjusting the bias current from 54.05 to 107.85 mA. The 3-dB bandwidth of the passband when centered at 10.0 GHz is shown to be variable from 680 to 1.43 GHz, by increasing the injected optical power from -1 to +5  dBm. During the bandwidth tuning, the amplitude ripple within the passband is maintained at less than ±0.5  dB. Excellent main to secondary sidelobe ratio exceeding 45 dB is achieved when the MPF is centered at 18.3 GHz.
authors.forename: Fan
authors.initials: F
authors.lastname: Jiang
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yu
authors.forename: Tong
authors.initials: T
authors.lastname: Cao
authors.forename: Haitao
authors.initials: H
authors.lastname: Tang
authors.forename: Jianji
authors.initials: J
authors.lastname: Dong
authors.forename: Xinliang
authors.initials: X
authors.lastname: Zhang