Tunable and configurable photonic microwave bandpass filter implemented in a radio-over-fiber link

A tunable and configurable photonic microwave bandpass filter with negative coefficient is proposed and demonstrated. Based on all-optical mixing in an intensity modulator and a phase modulator, the filter frequency response is related with the frequency of local RF signal (LO) signal and dc bias applied to the intensity modulator. The free spectral range of filter passband can be tuned conveniently by changing the LO frequency. When 8 GHz LO signal is applied, an equivalent bandpass filter with null-to-null bandwidth of 8.1 GHz is obtained for a 25 km radio-over-fiber link. Meanwhile, by varying the dc bias, the weights and the number of taps can be adjusted to tune the performance of filter. Therefore, a flexible transversal bandpass filter implemented in a radio-over-fiber link is realized along with the tunability and reconfiguration.