Reconfigurable and tunable multi-tap bandpass microwave photonic filter based on a hybrid-gain-assisted multi-wavelength fiber ring laser

A reconfigurable and tunable multi-tap bandpass microwave photonic filter based on a hybrid-gain-assisted multi-wavelength fiber ring laser (HMFRL) is proposed and experimentally demonstrated. The HMFRL containing a hybrid gain medium and a high birefringence fiber loop mirror serves as the multiple taps generator for the microwave photonic filter. In order to realize a bandpass filter, the multiple taps are phase modulated, then the modulated signal is launched into a coil of dispersion compensating fiber to introduce different time delays for each tap. As a result, a bandpass response is obtained at the output of a high speeding photodetector. By adjusting the bias of the semiconductor optical amplifier from 344 to 450 mA, the number of multiple taps can be increased without optical signal-to-noise ratio degradation. Thus, a multi-tap bandpass microwave photonic filter with bandwidth reconfiguring from 449 to 274 MHz is achieved. In addition, by changing the length of polarization maintaining fiber in the high birefringence fiber loop mirror, the wavelength spacing of the multiple taps can be adjusted, making the bandpass microwave photonic filter's free spectral range tunable.