Multi-passband Microwave Photonic Filter with Flexible Passband Selection Based on a Second-order Solc-Sagnac Interferometer

The multi-passband microwave photonic filter (MPF) with flexible passband selection based on a second-order Solc-Sagnac interferometer and dispersive medium is proposed and experimentally demonstrated. The second-order Solc-Sagnac interferometer is used as the spectrum slicer of the MPF, and by adjusting polarization controllers (PCs) inside the interferometer, the passband can be flexibly selected. Two output port of the optical coupler (OC) are connected with two sections of polarization maintaining optical fiber (PMF) and two PCs to form the second-order Solc-Sagnac interferometer. PMF with different length results in different FSR of the interferometer pattern of Sagnac interferometer and thus different frequency of the MPF's passband. By adjusting PCs in the second-order Solc-Sagnac interferometer, the visibility of the corresponding interference patterns can be changed, and as a result the passband of the MPF can be selected. In our experiment, by carefully adjusting the PCs in the Sagnac loop, multi-passband MPF with three selectable passbands has been implemented, whose passbands are located at the frequency of 0.219 GHz, 0.451 GHz, and 0.651 GHz, respectively when the length of two PMFs are 1 m and 2 m. In addition, we can also obtain MPF with flexible switching between single passband, double passbands and three passbands, respectively. And by designing the length of the PMFs in the second-order Solc-Sagnac interferometer, passbands at higher frequency can be realized, e.g. in our experiment, by using PMFs with the length of 2 m and 4 m, MPF with switchable passbands at 0.435 GHz, 0.877 GHz, 1.318 GHz has been realized, and the suppression ratio of the MPF is more than 25 dB.