Passband-Switchable and Frequency-Tunable Dual-Passband Microwave Photonic Filter

A passband-switchable and frequency-tunable dual passband microwave photonic filter (MPF) implemented using a broadband optical source (BOS) in a delay-line configuration is proposed and experimentally demonstrated. In the proposed MPF, the BOS is sliced by a Mach-Zehnder interferometer (MZI), in which a phase modulator (PM) is incorporated in the upper arm. The phase-modulated light signal combined with an unmodulated light at the output of the MZI is sent through a dispersive delay line and detected at a photodetector (PD). The entire operation is equivalent to a microwave bandpass filter with its central frequency determined by the time delay difference between the two arms of the MZI. To implement a dual passband MPF, a second lower arm with a different arm length corresponding to a different time delay is added. The independent switchability of the passband is realized by controlling the polarization state of the light wave in each of the lower arms to be parallel or orthogonal with that of the upper arm. The independent frequency tunability is achieved by tuning the time delay of each of the lower arms. The proposed MPF is experimentally evaluated. A dual-passband MPF with independent passband switchability and independent frequency tunability is demonstrated. The results show that each of the two passbands can be switched on and off with an extinction ratio of about 20 dB. The passband frequency can also be continuously tuned with a tunable range from 1 to 18 GHz.