Microwave Photonic Hilbert Transformer Based on a Single Passband Microwave Photonic Filter for Simultaneous Channel Selection and Signal Processing

A microwave photonic Hilbert transformer (MPHT) with a single passband and wide frequency tunable range based on a single passband microwave photonic filter (MPF) is proposed and experimentally demonstrated. The MPF is implemented using a broadband light source and a Mach-Zehnder interferometer (MZI) incorporating a phase modulator in one arm and a phase-shifted chirped fiber Bragg grating in the other arm. The optical signal at the output of the MZI is sent to a dispersion compensating fiber, and then, detected at a photodetector. The overall operation corresponds to a single passband MPF with a π phase-shift at the center of the passband, which has the frequency response corresponding to a microwave Hilbert transformer. The central frequency of the MPHT can be continuously tuned by tuning the length difference between the two arms of the MZI using a tunable delay line. A theoretical analysis is performed, which is verified by simulations and an experiment. In the experiment, an MPHT with a bandwidth of 1.70 GHz and a continuously tunable frequency from 5 to 15 GHz is demonstrated. The proposed MPHT can find applications in multi-channel microwave communications systems, where simultaneous channel selection and Hilbert transformation are needed.