A Photonic-Assisted Method for Generating Duty Ratio Tunable Triangular and Square Microwave Signals

We report a simple photonic-assisted triangular and square microwave waveforms generator with tunable duty ratio by utilizing a dual-polarization Mach-Zehnder modulator (DPol-MZM). The RF signal provided by the microwave source is split into two paths to drive x-MZM and y-MZM, respectively. An electrical phase shifter (PS) and an attenuator are inserted into these two branches individually to control the phase and amplitude of the RF signals applied to the modulator. By properly adjusting the PS and the direct current biases of the modulator to satisfy specific amplitude and phase relationship between different harmonics, triangular and square microwave signals with varies duty ratios can be obtained. Our proposed scheme features advantages of unfixed modulation index, adjustable repetition rate, and tunable duty ratio. In addition, no extra 90 degrees electrical hybrid coupler and optical bandpass filter are needed in our system, which brings great convenience in realistic applications. The proposed scheme is theoretically analyzed and experimentally verified.