Photonic Generation of Rectangular and Triangular Microwave Waveforms With Tunable Duty Cycle

We propose a microwave photonic scheme to generate rectangular and triangular waveforms by external modulation. Different from previous works, the duty circle of the generated waveforms in our scheme is freely tunable. The main structure is based on a Mach-Zehnder modulator and a tunable optical delay line. By power splitting and time-delay tuning on two polarization branches, triangular or rectangular waveforms can be obtained by the superposition of beating signals. Moreover, the RF modulation index in this work is unfixed, which increases the flexibility of the system. The proposed scheme is theoretically analyzed and experimentally verified. The triangular and rectangular waveforms at repetition rates of 4 and 5 GHz are successfully generated.