Photonic Generation and Transmission of Triangular and Square Waveforms With a Large Repetition Rate Tunable Range

A photonic approach to generate and transmit triangular and square-shaped microwave waveforms with a large repetition rate tunable range is proposed and experimentally demonstrated using a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) integrated in the DP-QPSK modulator, which is driven by a microwave signal, is properly biased to serve as an optical carrier-suppressed single-sideband modulator to generate a first-order optical sideband and an opposite third-order optical sideband. The lower DP-MZM in the DP-QPSK modulator, driven by dc voltage, functions as an optical phase shifter to tune the phase of the optical carrier. By properly controlling the phase of the optical carrier and the amplitude of the optical sidebands, a triangular or a square microwave waveform can be generated. In addition, the influence of the fiber dispersion on the shape of the waveform can be overcome by properly adjusting the phase of the optical carrier, so the generated microwave waveforms can be transmitted over an optical fiber. An experiment is performed. Triangular waveforms with a repetition rate from 3 to 13 GHz and square waveforms with a repetition rate from 3 to 7 GHz are generated. The compensation of the dispersion-induced distortion is also evaluated in the experiment.