Photonic generation of flexible and adjustable microwave waveforms based on a dual-polarization Mach-Zehnder modulator.

Abstract

We have proposed a photonic waveform generation scheme based on a dual-polarization Mach-Zehnder modulator (DPol-MZM). In this scheme, a dual-frequency optical signal generated by RF optical carrier suppression modulation via a Mach-Zehnder modulator (MZM) is divided into two beams; one is further modulated by the RF signal via a DPol-MZM to generate ±1st and ±3rd-order sidebands, and the other is further modulated by the RF signal via a second MZM to generate ±2nd-order sidebands. After two modulated optical signals are detected by a balanced photodiode, the second, fourth, and sixth-order harmonics without cross-beating terms are generated in the differential photocurrent. Since the harmonic amplitudes can be controlled independently by the optical power of the two optical beams and the DC biases of the DPol-MZM, the waveforms can be tuned conveniently. Based on the simulation, frequency-doubled triangular, rectangular, and sawtooth waveforms with a full-duty cycle at a repetition rate of 20 GHz are successfully generated with their harmonic amplitude ratio in the electric spectrum close to the ideal amplitude ratio, and the symmetry of the triangular waveform from 20% to 80% is tuned.