Generation of Phase-Coded Microwave Signals Through Equivalent Phase Modulation

A novel approach to generate phase-coded microwave signals using a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The key component of the proposed scheme is a DP-QPSK modulator, in which, the upper dual parallel Mach-Zehnder modulator (DP-MZM) modulated by a coding signal is properly biased to implement equivalent phase modulation, while the lower DP-MZM modulated by an RF signal functions as an optical wavelength shifter. A phase-coded microwave signal is generated by beating the phase-modulated optical carrier and the wavelength-shifted optical sideband at a photodetector. The proposed approach has a compact structure and great reconfigurability. By applying different coding signals, binary or quaternary phase-coded signals can be generated. A proof-of-concept experiment is carried out. The generation of binary and quaternary phase-coded signals with a microwave carrier frequency at 8 and 13 GHz is demonstrated.