Photonic Generation of Precisely $\pi$ Phase-Coded Microwave Signal With Broadband Tunability

A novel photonic approach to generating a phase-coded microwave signal with a precise π phase shift is proposed and demonstrated. The approach is realized based on a quadrature phase shift keying (QPSK) modulator. In the QPSK modulator, one Mach-Zehnder modulator (MZM) is biased at its minimal transmission point to achieve carrier suppressed modulation, and the other paralleled MZM is biased to achieve binary-phase shift keying modulation. When the CSM signal and the BPSK signal are combined at the output port of the QPSK modulator, a phase-coded microwave signal with a precise π phase shift is generated. Both simulation and experiment are carried out to verify our scheme. The scheme exhibits flexible reconfigurability of encoding different bit pattern chips, large bandwidth of phase-encoding, and broadband frequency tunability. In the experiment, phase-coded microwave signals at 5 and 10 GHz with a precise π phase shift are successfully generated.