Photonic generation of microwave frequency shift keying signals using a dual parallel structure

A novel photonic scheme to generate microwave frequency shift keying (FSK) signals with high frequency multiplication factors or flexible tuning carrier frequencies is proposed. A parallel structure is constructed in which the upper arm contains a dual parallel Mach–Zehnder modulator (DPMZM) while the lower one contains another DPMZM and a phase modulator (PM). From a theoretical analysis, the two DPMZMs can generate signals containing specific optical sidebands by properly biased, which serve as optical sidebands selector. The PM driven by a binary coding signal is employed to control the phase difference between the two arms. Simulation results show that when the output signal from the parallel structure is directly sent into a photodetector (PD), microwave FSK signals with frequency multiplication factors of 2/4 or 4/8 can be obtained. And when the output signal is mixed with a tunable optical source before being sent into the PD, microwave FSK signals with flexible tuning carrier frequencies can be obtained. The proposed scheme can generate two major categories of microwave FSK signal. Furthermore, polarization independence and good frequency tunability can be simultaneously achieved because no polarization multiplexing devices or frequency-dependent devices are applied. The impacts of phase deviation of phase shifter and non-ideal extinction radio of modulator are discussed.