Photonic generation of phase-coded microwave signals based on dual parallel phase modulators

Photonic generation of phase-coded signals with a dual parallel construction using two phase modulators (PMs) is proposed and demonstrated. In the proposed scheme, the continuous-wave (CW) light wave emitted from a tunable laser (TL) is split into the two beams light wave with equal power via a 50 ∶ 50 optical power splitter (OPS), one beam passes the upper arm of the dual parallel construction, which includes a PM (PM1) modulated by an injecting radio frequency (RF) microwave signal, and the other beam passes the under arm of the dual parallel construction, which includes the other PM (PM2) modulated by a binary coding pulse sequence. The two beams of phase-modulated light waves combine and intervene at a 50 ∶ 50 optical power combiner (OPC), and the phase-coded microwave signals are generated by beating at a high-speed photodetector (PD). The key significance of the technique includes two parts: firstly, the interference is used to convert phase-modulated microwave signal to intensity-modulated microwave signal because the PD cannot detect the phase-modulated signal. Secondly, a phase-coded microwave waveform with a phase shift of π can be generated without using any optical or electrical filter. In addition, this structure is easy to be integrated into one chip. The generation of a binary phase-coded microwave waveform with a π phase difference at 10 and 20 GHz microwave signal respectively corresponding to 2 Gbit/s and 2.5 Gbit/s coding rates is successfully demonstrated.