A coherent microwave photonic link With digital phase noise cancellation

A coherent microwave photonic (MWP) link with digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, the optical carrier is phase modulated by a microwave signal via a polarization modulator (PolM). Then, the phase-modulated optical signal is sent to the coherent receiver over a 25-km single mode fiber (SMF). At the receiver, the phase-modulated optical signal is detected by a polarization- and phase-diversity coherent optical receiver, to generate two signals. The phase noise introduced by both the transmitter laser source and the local oscillator (LO) laser source is converted into an amplitude noise at the output of the coherent receiver. Through multiplying the two signals from the coherent receiver, the phase noise can be completely cancelled. Error-free transmission of a 2.5-Gbps 16 quadrature amplitude modulation (QAM) microwave signal over a 25-km SMF is experimentally demonstrated. The error vector magnitude (EVM) of the recovered signal after the DSP-based phase noise cancellation (PNC) module can reach 6.11%.