A Microwave Photonic Link With Quadrupled Capacity Based on Coherent Detection and Digital Phase Noise Cancellation

A microwave photonic link (MPL) with quadrupled capacity based on coherent detection and digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, a continuous-wave (CW) light wave is intensity modulated by four independent microwave vector signals with two having an identical center microwave frequency at a dual-parallel Mach-Zehnder modulator (DPMZM) consisting of two dual-drive MZMs (DEMZMs) with the sub-DEMEMs biased at the quadrature transmission point. Four intensity-modulated optical signals are generated and transmitted over a single-mode fiber (SMF) to a coherent receiver. To perform coherent detection, a second CW laser source as a local oscillator (LO) is also applied to the coherent receiver. To recover the microwave vector signals, a novel digital phase noise cancellation algorithm is developed and applied to eliminate the joint phase noise from the transmitter laser source and the LO laser source as well as the unstable offset frequency between the two laser sources. A theoretical analysis is performed to show the recovery of the microwave vector signals which is verified by an experiment. For four independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals with a symbol rate of 0.5 GSymbol/s, error-free transmission over a 9-km SMF is achieved when the received optical power at the coherent receiver is higher than −18 dBm with forward error correction (FEC).