Microwave photonic link to transmit four microwave vector signals on a single optical carrier based on coherent detection and digital signal processing

Abstract

A microwave photonic link to transmit four independent microwave vector signals modulated on a single optical carrier based on coherent detection and digital signal processing (DSP) is proposed and experimentally demonstrated. At the transmitter, a continuous-wave (CW) light wave is modulated by four independent microwave vector signals with an identical center microwave frequency at a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM), to generate four intensity-modulated optical signals, with two signals sharing one of the two orthogonal polarization states. After transmission over a single-mode fiber (SMF), the optical signals are applied to a polarization- and phase- diversity coherent receiver to which a light wave from a second laser source as a local oscillator (LO) is also applied. To eliminate the joint phase noise and the unstable offset frequency from the transmitter and the LO laser sources and to perform polarization demultiplexing, a digital noise cancellation algorithm and a polarization demultiplexing algorithm are developed. The proposed approach is evaluated experimentally. For four independent 16 quadrature amplitude modulation (16-QAM) microwave vector signals at 4 GHz 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 -21 dBm with forward error correction (FEC).