Simple Noise Mitigation Scheme for Coherent Optical DMT Signal Transmission System

We propose and experimentally demonstrate a noise mitigation scheme for coherent optical discrete multitone (DMT) signal transmission system. The proposed scheme can mitigate the laser phase noise and additive white Gaussian noise (AWGN) simultaneously when optical DMT signal is coherently detected. In the digital signal process (DSP), the laser phase noise is first estimated and compensated through moving average filter. The AWGN is then reduced by considering the time-domain real-valued or frequency-domain symmetrical conjugation characteristic of DMT signal. Finally, we conduct an experiment to transmit dual-polarization (DP-) DMT signal based on a low complexity coherent detection structure with only two pairs of input and output ports. The experimental results prove that the proposed scheme can enhance the signal-to-noise ratio (SNR) and effectively reduce the effect of laser phase noise even the laser linewidth is as large as 10 MHz. The DP-DMT signal is successfully transmitted over 1920-km standard single mode fiber (SSMF) in the experimental demonstration. The analysis of computational complexity also indicates that the proposed DSP scheme requires less number of complex multiplication operations and has larger laser phase noise tolerance than other DSP schemes.