Simple Noise Mitigation Scheme for Coherent Optical DMT Signal Transmission System

Ke Li,Xiang Li,Yunlei Zhang,Zhong Liu,Lu Li,Tianye Huang,Liguo Liu,Qianqian Liu

doi:10.1109/access.2020.3023048

Abstract

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.

Highlights

With the fast development of design and fabrication techniques, the bandwidth of optoelectronic devices can reach more than 50 GHz, targeting for the baud rate up to 100 GBaud [1], [2]
The electrical spectrum of discrete multitone (DMT) signal after fine frequency offset compensation (FOC) based on external cavity laser (ECL) and distributed feedback (DFB) pairs are shown in Fig. 4(a) and (b), respectively
It can be seen that the spectral part of DMT information is significantly suppressed, which means the carrier phase information can be effectively extracted

Summary

Introduction

With the fast development of design and fabrication techniques, the bandwidth of optoelectronic devices can reach more than 50 GHz, targeting for the baud rate up to 100 GBaud [1], [2]. In the past few days, more attention may have been transferred to find the solutions for low-cost and small-size optical module in the fiber transmission network assuming these high-bandwidth optoelectronic devices are commercially available. Intensity modulation and direct detection (IMDD) technique is still popular even though coherent optical modules have been shown much better performances in all levels of fiber transmission networks [4]–[8]. This is mainly because optical module based on IMDD technique is much simpler requiring only 1 pair of input and output port, comparing with 4 pairs of input and output ports in coherent optical module. Based on high-bandwidth MachZehnder modulator (MZM), electrical driver and single-end photodetector (PD), several experimental demonstrations at data rate of 100 Gb/s and 200 Gb/s per wavelength have been reported [9]–[11]

Methods

Results

Conclusion