Coding to relax laser linewidth requirements for multichannel CPFSK coherent optical communications

A study of the multichannel coherent CPFSK communication system employing Reed-Solomon codes is reported. The crosstalk between adjacent channels, the impact of the laser phase noise, and selection of the optimum code rate are investigated. By applying a suitable coding scheme, the laser linewidth can be greatly relaxed, and the receiver sensitivity will be remarkably improved. A 100 Mbit/s system is used to verify the coding benefit. The results show that the impact of the laser linewidth can be largely alleviated by applying a (255, 223) Reed-Solomon code. When the linewidth is fixed (ΔνT=2%), this code can improve the receiver sensitivity by more than 15 dB.