Research On Parallel Receiving Technology In Digital Coherent Optical Communication Systems

With the increasing demand of the larger channel capacity,longer transmission distance and better receiver sensitivity,digital coherent optical communication technology became the key one in the next generation of the optical communication networks already.At the meantime,mostly the digital signal processing algorithms are off-line at the present stage,so the real-time coherent receiving and processing technology becomes one of the important research directions as the high-speed analog-to-digital converters and field programmable gate arrays appear.This paper introduces the basic principles of coherent optical communication,clarifies the digital processing algorithms in the coherent optical receiver,studies the parallelization of the carrier phase recovery algorithm,and provides the results and analysis of using it on the simulation platform and the experimental platform of QPSK coherent optical system.The main research contents include:(1)The basic principles of coherent optical receiving and the composition of digital coherent optical receiver and various algorithm modules are described.The typical algorithm modules and the working principle of each functional module are given.The coherent optical communication system simulation platform with QPSK modulation format is established.(2)The parallelization of off-line Viterbi-Viterbi carrier phase recovery algorithm is realized by Verilog language,and the simulation verification and resource analysis are carried out.The simulation results show that the parallel real-time carrier phase recovery algorithm and the traditional carrier phase recovery algorithm can obtain similar bit error rates under different signal-to-noise ratios and laser linewidths,in the 2.5Gbit/s QPSK coherent communication system.(3)The 2.5Gbit/s QPSK coherent communication experiment systems based on real-time sampling oscilloscope and FPGA circuit are established,and the parallelized carrier phase recovery is implemented in the Quartus ? environment for the coherent receiving data collected by the real-time sampling oscilloscope and FPGA.Experimental results show that when using oscilloscope to receive,the bit errors of the parallel real-time carrier phase recovery algorithm and the traditional carrier phase recovery algorithm are very close,and the deviation rate of only 1.32%.Using FPGA as the receiver,parallel carrier phase recovery algorithm can achieve zero error rate.