Research On Key Technologies For High-speed Multi-modulation Coherent Optical Communication

Coherent optical communication system has the advantages of high sensitivity,large communication capacity and adopting a variety of modulation formats.In recent years,coherent optical communication is developing towards long distance,high speed,high performance and low cost.In communication networks,due to the different transmission characteristics of different transmission links,it is necessary to use appropriate modulation format for different characteristics in order to obtain better bit error rate performance.Therefore,coherent receiver is facing the demand of receiving signals modulated by multiple modulation formats.Digital signal processing is an important part of the coherent receiver,and is the key to improve the receiving sensitivity.In order to achieve multi-modulation reception,it is necessary to study a digital signal processing scheme for multi-modulated signals.This paper focuses on the research of multi-modulation digital signal processing algorithms.The main research contents of this paper include:(1)The research status of multi-modulation coherent optical communication system is investigated and analyzed,and the basic principle and theoretical bit error performance of various modulation formats are introduced.A digital signal processing scheme for multi-modulated signals with low complexity is proposed,which can realize flexible digital signal processing of signals with different modulation formats through external input signal control.The numerical simulation of transmitting,receiving and digital signal processing of BPSK,QPSK and 16QAM signals is completed.(2)The parallel scheme of multi-modulation digital signal processing is proposed.A 15GBaud QPSK&16QAM multi-modulation offline experiment is completed,and the parallel multi-modulation digital signal processing algorithm is verified by the offline experiment.Experimental results show that the receiving sensitivities of QPSK and 16QAM signals are-45.2dBm and-32.1dBm respectively at the 1 X 10’3 forward error correction(FEC)bit error rate threshold.(3)The Verilog HDL programming of QPSK&16QAM multi-modulation digital signal processing algorithm for field programmable gate array(FPGA)is implemented,and the resource consumption statistics are carried out.The result shows that the resource consumption of multi-modulation algorithm is almost equivalent to that of single-modulation algorithm.A multi-modulation real-time coherent optical communication experiment of 15GBaud QPSK and 16QAM signals based on FPGA is carried out.At the FEC error rate threshold of soft decision 1 × 10-3,the receiving sensitivity of QPSK signal is-44.8dBm,which is 0.4dBm higher than that of offline experiment,and the receiving sensitivity of 16QAM signal is-31 dBm,which is 1.1 dBm higher than that of offline experiment.