Experimental Research On All-optical Signal Processing For QPSK Modulation Format

With the rapid development of Internet emerging services in recent years,communication traffic in the network exhibits explosive growth,establishing a super high-speed,long distance,large capacity optical communication network into research.The traditional optical network is a network system based on the electrical layer,which will perform "light-electric-light" conversion at the optical network node.With the rapid growth of traffic in the network,the "electronic bottleneck" will eventually restrict the optical communication system.High-speed transmission,the full-optical signal processing technology has become one of the current research hotspots because it can make full use of the huge bandwidth of the optical domain and reduce the processing time of the electro-optical conversion process.The QPSK modulation format has become one of the modulation formats commonly used in the optical communication system due to its superior transmission characteristics,and with its strong anti-interference and higher spectral utilization,and become the main modulation format in long distance light transmission network.The optical signal based on QPSK modulation format is widely used in a high-speed flexible optical transmission network,so the research of QPSK modulation format full-optical signal processing experimental is significant.The main research work and content of this thesis are as follows:Digital signal processing algorithm and its experimental research.Signal modulation and reception may cause signal IQ imbalance,affect subsequent signal judgment,IQ orthogonal algorithm should be used.In the experimental system of all-optical signal processing,the clock of receiver and transmitter is separated,the clock synchronization algorithm needs to be realized to solve the problem of signal transmission and reception clock.Due to the unstable environment and other factors,the center frequency shift of optical signal will occur during transmission,and the center frequency of the signal emitting terminal laser and the local oscillator laser cannot be guaranteed to be exactly the same,and since the laser will inevitably have line width,these conditions will initiate a signal to rotate in the constellation complex,thereby reducing the correctness of the signal decision.So it is necessary Implement the carrier recovery algorithm to solve the above problems.This thesis is designed to achieve the DSP algorithm for in-depth theoretical research,the IQ orthogonal algorithm,clock synchronization algorithm,carrier recovery algorithm,and decision decoding algorithm,and the simulation system are set up by the simulation system to verify DSP.By building the experimental platform of QPSK back-to-back transmission system,the performance of different signal modulation schemes on the experimental platform was analyzed using DSP algorithm.Finally,an integrated IQ modulator with better signal quality was selected to modulate optical signals,laying a foundation for the all-optical format conversion experiment.Experiment of all optical format conversion from QPSK to BPSK.QPSK optical signal is one of the high-order modulation formats commonly used in long distance WAN,and BPSK signal has become one of the modulation formats commonly used in short distance access networks because of its good anti-noise performance and easy reception.In network nodes,the use of all-optical signal processing technology to format the signal from high order to low order modulation format has become an important research hotspot.This paper first introduces the FWM effect and PSA process of format conversion,and deduces its principle theoretically.Secondly,all-optical format conversion schemes based on orthogonal decomposition principle and phase erasure principle is introduced.Respectively,the experimental system based on the two conversion schemes is built,and the accuracy of the experimental system is verified by spectrum diagram and constellation diagram.On this basis,the correct result of bit flow by the use of DSP algorithm verify the feasibility of transformation scheme.The experiment lays a foundation for further experimental research to realize more flexible high-speed all-optical signal processing.