Modeling And Impairment Monitoring Of Polarization Mode Dispersion In Optical Fiber Communication Channels

The emergence of optical fiber communication has promoted important breakthroughs in the field of science,technology and society.Due to the advantages of large transmission capacity,low loss,and long relay distance,optical fiber communication constitutes the backbone of the global communication network and undertakes most of the Internet information traffic transmission work.It is also one of the core technologies in the information age.The continuous emergence of various new technologies such as video conferencing,artificial intelligence,fifthgeneration mobile communications,and autonomous driving puts forward more requirements on the information transmission rate and capacity.Fast transmission rate and large transmission capacity of information are the development direction of optical fiber communication in the future.Thanks to the wide application of polarization division multiplexing,space division multiplexing,higher-order modulation formats,coherent detection technology and digital signal processing,the channel capacity is greatly improved.Around 2010,the single-carrier channel rate of the commercial coherent optical communication system reached 100 Gb/s,and the coherent detection technology as well as digital signal processing technology also received much more attention.The PDM coherent optical communication system,which is based on coherent detection and digital signal processing modules,is the key to meet demand of ultra-high speed,ultra-large capacity and ultra-long distance in the future development.Therefore,the research of PDM coherent optical communication system are of great significance.There are various time-varying linear and nonlinear impairments in the optical fiber channel,which lead to the distortion of signal and increase the bit error rate at the signal receiver.The main research content of this dissertation focuses on linear impairment and polarization impairment of the signal in coherent optical systems.As one of the most important factors limiting signal transmission quality and distance,researchers have proposed different methods to model polarization mode dispersion and achieved great impairment equalization effects based on these methods.With the improvement of the transmission rate and the broadening of the channel bandwidth,the original modeling method can no longer accurately describe the polarization effect in the wideband channel.In the meantime,the instantaneous injury can lead to the deterioration of a large number of symbols since the injury is dynamic and time-varying in the high-speed optical fiber communication channel.Reliability is important.Therefore,impairment monitoring for high-speed fiber channels is of great significance to ensure the robustness and reliability for transmission of information.Focusing on the modeling of polarization channel and polarization impairment monitoring in broadband communication systems,we study the physical mechanism and mathematical model of impairment especially the polarization impairment in polarization division multiplexing systems deeply and propose a time-frequency domain evolution model.Then,the theoretical principles of channel impairment monitoring are researched,and the polarization-related impairments are accurately monitored.The main research are as follows:First of all,we expound the physical mechanism and mathematical model of various impairments in fiber channel and analyze the influence of these impairments on the signal.Then we introduce the main structure of the coherent optical communication system,including the realization principle of transmitter and receiver.It is pointed out that with the increase of system transmission rate,the narrow-band polarization channel model has been impossible to accurately reflect the polarization effect in the channel and the high-order polarization mode dispersion needs to be considered.In order to solve this problem,we innovatively propose a broadband polarization channel model for evolution in the time-frequency domain.There is no specific mathematical model to describe the high-order polarization mode dispersion in the channel,but the frequency domain autocorrelation function can reflect the correlation of the PMD at different frequency points.Therefore,we propose to use the frequency domain autocorrelation function to reveal the all-order statistics of the PMD model.At the same time,the time domain autocorrelation function is used to reveal the time evolution characteristics of the PMD.Simulation experiments shows that our model is consistent with the principles of modeling,and the evolution characteristics in the time-frequency domain are consistent with real optical fiber link,which is of great significance for the design of the compensation algorithm at the receiver.Then we investigate channel impairment monitoring based on the proposed wideband channel model.Firstly,we introduce the theoretical basis for impairment monitoring using the tap coefficients of the FIR filter at the receiver in detail.Subsequently,we verify the accuracy of frequency domain CMA in impairment monitoring by the means of simulation experiments and compare it with time domain CMA.The results shows that the effective monitoring range of our frequency domain CMA for firstorder PMD reaches 1.4T0,the range for RSOP is up to 1.6 Mrad/s,and for PDL can reach 5dB.The maximum error of impairment monitoring is less than 5%.Compared to algorithms in the time domain,the complexity is significantly reduced while maintaining the same accuracy.