Research On Performance Monitoring And Impairments Equalization Techniques In High-speed Coherent Optical Transmission Systems

Driven by emerging bandwidth-consuming mobile traffic services such as driverless,digital twins,and intelligent terminals,the global mobile traffic demand explosively grows,coherent optical transmission systems with high spectrum efficiency is on its evolution and extension ways to elastic optical networks and short-reach optical interconnects networks.Optical performance monitoring and impairments equalization techniques can monitor the key optical performance parameters and deal with systems impairments,and provide the technical support for dynamic perception ability,reliable transmission performance,and expansibility of the optical network,which is benefit for intelligent management,optimization,and up-gradation of optical networks.Optical performance monitoring schemes mainly monitor the critical parameters,including modulation format,optical signal-to-noise ratio(OSNR),chromatics dispersion and et al.Impairments equalization schemes compensate the system impairments such as in-phase and quadrature(IQ)skew,polarization crosstalk,intersymbol-interference and phase noise.However,the existing optical monitoring schemes use original signal data as the features of monitored parameters,introducing those issues of high complexity and limited generality,increasing the management cost and risk of optical networks.Meanwhile,the existing impairments equalization schemes simply deal with impairments to reduce its complexity and modulation format dependence,introducing the issues of limited IQ skew tolerance and nonlinearity tolerance as well as dynamic frequency offset tolerance.Those issues would degrade optical networks’ transmission performance and expansibility.To address those issues effectively,the research contents in this dissertation have been carried out around the theme of low complexity and strong impairments tolerance optical performance monitoring and impairments equalization.Specifically,the research contents in this dissertation consist of low complexity joint optical performance monitoring scheme,strong impairments tolerance and modulation-transparent carrier recovery scheme,and low complexity and strong impairment tolerance simplified channel equalization scheme,respectively.The specific research contents are summarized in detail as follows:(1)The relationship between signal statistics features in multi-dimension space and modulation format and optical signal-to-noise ratio(OSNR)is investigated,and the influence of system impairments on signal statistics features is also analyzed.Kurtosis and amplitude variance in Jones space and ccumulative distribution function in Stokes spaced are directly dependent on OSNR and modulation format.Joint and low complexity modulation format and OSNR monitoring schemes are proposed and demonstrated according to statistics features and artificial neural network.Both numerical and experimental results indicate that two monitoring schemes can identify m-QAM signals,m-PSK signals,and OSNR simultaneously.(2)The operation mechanism of phase noise and high order statistics is investigated,and kurtosis of IQ component of received signals is a concave function of phase noise.The technical routes using kurtosis and kurtosis error minimization as the cost function are proposed in this dissertation.Nonlinearity tolerant modulation transparent carrier recovery schemes are demonstrated by combining the cost function based on statistical features,mean-shifting clustering algorithm,and advanced algorithms frameworks.Compared with the existing modulation transparent carrier recovery scheme,the advantages of Gaussian noise tolerance,nonlinearity tolerance and linewidth tolerance,and dynamic frequency offset tolerance in our scheme are confirmed by numerical simulation and experiment.(3)The impairments coupling mechanism,spectrum aliasing,and the advantages and disadvantages of existing simplified channel equalization schemes are investigated in detail.Impairments coupling and spectrum aliasing would degrade the performance of existing simplified equalization schemes.Strong impairment tolerant simplified channel equalization schemes are proposed and demonstrated according to the theoretical analysis on the impairment coupling mechanism and the structure and functionality of the equalizer.Compared with the simplified channel equalization scheme,the advantages of clock speed requirement,transceiver IQ skew tolerance,and chromatic dispersion tolerance in our scheme are confirmed.Based on the theoretical investigation on signal statistical characteristics and impairment coupling mechanism,optical performance monitoring and impairment equalization schemes with low complexity and generality as well as strong impairment tolerance are proposed and demonstrated in this dissertation by combing advanced algorithms framework and signal statistic features.Moreover,The proposed DSP scheme can improve the dynamic perception ability and reliable transmission performance of coherent optical transmission systems and enhance the competitiveness of short-reach coherent optical interconnects networks.