【作者】 蒋林；

【导师】 闫连山；

【作者基本信息】 西南交通大学 ， 信息与通信工程， 2020， 博士

【摘要】 近年来,随着人工智能、互联网+、大数据、云计算等多种信息技术的迅猛发展,以及全球宽带用户数量不断增多和智能终端种类的日益繁多,共同造成了网络数据流量呈现爆发增长趋势。以至于光纤通信系统需要不断扩容和升级来满足日益增长的数据流量需求。目前光纤通信系统主要从偏振维度、波长维度、空间维度、时间维度、调制格式维度等五个物理维度出发,探索单个维度以及多个维度联合提升光纤传输容量,即目前研究最为广泛的多维光纤通信系统。多维光纤通信系统的信号包含多个维度的信息,传统直接检测技术仅能探测光信号的强度信息无法适用于多维光纤通信系统。与直接检测技术相比,相干检测技术可完整获取信号的强度、相位、偏振、波长等相关信息,从而使各种维度信息能够被完整解调出来。然后通过接收端的数字信号处理模块对系统参数及性能进行监测、传输链路损伤进行均衡与补偿。在多维光纤通信系统的发射端被要求能够根据不同的链路条件和服务质量需求,动态改变调制格式、符号率、前向纠错编码等,以至于在接收端被期望在无任何先验信息的情况下自适应的获取调制格式信息。此外未来多维光纤通信系统的传输链路可能会根据整个网络需求灵活的动态的配置以至于传输链路的长度出现变化,以及由于传输链路中光纤老化、制造工艺与光纤类型不一致、链路节点功率波动等造成链路相关参量出现变化而致使损伤补偿不精准造成性能严重下降。因此精准的监测链路相关参数并补偿相应损伤在多维光纤通信系统中将至关重要。本文围绕多维光纤通信系统信号性能监测与均衡技术,主要开展了三个方面的研究:光调制格式监测、色散监测与均衡以及非线性损伤监测与均衡。具体相关工作描述如下:1、针对多维光纤通信系统发射端根据链路需求自主改变调制格式信息的情况,提出了三种光调制格式监测方案自适应的获取调制格式信息以优化信号解调。利用快速密度聚类算法监测调制格式在斯托克斯平面中簇点个数,实现了多种主流调制格式PDM-BPSK/-QPSK/-8PSK/-8QAM/-16PSK/-16QAM的高精度监控。实验结果表明,对所有调制格式都可在7%FEC阈值下实现95%的识别率,并且相对于传统的OPTICS和DBSCAN算法具有更低的复杂度和更高的识别精度。利用调制格式之间的强度波形轮廓不相同的特征通过傅里叶级数拟合辅助,在仿真和实验系统中,实现了多种高阶调制格式信号PDM-QPSK/-8QAM/-16QAM/-32QAM/-64QAM的识别并且监测精度相对较高(在7%FEC阈值下实现100%的识别率)。通过考虑强度噪声特性,进一步提升了调制格式的监测精度(在20%FEC阈值下实现100%的识别率),并验证了该方案对非线性具有很高的容忍性。(第3章)2、针对多维光纤通信系统传输链路跨段之间色散因子不一致、链路长度动态变化等因素造成链路累积色散变化的情况,提出了快速的自适应的两级色散监测与均衡算法。该算法第一级为粗估计操作,通过采用信号功率自相关方程确定粗估计色散区间;第二级精细估计操作根据该色散区间使用修改的恒常模方程获取精准的链路累积色散值,并对链路色散效应进行均衡。仿真和实验结果表明,在40/112Gbit/s PDM-QPSK和80/224Gbit/s PDM-16QAM系统中该算法可实现监测误差小于40ps/nm的高精度色散监测。并且可容忍很大范围的偏振模色散影响,在偏振模色散小于10ps范围内性能都保持不变。与传统的MCMA算法相比较,在色散监测精度相同的情况下时间复杂度仅为7%。(第4章)3、针对多维光纤传输系统传输链路跨段之间非线性因子不一致、节点功率波动等因素造成非线性补偿不精准的情况,提出了两种非线性损伤监测与均衡算法。一种是基于强度噪声方差的非线性参数监测与均衡算法,在40/112Gbit/s PDM-QPSK和224Gbit/s PDM-16QAM的仿真与实验系统中验证了算法的有效性和可行性。结果表明,该算法与基于相位噪声方差的方案相比,不需要重复使用频率偏移补偿算法以及载波相位恢复算法,因此可大幅度节约计算资源并具有更低的复杂度。相比于只补偿色散的情况发射功率可提升～2d B;另一种是基于Godard’s error的非线性多参量联合监测与均衡方案,在国际上首次实现了接收端功率、非线性因子、以及非线性补偿参数等多个参量的联合监测与均衡。并在传输距离为1040km的256Gbit/s PDM-16QAM的实验系统中验证了多参量联合监测方案的性能。(第5章)4、针对多维光纤传输系统相位共轭传输链路中相位共轭器需要严格放置在中间点进而严重影响其实用性的情况,提出基于KNN算法辅助的非线性损伤均衡方案,分别在两种光纤传输链路中进行仿真验证。在传输距离为800km的112Gbit/s 16QAM的色散管理相位共轭传输链路中,可使相位共轭器偏离中间点位置40km而性能不下降,相比于传统的对称传输系统,可提升相位共轭器在系统中～10%的灵活度;在传输距离为1200km的112Gbit/s 16QAM基于色散位移光纤的相位共轭传输链路中,可使相位共轭器可偏离中间点位置100km而不损失性能。相比于传统的对称传输系统,可提升相位共轭器在系统中～15.6%的灵活度。(第5章)综上所述,针对多维光纤通信系统发射端根据链路需求自主改变调制格式而接收端无法获取调制格式信息的情况,以及传输链路光纤老化、制造工艺与光纤类型不一致、链路节点功率波动等造成链路相关参量出现变化而致使损伤补偿不精准造成性能严重下降。本文围绕多维光纤通信系统信号性能监测与均衡技术,实现了光调制格式监测、色散监测与均衡以及非线性损伤监测与均衡。对提升光纤传输系统的智能化和实用化具有一定的参考意义。更多还原

【Abstract】 In recent years,with the rapid development of multiple information technologies（such as artificial intelligence,internet plus,big data,and cloud computing）,as well as the growing number of global broadband users and the increasing variety of intelligent terminals,the Internet data traffic presents an explosive growth trend.Thus,optical fiber communication system needs to be continuously expanded and upgraded for meeting the growing demand of data traffic.At present,the optical fiber communication system explores to utilize five fundamental physical dimensions（polarization,wavelength,space,time,modulation format）to individually or jointly improve the transmission capacity.The case is named as multi-dimensional optical fiber communication system which has been widely concerned by researchers and engineers.It is well known that the traditional direct detection technique can only detect the intensity information of optical signal,so it may not be suitable for multi-dimensional optical fiber communication system which may have multi-dimensional information（i.e.polarization,phase,intensity,et al.）.Fortunately,the other technique,coherent detection technique,which can be able to detect the polarization information,phase information,intensity information and wavelength information of transmission signals,would be considered to be used in the multi-dimensional optical fiber communication system to achieve signal detection.Subsquently,the transmission impairments can be equalized and the system performance can be monitored in the digital signal processing module.To meet the diversity of future network services,the transmitter of multi-dimensional optical fiber communication system is required to be able to change modulation format（MF）types,symbol rates,forward error correction（FEC）coding according to different link conditions and service quality requirements,so that the receiver would be expected to acquire the MF information of unknown signal adaptively without any prior information.In addition,the transmission link of multi-dimensional optical fiber communication system may be flexibly and dynamically configured according to network demand which would change transmission path.Meanwhile,due to fiber aging,different types and manufacturing process of fiber,and the fluctuation of the node power would cause inaccurate damage compensation and serious performance degradation.Therefore,it is crucial to accurately monitor the link parameters and compensate the related link damages.The thesis focuses on the signal performance monitoring and equalization which includes optical MF monitoring,chromatic dispersion（CD）monitoring and equalization,and nonlinearity impairments monitoring and equalization.First,there are three optical MF monitoring schemes which have been proposed and demonstrated in a series of numerical simulations and experiments for the case that the transmitter of multi-dimensional optical fiber communication system can independently change MF information according to the link requirements.The case one uses the clustering by fast search and find of density peaks algorithm to monitor the number of clusters in the two-dimensional Stokes plane for identifying various mainstream modulation formats（i.e.,PDM-BPSK/-QPSK/-8PSK/-16PSK/-8QAM/-16QAM）.The experimental results show that 95%identification accuracy can be achieved under 7%FEC limit(bit error ratio（BER）=3.8?10^–3)corresponding to the lowest required OSNR values for all modulation formats.Meanwhile,compared with traditional OPTICS and DBSCAN schemes,the proposed scheme can have higher recognition accuracy and lower complexity.Subsquently,the case two is a modulation format monitoring scheme based on intensity waveform profile feature which uses Fourier series fitting to identify PDM-QPSK/-8QAM/-16QAM/-32QAM/-64QAM.The simulation and experiment results show that the lowest required OSNR values to achieve 100%recognition rate for all modulation formats signals are much lower than the corresponding 7%FEC limit.Finally,the case three is that a modulation format monitoring scheme based on intensity fluctuation feature.Compared to the case two,the proposed scheme can also identify the same modulation format signals,while to achieve 100%recognition rate for all modulation formats can be under much lower OSNR conditions（the lowest required OSNR values are much lower than the corresponding 20%FEC limit）.Meanwhile,the tolerance to fiber nonlinear effect is detailed analyzed in this thesis.（Chapter 3）Second,for the case of the accumulate CD variation caused by different fiber types,and the dynamic change of transmission link length,a two-stage fast and adaptive CD monitoring and equalization scheme is proposed.The first stage of the proposed scheme is the coarse CD monitoring operation,which uses the signal power auto-correlation function to obtain the the approximate CD range.Then,based on the range obtained in the first stage,the second stage of the proposed scheme uses the modified constant-mode algorithm to monitor the accurate CD value.Subsequently,the obtained CD value is applied to compensate CD of transmission link.The effectiveness has been verified via numerical simulation and experiment in 40/112Gbit/s PDM-QPSK and 112/224Gbit/s PDM-16QAM systems.The results show that the scheme can achieve high-precision monitoring results（monitoring error less than 40ps/nm）,and has low time complexity（only 7%of the traditional MCMA scheme under the same monitoring accuracy）.Meanwhile,it can tolerate the influence of PMD under 10ps range.（Chapter 4）Thrid,there are two kinds of nonlinear parameter monitoring and equalization schemes for the inaccurate nonlinearity compensation caused by different fiber types and the fluctuation of node powers.The one is that nonlinear parameter monitoring and equalization based on the variance of intensity noise.The effectiveness and feasibility are verified via numerical simulation and experiment in 40/112Gbit/s PDM-QPSK and224Gbit/s PDM-16QAM transmission systems.The results show that our scheme does not require reusing frequency offset compensation and carrier phase recovery in monitoring process which would save a lot of computing resources under the same monitoring results compared with the previous scheme.Meanwhile,compared with only CD compensation,the lauching power can be increased by～2d B.In addition,the other scheme is nonlinear multi-parameter joint monitoring and equalization scheme based on Goddard’s error,which can jointly monitor and equalizate received power,nonlinearity factor and nonlinearity compensation parameter for the first time.Meanwhile,the feasibility is demonstarted in256Gbit/s PDM-16QAM experimental system with 1040km single mode fiber.（Chapter 5）Fourth,for the case that the optical phase conjugation（OPC）transmission link needs to place the phase conjugator in the middle point would seriously affect its practicability,an effective nonlinear impairment equalization scheme assisted k-nearest neighbor（KNN）is proposed to improve the performance of OPC by mitigating non-Gaussian impairments caused by nonlinear phase noise.The proposed scheme is demonstrated in two kinds of optical fiber transmission links.The one is 112Gbit/s 16QAM dispersion management fiber transmission link with 800km SMF.The simulation results show that the phase conjugator can offset about 40km relative to the middle point of transmission link.Compared with traditional OPC system,the flexibility of phase conjugator can be improved about 10%.Then,the other one is the 112Gbit/s 16QAM fiber transmission link with 1200km dispersion shifted optical fiber（DSF）.The simulation results show that the flexibility of phase conjugator can be improved about 15.6%（the phase conjugator can offset about100km relative to the middle point of transmission link）.（Chapter 5）In conlusion,for MF information changing in the transmitter according to the link requirements,this thesis proposes three optical MF monitoring schemes to adaptively monitor modulation format information for optimized demodulation.When fiber aging,different fiber types,the fluctuation of node powers cause accumulate CD variation and the inaccurate nonlinearity compensation,theis thesis propose some CD and nonlinearity parameters monitoring and equalization to monitor the accumulate CD,received power,nonlinearity factor and nonlinearity compensation parameter.Meanwhile,the effectiveness and feasibility of these schemes are demonstrated in numerical simulation and experiments.We believe that these effective schemes have certain reference significance for improving the intelligence and practicality of optical fiber transmission network.更多还原