直接检测的光正交频分复用信号光纤传输系统实验研究

研制了直接检测的光正交频分复用(OOFDM)光纤传输实验系统.实验中产生了2 Gbit/s的正交相移键控(QPSK)、正交频分复用(OFDM)光信号,并成功地在标准单模光纤中传输了200 km.测量得到在误码率为10-6时,单模光纤传输200 km后的功率代价小于2 dB.比较了光纤传输前后OFDM信号的波形、频谱以及星座图,发现光正交频分复用信号能很好地抵抗光纤中的色散效应.     

基于IQ/CD的单光子载波矢量信号传输系统设计

提出并验证了一种使用单光子载波、基于 IQ 调制和相干检测的新方法来传输两个矢量信号,单光子载波上的同一个偏振态光携带 IQ 调制信号,具有正交偏振状态的光载波直接通过光波调制光波传输,两个正交极化波的光发送到相干检测器中解调。仿真实验了在25 km 单模光纤两个 QPSK 信号以数据率为1 Gbps 传输时的传输性能。     

卷积码在光正交频分复用系统中的应用

将卷积码成功地应用到直接检测的光正交频分复用(OFDM)光纤传输实验系统。实验中,产生了2 Gb/s的QPSK OFDM编码光信号,并成功地在标准单模光纤中传输了200 km,和没有采用卷积码的相比,系统的误码性能获得明显提高。在误码率10-3时,可节省1 dBm左右的光功率。实验结果表明,卷积码可应用到OFDM系统。     

40/100Gb/s偏振复用相干检测光模块的技术分析

利用偏振复用四相相移键控(PM-QPSK)调制技术和相干检测技术,实现40/100 Gb/s光模块的长距离传输。基于相干检测的偏振复用四相相移键控调制格式是40/100 Gb/s长距离传输的主要研究方向,与直接检测系统相比,相干检测具有更高的频谱效率。现有的相干检测是基于高速模数转换器(ADC)的快速发展,ADC对混频后的基带信号采样,通过数字信号处理(DSP)芯片数字均衡的方式完成相干接收。数字信号处理芯片数字均衡的方式可以实现定时恢复、信号恢复、偏振和偏振模色散(PMD)跟踪,以及色散补偿。     

基于偏分复用技术的数字RoF系统研究

为有效缓解D-RoF系统高数字比特速率的不利影响,本文研究了偏振复用的D-RoF系 统,能有效 提高系统单波长的传输容量。分别在传统Stokes矢量检测和简化Stokes矢量检测下,采用一 路偏振态向量 追踪(OTV)与两路偏振态向量追踪(TTV)的DSP算法能够有效实现偏振解复用。仿真结果表明 ,两路偏振 态向量追踪方法能有效降低正交偏振复用D-RoF系统的功率预算,达到系统最终误码率时, TTV算法需要 的光功率要比OTV算法需要的光功率少2dBm。同时,可用TTV方法实现两路信号最小偏振复 用度为76° 的非正交偏振解复用,丰富了偏振复用的维度。该偏振复用D-RoF系统对其在未来5G无线传 输和有线数字电视传输具有重要意义。     

相干光检测系统中的DSP技术研究

相干光检测具有高灵敏度、高谱效率的优点,数字信号处理(DSP)技术能补偿任何形式的光纤传输损伤并实现信号光和本振光的载波同步,这两种技术的结合是下一代光纤系统发展的一个重要方向.主要介绍相干光通信系统中一些常见的DSP算法,并分析了各算法的优缺点.     

基于少模光纤的3×34 Gb/s PDM-QPSK信号模分复用实验

为了成倍地提高通信系统的传输容量,采用10 km少模光纤构建3×3模分复用实验平台,模式的转换及复用通过模式选择性光子灯笼实现,以相位调制-相干接收方式完成光信号的调制与检测,最终实现3×34 Gb/s偏振复用—正交相移键控(PDM-QPSK)信号的有效传输.研究结果表明:如果保持LP01、LP11和LP21的接收功率...     

基于偏振复用的单边带光生毫米波传输系统的研究北大核心CSCD

光子辅助的毫米波通信因其超带宽优势在下一代宽带无线接入网中有着广泛的应用前景,本文基于单个激光源和一个双极化马赫-曾德尔调制器(dual-polarization Mach-Zehnder modulator,DP-MZM)的光路结构产生了频率稳定的偏振复用毫米波信号,联合VPI与MATLAB仿真环境对单边带(single sideband,SSB)偏振复用四相相移键控(polarization-division-multiplexing,PDM)quadrature phase shift keying,QPSK、16阶正交幅度调制(16-ary quadrature amplitude modulation,16QAM)和32阶正交幅度调制(32-ary quadrature amplitude modulation,32QAM)信号分别实现了70 km、65 km与50 km的有效传输,并结合概率整形(probability shaping,PS)技术在28 GHz波段上,以相同净比特传输速率对比分析了均匀16QAM与PS-16QAM,均匀32QAM与PS-32QAM的SSB矢量毫米波(millimeter wave,MMW)信号在光纤传输条件下的误码率(bit error rate,BER)性能。仿真结果表明:在相同净比特速率,以硬判决阈值3.8×10^(-3)为判断条件,在普通单模光纤(single-mode fiber,SMF)传输系统中,PS-16QAM/32QAM信号光功率约有0.3 dBm的提升,非线性光纤(nonlinear fiber NLF)传输系统中,PS-16QAM信号光功率约有0.8 dBm的提升,PS-32QAM信号光功率约有0.5 dBm的提升,结果表明:经过PS后的MMW信号光纤传输性能有明显改善。     

量子密钥分配系统中非线性偏振耦合的研究

受传输光纤非线性偏振影响,量子密钥分配系统本振光与信号光耦合率下降,使形成偏振复用信号的抖动增强,系统的稳定性和安全性下降.为了提高量子光学中偏振编码技术的性能,经过理论分析和数值模拟,给出可操作性的实验方案,解决了光纤非线性偏振耦合导致的偏振抖动问题.结果表明,在同等条件下,以分光检测结果反馈控制本振光和信号光的非线性偏振耦合率,可增强偏振复用信号的稳定性,将系统传输容量提高61%.该结果有利于偏振编码技术在量子密钥分配系统的实际应用.     

PMD和PDL同时存在下偏振复用系统的ICA解复用

针对同时受到偏振模色散（PMD）和偏振相关损耗（PDL）作用的偏振复用系统,在系统接收端采用相干接收方式,利用基于负熵最大化的不动点复数ICA算法（T-CMN算法）对接收到的偏振复用信号进行解复用。仿真结果表明：ICA解复用后的偏振信号的传输质量明显改善,在系统中光信噪比大于20.86 dB时均能保持误码率小于10?9,符合通信系统的传输质量要求。     

Linear Fiber Impairments Mitigation of 40-Gbit/s Polarization-Multiplexed QPSK by Digital Processing in a Coherent Receiver

To provide higher capacity networks, 40-Gb/s transmission systems are under active development and their cost is on the way to be competitive with the one of 410 Gb/s. However, their lower tolerance to linear and nonlinear fiber impairments remains a major drawback for field deployment. To address the issue of linear impairments, coherent detection of multilevel formats with polarization division multiplexing appears as a promising solution by reducing the symbol rate to 10 Gbaud. Indeed, such coherent based systems have already demonstrated an improved tolerance to optical noise and an interesting capability to compensate for large amount of chromatic dispersion. In this paper, the tolerances to narrow optical filtering, chromatic dispersion, and polarization mode dispersion are investigated with coherent detection of 10-Gbaud quadrature phase shift keying (QPSK) with and without polarization division multiplexing. Moreover, the efficient mitigation of these linear impairments by digital processing in a coherent receiver is demonstrated in an ultralong haul transmission (4080 km) of 40-Gb/s QPSK polarization multiplexed data.     

光接入网络中的数字信号处理技术

采用先进的数字信号处理(DSP)技术,在发射机和接收机分别引入预处理和后处理,以提高光接入网络的频谱效率并延长传输距离。研究了一种基于光超奈奎斯特(Super-Nyquist)滤波的类9状态正交振幅调制(9QAM)信号多模均衡(MMEQ)后端DSP算法,使用这种方案,能够有效提高频谱效率,实现了频谱效率高达4 bps/Hz的正交移相键控(QPSK)信号传输;还研究了一种基于数字SuperNyquist信号前端预处理的方案,此方案的优点是不需要光预滤波即可达到相同的频谱效率。使用一个采用直接调制激光器(DML)、直接探测和数字均衡技术的高速无载波幅度相位-64状态正交振幅调制(CAP-64QAM)系统,在20 km标准单模光纤(SSMF)上实现了创纪录的60 Gbit/s CAP-64QAM信号传输;使用相干探测,实现了速率高达100 Gbit/s的64状态正交振幅调制-正交频分复用(16QAM-OFDM)实时传输系统,解决了实时OFDM信号处理中的关键问题。     

Transmission Performance Comparison of Direction Detection‐Based 100‐Gb/s Modulation Formats for Metro Area Optical Networks

Transmission performances of direct detection‐based 100‐Gb/s modulation formats are investigated and compared for metro area optical networks. The effects of optical signal‐to‐noise ratio sensitivity, chromatic dispersion, cross‐channel nonlinearity, and transmission distance on the performance of differential 8‐ary phase‐shift keying (D8PSK), differential phase‐shift keying plus three‐level amplitude‐shift keying (DPSK+3ASK), and dual‐carrier differential quaternary phase‐shift keying (DC‐DQPSK) are evaluated. The performance of coherent dual‐polarization quadrature phase‐shift keying (DP‐QPSK) with block phase estimation and coherent DP‐QPSK with digital differential detection are also presented for reference. According to our analysis, all three direct detection modulation formats could transmit a 100‐Gb/s signal over several hundred kilometers of a single‐mode fiber link. The results also show that DC‐DQPSK outperforms D8PSK and DPSK+3ASK, and the performance of DC‐DQPSK is comparable to that of coherent DP‐QPSK with digital differential detection. The maximum transmission distance of DC‐DQPSK is over 1,000 km, which is enough distance for metro applications.     

Electronic Dispersion Compensation

The performance of different electronic equalization and processing schemes for 40- and 10-Gb/s optical transmission over single-mode fiber (SMF) are discussed, from the point of their ability to compensate chromatic dispersion (CD) and polarization mode dispersion (PMD). In addition, the impact of fiber nonlinearity and modulation format on equalization is also investigated. The main objective of this paper is to present an overview and a comparison of the performances rather than a detailed explanation of the principles of the different equalization schemes. The equalizers which will be covered are analog equalizer (feedforward and decision feedback type), maximum likelihood sequence estimator (MLSE), electronic precompensation, coherent/intradyne detection with digital signal processing (DSP) equalization, DSP-based optical orthogonal frequency division multiplexing (OFDM), and turbo equalization.     

一种改进的光偏分复用16-QAM系统盲解复用算法的研究

在高速光纤偏分复用(PDM)16进制正交幅度调制(QAM)相干光通信系统中,偏分解复用算法是分离偏振信息和进行信号补偿的关键技术。针对传统盲解复用的恒模算法(CMA)易于陷入奇异性和独立成分分析(ICA)算法收敛性能一般的问题,本文提出了一种改进型ICA(MICA)算法。算法基于给出的一种全新收敛测量方法,通过计算补偿后信号点与理想星座点的距离,自适应的改变学习速率,达到了更好的误码率(BER)性能。在20Gbaud/s的PDM-16-QAW系统上的仿真结果表明,与传统CMA法相比,本文提出的算法完全消除了奇异性问题,与是否存在偏振相关损耗(PDL)无关。此外,算法还能在前向纠错编码门限上提供高达1dB的光信噪比(OS-NR)提升,并在收敛速率和精确度上都得到了提升。     

Compensating for Nonlinear Effects in Coherent Detection Optical Transmission Systems

Fiber nonlinearity is one of the most important limiters of capacity in coherent optical communications. In this paper, we review two nonlinear compensation methods: digital backward propagation (BP) and nonlinear electrical equalizer (NLEE) based on the time-domain Volterra series. These compensation algorithms are implemented in a single-channel 50 Gb/s coherent optical single-carrier frequency-division multiplexed (CO-SCFDM) system transmitting over 10 × 80 km of standard single-mode fiber (SSMF).     

PDM-16QAM系统中几种相位估计算法的性能与复杂度比较以及改进

在偏分复用的高速相干光通信系统中,16进制正交幅度调制(PDM-16QAM)是最有前景的调制格式,且载波相位估计是补偿发射端与接收端激光器对信号造成的相位失真的重要技术。该领域最经常使用的算法为QPSK分区算法与盲相位搜索算法,但他们都有自己的缺点,如估计效果不够好,适用范围不够广,或者计算复杂度过高。本论文实验搭建了224Gb/s PDM-16QAM波分复用传输640km相干检测系统平台,首先利用几种基于前述两种算法的相位估计方法对接收到的信号进行了数据处理,分别给出了误码率曲线图、误差向量幅度曲线图、计算复杂度分析表。然后基于性能最优与计算复杂度的平衡,提出了针对16QAM信号星座图中间圈的点的省略两级处理算法。将该改进的算法用于实验系统相位估计单元进行数据处理,结果表明,改进的算法P1,3/ML其误码率性能和误差向量幅度性能基本保持不变,但是计算复杂度降低为原来的1/2。