【作者】 胡辽林；

【导师】 刘增基；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2004， 博士

【摘要】 近几年来超大容量超长距离密集波分复用(WDM)技术发展十分迅猛，目前单个波长传输速率已达40Gb／s，单根光纤容量已超过10Tb／s。在如此高速率的光传输中，必然招致巨大的传输损伤，这些传输损伤有：噪声累积，主要是光放大器的放大自发辐射噪声(ASE)；色散，包括群速度色散(GVD)和偏振模色散(PMD)；非线性效应，包括自相位调制(SPM)、交叉相位调制(XPM)、受激拉曼散射(SRS)、受激布早渊散射(SBS)和四波混频(FWM)。为了克服这些传输损伤，必须解决若干关键技术：色散补偿、偏振模色散补偿、拉曼放大、纠错编码和调制格式等。其中新型调制格式是减轻传输损伤，提高频带利用率的一种重要手段。 WDM技术极大地提高了光纤的传输容量，随之带来了对电交换结点的压力和变革的动力，因此必须在交换方面引入光子技术，于是产生了WDM全光网。WDM光网络是在现有的传输网上加入光层，在光上进行分插复用(OADM)和交叉连接(OXC)。在WDM光网络中，还存在一种特殊的传输损伤，那就是串扰，特别是带内串扰(也称同频串扰)的影响较大。串扰是指在WDM光网络中，由于光器件隔离度的不理想，其它光通道的信号会泄漏到传输通道，形成串扰噪声，从而对传输性能造成影响。 本论文主要研究的是高速光传输中的新型调制格式和WDM光网络中的串扰，主要的研究内容及成果如下： 1．研究了适合10Gb／s系统的新型调制格式。这些调制格式包括光双二进制、光单边带和光四进制，这三种调制格式的信号的谱宽是二进制信号的一半。研究表明光四进制传输受噪声和激光器的边模等因素的影响较大，导致较大的代价；对10Gb／s系统，光双二进制和光单边带是比较理想的调制格式，在完全消光下其色散限制的中继传输距离是二进制(或双边带)的一倍：并且发现只有当消光比大于25dB(或20dB)时，光双二进制(或光单边带)相对于二进制(或双边带)的优越性才呈现出来。 2．研究了40Gb／s系统的若干关键技术。定性地分析了归零(RZ)码比非归零(NRZ)码的抗非线性能力强。对基于RZ的40Gb／s常规单模光纤传输系统进行了仿真，该系统的色散补偿分别采用前置补偿和后置补偿，结果发现在存在非线性情况下，其色散补偿采用后置补偿的传输性能明显优于采用前置补偿的传输性能。也对NRZ、RZ、载波抑制的RZ(CSRZ)和单边带RZ(SSB-RZ)四种调制格式在非零色散位移光纤(NZDSF)上单信道传输进行了仿真，结果表明：在色散完全补偿情况下，RZ、CSRZ和SSB-RZ抗非线性能力都比NRZ强，其中CSRZ最强；RZ、CSRZ和SSB-RZ三种格式抗EDFA噪声能力差不多，但都比NRZ强：并且CSRZ的谱宽适中。因此40Gb／s DWDM系统中，选择CSRZ作为调制格式是适‘宣的。3.针对五种基于空间光开关的OXC和两种具有组播通信能力的OXC，用最坏值 方法对其串扰进行了分析，推导出它们的功率输出方程，并对每种OXC的总 串扰随空}，nJ光开关和复用器/解复用器的串扰变化情况以及波长数和光纤数变 化情况进行了详细研究。通过研究发现，在五种基于空间光开关的OXC中， 一种基于分离的空间光开关和复用器/解复用器结构的OXC串扰性能最好;由 此得出OXC的串扰不仅与元件参量有关，也与其结构有关。虽然一般的OXC 中的串扰已有很多研究，但对具有组播通信能力的OXC的串扰研究在国内外 文献中还未见报道，又寸这两种具有纠播通信能力的OXC的研究发现，两种OXC 组播工作时串扰性能差不多，单播工作时在一定条件下基于MOSaD的OXC 优于基于SaD的OXC;在现有的技术条件下，即使光纤数入任2和波长数九介4， 两种OXC组播工作时的串扰也高达一17 dB。4.使用高斯模型和非高斯模型分别推导了串扰对WDM光网络传输性能的影响， 其中非高斯模型使用了格莱姆一查里级数，先求串扰噪声的特征函数，再求其 概率密度函数，最后得到误码率公式。并仿真了带内串扰和带间串扰对10Gb/s WDM光网络传输性能的影川句，得到了一些有用的结论:带内串扰对一传输性能 的影响比带间串扰要大得多;以10一9误码率为标准，无串扰时接收灵敏度为 一33.7dBlll，有带内串扰时接收灵敏度为一32.sdBm，功率代价为1.2dB;存在带 内串扰的情况下，消光比对误码率的影响比无串扰情况更为严重，这说明在 WDM光网络中，消光比的影响比对点到点光纤通信系统更严重，光网络对消 光比的要求更为严格;当带内串扰与信号的相对偏振角为90度(垂直)时，误 码率最小，相对偏振角为O度或180度(平行)时，误码率最大;对于10Gb/s 的信号和带间串扰，信号和串扰的中心频差至少要大于巧GHz。关键词:高速光纤通信传输损伤调制格式串扰更多还原

【Abstract】 Large-capacity and long-haul dense wavelength-division multiplexed (WDM) transmission technologies have been rapidly developed recently. Up to now, numerous WDM transmission experiments at 40Gb/s per wavelength have been reported, and have demonstrated the achievements of more than 10Tb/s capacity per fiber. Transmission at so high speed must be severely limited by transmission impairments. In high-speed optical fiber communication the impairments include accumulated ASE (Amplified Spontaneous Emission) noise from optical amplifiers, group-velocity dispersion (GVD), polarization mode dispersion (PMD) and fiber nonlinear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS) and four-wave mixing (FWM). In order to overcome these transmission impairments, several key enabling technologies such as GVD compensation, PMD compensation, distributed Raman amplification (DRA), forward error correction (FEC) and suitable modulation format, should be employed. Some modulation formats may overcome the transmission limitations and improve spectral efficiency.Today WDM systems being installed are mainly point-to-point systems where the switching and processing is made by electronics. The introduction of optical add/drop multiplexer (OADM) and optical cross-connect (OXC) is a natural evolution of WDM technology to include switching in the optical layer. Optical crosstalk imposes a major limit to the practical implementation of WDM optical networks. Two crosstalk mechanisms, interband and intraband crosstalk, caused by nonideal wavelength (de)multiplexer, space switch and optical filter. The intraband crosstalk, where the crosstalk elements fall within the signal wavelength carrier band, is much more deleterious to the network end-end transparency performance.This paper deals with modulation formats for high-speed optical transmission and crosstalk in WDM optical networks, and the main research work and results are listed as follows.1. The modulation formats suitable for 10Gb/s systems, which include optical duo-binary, optical single sideband (SSB) and optical quaternary, are studied. The bandwidth of the three kinds of modulated format signal is approximately one half that of conventional binary (or double sideband: DSB) signal. Simulation results show that optical quaternary transmission is more susceptible to noise and laser’s side mode, and results in large penalty. It is shown that transmission distance of theoptical duobinary (or SSB) signal due to chromatic dispersion limitation is about twice that of the conventional binary (or DSB) signal in the perfect extinction. It is discovered that the optical duobinary (or SSB) transmission has characteristic superior to that of the binary (DSB) transmission only if the extinction ratio is more than 25dB(or 20dB).2. Some key enabling technologies for 40Gb/s systems are studied. A 40Gb/s RZ-based standard single-mode fiber (SMF) transmission system is simulated which uses precompensationing dispersion or postcompensationing dispersion separately. It is shown that transmission performance which uses postcompensation is superior to that uses precompensation and it can be concluded that the postcompensation should be used for dispersion compensation in long-haul, high-capacity optical transmission in the case of the nonlinear effects. Four different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero(CSRZ) and single sideband return-to-zero (SSB-RZ), is introduced, and method of their modulated signal generation is described, and a comparison of their spectra and waveforms is made. 40Gb/s single channel transmission over nonzero dispersion-shifted fiber (NZDSF) is simulated for the four formats. It is shown that RZ. CSRZ or SSB-RZ format is more tolerant than NRZ in nonlinearities, and CSRZ tolerance to nonlinearities is the highest among the four formats. Compared to NRZ, CSRZ is 10.2dBm more tolerant in fiber input power. RZ, CSRZ and更多还原