DWDM技术及其典型工程应用

DWDM是在一对或一根光纤中同时传输几十、成百个光信号，可以实现在一个系统中进行各种信速、多种业务同纤大容量传输，即：按“一纤N波”工作。WDM的优点是充分利用了光纤自身具有的巨大带宽资源，缺点在于光器件较多，使得系统的故障概率上升，对光纤非线性效应要求严格等。     

光纤中非线性效应对高密度波分复用光信号传输的影响

在利用单根光纤不同波长传输不同信号的密集型波分复用系统中,由于在很小的光纤截面中,同时存在多个同向或异向的信号,很容易发生不同波长信号间的相互耦合,产生各种非线性光学效应,致使光学信号产生串扰,引起信号失真,造成光纤线性损耗外的非线性损耗,从而对通信系统的性能造成不良的影响,因此,必须对各种非线性光学效应加以研究,将非线性效应的不良影响限制在可容忍的范围之内。     

WDM光纤孤子通信系统中的关键技术

论述了WDM光纤孤子通信的发展现状,分析了WDM光纤孤子通信系统中的几个主要问题。信道间碰撞、集总放大效应、定时抖动等都将限制WDM技术的有效性,给出了解决问题的方案。对研究WDM光纤孤子通信系统具有指导意义。     

色散、偏振模色散和非线性

本介绍了光纤的色散和偏振模色散，及其对系统的影响，介绍了两种主要的色散补偿的方法；分析了在密集波分复用(DWDM)系统中，光纤的各种非线性效应及对系统性能的影响。     

基于相干光OFDM的WDM系统传输性能分析

首先对相干光OFDMWDM系统理论模型和基本原理进行了研究,然后基于Opt i syst em仿真软件,对相干光OFDMWDM传输系统进行了仿真分析,并研究了该系统的传输性能,发现基于相干检测的光OFDM技术和WDM技术结合,可以有效抑制光纤色散和非线性影响,提高系统的性能。将此系统与传统的NRZ WDM光传输系统进行比较,发现系统性能较NRZ系统有很大的提高。     

非线性光纤环镜及其应用

在介绍非线性光纤环境基本原理的基础上，系统地论述了其在光纤通信系统中的各种应用及发展动态。     

WDM系统使用的光纤技术

光纤是光纤通信的基础。随着光纤传输速率的提高,光纤的性能也不断得到改进。近年来,随着波分复用(WDM)技术的发展,对光纤又有一些新要求。 1 非线性效应对WDM的影响 以前由于进入光纤的功率不大,光信号在光纤中传输可以看作是线性关系。影响光纤传输特性的因素主要是损耗和色散。现在,光纤放大器能把     

WDM系统中的非线①性研究及仿真实验

利用分离信道的分步傅立叶法对信道间距为0.8nm的8路10 Gbit/s波分复用色散补偿系统进行仿真实验，分析了在具有级联光放大器系统中光纤色散和各种非线性效应（自相位调制SPM、交叉相位调制XPM、四波混频FWM）对系统传输的影响。仿真结果表明，在色散补偿WDM通信系统中，SPW对系统传输造成的损伤最大。并且由于非线性效应、传输损耗及噪声的综合影响，应当选取合适的系统输入功率。     

单模光纤非线性系数n2/Aeff的测量方法

通信距离的延长和WDM通道数的增加使光纤非线性效应日益显著，如何准确地测量非线性系数的大小成了人们关注的问题，文章介绍了几种非线性系数的测量方法，并对它们的优缺点进行了较全面的分析和比较。     

Nx10GDWDM系统设计的技术要点

从光纤的功率衰减、色度色散、偏振模色散、非线性效应几方面讨论在设计10G的WDM系统或者是从2．5G系统升级至10G系统时应注意的问题。     

Effects of nonlinear crosstalk in optical PMD compensation

We report on the effects of nonlinear crosstalk on the optical polarization-mode dispersion (PMD) compensation in wavelength-division-multiplexing (WDM) systems. An analytical model is presented to describe the effect of nonlinear crosstalk on the first-order PMD compensation. We also experimentally show that the performance of WDM systems could be degraded by nonlinear birefringence, even when the first-order PMD is completely compensated.     

Impact of nonlinear phase noise on direct-detection DQPSK WDM systems

The performance degradation of differential quadrature phase-shift keying (DQPSK) wavelength-division-multiplexed (WDM) systems due to self-phase modulation (SPM)- and cross-phase modulation (XPM)-induced nonlinear phase noise is evaluated in this letter. The XPM-induced nonlinear phase noise is approximated as Gaussian distribution and summed together with the SPM-induced nonlinear phase noise. We demonstrate that 10-Gb/s systems, whose walkoff length is larger than 40-Gb/s systems', are more sensitive to XPM-induced nonlinear phase noise than 40-Gb/s systems. Furthermore, DQPSK WDM systems show lower tolerance to both SPM- and XPM-induced nonlinear phase noise than differential phase-shift keying WDM systems.     

Comparison of FWM- and XPM-induced crosstalk using the Volterra series transfer function method

New analytical tools to calculate the variance due to cross-phase modulation (XPM) and four-wave mixing (FWM) induced intensity distortion are derived based on the Volterra series transfer function method. The analysis for both the XPM and FWM effects is based on the same system configuration with a continuous-wave (CW) probe channel plus modulated pump channels, which makes possible a fair comparison between the two nonlinear effects. Effective ways to reduce the XPM- and FWM-induced intensity distortion are given. The new results on the variance of the nonlinearity-induced intensity fluctuation also make it possible to study both synchronous wavelength-division multiplexing (WDM) systems with fixed channel delays and asynchronous WDM systems with random channel delays. The new analytical results provide accurate and efficient ways for system parameter optimization to reduce these two nonlinear effects.     

Integrated-optic timing tuner for high-speed WDM signals

We demonstrate an integrated-optic timing tuner, which is used for the fine adjustment of wavelength-division-multiplexing (WDM) signal delays. This tuner can be utilized to compensate for the bit skew of high-speed WDM bit-parallel links in the next generation or to reduce nonlinear effects in WDM transmissions. The tuner consists of an arrayed-waveguide grating and variable delay lines comprising asymmetrical Mach-Zehnder interferometers with different arm lengths. We demonstrate experimentally that our device is capable of accurate delay tuning for 16 /spl times/ 10 to 40-Gb/s systems.     

Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDMtransmission over standard fiber

Intrachannel cross-phase modulation and four-wave mixing in high-bit-rate WDM transmission systems employing standard single-mode fiber are investigated. The effects of imperfect third-order dispersion compensation are included in the study and analytical expressions giving optimum values of dispersion precompensation minimizing the distortion due to the intrachannel nonlinear effects are derived     

Dynamics of the chirped return-to-zero modulation format

We numerically simulated long-distance, high-bit-rate, wavelength division multiplexed (WDM) transmission in dispersion-managed systems. We investigated return-to-zero (RZ) and nonreturn-to-zero (NRZ) modulation formats with amplitude and phase modulation. Consistent with earlier experiments, we find that the chirped return-to-zero (CRZ) modulation format has significant advantages over the NRZ modulation format in WDM systems. We elucidate the physical reasons for these advantages. We then discuss, in detail, the dynamics of the CRZ systems, carefully distinguishing noise effects, single-channel nonlinear effects, and multichannel nonlinear effects. In this way, we provide a physical basis for understanding CRZ systems that should prove useful for future system design. In particular, we find that the pulse evolution is dominated by linear dispersion and that the spread in the eye diagrams is dominated by signal-spontaneous beat noise, just like in linear systems. However, we also find that symmetric dispersion compensation performs better than asymmetric dispersion compensation, due to the effects of nonlinearity. Additionally, we find that interchannel nonlinearities spread the eye diagrams without changing the dynamical behavior. Thus, the system is quasilinear in the sense that its properties resemble those of linear systems, but nonlinearity plays an important role     

Carrier-induced phase noise in angle-modulated optical-fiber systems

Phase noise in angle-modulated optical-fiber communication systems arising from optical power fluctuations is analyzed. The nonlinear refractive index of silica is the physical mechanism which converts power fluctuations into phase fluctuations. The effects of self-phase modulation (an optical wave acting on itself) and cross-phase modulation in wavelength-division multiplexed (WDM) systems (one optical wave modulating a channel at a different wavelength) have been calculated. The phase noise generated in single-channel systems is negligible for laser fluctuations less than 1-mW rms. In WDM systems containing as few as four channels the phase noise exceeds tolerable levels (0.15 rad) for power fluctuation of 1 mW in each channel.     

Performance Comparison of WDM Systems with Different Duty Cycle

The performances of nonlinear WDM systems with different duty cycle are compared by means of numerical simulation.The numerical results show that the optical pulse with duty cycle of 0.5 is superior to the conventional NRZ modulation schene.The conclusion is different from that of some references.The reason is that inter symbol interference is not included in some references.In fact,inter symbol interference plays an important role in monlinear WDM system.Although the larger the duty cycle is,the stronger the effect of the cross-phase modulation and self-phase modulation on nonlinear WDM is however,the larger the duty cycle is ,the stronger the inter symbol interference is.     

SCM/WDM系统中抑制载波的光学单边带调制技术

为了有效抑制SCM/WDM光纤通信系统中的群速度色散和非线性效应,利用SCM/WDM光纤通信系统中信号经过两次调制这一特性,提出了一种在SCM/WDM系统中容易实现的抑制载波的光学单边带调制技术。抑制载波的光学单边带调制信号具有很大的调制深度,即通过抑制载波可以有效的增大了调制深度,进而可以减小调制器的外加电压升高而激发的一系列有害的非线性效应。实测的调制信号的频谱只剩下了半个边频,有效地减小了光信号的频带宽度,从而可以有效地减小群速度色散对信号的劣化。接收机灵敏度的实测图表明,利用文中所述的抑制载波的光学单边带调制技术可以有效地提高接收机的灵敏度达3-5dB。