Benefit of SPM-based all-optical reshaper in receiver for long-haul DWDM transmission systems

The effectiveness of a self-phase modulation (SPM)-based all-optical reshaper with optically time-division-demultiplexing receiver was experimentally investigated using 42.7-Gb/s carrier-suppressed return-to-zero (CS-RZ) signals. We have confirmed that this scheme is quite effective to suppress the waveform degradation due to optical signal bandlimitation. We have demonstrated 80% spectral efficiency without using polarization demultiplexing by using the all-optical reshaper. We have also demonstrated 50-GHz-spaced 55/spl times/42.7 Gb/s signals transmission over 2500 km, using an optically bandlimited CS-RZ signal and the SPM-based all-optical reshaper in receiver without using polarization demultiplexing. A Q-factor improvement of about 1.5 dB was obtained by using the all-optical reshaper.     

Effective channel allocation to reduce inband FWM crosstalk in DWDM transmission systems

An accurate analysis of the four-wave mixing (FWM) impact on dense wavelength-division multiplexing optical systems is carried out for different types of fibers. Particular channel allocations on the ITU grid are studied to reduce the inband FWM crosstalk and guarantee high performances in different types of optical fiber. These schemes, with respect to the other known channel allocations, allow one to find an optimum tradeoff between the required bandwidth expansion and the maximum inband FWM crosstalk. A comparison between the system spectral occupation and the signal-to-crosstalk ratio (SXR) versus the channel input power for the equal channel spacing and the proposed channel allocations validates the proposed solutions in the case of single-mode, nonzero dispersion-shifted, and dispersion-shifted fiber. For a 32-channel system, SXR improvements up to 4 dB without bandwidth expansion, and bandwidth savings up to 15 nm with a guaranteed minimum SXR of 25 dB, are obtained with respect to an equally spaced channel allocation.     

High-capacity undersea long-haul systems

This paper reviews technologies and techniques that have been used in deployed long-haul wavelength division multiplexing (WDM) systems and emerging technologies that could be used for the next generation of cost-reduced systems. The overview of current generation technologies starts with a discussion of modulation formats, focusing on the superior properties of the chirped return to zero on-off shift keying (CRZ-OOK) modulation format. The use of 10-Gb/s CRZ-OOK modulation format together with advanced fiber types, more powerful forward error correction (FEC), and broadband erbium-doped fiber amplifiers resulted in the deployment of dense WDM systems with capacities per fiber in terabits per second range and trans-Pacific reach. Demand for the systems with large design capacity led to further development of broadband optical amplifiers. Laboratory demonstrations successfully expanded transmission into the full C-band and later in the C and L transmission bands. The current market conditions dictate the need for reducing the first cost of an installed system rather than reaching record capacity per fiber. Reducing first cost can be achieved by reducing the amount of optical amplifiers in the cable by utilizing an excess performance margin provided by available RZ-OOK technology. Further improvements would be possible if more powerful FEC and modulation formats with better receiver sensitivity are used. For example, the RZ differential phase-shift keying (RZ-DPSK) modulation format with 3-dB better receiver sensitivity and better nonlinear tolerance to large amounts of accumulated dispersion is a very promising technology. This paper will review long-haul transmission results using RZ-DPSK and will compare the transmission properties of RZ-DPSK signals versus RZ-OOK signals. Due to superior receiver sensitivity, the RZ-DPSK modulation format can be an enabling technology for 40-Gb/s per channel transoceanic transmission.     

Introduction of electrostriction-induced acoustic interaction inmodeling of high-capacity long-haul transmission systems

We present a method to implement an electrostriction-induced acoustic effect in the nonlinear Schrodinger equation (NLSE) and to validate it from a system point of view in particular, by comparison with experimental results. Special focus is devoted to acoustic cross effects between channels in wavelength-division multiplexing (WDM) transmission. The model is then applied to different realistic single-channel 40-Gb/s soliton systems in the presence of dispersion management or in-line optical regeneration to evaluate induced penalties     

Spectral efficiency limits and modulation/detection techniques for DWDM systems

Information-theoretic limits to spectral efficiency in dense wavelength-division-multiplexed (DWDM) transmission systems are reviewed, considering various modulation techniques (unconstrained, constant-intensity, binary), detection techniques (coherent, direct), and propagation regimes (linear, nonlinear). Spontaneous emission from inline optical amplifiers is assumed to be the dominant noise source in all cases. Coherent detection allows use of two degrees of freedom per polarization, and its spectral efficiency limits are several b/s/Hz in typical terrestrial systems, even considering nonlinear effects. Using either constant-intensity modulation or direct detection, only one degree of freedom per polarization can be used, significantly reducing spectral efficiency. Using binary modulation, regardless of detection technique, spectral efficiency cannot exceed 1 b/s/Hz per polarization. When the number of signal and/or noise photons is small, the particle nature of photons must be considered. The quantum-limited spectral efficiency for coherent detection is slightly smaller than the classical capacity, but that for direct detection is 0.3 b/s/Hz higher than its classical counterpart. Various binary and nonbinary modulation techniques, in conjunction with appropriate detection techniques, are compared in terms of their spectral efficiencies and signal-to-noise ratio requirements, assuming amplified spontaneous emission is the dominant noise source. These include a) pulse-amplitude modulation with direct detection, b) differential phase-shift keying with interferometric detection, c) phase-shift keying with coherent detection, and d) quadrature-amplitude modulation with coherent detection.     

A study of interchannel separation of moisture in nozzle cascades of turbines

Results obtained from an experimental study on analyzing the separation characteristics of moisture removing slits during interchannel separation are presented. Not only the flowrate of the liquid phase through the moisture removing slits, but also the flowrate of steam sucked together with liquid was measured during the study.     

DWDM技术在电力通信网应用的探讨

从波分复用技术原理入手,以湖北省电力通信网发展情况为例,提出了一种将密集波分复用(DWDM)技术应用于湖北电力通信网的设计方案,分析了引入DWDM技术的必要性和可行性。     

密集波分复用设备在江苏电力通信网中的应用

为解决江苏电力省市通信传输网带宽容量不足的现状,江苏电力通信采用DWDM+10 G SDH技术建设了省市主干传输网络.DWDM设备采用Alcatel 1626LM设备,采用多项先进技术,支持超长距离C波段高达192x 10 Gbit/s的网络应用.作为超大容量的传输系统在电力系统中的初次使用,DWDM设备在运行维护上要...     

FDTD analysis of crosstalk in multilayer printed circuits

A theoretical analysis has been developed to study the crosstalk in crossed bundles of parallel lines. The model is based on the theory of the coupled transmission lines and the resulting system of differential equations has been solved by means of the finite difference, time-domain (FDTD) method. The frequency response of the network has been achieved by the discrete fourier transform (DFT) algorithm; measurements, performed with a vectorial network analyser, show a good agreement with numerical simulation.     

Important parameters that influence crosstalk in multiconductor transmission lines

Transient surges in one of the overhead conductors, due to direct lightning strikes, causes crosstalk [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992] in other adjacent conductors. It is a common electromagnetic interference (EMI) phenomenon observed in power lines, communication lines and electrified railway lines. In this paper we investigate the crosstalk in multiconductor transmission lines (MTLs) above finitely conducting ground as a function of ground conductivity, heights of the receptor conductor and the terminal loads. For receptor conductor close to the ground, compared to the emitter conductor [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992], the decrease in ground conductivity increases the crosstalk peak currents at near end (end near to the source in the emitter conductor) of the receptor conductor, but at the far end it could either increase or decrease depending upon the line height and ground conductivity.     

DWDM+SDH在福建电力传输网中的应用

密集波分复用（DWDM）系统具有传输距离长、容量大、波道多、实施全透明传输、能组成全光层网络和工程造价相对较低等技术经济优势。文章阐明了DWDM与同步数字系列SDH的内在关系，介绍了整个DWDM系统的组网概况，并在DWDM传输平台上配置了SDH复用保护段设备，建设福建省调通中心到各地区电业局的光纤通信系统的传输平台。     

密集波分复用系统在山西电力通信网的应用研究

论述了密集波分复用系统（DWDM）是一种适合多业务、大容量的传输系统,其稳定性、可靠性以及安全性可以满足山西电力通信网未来的发展要求。首先介绍了DWDM系统的概念及系统组成,其次分析了山西电力主干通信网的发展趋势,从而引出DWDM系统在山西电力通信网中的发展及应用。     

多信道通信链路系统中的串扰分析与研究

随着信号速度的不断增快,串扰问题成为高速多信道通信链路系统设计、分析中不容忽视的重要问题.为研究通信系统中多信道串扰的影响,分析了通信链路系统中串扰产生的机理,采用信号完整性分析软件Hyperlynx7.5,构建了三线信道模型和总线结构模型.仿真结果表明,增加信道间距、减小信道介质层厚度、进行电阻匹配可以明显减小信道间串扰,而在多信道通信链路系统中,随着相邻多信道间距的增大,耦合噪声将会迅速下降.     

DWDM波长转换技术在超长距SDH传输网中的应用

SDH光信号在超长中继距离传输中存在信噪比下降的问题。文章介绍了在500kV东明开关站至三堡变光通信工程实施中，采用DWDM波长转换技术克服这一难题的成功经验。通过案例可以看出，在超长中继距离SDH光通信线路中，锁定SDH输出信号的中心频率并在接收端采用光过滤器对噪声进行抑制，是解决信噪比下降、保证传输质量的有效办法。     

DWDM波长转换技术在超长距SDH传输网中的应用

SDH光信号在超长中继距离传输中存在信噪比下降的问题.文章介绍了在500 kV东明开关站至三堡变光通信工程实施中,采用DWDM波长转换技术克服这一难题的成功经验.通过案例可以看出,在超长中继距离SDH光通信线路中,锁定SDH输出信号的中心频率并在接收端采用光过滤器对噪声进行抑制,是解决信噪比下降、保证传输质量的有效办法.     

Reducing the power envelope fluctuation of OFDM systems using side information supported amplitude clipping approach

OFDM is an important modulation technique currently in development in the field of communications systems. OFDM signals can combat multipath propagation and fading channels and can support large data rates. However, OFDM systems are multicarrier systems and experience problems due to the required summation of sinusoids when the in‐phase subcarriers are combined, which produces high power peaks. The large power envelope fluctuations that occur at the output cause in‐band and out‐of‐band distortions that result in degraded BER performance. The literature contains many qualified approaches to resolving the peak‐to‐average power ratio problem, including selected mapping, partial transmit sequence, and amplitude clipping techniques. The simplest technique is the amplitude clipping technique, and the selected mapping and partial transmit sequence techniques are excessively complicated for real‐time implementation. In this paper, we suggest a modification to the amplitude clipping method to produce a novel clipping technique called the side information supported amplitude clipping (SI‐SAC) method. The SI‐SAC technique involves sending certain bits of extra information so that the receiver can recover all of the clipped data. The SI‐SAC technique does not add computational complexity to the system, and simulation results show that the proposed method is superior to the conventional method. The peak‐to‐average power ratio was reduced by ≈2.5 dB, and the magnitude of the mean squared error vector is the same as that of the original signal that is not clipped. In contrast, the conventional amplitude clipping method produces a mean squared error vector with a large magnitude. Copyright © 2012 John Wiley & Sons, Ltd.     

密集波分复用数字光网络系统在山西电力系统中的应用

为解决电力通信网带宽低、不适应数据业务的突发特性、纤芯资源有限、传输能力不足等问题,山西省电力利用现有的电力光缆,采用密集波分复用系统,可完成大容量稳定快速的传输.简述了数字光网络系统DTN设备的特点,针对目前山西电力通信发展的现状,DTN与同类设备比较所具备的优势,光缆及纤芯的使用,对DWDM在山西电力系统中的应用进...     

福建电力DWDM环网光缆通信设计考虑

DWDM光纤系统具有带宽利用率高、扩容成本低、可传输多种格式信号、传输距离长等优点，为充分满足福建电力系统不断增长的业务要求，选择了DWDM通信系统以及环型路由结构，采用36芯G．655B和G．652B两种OPGW光缆，建设福建省调通中心至各地区电业局的光纤通信系统传输平台。文章详细地论述了DWDM系统建设中应该考虑的一系列问题。