利用半导体光放大器和滤波器组合实现高速波长转换和码型转换

将半导体光放大器(SOA)和滤波器组合使用是实现高速全光信号处理的有效途径。利用半导体光放大器和带宽为0.32nm的可调窄带滤波器同时实现了40Gbit/s的非归零(NRZ)信号的反相波长转换(WC)和非归零到伪归零(PRZ)信号的码型转换,波长转换和码型转换的结果差异取决于滤波器中心波长相对于探测光波长的失谐量。当滤波器的失谐量为-0.24nm时,输出反相的波长转换,此时滤波器起到加速半导体光放大器增益恢复的功能。当滤波器失谐量为 0.41nm和-0.48nm时,得到非归零到伪归零的码型转换,并且产生的伪归零脉冲分别出现在非归零信号的上升沿和下降沿,此时滤波器的作用是将探测光的相位信息转换为强度信息,并且该码型转换结果兼有波长转换的功能。     

40 Gbit/s 高速OOK到OFSK全光码型转换器的研究

全光码型转换器可以提高光网络的有效性和灵活性,是未来光网络中不可缺少的一部分.文章提出了一种基于半导体光放大器(SOA)中瞬时交叉相位调制(T-XPM)效应和光带通滤波器的开关键控(OOK)到光频移键控(OFSK)的高速全光码型转换方案.该方案结构简单,易于实现.在实验上实现了40 Gbit/s的OOK到OFSK的全光码型转换,并对其转换特性进行了实验研究.     

利用SOA和OBPF的40Gb/s RZ到NRZ全光码型变换

全光码型转换技术是实现未来全光网络的关键技术之一,为此提出了一种利用半导体光放大器（SOA）和光带通滤波器（OBPF）的归零（RZ）码到非归零（NRZ）码的信号转换方案。利用通信软件数值模拟了基于40 Gb/s的码型转换,仿真实现了稳定的不同占空比的RZ码到NRZ码的码型转换以及波长转换。     

基于半导体光放大器中交叉偏振调制效应的波长转换器

了改善基于半导体光放大器(SOA)中交叉偏振调制效应(CPM)的波长转换器的转换信号码型效应，对交叉偏振调制一半导体光放大器波长转换器的工作原理进行了分析；通过讨论交叉偏振调制一半导体光放大器波长转换脉冲的上升沿和下降沿的频率啁啾，结合滤波器的透过谱特性，提出了一种利用滤波器的波长正斜率边和波长负斜率边分别对正相转换信号和反相转换信号进行码型优化的方案，并进行了实验验证。在信号码率为10Gb／s的交叉偏振调制一半导体光放大器波长转换实验中，采用光带宽为0．3nm的JDS滤波器优化转换信号的波形，基本消除了转换信号中长“1”码和长“0”码的码型效应，并将正相转换信号和反相转换信号的功率代价分别改善了3dB以上。     

一种新型可调谐光阈值器件

提出一种基于超连续谱(SC)的新型可调谐非线性光阈值器件,通过调谐光带通滤波器(OTF)改变阈值器件特性。实验中,高非线性光纤(HNLF)输入光功率为21.0dBm时,测得滤波器中心波长一定时的最佳20dB带宽为12~18nm,滤波器带宽固定时的最佳中心波长为1 576nm。     

基于硫系光纤交叉相位调制的波长转换研究

全光波长转换器(AOWC)是全光通信网络的关 键器件,它是实现光波长路由的必要手段。本文提出了一种 基于硫系光纤交叉相位调制的波长转换方案。将信号光和探测光同时输入普通硫系光纤产生 XPM,然后用光带通滤波器(BPF) 滤得转换光的单个边带,从而实现相位-强度转换,还原出数字信号。本文详细分析了系统 的工作原理,并通过仿真,验证了 方案的可行性。该方案只需1m长度的光纤就能产生显著的XPM,对输入光信号峰值功率的要 求低,信号光可由40 Gb/s的归 零码数字信号驱动MZM调制获得,而不需要特殊的高功率超短脉冲激光。波长在1550 nm处的转换光信号眼图性能良好, 与原始信号相比,只有大约1dB的功率代价。该系统的波长转换的距离可达25 nm。该方案实现简单,不需要因为色散对硫 系光纤做特殊处理,适合于高速光传输系统,具有极大的应用前景。     

基于光纤光参量放大的多通道全光非归零/归零码转换器

提出了一种基于光纤光参量放大器(FOPA)的多通道全光非归零码(NRZ)/归零码(RZ)调制格式转换的方案.该方案中,非归零码信号与同步的时钟抽运光共同注入到高非线性光纤(HNLF)中,由高非线性光纤构成的参量放大器把非归零码信号转换为归零码信号,同时不改变信号光的波长.多通道的码型转换器以两路10 Gb/s的非归零码进行了实验论证.转换后的归零码信号的信噪比(SNR)高于7.6 dB,其脉冲宽度约为30 ps,并且具有3dB的消光比(ER)提高.根据多通道码型转换器的实现原理,该码型转换器可以应用于40 Gb/s或更高比特率的多通道码型变换操作.     

基于SOA交叉增益调制的2.5Gbit/s NRZ码全光波长转换实验研究

基于SOA交叉增益调制效应(XGM)进行了2.5Gbit/s 31位非归零(NRZ)伪随机码的全光波长转换实验,分析了该方案下转换信号的消光比、信噪比、平均功率与输入连续光、信号光功率、波长的关系.实验中转换信号的光信噪比可达40dB以上,消光比和信噪比均大于10dB,符合ITU-T G.691标准.信号波长向下转换间距可达60nm,是目前基于SOA中的XGM效应进行波长转换获得的最大的波长间距.     

利用单个半导体光放大器实现非反转归零码的可重构全光逻辑门

提出了一种新型非反转归零(RZ)码的可重构全光逻辑门方案.该方案基于单个半导体光放大器(SOA)和可调谐光带通滤波器(TOBPF).利用SOA的四波混频效应和交叉增益调别(XGM)效应,实现了RZ码信号的多种功能逻辑运算.在不改变实验装置的情况下,通过调节带通滤波器中心波长和信号光功率,可以在不同逻辑功能之间进行切换.实验实现了10 Gb/s全光信号间的"与","非","或非","同或","(A)·B","A·(B)"等基本逻辑运算.与用连续光作为探测光不同的是,本方案采用了时钟信号作为探测光,这样各个逻辑门的输出均为非反转RZ码,有利于不同逻辑门的进一步组合.     

周期极化反转铌酸锂光波导的新特性和新应用

周期极化反转铌酸锂(PPLN)光波导以其响应速度超快和无自发辐射噪声影响等独特优点在高速全光信号处理中表现出优越性能并获得广泛应用.传统上主要利用PPLN光波导对比特速率和调制格式透明的特性实现全光波长转换、全光逻辑门和全光码型转换等功能.我们发现PPLN光波导其实也存在其不透明的一面[1].当携带相位信息的信号光置于PPLN光波导准相位匹配(QPM)波长处时,经过级联倍频和差频(cSHG/DFG)信号光中的相位信息在转换空闲光中被擦除.     

Analogy between data networks and electric networks

It is shown that two fundamental laws, Ohm's law in electric circuits and Little's theorem for queueing systems, are highly analogous. For both single nodes and networks, there is a striking equivalence between the two laws that facilitates the teaching and understanding of the related concepts of current flow in a resistor network and data flow in a communication network     

Mesh networks: commodity multihop ad hoc networks

In spite of the massive efforts in researching and developing mobile ad hoc networks in the last decade, this type of network has not yet witnessed mass market deployment. The low commercial penetration of products based on ad hoc networking technology could be explained by noting that the ongoing research is mainly focused on implementing military or specialized civilian applications. On the other hand, users are interested in general-purpose applications where high bandwidth and open access to the Internet are consolidated and cheap commodities. To turn mobile ad hoc networks into a commodity, we should move to more pragmatic "opportunistic ad hoc networking" in which multihop ad hoc networks are not isolated self-configured networks, but rather emerge as a flexible and low-cost extension of wired infrastructure networks coexisting with them. Indeed, a new class of networks is emerging from this view: mesh networks. This article provides an overview of mesh networking technology. In particular, starting from commercial case studies we describe the core building blocks and distinct features on which wireless mesh networks should be based. We provide a survey of the current state of the art in off-the-shelf and proprietary solutions to build wireless mesh networks. Finally, we address the challenges of designing a high-performance, scalable, and cost-effective wireless mesh network.     

Global networks

The author discusses the global network for international communications being constructured by Cable and Wireless Ltd., entitled the Global Digital Highway (GDH), which will provide a digital, fiber-optic link connecting major commercial and financial centers around the world. He suggests that the world is waiting for basic global facilities that will be exclusively dedicated to facilitating international communications and networking. He examines the trend toward liberalization in telecommunications policies, led by the US, which has recently been joined by both the UK and Japan. He discusses the role of Cable and Wireless in the context of these liberalization policies     

Toroidal networks

The essential features of the toroidal network topology are examined, and its performance is evaluated. Some of the proposed applications of toroidal networks are described. Included in the discussion are metropolitan area network communication and multiprocessor interconnection, as well as the use of VLSI technology     

Circulator-capacitor networks

It is shown how filters requiring floating inductance and constant-resistance allpass networks may be made with loss-less circulators and capacitors; the filters, if matched in the passband, are insensitive to small changes in the capacitances.     

Metropolitan-area networks

Metropolitan-area networks (MAN), which fill the gap between local area networks (LANs) and wide-area networks (WANs), are discussed. MANs were originally oriented toward data, but now often carry voice and video traffic as well. Supplying more bandwidth than LANs, they support two-way communication over a shared medium such as an optical-fiber cable, and may offer point-to-point high-speed circuits or packet-switched communication. The two most favored topologies, double-star and double-ring, are described and emerging MAN protocols are examined