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光网络的组成•Couplers（耦合器）•lasers（激光器）•photodetectors（光检测器）•opticalamplifiers（光放大器）•opticalswitches（光转换）•filtersandmultiplexers（滤波器和复用器）Couplers•Usedto：combineorsplitopticalsignals（对光信号连接和分束）下图为2*2耦合器α耦合系数•Inawavelength-independentdevice,αisindependentofthewavelength•inawavelength-selectivedevice,αdependsonthewavelength3dBcoupler•在两根输出光线中光功率相等•分光比为50:50，但两个输出端口的光有∏/2相对相位差，即耦合到另一光线中的输出光与沿直通输出方向的光存在相位滞后•分光比：表示耦合器输出端口之间光功率分配比例IsolatorsandCirculators•Anisolator（分离器）isapassivenonreciprocaldevice静态单向设备•mainfunctionistoallowtransmissioninonedirectionthroughitbutblockalltransmissionintheotherdirection•Acirculatorissimilartoanisolator,exceptthatithasmultipleports环行器twokeyparametersofanisolator•insertionloss•thelossintheforwarddirection,andwhichshouldbeassmallaspossible•around1dB•Isolationloss•thelossinthereversedirection,andwhichshouldbeaslargeaspossible•around40-50dB隔离器两种偏振模式•horizontalandverticalmodes垂直和水平模式•SOP：stateofpolarization偏振状态Apolarization-independentisolator.•a.从左至右传输•b.从右至左传输filtersandmultiplexers（滤波器和复用器）•Multiplexersanddemultiplexers•multiplexanddemultiplexsignalsatdifferentwavelengthsinWDMsystems•（在WDM系统中对不同波长信号的复用和解复用）•toprovideequalizationofthegainandfilteringofnoiseinopticalamplifiers.•a）选通器：一根光线多波长只选通一个波长到出口光线处，其他波长从第三端口输出•b)复用器：多光纤的不同波长波长复用到一根光线opticalamplifiers（光放大器）•overcomefiberandothercomponentlosses（防止损耗，降低噪声）•usedtoamplifysignalsatmultiplewavelengths（在复用波长时放大信号）Transmitters•激光器：•Bothsemiconductoranderbiumfiberlasers（半导体或饵光纤激光器）arecapableofachievinghighoutputpowers（输出功率）,typicallybetween0and20dBm,althoughsemiconductorlasersusedasWDMsourcestypicallyhaveoutputpowersbetween0and10dBm.Detectors接收机•将承载信息的光信号变成电信号•光信号接收的基础在于光电检测器，可以实现直接监测和相干检测光电检测器•在所用光源的波长范围内有较高响应度•较小的噪声•响应速度快•对温度变化不敏感•与光纤尺寸匹配•工作寿命长光转换器和波长转换器•opticalswitches光转换•animportantroleasopticalnetworksbecomemoreagile•wavelengthconverters波长转换器•convertsignalsfromonewavelengthtoanother,attheedgesoftheopticalnetwork,aswellasinsidethenetwork.WavelengthConverters•convertsdatafromoneincomingwavelengthtoanotheroutgoingwavelength（将数据从一个输入波长到另一个输出波长）•wavelengthconvertersmaybeneededwithinthenetworktoimprovetheutilizationoftheavailablewavelengthsonthenetworklinks（提高利用率）•wavelengthconvertersmaybeneededatboundariesbetweendifferentnetworksifthedifferentnetworksaremanagedbydifferententitiesandtheseentitiesdonotcoordinatetheallocationofwavelengthsintheirnetworks（两个不同网络的交界处以协调各自的波长分配）