1模式的概念ConceptofModes:PropagationoflightalongawaveguidecanbedescribedintermsofasetofguidedelectromagneticwavescalledModeofwaveguide.2模式的分布特性EachModeisapatternofelectricandmagneticfielddistributionthatisrepeatedalongthefiberatequalintervals.AcertaindiscretenumberofModesarecapableofpropagatingalongthewaveguide.本征值方程是一個關于b的以n為參量的超越方程，通常使用數值方法求解。對于不同的n，可存在一組離散的b解，每一個b對應能在光纖中傳播的光場的一種空間分布，這種空間分布在傳播過程中只有相位的變化，而沒有分布形狀的變化，將這種空間分布稱為模式。根據不同的條件，光纖中可能存在許多模式35簡并模方法：每個LP0m模由HE1m模導出；每個LP1m模由TE0m、TM0m、HE2m構成；每個LPvm模（v>1）由HEv+1,m、EHv-1,m構成。例如LP01模只包含基模HE11LP11模由TE01、TM01、HE21構成；6階躍光纖中的功率分布當V→∞時，它的能量將聚集在纖芯中；當V→Vc時，能量的大部分是在包層里，這時的導波將成為輻射模。第三章Signalattenuation:isoneofthemostimportantpropertiesofanopticalfiber.Itlargelydeterminesthemaximumunamplifiedorrepeaterlessbetweenatransmitterandareceiver.Thebasicattenuationmechanismsinafiber:AbsorptionScatteringlossesRadioactivelossesmicroscopicvariationsinthematerialdensitycompositionalfluctuationsstructuralinhomogeneitiesdefectsoccurringduringfibermanufacture.Radiativelossesfiberundergoesabendoffiniteradiusofcurvature.Fibercanbesubjecttotwotypesofbends:1.macroscopicbends:havingradiithatarelargecomparedwiththefiberdiameter.2randommicroscopicbends:canarisewhenthefibersareincorporatedintocables.IntramodalDispersionIntramodalDispersionispulsespreadingthatoccurswithinasinglemode.Thespreadingarisesfromthefinitespectralemissionwidthofanopticalsource.Thisphenomenonisalsoknownasgroupvelocitydispersion.

1MaterialDispersion：arisesfromthevariationoftherefractiveindexofthecorematerialasafunctionofwavelength.2WaveguideDispersion：occursbecauseasingle-modelfiberconfinesonlyabout80%oftheopticalpowertothecore.3Theotherfactorgivingrisetopulsespreadingisintermodaldelay,whichisaresultofeachmodehavingadifferentvalueofthegroupvelocityatasinglefrequency.Ofthesethree,waveguidedispersionusuallycanbeignoredinmultimodefibers.However,thiseffectissignificantinsingle–modefibersSMF單模光纖mmF多模光纖Refractive-indexprofilesInthedesignofsingle-modefibers,dispersionisamajordistinguishingfeature,sincethisiswhatlimitslong-distanceandveryhighspeedtransmission.Insinglemodefibers:dispersionislowestat1300nm，ttenuationisaminimumat1550nmMethod:adjustthebasicfiberparameterstoshiftthezero-dispersionminimumtolongerwavelengths.第四章LD:Laser-DiodesOpticalOutputCoherent,Monochromatic,DirectionalLED:Light-EmittingDiodesOpticalOutputIncoherent,BroadSpectral,LargebeamLEDsaslightsourcefor100~200Mb/swithMMF1Simpledrivecircuitry2.Nothermaloropticalstabilizationcircuit3.BefabricatedlessexpensivelyAnLEDmusthave:1.Ahighradianceoutput2.Afastemissionresponsetime3.Ahighquantumefficiency光功率發射和耦合PowerLaunchingandCoupling Inanopticalfiberlink,twomajorsystemare:Howtolaunchopticalpowerintoaparticularfiber?Howtocoupleopticalpowerfromonefiberintoanother?Considerationinopticalpowerlaunching1NumericalapertureCoresizeRefractive-indexprofileCore-claddingindexdifferenceSize,radiance,angularpowerdistributionofsourceAsignificantfactorinanyfiberopticsysteminstallationistherequirementtointerconnectfibersinalow-lossmanner.Connection:permanentbondisgenerallyreferredtoasasplice,demountablejointisknownasaconnector.Everyjoiningtechniqueissubjecttocertainconditionswhichcancausevariousamountsofopticalpowerlossatthejoint.Theselossesdependonparameterssuchasinputpowerdistribution,lengthofthefiberbetweentheopticalsourceandthejoint,geometricalandwaveguidecharacteristicsofthetwofiberendsatthejoint,andthefiberend-facequalities.Character:HighsensitivityMinimumadditionnoiseFastresponsespeedTypesofphotodetectorsPhotomultiplierPyroelectric-detectorsPhototransistorPhotodiodesPhotodiodeisfitforfiberopticalsystemSmallsize,suitablematerial,highsensitivity,Fastresponsespeeddarknoisecurrent:Noincidentlight,currentcontinuesthroughthebiascircuit.bulkdarknoisecurrent:Fromelectronsandholeswhicharethermallygeneratedinthepnjunctionofthephotodiode.surfacedarknoisecurrent:Dependonsurfacedefect,cleanliness,biasvoltage,andsurfacearea.GainmechanismofAPDdependsonelectronandholeionizationrate:TemperaturesensitiveHighbiasvoltage第七章Typicalerrorratesrangesfrom10-9~10-12ThisBERdependsontheSNRatreceiver.SDH1．PDH存在的主要問題（1）兩大體系，3種地區性標準，使國際間的互通存在困難。（2）無統一的光接口，無法實現橫向兼容。（3）準同步復用方式，上下電路不便。（4）網絡管理能力弱，建立集中式電信管理網困難。（5）網絡結構缺乏靈活性（6）面向話音業務所謂SDH是一套可進行同步信息傳輸、復用、分插和交叉連接的標準化數字信號的結構等級。SDH網絡則是由一些基本網絡單元（NE）組成的，在傳輸媒質上（如光纖、微波等）進行同步信息傳輸、復用、分插和交叉連接的傳送網絡3．SDH的特點（1）新型的復用映射方式：同步復用方式和靈活的映射結構。（2）接口標準統一：全世界統一的NNI，體現了橫向兼容性。（3）網絡管理能力強：幀結構中豐富的開銷比特。（4）組網與自愈能力強：采用先進的ADM、DXC等組網。（5）兼容性好：具有完全的前向兼容性和后向兼容性。（6）先進的指針調整技術：可實現準同步環境下的良好工作。（7）獨立的虛容器設計：具有很好的信息透明性（8）系列標準規范：便于國內、國際互連互通SDH采用一套標準化的信息結構等級，稱為同步傳送模塊STM-N（N=1，4，16，64，…），相應各STM-N等級的速率為 STM-1 155.520Mbit/s STM