专业英语ppt课件.ppt

Part5OpticalFiberCommunicationWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsWordsandExpressionsInanopticalcommunicationsystem,informationistransmittedbylightpropagationinsideanopticalfiberintheformofacodedsequenceofopticalpulses.Thesignalweakensduringpropagationbecauseoffiberloss.

在光通信系统中，信息通过光在光纤中以编码序列的光脉冲的形式传播。由于光纤损耗，信号在传播过程中减弱。Thetransmissiondistancecanexceedafewthousandkilometersforsuchsystemsaslongasfiberdispersiondoesnotlimitit.Anovelapproachmakesuseofopticalsolitonsthatusefibernonlinearityforcompensatingfiberdispersion.

对于这样的系统，只要光纤色散不限制它，传输距离就可以超过几千公里。一种利用光孤子的新颖方法是通过光纤非线性来补偿光纤色散。Initssimplestform,anopticalfiberconsistsofacentralcoresurroundedbyacladdinglayerwhoserefractiveindexisslightlylowerthanthatofthecore.

在最简单的结构中，光纤由一个被包裹层包围的纤芯组成，其折射率略低于纤芯。Suchfibersaregenerallyreferredtoasstep-indexfiberstodistinguishthemfromgraded-indexfibersinwhichtherefractiveindexofthecoredecreasesgraduallyfromcentertothecoreboundary.

这种光纤通常被称为“阶跃折射率光纤”，以区别它们和梯度折射率光纤，在梯度折射率光纤中，其纤芯的折射率逐渐从中心向纤心边界逐渐减小。5.2.1OpticalLosses——光损耗

Severalfactorscontributetothelossspectrum,materialabsorptionandRayleighscatteringcontributingdominantly.Otherfactorsthatmaycontributetothefiberlossarebendinglossesandboundarylosses(duetoscatteringatthecore-claddingboundary).

（以上）几个因素导致了光谱损耗、材料吸收和瑞利散射。其他可能导致光纤损耗的因素是弯曲损耗和边界损耗（由于纤芯-包层边界的光散射）。5.2.2ChromaticDispersion——色散

Onafundamentallevel,theoriginofchromaticdispersionisrelatedtothecharacteristicresonancefrequenciesatwhichthemediumabsorbstheelectromagneticradiationthroughoscillationsofboundelectrons.

在一个基本的层面上，色散的起源与介质通过束缚电子振荡吸收的电磁辐射的特征