光纤的色散与非线性效应.ppt

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1、光纤的色散与非线性效应随着脉冲在光纤中传输，脉冲的宽度被展宽劣化的程度随数据速率的平方增大决定了电中继器之间的距离光纤的色散模间色散(ModeDispersion)色度色散(CromaticDispersion)偏振色散(PolarizationModeDispersion)色散对传输的限制Material(Chromatic)DispersionThisiscausedbythefactthattherefractiveindexoftheglassweareusingvaries(slightly)withthewavelength.So

2、mewavelengthsthereforehavehighergroupvelocitiesandsotravelfasterthanothers.Sinceeverypulseconsistsofarangeofwavelengthsitwillspreadouttosomedegreeduringitstravel.GroupVelocityDispersion”(GVD)NormalDispersionRegime:thelongwavelengthstravelfasterthantheshortones!Thusaftertrav

3、ellingonafibrewavelengthsattheredendofthepulsespectrumwillarrivefirst.Thisiscalledapositivechirp!AnomalousDispersionRegime:theshortwavelengths(blueendofthespectrum)travelfasterthanthelongwavelengths(redend).Aftertravelonafibretheshorterwavelengthswillarrivefirst.Thisisconsi

4、deredanegativechirp.PolarisationModeDispersion(PMD)ThereisusuallyaveryslightdifferenceinRIforeachpolarisation.Itcanbeasourceofdispersion,usuallylessthan.5ps/nm/km.Theeffectistocauseacircularorellipticalpolarisationtoformasthesignaltravelsalongthefibre.Dispersionresultingfro

5、mthebirefringentpropertiesoffibreiscalled“PolarisationModeDispersion”(PMD).WaveguideDispersionTheshape(profile)ofthefibrehasaverysignificanteffectonthegroupvelocity.Thisisbecausetheamountthatthefieldsoverlapbetweencoreandcladdingdependsstronglyonthewavelength.Thelongerthewa

6、velengththefurtherthetheelectromagneticwaveextendsintothecladding.sinceagreaterproportionofthewaveatshorterwavelengthsisconfinedwithinthecore,theshorterwavelengths“see”ahigherRIthandolongerwavelengths.Thereforeshorterwavelengthstendtotravelmoreslowlythanlongerones.传输使用的三种不同

7、类型的单模光纤G.652单模光纤（NDSF）G.653单模光纤（DSF）G.655单模光纤（NZ-DSF）常规G.655大有效面积G.655大多数已安装的光纤低损耗大色散分布大有效面积色散受限距离短2.5Gb/s系统色度色散受限距离约600km10Gb/s系统色度色散受限距离约34kmG.652+DCF方案升级扩容成本高结论:不适用于10Gb/s以上速率传输，但可应用于2.5Gb/s以下速率的DWDM。G.652单模光纤（NDSF）低损耗零色散小有效面积长距离、单信道超高速EDFA系统四波混频（FWM）是主要的问题，不利于DWDM技术结论:适

8、用于10Gb/s以上速率单信道传输，但不适用于DWDM应用，处于被市场淘汰的现状。G.653单模光纤（DSF）在1530－1565nm窗口有较低的损耗工作窗口较低的