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Chapter11OpticalAmplifier9/27/20231TheSch.OfInformationEngineering,WHUTChapter11OpticalAmplifier8Usedroutinelyforlosscompensationsince1995AmplifytheinputsignalbutalsoaddsomenoiseSeveralkindsofamplifiershavebeendeveloped

semiconductoropticalamplifier

raman-basedfiberamplifiererbium-dopedfiberamplifierEDFAsareusedmostcommonlyforlightwavesystemRamanamplifiersworkbetterforlong-haulsystem9/27/20232TheSch.OfInformationEngineering,WHUT8/5/20232TheSch.OfInformatiOUTLINEBasicconceptsSemiconductoropticalamplifier(SOA)RamanamplifierErbiumdopedfiberamplifierSystemapplicationofopticalamplifier9/27/20233TheSch.OfInformationEngineering,WHUTOUTLINEBasicconcepts8/5/2023311.1Basicconcepts11.1.1Gainspectrumandbandwidth11.1.2

Gainsaturation

11.1.3Amplifiernoise11.1.4Amplifierapplications9/27/20234TheSch.OfInformationEngineering,WHUT11.1Basicconcepts11.1.1Gain11.1.1GainspectrumandbandwidthAmplifierpumpedopticallyorelectricallytorealizeopticalgain.Opticalgainhasthegeneralform:

isthepeakvalueofthegain

istheopticalfrequencyoftheincidentsignal

istheatomictransitionfrequency

istheopticalpowerofthesignalbeingamplified

isthesaturationpower9/27/20235TheSch.OfInformationEngineering,WHUT11.1.1GainspectrumandbandwIntheunsaturatedregimeLorentzianspectrumwithbandwidthTypically(40nmorso)9/27/20236TheSch.OfInformationEngineering,WHUTIntheunsaturatedregime8/5/29/27/20237TheSch.OfInformationEngineering,WHUT8/5/20237TheSch.OfInformatiUsewithinitialconditionsignalpowergrowsasAmplificationfactoralsodependsonfrequencyasAmplifierbandwidthisdefinedastheFWHMofItisrelatedtogainbandwidthasItiseasytoshowthat9/27/20238TheSch.OfInformationEngineering,WHUTUsewithinit11.1.2GainsaturationIfG=G0/29/27/20239TheSch.OfInformationEngineering,WHUT11.1.2GainsaturationIfG=G0/11.1.3AmplifiernoiseOpticalamplifiersintroducenoiseanddegradeSNR.Sourceofnoise:SpontaneousemissionNoisespectraldensityPopulationinversionfactorAmplifiernoisefigureisdefinedas9/27/202310TheSch.OfInformationEngineering,WHUT11.1.3AmplifiernoiseOptical11.1.4Amplifierapplications9/27/202311TheSch.OfInformationEngineering,WHUT11.1.4Amplifierapplications811.2SemiconductorOpticalAmplifier11.2.1Amplifierdesign11.2.2

Amplifiercharacteristics

11.2.3

ProblemsofSOAs

9/27/202312TheSch.OfInformationEngineering,WHUT11.2SemiconductorOpticalAmp11.2.1AmplifierdesignAlaserbiasedbelowthresholdactsasaFPamplifier.FeedbackatfacetsprovidesmostgainnearFPresonances.Amplificationfactorobtainedconsideringmultiplereflections:1.FPA9/27/202313TheSch.OfInformationEngineering,WHUT11.2.1AmplifierdesignAlaseristhesinglepassamplificationfactor.reducestoGwhenAmplifierbandwidthsetbysharpnessofcavityresonances.9/27/202314TheSch.OfInformationEngineering,WHUTisthesinglepassampl2.TravelingwaveamplifiersFPamplifiersnotsuitablebecauseoftheirnarrowbandwidth.Feedbackatthecleavedfacetsmustbesuppressed.Commontocoatfacetswithanantireflectioncoating.ARcoatingshouldbegoodenoughtosuppressFPresonances.9/27/202315TheSch.OfInformationEngineering,WHUT2.TravelingwaveamplifiersFP9/27/202316TheSch.OfInformationEngineering,WHUT8/5/202316TheSch.OfInformat11.2.2Amplifiercharacteristics9/27/202317TheSch.OfInformationEngineering,WHUT11.2.2AmplifiercharacteristiWidegainspectrumwithnegligibleripples.Highgain(>25dB)atlowcurrents.Outputsaturationpowerintherange5-10mW.Noisefigureintherange5-7dB.9/27/202318TheSch.OfInformationEngineering,WHUTWidegainspectrumwithneglig11.2.3ProblemswithSOAs9/27/202319TheSch.OfInformationEngineering,WHUT11.2.3ProblemswithSOAs8/5/2SOAprovidePolarizationdependentgain:severalschemescansolvethisproblempartially.Largecouplinglosses(6-8dBormore).Relativelylargenoisefigure.9/27/202320TheSch.OfInformationEngineering,WHUTSOAprovidePolarizationdepen11.3Ramanamplifier11.3.1Ramangainandbandwidth11.3.2Ramangainsaturation11.3.2Ramanamplifierdesign9/27/202321TheSch.OfInformationEngineering,WHUT11.3Ramanamplifier11.3.1RamPumpedopticallyintheforwardorbackwarddirection.Usestimulatedramanscatteringforsignalamplification.Canworkatanywavelengthwithsuitablepumping.Fiberusedfordatatransmissioncanitselfbeused.Gaincanbemadepolarizationindependentusingorthogonallypolarizedpumpsateachwavelength.9/27/202322TheSch.OfInformationEngineering,WHUTPumpedopticallyintheforwar11.3.1Ramangainandbandwidth9/27/202323TheSch.OfInformationEngineering,WHUT11.3.1RamangainandbandwidtMaingainpeakshiftedby13.2THz(about100nm)frompumpwavelength.Ramangainspectrumextendsover>20THz.Gaincoefficientdependsonmodeareaofthepump.Candifferbyafactorof5ormoreforSMF,DSFandDCF.9/27/202324TheSch.OfInformationEngineering,WHUTMaingainpeakshiftedby13.211.3.2Ramangainsaturation30dBgainatapumppower-1WforL-1Km.Nogainsaturationupto0.5W9/27/202325TheSch.OfInformationEngineering,WHUT11.3.2Ramangainsaturation3011.3.3Ramanamplifierdesign9/27/202326TheSch.OfInformationEngineering,WHUT11.3.3Ramanamplifierdesign8Multiplepumpscanprovidewideandflatgainspectrum.NoiseissmallerforRamanamplifier.SufferfromdoubleRayleighscatteringandpumpnoisetransfer.Backwardpumpingprovidesabetterdesign.9/27/202327TheSch.OfInformationEngineering,WHUTMultiplepumpscanprovidewid11.4Erbiumdopedopticalamplifier11.11.1pumpingcharacteristics11.11.2gainspectrum11.11.3amplifiercharacteristics11.11.4amplifiernoise11.11.4amplifierdesign9/27/202328TheSch.OfInformationEngineering,WHUT11.4ErbiumdopedopticalamplDevelopedafter1987andcommercializedduringthe1990s.Fibercoredopedwitherbium(length20-200m).Pumpedusingdiodelasersoperatingat980or1480nm.Provide20-30dBgainatpumppowersbelow50mW.Gainbandwidthupto40nmpossible.Noisefigureintherange4-5dB.Providepolarizationindependentgain.Gainpatternindependent(responsetime-10ms).CanbedesignedtoworkinboththeCandLbands.9/27/202329TheSch.OfInformationEngineering,WHUTDevelopedafter1987andcomme11.11.1pumpingcharacteristics9/27/202330TheSch.OfInformationEngineering,WHUT11.11.1pumpingcharacteristicAmorphousnatureofsilicabroadensenergylevelsintobands.Semiconductorlasersat980and1480nmusedmostcommonly.30dBgainobtainedwithonly10-15mWofabsorbedpumppower.Pumpingefficiencyupto11dB/mWpossibleat980nm.Pumpingat1480nmrequireslongerfibersandhigherpowers.9/27/202331TheSch.OfInformationEngineering,WHUTAmorphousnatureofsilicabro9/27/202332TheSch.OfInformationEngineering,WHUT8/5/202332TheSch.OfInformat11.11.2Gainspectrum9/27/202333TheSch.OfInformationEngineering,WHUT11.11.2Gainspectrum8/5/20233Shapeofgainspectrumaffectedbyothercodopantssuchasgermaniaandalumina.Structuraldisordersofsilicaleadtoinhomogeneousbroadening.Starksplittingleadstohomogeneousbroadening.Effectivegainspectrum:isthedistributionfunctionwhoseformalsodependsonthepresenceofotherdopantswithinthefibercore.9/27/202334TheSch.OfInformationEngineering,WHUTShapeofgainspectrumaffecteNonuniformgainover1525-1565range.Again-flatteningfilterusedinpractice.Thegainspectrumofaluminosilicateglasseshasroughlyequalcontributionsfromhomogeneousandinhomogeneousbroadeningmechanisms.ThegainbandwidthofsuchEDFAstypicallyexceeds35nm.9/27/202335TheSch.OfInformationEngineering,WHUTNonuniformgainover1525-156511.11.3Amplifiercharacteristics9/27/202336TheSch.OfInformationEngineering,WHUT11.11.3AmplifiercharacteristL=10-15menoughtoprovide20-30dBgain.Foragivenpumppower,Gbecomesmaximumatanoptimumvalue

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