Low-noise-figure photonic links without pre-amplification

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1、Low-Noise-FigurePhotonicLinkswithoutPre-amplificationEdwardI.Ackerman,GaryE.Betts,WilliamK.Burns,CharlesH.Cox,MaryR.Phillips,andHaroldRoussellPhotonicSystems,Inc.,Billerica,MA01821Abstract-Usingopticalfibertoretrievesignalsfromremotelink’sinputandoutputports(bothusually50),inser

2、tingsensorshasseveraladvantagescomparedtoremotingbymeansthesematchingcircuitswillincreasethelink’samplifierlessofmetallicwaveguidessuchascoaxialcable.Fiber-opticgain[1–5].InFig.1thefivelinksthatbenefitedfromtheretrievalofanRFsignalcanbeachievedbydown-convertinginsertionofresonant

3、impedancematchingcircuitsareshownanddigitizingthesignalforconveyancebyadigitalfiber-opticusingredlines.Insomeoftheselinksresonantimpedancelink,oritcanbeachievedbyconveyingtheRFsignaloveranmatchingwascombinedwithoneoftheotherfouranalogfiber-opticlinkbeforedigitization.Thelatterapp

4、roachtechniqueswedescribe.canberealizedwithaminimumofhardwareanddcpowerrequiredatthesensingsite,providedthattheanalogfiber-opticlinkhasasufficientlylownoisefigurewithoutapre-amplifier.III.REFLECTIVEEXTERNALMODULATOREarlydemonstrationsof"amplifierless"analogfiber-opticMach-Zehnder

5、modulator-basedexternalmodulationlinklinkstypicallyreportedveryhighnoisefigures—inexcessof30dB.Inthelastdecadeorso,severaltechniqueshavebeengainisinverselyproportionaltothesquareofthedevelopedtoimprovethissituation.Wedescribefivesuchmodulator’shalfwavevoltageV.Intwolinksreported

6、techniquesandshowthattheyhaveresultedinmuchlowerhere[5,6],Vwasreducedbyafactoroftwobyusingameasurednoisefiguresforamplifierlesslinks.Onetechnique,reflectivedesignthatdoubledthedurationofinteractionforexample,hasyieldednoisefigures<5dBforamplifierlessbetweentheopticalcarrierandmi

7、crowavemodulationlinksatfrequenciesofupto10GHz.Theexistenceofsignal.InFig.1thetwolinksthatbenefitedfromtheuseofamplifierlesslinkswithsuchlownoisefiguresmayenableareflectiveexternalmodulatorareindicatedbyR’sateitherremotesensingofsignalsinsituationswherethesize,weight,endoftheplot

8、tedlines.andpower(SWAP)oftheremotehardwa