Single mode fiber

Introduction

Theexplanationof"single-modefiber"inacademicliterature:Generally,whenvislessthan2.405,onlyonewavecrestpassesthroughthefiber,soitiscalledsingle-modefiber.ItscoreThesubisverythin,about8-10microns,andthemodaldispersionisverysmall.Themainfactorsaffectingthewidthoftheopticalfibertransmissionbandarevariousdispersions,andthemodaldispersionisthemostimportant.Thedispersionofsingle-modefibersissmall,sothelightcanbeverywide.Thefrequencybandtransmitsverylongdistances.

Thesingle-modefiberhasacorediameterof10micron,whichcanallowsingle-modebeamtransmissionandcanreducethebandwidthandmodaldispersionlimitations.However,duetothesmallcorediameterofthesingle-modefiber,Itisdifficulttocontrolthebeamtransmission,soanextremelyexpensivelaserisrequiredasthelightsource.Themainlimitationofthesingle-modeopticalcableisthematerialdispersion.Thesingle-modeopticalcablemainlyusesthelasertoobtainhighfrequencybandwidth,andbecausetheLEDwillissuealargenumberofdifferentbandwidthsTherefore,thematerialdispersionrequirementsareveryimportant.

Comparedtomulti-modefiber,single-modefibercansupportlongertransmissiondistance.In100MbpsEthernetor1GGigabitnetwork,single-modefibercansupporttransmissiondistanceofmorethan5000m.

Fromacostpointofview,sincetheopticaltransceiverisveryexpensive,thecostofusingsingle-modefiberwillbehigherthanthatofmulti-modefiberopticcable.

SingleModeFiber(SMF)

Comparedwithmultimodefiber,single-modefiberhasamuchthinnercorediameter,only8-10μm.Becauseonlyonemodeistransmitted,thereisnointer-modedispersion,thetotaldispersionissmall,andthebandwidthiswide.Single-modefiberisusedinthe1.3-1.6μmwavelengthregion.Throughappropriatedesignofthefiberrefractiveindexdistribution,andselectionofhigh-puritymaterialstoprepareacladdingthatis7timeslargerthanthecore,thelowestlossandMinimumdispersion.

Single-modeopticalfiberisusedinlong-distance,large-capacityopticalfibercommunicationsystems,opticalfiberlocalareanetworksandvariousopticalfibersensors.

Classification

652single-modefiber

Thesingle-modefiberthatmeetstherequirementsofITU-TG652isoftencallednon-dispersionshiftedfiber,anditszerodispersionislocatedat1.3Inthelowlossareaof​​umwindow,theworkingwavelengthis1310nm(lossis0.36dB/km).Mostofthefiberopticcablesthathavebeenlaidinourcountryareofthistypeoffiber.Withthesuccessfuladvancementofthefiberopticcableindustryandsemiconductorlasertechnology,theworkingwavelengthofthefiberopticlinecanbetransferredtoalowerloss(0.22dB/km)1550nmfiberwindow.

653single-modefiber

Single-modefiberthatmeetstherequirementsofITU-TG653,oftencalleddispersion-shiftedfiber(DSF=DispersionShifledFiber),itszero-dispersionwavelengthshiftstolossVerylow1550nm.Thiskindofopticalfiberhasbeenpromotedandusedinsomecountries,especiallyinJapan,andithasalsobeenadoptedontheBeijing-Kowloontrunklineinmycountry.AmericanAT&TearlydiscoveredthatDSFhadseriousshortcomings.Theharmfulfour-wavemixingandotherfibernonlineareffectsexistedinthelowdispersionregionnear1550nm,whichhinderedtheapplicationoffiberamplifiersinthe1550nmwindow.However,inJapan,theuseofdispersioncompensationtechnology*inG.653single-modeopticalfiberlinescanstillsolvetheproblem,andthereisnoJapaneseG.655opticalfiber,whichseemstobeamystery.

655single-modefiber

Thesingle-modefiberthatmeetstherequirementsofITU-T.G.655isoftencallednon-zerodispersionshiftedfiberorNZDSF(=NonZeroDispersionShiftedFiber).Itisadispersion-shiftedfiber,butthedispersionisnotzeroat1550nm(accordingtoITU-TG655,thecorrespondingdispersionvalueinthewavelengthrangeof1530-1565nmis0.1-6.0ps/nm*km),whichisusedtobalancefour-wavemixing,etc.Non-lineareffects.CommercialfibersincludeAT&T'sTrueWavefiber,Corning'sSMF-LSfiber(withatypicalzero-dispersionwavelengthof1567.5nmandatypicalzero-dispersionvalueof0.07ps/nm2*km)andCorning'sLEAFfiber.mycountry's"Dabaoshi"opticalfiber,etc.

Maindifferences

ThesearethestandardtypesofopticalfibersspecifiedbytheITU:

G.651isamultimodeopticalfiber.

G.652isaconventionalsingle-modefiberwithazero-dispersionpointat1300nm,wherethedispersionisthesmallest;atthesametime,itisdividedintoG.652A,B,C,andDaccordingtoPMD.

G.653isadispersion-shiftedfiber(DSF),with1550nmasthezerodispersionpoint.Theprincipleistoperformdispersiontranslationthroughwaveguidedispersion,sothatlowlossandzerodispersionareatthesameoperatingwavelength.Butatthesametime,zerodispersionisnotconducivetomulti-channelWDMtransmission,becausewhenthenumberofmultiplexedchannelsislarge,thechannelspacingissmall,thenanonlinearopticaleffectcalledfour-wavemixing(FWM)willoccur.Theeffectmixestwoorthreetransmissionwavelengths,generatingnewandharmfulfrequencycomponents,leadingtocrosstalkbetweenchannels.Ifthedispersionoftheopticalfiberlineiszero,theinterferenceofFWMwillbeveryserious;ifthereisasmallamountofdispersion,theinterferenceofFWMwillbereduced.Inresponsetothisphenomenon,scientistshavedevelopedanewtypeofopticalfiber,NZ-DSF.

G.654opticalfiberisanultra-lowlossopticalfiber,mainlyusedfortransoceanicopticalcables.Itscoreispuresilica,whileordinaryopticalfibercoresneedtobedopedwithgermanium.Thelossnear1550nmisthesmallest,only0.185dB/km,butthedispersioninthisregionisrelativelylarge,about17-20ps/[nm*km],andthedispersioniszerointhe1300nmwavelengthregion.

G.655fiberisanon-zerodispersionshiftedfiber(NZ-DSF),dividedinto655A,B,C,themainfeatureisthatthedispersionof1550nmisclosetozero,butnotzero.Itisanimproveddispersion-shiftedfibertosuppressfour-wavemixing.

G.656fiberisthefutureguidingfiber.TheworkingwavelengthofG656hasbeensignificantlyincreased,includingS,CandLbands(1460to1625nm).

G.657opticalfiber,theInternationalTelecommunicationUnionITU-TissuedinDecember2006thestandardrecommendationof"CharacteristicsofBendLoss-InsensitiveSingleModeOpticalFiberandOpticalCableforAccessNetworks",namelyG.657Opticalfiberstandards.G.657opticalfiberisdividedintotypeAandtypeBfibers.Atthesametime,accordingtotheprincipleofminimumbendradius,thebendinggradeisdividedintothreegrades,1,2,and3,ofwhich1correspondstotheminimumbendingradiusof10mm,and2correspondsto7.5.mmminimumbendingradius,3correspondsto5mmminimumbendingradius.Combiningthesetwoprinciples,theG.657fiberisdividedintofoursub-categories,G.657.A1,G.657.A2,G.657.B2andG.657.B3.

Differences

1,single-modetransmissiondistanceislong

2,multi-modetransmissionbandwidthislarge

3,single-modedoesnothappenDispersion,reliablequality

4.Single-modeusuallyuseslaserasalightsource,whichisexpensive,whilemulti-modeusuallyusescheapLED

5.Single-modeismoreexpensive

6.Multi-modeischeap,andshort-distancetransmissionispossible.

Parametercomparison

TechnicalparametersSingle mode fiber

G.655

G.652

Workingwavelength(nm)

1530-1565

1310

1550

Attenuation(dB/km)

≤0.22

≤0.36

≤0.22

Zerodispersionwavelength(nm)

1300-1324

Zerodispersionslope(ps/nm2*km)

0.045-0.1

0.093

Dispersion(ps/nm*

km)

1≤|D|≤6

3.5

18

Dispersionrange(nm)

1530-1565

1288-1339

1550

PolarizationModeDispersion(ps/√km)

Singledisk:≤0.125link(≥20diskopticalcable):≤0.10

Singledisk:≤0.20link(≥20opticalcables):≤0.15

Opticaleffectivearea(m2)

55-85

80

Modefielddiameter(m)

8.0~11.0

8.8~9.5

10.5

Bendingcharacteristics(dB)

1.0

0.5

0.5

ItcanbeseenfromtheparametersinthetablethattheattenuationofthetwoopticalfibersThecoefficientisnotmuchdifferent.ThedispersioncoefficientofG.652fiberis18ps/nm*kmat1550nmwavelength.Whentransmitting10Gb/sTDMandWDMsystems,inordertoincreasetherelaydistance,itisnecessarytointervenethefiberwithnegativedispersioncoefficient.Performdispersioncompensation.G.655fiber1530-1560nmwavelengthregiondispersionisusually1.0-6ps/nm*km,whentransmittingthesame10Gb/ssystem,becausethedispersionisverylow,thereisnoneedtotakedispersioncompensationmeasures;butG.655fiberisat1550nmThedispersionissmaller,anditsnonlineareffectislargerthanthatofG.652fiber.TherecommendedPMDindexofG.652andG.655fiberisthesame.Inactualtest,thePMDindexofG.655fiberissmallerthanthatofG.652fiber.Atpresent,thepriceofG.655fiberisrelativelyhigh,anditsmarketpriceisabouttwicethatofG.652fiber.Theengineeringapplicationsofthetwoopticalfibersarelistedinthetablebelow.

Useopticalfibertype

Transmit2.5Gb/sTDMandWDMsystem

Transmit10Gb/sTDMandWDMsystem

G.652

satisfy

satisfy,butDispersioncompensationmeasuresarerequired

G.655

Satisfy

Satisfy

ThecomparisoninthetableshowsthatfortransmissionFor2.5Gb/sTDMandWDMsystems,bothtypesofopticalfibercanmeettherequirements.Forthetransmissionof10Gb/sTDMandWDMsystems,G.652opticalfiberneedstotakedispersioncompensationmeasures,anditisnecessarytoperformPMDtestingonthelaidopticalcables.Onlywhentherequirementsaremet,canthe10Gb/s-basedtransmissionsystembeopened..G.655fiberdoesnotrequirefrequentdispersioncompensationmeasures,butthefiberpriceisrelativelyhigh.

Developmentprocess

In1980,wheninternational,includingChinesescholars,werediscussingwhichisbetter,single-modefiberormulti-modefiber,AcademicianHuangHongjiaofShanghaiUniversityofScienceandTechnologyrealizedLong-wavelengthsingle-modefiberhastheadvantagesoflowlossandsmalldispersion,andisanidealmediumforlong-distancelarge-capacitycommunicationsystems.AresearchgroupheadedbyAcademicianHuangHongjiaputforwardaproposalforsingle-modefiberresearchin1979.ThisproposalwassupportedbytheShanghaiMunicipalScienceandTechnologyCommission,andlisted"SingleModeOpticalFiberResearch"asakeyscientificresearchprojectinShanghai.ThesecondphaseoftheresearchworkwascarriedoutinMay1982.WiththecollaborationbetweenShanghaiUniversityofScienceandTechnologyandShanghaiQuartzGlassFactory,ithasreceivedsupportandcooperationfromthe23rdInstituteofElectronics.InMay1982,theShanghaiMunicipalScienceandTechnologyCommissionpresidedovertheappraisalworkinvolving24expertsfrom9unitsinChina.TheAppraisalCommitteebelievesthat"thissingle-modeopticalfiberscientificresearchworkisfundamentalandpioneering.ItnotonlyfillsthegapinthisimportantresearchfieldinChina,butalsocatchesupwiththeinternationallevelatarelativelyfastspeed."

Characteristicparameters

①Attenuationcoefficienta:Itsprovisionsandphysicalmeaningsareexactlythesameasthoseofmultimodefibers,soIwon’tdescribethemhere.②DispersioncoefficientD(λ):Wealreadyknowthatthedispersionofopticalfibercanbedividedintothreeparts,namelymodaldispersion,materialdispersionandwaveguidedispersion.Forsingle-modefiber,becauseoftherealizationofsingle-modetransmission,thereisnoproblemofmodaldispersion,soitsdispersionismainlymanifestedinmaterialdispersionandwaveguidedispersion(collectivelycalledintra-modedispersion).Consideringthematerialdispersionandwaveguidedispersionofasingle-modefiber,collectivelyreferredtoasthedispersioncoefficient.Thedispersioncoefficientcanbeunderstoodlikethis:thepulsebroadeningvalueperkilometeroffiberduetotheunitspectralwidth.Therefore,thepulsebroadeningvalueofLkmfibercausedbychromaticdispersionis:σ=δλ·D(λ)·L(2.17)where:δλisthespectralwidthofthelightsourceandσistherootmeansquarebroadeningvalue.Thesmallerthedispersioncoefficient,thebetter.Thesmallerthedispersioncoefficientoftheopticalfiber,thelargerthebandwidthcoefficient,thatis,thelargerthetransmissioncapacity.Forexample,CCITTrecommendsthatthedispersioncoefficientofasingle-modefiberatawavelengthof1.31micronsshouldbelessthan3.5ps/km.nm.Aftercalculation,itsbandwidthfactorisabove25000MHz·km,whichismorethan60timesthatofmultimodefiber(thebandwidthfactorofmultimodefiberisgenerallybelow1000MHz·km).

③Modefielddiameterd:Themodefielddiametercharacterizesthedegreeofconcentrationoflightenergyinasingle-modefiber.Sinceonlythefundamentalmodeistransmittinginthesingle-modefiber,roughlyspeaking,themodefielddiameteristhediameterofthefundamentalmodespotonthereceivingendfaceofthesingle-modefiber(infact,thefundamentalmodelight

hasnospotClearboundaries).Itcanbeveryroughlyconsidered(notstrictlyspeaking)thatthemodefielddiameterdissimilartothecorediameterofasingle-modefiber.④Cut-offwavelengthλc:WeknowthatwhenthenormalizedfrequencyVofthefiberislessthanitsnormalizedcut-offfrequencyVc,single-modetransmissioncanberealized,thatis,onlythefundamentalmodeistransmittinginthefiber,andtheotherhigh-ordermodesareallcutoff.Inotherwords,inadditiontotheparametersofthefibersuchasthecoreradius,thenumericalaperturemustmeetcertainconditions,andtoachievesingle-modetransmission,thewavelengthofthelightmustbegreaterthanacertainvalue,thatis,λ≥λc.Thisvalueiscalledthecut-offofthesingle-modefiber.wavelength.Therefore,thecut-offwavelengthλcmeanstheminimumworkinglightwavewavelengththatenablestheopticalfibertoachievesingle-modetransmission.Inotherwords,althoughotherconditionsaremet,ifthewavelengthofthelightwaveisnotgreaterthanthecut-offwavelengthofthesingle-modefiber,itisstillimpossibletoachievesingle-modetransmission.

5.ReturnLoss---ReturnLoss:ReturnLossisalsocalledreturnloss.Itreferstothedecibelsoftheratiooftheback-reflectedlighttotheinputlightattheopticalend.Thegreaterthereturnloss,thegreaterthereturnloss.Goodtoreducetheimpactofreflectedlightonthelightsourceandthesystem.

Theopticaldeviceusedinsingle-modetransmissionequipmentisLD,whichisusuallydividedintotwowavelengths:1310nmand1550nmaccordingtothewavelength.Accordingtotheoutputpower,itcanbedividedintoordinaryLD,high-powerLD,DFB-LD(distributedFeedbackopticaldevice).Themostcommonfiberusedforsingle-modefibertransmissionisG.652,whichhasawirediameterof9microns.

FiberWavelength

Whenthelightof1310nmwavelengthistransmittedonG.652fiber,itistheattenuationfactorthatdeterminesthetransmissiondistancelimit;becauseatthewavelengthof1310nm,thefibermaterialdispersionandThestructuraldispersioncancelseachotherout,andthetotaldispersionis0,andtheopticalsignalwithasmallamplitudeatthe1310nmwavelengthcanrealizebroadbandtransmission.

Whenthelightof1550nmwavelengthistransmittedonG.652fiber,theattenuationfactorisverysmall.Consideringtheattenuationfactoronly,thedistanceoflightof1550nmwavelengthunderthesameopticalpowerisgreaterthanthatoflightof1310nmwavelength.Transmissiondistance,buttheactualsituationisnotthecase.Therelationshipbetweenthesingle-modefiberbandwidthBandthedispersionfactorDis:B=132.5/(Dl*D*L)GHz

whereListhelengthofthefiber,DlIsthespectrallinewidth.Forlightwithawavelengthof1550nm,thedispersionfactoris20ps/(nm.km)asshowninTable3.Assumingthatthespectralwidthisequalto1nmandthetransmissiondistanceisL=50kilometers,thenthereis:B=132.5/(D*L)GHz=132.5MHz

Applicationsituation

Introduction

Becausethecurrentopticalfibermostlyusesplasticasthecore.Thecostisalreadyverylow.Forexample,thefour-coresingle-modefibersoldonthemarketisonly2to3yuan/m

andthepriceofsingle-mode/multi-modefibertransceiversisalsobetween300-500.Soitsapplicationcostisverylow.,

Inthepast,ourtraditionalconceptwhenbuildingnetworkswasthatLANsonlyusetwisted-paircables,andopticalfibersareonlyusedwhenconnectingtotheInternetatahighspeed.SomeenterprisesorfactoriesandmineshavelargeLANsandarestabletothenetwork.Theperformancerequirementsarehigher.Herewerecommendtheuseofopticalfiber.Thecostofusingopticalfiberisnotmuchhigherthanthatofusingup-to-standardCategory5twistedpair.Andyoudon’thavetoworryaboutlightningstrikes,andyoudon’tneedtoconsidertheeffectivedistanceoftheLAN.Youcanrefertoitinyourfuturework.

Relatedreading:"Opticalfibernetworkingisnotfarfromyou,examplesexplaintheapplicationofopticalfiberLAN"

ProductSelectionGuide

Nominalcorewireofsingle-modeopticalfiberThediameterspecificationis(8~10)μm/125μm.Specifications(numberofcores)are2,4,6,8,12,16,20,24,36,48,60,72,84,96cores,etc.Theoutersheathmaterialofthecablehasordinarytype;ordinaryflameretardant;low-smokehalogen-freetype;low-smokehalogen-freeflame-retardanttype.

Whentheuserhasconfidentialityrequirementsforthesystemanddoesnotallowthesignaltobetransmittedoutside,orthesystememissionindexcannotmeettherequirements,shieldedcoppercorepaired-paircablesandshieldedwiringequipmentshouldbeused,oranopticalcablesystemshouldbeused.

Keypointsofconstructionandinstallation

Becausethecoreoftheopticalfiberismadeofquartzglass,itisveryeasytobreak.Therefore,theminimumbendingradiusmustnotbeexceededduringconstruction.Secondly,thetensilestrengthofopticalfiberislowerthanthatofcables,sowhenoperatingopticalcables,itisnotallowedtoexceedthetensilestrengthofvarioustypesofopticalcables.Afterthefiberopticcableislaid,bundlethefiberopticcabletogetherintheequipmentroomandthefloorwiringroom,andthenperformthefiberopticconnection.Theopticalfiberterminationdevice(OUT),opticalfibercoupler,andopticalfiberconnectorpanelcanbeusedtoestablishmodularconnections.Whenthelayingoftheopticalcableiscompletedandtheinterconnectionmoduleisestablishedintheproperposition,theopticalfiberconnectorcanbeaddedtotheendoftheopticalfiberandtheopticalfiberconnectioncanbeestablished.

Forothers,pleaserefertotherequirementsin"CodeforAcceptanceofBuildingsandBuildingsIntegratedWiringSystemEngineering"GB/T50312-2000and"CodeforConstructionandAcceptanceofBuildingsandBuildingsIntegratedWiringSystemEngineering"CECS89:97.

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