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,anditszerodispersionislocatedat1.3Inthelowlossareaofumwindow,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
Technicalparameters | 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.