Classification
Therearebasicallytwotypesofmultimodefibers, oneisgradedandtheotherisstepped.Forgradedfibers, Inotherwords, therefractiveindexofthecoreisthesmallestattheperipheryofthecoreandgraduallyincreasestowardthecenterpoint, therebyreducingthemodaldispersionofthesignal.Forsteppedindexopticalcables, therefractiveindexisbasicallynotaverage.Change, andonlyonthesurfaceofthecladdingwillitsuddenlydecrease.Steppedfibersgenerallyhavealowerbandwidththangradedfibers.Innetworkapplications, themostpopularmultimodefiberis62.5 / 125,62.5 / 125meansthatthefibercorediameteris62.5μmandthecladdingdiameteris125μm, andtheothermorecommononesare50 / 125and100 / 140.
Comparaison
Par rapport à la paire torsadée, la fibre multimode peut prendre en charge une distance de transmission plus longue. Dans Ethernet 10 Mbps et 100 Mbps, la fibre multimode peut prendre en charge jusqu'à 2 000 mètres.
Guide de sélection
Le diamètre nominal du fil central de la fibre multimode est de 62,5 μm/125 μm ou de 50 μm/125 μm. type sans fumée d'halogène ; type ignifuge sans halogène à faible dégagement de fumée.
Potentiel d'application
Le marché des années 1990
Dans les années 1990, la fibre optique multimode a toujours détenu une part stable du marché mondial de la fibre optique.
Après la montée dans les années 1970
Inthe1970s, opticalfiberenteredthepracticalstagefromtheinterofficerelayofmultimodeopticalfiber.Overthepasttwodecades, newvarietiesofsingle-modeopticalfibershavecontinuedtoappear.Thefunctionsofopticalfibershavebeencontinuouslyenrichedandenhanced, andtheperformance-priceratiohascontinuedtobedemanding.However, multi-modeopticalfibershavenotbeenreplacedbuthavealwaysmaintainedastablemarketshareanddevelopedsimultaneouslywithothervarieties.Thereasonisthatthecharacteristicsofmultimodefiberjustmeettherequirementsofnetworkfiber.Comparedwithlong-distancetrunklines, thecharacteristicsofopticalfibernetworksare: relativelylowtransmissionrate; relativelyshorttransmissiondistance; morenodes, morejoints, andmorebends; largeamountofconnectorsandcouplers, à petite échelle, andthenumberoflightsourcesusedperfiberlengthmany.
Caractéristiques
Thelowtransmissionrateandshorttransmissiondistancecanjusttakeadvantageofthecharacteristicsofmultimodefiberbandwidthandtransmissionlossnotasgoodassinglemodefiber.Butsingle-modefiberischeaperandhasbetterperformancethanmulti-modefiber.Whyissingle-modefibernotusedinthenetwork Thisisbecauseintheabove-mentionednetworkcharacteristics, thelossofmultiplebendsislarge;? Thenumberofnodesmeansthattheopticalpowersplitsfrequently, whichrequiressufficientopticalpowertransmissioninsidetheopticalfiber.Multi-modefiberhasalargercorediameterandlargernumericalaperturethansingle-modefiber, andcancouplemoreopticalpowerfromthelightsource.Theamountofconnectorsandcouplersinthenetworkislarge.Single-modeopticalfiberpassivecomponentsaremoreexpensivethanmulti-modeopticalfibers, andarerelativelypreciseandhavesmalltolerances.Theoperationisnotasconvenientandreliableasmulti-modecomponents.Single-modefibercanonlyuselaser (LD) comme source de lumière, et son coût est beaucoup plus élevé que celui des diodes électroluminescentes (DEL) utilisées dans la fibre multimode. r, thenetworkscaleissmall, andthenumberoflightsourcesusedperunitfiberlengthislarge.Onelightsourcemaybeusedforseveralhundredkilometersinthetrunkline, andeachnetworkofmorethantenkilometersorevenafewkilometershasitsownindependentlightsource.Ifthenetworkusessingle-modefiberwithlasers, theoverallnetworkcostwillbegreatlyincreased.Theverticalcavitysurfaceemittinglaser (VCSEL) hasbeencommerciallyavailable, anditspriceisclosetothatofLEDs.ItscircularbeamsectionandhighmodulationratejustcompensatefortheshortcomingsofLEDs, andmaketheapplicationofmultimodefiberinthenetworkmorevigorous.Itisnotdifficulttoseefromtheaboveanalysisthatitisnotcomprehensivetoconsiderthatsingle-modefiberhashighbandwidthandlowloss, andcanbeusedinthenetwork "onceinplace" .Corninghascalculatedandcomparedthesystemcostofusingsingle-modefiberandmulti-modefiberinthenetwork.Thecostofusingsingle-modefiberisfourtimesthatofmulti-modefiber.Thesystemcostofusing62 .5μmet50μmfibremultimodesontidentique,ladifférence résidedanslesdifférentstypesdeconnecteurs. Le coût du système de connecteur enfichable à virole non métallique (système multimode B) peut être réduit de 1/2 par rapport au connecteur avec une connexion à vis à virole métallique, comme le type FC (système multimode A).
Augmenter
Inordertomeettheneedsofnetworkcommunication, fromthelate1970stotheearly1980s, countriesvigorouslydevelopedlargecorediameterlargenumericalaperturemulti-modeOpticalfiber (alsoknownasdataopticalfiber) .Atthattime, theInternationalElectrotechnicalCommissionrecommendedfourgradedindexmultimodefiberswithdifferentcore / cladsizes, namelyA1a, A1b, A1candA1d.Theircore / claddingdiameter (pm) /numericalapertureare50/125/0.200,62.5/125/0.275,85/125/0.275and100/140 /0.316,respectively.Generallyspeaking,alargecore/packagesizeresultsinhighproductioncosts,poorbendingresistance,andanincreaseinthenumberoftransmissionmodulesandadecreaseinbandwidth.Inadditiontotheaboveshortcomingsof100/140μmmultimodefiber,itscladdingdiameteristoolarge,whichdoesnotmatchthetestequipmentandconnectingdevices,andwillnotbeusedindatatransmissionsoon,butisonlyusedforspecialoccasionssuchaspowertransmission.The85/125μmmultimodefiberhasbeengraduallyeliminatedduetosimilarreasons.TheIEC"SC"86A"GW1expertgroupmeetingheldinKyoto,JapaninOctober1999revis edthemultimodeopticalfiberstandard.InthereviseddraftpublishedinMarch2000, the85 / 125μmmultimodeopticalfiberhasbeencancelled.The50 / 125μmmultimodefiberdevelopedbyCorningin1976andthe62.5 / 125μmmultimodefiberdevelopedbyLucentBellLabsin1983havethesameouterdiameterandmechanicalstrength, buthavedifferenttransmissioncharacteristics.Theyhavealwaysbeen indatacommunicationnetworks "compétitifs". ".
Avantages
62.5μmcorediametermultimodefiberhaslargercorediameterandhighernumericalaperturethan50μmcorediametermultimodefiber, whichcanbecoupledfromLEDlightsourceMoreopticalpower, sothe62.5 / 125μmmultimodefiberwasfirstadoptedbytheUnitedStatesasanumberofindustrystandards.SuchasAT & T'sindoorwiringsystemstandard, AmericanElectronicsIndustryAssociation (EIA) LANstandard, AmericanNationalStandardsInstitute (ANSI) 100Mb / stokennetworkstandard, IBM'scomputeropticalfiberdatacommunicationstandard, etc.50 / 125μmmultimodefiberismainlyusedasadatacommunicationstandardinJapanandGermany, andithasahistoryof18years.However, duetothelargeamountofopticalfiberinNorthAmericaandtheleadingroleofopticalfibermanufacturingandapplicationtechnologyintheUnitedStates, mostcountries, includingmycountry, use62 .Depuislemilieudesannées80,lafibreoptique62,5/125μmestpresquedevenuleproduitprincipaldumarchédelafibreoptiquedecommunicationdedonnées.
Suivi du développement
Theabovesituationwasmaintaineduntilthemidtolate1990s.Inrecentyears, withthecontinuousupgradeofthetransmissionrateofthelocalareanetwork, the50μmcorediametermultimodefiberhasattractedmoreandmoreattention.Since1997, thelocalareanetworkhasdevelopedto1Gb / s, andthebandwidthofseveralhundredmegabytesof62.5 / 125μmmultimodefiberwithLEDasthelightsourceobviouslycannotmeettherequirements.Comparedwith62.5 / 125 pm, 50 / 125μmfiberhassmallernumericalapertureandcorediameter, anditsbandwidthishigherthanthatof62.5 / 125μmfiber, andtheproductioncostcanbereducedby1 / 3.Therefore, industriesinvariouscountrieshaveproposedtore-enAble50 / 125μmmultimodefiber.Afterresearchanddemonstration, l'International Organization for Standardization a formulé des normes correspondantes. Cependant, étant donné qu'un nombre considérable de fibres multimodes 62,5/125 μm ont été installées et utilisées dans les réseaux locaux par le passé, la norme IEEE802.3zGigabit Ethernet stipule que les fibres multimodes 50/125 μm et 62,5/125 μm peuvent être utilisées comme Ethernet de transmission. fornewnetworks, 50 / 125μmmultimodefiberisgenerallypreferred.There-launchof50 / 125μmmultimodefiberhaschangedthesituationwhere62.5 / 125μmmultimodefiberdominatesthemultimodefibermarket.Followingthesestandards, CorningannouncedthelaunchoftwonewmultimodefibersinSeptember1998.ThefirsttypeisInfiniCor300, accordingtothe62.5 / 125μmstandard, itcantransmit300metersatawavelengthof850nmand550metersatawavelengthof1300nmatarateof1Gb / s.ThesecondistheInfiniCor600type.Accordingtothe50 / 125μmstandard, atarateof1Gb / s, both850nmand1300nmwavelengthscantransmit600meters.
Impactdelalibération
AlthoughthenewlyreleasedIEEE802.3zstandardin1998proposedaspecificationfortheuseofmultimodefiberin1Gbit / snetworks, Thedevelopmentofnetworkupgradesisfasterthantheformulationofstandards.Thismakesthebandwidthlimitationof62.5 / 125μmmultimodefibermoreprominent.Inordertosolvethisproblem, suchasCorning'sInfiniCorCL1000andInfiniCorCL2000, Lucent'sLazr VITESSE, Alcatel'sGIGAliteandsoon.Corningsaidinthereleaseofthisopticalfiber: "Corningusesskilledtechnologyandnewrefractiveindexdistributioncontroltointroducethistypeofcharacteristicsthatonlysingle-modeopticalfibercanprovidebeforeandcanbeusedinthenetwork.Costsystem."
Lanouvellegénérationdefibreoptiquemultimode
Onthebasisoftheabovebackground, majorcompaniessuchasCorningandLucentoftheUnitedStateshaveproposed "Thenewgenerationofmultimodeopticalfiber" concept.ThestandardofthenewgenerationofmultimodeopticalfiberisbeingresearchedanddraftedbytheInternationalOrganizationforStandardization / InternationalElectrotechnicalCommission (ISO / IEC) andtheUnitedStatesTelecommunicationsIndustryAssociation (TIA-Tr42) .ItisexpectedtobelaunchedfromMarchtoApril2002.Anewgenerationofmultimodeopticalfiberwillalsobeusedasthetransmissionmediumof10Gb / sEthernetandbeincludedintheIEEE10Git / sEthernetstandard.TheEnglishabbreviation "NGMMF" (NewGenerationMultiModeFiber) forthenewgenerationofmultimodefiberhasbeenusedinternationallyandcanbeusedasakeywordtosearchoninternationalwebsites.Thecomprehensivetechnicalindicatorsofthenewgenerationofmultimodeopticalfiberhavenotbeenofficiallyannounced, butthefollowingexactinformationcanbeobtainedfromtherelevantreportsofthestandardformulationandrelatedtechnicalwebsites:
Taper
ThenewgenerationofmultimodeThefiberisa50 / 125μmmultimodefiberwithagradedrefractiveindexprofile.The50μmcorediameterisusedbecausethenumberoftransmissionmodesinthisfiberisapproximately1 / 2.5ofthatina62.5μmmultimodefiber.Thiscaneffectivelyreducethemodaldispersionofthemultimodefiberandincreasethebandwidth.For850nmwavelength, thebandwidthof50 / 125μmcomparedto62.5 / 125μmmultimodefibercanbeincreasedthreetimes.AccordingtotheIEEE802.3zstandardrecommendation, atarateof1Gbit / s, a62.5μmcorediametermultimodefibercanonlytransmit270meters; anda50μmcorediametermultimodefibercantransmit550meters.Infact, recentexperimentshaveconfirmedthatusing850nmverticalcavitysurfaceemittinglaser (VCSEL) asthelightsource, atarateof1Gbit / s, astandardmultimodefiberwithacorediameterof50μmcantransmit1750meterswithouterror (5pairesdeconnecteursdanslaligne).Unenouvellegénérationdefibremultimodeavecundiamètrecœurde50μmpeuttransmettre2000mètressanserreur(2pairesdeconnecteurssontinclusdanslaligne).
Anotherreasonforadoptingacorediameterof50μmisthattheadvantagesofmultimodefiberwithacorediameterof62.5μmhavebecomeirrelevantwiththeadvancementoftechnology.Intheearlyandmid années 1980, theoutputpoweroftheLEDlightsourcewaslow, thedivergenceanglewaslarge, andtheconnectorlosswaslarge.Itisnecessarytoconsidertheuseoffiberswithlargecorediameterandnumericalaperturetoinjectasmuchopticalpoweraspossible.Atthattime, nooneseemedtothinkthattherateoftheLANmightexceed100Mbit / s, thatis, thebandwidthperformanceofmultimodefiberwasnotoutstanding, especiallywhenVCSELwasused, opticalpowerinjectionwasnolongeraproblem.Thecorediameterandnumericalaperturearenolongerasimportantasbefore, andthetransmissionrateof10Gbit / shasbecomethemaincontradiction.The50μmcorediametermultimodefiberthatcanprovidehigherbandwidthisfavored.
Source de lumière
Inthepast, traditionalmulti-modefiberopticnetworksusedlight-emittingdiodes (LED) aslightsources.Thisisaneconomicalandreasonablechoiceinlow-speednetworks.However, thediodeemitslightbyspontaneousemission, andthelaseremitslightbystimulatedemission.Thecarrierlifeoftheformerislongerthanthatofthelatter.Therefore, themodulationrateofthediodeislimitedandcannotbeusedinagigabitratioandabovenetworks.Inaddition, comparedwithalaser, adiodehasalargerbeamdivergenceangleandawiderspectralwidth.Afterinjectingthemultimodefiber, morehigh-ordermodesareexcited, andmorewavelengthcomponentsareintroduced, whichreducesthefiberbandwidth.Fortunately, the850nmverticalcavitysurfaceemittinglaser (VCSEL) Non seulement le laser mentionné ci-dessus a des avantages en tête, mais le prix est fondamentalement le même que celui de la LED. dpourlafibremultimode.Acettelongueurd'onde,desdétecteursausiliconepeu coûteuxpeuventêtreutilisésetontunebonneréponsehautefréquence;unautreavantageremarquableestqueleprocessusdefabricationVCSELpeutcontrôlerfacilementladistributiondelapuissancelumineuseémisée,cequiestutilepouraugmenterlabandepassantedesfibresoptiquesmultimodes.Trèsavantageux.
Bande passante
Accordingtothecomparisonbetweenthelaserandthelight-emittingtubedescribedabove, themultimodefiberusesalaserasthelightsource, anditstransmissionbandwidthshouldbegreatlyimproved.ButpreliminaryexperimentalresultsshowthatsimplyusinglasersinsteadofLEDsaslightsources, thebandwidthofthesystemisnotimprovedbutreduced.AftertheresearchoftheIEEEexpertgroup, itisfoundthatthebandwidthofamultimodefiberisalsorelatedtothemodepowerdistributionorinjectionstateinthefiber.Inthepreformmanufacturingprocess, theaxisoftheopticalfiberispronetorefractiveindexdepression.Inthepast, LEDswereusedasthelightsource, whichwasoverfilled (OFL-OverFilledLaunch) .Allmodes (severalhundreds) ofthefiberwereexcited, andeachmodecarrieditsownpartofthepower.Thedistortionoftherefractiveindexofthefibercenteronlyaffectsthedelaycharacteristicsofafewmodes, andtheinfluenceonthefibermodebandwidthisrelativelylimited.ThemeasuredbandwidthofthemultimodefiberiscorrectforthesystemusingLEDasthelightsource.Inotherwords, thebandwidthdatameasuredinthiswaycanbeus edtoestimatethetransmissionrateanddistanceofthesystem.However, whenalaserisusedasalightsource, thelaserspotisonlyafewmicronsandthedivergenceangleissmallerthanthatoftheLED, soonlyafewmodestransmittedinthecenterofthefiberareexcited, andeachmodecarriesaconsiderablepartofthepower, andtherefractiveindexofthefibercenterisdistorted.Theimpactonthedelaycharacteristicsoftheseonlyandfewmodeshassignificantlyreducedthebandwidthofthemultimodefiber.Therefore, thetraditionaloverfillinjection (OFL) methodcannotbeusedtomeasurethebandwidthofamultimodefiberwithalaserasalightsource.
Thenewstandardwillusethelimitedmodeinjectionmethod (RML-RestrictedModeLaunch) tomeasurethebandwidthofanewgenerationofmultimodefiber.Thebandwidthmeasuredbythismethodiscalled "laserbandwidth" ou "mode limitedbandwidth" .ThebandwidthmeasuredbyusingLEDasalightsourceiscalled "overfilledinjectionbandwidth" .ThetworespectivelyrepresentthebandwidthofthemultimodefiberwhenlaserandLEDareusedforlightsourceinjection.Thestandardsformode-limitedinjectionandbandwidthofmultimodefiberlasersweredraftedbytheTIAFO-2.2.1taskgroup.Thecontentisasfollows:
FOTP-203specifiesthepowerdistributionofthelightsourceusedtomeasurethebandwidthofamultimodefiberlaser.Thelightsourceisrequiredtopassthroughashortmultimodefibercoupling, anditsnear-fieldintensitydistributionshouldsatisfythattheluminousfluxinthecenter30μmrangeisgreaterthan75%, andtheluminousfluxinthecenter9μmrangeisgreaterthan25% .Inthenewstandard, itisnotrecommendedtouseVCSELasalightsourcetomeasurebandwidth.ThisisbecausetheopticalpowerdistributionofVCSELsfromdifferentmanufacturersisverydifferent.
FOTP-204specifiestheuseofmode-limitedfibertocouplethelightsourceintoamultimodefiberforlaserbandwidthmeasurement.Themode-limitedfiberisusedtofiltertheoverfilledstateandlimittheexcitationofthehigh-ordermodeofthemultimodefiber.Themode-limitedfiberisasectionofgradedindexmultimodefiberwithacorediameterof23.5μmandanumericalapertureof0.208.Therefractiveindexgradientindexofthismultimodefiberiscloseto2.Under850nmand1300nmoverfillconditions, thereshouldbeabandwidthgreaterthan700MHz.km.Thelengthofthemode-limitedfibershouldbegreaterthan1.5meterstoeliminatetheleakagemode, andlessthan5meterstoavoidtransientloss.Thecorediameterof23.5μmischosenbecausetheinjectionstateitproducesisclosesttotheVCSEL.
Injection de source lumineuse
introduction
Enutilisationréelle,lecouplagelaseretfibremultimodepeutsuivrelaméthodepréconiséedelanormeEthernetGbit/s :
Biaisinjection
Inordertoavoidthebandwidthdegradationcausedbythedirectinjectionofthelaserintothemultimodefiber, thestandardstipulatesthatthemodeadjustmentconnection (ModeConditioningPatchCord-MCP) isusedtocouplethelaseroutputintothemultimodefiber.Modefiber.Themodeadjustmentconnectionisashortsingle-modefiber, oneendofwhichiscoupledwiththelaser, andtheotherendiscoupledwiththemultimodefiber.Thestandardstipulatesthattheoutputspotofthesingle-modefiberdeliberatelydeviatesfromtheaxisofthemulti-modefiberbyacertaindistance, andtheallowabledeviationrangeis17 ~ 24μm.Thepurposeistoavoidthecentralrefractiveindexdepression, butnotdeviatetoofar, butselectivelyexciteasmallgroupLowerordermode.
Injection centrale
Pour le profil d'indice de réfraction idéal, la fibre multimode sans évidement central peut utiliser l'injection centrale au lieu des connexions d'ajustement de mode.
Ladifférenceentremonomodeetmultimode
1, la distance de transmission monomode est longue
2, bande passante de transmission multimode aussi large
3, dispersion sans chromatique monomode, qualité fiable
4. Le monomode utilise généralement le laser comme source de lumière, ce qui est coûteux, tandis que le multi mode utilise généralement des LED bon marché
5. Le monomode est plus cher
p>
6. La transmission multi-mode est bon marché et la transmission à courte distance est possible