Fonction de transmission de puissance complète
USLariancompanysuccessfullycompletedthepowertransmissionfunctionusingopticalfiber, openingupanewwayinthepowerfield.Theyusesemiconductorlaserdiodesatthetransmittingendtoconvertelectricalenergyintolaserlightfortransmissioninopticalfibers, andusesolarcellsasthereceivingenddevice.Thisdeviceuses300 micron-thickgalliumarsenideasaninsulatingsubstrate, coveredwitha20-micron-thicksolarcell.Itisdividedinto6independentareas, whichareconnectedinseriesbygold-platedairbridges.Whenthelaserlighttransmittedbytheopticalfiberhitsthesolarcell, thelightenergyimmediatelybecomeselectricalenergy.Thevoltagegeneratedbyeachareaisexactly1volt, andsixareasinserieshave6volts, whichisenoughforthecontrolcircuitofmostsensors.
Large application
Ifthepowerofthelaserdiodeiscontinuouslyincreased, coupledwithacompletepowertransmissionsystem, opticalfibertransmissioncanbewidelyusedinmilitary, industriel, commercialandotheraspects.TheFrenchBogenlaboratory, whichspecializesincomputers, electronicequipment, signalprocessingandimagetechnology, useslightsolitonsandshortpulsestoachievedistortion-freetransmissioninopticalfibers.Thistechnologycansolvetheproblemsofdispersionandnon-lineareffects, andthereisnoneedtoinstallmultipleregenerationdevicesalongtheopticalcable.Itonlyneedstosetupanamplifierevery100kilometersorsowhenworking.Thesolitarywaveletscantraverseeachotherwithoutinterferingwitheachother.Itissaidthatthisnewtechnologyisusedforsubmarinesubmarinewithintherangeof6450-12900kilometers, whichcansolvetheproblemofcommunicationdifficulties.AnirregularcarriersignalopticalfibercommunicationtechnologydevelopedbyAmericancommunicationsecurityexpertsisspecificallydesignedtodealwithtoday'sincreasinglyrampantandsophisticatedeavesdroppers.Thistechnologyfirs tconvertsusefulinformationsuchasvoiceintodigitalpulsesignals, andthenencodesthesedigitalpulsesignalsandmodulatesthemontorandommicrowavecarriersthatchangeirregularly.Whensending, thelasertransmittingdevicetransmitstheirregularcarriersignalcarryinginformationtothereceiverthroughtheopticalfibercommunicationsystem.Thereceiver'slaserreceiverusesspecialtechnologytosynchronizeanddynamicallycoordinatewiththesendinglaserdevice, andfinallycompletesthetaskofdemodulatingtheusefulsignalfromtheirregularcarrier.Usingthistechnology, theeavesdropperswillnolongerbeuseful, theywillonlyhearchaoticnoises.TheAustralianPaulineCompanyhasrecentlydevelopedanopticalfiberscalethatcanweightruckswithoneopticalfiberandonelaser.Thiskindoffiberweigherusesakindoffiberwithveryspecialresistancecharacteristics.Whenitisunderpressureortension, thefiberwillbeslightlydeformed, causingthecharacteristicsofthelasertochange.Atthistime, thedetectorwillimmediatelylearnthischangeandconvertitintoanelectricalsignalchange.Thisisreflectedonthed estlepanneaudejeudel'instrument.Étant donné quelafibre optiqueenverre,résistantàl'humiditéetauxrayonnements.Plus important,estfacileàinstalleretàmaintenir,etestadaptéeàl'installationsurdes routes principalesenzone urbaine,autour desusines,des aéroportsetdespistes,desentrepôtsetdesports.
Fibre optique plastique
AccordingtoarecentreportintheUS, aplasticopticalfiberdevelopedbyBostonOpticalFiberCorporation, Massachusetts, hasatransmissionspeed30timesfasterthanthecurrentstandardcopperwire.Moreover, itislighterinweight, moreflexibleandlowerincostthanglassfiber.Thiskindofopticalfiberusestherefractionoflightorthejumpingmodeoflightinthefibertoreachahighertransmissionspeed, andcantransmitdataataspeedof3megabitspersecondwithin100meters.Atpresent, 370,000kilometersofsubmarineopticalcableshavebeenlaidallovertheworld.Thislengthcanalmostcircletheearth10times.Moreover, becauselasersareusedatbothends, thereisnolongeraneedforrepeaterstoamplifysignalsduringtransmission.Thiswillgreatlyreducethecostandcallcosts.Accordingtoreports, theworld'slargestcapacitysubmarineopticalcableconnectingEuropeandtheUnitedStatesisabouttoopen.Thissubmarinecommunicationfiberopticcablethatconnectstheworldisbeinglaid.Thisisthemostmagnificentprojectinthefieldofcommunicationinthe20thcenturyandissupportedby30internationaltelecommunicationsorganiza Il traverse l'océan Atlantique, la mer Méditerranée, la mer Rouge et l'océan Indien, et traverse le détroit de Malaccain jusqu'à l'océan Pacifique.
Principedecomposition
La technologie de la fibre optique se compose généralement de trois parties : l'extrémité émettrice du signal optique, la fibre optique utilisée pour transmettre le signal optique et l'extrémité recevant le signal optique.
Thefunctionoftheopticalsignaltransmittingendistoconverttheelectricsignaltobetransmittedintoanopticalsignalthroughanelectro-opticalconversiondevice.Currently, thetransmittingendelectro-opticalconversiondevicegenerallyusesalight-emittingdiodeorasemiconductorlasertube.Theoutputlightpowerofthelight-emittingdiodeisrelativelylow, thesignalmodulationrateisrelativelylow, butthepriceischeap, andtheoutputlightpowerandthedrivingcurrentarebasicallylinearwithinacertainrange, whichismoresuitableforshort distance, à basse vitesse, andanalogsignaltransmission; Theoutputpowerofthediodeislarge, thesignalmodulationrateishigh, butthepriceisrelativelyhigh, anditissuitableforlong distance, à haute vitesse, digitalsignaltransmission.Thefunctionoftheopticalfiberistotransmittheopticalsignalatthetransmittingendtothereceivingendoftheopticalsignalwithaslittleattenuationanddistortionaspossible. Actuellement, la fibre optique est généralement utilisée dans la bande proche infrarouge de 0,84 µm, 1,31 µm, 1,55 µm avec une bonne transmission de la fibre de silice multimode ou monomode. ctionoftheopticalsignalreceivingterminalistorestoretheopticalsignaltothecorrespondingelectricalsignalthroughthephotoelectricconversiondevice.Thephotoelectricconversiondevicegenerallyusesasemiconductorphotodiodeoranavalanchephotodiode.Thelightemittingwavelengthofthelightsourceconstitutingtheopticalfibertransmissionsystemmustmatchthewavelengthbandofthelowlosswindowofthetransmissionfiberandthepeakresponsebandofthephotoelectricdetectiondevice.Thetransmittingendelectro-opticalconversiondeviceusesahigh-brightnessnear-infraredsemiconductorlight-emittingdiodewithacentralemissionwavelengthof0.84μm, thetransmissionfiberusesamultimodequartzfiber, andthereceivingendphotoelectricconversiondeviceusesasiliconphotodiodewithapeakresponsewavelengthof0.8μmto0.9μm.Afurtherintroductiontoeachpartisgivenbelow.
Transmetteur de signal optique
Thedrivingandmodulationcircuitofthelight-emittingdiodeusedinthesystemisshowninFigure2.Thesignalmodulationadoptsthemethodoflightintensitymodulation, andthelightintensityadjustmentpotentiometerisusedtosendAdjustthestaticdrivingcurrentflowingthroughtheLED, therebychangingtheemittedlightpowerofthelight-emittingdiodeaccordingly.Thesetstaticdrivingcurrentadjustmentrangeis0-20mA, correspondingtothepanellighttransmissionintensitydrivingdisplayvalue0-2000units, whenthedrivingcurrentWhenitissmaller, theemittedlightpowerofthelight-emittingdiodeandthedrivingcurrentarebasicallylinear.Theaudiosignalisisolatedbythecapacitor, resistornetworkandtheopampandcoupledtothenegativeinputofanotheropamp, overlappingwiththestaticdrivingcurrentofthelight-emittingdiodeThelight-emittingdiodeisaddedtosendanopticalsignalthatchangeswiththeaudiosignal, andtheopticalsignaliscoupledtothetransmissionfiberthroughanopticalfibercoupler.Thelowendofthetransmittablesignalfrequencycanbedeterminedbythecapacitorandresistornetwork, andthelo wla réponse en fréquence du système n'est pas supérieure à 20 Hz
Lesignal optiqueréceptionfin
istheworkingprinciplediagramoftheopticalsignalreceivingend, thetransmissionfiberTheopticalsignalfromthetransmittingendcouplestheopticalsignaltothephotoelectricconversiondevicephotodiodethroughtheopticalfibercoupler.Thephotodiodeconvertstheopticalsignalintoacurrentsignalproportionaltoit.Thephotodiodeshouldbereversebiasedwhenitisused.Current à voltageconversionconvertsthephotocurrentsignalintoavoltagesignalproportionaltoit.Theaudiosignalcontainedinthevoltagesignaliscoupledtotheaudiopoweramplifierviaacapacitorandresistancetodrivethespeakertosound.Thefrequencyresponseofthephotodiodeisgenerallyhigh, andthehighfrequencyresponseofthesystemmainlydependsontheresponsefrequencyoftheoperationalamplifier.
Fibre de transmission
À l'heure actuelle, theopticalfiberusedforopticalcommunicationgenerallyusessilicafiber, whichiscoveredwithalayerofrefractiveindexn1insidethecorewithalargerrefractiveindexn1.Inthecladdinglayer, thelightistotallyreflectedattheinterfacebetweenthecoreandthecladdinglayerandisrestrictedtopropagateinthecore.AsshowninFigure5, theopticalfiberisactuallyadielectricwaveguide.Transmissionalongthefiber, thecorediameterofthefiberisgenerallyfromafewmicronstohundredsofmicrons.Accordingtothetransmissionmode, itcanbedividedintomulti-modefiberandsingle-modefiber.Accordingtotherefractiveindexdistributionmodeofthefiber, itcanbedividedintorefractiveindexsteptypeandrefractiveindex.Gradedopticalfiber.Therefractiveindexsteptypefibercontainstwocircularlysymmetricalcoaxialmedia, bothofwhichareuniformintexture, buthavedifferentrefractiveindexes.Therefractiveindexoftheouterlayerislowerthanthatoftheinnerlayer.
Gradientindexfiberisakindoffiberwhoserefractiveindexisgradedalongthecrosssectionofthefiber.Thepurposeofchangingtherefractiveindexistomakethegroupvelocityofvariousmodessimilar, therebyreducingmodaldispersionandincreasingcommunicationbandwidth.Multimoderefractiveindexstep-typefibersproduceinter-modedispersionduetothedifferentgroupvelocitiesofeachmodetransmission, andthetransmissionbandwidthislimited.Multimoderefractiveindexgradedfiberincreasesthebandwidthofsignaltransmissionduetoitsspecialrefractiveindexdistribution, whichmakesthegroupspeedoftransmissionofeachmodethesame.Single-modefiberisafiberthatonlytransmitsasingleopticalmode.Atpresent, unique modeopticalfibersaremostlyusedinlong-distanceopticalcommunications.
Themaintechnicalindicatorsofsilicafiberincludeattenuationcharacteristics, numericalapertureanddispersion.Numericalaperture: Numericalaperturedescribesthecharacteristicsofopticalfiberwhencoupledwithlightsources, detectorsandotheropticaldevices.Itssizereflectstheabilityoftheopticalfibertocollectlight.AsshowninFigure5, thelightincidentontheendfaceoftheopticalfiberwithinthesolidangle2θmaxistotallyreflectedattheinternalinterfaceoftheopticalfiberandistransmitted, andthelightincidentontheendfaceoftheopticalfiberoutsidethe2θmaxrangeisTheinternalinterfaceofthefiberdoesnotproducetotalreflectionbutistransmittedtothecladdingandisimmediatelyattenuated.Thenumericalapertureofthefiberisdefinedas: NA = Sinθmax, anditsvalueisgenerallybetween0.1and0.6, correspondingtoθmaxIntherangeof90to330, multimodefibershavelargernumericalapertures, andsingle-modefibershaverelativelysmallnumericalapertures.Therefore, single-modefibersgenerallyrequireLDsemiconductorlasersastheirlightsources.