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LED

  1. 1. 9/12/2013 Mahesh J. vadhavaniya 1
  2. 2. 9/12/2013 Mahesh J. vadhavaniya 2
  3. 3. Objectives…Objectives…Objectives…Objectives…Objectives…Objectives…Objectives…Objectives… IntroductionIntroduction ExplainExplain withwith helphelp ofof energyenergy bandband structure,structure, thethe processprocess ofof opticaloptical emissionemission fromfrom semiconductorsemiconductor.. 9/12/2013 Mahesh J. vadhavaniya 3 LEDLED StructuresStructures LEDLED CharacteristicsCharacteristics AdvantagesAdvantages && disadvantagesdisadvantages ofof ILDILD overover LEDLED forfor longlong haulhaul opticaloptical fiberfiber cc00mmunicationmmunication
  4. 4. Point of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of Discussion ExplainExplain withwith thethe helphelp ofof energyenergy bandband structure,structure, thethe processprocess ofof opticaloptical emissionemissionstructure,structure, thethe processprocess ofof opticaloptical emissionemission fromfrom semiconductorssemiconductors.. 9/12/2013 Mahesh J. vadhavaniya 4
  5. 5. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission ToTo allowallow considerationconsideration ofof semiconductorsemiconductor opticaloptical sourcessources itit isis necessarynecessary toto reviewreview somesome ofof thethe propertiesproperties ofof semiconductorsemiconductor materials,materials, especiallyespecially withwith regardregard toto pp--nn junctionjunction.. semiconductorsemiconductor IntrinsicIntrinsic ExtrinsicExtrinsic 9/12/2013 Mahesh J. vadhavaniya 5
  6. 6. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission AA perfectperfect semiconductorsemiconductor crystalcrystal containingcontaining nono impuritiesimpurities andand latticelattice effecteffect.. Intrinsic Semiconductor :Intrinsic Semiconductor : Extrinsic Semiconductor :Extrinsic Semiconductor : AA semiconductorsemiconductor crystalcrystal whichwhich isis mademade upup byby thethe processprocess ofof doping,doping, ii..ee.. addingadding impurityimpurity toto itit.. 9/12/2013 Mahesh J. vadhavaniya 6
  7. 7. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission The energy band structureThe energy band structure The FermiThe Fermi--Dirac probability distributionDirac probability distribution 9/12/2013 Mahesh J. vadhavaniya 7
  8. 8. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission ForFor aa semiconductorsemiconductor inin thermalthermal equilibriumequilibrium thethe energyenergy levellevel occupationoccupation isis describeddescribed byby fermifermi diracdirac distributiondistribution functionfunction.. ConsequentlyConsequently thethe probabilityprobability P(E)P(E) thatthat anan electronelectron gainsgains sufficientsufficient thermalthermal energyenergy atat anan absoluteabsolutegainsgains sufficientsufficient thermalthermal energyenergy atat anan absoluteabsolute temperaturetemperature TT suchsuch thatthat itit willwill bebe foundfound occupyingoccupying aa particularparticular energyenergy levellevel E,E, isis givengiven byby thethe FermiFermi--DiracDirac distributiondistribution.. KTEE EP F )exp(1 1 )( −+ = 9/12/2013 Mahesh J. vadhavaniya 8
  9. 9. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission TheThe FermiFermi levellevel isis defineddefined asas thethe highesthighest occupiedoccupied molecularmolecular orbitalorbital inin thethe valencevalence bandband atat 00 K,K, soso thatthat therethere areare manymany statesstates availableavailable toto acceptaccept electrons,electrons, ifif thethe casecase werewere aa metalmetal.. ThisThis isis notnot thethe casecase inin insulatorsinsulators andand semiconductorssemiconductors sincesince thethe valencevalence andand conductionconduction bandsbands areare separatedseparated.. ThereforeTherefore thethe FermiFermi levellevel isis locatedlocated inin thethe bandband gapgap.. TheThe probabilityprobability ofof thethe occupationoccupation ofof anan energyenergy levellevel isis basedbased onon thethe FermiFermi functionfunction.. 9/12/2013 Mahesh J. vadhavaniya 9
  10. 10. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission EnergyEnergy Energy Band DiagramsEnergy Band Diagrams nn–– type semiconductortype semiconductor pp–– type semiconductortype semiconductor 9/12/2013 Mahesh J. vadhavaniya 10
  11. 11. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission TheThe pp--nn junctionjunction diodediode isis formedformed byby creatingcreating adjoiningadjoining pp andand nn typetype semiconductorsemiconductor layerslayers inin singlesingle crystalcrystal.. AA thinthin depletiondepletion regionregion isis formedformed atat thethe junctionjunction throughthrough carriercarrier recombinationrecombination.. ThisThis establishesestablishes aa potentialpotential barrierbarrier betweenbetween thethe pp andand nnThisThis establishesestablishes aa potentialpotential barrierbarrier betweenbetween thethe pp andand nn typetype regionsregions whichwhich restrictsrestricts thethe interinter diffusiondiffusion ofof majoritymajority carrierscarriers fromfrom theirtheir respectiverespective regionsregions.. AnAn externalexternal appliedapplied voltagevoltage formform currentcurrent flowflow throughthrough thethe devicedevice asas theythey continuouslycontinuously diffusediffuse awayaway fromfrom thethe interfaceinterface.. However,However, thisthis situationsituation inin suitablesuitable semiconductorsemiconductor allowsallows carriercarrier recombinationrecombination withwith thethe emissionemission ofof lightlight.. 9/12/2013 Mahesh J. vadhavaniya 11
  12. 12. Process of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical EmissionProcess of Optical Emission 9/12/2013 Mahesh J. vadhavaniya 12
  13. 13. 9/12/2013 Mahesh J. vadhavaniya 13
  14. 14. AA PNPN junctionjunction (that(that consistsconsists ofof directdirect bandband gapgap semiconductorsemiconductor materials)materials) actsacts asas thethe activeactive oror recombinationrecombination regionregion.. WhenWhen thethe PNPN junctionjunction isis forwardforward biased,biased, electronselectrons andand Semiconductor Light SourcesSemiconductor Light SourcesSemiconductor Light SourcesSemiconductor Light SourcesSemiconductor Light SourcesSemiconductor Light SourcesSemiconductor Light SourcesSemiconductor Light Sources holesholes recombinerecombine eithereither radiativelyradiatively (emitting(emitting photonsphotons)) oror nonnon--radiativelyradiatively (emitting(emitting heat)heat).. ThisThis isis simplesimple LEDLED operationoperation.. InIn aa LASER,LASER, thethe photonphoton isis furtherfurther processedprocessed inin aa resonanceresonance cavitycavity toto achieveachieve aa coherent,coherent, highlyhighly directionaldirectional opticaloptical beambeam withwith narrownarrow lineline widthwidth.. 9/12/2013 Mahesh J. vadhavaniya 14
  15. 15. The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED ) LEDsLEDs isis usedused toto convertconvert electricalelectrical energyenergy intointo lightlight AA lightlight emittingemitting diodediode (LED)(LED) isis essentiallyessentially aa PNPN junctionjunction optoopto--semiconductorsemiconductor thatthat emitsemits aa monochromaticmonochromatic (single(single color)color) lightlight whenwhen operatedoperated inin aa forwardforward biasedbiased directiondirection.. LEDsLEDs isis usedused toto convertconvert electricalelectrical energyenergy intointo lightlight energyenergy byby recombinationrecombination ofof holesholes andand electronselectrons atat thethe PP NN JunctionJunction.. 9/12/2013 Mahesh J. vadhavaniya 15
  16. 16. Light EmissionLight EmissionLight EmissionLight EmissionLight EmissionLight EmissionLight EmissionLight Emission BasicBasic LEDLED operationoperation :: WhenWhen anan electronelectron jumpsjumps fromfrom aa higherhigher energyenergy statestate ((EcEc)) toto aa lowerlower energyenergy statestate ((EvEv)) thethe differencedifference inin energyenergy EcEc -- EvEv isis releasedreleased eithereither ……EcEc -- EvEv isis releasedreleased eithereither …… asas aa photonphoton ofof energyenergy EE == hhνν ((radiativeradiative recombination)recombination) asas heatheat (non(non--radiativeradiative recombination)recombination) 9/12/2013 Mahesh J. vadhavaniya 16
  17. 17. The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED ) ForFor fiberfiber--optics,optics, thethe LEDLED shouldshould havehave aa highhigh radianceradiance (light(light intensity),intensity), fastfast responseresponse timetime andand aa highhigh quantumquantum efficiencyefficiency EmittedEmitted wavelengthwavelength dependsdepends onon bandband gapgap energyenergy λν /hchEg == EmittedEmitted wavelengthwavelength dependsdepends onon bandband gapgap energyenergy (eV) 2399.1 m)( gE =µλ λλ = wavelength in microns= wavelength in microns h = Planks constanth = Planks constant c = speed of lightc = speed of light E = Photon energy inE = Photon energy in eVeV 9/12/2013 Mahesh J. vadhavaniya 17
  18. 18. ForFor photonicphotonic communicationscommunications requiringrequiring datadata raterate isis 100100--200200 Mb/sMb/s withwith multimodemultimode fiberfiber withwith tenstens ofof microwatts,microwatts, LEDsLEDs areare usuallyusually thethe bestbest choicechoice LEDLED configurationsconfigurations beingbeing usedused inin photonicphotonic communicationscommunications:: The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED )The Light Emitting Diode ( LED ) communicationscommunications:: 11 -- SurfaceSurface EmittersEmitters (Front(Front Emitters)Emitters) 22 -- EdgeEdge EmittersEmitters 9/12/2013 Mahesh J. vadhavaniya 18
  19. 19. Surface Emitting LEDSurface Emitting LEDSurface Emitting LEDSurface Emitting LEDSurface Emitting LEDSurface Emitting LEDSurface Emitting LEDSurface Emitting LED Schematic of high-radiance surface-emitting LED. The active region is limitted to a circular cross section that has an area compatible with the fiber-core end face. 9/12/2013 Mahesh J. vadhavaniya 19
  20. 20. Edge Emitting LEDEdge Emitting LEDEdge Emitting LEDEdge Emitting LEDEdge Emitting LEDEdge Emitting LEDEdge Emitting LEDEdge Emitting LED Schematic of an edge-emitting double heterojunction LED. The output beam is lambertian in the plane of junction and highly directional perpendicular to pn junction. They have high quantum efficiency & fast response. 9/12/2013 Mahesh J. vadhavaniya 20
  21. 21. Light Source MaterialLight Source MaterialLight Source MaterialLight Source MaterialLight Source MaterialLight Source MaterialLight Source MaterialLight Source Material MostMost ofof thethe lightlight sourcessources containcontain IIIIII--VV ternaryternary && quaternaryquaternary compoundscompounds byby varyingvarying xx itit isis possiblepossible toto controlcontrol thethe bandband--gapgap energyenergy andand therebythereby thethe emissionemission wavelengthwavelength overover thethe rangerange ofof 800800 nmnm toto 900900 nmnm.. TheThe spectralspectral widthwidth AsAlGa xx1− isis aroundaround 2020 toto 4040 nmnm byby changingchanging 00<x<<x<00..4747;; yy isis approximatelyapproximately 22..22x,x, thethe emissionemission wavelengthwavelength cancan bebe controlledcontrolled overover thethe rangerange ofof 920920 nmnm toto 16001600 nmnm.. TheThe spectralspectral widthwidth variesvaries fromfrom 7070 nmnm toto 180180 nmnm whenwhen thethe wavelengthwavelength changeschanges fromfrom 13001300 nmnm toto 16001600 nmnm.. TheseThese materialsmaterials areare latticelattice matchedmatched.. y1yxx1 PAsGaIn −− 9/12/2013 Mahesh J. vadhavaniya 21
  22. 22. 9/12/2013 Mahesh J. vadhavaniya 22
  23. 23. Spectral width of LED typesSpectral width of LED typesSpectral width of LED typesSpectral width of LED typesSpectral width of LED typesSpectral width of LED typesSpectral width of LED typesSpectral width of LED types 9/12/2013 Mahesh J. vadhavaniya 23
  24. 24. PLANAR LEDPLANAR LEDPLANAR LEDPLANAR LEDPLANAR LEDPLANAR LEDPLANAR LEDPLANAR LED Light Output Ohmic Contacts p – type epitaxial layer n – type substrate Light Output SimplestSimplest ofof thethe structuresstructures availableavailable.. PP typetype diffusiondiffusion intointo nn typetype substratesubstrate.. LambertianLambertian spontaneousspontaneous emissionemission.. LightLight emitsemits fromfrom allall surfacessurfaces.. TotalTotal internalinternal reflectionreflection.. RadianceRadiance isis lowlow.. 9/12/2013 Mahesh J. vadhavaniya 24
  25. 25. DOME LEDDOME LEDDOME LEDDOME LEDDOME LEDDOME LEDDOME LEDDOME LED Semiconductor material is shaped like a hemisphere HemisphereHemisphere ofof nn typetype GaAsGaAs isis formedformed aroundaround pp typetype regionregion.. HigherHigher amountamount ofof internalinternal n+ Electrodes p HigherHigher amountamount ofof internalinternal emissionemission reachingreaching thethe surfacesurface withinwithin thethe criticalcritical angleangle ofof GaAsGaAs airair interfaceinterface.. HigherHigher externalexternal efficiencyefficiency thanthan thethe PlanarPlanar LEDLED.. 9/12/2013 Mahesh J. vadhavaniya 25
  26. 26. Why do we need the DOME ?Why do we need the DOME ?Why do we need the DOME ?Why do we need the DOME ?Why do we need the DOME ?Why do we need the DOME ?Why do we need the DOME ?Why do we need the DOME ? Semiconductor material is shaped like a hemisphere Plastic Dome n+ Electrodes p pn Junction Electrodes To reduce TIR …To reduce TIR … 9/12/2013 Mahesh J. vadhavaniya 26
  27. 27. How to solve TIR problem ?How to solve TIR problem ?How to solve TIR problem ?How to solve TIR problem ?How to solve TIR problem ?How to solve TIR problem ?How to solve TIR problem ?How to solve TIR problem ? GaAsGaAs--airair interface,interface, thethe θθ == 1616oo whichwhich meansmeans thatthatGaAsGaAs--airair interface,interface, thethe θθcc == 1616oo whichwhich meansmeans thatthat muchmuch ofof thethe lightlight sufferssuffers TIRTIR.. ToTo solvesolve thethe problemproblem wewe couldcould::ToTo solvesolve thethe problemproblem wewe couldcould:: 1.1. ShapeShape thethe surfacesurface ofof thethe semiconductorsemiconductor intointo aa1.1. ShapeShape thethe surfacesurface ofof thethe semiconductorsemiconductor intointo aa domedome oror hemispherehemisphere soso thatthat lightlight raysrays strikestrike thethedomedome oror hemispherehemisphere soso thatthat lightlight raysrays strikestrike thethe surfacesurface anglesangles << θθcc thereforetherefore doesdoes notnot experienceexperience TIRTIR.. ButBut expensiveexpensive andand notnot practicalpractical toto shapeshape pp--nn junctionjunction withwith domedome--likelike structurestructure.. 22.. EncapsulationEncapsulation ofof thethe semiconductorsemiconductor junctionjunction22.. EncapsulationEncapsulation ofof thethe semiconductorsemiconductor junctionjunction withinwithin aa domedome--shapedshaped transparenttransparent plasticplastic mediummedium (an(an epoxy)epoxy) thatthat hashas higherhigher refractiverefractive indexindex thanthan airair.. 9/12/2013 Mahesh J. vadhavaniya 27
  28. 28. Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED ) 9/12/2013 Mahesh J. vadhavaniya 28
  29. 29. TheThe surfacesurface layerlayer isis keptkept asas thinthin asas possiblepossible ((1010--1515 µµm)m)TheThe surfacesurface layerlayer isis keptkept asas thinthin asas possiblepossible ((1010--1515 µµm)m) toto minimizeminimize reabsorptionreabsorption.. Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED )Surface Emitter LED ( SLED ) AA wellwell isis etchedetched inin aa GaAsGaAs substratesubstrate toto preventprevent heavyheavyAA wellwell isis etchedetched inin aa GaAsGaAs substratesubstrate toto preventprevent heavyheavy absorptionabsorption ofof thethe emittedemitted radiationradiation && toto physicallyphysically accommodateaccommodate thethe fibrefibre.. PhotonsPhotons areare generatedgenerated inin thethe thinthin pp--GaAsGaAs && regionregionPhotonsPhotons areare generatedgenerated inin thethe thinthin pp--GaAsGaAs && regionregion emissionemission fromfrom thethe toptop surfacesurface isis ensuredensured heterostructureheterostructure && PhotonsPhotons areare generatedgenerated inin thethe thinthin pp--GaAsGaAs && regionregion emissionemission fromfrom thethe toptop surfacesurface isis ensuredensured heterostructureheterostructure && reflectionreflection fromfrom thethe backback crystalcrystal faceface.. ThusThus forwardforward radianceradiance ofof thesethese devicedevice isis veryvery highhigh.. TheThe toptop nn--GaAsGaAs contactcontact layerlayer ensuresensures lowlow contactcontactTheThe toptop nn--GaAsGaAs contactcontact layerlayer ensuresensures lowlow contactcontact resistanceresistance && thermalthermal resistance,resistance, thereforetherefore allowingallowing forfor highhigh currentcurrent densitiesdensities && highhigh raditionradition intensityintensity.. TheThe internalinternal absorptionabsorption inin thisthis devicedevice isis veryvery lowlow duedue totoTheThe internalinternal absorptionabsorption inin thisthis devicedevice isis veryvery lowlow duedue toto thethe largerlarger bandgapbandgap confiningconfining layerslayers.. 9/12/2013 Mahesh J. vadhavaniya 29
  30. 30. Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED ) 9/12/2013 Mahesh J. vadhavaniya 30
  31. 31. N+- GaAlAs GaAs(n) substrate Metal contact Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED ) Active layer n- GaAlAs N GaAlAs N+- GaAlAs Metal contact P GaAlAs P+ GaAlAs n- GaAlAs Light emits from the edge 9/12/2013 Mahesh J. vadhavaniya 31
  32. 32. ActiveActive layerlayer isis usuallyusually lightlylightly dopeddoped oror undopedundoped && aa veryveryActiveActive layerlayer isis usuallyusually lightlylightly dopeddoped oror undopedundoped && aa veryvery largelarge populationpopulation forfor recombinationrecombination isis createdcreated inin thisthis regionregion byby forwardforward biasbias injectioninjection.. Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED )Edge Emitter LED ( ELED ) PhotonsPhotons areare generatedgenerated inin thethe veryvery thinthin activeactive regionregion &&PhotonsPhotons areare generatedgenerated inin thethe veryvery thinthin activeactive regionregion && spreadspread intointo thethe guidingguiding layers,layers, withoutwithout reabsorptionreabsorption becausebecause ofof theirtheir largelarge bandgapsbandgaps.. MostMost ofof thethe propagatingpropagating lightlight isis emittedemitted atat oneone edgeedge ofofMostMost ofof thethe propagatingpropagating lightlight isis emittedemitted atat oneone edgeedge ofof structurestructure byby puttingputting aa reflectivereflective coatingcoating atat thethe nonnon emittingemitting endend &&structurestructure byby puttingputting aa reflectivereflective coatingcoating atat thethe nonnon emittingemitting endend && puttingputting anan antireflectiveantireflective coatingcoating atat thethe emittingemitting endend.. TheThe waveguidewaveguide reducesreduces thethe divergencedivergence ofof thethe emittedemittedTheThe waveguidewaveguide reducesreduces thethe divergencedivergence ofof thethe emittedemitted radiationradiation.. InIn directiondirection perpendicularperpendicular toto thethe planeplane ofof layerslayers ,the,the halfhalfInIn directiondirection perpendicularperpendicular toto thethe planeplane ofof layerslayers ,the,the halfhalf powerpower widthwidth isis approxapprox.. 3030 degdeg.. InIn thethe planeplane ofof thethe layerlayer thethe outputoutput isis stillstill lambertianlambertian && halfhalfInIn thethe planeplane ofof thethe layerlayer thethe outputoutput isis stillstill lambertianlambertian && halfhalf powerpower widthwidth isis approxapprox.. 120120 degdeg.. TheThe waveguidewaveguide andand reducedreduced beambeam divergencedivergence allowsallows moremoreTheThe waveguidewaveguide andand reducedreduced beambeam divergencedivergence allowsallows moremore efficientefficient couplingcoupling ofof thethe radiatedradiated beambeam intointo fibrefibre.. 9/12/2013 Mahesh J. vadhavaniya 32
  33. 33. Advantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LED AdvantagesAdvantages :: EfficientEfficientEfficientEfficient ColorColor SizeSize OnOn // OffOff timetime CyclingCyclingCyclingCycling DimmingDimming CoolCool LightLight SlowSlow FailureFailure LifeLife timetime ShockShock resistanceresistance FocusFocus RobustRobust LinearLinear 9/12/2013 Mahesh J. vadhavaniya 33
  34. 34. LargeLarge lineline widthwidth ((3030--4040 nm)nm)LargeLarge lineline widthwidth ((3030--4040 nm)nm) LargeLarge beambeam widthwidth (Low(Low couplingcoupling toto thethe fiber)fiber) LowLow outputoutput powerpower LowLow E/OE/O conversionconversion efficiencyefficiency Advantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LEDAdvantage & Disadvantages of LED DrawbacksDrawbacks :: LowLow E/OE/O conversionconversion efficiencyefficiency TemperatureTemperature dependancedependance VoltageVoltage sensitivesensitive HighHigh initialinitial priceprice 9/12/2013 Mahesh J. vadhavaniya 34
  35. 35. Point of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of DiscussionPoint of Discussion AdvantagesAdvantages && disadvantagesdisadvantages ofof ILDILD overover LEDLED forfor longlong haulhaul OpticalOptical fiberfiberoverover LEDLED forfor longlong haulhaul OpticalOptical fiberfiber communicationcommunication.. 9/12/2013 Mahesh J. vadhavaniya 35
  36. 36. ILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LED AdvantagesAdvantages :: 1.1. Modulation CapabilitiesModulation Capabilities 2.2. High radianceHigh radiance 3.3. Narrow line widthNarrow line width 4.4. Relative temporal coherenceRelative temporal coherence 5.5. Good spatial coherenceGood spatial coherence 6.6. More focused radiation pattern, small fiberMore focused radiation pattern, small fiber6.6. More focused radiation pattern, small fiberMore focused radiation pattern, small fiber 7.7. Much higher radiant power, longer spanMuch higher radiant power, longer span 8.8. Faster ON, OFF time; higher bit rates possibleFaster ON, OFF time; higher bit rates possible 9.9. Monochromatic light, reduces dispersionMonochromatic light, reduces dispersion DisadvantagesDisadvantages :: 1. Much more expensive 2. Higher temperature, shorter lifespan 9/12/2013 Mahesh J. vadhavaniya 36
  37. 37. LEDLEDLEDLED ILDILDILDILD • Lower Efficiency •Higher Efficiency • Slow response rate •High response rate • Lower data transmission rate •Higher data transmission rate ILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LEDILD Versus LED • Simple construction •Construction is complicated • Higher distortion level at output •Lower distortion level at output • Higher dispersion •Lower dispersion • In coherent beam •Coherent beam 9/12/2013 Mahesh J. vadhavaniya 37
  38. 38. 9/12/2013 Mahesh J. Vadhavaniya 39

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