光通信技術(shù)課件lecture5

1、FiberFiber modeWhat is it?Why it is discrete?Condition for single propagation modeAttenuationFunction of wavelengthCalculationCausesDispersionIntramodal dispersionIntermodal dispersionPolarization mode dispersionHigher order dispersion Fiber CablesConstruction elementsOptical characteristicsFiber co

2、nnecterizationConnectorsConnector types / structureSplicesEnergy BandIn a pure crystal at low temperatures, the conduction band is empty and valence band is fullThese two energy band is separated by band gapWhen temperature is raised, some electrons are excited cross the gap Extrinsic Semiconductors

3、 n-type silicon Impurity with donor atoms Majority carrier is electrons Minority carrier is holesp-type siliconImpurity with acceptor with atoms Majority carrier is holes Minority carrier is electronsN region+ve chargep region-ve chargeElectrical neutralDiffusion potentialIndirectdirectDiffusion of

4、majority carriers across the depletion region Carrier injection Injected minority carriers bine with majority Radiative/non-radiative binationWhat is a possible measure to make it happen?Thats what we wantK-selection rule:k1k2Photon emission unlikely: 10-2 10-4 sRadiative biation possible: 10-8 10-1

5、0 sThe forward current injects electrons into the depletion region and bines with holes radiatively and non-radiativelyEmitter Characteristics, (a) LED, (b) Laser tENPp/ )(inttNeI/)()()(intmAIeVEmWPpCoupling of SLED into a step-index fiber Pin=P0(NA)262.5/125 MM fiber: NA=0.275 P0=100W -Pin=7.56 WSp

6、ectral widthSLED 170 nmELED 65 nm (LD 1nm)WavelengthIncrease with temperature 0.38nm/CIncrease with driving current 0.69 nm/mARise time0.4-10 nsDetermined by bination timeModulation bandwidth BW=1/rnonradradprICKTt/1/1/1/ )107 . 1 ( 2 . 2int4Refractive index changes with temperatureGeneralized Coupl

7、ed PowerLambertian Source radiance distributionSchematic of a typical assembly of coupling opticsTransmitters employing a) butt-coupling and b) lens-coupling designsTransmission LineMatching ResistorContact ResistanceLaser JunctionJunction CapacitanceBonding Inductance-VeeBonding InductancePad Capac

8、itance-VeeBonding InductancePad CapacitanceContact ResistanceLaser JunctionJunction CapacitanceDrive TransistorLaserPackaged Laser DriverLaser DriverTransmission LineLaser DiodeThin Film ResistorPackaged LaserPackaged Laser DriverLaser DriverLaser DiodeBondwireUse a transmission line and impedance m

9、atchKeep it close and dont worry about the matchAverage and Peak Power StabilizationLaserDataMonitor PhotodiodeDataDataDataVref1Vref2Vref1Vref2LavLppDuty CycleMeasurem entPeak Detector-+-5V-+-+Average Power, Mark Density and ModulationA variety of feedback approaches are available to compensate for

10、laser imperfections and the consequences of temperature variation and agingBostica et. al., IEEE Transactions on Advanced Packaging, Vol. 22, No 3, August 1999Drawing of Packaging ApproachOptical Module (a), Electrical module (b)Close-up of assembled moduleCompleted module integrated on test board10

11、 Channels12.5 Gb/s aggregate bandwidth1300 nm commercial laser array50/125 Multimode fiber ribbon130 mW/channelCMOS Driver ArrayBER high current density - low power consumptionHigh switch time?Hottest area of transmitter!Short cavity; 2m, adjacent longitudinal mode spacing=72 nmnaturally single-mode

12、 operationSmall footprint; be able to packaged into dense arraysSmall active region - high current density - low power consumptionHigh switch time?Spontaneous emission: photons are emitted in random direction with no phase relationship among them Stimulated emission: initially by an photon, and the emitted photon matches the original photon not only in energy but also in other characteristics, such as the direction of propagation. All the lasers, including semiconductor lasers emit light through the process of stimulated emission LED emits light through the spontaneous emission.