光钎通信作业合集

1.1Areceiverrequires10mWasinputpower.Ifallthesystemlossesaddupto50dB,thenhowmuchpowerisrequiredfromthesource?1.2Thereare1010photonspersecondincidentonaphotodetectoratwavelength0.8m,Computerthepowerincidentonthedetector.Ifthisdetectorconvertslighttocurrentatarateof0.65mA/mW,whatcurrentisproduced?1.3Thepowerincidentonadetectoroflightis100nW.(a)Determinethenumberofphotonspersecondincidentonthedetectorifthewavelengthis800nm.(b)Repeatthecalculationifthewavelengthis1550nm.(c)Whichwavelengthrequiresthemostphotonstoproducethe100nWofpower?1.4Tooperateproperly,afiberopticreceiverrequires-34dBmpower.Thesystemlossestotal31dBfromthelightsourcetothereceiver.Howmuchpowerdoesthelightsourceemit(inmW)？2.1Auniformcollimatedbeamisfocusedbyalenswhosefocallengthis20mmandwhosediameteris10mm.Thewavelengthis0.8m.Computethefocusedspotsize.2.2ComputethedivergenceangleofaGaussianbeamofwavelength0.8mandspotsize1mm.Ifthisbeamisaimedatthemoon,whatisthespotsizeonthemoon’ssurface?(Thedistancebetweentheearthandthemoonis83.810m)3.1Forsilica,computethemagnitudeofthepulsespreadperunitlengthifthesourcewavelengthis0.85m.Thespectralwidthis30nm.Repeatforaspectralwidthof2nm.(Supposethedispersionat0.85misabout90psnmkm)3.2Iftheattenuationcoefficient()forthewaveintheEqsin()zoEEetkzhasthevalue51210cm,computethepowerlossindBfor1km.Ifthelossinamediumis0.2dB/km,thenfindtheattenuationcoefficient.3.3Considersolitonpulseshavingapulsewidthof20psatthetransmitter,theypropagateinasinglemodefiberatawavelengthof1550nmwithnopulsedistortion.Ifthedispersionis2psnmkm.a)Whatisthemaximumdataratethatcanbetransmittedbyusingthesesolitonpulses.b)Whatwilllimitthelengthoffiberoverwhichthisdatacanbetransmitted.5.1ConsideraSIfiberwith1n1.5and2n1.485at0.82m.Ifthecoreradiusis50m,howmanymodescanpropagate?Repeatifthewavelengthischangedto1.2m.5.2Forasingle-modeandamultimodeGRINfiber,1n1.48and2n1.46,wavelength=0.82m,linewidth=20nm.(a)Computethe3-dBbandwidth-lengthproduct.Neglectwaveguidedispersion.(b)Repeatiflinewidth=1nm.(c)Repeatifwavelength=1.5m,linewidth=50nm.(d)Repeatifwavelength=1.5m,linewidth=1nm.5.3FindthetotalnumberofpropagatingmodesinanSIfiberhavinganormalizedfrequencyof4.5whenthewavelengthis800nm.5.4ComputethecoreradiusforanSIsingle-modefiber.Thecutoffwavelengthis1250nm,theoperationalwavelengthis1550nm,thecoreindexhas1n1.465,andthefractionalrefractive-indexchangeis0.0034.Also,computethespotsizeattheoperatingwavelength.5.5ComputethebandwidthinHertzoftheS-band,theC-band,theL-band–thatis,computetherangefromthelowesttothehighestfrequencyineachband.6.1WhenanLEDhas2Vappliedtoitsterminals,itdraws100mAandproduces2mWofopticalpower.WhatisLED’sconversionefficiencyfromelectricaltoopticalpower?6.2AGaAslaserdiodehasa1.5-nmgainlinewidth,anditscavitylengthis0.5mm,Sketchtheoutputspectrum,includingasmanydetailsasyoucan(forexample,theemittedwavelengthandthenumberofthemodes).6.3Anerbium-dopedfiberamplifierhasanoisefigureof6andagainof100.Theinputsignalhasa30-dBsignal-to-noiseratioandasignalpowerof10W.Computerthesignalpower(indBm)andsignal-to-noiseratio(indB)attheamplifier’soutput.6.4ForanLED,computethefractionofinjectchargesthatproducephotonsif2mWofopticalpowerareradiatedwithadrivecurrentof50mAat1.3m.6.5Sourceemittingatdifferentwavelengthcanbemultiplexedontoasinglefiber,providingmultiplechannelsofinformation.Assumingaspectralwidthof0.02nmforeachlasersourceandachannelseparationof0.05nm(toavoidcrosstalk),howmanychannelscanbefittedintotheCband.6.6Anerbium-dopedfiberamplifiersat1550nmandispumpedat980nm.Computetheamplifierefficiencyiftheonlyenergylossisduetothefactthatittakesone980nmphotontoproduceone1550nmphoton.6.7Ramanscatteringresultsinadownshiftintheopticalfrequencyofabout13.2Thz.Iftheinputwavelengthis1540nm,computeboththeinputfrequencyandthedownshiftedfrequency.7.1Howmuchcurrentisproducedbyaphotodetectorwhoseresponsivityis0.5A/Wiftheincidentopticalpowerlevelis-43dBm?7.2Findtheoutputcurrentofaphotodetectorwhosequantumefficiencyis0.9.Thewavelengthis1300nm,andtheincidentpowerlevelis-37dBm.Also,computetheresultingoutputvoltagewhentheloadresistanceis50Ω,1000Ω,1MΩ.7.3ComputetheresponsivityofanInGaAsAPDoperatingat1.55mandhavingthequantumefficiency0.7ifitsgainis10.Howmuchopticalpowerisneededbythisdetectortoproduce20nA?7.4APINdetectorhastheresponsivity1AWat1550nm.Thedetectorfeedsintoa50KΩresistor.Whatopticalinputpowerisrequiredtoproduce10Wintheresistor?7.5SupposethataPINphotodiodehasadepletionwidthof30m,acarriervelocityof4510ms,andajunctioncapacitanceof6pF.a)Computethetransit-time-limitedbandwidth.b)Iftheloadresistanceis10,000,computethebandwidthagain.