半導(dǎo)體放大器雙穩(wěn)的畢業(yè)論文

目錄目錄II.GAINANDBANDWIDTHAcommonmodelingapproachtoverticalcavitylasersisthereplacementoftheDBRsbyhardmirrorsofthesamereflectivitywhichareseparatedbyaneffectivecavitylengthLc.Thisway,wecanstartwiththewellknowngainformulasofFabry-Perotamplifiers(GR-reflectionmode,GT-transitionmode)withthefrontmirrorreflectivityRf,thebackmirrorreflectivityRb,thesinglepassgainGs,andthesinglepassphasedetuningΦ.ThemaximumgainisachievedwithΦ=0,whenthesignalwavelengthisidenticaltotheFabry-Perotresonance.VCLAsexhibitmuchsmallervaluesGsandlargerreflectivitiesthanin-planedevices.ForVCLAs,thepeakreflectivityoflosslessDBRswithmperiods(2mlayers)isgiven.usingthelow-to-highrefractiveindexratiosofthetwoDBRlayers(p),aswellasatthefirst(q)andthelast(a)DBRinterface.Assumingrefractiveindicesof3.45(GaAs)and2.89(AlAs),wecalculateRf=0.985andRb=0.999forourdevice.Absorptionordiffractionwithinthemirrorreducesthereflectivity.ThewavelengthdependenceoftheDBRreflectivityisignoredheresincethereflectionbandwidthoftypicalDBRsismuchlarger(about100nminourcase)thantheamplifierbandwidthandthecavityresonancewavelengthλcisassumedidenticaltotheDBRcenterwavelength.Ourone-dimensionalmodelalsoneglectsthetransversalopticalmodestructure.Resonancewavelengthsdifferslightlyamongtransversalmodes.ThephaseΦinEqs.1-2givesthedeviationofthesignalwavelengthλfromλc.withthecavityrefractiveindexnc.TheeffectivecavitylengthLcislargerthantheDBRdistanceLmanditincludesthephasepenetrationdepthsLfandLbintofrontandbackDBR,respectively(Lc=Lf+Lm+Lb).ThephasepenetrationdepthLpofalosslessDBRatcenterwavelengthλcisgiven.Withnc=3.2,theDBRpenetrationdepthinourdeviceisabout585nm,resultingintheeffectivecavitylengthLc=2.2μm.Duetothehighindexcontrast,AlAs/GaAsDBRsexhibitsmallerpenetrationdepthsthanmirrorsgrownonInP.ThecavityrefractiveindexncisobtainedbyaveragingoveralllayersbetweenthetwoDBRs.Typically,itissomewhathigherthantherefractiveindexofthespacermaterial(InP)atthetargetwavelength,however,itcanbeaffectedbythequantumwellcarrierdensityaswellasbydeviceheating.TheremainingparameterinEqs.1-2tobediscussedisthesinglepasssignalgainGs.Assuminglaterallyuniformmaterialpropertiesacrossthesignalspot,thesinglepassgaininaVCLAiscalculatedfromtheactiveregionmaterialgaingbywiththegainenhancementfactorξ(ξ<2),thetotalthicknessLaofallquantumwells,andtheaveragecavitylosscoefficientαc.Gainenhancementresultsfromtheplacementoftheactiveregion(s)atthepeak(s)ofthestandingopticalwavewith[14](LMQW-thicknessofeachMQWstack).Wecalculateξ=1.75forourperiodicgainstructure.ComputationofthequantumwellmaterialgaingisthemainchallengeofVCLAmodeling.TheopticalgaindependsontheQWcarrierdensityN,thesignalwavelengthλ,thetemperatureT,andthephotondensityS.Assumingλ=λc,roomtemperature,andrelativelylowphotondensities,thequantumwellgaincanbeapproximatedbyTheseformulasgivethefullwidthathalfmaximum(-3dB).Ingeneral,thebandwidthdecreasesasthepeakgainincreases.Thesquarerootofthepeakgaintimesthebandwidthgiveafigureofmeritthatispracticallyconstant(gain-bandwidthproduct).Thethresholdconditionandtheapproximationsin(x)=x(forsmallx)leadstothesimpleformulas.TheseequationsarevalidforanyFabry-Perotamplifierandtheirresultsareidenticalforsymmetricaldevices(Rf=Rb).Inthereflectioncase,Eq.11isrestrictedtogainvalueswellabove3dBsincetheinitialreflectioncausesasingularityofEq.9.Remarkably,thegain-bandwidthproductinreflectionmodedoesnotdependonthebottomreflectivityRbandgain-bandwidthmeasurementscanbeusedtoverifythefrontreflectivityRfortheopticalcavitylengthncLc.Figures3and4plotthegain-bandwidthproductasfunctionoftheoutputmirrorreflectivityforreflectionandtransmissionmode,respectively.ThedotsinFig.3givemeasuredresultsofour1.3μmVCLAswhichconfirmourmodel.Lowerreflectivitygiveshigherbandwidthinbothcases.Thereflectionmodecurvecrossestransmissionmodecurvesforsymmetricdevices(Rf=Rb).Thisleadstotheintuitiveresultthatthetransmissionmodegivesahighergain-bandwidthproductthanthereflectionmodeifRb<Rf(andviceversa).外文資料譯文

外文資料譯文半導(dǎo)體激光放大器的建模與優(yōu)化二．增益和帶寬對垂直腔激光器一個常見的建模方法是由具有相同的反射率的，有效腔長度為LC，分開的平面鏡來代替DBRS。這樣，我們就可以從著名的法布里珀羅特放大器增益公式的開始研究（GR反射模式，GT轉(zhuǎn)換模式）前鏡反射率為Rf、后鏡反射率Rb、單程增益GS，和單通道相位失諧Φ。當(dāng)信號的波長與法布里珀羅特諧振波長相同時(shí)，最大增益是Φ=0。相比與平面器件，vclas具有更小的GS和較大的反射率。使用兩層DBR從低到高的折射率比值，同時(shí)也加入第一（q）和第二（a）的DBR界面。假設(shè)使用折射率為3.45的（GaAs）和折射率為2.89（AIAs）。我們計(jì)算出計(jì)算出我們的裝置的RF=0.985以及RB=0.999。反射鏡的吸收或衍射降低了反射率。因?yàn)榈湫虳BR的反射帶寬遠(yuǎn)大于（在我們的例子中，約100nm）放大器的帶寬和空腔諧振波長λC，假定DBR中心波長相同，依賴DBR反射率的波長在這里忽略。我們的一維模型也忽略了橫向的光學(xué)模式結(jié)構(gòu)。在不同的橫向模式中，共振波長略有不同。腔折射率nc，有效空腔長度Lc大于DBR距離LM，包括前后DBR的相滲透深度LF和LB，分別為(Lc=Lf+Lm+Lb)，無損DBR在中心波長λc的相滲透深度由下面給出當(dāng)NC=3.2時(shí)，我們設(shè)備的DBR的穿透深度約為585nm。導(dǎo)致有效空腔長度lc=2.2μM。由于高指標(biāo)對比，AlAs/GaAsDBR比以Inp為反射鏡有較小的穿透深度。腔折射率Nc是通過兩層DBR間所有層來求平均求得。通常情況下。在目標(biāo)波長，它比襯墊材料的折射率高，但是它可以影響影響量子阱載流子密度以及裝置的加熱。剩余的需要研究的參數(shù)方程是單通道信號增益GS，假設(shè)橫向均勻的材料性能達(dá)到信號點(diǎn)