ABSTRACT
One of the frequently posed targets of silicon photonics is the monolithically integrated superchip. ™e basicpremiseofsuchasuperchipisthatitincorporatesallofthenecessarycomponentstodetect,route, convert,multiplex,encode,reroute,demultiplex,amplify,orevencreateopticalsignalsthatcouldsubsequentlybeinterrogatedbyelectricalcircuitry.InSoref ’searlyvisionofsuchachip,opticalfibers wereproposedasameanstobutt-coupletowaveguidesonthechip.™efibersweretobesupportedby high-precision v-grooves etched into the silicon substrate [6]. It is interesting to note that passive alignmentoffiberstowaveguidesonasiliconphotoniccircuitremainsachallengetoday,partlyduetothe morerecenttrendtosmallercross-sectionaldimensionsofwaveguidesanddevices.™eopticalsignals wouldtheneitherbedetectedbyaSiGeorGephotodiodeforelectronicinterrogationorpassedtoother devicesforopticalprocessingbymeansofwaveguide-baseddevices.Duetolossesand/orpenalties inotherpartsofthesystem,thelightcouldalsobeamplified,orperhapsreshapedandreencodedvia anopticalmodulatorbeforeretransmission.However,Soref ’searlyvisionenvisagednotamonolithic chip,buthybridintegrationofarangeofmaterialstoperformtheindividualfunctions.Today,many authorsenvisageatrulymonolithicsuperchip,althoughrecentworkpioneeredbyBowersetal.(e.g., [7,8])inthedevelopmentofIII-Vlasersintegratedontoasiliconwaveguideplatformhavereinvigorated the“hybrid”viewoftheintegratedchip,oratleastthehybridlaser.Otherdevicevisionsremainpredominantlyinthemonolithicarena,althoughsilicon-compatiblecompoundssuchasSiGe(orperhaps evenpuregermanium)arealsocommonlyutilizedfordetectorwork,andhencebroaderapplication ofsuchmaterialsisanaturalnextstep.WithrecentworkinRamanamplificationandlasers[9,10], andfastmodulators[11,12],wecannowlookforwardtomonolithicversionsoftheopticalsuperchip. Furthermore,thevisioncanalsoincludetraditionalelectroniccomponentstocontrol,drive,andtime thesefunctions,typicallyinCMOS,butalsotheopportunityofotherformsofelectronicandphotonicintegrationarealsoenvisaged,suchas,forexampleSiGe-basedBiCMOS,withSi-basedphotonics. Opticalandelectronicintegrationhastakenplaceonlyinaverysimplewaytodate(e.g.,[13]),and remainsachallenge.However,recentinitiativessuchastheDARPAEPICprogram[14],andtheMURI programintheUnitedStates,andnumerousEuropeanprojects,notablyHELIOS,willalsobeginto address these issues.
