MaterialsTodayVolume17,Number3April2014 COMMENT
Comment
Mihaela Girtan
PhotonicsLaboratory,AngersUniversity,France [email protected]
Is photonics the new electronics?
Mihaela Girtan discusses electronics and the rise of photonics, and asks what the future has in store for technology
Silicondioxide,alsoknownassilica,iscommonlyfoundinnature, in sandor quartz, and is one of the most abundant chemical compoundsonearth.Humansdiscoveredhowtotransformthe silicaintosilicon,andtodayalmostallofourmoderntechnology isbasedonthissinglestartingmaterial.
Thefourbasicelementsofelectronicsare:(1)electronsascarrier vectors,(2)electricalcablesandcircuits,(3)thegeneratorsand(4) transistors. Progress in photonics provides the opportunity to replace electron flow, for transmission and computing, with a photonic flow or a plasmonic flow; harnessing the interaction between the surface electrons of nanostructured circuits and photons.
Theinformationcarriervectorsinphotonicscanbephotons, solitons,lightballs,orplasmons.Theplasmonisaquasi-particle associatedwith the plasmaoscillationsoffree electrondensity.
Theassociationofthisparticle,resultingfromexistingelectrons presentinthematerialandinjectedphotons,offersatleasttwo, unique,highlyimportantbenefits:(1)thepossibilitytotransmit informationwithhigherfrequency(about100THz)and(2)the abilitytoconfinelightinverysmalldimensionobjects.Lasersand spasersaretheopticalequivalentofelectricalgenerators;optical wave guides and optical fibers act as the transport cables; and plasmonsters and opticaltransistors arethe equivalentsofelec- tricalswitchesandelectronictransistors.
Thesenewphotonicstructuresareverysimilartothosefoundin electronics.Forinstance,intransparentflexibleelectronicsandin
thirdgenerationsolar cells, newpromising electrodesare com- posed ofthree-layeroxide/metal/oxide [1]. Wefindthese same structuresinphotonicsforplasmonicwaveguides[2].Thisisalso thecase fororganic solarcells[3]and organic waveguides[4].
Electronicshasalsoinspiredphotonicsforopticalcircuits,andby combining these two sciences, plasmonics circuits have been realizedinthelastfewyears.
Bycomparingthebasicelementsfromthesetwosciences–the electron in electronics vs the photon, soliton and plasmon in photonics;electricalcablesvsopticalfibersandplasmonicwave guides;electricalcircuitsvsopticalcircuits;electricaltransistorsvs optical transistors and plasmonsters; electrical generators vs pulsedlasers and spasers– we remarkthat photonics has built up,stepbystep,allthetoolsalreadyavailableinelectronics.These similaritiesleadtotheideathat,inthefuture,wemaybeableto replacedevicesthatuseanelectronicflow(mobilephones,com- puters,displays,etc.)withequivalentdevicesthatuseaphotonic oraplasmonicflow.Furthermore,inthecaseofaphotonicflow,it maybepossible totakeadvantage oftheultimatephoton gen- eratorasapowersource:theSun.
This presentsa familiar problem faced in the application of photovoltaic systems: the night–necessitating the storage of energy.However,if we think ona global scale, thereisalways lightavailable(earthrotates).Thus,oneofthebiggestchallenges of taking advantage of solar energy won’t just be to store the energy, but to create a global photovoltaic energy network.
Indeed, optical fiber networks are already in place and could representafirststepinconnectingfutureplasmoniccomputers.
While current electronics and photonics are based on sand (siliconandsilicondioxide),carbon,inbothbulkandgraphene form,mightbethefutureelementofchoice.Grapheneisavery interestingmaterialforelectronicapplications,asa transparent electrodewithverygoodmechanicalproperties,withnewtransfer techniquesallowingdepositiononlargeareaflexiblesurfaces.Due to the absence of an optical band gap, graphene absorbs all photonsatanywavelength.However,ifincidentlightintensity becomesstrongenough,duetothePauliblockingprinciple,the generatedcarriersfillthevalencebands,preventingfurtherexcita- tion of electrons at valance band. Hence this property could potentiallybe exploited to realize shortand very intense light pulses lasers with a wide optical response ranging through
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ultra-violet,visible,infraredtoterahertz.Theselasersmightbethe futureofpulsedsignalphotonicgenerators.Moreover,graphene’s structurespecificityandchargetransportpropertiesopenupnew researchpossibilitiesthroughgraphenenanoplasmonics.
While humanity has proved it can thrive on technologies derivedfromsand,itremainstobeseenwhetherthe samecan besaidofcarbon.Butperhapsthebiggerquestionsare;ifphotonic informaticsbecomesareality,willwestillneedelectricity?And whatwillthesolarpowereddevicesoftomorrowresemble?
Todaywetransformdifferentformsofenergyintoelectricityto meet most of ourneeds. But,will it be possible to avoid the transformationoftheenergyin electricityanddirectlyexploit solarenergy forallourrequirements?Forheating,wecanand oftendoalreadyusesolarenergydirectly,withouttransforming it.Iflightstorageispossiblethroughplasmons,lasercavities,or lighttrappingasintheblackbodymodel,itwillbepossibleto directlyusesolarenergyforlightingtoo.Opticalmanipulation andopticalengineconcepts havealreadybeenexperimentally demonstrated [5], and theprogress in photonicswith optical circuits, optical transistors, etc. has shown that photonic or plasmonicinformaticsmightbepossibletoo.Iflaserpropulsion can beachieved, andoptical engines work,we mayalsohave motorsworkingwithlight.
Todaywetransformsolarenergyintoelectricity,buttomorrow wemaybeusingsolarenergydirectly,forall ourtechnological needs.
Furtherreading
[1]M.Girtan,Sol.EnergyMater.Sol.Cells100(2012)153.
[2]J.Park,etal. Opt.Express18(2.)(2010).
[3]M.Girtan,M.Rusu,Sol.EnergyMater.Sol.Cells94(3)(2010)446.
[4]B.Zhang,etal. Appl.Phys.Lett.96(10)(2010).
[5]V.Garces-Chavez,etal. Nature419(6903)(2002)145.
MaterialsTodayVolume17,Number3April2014 COMMENT
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