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THE NANO OPTOELECTRONICS GROUP

ANDREA REALE

Andrea Reale

AssociateProfessor
Nano&Optoelectronicsgroup(OLAB)

Dept.ElectronicsEngineering
UniversityofRome"TorVergata"
viadelPolitecnico1,00133Roma(Italy)

Tel   +390672597372
Fax+390672597939

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PROFILE

Dr.AndreaRealeisAssistantProfessorattheDepartmentofElectronicEngineeringoftheUniversityofRomeTorVergatasince2004.
MSCinElectronicEngineeringin1997,andPhDinMicroelectronicsandTelecommunicationsin2001.

LocalCoordinatorofaPRIN(MIUR,MinistryofUniversityandReseach)project,WGLeaderintheCEActionCOST267.

RESEARCHACTIVITY

 


 

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Strainsensors
Carbonnaotubes(mats,mebranesorCNT-polimernanocomposites)canbeusedtodetectstrainbymeansofpiezoresistivitybehaviourofthesematerials.


Gassensors
Carbonnanotubeshaveextremelyhigheffectivearea(surfaceareaperunitsurface).Thismakessuchmaterialsverysuitableforgassensing,duetothehighinteractionsurfacebetweenCNTandgasmolecules.Moreover,thesensorcanbeoptimizedtoacceleratethesensorresponsetime(gasdetection)andresettime(gasdesorption).Comparedtostandardgassensordevicesbasedonelectricalconductancemodification,athreeelectrodeconfigurationcanbeused,whereacontrolelectrode(actingasagate)inducesanelectrostaticalcontrolofthemolecules-cntinteractiondetectedasresistancechangebetweenthestandardelectrodes(actingassourceanddrain).Thefigurebelowshowsthealmostimmediateresistancechange(a)inducedbyexposuretoammoniagas(b)undertheeffectofacontrolsignal(c)acceleratingtheabsorptionandthedesorptionofthegas.

PhotoluminescenceandCathodoluminescencearespectroscopicaltoolsthatallowadetailedinvestigationofheterostructures.InGaNbasednanostructuresthesetechniquescanbeusedtostudytheeffectoftheinternalpolarizationfieldsinducedbyspontaneousandpiezoelectricpolarization.Inthefigurebelow,thestrongeristheexcitation(beamcurrrentinCLexperiment,opticalintensityinPLexperiment),thestrongeristhescreeningoftheinternalfields.



Asaresult,theinducedopticaltransitionsrevealablueshiftduetotheflatteningoftheconductionband(CB)andvalenceband(VB)profile.


TherealprofileofthebandsmustbeevaluatedbymeansofselfconsistentsimulationcouplingthecalculationofthequantizedstateswithSchroedingerequationtothesolutionofthePoissonequationforthedeterminationoftheinternalfields.Oncethatthecorrecttransitionenergiesareknown,opticaltransitionsandrecombinationratescanbecalculated.ArateequationmodelcanbeusdtostudyPLandCLexperiments.

Photoconductanceisapowerfulmethodtoevaluatethethermalresistanceofelectronicdevices.Theabsorptionspectrumiscorrelatedtotemperature,andacalibrationlawisextracted.Duringnormaldeviceoperation,theeffectofselfheatingismonitoredmeasuringtheshiftoftheabsorptionspectra.Thacalibrationprocedureallowstotransformspectralshifttotemperaturevariations.
Adetailedmapoftemperaturedistributioncanbeobtainedthroughfiberopticscanofthedevicelayout,asshownbelow.


Atemperaturemapisshownbelow:possibledisuniformitiesoftemperaturebetweensourceanddraincanbedetectedwithmicrometricresolution.

SemiconductorOpticalAmplifiers(SOA)areversatiledevicesthatcanbeusedinmanydifferentcontextforopticalsignalprocessing.
SOAcanbeoperatedtoperformlinearsignalprocessingsuchassimplelowcostopticalamplification,inspecificcontextssuchaslowpowersignalpreamplificationwherethepossiblenonlinearitiesthatmayoccurintheSOAareprevented.
WhentheoperatingconditionsexploitthenonlinearbehaviourofSOAdevices,exceptionalfunctionalitiescanbeachieved,suchasnonlinearopticalsignalprocessing.ThereisanumberofexampleswherenonlineareffectsinSOAshavebeenusedtoreshapewaveforms,toextractretimingsignals,toperformwavelengthconversionforwavelengthmultiplexedsystems(WDM),tocompensatefiberopticdispersion,etc...
ThenonlineareffectsthatcanbeinducedinSOAhavedifferentorigin.
First,opticalsignalcaninducethemselvesastrongmodulationofthegainoftheactivesemiconductorwaveguide.Inthisway,acontrolsignalcanmodifythepropagationofotheropticalinput.ThisisuedforexampleinCrossGainModulation(XGM)forwavelengthconversion,asshownbelow.


Theoutputsignal(afterfiltrationat1535nm)presentsintensityfluctuationsgivenbythegaincompressionmechanisminducedbythepumppulses(at1550nm).Evenifthelogicalcontentisnegated,thewavelengthconvertedsignalcanbeusedintheremainingsectionoftheopticallinkwithoutlossofinformationatbitratesupto10Gb/s.
Anotherimportantexamplewheregaincompressionisexploitedisalloptical3Rregeneration(Reamplification,ReshapingandRetimingofopticalsignals).
Anopticalloopcanbeusedtogenerateclockcomponentsinrandomdigitaldata,andaftersignalreshapingwithXGMstage,anidealopticalclocksignalcanbeextracted,evenfromNRZdigitalsignalformatwhereclockextrationisknowntobeverydifficult(noclockcomponentsintheRFelectricalspectrum).
Theimagebelowshowtheopticalloop.

 

TheimagebelowshowtheXGMstage.



TheimagebelowshowtheinputrandomNRZsequence(left),theclockextractedfromtheloop(center)andthereshapedclockwaveformafterXGMstage(rigth).



AnotherimportantkindofnonlinearitythatcanbeinducedinSOAsisrelatedtoKerreffect,whereelectromagneticsusceptibilitybecomesdependentontheincomingopticalfields.FourWaveMixing(FWM)canoccurr,andcomplexintensityandphaseinteractionbetweenopticalsignalscanoccurr,inasimilarwaytowhathappensinnonlinearefffectsinopticalfibers.SOAhavetheinterestingfeaturethatnonlinearitiesaresostrongthatthinteractionoccurrinfewhundrethsofmicronsratherthankmofopticalfibers.
FWMinteractioncanbeusedindifferentmanners,suchassampling,logicalANDoperationandwavengthconversion.
Anexampleofasamplingshemeisshownbelow.Thisistipycalofformatconversionschemes(forexample,NRZtoRZinOTDMsystems).



AnNRZsignalisconvertedtoRZformatbymeansofFWMinteractionwitatrainofopticalpulses.
AnexampleofNRZtoRZformatconversionisgivenbelow.

 

TEACHING

Optoelectronics2,LaboratoryofOptoelectronics,LaboratoryofOpticalCommunications,coauthorofabookonthefundamentalsofoptoelectronicsadoptedasreferencetextbookforOptoelectronics1.
MemberofthedoctoralcommitteeofthePhDprogramonEngineeringofSensorialSystems.

PUBLICATIONS

Prof.AndreaRealeisAssociateProfessorattheDepartmentofElectronicEngineering,UniversityofRomeTorVergatasince2014.In2013qualifiedfor“AbilitazioneNazionale-SecondaFascia”forthescientificsector09/E3–“Elettronica”accordingtolawn.240/2010.Formerlyfrom2004to2014wasAssistantProfessoratthesameUniversity.Prof.AndreaRealegraduatedcumlaudeinElectronicEngineeringin1997andreceivedhisPhDinTelecommunicationsEngineeringandMicroelectronicsin2001.

Theresearchcanbeclassifiedinto3mainareas:

•Devicesbasedonorganicsemiconductorsandhybridsorganic-inorganicsystems,withparticularattentiontothetechnologicalaspectsofscale-uponlargeareaofphotovoltaicdevicesandtodevicesfortelecommunications(visibleandIRphotodetectors,IRemitters);

•Experimentalstudyofnanostructuredmaterialssuchascarbonnanotubesandrelatedtechnologicalapplications(thermalmanagment,strainsensors);

•Theoreticalandexperimentalanalysisoftheoptical,electro-opticalandelectricalpropertiesofheterostructuredevicesforelectronicsandtelecommunications.

Prof.A.Realehasco-authored103publicationsininternationaljournalswithpeerreview,severaltensofpublishedproceedingsofinternationalconferences,1textbookinOptoelectronics,3chaptersinbooksreviewsonphotovoltaics,7internationalPCTpatents(including1acquiredbySelexSI,and6acquiredbytheconsortiumDyepower).Realeisrefereeforseveralinternationaljournals(Elsevier,IEEE,OSA,Wiley,etc.)asSensorsandActuatorsB,andIEEEPhotonicsTechnologyLetters,OpticalCommunications,IEEEJournalofQuantumElectronics,OpticExpress,OrganicElectronics,JournalofExperimentalNanoscience,PhysicalChemistryChemicalPhysics,ElectrochimicaActa,JournalofComputationalElectronics,JournalofNanophotonics,IEEEJournalofOpticalCommunicationsandNetworking.Realeparticipatedasaco-authortoapproximately80differentinternationalconferenceswithoralandposterpresentations(including6presentationsbyinvitation).

Prof.Realepresentsthefollowingsyntheticalbibliometricindexesdescribingitsscientificactivity:

Hfactor=22(source:Scopus),n.ofpublications:103,n.ofinvitationstoconferences:6,n.ofscientificawards:2,organizationofinternationalconferences:2,n.ofproceedingsoninternationalconferences:67,n.ofpatents:7,books:1,contributionstovolumes:3.

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