Design and Characteristics of an Opto fl uidic Phase Modulator Based on Dielectrowetting - Liang et al. - 2021 - Unknown

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pubs.acs.org/LangmuirArticleDesignandCharacteristicsofanOptofluidicPhaseModulatorBasedonDielectrowettingZhongchengLiang,WenxuanDing,RuiZhao,*YayanHuang,MeimeiKong,andTaoChenCiteThis:Langmuir2021,37,769−773ReadOnlineACCESSMetrics&MoreArticleRecommendationsABSTRACT:Inthispaper,anoptofluidicphasemodulatorbasedondielectrowettingisdesignedandfabricatedtoadjusttheopticalphase.Twoliquidsarefilledinthedevice,andatransparentsheetisemployedattheliquidinterfacetokeeptheinterfaceflat.Whendifferentvoltagesareappliedtothemodulator,theflatinterfacemovesupanddown,leadingtothevariationoftheopticalphase.Atheoreticalmodelisconstructedtopredicttheopticalphaseshiftquantitatively,andthephaseregulationabilityisalsotestedexperimentally.Ourmodulatorrealizescontinuousadjustmentoftheopticalphaseinacertainrangebytheoperationofvoltageadjustment.Whenthevoltageisincreasedto150V,theopticalphasemodulationrangeofourproposedmodulatorcanreach9.366π.■INTRODUCTIONeffectsofviscosity,ACfrequency,andvolumeofsiliconeoilon20liquidbehavior.ThefocallengthofatunabledielectricliquidOpticalphasemodulationishighlyappliedinindustriallenschangesfrom14.2to6.3mmwhenthevoltageismanufacturingandscientificresearch.Intheopticalcoherence21tomographyimagingsystem,1−3toobtainthetomographicincreasedfrom0to125V.A.OusatiAshtianiandH.Jiangimageofthemeasuredobject,theopticalpathofonearminreportedanopticalphasemodulatoractuatedbyelectro-theinterferometerneedstobeadjustedtorealizeinterferencewetting,andanopticalphaseshiftof171°issuccessfully4,5achievedunderavoltageof100V.22,23LeiLiproposedapatterns.Thephase-shiftinginterferometrytechnology,asanewimagingandmeasurementtechnology,anddifferentphasedisplaceableandfocus-tunableelectrowettingoptofluidiclens,shiftsontheinterferometricreferencearmarerequiredtowhereametalcylinderisemployedasthesidewallelectrodegenerateinterferencepatternswithcorrespondingdifferentandtheliquidcombinationsareNaClandsiliconeoil.Thephaseshiftsontherecordingplane.Incommunicationlargestdisplaceabledistanceofthislensis8.3mmandits6,724systems,electro-opticmodulatorsmodulatetheopticalrelativezoomratiois1.31×.QionghuaWangdesignedanphaseoflighttoachievesignaltransmission.Generally,thereopticalpathmodulatorbasedonelectrowettingtomodulateDownloadedviaUNIVOFCALIFORNIASANTABARBARAonMay16,2021at08:22:03(UTC).Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.aremainlytwomethodstoadjusttheopticalphase.Oneistothebackfocallengthintheimagingsystem,wheretherelativechangethegeometriclengthofthelightbymechanically25opticalpathlengthchangeis1.15mm.Theseworksprovide8,9movingtheopticalelements,andtheotheristochangethereferencestotheopticalphasemodulatordesign.refractiveindexofthetransmissionmedium(e.g.,liquidInthiswork,anoptofluidicphasemodulatorbasedon10,11crystal).However,thesetraditionaldeviceshaveproblemsdielectrowettingisproposedtomodulatetheopticalphase.suchascomplexstructures,bigsize,polarizationdependence,Thedeviceisfilledwithtwoimmiscibleliquids,andaelectromagneticinterference,andsoon.Asaconsequence,atransparentsheetisfixedbetweentheliquidandliquidtransmissiveopticalphasemodulationwithpolarizationinterfacebyanelasticfilm26togenerateaflatinterface.Aindependence,simplestructure,easyminiaturization,highmeasurementplatformisestablishedtomeasuretheperform-modulationaccuracy,andnoelectromagneticinterferenceisstillverydesirableforhigh-performanceopticalsystems.Microfluidictechnology12−19hasbeendevelopedinrecentReceived:October21,2020years,andrelativedeviceshavebeendevelopedandwidelyRevised:December22,2020usedbecauseofnoelectromagneticinterference,simplePublished:January5,2021structure,polarizationindependence,andsoon.ChihChengYangdevelopedaliquidmicrolensdrivenbydielectricforceandanalyzedthedynamicbehaviorofdielectricliquids,the©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.langmuir.0c03064769Langmuir2021,37,769−773

1Langmuirpubs.acs.org/LangmuirArticleFigure1.Structuredrawingoftheopticalphasemodulator(section).anceoftheopticalphasemodulator.Theresultsshowthatourproposedmodulatorcanchangetheopticalphasecontinu-ously.Themaximumrangeoftheopticalphasemodulationisabout9.366πwhenthevoltageis150V.Relatedresearchwillpromotethedevelopmentofopticalphasemodulatorsand■provideareferenceforphasemodulationinopticalsystems.STRUCTURALDESIGNANDDEVICEFABRICATIONStructuralDesign.Figure1showsthecrosssectionofouropticalphasemodulator,whichismainlycomposedofanuppercoversheet,alowercoversheet,anoutercylindricalchamber,aninnercylindricalchamber,andatransparentsheet.Tosimplifythestructuredesignandfabricationprocedure,anFigure3.Workingprinciplediagramoftheopticalphasemodulator.indiumtinoxide(ITO)planarelectrodeshowninFigure2is(a)InitialstateU=0V.(b)OperatingstateU=100V.andanelasticfilmisattachedattheliquid−liquidinterfacetoholdthetransparentsheet.Duetotheexistenceofthetransparentsheet,theinterfacewherethelightpassesthroughisalwaysflat,andtherefore,noadditionalaberrationsareintroduced.Theopticalpathdifference(OPD)inFigure3a,bcanbeexpressedasOPD=nlloo(′−+o)nlgg(′−=lg)ΔnlΔo(1)whereΔlo=lo′−lo,ΔloisthevariationofthedropletheightFigure2.Structureoftheinterdigitatedelectrode.afterapplyingvoltage,Δn=ng−no,ngistherefractiveindexofethyleneglycol,andnoistherefractiveindexofsiliconeoil.usedintheoptofluidicphasemodulator.AsiliconeoildropletTheshapeoftheinsulatingdropletinFigure3canbeisdroppedatthebottomcenterofthedevice,andtheregardedasthedifferencebetweentwosphericalcaps.Becausesurroundingisfilledwithethyleneglycol.Atransparentsheetisoftheconstantvolumeofthedroplet,therelationshipbetweenfixedatthebottomoftheinnercylindricalchamberbyanthechangeofdropheightΔloandthevoltageUcanbederivedelasticfilm,whichseparatesethyleneglycolandsiliconeoilandbasedontheminimizationofthesurfacefreeenergyadherestotheliquid−liquidinterface.Becauseoftheexistence2/32/3oftheelasticfilm,thetransparentsheetcanmoveupandijjεπ00ΔεV24πVV0yzzijj4π0yzzdown,whichisthekeytotheopticalphasecompensation.Δlo=jjjU+−zzzjjjzzz5πδγ5π5πWorkingPrinciple.Theworkingprincipleisdepictedinklf{k{Figure3.Whenavoltageisappliedtotheplanarelectrode,the(2)dielectricconstantofthesiliconoildropislowerthanthatofwhereε0isthevacuumdielectricconstant,Δε=εf−εl,εfistheethyleneglycol,causingthedielectricforcetosqueezethetherelativedielectricconstantofethyleneglycol,εlisthesiliconoildropletinwardandincreasethecontactanglewithrelativedielectricconstantofsiliconeoil,V0isthevolumeof21thebottomsurface.Beingsqueezed,theheightofthesiliconethesiliconeoildroplet,δisthepenetrationdepthoftheoildropletincreases,andthenthesiliconeoilpushestheelectricfield,andγlfistheinterfacialtensionbetweensiliconetransparentsheetupward.Oncethevoltageisdecreased,theoilandethyleneglycol.heightofthesiliconeoildrops,andthefloatingsheetmovesAccordingtothetheoryofphysicaloptics,therelativedownward.Therefore,theliquid−liquidinterfacecanmoveupvariationoftheopticalphaseisordownhorizontallybycontrollingthevoltage,whichcauses2πthevariationoftheopticalpathintheverticaldirectionandΔφ=·Δ·Δnloλ(3)realizesthemodulationoftheopticalphase.Here,atransparentsheetisfixedonthetopoftheinsulatingdroplet,whereλisthewavelengthofthebeam.770https://dx.doi.org/10.1021/acs.langmuir.0c03064Langmuir2021,37,769−773

2Langmuirpubs.acs.org/LangmuirArticleFigure4.Fabricationprocedureoftheoptofluidicphasemodulator:(a)deviceofthephasecompensator,(b)sheet,(c)outercylindricaltube,(d)lowercoversheet,(e)uppercoversheet,(f)innercylindricaltube,(g)electrode.Combiningeqs1−3,thevariationoftheopticalphasewithTable1.ParametersoftheLiquidMediumvoltagecanbeexpressedassiliconeoilethyleneglycolglycerolÄÅÅ2/3density(g/cm3)0.961.11551.263−1.3032πÅÅÅÅijjεπ00ΔεV4πVyzzΔφ=Δ·nkÅÅjjU2+0zzdielectricconstant2.1737−4156.2λÅÅÅÅj5πδγ5πzrefractiveindex1.411.431.47ÅÇklf{Ésurfacetension(mN/m)15.9−21.546.4961.92/3ÑÑijj4πVyzzÑÑviscosity(mPa·s)9625.6615000ÑÑ−jjzzÑÑj5πzÑÑtheactionofthefloatingsheet,thesphericalliquid−liquidk{ÑÑÑÖ(4)interfaceturnsintoaplanarinterface.wherekistheempiricalcoefficient.Byusingeq4,thevariation■oftheopticalphasecanbecalculatedandwillbecomparedEXPERIMENTALSECTIONwiththeexperimentaldata.Figure5istheschematicdiagramoftheopticalphasemeasurementoftheoptofluidicphasemodulator.AMichelsoninterferometerisDeviceFabrication.ThefabricationprocedureoftheoptofluidicphasemodulatorisprovidedinFigure4.High-transparencymaterialsareemployedtofacilitatethepassageandobservationoflight.TheITOplanarelectrode(30mm×30mm)iscoatedwithSU8(∼5μmthickness)andFluoroPelsuccessively.ItshouldbenotedthatFluoroPelisonlycoatedonthecentralarea(∼9mmindiameter)asahydrophobiclayertoconfinethesiliconoildroplet,therangecoveredbyCytop,andatthesametimereducethefrictionduringthemovementoftheoildroplets.Acylindricalpolymethylmethacrylate(PMMA)cavitywiththesizeof15mm(diameter)×10mm(height)isusedastheFigure5.OpticalphasemeasurementoftheoptofluidicphaseouterchamberwhichisfixedonthebottomsubstrateinFiguremodulator.4c.Inordertofacilitatetheliquidsflowfluently,fourcircularholes(1.5mmindiameter)aremadeontheinnercylindricalemployed,anda632.8nmhelium−neonlaserisusedasthelightchamber.Theinnerchamber(diameter7mm×height8mm)source.Theemittedlightpassesthroughtwopolarizers,abeamisaneffectivepartofthedevice,whichisconnectedwithaexpander,andasmallaperturediaphragminturnandthenilluminatesthebeamsplitteroftheinterferometeratanangleof45°.ThePMMAannularsheet(6mmindiameter).Thetransparentvariationoftheopticalphasethroughourdeviceisreflectedinthepartitionisfixedatthebottomoftheinnerchamberbyanmovementoffringes.ACCDcamera(MV-GE202GM-T:2/3″elasticfilmpolydimethylsiloxane(PDMS,∼100μmthickness).CMOS)isemployedtocapturetheevolutionofinterferencefringes.Thesiliconeoil(DowCorningOSsiliconeoils,n=1.41,Avideooftheinterferenceringmovementisprovidedinthedielectricconstant=2.17)andethyleneglycol(orglycerol)areappendix.employedasworkingsubstances,whichareinjectedintothechamberseparatelybyusingasyringepipette.Therelative■RESULTSANDDISCUSSIONparametersarelistedinTable1(roomtemperature20°C).InordertoimprovetheperformanceofouroptofluidicphaseWhenthevoltageiszero,becausethedensityofthetwomodulator,thedielectrowettingbehaviorofsiliconeoilliquidsisapproximatelyequalandtheyareimmisciblewithdropletswiththetransparentsheetfastenedbyanelasticeachother,asphericalliquid−liquidinterfaceisformed.Underfilminanethyleneglycolisexperimentallyanalyzed.Figure6771https://dx.doi.org/10.1021/acs.langmuir.0c03064Langmuir2021,37,769−773

3Langmuirpubs.acs.org/LangmuirArticleASi-AmplifiedDetector(PDA10A-EC,ThorlabsInc.,Newton,NJ,USA)replacestheCCDcamerashowninFigure5tocalculatetheopticalphasemodulationvaluesbydetectingtheintensitiesoftheinterferencefringes.Figure8showstheFigure8.Variationofopticalphasedifferencevsvoltage.Figure6.Dielectrowettingbehaviorofthesiliconoildropletinvariationofopticalphaseforourmodulatoratdifferentethyleneglycol.(a)U=0V,(b)U=130V,(c)thecontactangleofvoltages,wherethehollowcircle(○)istheexperimentaldata,siliconeoildropletvsvoltage.whilethelinewiththehollowsquare(□)isthetheoreticalvaluescalculatedbyeq3.Thedataoftheoreticalpredictionandexperimentshowgoodagreement.Themaximumphaseshowsthevariationtrendsofthecontactangleandheightofshiftreachesapproximately9.366π.Thereisnosignificantthesiliconoildropletwithvoltageinethyleneglycol.Figure6achangeintheopticalphasewhenthevoltageissmallerthan70showstheinitialstateoftheoildroplets,whilethevoltageisV.Whenthevoltagechangesfrom80to110V,theoptical130VasshowninFigure6b.Whenthedropletisconstrainedphaseofourdevicevarieslinearlywithvoltages,thatis,ourbytheelasticmembraneandsheet,itscontactanglechangesdeviceisworkinginthelinearregion.Oncetheworkingwiththevoltageobviously,whileitsheightchangesslightly.voltagereachesabove150V,instabilityofpropertyandbadFigure6cshowsthatthecontactangleofthesiliconeoilapplyingabilityexistforthismodulator.Afteraseriesofdropletincreaseswithvoltage.runningtests,theresultsshowthatouropticalphaseFigure7providestheinterferenceringscapturedatU=95modulatorhasstableperformanceinopticalphasemodulation.−150V,respectively.Whenthevoltageisintherangeof0−Inthefuture,theoptimumliquidcombinationswithalarger70V,thereisnoobviousmovementintheinterferencefringe.refractiveindexdifferencewillbeinvestigatedforachievingaHere,70Visdefinedastheoperatingthresholdofourdevice.broadermodulationrangeofopticalphaseshiftatalowerTheauthorssuggestthatthethresholdiscausedbythepinning27voltage.effectofdielectrowettinginconjunctionwiththepotentialrequiredformechanicaldeformationoftheelasticfilm.When■thevoltageisincreasedupto70V,theinterferenceringsstartCONCLUSIONStoshrinkinward,monitoredbytheCCDcamera.WhentheInthispaper,anoptofluidicphasemodulatorbasedonvoltageis150V,theshiftnumberoftheinterferencefringeisdielectrowettingisdesignedandexperimentallyfabricated.Anabout9.Theproblemsofnonstandardandedge-blurringringsopticalphasedetectionsystemisestablishedtotesttheinourinterferencefringesareassumedtobecausedbytheperformancesofthephasemodulator.Atheoreticalmodelisunevencoatingofthedielectriclayerinthefabricationprocessconstructedtopredicttheopticalphaseshiftasafunctionofandpoorlighttransmissioninmeasurement.voltage.TherelativedataofpredictionshowgoodagreementFigure7.Evolutionofinterferencefringesvsvoltage(thefringes“spitout”).(a)95V,(b)100V,(c)105V,(d)110V,(e)115V,(f)120V,(g)125V,(h)130V,(i)135V,(j)140V,(k)145V,(l)150V.772https://dx.doi.org/10.1021/acs.langmuir.0c03064Langmuir2021,37,769−773

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