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1、Fiber-opticbiosensorbasedonself-mixinginterferometryaaabaMiiaMäättälä*,JanneLauri,MattiKinnunen,JukkaHast,RistoMyllyläaOptoelectronicsandmeasurementtechniqueslaboratory,P.O.Box4500,90014UniversityofOuluandInfotechOulu,Oulu,Finland;bVTTTechnicalResearch
2、CentreofFinland,Kaitoväylä1,90570Oulu,FinlandABSTRACTSelf-mixinginterferometryisapromisingtechniqueforavarietyofmeasurementapplications.Usingalaserdiodewithanexternalcavityasinterferometer,thetechniqueoffersseveraladvantagesovertraditionalinterferometr
3、icconfigurations.Thisresearchusedaself-mixinginterferometerbuiltinourownlaboratory.ItisbasedonablueemittingGaNlaserdiodewithawavelengthof405nm.Lightisdirectedthroughanopticalfiberfromwhicha1-cmsectionofcladdinghasbeenremoved,andacuvetteforholdingthesam
4、pleisfixedaroundthispart.Interferencepatterns,createdinthelasercavity,areacquiredwithacomputer-baseddataacquisitionsystemandlaterprocessedusingMatlabsoftware.Sincesampleswithdifferentrefractiveindicescreateinterferencepatternswithdifferentphases,evensm
5、allchangesinsampleconcentrationscanbemeasured.However,couplinglightintoasingle-modeopticalfiberisaverychallengingtask,andthesetupisverysensitivetoexternalinterferencelikeairflowsorvibrations.Experimentswiththedeviceshowedthat,instabilitymeasurements,th
6、estandarddeviationoftherecordedfringepatternshiftswasonly1.7nm.Insamplemeasurements,therefractiveindexchangeinthesamplechambervariedfrom1.0029to1.33,correspondingtoafringepatternshiftof297±4nm.Keywords:Self-mixinginterferometry,laserdiode,opticalfiber,
7、externalcavity,refractiveindexchange.1.INTRODUCTIONInrecentyears,wirelesscontinuousmeasurementmethodshavebeenaconstantsubjectofresearch,especiallyinhealthcare,andeveryyearnewerandmoresophisticatedmethodsarecommercializedandintegratedintodifferenthealth
8、parametersupervisionsystems.Whencombinedwithwirelesscommunicationdevicesandanalyzingprograms,thesesystemscanbeusedforarangeofapplications,includingthesupervisionormonitoringofdailyactivities.Mostcommonlymeasuredparameters,orvitalsigns,a