国外分布式光纤传感文献1

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JOURNALOFLIGHTWAVETECHNOLOGY,VOL.23,NO.6,JUNE20052081

DistributedFiber-OpticIntrusionSensorSystem

JuanC.Juarez,Member,IEEE,EricW.Maier,KyooNamChoi,Member,IEEE,and

HenryF.Taylor,Fellow,IEEE,Fellow,OSA

Abstract—Adistributedsensorsystemfordetectingandlo-catingintrudersbasedonthephase-sensitiveoptical-time-domainreﬂectometer(-OTDR)isdescribed.Thesensingelementisacabledsingle-modetelecommunicationsﬁberburiedalongthemonitoredperimeter.Lightpulsesfromacontinuous-waveEr:ﬁberFabry–Pérotlaserwithanarrow(3kHz)instantaneouslinewidthandlow(fewkilohertzpersecond)frequencydriftareinjectedintooneendoftheﬁber,andthebackscatteredlightismonitoredwithaphotodetector.Theeffectofphasechangesresultingfromthepressureoftheintruderonthegroundimmedi-atelyabovetheburiedﬁberaresensedbysubtractinga-OTDRtracefromanearlierstoredtrace.Inlaboratorytestswithﬁberonreels,theeffectsoflocalizedphaseperturbationsinducedbyapiezoelectricﬁberstretcheron-OTDRtraceswereobserved.Inﬁeldtests,peoplewalkingonthegroundaboveaburiedﬁbercableinducedphaseshiftsofseveral-radians.

IndexTerms—Distributedsensor,Er:ﬁberlaser,ﬁbersensor,in-trusionsensor,optical-phasesensor,optical-time-domainreﬂec-tometer(OTDR),perimetersecurity.

I.INTRODUCTIONTHEoptical-time-domainreﬂectometer(OTDR),initially

demonstratedovertwodecadesago[1]–[3],isnowwidely

usedforlocatingbreaksandotheranomaliesinﬁber-opticlinks

andnetworks.InanOTDRsystem,lightpulsesfromasemicon-

ductorlaserareinjectedintooneendofaﬁber,andRayleigh-

backscatteredlightreturnedfromtheﬁberismonitoredwitha

photodetector.Thesystemdetectsthepresenceandlocationof

perturbationsthataffecttheintensityofthelightreturnedfrom

theﬁberbutdoesnotingeneralrespondtothephasemodulation

ofthelight.Thespectralwidthofthemodulatedlaserisvery

broad(gigahertztoterahertzrange)sothatﬂuctuationsinthe

returnsignalduetointerferenceofbackscatteredcomponents

fromdifferentpartsoftheﬁberare,forthemostpart,avoided.

Whenpresenttoanoticeableextent,coherenteffectsrepresent

anundesirablesourceofnoiseinanOTDRtrace.

Thedistributedsensordescribedinthispaperutilizesa

phase-sensitiveOTDR(-OTDR)systemdesignedtoenhance

coherenteffectsratherthanavoidthem[4].Phasesensitivity

ManuscriptreceivedSeptember10,2004;revisedJanuary25,2005.J.C.JuareziswiththeDepartmentofElectricalEngineering,TexasA&MUniversity,CollegeStation,TX77843-3128USA(e-mail:jcj@tamu.edu).E.W.MaierwaswiththeDepartmentofElectricalEngineering,TexasA&MUniversity,CollegeStation,TX77843-3128,USA.HeisnowwiththeMissionOperationsDirectorate,FlightControl,NationalAeronauticsandSpaceAdministration(NASA),Houston,TX77058USA(e-mail:eric.maier1@jsc.nasa.gov).K.N.ChoiiswiththeDepartmentofCommunicationEngineering,IncheonCityCollege,Incheon402-750,SouthKorea(e-mail:knchoi@icc.ac.kr).H.F.TayloriswiththeDepartmentofElectricalEngineering,TexasA&MUniversity,CollegeStation,TX77843-3128USA(e-mail:taylor@ee.tamu.edu).DigitalObjectIdentiﬁer10.1109/JLT.2005.849924resultsfrominterferenceofthelightbackscatteredfromdif-

ferentpartsoftheﬁber,whicharrivesimultaneouslyatthe

photodetector.Asapracticalmatter,the-OTDRcandetect

perturbationsmuchtoosmalltobeperceivedwithaconven-

tionalOTDRsystem.

Inpriorresearch,the-OTDRhasbeenappliedwithboth

pulsedandcontinuous-wave(CW)laserlightsourcestode-

tectanddeterminethelocationofphaseperturbationscaused

bystretchingorheatingopticalﬁbers.Arepetitivelypulsed

-switchedyttriumaluminumgarnetlaserwasthelightsource

inasystemforobservingapiezoelectricallyinducedlength

change,andapulsedsemiconductorlaserwasusedinthedetec-

tionofarapidlyincreasingtemperature[5].Asingle-frequency

CWsemiconductorlaserinconjunctionwithanexternalacous-

toopticmodulatorwasusedtosensealocalizedthermalper-

turbation[6],[7],andanEr:ﬁberlaser,incombinationwithan

electroopticmodulator,wasappliedtoobserveapiezoelectri-

callyinducedlengthchange[8].

Otherdistributedsensorsapplicableforintrusionsensing

arebasedontheSagnacinterferometer.Theﬁrstreported

wasatwo-interferometerconﬁgurationincorporatinga

Mach–Zehndertomeasurethephase-changeratewiththe

Sagnacinterferometertodetectnonreciprocalphasepertur-

bances[9].Modiﬁedversionshavebeenproposedtoeliminate

thepositionsensitivityoftheSagnacinterferometerwitha

phaseshifterortheneedforahighlycoherentlightsource

withwavelength-division-multiplexing(WDM)techniques

[10].AfrequencymodulationCWtechniquewasapplied

toabirefringentSagnaclooptousetheintensityandfre-

quencyofabeatsignalproducedbytwoforward-coupled

modebeamstodeterminetheamplitudeandlocationofan

appliedstress,respectively[11].Adual-wavelength,merged

SagnacandMichelsoninterferometersystemhasbeenpro-

posedwithabroad-bandsourceforoptimaloperationofthe

Sagnac[12].Two-loopandvariable-loopSagnacinterferometer

systemshavebeeninvestigatedtopreservetheinherentinsen-

sitivitytoreciprocaldisturbancesoftheSagnac[13],[14].A

single-source,single-detectorWDMsystemincorporatingdual

40-kmSagnacloopshasbeenappliedwithreal-timelocation

ofmultipletime-varyingdisturbances[15].

Inthedistributedintrusionsensorreportedhere,thephase

changesofinterestresultfromthepressureofanintruderon

thegroundabovetheburiedﬁbercable[4],[16],asillustrated

inFig.1.LightpulsesfromaCWlaseraregatedintooneend

oftheﬁberviaapulsedintensitymodulator,andthebackscat-

teredlightfromtheﬁberismonitoredwithaphotodetector.As

withtheconventionalOTDR,the-OTDRtraceisaplotofre-

turnedopticalpowerversustime.Whenthesensingﬁberand

lightsourcearestabilized,theresultingtraceexhibitsaunique

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