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Measurement of Apex Offsets for Fiber Connector End Faces

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Measurement of Apex Offsets for Fiber Connector End Faces

    Measurement of Apex Offsets for Fiber

    Connector End Faces

VO1.12SemiconductorNov.2006

    No.4PhotonicsandTechnologyTotalNo~46

    MeasurementofApexOffsetsforFiberConnectorEndFaces

    xuYongxiang,ZHURihong,CHENLei

    (CollegeofOpto-electronicTechnology,NaingUniversityofScienceandTechnology,Nanjing210094,CHN)

    Abstract:AsoneofthemostimportantgeometricparametersforaPC

    typefiberconnectorendface,apex

    offsetcancontributetohighinsertionlossandhighback

    reflectionreading.Anovelmeasurementmethodfor

    theparameter,connectorrotating

    ,cmethod.isproposed.Withthemethod.theapexoffsetofacommon

    connectorendfaceismeasured.TheresultiscomparedwiththatmeasuredbyaNorland3000fiberconnector

    endfaceinterferometer.Itisfoundthatthedifferencebetweentworesultsis1.8"m.Meantime.the

    influencesofrelevanterrorresourcesonapexoffsetmeasurementunderrotating

    7cmethodandaDex一?re

    methodarerespectivelyanalyzed,andtwoerrorequationsarederived.Theanalyticalresultshowsthat,

    comparedwithapex-coremethod,iftwoadditionalsub-tiltsofaxiswithinandinthedirectionperpendicularto

    principalplanecausedbyitsrotationarenotbiggerthantheoriginalaxistiltangle,themax.measurement

errorwillthenbereducedbyatleast22.5withrotating

    ,cmethod.Thepracticabilityofthemethodis

    confirmedbytheexperiments.

    Keywords:Apexoffset;Fiberconnector;Phaseshiftinginterferometry;Algorithm. CLCnumber:TN29Documentcode:AArticleID:10070206(2006)04027006

    lIntrOducti0n

    Asisknown,fiberconnectors[1I2]areimportantsource

    freecomponentsinfibercommunications.

    amongwhichthePC

    typeisthemostconstantlyused.Afterpolishing.adistancewillinevitablydevelop betweenfibercoreandtheapexoftheendface,whichiscalledapexoffset(AO)oreccentricityofpolish.

    AsAOcancontributetohighinsertionlossandbackreflectionreading[3I4jinlighttransmission.TIA(also

    TelcordiaGR326COREandIEC6087414

    n)hasaspecifiedcriterionontheparameter[,i.e.,?50?m.

    Therefore,howtopreciselymeasuretheapexoffsetbecomesanimportanttaskforensuringconnector

    performances.

    AcommonapproachforAOmeasurementiswhatwecallapexcore

    coordinatesmethod[?',i.e.,by

    measuringthecoordinatesofthecentersofcladdingimage(correspondingtofibercore)[14~16]andof

    interferencefringes(correspondingtotheapex)[17I8]soastogettheAOvalue. Whenapplyingthis

    approach,itisnecessarythattheaxisofconnectorisadjustedtobestrictlyparalleltothatofthe interferometricobjective.However,becauseofinaccuracyinjudgingthecentersofthecoreandoffringes,

    etc.'acertainaxistilterrorwillremainbeforeactualmeasurementinadjustingconnectoraxis. Subsequentanalyticalresultindicatesthatoffsetmeasurementerroriscloselyrelatedtothetil

terror.with

    aproportionalcoefficientbeingradiusofcurvatureR.Forthis,aprecisiontiltadjustingmechanismis

    necessaryforadjustmentoftiltangleofthetestconnector[?.Andthiscertainlywillleadtoagr

    eat

    increaseintheinstrumentdevelopmentcost.Inthiscondition,anewapproach,connectorrotating-7c

    method,ispresented.Underthismethod,aprecisiontiltadjustingmechanismisunnecessary.Withit.a

    connectorendfaceapexoffsetisdeterminedbysimplyapplyingacommon3

    dimentionalconnector

    adjustmentmount.Experimentsandanalyticalresultshowthatrotating-7cmethodispracticable.

    Receiveddate:20060515;reviseddate:20060531

    Foundationitem:ResearchProjectsofNanjingUniversityofScienceandTechnology

    V0I.12No.4XUYX,eta1.MeasurementofApexOffsetsforFiberConnectorEndFaces271 2Apex-coreMethodandCorresponding'ErrorAnalysis

    Whenapplyingapex-coremethod,wefirstneedtoadjustconnectoraxisforittobecomeparallelwith

    thesvstemaxis,andthenmeasurethedistancebetweenthecentersoffringesandofcladdingimage.To

    makethetwoaxesparallel,weneedtorotatetheconnectortosomedifferentpositionsarounditsaxis'

    comDarethecorrespondingdistancesbetweenthetwocentersandadjusttheaxisdirectionuntilthe

    distancesbecomethesame.However,asthereexisterrorsindecidingthetwocentersandchangeotaxls

    directionduringconnectorrotation,etc.,wemaythinkthetwoaxesbecomeparallelafteradjustment'but

    infactacertainaxistilterr0rastillexists.NowwemakeflbriefanalysisofitsinfluenceonAOmeasurement.

    Forconvenienceofstatement,wecalltheplane

    asprincipalplane(PP.PP)whichisformedbythe

    axesoftheconnectorandthesystem,andcallthe

    planeasmaincrosssection(MCS,MCS)whichis

    formedbythecurvaturecenteroftheendfaceand

    connectoraxis.WhatFig.1showsisthecasewhenFi1.

    MCSisparallelwithPP.Now,wesetupflcoordinatesystem

    Anaxistiltofisleftoverafteradjustment

    withoriginOatthefibercenteroftheend

    faceandthe()-Zplanecoincidingwiththeprincipalplane,andtakeitpositivewhenMCSturnsin

    clockwisedirection(seendownward)relativetothePP.Asaresult,foranarbitraryincludedangle0

    betweenMCSandPP,thecoordinatevectorcorrespo

    Q4~sin0?i+(~cos0+Rsin)?J

    ndingtotheapexcanbewrittenas.

    一?sinCOS0?k一不?0<(1)

    wherei,_andkareunitvectorsinthedirectionsofx,yand,respectively,Rreferstotheradiusof curvature(ROC)ofthetestedconnectorendface.

    ?referstoapexoffset,OandCrepresentapexand

    curvaturecenteroftheendface,respectively.Thus,foranarbitrarypositionoftheMCS,the correspondingapexoffsetmeasurementerrorunderapex-coremethodis -

    ??一llQ?I一?II(?+2Reginac0s+R),2一?I(2)

    Eq.(2)indicatesthatAOerrorbearsflrelationwith

    0,asshowninFig.2.Unfortunately,throughout

    themeasurement,0remainsunknown.Thusthe

    apexoffseterrorshouldbeevaluatedbymax.error

for0?90..Asthetiltangleisusuallyvery

    small.themax.abs.errormayapproximatelybe

    expressedas

    ??l?Ra(3)

    Itindicatesthat,underapex-coremethod,max. 7

    6

    g5

    4

    q3

    2

    1

    Fig.2.Relationofapexoffseterrorwiththepositionofthe MCSoffiberconnectorunderapex-coremethod

    AOerrorismuchinfluencedbythetilterrorofconnectoraxis. 3PrincipleofRotating-~Method

    3.1MeasurementApproach

    Themeasurementapproachofrotating

    7rmethod:Firstlyperformparalleladiustmentofconnector axis(strictlvparallelunnecessary);Secondlytakephase

    shifting"interferogramsandthecladdinglmg' applyingphaseshiftingalgorithmandimageprocessingtogetpre

    rotationcoordinatesofthePxandnb

    core,A(z1,Y1)andO(zo1,y01),respectively;Finallyrotatetheconnectorforanangleroundtt

    sax.s,

    applyingthesameprocessingmeansasabovesoastogetpost

    rotationcoordinatesoftheapexandtlber

    core,A(z2,y2)andO(x,Y).Intheidealcasewherefibercorehasnodisplacementandconntoax

    is

    dhectionremainsunchanged,thefollowingresultcanbeobtainedfromEq.(1).

272SemiconductorPhotonicsandTechnologyNov.2006

    eIAAl/Z=e(4)

    3.2ErrorAnalysisonRotating-~Method

    Infact.duetoconnectorrotation,thepositionofcoreanddirectionoftheaxiswillinevitablychange,

    moreor1ess,comparedwithpre

    rotation.Inaddition,theangleofrotationwillalsobearalittledifference fromtheidealvalueof7

    .Amongthechanges,theshiftofcoreiscausedbytwopossibleaspects, displace.mentoftheconnectorasawholeandthechangeofitsaxisdirection,thelattercapableofbeing

    decomposedintotwosub-changeswithinPPandalongthedirectionperpendiculartotheplane.Nowwe

    makeaquantitativeanalysisonthem,respectively.

    3.2.1InfluenceofConnectorDisplacement

    Withtheoriginsetatthefibercenter,theconnectordisplacementapparentlycausesnoerror;when

    calculatingapexoffsetfromphaseshiftinterferograms,however,thecorrespondingexpressionshouldbe

    asfollows.

    ?===

    3.2.2InfluencesofC

    =I__二二__二二_L[(y)(y0)](5)

    hangesofAxisDirectionandofRotationAngleError

    AsshowninFig.3,letOAoandOA2bepre

    rotationandpostrotationaxisdirections,

    respectively.OA2differsfromOAo,withinplane

    PPandalongthedirectionperpendiculartoitby

    angles8aland8a2,whichbeararelationtothe

additionaltiltangleoftheaxis6aasfollows.

    6a=COS(COS6al?cos6a2)(6)

    C1andC2representpre-turnandpostturnendface

    curvaturecenters,respectivelyandOC1OC2

    R.Fig.3.Axisdirectionchangecausedbyconnectorrotation

    A,standsforrotationcenterofthecurvaturecenterroundtheaxis,thusA2C1A2C2

    e.Accordingto

    theassumptioninFig.1,theangleincludedbetweenA2C1andprincipalplaneYOZis0.LetC1A2C2

    7+80(therotatingdirectionoftheconnector),where80referstorotationerror. Throughanalysis,thepreturncoordinatesofcurvaturecenterC1arederivedasfollows. fc1Rsina2+csin0

    lYc1=Rcod2sin(a+1)csinsin0sin(a+1)(7)

    I——..—【

    cos(a+1)~/eCOS0(Rsin+csin0sin~a2)

    Bysubstituting(+7

    +80)for0inEq.(6),wewillobtaintheXandYcoordinatesofC2.Furthermore, theapexesbeforeandafterrotationsaresimplyprojectionsofC1andC2inplaneXOY,respectively,and

    arebothatadistanceofRfromC1andC2.Thus,inthecasewhenthereexistadditionalaxistiltand

    rotationerror,theapexoffsetunderrotating7methodisthenobtainedby

    e{[-Rsin6a2csin(0+80)csin]+Rcos6a2sin(a+6a1)+

    csinSa2sin(0+80)sin(a+6a1)cos(a+6a1)(eCOS(+80)

    (Rsin6a2csinSa2sin(0+80)))$COS0Rsina]}./Z(8)

    WenotethatEqs.(8)and(5)areequivalentinevaluatingtheapexoffset. IntermsofEq.(8),wemayanalyzetheinfluencesof1,6a2and80onmax.AOmeasurementerror

    (for0?

    90.),respectively,asshowninFig.4(b,C,d),wheretheinfluencesof6a1and6a2arealmost

    thesamewitheachotherwhilethatof80iscomparativelyextremelysmal1.When6a1,6a2and80allexist,

    thecomputationresultshowsthatmax.AOerrorisirrelevanttotheoriginaltiltanglea,andisalmost

    decidedbyonly1and2,whichisshowninFig.4(a),whereII=10..Forthesakeofcomparison, someerrorresultsaregiveninTab.1fora0.5,0.7and1respectivelybyrotating7

    andapex-core

    V0I.12No.4XUYX,eta1.MeasurementofApexOffsetsforFiberConnectorEndFaces273 methods.Itcanbeseenfromthedatathat,if6l(or62)0and62(or61)6,AOerrorwith

    rotating7cmethodishalfthatwithapex-coremethod,andwhen62(or61)===6

    2a,theAOerrorsare

    neartoeachotherunderthetwomethods.Onconditionthat6land62bothexistand6】一

    62,when

    theyaresmallerthan,themax.errorundertheformermethodwillbeatleast22.5sma11erthanthat

    underthelatter;onlywhen6l=62

    1.4,willthetwomethodsresultinthesameAOerror.Itshould

    bestatedthat,whenapplyingapex

    coremethod,itisalsonecessarytorotatetheconnectorbeforetestso

    astochecktherelevantvaluesfordifferentpositionsoftheconnectorandtoadjustit.Correspondingly,

    therotationofitwillalsoleadtothechangeofitsaxisdirectionandthereforecausesmeasurementerror.

    which,however,isnottakenintoaccountinTab.1.

    5

    4

    3

    

2

    1

    0

    

    i

    \

    

    

    Fig.4.Influencesoferrorsourcesonapexoffsetmeasurement:(a)influencesofboth(b)and(c)

    whererotationerror6口一

    10.;(b)changeofaxisdirectionwithinprincipalplaneonly;(c)changeofaxisdirectioninthedi

    rectionperpendicular

    toprincipalplaneonly;(d)angleerrorofconnectorrotationonly.Parametervaluesassumed:

    ROC:15mm;A():

    ?一40"m,originalaxistilt:=1?

    Tab.1.Acomparisonofmax.measurementerrorsbetween~-rotationmethodandapex-core

    methodintheconditionofthesame axistilterrors

    Assumedparameters:ROC:15mm;AO:?一40"m

    Axistiltn-rotationmethod(8010.)(Unit:t?m)Apex-coremethod(Unit:"m) lll=0,l82l=0.5;lll0.5,l82l01.2

    llll82l-0.51.7

    =0.52.2

    lll=0,l82lO.7;lll0.7,l2}=01.7

    lll-l82l-O.72.3

    lll=0,l82l0.5;lllO.5,l82l-O1.2

    lllll-0.51.7

    JlJ-O,fPJ=0.7;J3aj0.7,J2J01.7

    a=0.73.3l

.ll82l0.72.3

    lll0,l82l1;ll=1,}lO2.3

    l.l=l.l13.2

    l8I0,ll0.7;lll=0.7,ll01.7

    llll82lO.72.3

    lllO,l2l-1;lI=1,l2l02.3

    a=14.4l

    ll0.5,l2l=1;l8ml=1,lal0.52.6

    llII2l13.2

    lll-la2I1.44.5

    274SemiconductorPhotonicsandTechnologyNoy. 2006

    4TestResult

    Withrotatingmethod,10groupsofphase

    shiftdeterminationsaremadeontheend-faceapex offsetofanSTtypeceramicfiberconnector,

    withoutextractingitduringthecourse.Andthat showninFig.5isthecorrespondingsetup,where

    theoPticallayoutbelongstoLinniktype.By applying4stepaveraging(4+1)algorithmE?.]to

    thephaseshiftinginterferograms(Fig.6),10 groupsofapexcoordinatesarederivedforbothpre

    rotationandpostrotation;meantime,through

    imageprocessing[?ls]andanalysis.10groupsof fibercentercoordinatesareobtainedalsoforboth pre-rotationandpostrotation.ByEq.(5),10

    determinationvaluesfortheapexoffsetare obtained,withdatalistedinTab.2.Andthat showninFig.7isthe3Dprofileofthetestedfiber

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