Optical Fiber Sensors For Nuclear Environments

Optical Fiber Sensors For Nuclear Environments
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  Optical Fiber Sensors For NuclearEnvironments Gaspar M. Rego *  , Alberto Fernandez Fernandez  , José L. Santos  ,Henrique M. Salgado  , F. Berg!ans   and Andrei Gusaro"    *  Escola Superior de Tecnologia e Gestão, Instituto Politécnico de Viana de Castelo, Av. do Atlântico, !"" Viana do Castelo, Portugal    I#ESC Porto, $nidade de %ptoelectr&nica e Siste'as Electr&nicos, (ua do Ca'po Alegre )+, )!-""+ Porto, Portugal    ep. de Eng. Electrotécnica e de Co'putadores, /ac. de Engen0aria, $niversidade do Porto, (ua r. (o1erto /rias, 2""-)3 Porto, Portugal    ep. de /4sica, /aculdade de Ci5ncias, $niversidade do Porto,  (ua do Ca'po Alegre )+, )!-""+ Porto, Portugal   SC67CE#, 8elgian #uclear (esearc0 Center, Instru'entation epart'ent, 8oeretang 2"", 8-2"", 9ol, 8elgiu' Abstract. #e a"e e$peri!entall% studied te e&&e't o& ionizing radiation on te properties o& L(Gs &abri'ated in a pure)sili'a &iber using te ar' dis'arge te'nique. e goal o& te stud% isto assess te possibilit% o& using su' gratings in radiation en"iron!ents &or sensing appli'ations. INTRODUCTION e +ell)no+n properties o& te FBG)based opti'al &iber sensors -FS/ !aete! "er% attra'ti"e &or te appli'ation in te nu'lear industr% +ere te% 'an per&or!,a!ong oters, stru'tural integrit% and te!perature !onitoring 012. e i!ple!entationo& su' sensors is 'o!pro!ised b% teir sensiti"it% to radiation. 3t is, tere&ore, o& interest to stud% te e&&e't o& radiation on FBGs +ritten in pure)sili'a)'ore &ibers,+i' are usuall% e$pe'ted to be !ore radiation)resistant as 'o!pared +itger!aniu!)doped &ibers 042. Gratings &abri'ation in pure)sili'a)'ore &ibers requirestat te ins'ription be based on 5 4  lasers 062 or ar')dis'arges 072. ose te'niques allo+ a "er% ig te!perature stabilit% o& te gratings. Re'entl%, te possibilit% o& teuse o& a 186)n! e$'i!er laser as also been de!onstrated 092. GRATINGS FABRICATION AND CARACTERISATION Long)period &iber gratings -L(FGs/ used in te present stud% a"e been +ritten in a pure)sili'a)'ore &iber -: 'ore  ; 8  ! and <.A. ; =.11/ using te ele'tri' ar')dis'argete'nique 0>2. e &abri'ation 'onsists in pla'ing a &iber under a tension bet+een teele'trodes o& a spli'ing !a'ine, +i' produ'es a sort duration ar' dis'arge. en,  te &iber is !o"ed b% a grating period  . e sequen'e ?ar' dis'arge ) &iber displa'e!ent@ is repeated se"eral ti!es and is 'o!puter 'ontrolled. 3t sould be notedtat te opti!al +riting para!eters are to be de&ined &or ea' &iber t%pe indi"iduall%.3n te preset 'ase a grating period    6=  ! +as 'osen so tat a resonan'e pea appeared in te tird tele'o!!uni'ation +indo+. Figure 1 so+s te trans!issionspe'tra o& &our gratings +ritten in te Si 4 )'ore &iber under di&&erent 'onditions. As it'an be seen, an in'rease o& te tension and a de'rease o& te ar' duration lead to astronger 'oupling. e in&luen'e o& te dis'arge 'urrent +as brie&l% studied and teresults indi'ate tat its in'rease !a% speed)up te gro+t o& gratings altoug anin'rease o& te 'urrent does not ne'essaril% !ean a ig a!plitude o& te trans!issiondip, unless a 'ertain ?tresold tension@ is also used. For e$a!ple, +en a !ass o& 1.7 g +as applied in 'o!bination +it a dis'arge 'urrent o& 11 !A +it duration 1 sor =.6 s no grating or a +ea grating - =. dB/ +ere &or!ed a&ter 49 periods,respe'ti"el%. 3t !a% be rele"ant to note tat bot an in'rease o& te tension and te'urrent also 'ontributes to a iger insertion loss and tere&ore a 'o!pro!ise isrequired to obtain a grating +it use&ul para!eters 0>2.L(FGs +ere also +ritten in a &iber pre)annealed at 1=== C5 during 8= !in. Dsingte sa!e +riting 'onditions as &or L(FG E6 onl% 67 ar' dis'arges +ere required toobtain a resonan'e 'entered at 1>66.> n! +it a loss)pea isolation o& 46 dB. 135014001450150015501600-16-14-12-10-8-6-4-20   LPFG #1: 22.8 g_9 mA_1 s_75 LPFG #2: 36.3 g_9 mA_1 s_75 LPFG #3: 5.1 g_9 mA_0.5 s_95 LPFG #4: 36.3 g_9 mA_0.5 s_72    T  r  a  n  s  m   i  s  s   i  o  n   (      !   " a$%&%ng' (nm" FIGURE !.  rans!ission spe'tra o& te gratings +ritten in te Si 4 )'ore &iber using di&&erent para!eters -e$ternal applied tension 9.1 g to 6>.6 g 'urrent 8 !A ar' duration =.9 to 1 s and nu!ber o& dis'arges 4 to 89/. 3n order to deter!ine te te!perature dependen'e o& te trans!ission dip position&or te L(FGs +ritten in te Si 4 )'ore &iber t+o gratings +ere pla'ed inside a tubular o"en under a sligt tension -a suspended !ass o& 1.7 g +as used/. e te!perature o& te o"en +as in'reased at a lo+ rate and te trans!ission spe'tra o& te gratings +ere periodi'all% re'orded. Figure 4 so+s tat te position o& te trans!ission dip !o"esto+ards longer +a"elengts as te te!perature rises up to 69=)7== C5. At iger te!peratures te% !o"e to+ards sorter +a"elengts. 3n standard &ibers su' a   bea"ior 'an onl% be seen at "er% ig te!peratures. e ?strain point@ &or tis &iber,i.e., te te!perature at +i' te annealing o& intrinsi' stresses begins, o''urs atte!peratures +ell belo+ a ==)8== C5 range obser"ed &or oter &ibers 0>2. ete!perature sensiti"it% o& te gratings -1= ) 6= p!C5/ is also signi&i'antl% lo+er as'o!pared +it tat &or gratings +ritten in standard &ibers &or latter 'ase it 'an be asig as I= p!C5, &or te!peratures in a range = ) 149 C5. 3t is ne'essar% to note tat adi&&eren'e &or te te!perature sensiti"it% o& te t+o L(FGs studied +as obser"ed. ee&&e't 'an be probabl% related +it te di&&eren'e in te ar' duration used &or teir ins'ription. A &urter +or is required to address tis bea"ior 'orre'tl%. 3rre"ersible'anges in te sape o& te spe'tru! start abo"e >9= C5.o !easure te strain sensiti"it% o& te grating te &iber +as &i$ed at t+o pointsseparated b% 9= '!, one o& te! being on a !i'ro!eter positioner. e L(FG +asten pulled in steps o& =.=9 !! +it te total displa'e!ent up to =.> !!. Figure 6so+s te strain !easure!ent results &or L(FG E4 and L(FG E7. e strain sensiti"it%o& te L(FG E6 +as deter!ined to be =.67 p!   a&ter te grating being sube't to ate!perature o& about 79= C5. ere&ore, it is possible tat te annealing and te+riting 'onditions also a&&e't te strain sensiti"it%. For 'o!parison, te strainsensiti"it% o& gratings +ritten in standard Ge)doped &ibers +as &ound to be in a range=.I)1.1 p!  . 0501001502002503003504004505005506006501527153015331536153915421550155215541556   21 )m*+,29 )m*+,13 )m*+,  LPFG #3 LPFG #2    #  a  $  %   &  %  n  g   '      (  n  m   " T%m)%ra'-r% (+," 01002003004005006007008009001000110012001533.51534.01534.51559.51560.01560.5  LPFG #4 LPFG #2 1.14 )m*    0.81 )m*     #  a  $  %   &  %  n  g   '      (  n  m   " 'rain (  " FIGURE ".  e!perature sensiti"it% o& t+ogratings +ritten using di&&erent ar' duration. FIGURE #.  Strain sensiti"it% o& t+o gratings+ritten +it di&&erent para!eters -tension and ar'duration/. GA$$A IRRADIATION OF %&FGs e L(FGs +ere inserted into stainless steel 'apillar% tubes to be prote'ted duringga!!a irradiation. e trans!ission spe'tra +ere !easured using broadband LK:s&ro! B#)e, an A<: A>619B opti'al spe'tral anal%zer -SA/ and t+o SMopti'al s+it'es -S/-see Figure 7/. e e!ission o& te opti'al sour'es +as'ontinuousl% !onitored "ia an internal re&eren'e &ibre. e use o& a te!perature)stabilized FBG as an e$ternal +a"elengt re&eren'e allo+ed a +a"elengt!easure!ent stabilit% better tan 4= p! trougout te e$peri!ent.    FBG re&   B#K SA A' (#!)B S S SM 'oupler    Fiber re&eren'e FBGs Radiation sield B#K FIGURE *  pti'al !easure!ent set)up e L(FGs +ere e"aluated under >= 5o irradiation in te R3A -Radio 3sotope estArrange!ent/ &a'ilit% -S5N5K<, Belgiu!/, des'ribed in details in 02. For te present e$peri!ent te ga!!a dose rate +as about 1 G% 0H 4 2 +it te total doseabout 9>= G%. e te!perature in te irradiation rig +as ept 6.7 O =.1 P5. e e&&e't o& ga!!a)radiation on te trans!ission spe'tra strongl% depends on tegrating &abri'ation 'onditions. K.g., Figures 9 and > depi't results &or L(FG E1 and E6,respe'ti"el%. 3t 'an be seen tat &or L(FG E1 te a!plitude o& te 19== n! pea isde'reasing, +ile &or L(FG E6 it is in'reasing. Su' a bea"ior sould be attributed toa !odal inde$ 'ange under radiation. 3t is no+n tat te radiation sensiti"it% o& puresili'a is "er% lo+. Ho+e"er, te re&ra'tion inde$ o& te F)doped 'ladding 'an be'anged b% radiation. A !ore detailed anal%sis o& te !odal stru'ture, in'ludingnu!eri'al si!ulations, is planned &or a &uture. 135014001450150015501600-18-16-14-12-10-8-6-4-20Wavelength (nm)    O  p  t   i  c  a   l  p  o  w  e  r   (   d   B   ) 1 !"118 !"306 !"4#3 !" $ncrea%ing gamma do%e 135014001450150015501600-30-25-20-15-10-50Wavelength (nm)    O  p  t   i  c  a   l  p  o  w  e  r   (   d   B   ) 1 !"118 !"4#3 !"306 !" Increasing gamma dose Fi+ure ),  e&&e't o&  )radiation on L(FG E1 Fi+ure (,  e&&e't o&  )radiation on L(FG E6  DISCUSSION AND CONC%USION e basi' 'ondition &or i!ple!entation o& a L(FG &or strain sensing in a radiationen"iron!ent is tat te grating sur"i"es under radiation. ur results so+ tat e"enunder a dose in e$'ess o& =.9 MG% te trans!ission deeps o& te L(FGs are easil%dete'table. e radiation does 'ange te a!plitude and te positions o& te peas.Ho+e"er, te gratings &abri'ated under di&&erent +riting 'onditions a"e oppositetrends in te para!eters 'ange. at !eans tat b% adusting te +riting 'onditions itsould be possible to &abri'ate a grating &or +i' te dip position orand a!plitudeare not 'anged b% radiation. 3n 'on'lusion, L(FGs +ritten in a pure)sili'a)'ore &iber +ere 'ara'terized in ter!so& te te!perature and strain sensiti"it%. e e&&e't o& ionizing radiation on teir  properties as also been in"estigated. e results o& te irradiation e$peri!ents enableto 'on'lude tat ar')indu'ed gratings in pure)sili'a)'ore &ibers 'an be used to per&or!!ulti)para!eter si!ultaneous !easure!ent in radiation en"iron!ents. AC-NO%EDG$ENTS G. M. Rego is tan&ul &or te grant troug te (rogra! (R:K( 333 ) Medida 9 )A'Qo 9.6. ) For!aQo A"anQada de :o'entes do Knsino Superior, integrada no Ki$o6. A. Fernandez Fernandez +is also to a'no+ledge te &inan'ial support o& teKuropean 5o!!ission  KDRAM Fusion e'nolog% (rogra!. e 'ontent o& te publi'ation is te sole responsibilit% o& its publisers and it does not ne'essaril%represent te "ie+s o& te 5o!!ission or its ser"i'es. REFERENCES 1.Gusaro", A., :e&osse, T., :eparis, ., Blondel, M., Fernandez Fernandez, A., Berg!ans, F., and:e'réton, M., ?K&&e't o& ionizing radiation on te properties o& &iber Bragg gratings +ritten in Ge)doped &iber@ in (ro'. Bragg Gratings, (otosensiti"it% and (oling in Glass #a"eguides, Stresa, 3tal%, paper B56=)1, 4==1.4.auta, ., Saasai, ., Sia!a, ., <arui, M., and Saga+a, .,  :. #ucl. 9ater.   ")/0"(# , 1I86)1I8> -188I/.6.Ai%a!a, M., <iside, ., Si!a, ., #ada, A., and Ta!au'i, R., ?A no"el longUperiod &iber grating using periodi'all% released residual stress o& pure)sili'a 'ore &iber@ in (ro'. pti'al Fiber 5o!!uni'ations, paper G1, 188I, pp. 4>)4.7.Kno!oto, ., Sigeara, M., 3sia+a, S., :anzua, ., and ana!ori, H., ?LongUperiod &iber grating in a pure)sili'a 'ore &iber +ritten b% residual stress rela$ation@ in (ro'. pti'al Fiber 5o!!uni'ations, paper G4, 188I, pp. 4)4I.9.Albert, J., Foine, M., and Margulis, #., ?Grating &or!ation in pure sili'a)'ore &ibers@ in (ro'.Bragg Gratings, (otosensiti"it% and (oling in Glass #a"eguides, Stresa, 3tal%, paper B58)1,4==1.>.Rego, G., otnio", ., :iano", K., and Souli!o", V., ?Hig e!perature Stabilit% o& LongU (eriod Fiber Gratings (rodu'ed Dsing an Kle'tri' Ar'@,  :. ;ig0t<ave Tec0nol.   !1 , 197)198-4==1/..Fernandez Fernandez, A., o!s, H., Bri'ard, B., 5oe', M., 5oenen, S., Berg!ans, F., and:é'reton., M., WS5X5K< irradiation &a'ilities &or radiation toleran'e assess!entW, in (ro'. 3KKK <SRK5 4==4, Radiation K&&e't :ata #orsop, (oeni$, DSA, 4==4.
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