Simultaneous strain andtemperature fibre Bragggrating sensor based onthe measurement ofoneStokes parameter

systems andforsensing purposes. Theyallow simultaneous strain andtemperature measurement, whichisnotpossible witha single grating written intoconventional single modefibre. Discrimination between strain andtemperature effects implies themeasurement oftwodistinct resonant wavelengths induced bybirefringence. Manypractical applications suchasthecuremonitoring ofcomposite materials require miniaturized PM-FBG.Short length PM-FBGcanproduce theoverlap oftheresonant peaks sothat themeasurement isonlypossible intwosteps bymeansofapolarization controller andalinear polarizer. Toavoid this complexity andthemeasurement errors that itinvolves, wepropose a sensor based onthemeasurement ofthefirst Stokes parameter ofthetransmitted signal byashort length PM-FBG. Since itisimportant tocharacterize thepolarization properties ofPM-FBGforalotofapplications, wealso present theoretical andexperimental studies ofthereflected andtransmitted Stokes parameters. TheStokes parameters represent thestate ofpolarization. Theycanbededuced fromtheJones vector bymeansofthe following equations [I1: S, + , Si= _ , S2=2Re[ ] andS3=2Im[ ]. Inthese expressions, thenotation x(y) represents theslow(fast) axis characterized byaneffective refractive index neffx=neff+An/2 (neffy=ne)-An/2) wherenL,, isthemeaneffective index ofthefibre andAnisthefibre birefringence. IfKqy) andOX(y) are theamplitude andphase angles ofthex(y) component oftheelectric fields, theJones vectors corresponding tothe reflected Erandtransmitted E,signals aregiven by: