Enhanced Sensitivity in Humidity Sensorsbased on Long PeriodFiberGratings

Inthis workanewrelative humidity sensor based on thedeposition ofa subwavelength thickness overlay of alumina (Al203) andpoly(Sodium 4-StyreneSulfonate) (PSS) onthecladding ofa Long-Period FiberGrating (LPFG)is presented. Thismaterial has a lowerrefractive index comparedtotherefractive indexoftheoptical fiber. This characteristic limits thesensitivity ofthesensor. Inorderto enhance thesensitivity tohumidity ithasbeenintercalated a highrefractive indexlayer, whichpermits toimprovethe sensitivity ofLPFG sensors bya ratio offour. Themethod proposed herewidensthedesign ofLPFG basedsensors characterized byoverlays oflowrefractive index, andcouldbe usedforother applications suchasthedesign ofoptical filters.