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Effect of doping swelling polymer cladding with phthalocyanine dye in plastic optical fiber humidity sensors

We have developed and tested plastic optical fiber (POF)-type humidity sensors, which consist of a dye-doped swelling polymer cladding. POF-type humidity sensors consist of a hydroxyethyl cellulose or polyvinylpyrrolidone (PVP) cladding layer that surrounds a poly(methyl methacrylate) core. The operation of these sensors is based on the change in refractive index caused by swelling of the cladding layer. To improve the sensitivity of the humidity sensor, we have investigated the effect of doping the cladding polymer with phthalocyanine dye. The results indicate that the POF-type humidity sensor using PVP is three times more sensitive for relative humidities above 80% when the dyedoped swelling-polymer cladding is used.