Improvement in the sensitivity of dye-doped POF-type moisture sensor

A humidity sensor with a plastic optical fiber (POF) that consists of a dye-doped swelling polymer cladding and a polymethyl methacrylate core has been developed and tested. Humidity in air causes swelling of the polyvinylpyrrolidone in the cladding, leading to a decrease in the refractive index of the cladding. Thus, humid air changes the characteristics of the POF´s propagating mode from leaky to guided, causing significant increase in the light intensity passing through the sensor head. In this study, to improve the sensitivity of the humidity sensor, we have investigated the effect of a phthalocyanine-dye-doped polymer cladding on the absorption of light reflected from the boundary surface between the cladding and the air when the POF sensor is operated in the leaky wave mode. The results indicate that the sensor is three times more sensitive when the dye-doped polymer cladding is used.