Improvement in response of swelling clad-type POF humidity sensor using a multicladding layer

In this study, we develop a leaky-waveguide mode conversion-type plastic optical fiber (POF) sensor and examine its response to humidity. The cladding of this optical fiber is formed of a polymer that swells and decreases its refractive index in response to changes in moisture. In this study, we show that the absorbance of light in the cladding is effectively increased by dye-doping the swelling polymer cladding. Therefore, in this study, we attempt to improve the response characteristics of the POF sensor by making the cladding layer a multilayer structure consisting of a swelling polymer layer and a dye-doped swelling polymer layer.