Humidity sensor based on tapered single mode fiber coated with a hydroxyethyl cellulose/poly-vinylidene fluoride composite

A simple humidity sensor is suggested basing on a tapered single-mode fibre coated with a mixed polymer composite hydroxyethyl cellulose/polyvinylidene fluoride. The tapered fibre produced by an etching technique and coated with a humidity-sensitive cladding creates intermodal interference which enables detecting humidity changes. The performance of the sensor is studied for the two fibre diameters, 50 and 87.5 mu m. As the relative humidity increases, the interference spectrum shifts towards longer wavelengths. The highest sensitivity, 0.0116 nm/%, is obtained at the smallest tapered-fibre diameter of 50 mu m, with the linearity being more than 98.20%.