U-shaped microfiber coupler coated with polyvinyl alcohol film for highly sensitive humidity detection

Abstract A probe-type relative humidity (RH) sensor was proposed and developed by combination of a U-shaped microfiber coupler (MFC) and a polyvinyl alcohol coating. Optical MFC is considered as an excellent kind of humidity sensor due to its highly sensitive to the environmental RI changes. By covering one layer of PVA film onto the surface of the waist region of the MFC, the sensitive of the proposed sensor was further increased. Experiment results indicated that the proposed sensor exhibited a good linear relationship between the wavelength and relative humidity over the 15%–85%RH range and which also exhibited sensitivity are about 318.1 pm/%RH. And temperature experiment results showed that the temperature sensitivity of the proposed sensor is about 13.9 pm/°C over the 20 °C to 50 °C rang, which indicated that the proposed sensor has the performance of being low temperature sensitive.