A real-time response relative humidity sensor based on a loop microfiber coated with polyvinyl alcohol film

Abstract A high sensitivity optical fiber loop-based relative humidity (RH) sensor coated with polyvinyl alcohol (PVA) film is demonstrated, which has low-temperature sensitivity. The loop region of the sensor (micron-sized diameter) is very sensitive to the environmental medium due to strong evanescent fields out of fiber cladding. The refractive index (RI) sensitivity is as high as 2979 nm/RIU, while the temperature sensitivity is relatively low at 0.0075 nm/°C. The experimental results show that the sensor has the RH sensitivity of 0.533 nm/%RH (wavelength modulation) and −0.213 dBm/%RH (intensity modulation). The proposed sensor has good real-time, stability and repeatability, which provides a guarantee for accurate RH measurement.