High-sensitivity whispering-gallery mode sensor for simultaneous measurement of humidity and temperature.

A novel, to the best of our knowledge, optical fiber whispering-gallery mode (WGM) sensor for simultaneously measuring humidity and temperature is proposed and investigated. The proposed sensor is realized by a polyvinyl alcohol (PVA)-coated capillary tube coupling with an optical single-mode fiber (SMF), which is integrated with a fiber Bragg grating (FBG). The as-fabricated sensor can be used not only for relative humidity (RH) sensing but also for temperature detection. The achieved humidity and temperature sensitivities are -181.2 pm/%RH and 10.5 pm/°C, respectively. The easy fabrication and very high sensitivity of the proposed sensor are attractive features for high-precision and wide-range RH sensing applications.