Integrating microsphere resonator and ZnO nanorods coated glass for humidity sensing application

A humidity sensor is proposed by integrating a microsphere resonator onto ZnO nanorods coated glass surface. The glass substrate was coated with ZnO nanorods for 12 h using the hydrothermal method and the microsphere was set at a diameter of 234 mu m. The proposed sensor produced sensitivity of 0.0748 dBm/%RH and 0.0142 nm/ %RH when exposed to humidity level ranging from 35 %RH to 85 %RH. Standard deviation and resolution of the proposed sensor improve by a factor of 1.7 and 2.4 respectively as compared to the straight microfiber laid on the ZnO nanorods coated glass. It utilized the ultra-high Q factor of microsphere and the changeable refractive index of the ZnO nanorods coated glass. Combination of these elements enhanced the interaction between the whispering gallery mode evanescent components with surrounds analyte. It also solves the issues pertaining to the complicated handling of microfibers during the coating process. The proposed sensor has shown exceptional experiment results for humidity sensing applications.