LAUSR

Because relative humidity is an important indicator to evaluate the environment quality of production and daily life, humidity sensors have been widely used in various fields. In this work, we proposed a high-sensitivity evanescent field humidity sensor based on micro-capillary and graphene oxide (GO) film. The capillary wall was coated by GO sheets for 1, 3 and 5 cycles, and the interaction between GO and the evanescent field on the capillary wall was experimentally and theoretically investigated. We tested the performance of the sensor with a relative humidity range of 30%RH-70%RH at 25°C. The experimental results show that the sensitivity of the sensor to humidity increases with the compactness of the GO coating. In addition, considering the extinction caused by the GO sheet, the transmission loss and the number of reflections in the capillary wall, the optimal length of the capillary was investigated in order to obtain a good spectral response. Since the cycle of GO coating was controllable, we found that the sensor has a tunable humidity sensitivity. This evanescent field humidity sensor can be applied in all-fiber optic networks for environmental sensing and health monitoring.