Humidity sensor based on unsymmetrical U-shaped microfiber with a polyvinyl alcohol overlay

A relative humidity (RH) sensor based on unsymmetrical U-shaped microfiber (MF) with a polyvinyl alcohol overlay is demonstraded in this paper. The microfiber is fabricated by the flame-heated taper drawing technique from the single-mode fiber (SMF), and then coated a PVA overlay on the surface of this MF. In order to form an interferometer and reduce the size of this sensor to make it conveniently to measure, the sensor is fixed as unsymmetrical U-shaped. The sensor can measure a broad RH interval ranging from 30%RH to 95%RH at room temperature (20 °C). And the proposed sensor with a thinner waist diameter of 3.26 μm can realize the highest RH sensitivity of 186.5 pm/%RH. The experimental results demonstrated that the proposed sensor is expected to be useful in the application of high sensitivity relative humidity measurement.