Optical Fiber Humidity Sensor With Enhanced Sensitivity by Double-Sided Contact Film

A highly sensitive humidity sensor based on open cavity fiber Fabry-Perot interferometer (FPI) with double-sided contact film is proposed. The sensor is fabricated by inserting a section of single-mode fiber (SMF) into a hollow-core fiber (HCF), and coating with polyvinyl alcohol (PVA) on the end of HCF. The difference in diameter between the two fibers is used to form an air channel so that both the left and right sides of the moisture-sensitive membrane can interact with moisture, which enhances the sensitivity. The humidity characteristics of the sensors with different cavity lengths are investigated experimentally. The results show that in the relative humidity range of 35%–85%RH, the sensor with a cavity length of $100~\mu $ m has a high sensitivity of 2.103 nm/%RH. By comparing the humidity performances of the open cavity with the closed cavity, it is verified that the sensitivity of the open cavity sensor is specifically increased to 1.56 times that of the closed cavity. The open cavity sensor exhibits high sensitivity, simple structure, and rapid response time.