Optical fiber humidity sensor based on the vernier effect of the Fabry-Perot interferometer coated with PVA

In this paper, a relative humidity (RH) sensor based on vernier effect of two parallel Fabry-Perot interferometers is proposed and experimentally demonstrated. The polyvinyl alcohol (PVA) is chosen as the humidity sensitive material. The sensor consists of a reference cavity formed by single mode fiber – fiber capillary - single mode fiber (SMF-FC-SMF) structure and a sensing cavity formed by SMF-FC-coated structure. The sensor shows the high sensitivity of 1.78 nm/%RH in the range of 55%RH-85%RH. We measured the stability of the sensor at 45%RH and 75%RH, and the response time between 55%RH and 75%RH is 12 s. In addition, it also has the advantages of low temperature disturbance, simple principle, and easy manufacture.