Highly Sensitive Fiber-Optic Humidity-Sensing System by Using GO-FPI-Based Microwave Photonic Filter

In this article, a microwave photonic filter (MPF)-based fiber-optic humidity sensor is proposed and experimentally demonstrated. An Fabry-Pérot (FP) cavity using a single-mode fiber (SMF) end face and a graphene oxide (GO) film is fabricated as the sensing head, and by tracing the central frequency of the MPF’s passband, the humidity can be measured. The sensitivity of the sensor can be tailored by fabricating GO films with different thicknesses. The experimental results indicate that the thinner the GO film, the higher the sensitivity, and the sensitivity can reach 1.31 MHz/%RH when the thickness of the GO film is 116.3 nm. The response time is measured to be 40 ms, and the temperature cross-sensitivity can be as low as 0.0035%RH/°C. The proposed sensing system enjoys the advantages of high sensitivity, rapid response, good stability, low cross-sensitivity to temperature, low cost, and straightforward fabrication.