Dual-parameter optical fiber sensor for temperature and humidity based on PMMA-microsphere and FBG composite structure

•The manufacturing method for the sensor is simple and novel. By using an electronic iron as heating source, the Fabry-Pérot (F-P) is formed between PMMA-microsphere and the fiber end-face.•The humidity sensing without any coating or humidity-sensitive materials has high humidity sensing sensitivity.•An integrated optical fiber temperature and humidity sensor is proposed and experimentally demonstrated. The sensor can simultaneously measure temperature and humidity through analyzing the wavelength shifts of FBG and F-P. In this work, we proposed and experimentally demonstrated an optical fiber temperature and humidity sensor composed of a polymethyl methacrylate (PMMA)-microsphere and a fiber Bragg grating (FBG), and realize monitoring the environment temperature and humidity simultaneously. The experimental results show that when the relative humidity (RH) change from 35% to 85%, the response sensitivity of the Fabry-Pérot (F-P), which is formed between PMMA-microsphere and the fiber end-face, is about 127 pm/%RH. However, the FBG in the structure is not sensitive to humidity. When temperature changes from 33 °C to 58 °C, the response sensitivity of the F-P and FBG are about 45.68 pm/°C and 10 pm/°C, respectively. When temperature and humidity change simultaneously, these two-parameters can be monitored simultaneously by using the dual-parameter measurement matrix method. The optical fiber dual-parameter sensor offers numerous advantages, such as low cost, high sensitivity, and easy fabrication.