A Simultaneous Distinguishing Measurement Method of Carbon Dioxide Gas Concentration and Air Humidity Based on Double Fiber Bragg Gratings

Due to the advantages of small size, high sensitivity, and strong anti-interference ability, optical fiber sensors are widely used in gas detection. Meanwhile, concentration and humidity detection based on optical fiber sensing are paramount technologies in the field of gas sensing. However, how to solve the issue of cross sensitivity of concentration and humidity of optical fiber gas sensors and realize synchronous detection of two parameters are current common challenges. In this study, taking carbon dioxide as an example, a detection method based on double fiber Bragg grating (FBG) string is proposed to measure carbon dioxide (CO
₂
) concentration and air humidity simultaneously. Here, a pair of FBGs are welded in series on an optical fiber after being filled with special materials. Using the control variable method, the performance parameters of the sensor can be determined through calculation. The experimental results demonstrate that the gas concentration sensitivity is 0.5952 pm/ppm in the range of 0–2250 ppm. In the range of 25%–65%, the air humidity sensitivity is 28.62 pm/RH. Moreover, it is less affected by temperature and has satisfactory repeatability and reproducibility. The sensor realizes high sensitivity and low crosstalk measurement of concentration and humidity and can be applied to the simultaneous detection of CO
₂
concentration and air humidity in specific confined space.