A novel fiber optic humidity sensor based on Mach-Zehnder interference and peanut structure

Real-time monitoring of relative humidity plays a key role in ensuring industrial safety and production quality in nuclear power plants. This study presents a novel optical fiber humidity sensor based on Mach-Zehnder interference and a double peanut structure coated with gelatin film. The double peanut structure is distributed at both ends of the optical fiber humidity sensor and is formed by splicing the single-mode fiber core, which can achieve beam expansion and focusing on optical path transmission. The multimode fiber is spliced between the double peanut structures, enabling the excitation of high-order core modes during optical path transmission. The overall structure forms a Mach-Zehnder interferometer and is coated with a humidity-sensitive layer of gelatin. By analyzing the intensity fluctuation of the resonant peaks in the transmission spectrum, the relative humidity can be monitored. Experimental results show that the humidity sensor exhibits a high relative humidity sensitivity of 0.2289 nm/%RH within a wide humidity range of 30% to 90% RH. The proposed optical sensor has advantages such as a simple structure, economical and efficient manufacturing, excellent stability, and high performance, making it suitable for wide application in nuclear power plant structure and health monitoring systems.