High-Sensitivity Fiber-Optic Microcavity Relative Humidity Sensor With a Silicon-Based Sulfide Thin Film

A high-sensitivity fiber-optic microcavity relative humidity (RH) sensor with a silicon-based sulfide thin film is presented. With the magnetron sputtering technique, a 280-nm MoS2 film is effectively deposited on a single-side polished silicon (SSPS) wafer and serves as both an inner reflective surface and a moisture-sensitive film for an open optical microcavity. The microcavity is constructed on the end surface of a single-mode fiber (SMF) using a laser 3-D printing technique. Surface defects and active sites present in polycrystalline MoS2 cause the adsorption of water molecules, altering the effective refractive index (RI) and thickness of the inner MoS2 material layer and leading to phase changes in the optical microcavity. Moreover, the MoS2/SSPS-enabled optical cavity is introduced, which constructs an optical Vernier effect (OVE) that further and effectively enhances the sensor’s sensitivity. Experimental results show that the sensor has a high humidity sensitivity of 1.057 nm/%RH over an RH range of 28.5%–84.1%, with a fast response time and recovery time of 1.95 and 2.90 s, respectively. It can be used for high-performance human breathing monitoring. The sensor exhibits inherent advantages, such as compact structure, high sensitivity, fast response time, good repeatability, and stability. Therefore, it has potential applications in chemical, medical, and biological fields related to RH detection.