High-Sensitivity Hydrogen Detection Based on Thermo-Optical Effect of Liquid Sealed in a Hollow-Core Fiber Interferometer

A highly sensitive hydrogen sensor based on a liquid-filled hollow-core fiber (HCF) interferometer with Pt-loaded WO3 (Pt-WO3) coating is proposed and experimentally verified. It is manufactured by inserting a segment of HCF filled with dimethyl silicone oil (DSO) between two single-mode fibers (SMFs) via a short multimode fiber (MMF) at both ends to form an in-fiber Mach-Zehnder interferometer (MZI), and the outer surface of the interferometer is coated with hydrogen sensitive material of Pt-WO3. When the sensor is exposed to hydrogen, an exothermic reaction occurs between the WO3 and the hydrogen with the help of Pt catalyzer, and then the transmission spectrum of the MZI shifts accordingly due to the thermo-optical effect of liquid in HCF. The experimental results reveal that the sensor has an excellent linear response to hydrogen concentration with a high sensitivity of up to 11.75 nm/% (vol %), as well as good repeatability and stability within the range of 0%–1.5% (vol %). Moreover, it features a small size (~1.4 mm in total length) and low ambient humidity crosstalk. All these advantages indicate that the proposed sensor is a promising candidate for highly sensitive hydrogen detection.