1：Experimental Design and Method Selection:

A Mach-Zehnder interferometer based on optical fiber sensor is proposed, consisting of two peanut-type structures. The sensing part is coated with a layer of PDMS film wrapped in WO3/SiO2 hybrid powder.

2：Sample Selection and Data Sources:

The optical fiber sensing structure is placed in the air chamber and connected with broadband source (BBS). An optical spectrum analyzer (OSA) is used to record the transmission spectra of the sensor.

3：List of Experimental Equipment and Materials:

BBS uses the wavelength range from 1432 nm to 1632 nm as the input light. The wavelength resolution of the OSA (AQ6317B, Advantest, Japan) is 0.02 nm. The concentration of hydrogen is controlled by a computer connected to the flow controller, ranging from 0% to 1%.

4：02 nm. The concentration of hydrogen is controlled by a computer connected to the flow controller, ranging from 0% to 1%. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Before coating, the optical fiber sensor is cleaned with alcohol. PDMS is a mixture of polymer precursor (Sylgard 184A) and curing agent (Sylgard 184B) in a ratio of 5:1. The optical fiber sensor is suspended in the hose with an optical fiber clamp and injected into PDMS. After removing the hose, WO3 and SiO2 powders were smeared on surface of PDMS, and were heated for 5 hours on the heating plate at 60℃. The thickness of PDMS film is 5 mm.

5：The optical fiber sensor is suspended in the hose with an optical fiber clamp and injected into PDMS. After removing the hose, WO3 and SiO2 powders were smeared on surface of PDMS, and were heated for 5 hours on the heating plate at 60℃. The thickness of PDMS film is 5 mm. Data Analysis Methods:

5. Data Analysis Methods: The relationship between the transmission and hydrogen concentration is analyzed, showing a linear fitting function of y=24.59008–0.47217x.