A fiber-optic hydrogen gas sensor based on a shift of Bragg wavelength induced by reaction heat and strain was developed. Platinum-supported tungsten trioxide (Pt/WO_3) film which was utilized as hydrogen sensitive material was derived by sol-gel method. In this study, two types of the sensor structures were fabricated and evaluated. The sensor device where fiber Bragg grating (FBG) was fixed on the quartz glass substrate coated with the Pt/WO_3 film using adhesive tape showed good sensitivity. It was found that both reduction of WO_3 and oxidation of tungsten bronze were exothermic reaction. The heat generated by the oxidation process was considerably larger than that of reduction. The response behavior of the other type FBG sensing device directly coated with the Pt/WO_3 film was complicated. It was suggested that there seemed to be competitive response mechanisms related to generation of reaction heat and strain in reduction and oxidation process of sensing film.
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