<title>Fiber optic Bragg grating sensors for hydrogen gas sensing</title>

Abstract

We report a new type of optical hydrogen sensor with a fiber optic Bragg grating (FBG) coated with palladium. The sensing mechanism in this device is based on the mechanical stress that is induced in the palladium coating when it absorbs hydrogen. The stress in the palladium coating stretches and shifts the Bragg wavelength of the FBG. Using FBGs with different wavelengths many such hydrogen sensor can be multiplexed on a single optical fiber. Operation of two multiplexing sensors is demonstrated. Moreover, hydrogen and thermal sensitivities of the senors were measured and calculated using a simple elastic model. Moreover, to quantify the amount of stress in the palladium film as a function of hydrogen concentration, a novel and very sensitive method was devised and used to detect deflections in a Pd-coated cantilever using an evanescent microwave probe. This stress was in the range of 5.26 - 8.59 X 107 Pa for H2 concentrations of 0.5 - 1.4% at room temperature, which is about three times larger than that found in the bulk palladium for the same range of H2 concentrations.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.