An optical fiber hydrogen sensor based on the measuring principle of surface plasma resonance is introduced. The
structure of the hydrogen-sensitive head which is coated with Pd-Ag alloy film on the surface of the etched optical fiber
is investigated theoretically. When hydrogen gas is absorbed into the Pd thin layer of the sensing head, the Pd hydride is
formed and then the refraction index of the etched optical fiber surface will be changed with different hydrogen gas
concentration. The surface plasma wave is stimulated by the light wave in optical fiber and the surface plasma resonance
occurs between the thin metal layer and the medium surface of hydrogen gas. The Pd-Ag alloy film thickness versus the
sensitivity of hydrogen sensing head is analyzed and optimized via the numerical method. The sensing head which is
based on surface plasma resonance is manufactured and used in the experiment system of hydrogen gas detecting, and
the experiment results demonstrate that the detecting system has high sensitivity with the hydrogen concentration in the
range of 0%-4%, the accuracy, resolution and response time are respectively 5%, 0.1% and 30s. This sensor structure can
be applied to detecting the low concentration of hydrogen gas.
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