Hydrogen sensor using fiber gratings covered by a catalytic sensitive layer

In this paper, we present hydrogen sensors based on uniform fiber Bragg gratings and long period fiber gratings covered by a catalytic sensitive layer made of a ceramic doped with noble metal. In presence of hydrogen in air, the sensitive layer has the unique property of being the siege of an exothermic reaction. Hence, for increasing hydrogen concentrations, this chemical reaction leads to an increase of temperature around the fiber gratings, which consequently shifts the resonance wavelength. The sensing mechanism is thus based on the monitoring of the resonance wavelength shift. For both kinds of gratings, the sensor response is linear and without hysteresis between increasing and decreasing hydrogen concentrations. It is also selective and extremely fast. Different experiments obtained on uniform fiber Bragg gratings of different physical lengths and on long period fiber gratings are reported in this paper.