Patent ID: 8025844

Claim:
A hydrogen sensor, comprising: a planar optical transmission medium; a thin film layer formed on a top surface of the planar optical transmission medium to create a first interface between the thin film layer and the planar optical transmission medium; a catalyst layer formed on a top surface of the thin film layer; a substrate joined to a bottom surface of the planar optical transmission medium to create a second interface between the substrate and the planar optical transmission medium; an entrance section for introducing light emitted from a light source into a first end portion of the planer optical transmission medium; and an exit light-collecting section for collecting and transmitting the light that is introduced into the first end portion, transmitted inside the planer optical transmission medium and exits from a second end portion of the planar optical transmission medium, to an optical sensor, wherein said entrance section includes means for spreading the light emitted from the light source in the direction of thickness of the planar optical transmission medium and introducing the light into the planar optical transmission medium, and/or means for spreading the light emitted from the light source in the direction of width of the planar optical transmission medium and introducing the light into the planar optical transmission medium; said planar optical transmission medium transmits the light introduced into the first end portion, by causing it to be reflected by the first and second interfaces alternately; and said catalyst layer hydrogenates the thin film layer, when contacted by hydrogen gas present in an atmosphere, and thereby reversibly changes optical reflectance of the thin film layer and the first interface.