Extrinsic Fabry-Perot interferometric optical fiber hydrogen detection system.

We present a new hydrogen sensor system based on the use of an optical fiber extrinsic Fabry-Perot interferometer coated with palladium silver (Pd-Ag) film. The sensing mechanism of such a sensor is based on the mechanical stress that is induced in the Pd-Ag film when it absorbs hydrogen. To obtain the absolute length of the air gap, a modified cross-correlation signal processing method is introduced. Results are presented for a comparison between two Pd-Ag films of different thicknesses. A temperature compensation method based on an optical switch is presented. The sensor is suitable for monitoring concentrations of hydrogen below the lower explosive limit.