In-line highly sensitive hydrogen sensor based on palladium-coated single-mode tapered fibers

We report a fiber-optic sensor for detecting low concentrations of hydrogen. The sensor is based on the absorption change of the evanescent fields in a Pd-coated, single-mode tapered fiber. We fabricated a collection of polarization-sensitive and polarization-insensitive devices and we studied the effect of the different parameters on the sensitivity of the device. We found that the sensor´s response is wavelength dependent and it can be adjusted with the taper diameter. Dramatic transmission changes were observed when the sensors were exposed to hydrogen concentrations below 4%. We complement the experimental results with theoretical calculations of the attenuation constant of the fundamental fiber-mode.