Fast response fiber optic hydrogen sensor based on palladium and gold nano-layers

We present an experimental study performed to determine the hydrogen sensing characteristics of a stack of Pd and Au nano-layers. Hetero-core optical fibers were coated with a stack of 1, 2, 3, 4 and 5 double layers of 1.4 nm of Pd and 0.6 nm of Au, alternately deposited by thermal evaporation. The presence of hydrogen produces a decrease in the palladium refractive index, which causes attenuation changes in the optical fiber evanescent wave. Several samples, hetero-core optical fibers coated with different thin film thicknesses, were fabricated and tested in a very simple optical transmission measurement setup. A mixture of hydrogen and nitrogen (carrier gas) was used to test the devices. We observed a response time of 4.5 s for hydrogen concentration of 4%. When hydrogen flow was turned off, the multilayer thin film desorbs the gas in 13 s, indicating a fast recovery response.