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An optical fibre surface plasmon resonance (SPR) sensor has been developed for the detection of hydrogen leakages. A thin palladium layer deposited on the bare core of a multimode fibre was used as the transducer. In this device, modification of the SPR is due to variation in the complex permittivity of palladium in contact with gaseous hydrogen. This effect is enhanced by using selective injection of high-order modes in the fibre via a collimated beam with non-normal incidence on the input end of the fibre. Measurements of concentrations as low as 0.8% of hydrogen in pure nitrogen have been found to be possible. The response time varies between 3 s for pure hydrogen and 300 s for the lowest concentrations. Such a large range can be explained by the two different crystallographic phases of the palladium-hydrogen system. Moreover, the response of the sensor is dependent on the length of the sensing area. In preliminary experiments, it has been possible to split the sensing area in order to achieve a two-point detection device.

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The authors demonstrate a unique low cost process to print 2D, submicron size, and high refractive index nanopillars using a direct colloidal-photolithography process. A well collimated i-line source emitting at 365 nm wavelength illuminates a mono layer of silica microspheres of 1 μm diameter deposited on a photosensitive TiO2-based sol-gel layer. No etching process is needed since this layer is directly UV photo patternable like a negative photoresist. Furthermore, this thin layer offers interesting optical properties (high refractive index and optical transparency) and good mechanical and chemical stability and thus can be directly used as a functional microstructure (for PV or sensor applications, for example). The paper describes the modeling of the electric field distribution below the spheres during the illumination process, the photochemistry of the TiO2 sol-gel layer process, and preliminary results of TiO2 nanopillars of around 200 nm in diameter fabricated on a three-inch substrate.

Liquid hydrogen has been intensively used in aerospace applications for the past 40 years and is of great interest for future automotive applications. Following major explosive risks due to the use of hydrogen in air, several studies were carried out in order to develop optical fibre sensors for the detection of hydrogen leakage. This paper aims at the presentation of new hydrogen sensors based on the use of fibre Bragg gratings (FBG) and long period gratings (LPG) coated by palladium nanolayers. The sensing principle based on the palladium-hydrogen interaction is presented, as well as experimental results. It is shown that both techniques could be used for hydrogen sensing but with a sensitivity enhanced by a factor up to 500 when using a LPG sensor. FBG sensors appear to be pure strain sensors and LPG sensors are mainly based on the coupling between the cladding modes and evanescent or surface plasmon waves. Preliminary results obtained with an in-fibre Mach-Zehnder interferometer configuration with in-series LPG sensors are also presented. They show potential interest to compensate for the thermal sensitivity of the fibre gratings.

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