Abstract
Optical fiber sensors of hydrogen gas (H2) are conventionally based on the reaction of a sensitive material deposited on the surface of a fiber. Long-term applications of H2 monitoring require more robust configurations, less sensitive to the degradations of the sensitive layer. To overcome this issue, we develop disruptive polarisation-maintaining optical fibers composed of a sensitive material (Palladium, Pd) integrated into the silica cladding. We present the development of two Panda-type optical fibers with or without embedded Pd particles. These fibers have been fabricated for evaluating, through the measurement of the birefringence, the contribution of Pd particles on the detection of H2 gas. We have specially developed a gas chamber for measuring on-line the detection of H2 during its diffusion into the fiber. Dynamic comparisons between both fibers demonstrate the contribution of Pd particles resulting in a faster response time (of about 20 h for our experimental conditions). These results pave the way to the realization of robust optical fibers with enhanced sensitivity to H2 gas for developing sensing systems compatible with long-term hydrogen monitoring applications in extreme and harsh environments, such as radioactive waste repositories.
Highlights
It is well known that hydrogen is an explosive gas at low concentrations in air [1]
We propose an optical fiber composed of a sensitive material (Palladium, Pd) integrated into the silica cladding in order to protect the sensing metal from harsh environments
At the maximum, the shift of wavelength dip of the SALP-fiber is 32 % time larger than the shift at saturation, while it is only 6 % for the SAL-fiber. These results demonstrate that Pd particles embedded in the SAP enhance the impact of H2 gas diffusion into the fiber on the birefringence properties
Summary
It is well known that hydrogen is an explosive gas at low concentrations in air (from 4% to 75% Vol) [1]. The direct contact between the sensitive material and H2 enables fast response time, in the order of few seconds [10].Optical fiber sensors are able to detect H2 under harsh and explosive conditions, most fiber optic sensors are based on a deposit of a thin layer of sensitive material on the surface of the fiber This configuration limits the sensor robustness and causes stability issues related to the degradation of the film after several exposure cycles [11]. The detection of H2 is expected to be realized by exploiting the mechanical strain induced by the crystal lattice expansion of Pd particles in contact with H2 gas, which one affects the optical properties of the propagated light through the elasto-optic effect In this purpose, we have already demonstrated the fabrication of an optical fiber with Pd particles embedded in the cladding, but without H2 sensing tests [13]. The fabrication of the fibers, the experimental setup and the experimental results and their analyses are presented
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