Capteurs à fibre optique pour la surveillance et l’observation du stockage de déchets radioactifs en couche géologique profonde

National audienc

Hybrid optical fibre nanostructured by the sol-gel process

A hybrid silica-zirconia nanostructured optical fibre is elaborated using the chemical sol-gel process and the dipcoating method, associated to the classical fibre drawing process. The SiO2-ZrO2 system presents a miscibility gap in the liquid state which can be extended to the solid state. After an appropriate heat treatment, there is a phase separation between SiO2 and ZrO2, with a crystallisation in the tetragonal phase of ZrO2. The ZrO2 nanocrystals diameter is near 10 nm and are dispersed in an amorphous silica matrix. ZrO2 is an interesting matrix to trap rare-earth ions, to limit their clusterization and to exacerbate their luminescence properties. Thanks to low phonon energy (470 cm-1), it becomes possible to stimulate upconversion mechanisms in the rare earth ions trapped in the nanocrystals and to achieve original emission wavelengths. Previous studies realized on bulk, thin films and powder of nanostructured zirconia xerogels doped with erbium ions excited with a 982 nm wavelength source, demonstrate that a significant upconversion process can take place at 550 nm and 670 nm. This kind of nanostructure is thus synthesized in the core of optical fibres. The high refractive index of ZrO2 (1.94 at 980 nm) considerably rise up the refractive index of the core (Δn = 0.02- 0.06) without hampering on the waveguiding properties of the optical fibre. The measured attenuation losses are 0.7 dB/m at 1064 nm and the calculated cut-off wavelength is 714 nm. The illumination of the fibre with a supercontinuum source shows that the light is guided over the entire range studied [350 nm-1750 nm], except at 1388 nm because of the OH groups absorption. The first erbium doped silica-zirconia nanostructured optical fibre has been realized and is currently studied. The 4I11/2 →4I15/2 radiative transition of Er3+ is observed when the fibre is pumped with a CW laser-diode at 982 nm. The optimization of the gel composition and dopant concentrations are worth studying to stimulate the radiative transitions 4F9/2→4I15/2 and 4S3/2→4I15/2 in erbium ions. The zirconia nanocrystals apear as a multitude of quantum dots and a luminescence of ZrO2 nanocrystals is expected in the short wavelengths of the visible range under particular excitation conditions

Fabrication of optical fibers with palladium metallic particles embedded into the silica cladding

International audienceAbsorption of hydrogen gas (H2) in contact with palladium (Pd) makes Pd a material of choice for numerous H2 sensors. In this paper, we present the fabrication of optical fibers with embedded Pd particles in the silica cladding of the fibers. Fiber preforms prepared with a powder mixture of silica and palladium oxide (PdO) are heat-treated under specific conditions to reduce PdO to metallic Pd particles, dispersed in the silica matrix. Optical fibers with different topologies have been fabricated with lengths of several hundred meters and PdO concentration ranging from 0.01% to 5% mol (in addition to silica). Oxidation state, homogeneity, shape and size distribution of the particles embedded in the cladding of the preform and the fiber samples are studied with structural and micro-structural characterizations. Optical properties of the fibers are finally studied for evaluating the potential of this proof-of-concept work

Study of the hydrogen influence on the acoustic velocity of single-mode fibers by Rayleigh and Brillouin backscattering measurements

International audienceWe study the effect of hydrogen gas diffusion in silica optical fibers on Brillouin and Rayleigh scatterings. By modeling hydrogen diffusion kinetics as a function of temperature and pressure and by measuring simultaneously Rayleigh and Brillouin scattering on G652 single-mode fiber samples during H2 desorption (previously exposed to 175 bars H2 at 80°C), we have demonstrated experimentally that acoustic velocity increases linearly with H2 concentration with a ratio of about (4.8 m/s) / (%mol H2)

Nanostructured optical fibre obtained by the sol-gel process

International audienc

Development of original process for the realization of multi-materials optical fibers

International audienc

Capteurs à fibre optique pour la surveillance et l’observation du stockage de déchets radioactifs en couche géologique profonde

National audienc