We 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).
In this paper, we report the fabrication and characterization of a new concept of optical fibers whose cladding is composed of palladium particles embedded into the silica glass cladding. Since conventional fiber processes are not suitable for such realizations, we developed an original process based on powder technology to prepare our specific preforms. Step, graded index and photonic crystal optical fibers with original shapes were realized. The use of high purity powders as raw materials combined to a specific preforms heat treatment allowed the fabrication of resistant and long length metal-cladding optical fibers. Microstructured Pd-SiO2 composite cladding optical fibers with single-mode behavior and optical losses lower than 2 dB/m at 1530 nm were characterized. Hydrogen-induced attenuation sensitivity of these fibers at the 1245 nm wavelength was demonstrated after long H2 exposure. Dehydrogenation kinetics calculations and experiments were studied.
We report on SiO2-Al2O3-La2O3 glasses – with and without Yb2O3 – suitable for nonlinear and fiber laser applications. We also present successful supercontinuum generation and fiber laser operation around 1060 nm in step-index fibers. We have optimized the glass compositions in terms of thermal and optical requirements for both a high La2O3 (24 mol%) and Yb2O3(6 mol%) concentration. The aluminum concentration was adjusted to about 21 mol% Al2O3 to increase the solubility of lanthanum and ytterbium in the glass beyond possible MCVD based techniques. The glasses have been characterized by dilatometrical methods to find transition temperatures from 860 to 880°C and thermal expansion coefficients between 4.1 and 7.0 × 10-6 K-1. Structured step index fibers with a SiO2-Al2O3-La2O3 core and silica cladding have been realized showing a fiber loss minimum of about 500 dB/km at 1200 nm wavelength. The chromatic dispersion could be adjusted to shift the zero dispersion wavelength (ZDW) close to the pump wavelength of 1550 nm in a supercontinuum generation setup. First fiber laser experiments show an efficiency of about 41 % with a remarkably reduced photodarkening compared to MCVD based fibers.