Imène Reghioua

Irradiation Temperature Influence on the In Situ Measured Radiation Induced Attenuation of Ge-Doped Fibers

We report an experimental investigation on the radiation-induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-ray (10 keV) exposure at different temperatures. The objective is to characterize the impact of the irradiation temperature on the RIA levels and kinetics. Our data highlight that for dose exceeding 1 kGy(SiO2) the RIA spectrum changes with the irradiation temperature. In particular, for wavelengths below 470 nm the RIA depends both on the dose and on the irradiation temperature, whereas at higher wavelengths the RIA depends only on the dose. From the microscopic point of view the origin of this behavior is explained by a larger impact of the irradiation temperature on the Ge(1) defects generation mechanism with respect to the one of GeX defects, which appears as poorly temperature sensitive in the tested range. This finding prevents us from easily establishing a conclusive relation between the generation mechanisms of these two types of defects. The lower content of radiation induced Ge(1), in fiber irradiated at higher temperature, is supported by the electron paramagnetic resonance (EPR) results acquired after the irradiation. In situ RIA and postmortem EPR data show a significant correspondence of the Ge(1) growth as a function of the dose. Confocal microscopy luminescence experiments indicate that the non-bridging oxygen hole center concentration is higher at 473 K in comparison with those observed at 300 and 373 K.

Effect of irradiation temperature on the radiation induced attenuation of Ge-doped fibers

The UV-visible radiation induced attenuation (RIA) was studied in Ge-doped optical fibers, during X-ray (10 keV) irradiations at different temperatures. By comparing the spectra recorded in dissimilarly irradiated samples we evidenced the impact of the irradiation temperature. In details, we highlighted that, from a certain dose, increasing the temperature the RIA decreases for wavelengths lower than 470 nm, whereas at higher wavelengths the RIA depends only on the dose. Such findings suggest that it is possible to distinguish the irradiation temperature by comparing the signal at two different wavelengths. From the microscopic point of view, it appears that the RIA behavior is mainly related to a dissimilar content of induced Ge(1) defects, whereas the so called GeX defects features only small variations. The impact of the irradiation temperature on the Ge(1) induced concentration, as a function of the irradiation temperature, is confirmed by the post-irradiation electron paramagnetic resonance measurements that we acquired for samples that were irradiated at room temperature and at 200 °C.

Study of point defects in as-drawn and irradiated Ge-doped optical fibers using cathodoluminescence

In the present paper, we report an experimental investigation of Ge-doped Optical Fibers (OFs) which were investigated by Cathodoluminescence (CL) measurements. We followed the evolution, under 10 keV electron exposure, of the emissions present in three different samples: the first one was the as-drawn fiber (pristine), the second one was irradiated with a CW UV laser at 244 nm and the last one was irradiated at the dose of 9 MGy (SiO2) by γ-rays. Moreover, taking advantage of the employed experimental set-up, which allows to perform spatially-resolved (<1μm) CL measures, we were able to investigate the emission evolution in two differently doped zones of the fiber. Our data indicate that (i) the CL spectra of our three samples are dominated by the 400 nm emission band related to the Germanium Lone Pair Center (GLPC), (ii) the spatial distribution of this defect differs in the three fibers and (iii) the electron exposure decreases the GLPC concentration in all samples (pristine, UV and γ irradiated). A comparison between the CL and photoluminescence (PL) measurements shows comparable results.

Cathodoluminescence Characterization of Point Defects in Optical Fibers

We evaluate the potential of the cathodoluminescence (CL) spectroscopy to characterize the nature and the spatial distribution of point defects in the main classes of optical fibers (OFs): Telecom-grade, radiation-hardened, and radiation sensitive. Canonical samples, that are differently doped in their cores (Ge, N, P, Ce) or their claddings (F), have been investigated through CL technique using a 10-keV electron beam. Obtained results are compared with those obtained by photoluminescence spectroscopy. CL benefits and limits are discussed on the basis of the obtained experimental data. CL is shown to be efficient to investigate the kinetics of defect generation and bleaching under the electron exposure, being the unique technique allowing us to determine in situ the spatial distribution of emitting defects in the fiber transverse cross sections. New insights are given for some of the defects related to the Ge, P, Ce and N dopants.

Investigation of point defects in silica-based optical fibers by cathodoluminescence

We demonstrate the high potential of cathodoluminescence (CL) spectroscopy for the study of point defects in the main classes of optical fibers: Telecom-grade, radiation-hardened, and radiation sensitive. Canonical samples, differently doped in their core (Ge, P, N) or their cladding (F), have been investigated by CL using electrons of energy ranging from 5 to 30 keV. Advantages and limitation of the CL tool are discussed on the basis of the obtained experimental results.

Ge-doped silica nanoparticles: production and characterisation

Silica nanoparticles were produced from germanosilicate glasses by KrF laser irradiation. The samples were investigated by cathodoluminescence and scanning electron microscopy, providing the presence of nanoparticles with size from tens up to hundreds of nanometers. The emission of the Germanium lone pair center is preserved in the nanoparticles and atomic force microscopy revealed the presence of no spherical particles with a size smaller than ~4 nm. The absorption coefficient enhancement induced by Ge doping is reputed fundamental to facilitate the nanoparticles production. This procedure can be applied to other co-doped silica materials to tune the nanoparticles features.