Xavier Bidault

A simple transferable adaptive potential to study phase separation in large-scale xMgO-(1-x)SiO2 binary glasses

A simple transferable adaptive model is developed and it allows for the first time to simulate by molecular dynamics the separation of large phases in the MgO-SiO2 binary system, as experimentally observed and as predicted by the phase diagram, meaning that separated phases have various compositions. This is a real improvement over fixed-charge models, which are often limited to an interpretation involving the formation of pure clusters, or involving the modified random network model. Our adaptive model, efficient to reproduce known crystalline and glassy structures, allows us to track the formation of large amorphous Mg-rich Si-poor nanoparticles in an Mg-poor Si-rich matrix from a 0.1MgO-0.9SiO2 melt.

Molecular dynamics study of rare-earth doped Mg-silicate nanoparticles in vitreous silica: from the preform to the fiber

Formation of rare-earth doped nanoparticles into silica matrix has been modelized by Molecular Dynamics simulations. Preforms with molar composition 0.10MgO–0.90SiO2 and 0.01EuO3/2–0.10MgO–0.89SiO2 have been investigated to have an insight on the structure and chemical composition of the nanoparticles, as well as the rare-earth ions local environment and their clustering. We have finally applied a uniaxal elongation of the rare-earth doped preform in order to mimic the drawing step that changes a preform into a fiber. We present herein first results on the modification of the nanoparticles size distribution.

Erbium-doped transparent glass ceramic optical fibres: Characterization using mass spectroscopy and molecular dynamics modeling

Rare earth (RE) doped silica-based optical fibres with transparent glass ceramic (TGC) core were fabricated through the well-known modified chemical vapor deposition (MCVD) process without going through the commonly used stage of post-ceramming. The main characteristics of the RE-doped dielectric nanoparticles (DNP), their density and mean diameter in the fibres are dictated by various parameters. This paper reports on progresses in the fine characterization of the nanoparticles, particularly their dimensions and composition, using nanoscale mass spectroscopy and molecular dynamics modeling, and alteration of the spectroscopic properties of the erbium ions embedded within the phospho-silicate DNP. These results permit to get more insight into the complex process of the DNP self-nucleation and growth during the fibre fabrication process. This fabrication route could have important potentials in improving rare-earth-doped fibre amplifiers and laser sources.

Characterization of erbium-doped nanoparticles in transparent glass ceramic optical fibres

We report on using nanometric mass spectroscopy and molecular dynamics modelling to characterize the composition and structure of self-grown erbium-doped nanoparticles in transparent glass ceramic optical fibres fabricated by modified chemical vapour deposition without post-ceramming.