Bertrand Poumellec

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It is reported that reversible changes in the reflectivity of Bragg gratings can be induced by a change in the temperature of the grating (77 K < T < K). The changes have proved to be greater in highly doped Ge fibers than in standard fibers, whereas they could hardly be detected in hydrogenated fibers. The sign of the change for type I gratings was(More)
We ascertain by measuring the surface topography of a cleaved sample in which damage lines have been written in volume by scanning with a femtosecond laser, that matter shearing occur along the laser track with alternating sign (scissor or chiral effect). We note that the shearing in the head of the laser tracks change its sign with the change in scanning(More)
We reveal stress fields induced by femtosecond laser irradiation by investigating the topography of surface relaxation of a cleavage of silica plates in which irradiation was performed, varying intensity, laser polarization and displacement of the writing beam. The stress field appears to depend on the writing parameters differently according to the laser(More)
We demonstrate crystals (LiNbO(3)-like) that were space-selectively nucleated and grown in the bulk of silica-based glass by femtosecond laser irradiation at a high repetition rate (typ. 300 kHz). Oriented crystals with their polar axis mostly aligned with or perpendicular to the laser scanning direction have been fabricated by manipulation of the(More)
We compare the results of thermally induced isochronal and isothermal decays of fiber Bragg gratings written through cw exposure of an unloaded germanosilicate fiber. We show that isochronal step decays can be used to predict isothermal decays, provided that some corrections are carried out to take into account a reversible change in grating reflectivity(More)
This paper is dedicated to the lifetime prediction of Type I Fiber Bragg gratings (FBG) and to problems that happen when stabilization (also called passivation) conditions or the industrial conditioning procedure depart from ageing ones (e.g., presence of hydrogen during the passivation process). For the first time, a reliable procedure to certify the(More)
The impact of fictive temperature (T<sub>f</sub>) on the evolution of point defects and optical attenuation in non-doped and Er<sup>3+</sup>-doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by the densification of(More)
We demonstrate a new kind of form birefringence in lithium niobium silicate glass induced by femtosecond laser direct writing. By combining electron backscatter diffraction and transmission electron microscopy, we reveal a self-assembled nanostructure consisting of periodic phase change: nonlinear optical nanocrystals embedded in a network of "walls" in a(More)
We report on nanostructures induced by femtosecond laser pulses in the bulk of Germanium-doped silica glasses. For studying structural properties of the nanostructure constituents small-angle x-ray scattering and SEM served to map pore size, filling factor and periodicity. Our results show that with increasing the Ge doping concentration, the aspect ratio(More)