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Author: Unger, Sonja × DDC: 620 ×

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    Germania and alumina dopant diffusion and viscous flow effects at preparation of doped optical fibers
    (Ostrava : VSB - Technical University of Ostrava and University of Zilina Faculty of Electrical Engineering, 2017) Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Unger, Sonja; Schwuchow, Anka; Elsmann, Tino; Dellith, Jan; Aichele, Claudia; Fatobene Ando, Ron; Bartelt, Hartmut
    We report on germania and alumina dopant profile shift effects at preparation of compact optical fibers using packaging methods (Stack-and-Draw method, Rod-in-Tube (RiT) technique). The sintering of package hollow volume by viscous flow results in a shift of the core-pitch ratio in all-solid microstructured fibers. The ratio is increased by about 5% in the case of a hexagonal package. The shift by diffusion effects of both dopants is simulated for typical slow speed drawing parameters. Thermodynamic approximations of surface dissociation of germania doped silica suggest the need of an adequate undoped silica barrier layer to prevent an undesired bubble formation at fiber drawing. In contrast, alumina doping does not estimate critical dissociation effects with vaporous aluminium oxide components. We report guide values of diffusion length of germania and alumina for the drawing process by kinetic approximation. The germania diffusion involves a small core enlargement, typically in the sub-micrometer scale. Though, the alumina diffusion enlarges it by a few micrometers. A drawn pure alumina preform core rod transforms to an amorphous aluminosilicate core with a molar alumina concentration of only about 50% and a non-gaussian concentration profile.
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    Two-Step-Model of Photosensitivity in Cerium-doped Fibers
    (Washington D.C. : Optical Society of America, 2019) Elsmann, Tino; Becker, Martin; Olusoji, Olugbenga; Unger, Sonja; Wondraczek, Katrin; Aichele, Claudia; Lindner, Florian; Schwuchow, Anka; Nold, Johannes; Rothhardt, Manfred
    The photosensitivity of various cerium-doped fibers has been experimentally investigated for both excimer- and femtosecond-laser illumination. The results of single-pulse, few-pulse and multi-pulse inscription of fiber-Bragg-gratings with both laser systems and the thermal aging of those gratings demonstrated the restrictions of the conventional color center model for cerium-doped fibers. To explain the short-term stability of single-pulse gratings against long-term stability of multi-pulse gratings, an extension into a two-step-model was deduced.
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    Viscosity of fluorine-doped silica glasses
    (Washington D.C. : Optical Society of America, 2018) Kirchhof, Johannes; Unger, Sonja; Dellith, Jan
    The viscous behavior of fluorine-doped synthetic silica is studied using collapsing experiments with different fluorine-doped tubes on a modified chemical vapor deposition (MCVD) lathe. The principles, techniques, and evaluations of this method are the same as the ones demonstrated previously in detail with pure and doped silica. The present investigations provide information about the influence of fluorine doping up to a concentration of about 10 mol% F (3.4 wt% F) in a temperature range between 1600°C and 2000°C. Fluorine doping leads to a systematic decrease in the viscosity, combined with a decrease of the activation energy of the viscous flow and a certain increase of the pre-exponential factor. In summary, this demonstrates the weakening influence of fluorine on the glass network, similar to the incorporation of hydroxyl or chlorine.