Fabrication of high optical quality Ge-As-Se glasses for the development of low-loss microstructured optical fibers

In the last twenty years the field of chalcogenide glasses has seen increasing interest, due to their broad transparency window in the mid-IR. Furthermore, chalcogenides are showing one of the highest nonlinear refractive indices among glasses. Due to these reasons, the development of chalcogenide microstructured optical fibers with low optical losses can allow for new breakthroughs in various research fields, e.g. new mid-IR laser sources, mid-IR spectroscopy, sensing and applications based on nonlinear effects, like supercontinuum generation. In this framework, chalcogenide glasses with the lowest possible amount of impurities are needed to minimize absorption losses. This study is focused on the attempt of eliminating the pollutants usually giving rise to absorption peaks inside the transparency windows: oxygen, hydrogen, carbon and water. Samples were prepared using a double distillation method: getters that can react with the impurities during the synthesis were added to the initial charge, and the reaction byproducts were eliminated by a two-steps distillation process. Ge10As22Se68 was chosen as the system to study because of its nonlinear, optical and thermomechanical properties. Different combinations of chlorides (for the elimination of hydrogen and carbon) and metals (for the elimination of oxygen) were used, and the attenuation spectra of the resulting glasses were compared. The chosen chlorides are TeCl4, SeCl4, SbCl3, GaCl3; the metals are Mg, Al, Zr, Ni. A holey fiber has been realized by casting method using the best sample, showing that the method is suitable for this composition and that the attenuation before and after the casting are comparable.