RESUMEN

We report on an extensive investigation of photodarkening in Yb-doped silica fibers. A set of similar fibers, covering a large Yb concentration range, was made so as to compare the photodarkening induced losses. Careful measurements were made to ensure equal and uniform inversion for all the tested fibers. The results show that, with the specific set-up, the stretching parameter obtained through fitting has a very limited variation. This gives more meaning to the fitting parameters. Results tend to indicate a square law dependence of the concentration of excited ions on the final saturated loss. We also demonstrate self-similarity of loss evolution when experimental curves are simply normalized to fitting parameters. This evidence of self-similarity also supports the possibility of introducing a preliminary figure of merit for Yb-doped fiber. This will allow the impact of photodarkening on laser/amplifier devices to be evaluated.

Asunto(s)

RESUMEN

The present work describes photodarkening from the viewpoint of cooperative luminescence. The temporal evolution of both effects was measured simultaneously by means of ytterbium doped aluminosilicate fibers for concentrations up to 1.8 wt% Yb3+. The quadratic dependence of photodarkening and cooperative luminescence versus dopant concentration was observed. The change in the photodarkening and cooperative luminescence mutual dynamics for highly and low doped fibers is ascribed to a different ion number which forms the cluster. Cooperative luminescence is proved to be a natural probe for photodarkening since it provides new pieces of information and contributes to the photodarkening mechanism description.

Asunto(s)

RESUMEN

We report significant advances in the fabrication of low loss chalcogenide microstructured optical fiber (MOF). This new method, consisting in molding the glass in a silica cast made of capillaries and capillary guides, allows the development of various designs of fibers, such as suspended core, large core or small core MOFs. After removing the cast in a hydrofluoric acid bath, the preform is drawn and the design is controlled using a system applying differential pressure in the holes. Fiber losses, which are the lowest recorded so far for selenium based MOFs, are equal to the material losses, meaning that the process has no effect on the glass quality.

RESUMEN

We report recent progress on fabrication of solid core microstructured fibers in chalcogenide glass. Several complex and regular holey fibers from Ga5Ge20Sb10S65 chalcogenide glass have been realized. We demonstrate that the "Stack & Draw" procedure is a powerful tool against crystallisation when used with a very stable chalcogenide glass. For a 3 ring multimode Holey Fiber, we measure the mode field diameter of the fundamental mode and compare it successfully with calculations using the multipole method. We also investigate, via numerical simulations, the behaviour of fundamental mode guiding losses of microstructured fibers as a function of the matrix refractive index, and quantify the advantage obtained by using a high refractive index glass such as chalcogenide instead of low index glass.