The Effect of thermal and mechanical processing on the fluorescence lifetime of Yb-doped silica preforms and fibers for use in nanostructured-core fiber lasers

In this paper, we investigate the influence of various nanostructured-core fiber fabrication processes, such as preform elongation or fiber drawing, on the fluorescence lifetime of Yb3+ ions. The optical fiber preform was prepared using Modified Chemical Vapor Deposition (MCVD) method combined with Al2O3 nanoparticle doping. The optical fiber preform was subjected to various processing treatments involving heat and mechanical stresses, i.e. preform elongation and fiber drawing, and the fluorescence lifetime was measured in all stages of fiber fabrication, i.e. original preform, elongated preform (cane), fiber and overcladded fiber. It was found that the time-resolved photoluminescence properties of Yb3+ ions in silica glass are strongly dependent on the processing of the material. The fluorescence lifetime of the F-2(5/ 2) level of Yb3+ ions decreased with the heat and mechanical treatment, which was explained by the break-up of Al2O3 nanoparticles, diffusion of dopants and changes in the Yb3+ phonon environment as well as clustering of the Yb3+ ions. The fiber drawing exhibited a stronger effect compared to preform elongation which was ascribed to the high rate of cooling and mechanical stresses during the drawing process. In general, the heat and mechanical processing of Yb-doped optical fiber preforms leads to a deterioration of time-resolved photoluminescence properties.