The effect of fiber fabrication process on the photoluminescence properties of RE-doped optical fiber preforms and fibers

Holmium- doped aluminosilicate fibers are frequently used in holmium-doped fiber lasers (HDFL) thanks to their strong emission at 2 mu m. Fluorescence lifetime is one of the most important parameters to determine the suitability of holmiumdoped optical fibers for use in fiber lasers. One of the potential mechanisms for the shortening of fluorescence lifetime is the diffusion of RE ions and Al2O3 at high temperatures during the fiber preparation process. We have prepared a Hodoped aluminosilicate optical fiber preform using MCVD combined with nanoparticle doping. The prepared preform was subjected to various fabrication processes such as preform elongation, fiber drawing or additional heat treatment, the fluorescence lifetime was measured in all stages of the experiment and its dependency on the fabrication process was discussed. The original preform exhibited a long fluorescence lifetime of 1.433 ms. Gradual application of fiber fabrication processes such as preform elongation or fiber drawing resulted in a decline of fluorescence lifetime down to 1.174 ms in the case of overcladded optical fiber. The decrease of fluorescence lifetime was ascribed to the diffusion of dopants and the changes in the Ho3+ ion environment, which increased the rate of multiphonon relaxation, as well as clustering of holmium ions, which increased concentration quenching.