Abstract
Combining the sol-gel method for fiber material production with the granulated silica method for preform assembly results in a robust method that offers a high degree of freedom regarding both the composition and the geometry of the produced fiber. Using this method, two types of Yb-doped silica glass composition, that feature an excess in P concentration with respect to Al, have been prepared. The elemental distributions in a fiber core were analyzed by scanning transmission electron microscopy (STEM). The elemental mapping shows a similar localization of Al, P and Yb through the microstructure. In addition, the influence of the variation in the co-dopant concentration, with respect to Yb, on the fiber properties has been investigated. The results show an increase in the refractive index step and in the fiber’s transmission loss as the excess concentration of P increases. A significant contribution to the losses can be assigned to the existence of impurities such as iron, which was detected in our samples by mass spectrometer. Single exponential fluorescence decays with lifetimes of around 0.88 ms were measured for the two compositions. Finally, pumping at 976 nm a laser slope efficiency of 67% at 1031 nm was achieved for one of the fiber compositions.
Highlights
Optical fibers doped with ytterbium (Yb) ions have attracted increasing interest for the development of high-power laser systems for applications requiring bright and high power beams, such as materials processing, medicine and telecommunications [1,2,3,4,5,6]
Because of the low solubility of Yb ions in pure silica glass, the RE cations with their high field strength require a high number of non-bridging oxygens to coordinate with, in order to compensate for the positive charge [10]
It has been reported that silica powder based on the sol-gel method can show and flexibility of the sol-gel process enables freedom for adopting varied dopant and co-dopant lower impurities compared thereported naturalthat quartz is commonly used for producing materials
Summary
Optical fibers doped with ytterbium (Yb) ions have attracted increasing interest for the development of high-power laser systems for applications requiring bright and high power beams, such as materials processing, medicine and telecommunications [1,2,3,4,5,6]. Yb and RE ions in general tend to form microstructural clusters when doped in silica glass and co-doping with high field strength ions such as aluminum. Because of the low solubility of Yb ions in pure silica glass, the RE cations with their high field strength require a high number of non-bridging oxygens to coordinate with, in order to compensate for the positive charge [10]. This is difficult to achieve in a network that has few non-bridging oxygen hole centers, like that of SiO2 [14,15]. With poor solubility of RE ions in molten silica glass, these RE microstructural clusters form even at very low concentrations [11,17]
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