Fabrication and Characteristics of Yb-Doped Silica Fibers Produced by the Sol-Gel Based Granulated Silica Method

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.

Multimode Ytterbium–Aluminosilicate Core Optical Fibre for Amplification and Laser Applications

“…The fluorescence lifetime of the fabricated fibre was measured at 1.2 ms, which suggests that there are no significant ion clustering and quenching effects occurring in the fabricated fibre. The measured lifetime is also significantly higher than the values in previous studies using comparable powder-based techniques with lower or similar Yb concentrations that exhibit lifetimes in the order of 0.86 ms [10].…”

“…However, these have shown limitations in terms of achievable geometry, doping concentration and refractive index homogeneity [5]. In contrast, sol-gel [9,10], powder-based [4,11] and Reactive Powder Sintering of Silica (REPUSIL) technologies [12] offer improved flexibility in concentration, the production of large core diameters and the ability to tailor the index step between different fibre regions.…”

“…Studies focused on preform fabrication techniques, in which oxide powders are annealed and sintered into rods, have yielded maximum concentrations of 0.128 mol% Yb 2 O 3 and 1.112 mol% Al 2 O 3 [14]. Optical fibres produced with powder-based technology [10], aiming to investigate the influence of the materials on their refractive index and transmission, presented two optical fibres with ytterbium as a constant element and fixed alumina concentrations (with respect to phosphorus): Fibre 1 with 9 at.% Al and 11 at.% P and Fibre 2 with 4.5 at.% Al and 5.5 at.% P, with a constant concentration of 0.3 at.% Yb.…”