Yb<sub>2</sub>O<sub>3</sub>doped yttrium-rich alumino-silicate nano-particles based D- and P- (pentagonal) shaped optical fibers with core diameter ~30–35 µm are fabricated using the conventional MCVD process and solution doping technique. Parameters of different stages of the fiber preforms fabrication are optimized to get uniform distributions of Al, Y, F, and Yb ions in the core region, ensured by the data of an EPMA analysis. In the presence of small amounts of fluorine, the size of nano-particles is maintained within 5–10 nm; the EDX data reveal that the nano-particles are rich in yttrium-alumino-silicate phase and are dispersed uniformly across the preforms core. The critical parameters of the processes involved at the fibers fabrication along with the nano-structuring and spectroscopic features are highlighted. It is shown experimentally that the drawn D- and P- shaped fibers support high laser efficiency (~80% at 976-nm pumping) and demonstrate negligible photodarkening.
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