Preparation and performance study of a Tm³⁺-doped silica optical fiber by sol-coating and laser drawing technology

High-concentration <i>T</i> <i>m</i> ³⁺-doped silica optical fibers have significant application value in areas such as single-frequency lasers. This paper investigates the sol-coating in the silica capillaries process and <i>C</i> <i>O</i> ₂ laser drawing technology and successfully fabricates a <i>T</i> <i>m</i> ³⁺-doped single-mode silica optical fiber. The core composition adopts a Tm-La-Al-Si system; the <i>T</i> <i>m</i> ³⁺ doping concentration is 0.5 mol%; the core and cladding diameters are 5 and 130 µm, respectively; and the numerical aperture (NA) is 0.28. A laser seed source with a wavelength of 1940 nm is established, and the laser gain characteristics of the optical fiber are tested. The small-signal net gain coefficient at the wavelength of 1940 nm is measured to be 0.15 dB/cm. The sol-coating method employed in this study enhances the doping concentration of Tm ions, while the laser drawing technique mitigates ion diffusion effects. The results indicate that this <i>T</i> <i>m</i> ³⁺-doped silica fiber preparation method offers a novel, to the best of our knowledge, approach for manufacturing high-concentration doped silica fibers and holds significant reference value for related research fields.