The Influence of the MCVD Process Parameters on the Optical Properties of Bismuth-Doped Phosphosilicate Fibers
Aleksandr Khegai, Fedor Afanasiev, Yan Ososkov, Konstantin Riumkin, V. F. Khopin, Alexey Lobanov, Mikhail V. Yashkov, Elena Firstova, Alexey Abramov, Mikhail Melkumov, Alexey Guryanov, Sergei Firstov
Abstract
In this article, we describe the technology for manufacturing of the phosphosilicate bismuth-doped optical fibers providing optical amplification near 1.32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m. The effect of preforming sintering process and fiber drawing on the optical properties of the fabricated fibers were studied. We showed that an increase in the vitrification temperature of the P-doped silica glass soot layers deposed on the inner surface of a fused silica tube from 1850 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {\sim \text{2000}}$</tex-math></inline-formula> °C (while keeping other parameters unchanged) provides a noticeable reduction of the unsaturable losses. We also found that the fiber drawing speed significantly affects the optical properties of bismuth-doped fibers. In particular, an increase in the drawing speed from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 1 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 80 m/min led to a decrease of both active absorption and unsaturable losses, while the ratio of active absorption to unsaturable losses became greater. As a result, the laser efficiency of the bismuth-doped fibers grew two-fold from 19.5% to 37%.