The Influence of the MCVD Process Parameters on the Optical Properties of Bismuth-Doped Phosphosilicate Fibers

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%.