The Brillouin gain coefficient of Yb-doped aluminosilicate glass optical fibers

Provided herein is a detailed analysis of the Brillouin spectroscopy of the ytterbia (Yb₂O₃) dopant in aluminosilicate glass optical fibers. Yb-doped fiber lasers have become ubiquitous, and the results presented here may be used to design lasers and amplifiers for narrow linewidth systems and applications. It is found, with a high degree of certainty, that Yb ₂O₃ has an acoustic velocity that is lower than that of silica, a Brillouin spectral width (or material acoustic damping coefficient) that is about 80 times greater than that of silica, and photoelastic constants (Pockels' coefficients) that are negative. It is found that the primary influence of ytterbia in concentrations typical of active fibers is to broaden the Brillouin gain spectrum, thereby reducing the peak Brillouin gain. A set of design curves is provided outlining the Brillouin gain coefficient as a function of alumina concentration for several ytterbia concentrations, which can be utilized to design fiber structures with reduced Brillouin gain. The Yb-doped aluminosilicate fiber system is compared to the Yb-doped phosphosilicate system, and a high degree of similarity is found between them at low Al ₂O₃ or P₂O₅ doping levels. However, for fiber produced utilizing conventional techniques, the phosphosilicates are found to have the potential for lower Brillouin gain since more P ₂O₅ can be reliably incorporated into the glassy matrix.