The Acoustic Velocity of Ge-Doped Silica Fibers: A Comparison of Two Models

Two models are compared with measured data for the longitudinal acoustic velocity of Ge-doped silica fibers as a function of GeO₂ content in order to determine if either of them can be used in designing the acoustic velocity profile of an optical fiber. These are the Makishima-Mackenzie and additive (AD) models. Both models are found to fit measured data very well in the available test samples, and as a result both models offer a means to accurately design doping profiles for a number of Brillouin scattering applications. The major difference between these models lies in the slope of the curve between pure silica and pure GeO₂ acoustic velocity values, the latter of which lies outside the range of our experimental data (<40mol% GeO₂ in silica). The AD model is also shown to fit the Sellemeier equation very well.