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 (<40 mol% GeO2 in silica). The AD model is also shown to fit the Sellemeier equation very well.