Accurate Modeling of the Intrinsic Brillouin Linewidth via Finite-Element Analysis

We present a finite-element analysis of the Brillouin gain spectrum of a highly Ge-doped azimuthally symmetric nonuniform fiber treating the heterogeneous viscosity profile in detail. Measured Stokes' frequencies and spectral widths for the acoustic modes, and the peak Brillouin gain coefficient are found to be in excellent agreement with the model. An approximate expression for the Brillouin spectral width in azimuthally symmetric, nonuniform fibers is presented and verified for estimating this quantity using simplified boundary-value models.