The analysis of optical and acoustic properties of optical fibers is required for accurate Brillouin gain spectrum (BGS) determination. We present a full modal-analysis of the guided optical and acoustic modes based on a two-dimensional finite-element method (2D-FEM) for BGS calculation using COMSOL Multiphysics. We believe that this method will be helpful in analyzing and designing special fibers for applications, such as fiber amplifiers with significant SBS (Stimulated Brillouin Scattering) suppression or Brillouin-based fibersensors. The model is adapted for BGS evaluation of any single mode fiber (in term of optical mode) based on its profile, namely its geometry, and its doping composition. Compared to standard multi-layer methods limited to axially-symmetric fibers [1], the 2D-FEM analysis enables the BGS computation even for more complicated geometries, such as PANDA polarization-maintaining fiber where the optical index and the material stress are azimuthally dependant. The results of numerical modeling have shown good agreement with measured Brillouin spectra for different types of silica fibers. Examples are given for a standard GeO2-doped core fiber (standard fiber for telecommunication applications), Fluor-doped cladding fiber (acoustic anti-waveguide) and PANDA fiber.
