A quasi-mode interpretation of acoustic radiation modes for analyzing Brillouin gain spectra of acoustically antiguiding optical fibers

Abstract

We propose a novel quasi-mode interpretation (QMI) method to represent acoustic radiation modes in acoustically antiguiding optical fibers (AAOFs) in terms of discrete quasi-modes. The QMI method readily enables one to obtain the full quasi-modal properties of AAOFs, including the complex propagation constants, mode center frequencies, and field distributions in an intuitive and much simplified way, compared to other previous methods. We apply the QMI method to analyze the Brillouin gain spectrum of an AAOF that has typically been used to mitigate stimulated Brillouin scattering of optical waves. The result based on the QMI method is in good agreement with the numerical and experimental results for the same fiber structure previously reported in the literature. Considering the effectiveness and simplicity of its numerical procedure, we expect the use of the QMI method can further be extended to even more complicated numerical analyses with acoustic radiation modes, which include the acoustically antiguiding, large-core optical fibers in multi-mode regimes.