Interpolarization Forward Stimulated Brillouin Scattering in Standard Single-Mode Fibers

Forward stimulated Brillouin scattering in standard single-mode fibers draws increasing interest toward sensing and signal processing applications. The process takes place through two classes of guided acoustic modes: purely radial ones and torsional-radial modes with twofold azimuthal symmetry. The latter case cannot be described in terms of scalar models alone. In this work, the polarization attributes of forward stimulated Brillouin scattering in single-mode fibers are investigated in analysis and experiment. Torsional-radial acoustic modes are stimulated by orthogonally polarized pump tones, a first such report in standard single-mode fibers. The scattering of optical probe waves by torsional-radial modes may take up the form of phase modulation, cross-polarization coupling, or a combination of both, depending on polarization. Lastly, this analysis predicts that circular and orthogonal pump tones may stimulate acoustic vortex beams: torsional-radial modes that are rotating. The rotation represents the transfer of angular momentum between the polarization degree of freedom of the light field and the acoustic wave.