Fig. 1: Calculated opto-mechanical spectra \(\left|\boldsymbol\gamma \left(\boldsymbol\Omega /\boldsymbol2\mathbf\pi \right)\right|\) in a few-mode fiber.

a Intra-modal forward Brillouin scattering between two optical waves in the fundamental \(L{P}_{01}\) mode, through radial acoustic modes \({R}_{0m}\). b Same as panel a, with torsional-radial acoustic modes of two-fold azimuthal symmetry \({{TR}}_{2m}\)