Fig. 3: Calculated opto-mechanical gain coefficients \({\mathbf{Im}}\left\{\boldsymbol\gamma \left(\boldsymbol\Omega /\boldsymbol2\mathbf\pi \right)\right\}\) in a few-mode fiber.

a Inter-modal forward Brillouin scattering between one optical wave in the \(L{P}_{01}\) mode and another in the \(L{P}_{02}\) mode, through radial acoustic modes \({R}_{0m}\). b Same as panel a, with torsional-radial acoustic modes of two-fold azimuthal symmetry \({{TR}}_{2m}\)