Inter-Mode Forward Brillouin Scattering in Nanofibers

We investigate the inter-mode forward stimulated Brillouin scattering (FSBS) in nanofibers in this article. An extraordinary high Brillouin peak value is predicted for the interaction between the HE
₁₁
and the high-order optical mode (TE
₀₁
). The corresponding excited acoustic mode (R
₁₁
) has the characteristics of the relatively uniform large normalized displacements and the phase velocity less than the shear acoustic velocity of silica, which completely differs from the transverse acoustic mode in the intra-mode FSBS process of the HE
₁₁
. The Brillouin peak value by the contribution of R
₁₁
can reach 260.5 W
^-1
m
^-1
at a frequency of 0.1905 GHz, which is at least an order of magnitude higher than the maximum peak value in the intra-mode forward Brillouin gain spectrum (BGS). Moreover, for a nanofiber radius of 0.57 to 1 μm, the contribution of R
₁₁
is always the most prominent to the BGS. This work provides further insight into phonon-photon coupling in nanofibers.