Characterization of intra-mode forward Brillouin scattering induced by vector high-order optical mode in nanofibers

We present the characteristics of intra-mode forward stimulated Brillouin scattering (FSBS) induced by HE11 and high-order optical mode (HOM) in nanofibers, respectively. Multiple transverse acoustic modes (TAMs) would be excited in the FSBS process. However, only a few specific low-order TAMs participate in the interaction of different optical mode pairs and then contribute to Brillouin gain. Meanwhile, the changes of dominating Brillouin peaks with the nanofiber radius are shown in detail, which further clearly confirms the difference in the gain characteristics of different intra-mode Brillouin gain spectrums. Especially, several obvious maximum and minimum gain values exist at the nanofiber radius of around 0.8 μm. The HOM induced intra-mode FSBS is of great importance for understanding of the phonon–photon interaction in multi-mode waveguides.