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Forward Brillouin scattering between vector high-order optical modes in a few-mode nanofiber

Gain and acoustic characteristics of inter-mode forward stimulated Brillouin scattering (FSBS) induced by discrete vector high-order optical mode (HOM) pairs in a few-mode nanofiber (FMNF) are presented in this paper. Three completely different acoustic modes of TA02, R22, and R21 preferentially interact with the TE01–TM01, TE01–HE21, and TM01–HE21 mode pairs, respectively, and dominate the highest Brillouin peak at different frequencies. Moreover, the influence of FMNF radius on Brillouin gain spectrum (BGS) characteristics is also investigated. The R21-caused Brillouin peak in the BGS of TM01–HE21 is much higher than that of TE01–TM01 (TE01–HE21). Especially, the R21 acoustic mode that interacts with the TM01–HE21 mode pair can provide the maximum Brillouin gain, which is also the highest peak at frequency ranges greater than 1 GHz, compared with all inter-mode and even intra-mode BGSs. And a definite functional relationship is found between the incident wavelength, the optimal FMNF radius, and the maximum of R21-caused Brillouin gain. Vector HOMs induced inter-mode FSBS may provide a promising approach for applications, such as sensing and nonlinear dynamics of the Brillouin interaction.