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 TA(02), R-22, and R-21 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 R-21-caused Brillouin peak in the BGS of TM01-HE21 is much higher than that of TE01-TM01 (TE01-HE21). Especially, the R-21 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 R-21-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.