In this paper, we analyzed the Brillouin scattering characteristics in micro-nano fibers. According to the elastic mechanics equation and the Helmholtz equation, the mathematical model of the acoustic wave field and the optical field in the cylindrical waveguide with the sub-wavelength scale were established. According to the relationship between intrinsic acoustic mode and dispersion, the mechanism of Brillouin scattering in micro-nano fiber was analyzed. Considering the effects of electrostriction and radiation pressure comprehensively, the influence of two main physical effects, photo-elastic effect and moving-boundary effect on Brillouin gain in the process of acousto-optic coupling was studied. On this basis, the influence of the structure, material, and size of the micro-nano fiber on the Brillouin frequency shift and gain was analyzed and verified experimentally by Brillouin optical correlation domain analysis.
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