In order to reduce inter-mode crosstalk,a coupling ring-assisted multi-mode fiber structure was proposed,and the mathematical model of its excited Brillouin scattering gain spectrum was established.Theoretically,the excited Brillouin scattering threshold of the coupling ring-assisted multi-mode fiber was analyzed,as well as the effects of fiber parameters and modes on the excited Brillouin scattering spectral threshold.The results show that the coupling ring-assisted structure increases the effective refractive index difference to 1.75 times that of the conventional type step-index multi-mode fiber.The threshold of the excited Brillouin scattering spectrum in coupling ring-assisted multi-mode fiber follows the increase of the fiber length from a sharp decrease to a slow one and finally converges to a constant value of 30 dBm at 18 km,which is higher than that of the conventional step refractive index multi-mode fiber.Other things being equal,the threshold increases linearly with the attenuation coefficient,the effective cross-sectional area of the fiber core,and the mode order of the fiber;it increases exponentially with the increase of the core radius.This study provides a theoretical reference for enhancing the transmission distance and channel capacity of fiber optic communication systems.
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