Threshold of Brillouin Scattering in a Few-Mode Fiber
ZHANG Yan-jun, GAO Hao-lei, FU Xing-hu*, TIAN Yong-sheng, WANG Hui-min, ZHANG Yi-nan
School of Information Science and Engineering, The Key Laboratory for Special Fiber and Fiber Sensor of Hebei Province, Yanshan University, Qinhuangdao 066004, China
Abstract：Stimulated Brillouin scattering can affect the signal-to-noise ratio, transmission distance and transmission capacity in few-mode fiber transmission system. Stimulated Brillouin scattering is an important factor limiting the input power scaling of the fiber transmission system. In this paper, the threshold of stimulated brillouin scattering in few-mode fiber was studied. Based on the mathematical model of Brillouin scattering spectrum and intermodal spectrum, the scattering characteristics of the few-mode fiber were analyzed. The Brillouin scattering gain spectrum and the threshold gain coefficients of few-mode fiber were analyzed respectively, as well as the influence of optical fiber parameters on the stimulated brillouin scattering spectrum threshold of few-mode fiber is numerically studied. The results showed that SI-10 step few-mode fiber can transmit five models, and each mode had its own transmission constant and effective refractive index. And each mode interaction leaded to the mode broadening and the gain reduction. At the same time, the Brillouin scattering spectrum gain of the few-mode fiber was 3.9×10-11 m·W-1. The threshold gain coefficient was affected by the distance of the optical fiber sensor, and the threshold gain coefficient was about 18.1 when the fiber was long enough to 22 km. The threshold value of Few-mode Fiber decreased with the increase of the length of the fiber, and the decreasing trend gradually slowed down to a constant about 20.5 dBm. The threshold for each mode of few-mode fiber also decreased with the increase of the length of the fiber, eventually tending to be constant. Moreover, the threshold of different modes increased with the increase of the mode order. The threshold value of few-mode fiber increased with the increase of the fiber attenuation coefficient and the core radius. With the increasing of fiber attenuation coefficient and core radius, the increasing trend of threshold increased slowly. The threshold value of the fiber with different attenuation coefficient tended to be constant at different length. The stimulated Brillouin scattering threshold value of fiber was larger and likely to be a constant with the increase of the attenuation coefficient of fiber.
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