受激布里渊散射会影响少模光纤传输系统中的信噪比、 传输距离与传输容量, 是影响传输系统入纤功率提高的重要因素。 对阶跃型少模光纤的受激布里渊散射谱的阈值进行了研究, 运用了布里渊散射谱、 模式联运谱的数学模型对少模光纤散射特性进行了分析, 探讨了少模光纤布里渊散射增益谱、 阈值增益系数, 以及光纤各参量对少模光纤阈值的影响。 分析结果表明: SI-10阶跃型少模光纤中存在五种不同的传播模式, 不同模式有各自的传输常数以及有效折射率, 各模式相互作用导致模式展宽、 增益降低, 且布里渊散射谱峰值增益系数为3.9×10-11 m·W-1。 阈值增益系数受到光纤传感距离的影响, 在相对较短距离传输中阈值急速下降, 且其趋势随长度增加渐趋平缓, 当光纤长度达到22 km时阈值增益系数趋于常数18.1。 少模光纤的阈值因光纤长度的递增而递减, 且递减趋势渐缓趋于常数20.5 dBm; 少模光纤不同模式受激布里渊散射的阈值也因光纤长度的递增而递减最终趋于常数, 且不同模式的阈值因模式阶数的递增而递增; 少模光纤的阈值随着光纤衰减系数和纤芯半径的递增而递增, 且增加趋势缓慢增大。 不同衰减系数的光纤其阈值在不同长度趋于常数, 衰减系数越大受激布里渊散射阈值越大越容易趋于一常数。

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.