一种利用布里渊谱宽确定光纤SBS阈值的新方法

针对传统的通过功率信息测量所得受激布里渊散射阈值偏高的问题，提出了一种利用布里渊散射谱宽确定光纤受激布里渊散射阈值的新方法。分析了本地外差检测的原理及布里渊散射谱宽与入纤光功率的关系；设计了基于本地外差检测的布里渊散射谱测量系统，在常温下对不同长度标准单模光纤的受激布里渊散射阈值进行了测量。实验结果表明:当光纤长度分别为48.8 km和9.5 km时，根据功率信息获得的受激布里渊散射阈值对应的布里渊散射谱宽均接近恒定值10 MHz，此时已发生严重的泵浦耗尽效应。利用布里渊散射谱表现出的低入纤功率时谱宽的线性下降特性和高入纤功率时谱宽的功率无关特性确定的两种光纤长度下的受激布里渊散射阈值分别为1.12 mW和3.8 mW，对应的布里渊散射谱宽分别为24.86 MHz和23 MHz，其值近似等于布里渊自然线宽。文中的研究结果对布里渊光时域反射系统最大入纤光功率的确定具有重要的参考价值。

New method for the determination of SBS threshold in an optical fiber by employing Brillouin spectrum width

To solve the problem that the obtained stimulated Brillouin scattering(SBS) threshold from the measurement of backscattered power and forward transmitted power was higher than its real value, a new method employing Brillouin scattering spectrum width for fiber SBS threshold determination was proposed. The principle of local optical heterodyne detection and the relationship of the Brillouin scattering spectrum width with the fiber input power were theoretically analyzed. Experimental setup for Brillouin scattering spectrum measurement based on local optical heterodyne detection was designed, and the SBS thresholds of two standard single-mode fibers with different length were measured at room temperature. The results show that the Brillouin scattering spectrum widths corresponding to the SBS thresholds of 48.8 km and 9.5 km long fibers obtained from the power information are all approximate to a constant value of 10 MHz, and the serious pump depletion effect has occurred. The SBS thresholds are 1.12 mW and 3.8 mW for 48.8 km and 9.5 km long fibers determined by using the characteristics of the linear decline of Brillouin scattering spectrum widths at low fiber input power and the power independence of spectrum widths at high input power presenting in the Brillouin scattering spectra. The corresponding Brillouin spectrum widths are 24.86 MHz and 23 MHz, respectively, which are approximately equal to the natural Brillouin linewidth. The results of this study can provide a theoretical basis for the determination of the maximum fiber input power in Brillouin optical time domain reflectometer system.