分析了激光束在光纤中的非线性传输损耗,理论上证明了受激布里渊散射(SBS)是光纤传输能力的主要限制因素; 实验上在532 nm波段对长度为5 m,纤芯半径为1.75 μm,数值孔径(NA)为0.11的单模光纤的传输能力进行了测定,结果与理论一致。采用模场耦合理论,推导出多模光纤与单模光纤的直接耦合效率表达式,计算得到耦合效率与所选用的多模光纤和单模光纤的纤芯芯径之间的模拟关系。激光器输出波长为532 nm;多模光纤的数值孔径为0.11,纤芯半径为12.5 μm; 单模光纤的数值孔径为0.11,纤芯半径为1.75 μm,实验结果与理论基本吻合。根据理论和实验结果,设计出多模光纤与单模光纤混合传输方案,在柔性传输较高激光功率的同时可以得到高光束质量。

The nonlinear scattering loss in the single-mode fiber is analyzed. It is proved theoretically and experimentally that the maximal transmitting power in an optical fiber is limited by the stimulated Brillouin scattering (SBS). Based on mode field coupling theory, a model to calculate the butt-joint coupling efficiency between a multi-mode fiber and a single-mode fiber is presented. The dependence of the coupling efficiency between the multi- and single-mode fibers on the core radius of the multi-mode fiber is investigated. A experiment is conducted with 532 nm laser, multi-mode fiber (NA=0.11, a=12.5 μm) and single-mode fiber (NA=0.11, a=1.75 μm) to measure the butt joint coupling efficiency of multi-mode fiber to single-mode fiber. Good agreement is obtained between the experimental results and the theoretical predictions. A combined multi- and single-mode fiber relay system is proposed to transport laser beams with high power and good beam quality.