熔融侧面泵浦耦合器光纤夹角对耦合效率的影响

泵浦耦合器是高功率光纤激光器的关键无源光器件，其制作工艺是采用泵浦光纤和主光纤侧面熔融的方法，该方法可以保持主光纤中信号光的低插入损耗，但泵浦光纤和主光纤之间的夹角对耦合效率影响较大。为解决这一问题，根据熔融侧面泵浦耦合器的结构特点，建立了物理模型，推导出各光纤中光功率与夹角关系的方程组，进行了数值仿真和实验论证，结果是随着泵浦光纤和主光纤之间夹角的减小，耦合效率会逐渐增大，但存在临界值，NA值小的泵浦光纤耦合效率高且临界角大，NA为0.22的泵浦光纤，夹角小于9.7时耦合效率最大值为96.9%，NA为0.15的泵浦光纤，夹角小于11.5时耦合效率最大值为97.8%。

Influence of fused side-pump coupler fiber angle on coupling efficiency

Pump coupler is the key passive optical device of the high-power fiber laser. Its producing process is the side-fusing of the pump fiber and the main fiber. This producing process can keep the insertion loss of the main fiber low, but the angle between the pump fiber and the main fiber has a great influence on the coupling efficiency. In order to solve this problem, the theoretical model was established according to the structural characteristics of the fused side pump coupler. The equations of the power and the fiber angle were derived. The simulation results were obtained and were demonstrated by the experiments. The conclusions are as follows: the pump coupling efficiency gradually increases with the decrease of the fiber angle between the pump fiber and the main fiber, but the critical fiber angle exists. When the numerical aperture (NA) of the pump fiber is smaller, the couple efficiency and the critical angle are larger. The critical fiber angle is 9.7 and the maximum coupling efficiency is 96.9% when the pump fiber NA is 0.22. The critical fiber angle is 11.5 and the maximum coupling efficiency is 97.8% when the pump fiber NA is 0.15. The conclusions are instructive for the designs and the productions of the high power fiber coupler.