聚焦光斑光强与光纤出射端总光强的比值(光斑聚焦效率)直接影响基于液晶空间光调制器(SLM)的单光纤数字扫描采样的信噪比。采用顺序坐标上升优化算法控制多模光纤输入端光场分布，实现多模光纤出射端光斑聚焦，通过理论和实验证明了归一化目标函数值与光斑聚焦效率的和近似为常数。为了提高光斑聚焦效率，必须尽可能降低归一化目标函数值。分析了多模光纤出射端总光强对归一化目标函数收敛性的影响，通过仿真和实验证明随着多模光纤出射端总光强的增大，归一化目标函数收敛速度变慢，光斑聚焦效率变差。

The ratio between the intensity of focused spot and the total intensity of the fiber output, which is spot focusing efficiency, affects the sampling signal to noise ratio of single-fiber digital scanning based on liquid crystal spatial light modulator (SLM). Using sequence coordinate ascend algorithm to control the input field, the light emitted from the multimode fiber can be focused. The theoretical and experimental results show that the sum of normalized objective function and spot focusing efficiency is approximately constant. In order to improve spot focusing efficiency, the normalized objective function value must be minimized. The affect of the multimode fiber output light intensity on the convergence of the normalized objective function is analyzed. The numerical simulations and experiments show that the normalized objective function convergence rate changes slowly and spot focusing efficiency deteriorates with the output light intensity increasing.