介绍了随机并行梯度下降(SPGD)算法用于相干合成的基本理论, 利用数值模拟的方法对实际相干合成实验中涉及到的算法评价函数、扰动电压分布等参数进行优化选取, 确定了实验中应选择的最佳评价函数、扰动电压分布和扰动方式。利用数字信号处理器(DSP)执行SPGD算法, 实时控制各路光束的相位, 实现了三路瓦量级保偏光纤放大器输出光束的相干合成。实验结果表明, SPGD算法能够有效控制各路光纤激光的相位, 系统闭环将合成光束目标圆孔内的能量提高了2.62倍, 合成效率达到了理想情形的87%, 远场光斑对比度为85%。

The fundamental theory for coherent beam combining using SPGD algorithm is introduced. The evaluation function, perturbation mode and the distribution character of perturbation voltages are optimized by using numerical simulation. Coherent beam combining of three W-level polarize-maintained fiber amplifiers is accomplished by implementing SPGD algorithm on a digital signal processor. The experimental results demonstrate that the optical phase for each beam channel can be effectively controlled by the SPGD algorithm, the energy encircled in the target pinhole is increased by a factor of 2.62, and the combining efficiency is as high as 87% compared with its ideal counterpart when the system is in the close-loop.