提出了一种基于3-dB光纤耦合器的级联式激光相干合成新方法。理论分析了基于3-dB耦合器的两单元相干合成模块的工作原理, 仿真分析了光强失配及相位失配对相干合成效率的影响；搭建了基于随机并行梯度下降优化算法的相位控制平台, 实验验证了两单元模块的可行性。实验结果表明, 闭环后归一化合成光强的平均值从0.50提升至0.92, 均方误差从9.27%下降至0.062%, 而实现两单元模块输入端相位锁定和光强匹配是获取高效、高稳定相干合成效果的关键。最后, 基于两单元模块提出了可拓展的级联式激光相干合成结构, 并以八单元为例进行了相干合成的仿真。

A new method of cascaded coherent combining of fiber lasers based on 3-dB fiber couplers is proposed. The theoretical model of two-unit coherent combining module based on 3-dB fiber coupler is analyzed, and the effects of light intensity and phase mismatch on coherent combining efficiency are studied. The phase-control setup using stochastic-parallel-gradient-descent algorithm is established to investigate the feasibility of the two-unit coherent combining module. As the experimental results show, the average value of the normalized combined intensity increases from 0.50 in open loop to 0.92 in closed loop, the mean square error decreases from 9.27% to 0.062%, and the phase locking and intensity matching are crucial to achieve high and stable effect of the coherent combining. Additionally, an extended cascaded structure of coherent combining of fiber lasers based on two-unit coherent combining module is presented and the simulation of eight-unit structure is performed.