利用光栅外腔的方法对半导体激光阵列(LDA)进行光谱合束时常采用平凸或双凸柱透镜作为变换透镜，然而它会导致外腔的反馈效率低下，经研究发现LDA轴上发光单元的反馈效率为80.5%，对于边缘发光单元甚至降到了49.7%。针对该问题提出了采用双分离柱透镜作为变换透镜，从而可以提高外腔的反馈效率。将传统LDA光谱合束光路展开，并利用Zemax画出它的等效光路，以此来求出平凸变换透镜LDA每个发光单元的反馈效率；根据像差理论分析了平凸变换透镜的成像特点，发现平凸变换透镜的球差和慧差较大，需要对其进行矫正；根据初级像差理论，利用PW法设计了双分离变换透镜，并利用Zemax进行了优化。结果发现，优化后双分离变换透镜可以使10 mm宽LDA发光单元的反馈效率达到94.2%以上。研究结果表明使用双分离变换透镜法可提高光谱合束效率。

Plane-convex lens or bi-convex lens are commonly used as transform lens while the beam of laser diode array (LDA) is spectrally combined by grating-external cavity method. However, the feedback efficiency of external cavity is rather low for each emitter. For example, feedback efficiency for on-axis emitter is just 80.5% and even decreases to 49.7% for edge emitter. In order to solve the problem, a method that discretely doublet lenses are applied as transform lenses to enhance the feedback efficiency. An equivalent optical setup of traditional spectrally beam combination for LDA is drawn and studied by Zemax optical software. At the same time, feedback efficiency of each emitter will be computed. The imaging characteristic of plane-convex lens is learned by aberration theory and the fact that spherical aberration and coma of plane-convex lens are relative large, which will decrease the feedback efficiency. Funthermore according to primary aberration theory, a discretely doublet is designed by PW method and the doublet is also optimized by Zemax. The feedback efficiency of each LDA emitter whose width is 10 mm is more than 94.2% by using optimized doublet, which is dramatically larger than that of plane-convex lens.The results show that the method is helpful for increasing the coupling efficiency of LDA.