针对传统的二次非球面折射型激光扩束器存在不易加工、装调困难、体积大、重量大，特别是难以获得高填充比阵列透镜等不足，提出了一种利用衍射型台阶化面型近似二次非球面的激光扩束器方案，结果表明：对于典型的束腰半径为2 mm的高斯光束，衍射型激光扩束器可实现2.8倍的理论扩束比。为了保持扩束过程中激光模式的稳定性，提出了不同区域给定不同台阶数的两类复合结构，解决了扩束过程中保真度和二元衍射元件加工特征尺寸无法同时满足的问题，改进后的系统保真度达95.82%，各区域最小光刻线宽均大于2 μm，能够满足现有光刻加工技术要求。对影响系统保真度主要误差的分析结果表明：离轴误差在-1~1 mm，目镜和物镜倾斜误差分别小于0.1 mm和1.68 mm时，系统保真度仍大于95%，方便装调。

For traditional conic refractive laser beam expanders being difficult of fabrication, hard of equipment, bulky and heavy weight, especially difficult to achieve lens array with high fill factor, an approach of laser beam expander by using stepped diffractive surface to approximate conic aspherical surface is proposed. It is shown that the incoming Gaussian beam with typical waist radius of 2 mm is enlarged to the designed expanding ratio of 2.8 times by the diffractive laser beam expander. By making the different sections of the surface with different steps to get two types of improved structure, which aims at keeping the stability of laser mode, the problem of fidelity and typical fabrication line-width of binary diffractive elements being not fulfilled at the same time is solved. The fidelity is raised to 95.82% with the minimum lithography line-width above 2 μm of each section, which meets the fabrication requirement of existing lithography technology. Analysis of the main errors affecting the system fidelity shows that the value is still above 95% when defocused error is -1~1 mm and decenter error is below 0.1 mm of eyepiece and 1.68 mm of objective lens, which make the system easy to install.