Cao Hongchao, Wu Jun, Yu Junjie, Ma Jianyong
Appl Opt. 2018 Feb 1;57(4):900-904. doi: 10.1364/AO.57.000900.
A high-efficiency polarization-independent wideband multilayer dielectric reflective bullet-alike cross-section (combination of trapezoidal-rectangular grating profile) fused-silica beam combining grating (BCG) used in the -1st order for spectral beam combining (SBC) is designed and fabricated. Exact grating profile parameters are optimized by using the rigorous coupled-wave analysis and simulated annealing algorithm. As a comparison, traditional pure trapezoidal and pure rectangular gratings are also designed. Numerical results show that such a bullet-alike cross-section BCG exhibits wide bandwidth with the lowest maximum electric field enhancement in the grating material, which is greatly beneficial for the promotion of the power scaling level of the grating-based SBC system. A two-step dry-etching procedure is developed to fabricate such a grating. The averaged diffraction efficiency of greater than 91% was experimentally demonstrated.
设计并制作了一种用于一阶光谱合束（SBC）的高效偏振无关宽带多层介质反射子弹形横截面（梯形 - 矩形光栅轮廓组合）熔融石英光束合束光栅（BCG）。通过严格耦合波分析和模拟退火算法优化精确的光栅轮廓参数。作为对比，还设计了传统的纯梯形和纯矩形光栅。数值结果表明，这种子弹形横截面BCG具有宽带宽，且光栅材料中的最大电场增强最低，这对于提高基于光栅的SBC系统的功率缩放水平非常有利。开发了一种两步干法蚀刻工艺来制作这种光栅。实验证明平均衍射效率大于91%。
