Zhang Zifeng, Dong Wenhui, Fang Zhibo, Chen Rongquan, Liu Jinbiao, Deng Shijie, Chen Ming
Appl Opt. 2025 Aug 1;64(22):6235-6241. doi: 10.1364/AO.562720.
The majority of current beam conversion techniques rely on bulky lens systems for operation. In this paper, we propose a terahertz metasurface that can effectively convert a Gaussian beam into a flat-top beam and convert linearly polarized terahertz waves into their orthogonal counterparts. An improved Gerchberg-Saxton (GS) algorithm was employed in this study to precisely calculate the required phase distribution for the beam shaping device. By adjusting the opening angle of the metal split ring in the middle layer of the metasurface, a full 2 phase coverage was achieved, ensuring precise control over the phase distribution. Simulation results indicate that within the range of 0.4-1.1 THz, the cross-polarization conversion efficiency is greater than 70%, with a relative bandwidth of 93.3%. The root-mean-square error (RMS) can reach 0.143 at 0.75 THz, the non-uniformity of the rectangular spot in the target region is 0.126, and the energy ratio of the rectangular spot to the whole focal plane is 78.03%, demonstrating the achievement of a high-quality flat-top beam. The metasurface beam shaping device we proposed, with its wide operating bandwidth, low transmission loss, high shaping efficiency, and compact structural design, offers an innovative solution for beam shaping techniques in the terahertz frequency band.
当前大多数光束转换技术的运行都依赖于庞大的透镜系统。在本文中，我们提出了一种太赫兹超表面，它可以有效地将高斯光束转换为平顶光束，并将线偏振太赫兹波转换为其正交偏振波。本研究采用了一种改进的格尔奇伯格 - 萨克斯顿（GS）算法来精确计算光束整形器件所需的相位分布。通过调整超表面中间层金属裂环的开口角度，实现了完整的2π相位覆盖，确保了对相位分布的精确控制。仿真结果表明，在0.4 - 1.1太赫兹范围内，交叉极化转换效率大于70%，相对带宽为93.3%。在0.75太赫兹时，均方根误差（RMS）可达0.143，目标区域矩形光斑的不均匀性为0.126，矩形光斑与整个焦平面的能量比为78.03%，表明实现了高质量的平顶光束。我们提出的超表面光束整形器件具有宽工作带宽、低传输损耗、高整形效率和紧凑的结构设计，为太赫兹频段的光束整形技术提供了一种创新解决方案。
