基于几何相位的高透射型太赫兹超表面设计

Design of high transmission⁃type terahertz metasurface based on geometric phase

文中提出一种基于几何相位的透射型超表面,通过对超表面单元结构的设计和排布实现了对入射圆极化波的波前任意操控和太赫兹涡旋波的产生。该超表面单元由典型的“三明治”型结构,即金属-介质-金属结构组成,顶层和底层金属图案均是由“C”型和矩形组成。利用几何相位原理,在工作频点下通过旋转金属结构对其相位进行调控,同时交叉极化透射幅度较高(>0.9)。通过对单元结构进行旋转编码,可以形成用于产生异常偏折现象、不同拓扑荷数涡旋光束的编码超表面。仿真结果表明,在0.63 THz处,设计的编码超表面能够对电磁波进行良好的调控,产生折射角为±50.1°和30°的异常折射现象,拓扑荷数l=±1两种模态的涡旋波束,在激光雷达和太赫兹大容量通信等领域具有潜在的应用价值。

A transmission⁃type metasurface based on geometric phase is proposed.By designing and arranging the unit structures of the metasurface,the wavefront of the incident circularly polarized waves is manipulated arbitrarily and the terahertz vortex waves are generated.The metasurface unit consists of a typical″sandwich″structure,that is,a metal⁃dielectric⁃metal structure,the top and bottom metal patterns of which are composed of C⁃shaped and rectangular elements.By utilizing the principles of geometric phase,the phase of the transmitted light can be controlled by rotating the metal structure at the operating frequency,while maintaining a high cross⁃polarization transmission amplitude(>0.9).By rotating code of the unit structures,an encoded metasurface is formed capable of generating anomalous deflection phenomena and vortex beams with different topological charges.Simulation results demonstrate that at 0.63 THz,the designed encoded metasurface exhibits effective control over electromagnetic waves,producing anomalous refraction with deflection angles of±50.1°and 30°,as well as vortex beams with topological charges of l=±1.This research holds potential applications in areas such as laser radar and terahertz high⁃capacity communication.