长焦深与偏振可控的太赫兹超构表面透镜

为了提高太赫兹超透镜成像的纵向容忍度，设计了一种纯几何相位全介质长焦深超构表面透镜器件。采用纯几何相位自旋解耦的设计方法，并结合时域有限差分（FDTD）方法，对设计的超构表面透镜进行了数值仿真。研究结果表明，所设计的太赫兹超构表面透镜具有偏振可控和长焦深的特性，在沿着传播方向上焦深达到了8 mm，而普通超构表面透镜只有4.5 mm焦深。设计并数值仿真验证了两个太赫兹长焦深聚焦复用的超构表面透镜，并使得横向复用的两个长焦深焦点具有相互正交的偏振态。相关研究有望应用于层析成像和信息加密等方面。

Terahertz metalens with extended focal depth and polarization controllable

In this letter, a pure geometric phase based all-dielectric metalens is designed and aimed to enhance the tolerance of imaging in the longitudinal direction. Numerical simulation for the designed metasurface is carried out using the pure geometric phase spin decoupling design method combined with the finite difference time domain (FDTD) method. The calculated results show that designed metasurface enables the characteristics of controllable polarization and extended focal length, achieving a focal depth of 8 mm along the propagation direction, compared with 4.5 mm for a conventional metalens. Furthermore, we also design and numerically validate a terahertz metalens that can generate two focal points with extended focal length, and the polarization states of the two extended focal points are orthogonal to each other, demonstrating the multiplexing functionality of the designed metalens. The unique and effective approach may open a new avenue for tomography and information encryption.