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中国物理学会期刊

空间与时空涡旋光独立调控的太赫兹超表面

CSTR: 32037.14.aps.75.20251078

Terahertz metasurface independently controlled by spatial vortex and spatiotemporal optical vortex

CSTR: 32037.14.aps.75.20251078
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  • 光学空间涡旋(OV)和时空涡旋光(STOV)是携带不同形式轨道角动量(OAM)的特殊光束. OV具有纵向OAM, 而STOV则展示了横向OAM, 并且与时间协同调控. 由于它们依赖于不同的物理机制, 因此传统的光学平台难以同时实现这两种涡旋光的独立调控. 本文提出一种基于二氧化钒(VO2)相变材料的太赫兹(THz) 超表面器件, 能够在同一超表面平台中实现OV和STOV的动态切换. 当VO2处于绝缘态时, 使用圆偏振波反射生成拓扑黑暗点和拓扑暗线, 激发STOV; 当VO2转变为金属态时, 通过合理排列超表面编码元素结合Pancharatnam-Berry (PB)相位, 生成多通道和多功能的OV. 随后, 通过对结构参数的影响进行详细分析, 发现两种涡旋光在不同条件下具有较强的拓扑稳定性, 可以通过温度调控进行可逆切换. 本文为实现太赫兹频段的多功能涡旋光生成提供了新的思路, 并为涡旋光在太赫兹通信和光信息处理中的应用拓展了新途径.

     

    The optical vortex (OV) and spatiotemporal optical vortex (STOV) are special beams carrying different forms of orbital angular momentum (OAM). The OV has longitudinal OAM, whereas the STOV has transverse OAM and is coordinated with time to achieve control. Due to their reliance on different physical mechanisms, traditional optical platforms are difficult to independently control these two vortex beams on the same platform. This limitation, to some extent, hinders the understanding of the unified physical mechanism underlying spatial and spatiotemporal orbital angular momentum and also slows the development of multi-dimensional light field manipulation technology. This paper proposes a terahertz (THz) metasurface device based on vanadium dioxide (VO2) phase change material. The device integrates in-plane asymmetry, provided by triangular pores and required to excite STOV, with anisotropic phase units, realized by VO2 broken rings and needed to generate OV, into one metasurface platform, This integration enables dynamic switching of OV and STOV on the same metasurface platform. The uniqueness of its design and the key to achieving functional integration lie in the selection of Si and VO2 materials for the upper layer of the metasurface. When VO2 is in the insulating state, its dielectric constant in the THz band is similar to that of Si and its conductivity is very low. Different rotation angles of the units can still be considered as a periodic structure with the same symmetry on a macroscopic scale. The structure uses circularly polarized waves for reflection, generating a topological dark point at approximately 1.376 THz and a topological dark line between 1.3765 THz and 1.378 THz, which excites STOV. When VO2 transforms into a metallic state, its high conductivity makes the broken ring a dominant scatterer. By reasonably arranging the encoded units of the metasurface and combining the Pancharatnam-Berry (PB) phase, not only can OV with different topological charges be generated, but also multi-channel and multi-functional OV can be created through convolution theorem and shared aperture theorem. Subsequently, the influence of structural parameters is analyzed in detail. By changing the shape of the triangular pores and the thickness of the broken ring, the two vortex beams are adjusted, and it is found that they have strong topological stability under different conditions and can be reversibly switched through temperature control. This research provides a new idea for realizing multifunctional vortex light generation in the terahertz frequency band and opens up new avenues for the application of vortex light in terahertz communication and optical information processing.

     

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