Geometric Phase-Based Metasurfaces for Focusing and Vortex Longitudinal Polarization Evolution

超构表面在纵向方向上的调控为控制偏振状态引入了新的维度，为了实现偏振态随传播方向的演化，文章提出了一种基于几何相位调制的超构表面，可以同步实现纵向聚焦、涡旋及偏振态的演化。该设计基于复振幅的叠加方法来构建结构，并通过时域有限差分方法(FDTD)进行了数值仿真验证。仿真的结果表明，所设计的超构表面在纵向上从焦点演化到涡旋的过程中，可以同时实现正交线偏振态的演化；进一步设计了双涡旋的纵向偏振演化，同时也实现了涡旋拓扑荷的演化。这种沿传播方向动态调控偏振态的方法，为开发光控可切换器件及推动光–物质相互作用的研究开辟了新的应用前景。Metasurfaces with longitudinal modulation capabilities introduce a new dimension for polarization state control. To achieve polarization evolution along the propagation direction, this article proposes a geometric-phase-modulated metasurface that simultaneously enables longitudinal focusing, vortex generation, and polarization evolution. The design employs a complex-amplitude superposition method for structural configuration, validated through finite-difference time-domain (FDTD) numerical simulations. Results demonstrate that the metasurface facilitates orthogonal linear polarization evolution during the longitudinal transition from focused spots to vortex beams. Furthermore, we implement dual-vortex configurations exhibiting longitudinal polarization evolution while enabling dynamic modulation of vortex topological charges. This approach to dynamically manipulate polarization states along the propagation axis opens new prospects for developing optically controlled switchable devices and advancing light-matter interactions.