Polarization-multiplexing terahertz metasurface zone plate for implementing arbitrary spatial coordinate focusing

The design of metasurface structures based on the generalized Snell's law enables diverse functionalities for regulating light fields through abrupt phase changes. However, addressing complex regulatory demands, such as polarization multiplexing, requires identifying multiple meta-atom structures that meet specific transmission and phase criteria. This process is often time-consuming and restrictive. Simplifying the design process for metasurface structures while preserving their functionality is, therefore, a key research area. In this paper, we demonstrate independent phase modulation of orthogonal linear polarization components by a simple structure integrating a Fresnel zone plate-a two-phase device-with a metasurface. We design and experimentally validate three metasurfaces: Sample M1 realizes concentric focusing at different focal lengths for x- and y-linearly polarized terahertz waves. Sample M2 enables off-axis dual-focus with orthogonal linear polarization multiplexing. Sample M3 employs a checkerboard distribution to achieve multi-focal focusing within a single channel. The simulation results are consistent with the experimental findings, confirming the feasibility of the proposed scheme and implementing arbitrary spatial coordinate focusing with dual channels. This work significantly simplifies the terahertz metasurface design process, reducing both complexity and time investment. It has the potential to promote the development of wavefront control devices towards miniaturization and multifunctionality.