Asymmetric spin–orbit interaction (ASOI) breaks the limitations in conjugate symmetry of traditional geometric phase metasurfaces, bringing new opportunities for various applications such as spin-decoupled holography, imaging, and complex light field manipulation. Since anisotropy is a requirement for spin–orbit interactions, existing ASOI mainly relies on meta-atom with C1 and C2 symmetries, which usually suffer from an efficiency decrease caused by the propagation phase control through the structural size. Here, we demonstrate for the first time that ASOI can be realized in meta-atoms with rotational symmetry ≥3 by combining the generalized geometric phase with the propagation phase. Utilizing an all-metallic configuration, the average diffraction efficiency of the spin-decoupled beam deflector based on C3 meta-atoms reaches ∼84 % in the wavelength range of 9.3–10.6 μm, which is much higher than that of the commonly used C2 meta-atoms with the same period and height. This is because the anisotropy of the C3 metasurface originates from the lattice coupling effect, which is relatively insensitive to the propagation phase control through the meta-atom size. A spin-decoupled beam deflector and hologram meta-device were experimentally demonstrated and performed well over a broadband wavelength range. This work opens a new route for ASOI, which is significant for realizing high-efficiency and broadband spin-decoupled meta-devices.

中文翻译：

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基于高阶复合相位调制的高效宽带非对称自旋-轨道相互作用


不对称自旋-轨道相互作用 （ASOI） 打破了传统几何相位超表面共轭对称性的限制，为自旋解耦全息术、成像和复杂光场操纵等各种应用带来了新的机会。由于各向异性是自旋-轨道相互作用的要求，现有的 ASOI 主要依赖于具有 C1 和 C2 对称性的超原子，这通常是由于通过结构尺寸进行传播相位控制而导致的效率降低。在这里，我们首次证明，通过将广义几何相与传播相相结合，可以在具有旋转对称性 ≥3 的元原子中实现 ASOI。利用全金属构型，基于 C3 超原子的自旋解耦光束偏转器在 9.3–10.6 μm 波长范围内的平均衍射效率达到 ∼84 %，远高于相同周期和高度的常用 C2 超原子。这是因为 C3 超表面的各向异性源于晶格耦合效应，该效应对通过超原子大小的传播相位控制相对不敏感。实验演示了自旋解耦光束偏转器和全息图超设备，并在宽带波长范围内表现良好。这项工作为 ASOI 开辟了一条新的路线，对于实现高效、宽带自旋解耦的元器件具有重要意义。