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


非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、成像和复杂光场操纵等各种应用带来了新的机遇。由于各向异性是自旋轨道相互作用的必要条件，现有的ASOI主要依赖于具有C1和C2对称性的元原子，通常会因通过结构尺寸控制传播相位而导致效率下降。在这里，我们首次证明，通过将广义几何相位与传播相位相结合，可以在旋转对称性≥3的元原子中实现ASOI。采用全金属结构，基于C3元原子的自旋解耦光束偏转器在9.3~10.6μm波长范围内的平均衍射效率达到~84%，远高于常用的C2元原子-具有相同周期和高度的原子。这是因为C3超表面的各向异性源于晶格耦合效应，其对超原子尺寸的传播相位控制相对不敏感。自旋解耦光束偏转器和全息图元器件经过实验验证，并在宽带波长范围内表现良好。这项工作为ASOI开辟了一条新路线，对于实现高效、宽带自旋解耦元器件具有重要意义。