Optical dielectric metasurfaces composed of arrayed nanostructures are expected to enable arbitrary spatial control of incident wavefronts with subwavelength spatial resolution. For phase modulation, one often resorts to two physical effects to implement a 2π-phase excursion. The first effect relies on guidance by tall nanoscale pillars and the second one exploits resonant confinement by nanoresonators with two degenerate Mie resonances. The first approach requires high aspect ratios, while the second one, known as Huygens’ metasurfaces, is much flatter, and thus easier to manufacture. The two approaches are compared, more focusing on conceptual rather than technological issues, and fundamental limitations with the latter are identified. The origin of the limitations based on general arguments are explained, such as reciprocity, multimode/monomode operation, and symmetry breaking.

中文翻译：

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惠更斯超表面对光束整形的基本限制

由阵列纳米结构组成的光学介电超表面有望实现对具有亚波长空间分辨率的入射波前的任意空间控制。对于相位调制，通常采用两种物理效应来实现 2π 相位偏移。第一个效应依赖于高纳米柱的引导，第二个效应利用具有两个简并 Mie 共振的纳米共振器的共振限制。第一种方法需要高纵横比，而第二种方法，称为惠更斯超表面，更平坦，因此更容易制造。比较这两种方法，更侧重于概念而不是技术问题，并确定了后者的基本局限性。解释了基于一般论点的限制的起源，例如互惠，