基于耦合调谐相同纳米柱的不规则连续结构的“无超原子”架构实现高效消色差超表面
'Meta-atomless' architecture based on an irregular continuous fabric of coupling-tuned identical nanopillars enables highly efficient and achromatic metasurfaces
AI总结：
本文提出由相同介质纳米柱经连续耦合调谐构成的无超原子不规则晶格，实现400–700 nm全波段、聚焦效率超85%的偏振无关消色差超透镜。
摘要：
超表面是由离散超原子组成的亚波长厚度结构，可提供离散级别的相位累积，共同近似实现所设计的光学功能。利用几何相位和偏振转换结构的超原子，已经在包括超透镜在内的光学元件中产生了令人鼓舞的实现。然而，迄今为止，这种方法一个悬而未决的根本问题是所得元件器件效率较低，这是为防止超原子之间相互耦合而采用大晶格常数所带来的不良副作用。尽管利用近场耦合调谐电磁共振已被用于构建高效的窄带设计，但此类结构无法在宽光谱范围内提供高效率。在此，我们提出并证明，由相同介质纳米柱波导构成、具有连续调谐互耦距离的紧密堆积结构，可以成为出色且完整的消色差超表面元件。该架构使散射体能够以极高效率与入射波相互作用。作为概念验证演示，我们展示了一种消色差柱面超透镜，它以“无超原子”的方式，由单一几何形状、强耦合的介质纳米柱作为连续设置的相位元件构建而成，可在整个400–700 nm波段工作。该超透镜在整个光谱范围内实现超过85%的聚焦效率。为克服偏振敏感性，我们采用六边形堆叠的纳米柱建立偏振无关散射体库。最终，获得了一种具有偏振无关工作和消色差聚焦能力的圆形超透镜。通过将相同纳米柱耦合进经精细调谐构建的不规则晶格中，这代表了消色差超表面架构制造的范式转变。
英文摘要：
Metasurfaces are subwavelength-thick constructs, consisting of discrete meta-atoms, providing discretized levels of phase accumulation that collectively approximate a designed optical functionality. The meta-atoms utilizing geometric phase with polarization-converting structures produced encouraging implementations of optical components including metalenses. However, to date, a pending and fundamental problem of this approach has been the low device efficiency that such resulting components suffer, an unwanted side effect of large lattice constants used for preventing inter-coupling of their meta-atoms. Although the use of near-field coupling for tuning electromagnetic resonances found its use in constructing efficient narrow-band designs, such structures fell short of providing high efficiency over a broad spectrum. Here, we propose and show that tightly packed fabric of identical dielectric nanopillar waveguides with continuously-tuned inter-coupling distances make excellent and complete achromatic metasurface elements. This architecture enables the scatterers to interact with the incoming wave extremely efficiently. As a proof-of-concept demonstration, we showed an achromatic cylindrical metalens, constructed from strongly coupled dielectric nanopillars of a single geometry as continuously-set phase elements in a 'meta-atomless' fashion, working in the entirety of 400-700 nm band. This metalens achieves over 85 percent focusing efficiency across this whole spectral range. To combat polarization sensitivity, we used hexagonally stacked nanopillars to build up a polarization-independent scatterer library. Finally, a circular metalens with polarization-independent operation and achromatic focusing was obtained. This is a paradigm shift in making an achromatic metasurface architecture by wovening identical nanopillars coupled into an irregular lattice constructed via careful tuning.
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