Controlling the dispersion characteristic of metasurfaces (or metalenses) along a broad bandwidth is of great importance to develop high-performance broadband metadevices. Different from traditional lenses that rely on the material refractive index along the light trajectory, metasurfaces or metalenses provide a new regime of dispersion control via a sub-wavelength metastructure, which is known as negative chromatic dispersion. However, broadband metalenses design with high-performance focusing especially with a reduced device dimension is a significant challenge in society. Here, we design, fabricate, and demonstrate a broadband high-performance diffractive-type plasmonic metalens based on a circular split-ring resonator metasurface with a relative working bandwidth of 28.6%. The metalens thickness is only 0.09λ0$0.09{\lambda }_0$ (λ0${\lambda }_0$ is at the central wavelength), which is much thinner than previous broadband all-dielectric metalenses. The full-wave simulation results show that both high transmissive efficiency above 80% (the maximum is even above 90%) and high average focusing efficiency above 45% (the maximum is 56%) are achieved within the entire working bandwidth of 9–12 GHz. Moreover, an average high numerical aperture of 0.7 (NA=0.7$\mathrm{NA}=0.7$) of high-efficiency microwave metalens is obtained in the simulations. The broadband high-performance metalens is also fabricated and experimental measurements verify its much higher average focusing efficiency of 55% (the maximum is above 65% within the broad bandwidth) and a moderate high NA of 0.6. The proposed plasmonic metalens can facilitate the development of wavelength-dependent broadband diffractive devices and is also meaningful to further studies on arbitrary dispersion control in diffractive optics based on plasmonic metasurfaces.

中文翻译：

---

具有负色散特性的宽带高效等离子体超透镜

在宽带宽上控制超表面（或超透镜）的色散特性对于开发高性能宽带超器件非常重要。与依赖光轨迹上的材料折射率的传统透镜不同，超表面或超透镜通过亚波长超结构提供了一种新的色散控制机制，这被称为负色散。然而，具有高性能聚焦（尤其是减小设备尺寸）的宽带超镜头设计是社会面临的重大挑战。在这里，我们设计、制造并演示了一种基于圆形裂环谐振器超表面的宽带高性能衍射型等离子体超透镜，相对工作带宽为 28.6%。超透镜厚度仅为0.09 λ 0$0.09{\lambda }_0$（λ 0${\lambda }_0$位于中心波长），比之前的宽带全电介质超透镜要薄得多。全波仿真结果表明，在9~12整个工作带宽内，实现了80%以上（最高可达90%以上）的高传输效率和45%以上（最高56%）的平均聚焦效率。兆赫。此外，在模拟中获得了平均高数值孔径0.7（NA = 0.7$\mathrm{NA}=0.7$）的高效微波超透镜。还制造了宽带高性能超透镜，实验测量验证了其更高的平均聚焦效率（55%）（在宽带宽内最大值高于 65%）和 0.6 的中等高 NA。所提出的等离子体超透镜可以促进波长相关的宽带衍射器件的发展，并且对于进一步研究基于等离子体超表面的衍射光学中的任意色散控制也有意义。