We report the design of ultra-broadband, highly reflective all-dielectric reflectors covering the entire visible regime based on two cascaded subwavelength high-index-contrast gratings (HCGs). We find that the spectral distance between the two gratings’ reflective bandwidths, which should be appropriately designed in order to extend the overall bandwidth for high reflectivity, is analogous to the well-known Rayleigh, Abbe and Sparrow criteria for resolution limits. Results illustrated with TM-polarized normal incidence show that high reflectivity above 98.5% covering 400–800 nm can be achieved for two cascaded HCGs with an appropriate spectral distance. The effects of key structural parameters on the bandwidth extension are discussed with physical insights. We expect this work will advance the engineering and applications of HCGs as ultra-thin, ultra-broadband and all-dielectric reflectors.

中文翻译：

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基于级联高折射率对比度光栅的超宽带反射器覆盖整个可见区域

我们报告了基于两个级联亚波长高折射率对比度光栅 (HCG) 的超宽带、高反射全介电反射器的设计，该反射器覆盖整个可见光区域。我们发现两个光栅反射带宽之间的光谱距离，应该适当设计以扩展高反射率的整体带宽，类似于众所周知的瑞利、阿贝和斯帕罗分辨率极限标准。用 TM 偏振法向入射说明的结果表明，对于具有适当光谱距离的两个级联 HCG，可以实现 98.5% 以上的高反射率，覆盖 400-800 nm。通过物理见解讨论了关键结构参数对带宽扩展的影响。我们预计这项工作将推动 HCG 的工程和应用成为超薄、