Appl Opt. 2023 Mar 1;62(7):B19-B24. doi: 10.1364/AO.476842.
Diffractive optical elements (DOEs) play an important role in modern optical applications such as spectral and imaging systems, but it is challenging to balance the diffraction efficiency with the working bandwidth. The core issue is controlling the broadband dispersion of all phase units to achieve achromatic 2-phase modulation in the broadband domain. Here, we demonstrate broadband DOEs utilizing multilayer subwavelength structures with different materials, making it possible to freely control the phase and phase dispersion of the structural units on a much larger scale than monolayer structures. The desired dispersion-control abilities arose due to a dispersion-cooperation mechanism and vertical mode-coupling effects between the top and bottom layers. An infrared design comprised of two vertically concatenated and Si nanoantennas separated by a dielectric spacer layer was demonstrated. It showed an average efficiency of over 70% in the three-octave bandwidth. This work shows enormous value for broadband optical systems with DOEs such as spectral imaging and augmented reality.
衍射光学元件（DOE）在现代光学应用中起着重要作用，例如光谱和成像系统，但在平衡衍射效率和工作带宽方面存在挑战。核心问题是控制所有相位单元的宽带色散，以在宽带域中实现消色差的 2 相调制。在这里，我们展示了利用具有不同材料的多层亚波长结构的宽带 DOE，使得在比单层结构大得多的范围内自由控制结构单元的相位和相位色散成为可能。由于色散协同机制和顶层与底层之间的垂直模式耦合效应，出现了所需的色散控制能力。演示了一个由两个垂直串联的 和 Si 纳米天线组成的红外设计，它们之间由一个 介电间隔层隔开。它在三个倍频程带宽内显示出超过 70%的平均效率。这项工作对于具有 DOE 的宽带光学系统（例如光谱成像和增强现实）具有巨大的价值。
