A key goal of metalens research is to achieve wavefront shaping of light using optical elements with thicknesses on the order of the wavelength. Such miniaturization is expected to lead to compact, nanoscale optical devices with applications in cameras, lighting, displays and wearable optics. However, retaining functionality while reducing device size has proven particularly challenging. For example, so far there has been no demonstration of broadband achromatic metalenses covering the entire visible spectrum. Here, we show that by judicious design of nanofins on a surface, it is possible to simultaneously control the phase, group delay and group delay dispersion of light, thereby achieving a transmissive achromatic metalens with large bandwidth. We demonstrate diffraction-limited achromatic focusing and achromatic imaging from 470 to 670 nm. Our metalens comprises only a single layer of nanostructures whose thickness is on the order of the wavelength, and does not involve spatial multiplexing or cascading. While this initial design (numerical aperture of 0.2) has an efficiency of about 20% at 500 nm, we discuss ways in which our approach may be further optimized to meet the demand of future applications.

金属元素研究的关键目标是使用厚度约为波长的光学元件实现光的波阵面整形。期望这种小型化将导致紧凑的，纳米级的光学设备在照相机，照明，显示器和可穿戴光学器件中的应用。然而，事实证明，在减小设备尺寸的同时保持功能性尤其具有挑战性。例如，到目前为止，还没有展示覆盖整个可见光谱的宽带消色差金属感的演示。在这里，我们表明，通过明智地设计表面上的纳米鳍片，可​​以同时控制光的相位，群延迟和群延迟色散，从而获得具有大带宽的透射消色差金属离子。我们展示了从470到670 nm的衍射极限消色差聚焦和消色差成像。我们的金属元素仅包含一层纳米结构，其厚度约为波长，并且不涉及空间复用或级联。尽管此初始设计（0.2的数值孔径）在500 nm处的效率约为20％，但我们讨论了可以进一步优化我们的方法以满足未来应用需求的方法。