In recent years there has been a lot of interest in flat lenses, a category that includes diffractive lenses and metalenses. These lenses have the potential of reducing the size and cost of optical systems by replacing conventional refractive optical elements. A major obstacle to the widespread use of flat lenses is their inherent large chromatic aberration, associated with diffraction effects. To meet this challenge, achromatic diffractive lenses and metalenses have been developed. In this paper we review previously reported metalens performance limits, derive limits on the performance of achromatic diffractive lenses, and compare the two. We show that such lenses can support a wide spectral range, limited only by loss of efficiency caused by manufacturing limitations related to feature depth and size. On the other hand, we show that these lenses can provide near-diffraction-limited performance only at very low Fresnel numbers, i.e., they cannot provide large focusing power and broadband response simultaneously. We then go on to compare the limits of achromatic metalenses and diffractive lenses, in attempt to understand the potential of different types of flat lenses. Our findings facilitate better understanding of flat lens capabilities and limitations, and the exploration of novel design concepts and applications.

中文翻译：

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消色差平透镜性能限制

近年来，人们对平面透镜产生了很大的兴趣，平面透镜包括衍射透镜和超透镜。这些透镜有可能通过替代传统的折射光学元件来减小光学系统的尺寸和成本。平面透镜广泛使用的一个主要障碍是它们固有的大色差，与衍射效应相关。为了应对这一挑战，已经开发了消色差衍射透镜和超透镜。在本文中，我们回顾了先前报道的超透镜性能限制，推导出消色差衍射透镜的性能限制，并比较两者。我们表明，这种镜头可以支持很宽的光谱范围，仅受与特征深度和尺寸相关的制造限制导致的效率损失的限制。另一方面，我们表明这些透镜只能在非常低的菲涅耳数下提供接近衍射极限的性能，即它们不能同时提供大的聚焦能力和宽带响应。然后我们继续比较消色差超透镜和衍射透镜的限制，试图了解不同类型平面透镜的潜力。我们的发现有助于更好地理解平面透镜的功能和局限性，以及对新颖设计概念和应用的探索。