Optimizing the spectral range of diffractive metalenses for polychromatic imaging applications

Recent progress has made matalenses a reality, with many publications relating to methods of implementation and performance evaluation of these elements. Basic metalens function is similar to that of a continuous (kinoform) diffractive lens, but the advantage is that they can be manufactured as a binary component. A significant limitation of metalenses, is its strong chromatic aberration. Recently there has been some success in correcting metalens chromatic aberration, albeit at the expense of transmission efficiency towards the desired diffraction order. Clearly, there is a tradeoff between parameters such as spectral bandwidth and spatial resolution. Hence, a major goal of this paper is to set up a metric for evaluation of metalens performance, allowing fair comparison of novel metalens technologies, such as achromatic metalenses, in terms of optical performance. Furthermore, we explore possibilities for practical use of non-chromatically corrected metalenses in polychromatic applications, by optimizing the metalens parameters. It is our hope that the current manuscript will serve as a guide for the design and evaluation of metalenses for practical applications.