A plethora of metalenses and diffractive lenses (“flat lenses”) have been demonstrated over the years. Recently, attempts have been made to stretch their performance envelope, particularly in the direction of wide-band achromatic performance. While achromatic behavior has been demonstrated, showing an actual improvement in imaging performance relative to conventional (non-chromatically corrected) flat lenses has remained a major challenge. The reasons for this are use of inappropriate performance metrics, lack of comparison to a baseline conventional design, and lack of a performance metric that combines signal-to-noise ratio and resolution. An additional problem is that different published flat lens designs use different first order parameters, so they cannot be compared. In this work we present an overall performance metric that will allow comparison of different types of flat lenses, even if their first order optical parameters are not the same. We apply this metric to several published achromatic flat lens designs and compare them to the equivalent conventional flat lens, which we consider as the lower bound for achromatic flat lens performance. We found that the performance of the achromatic flat lenses studied does not surpass that of a conventional diffractive lens. Use of this metric paves the way for future developments in the field of achromatic flat lenses, which will display proven progress.

中文翻译：

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宽带平面透镜性能比较的广义度量

多年来，已经展示了过多的超透镜和衍射透镜（“平面透镜”）。最近，已经尝试扩展它们的性能范围，特别是在宽带消色差性能的方向上。虽然已经证明了消色差行为，但相对于传统（非色度校正）平面镜头而言，成像性能的实际改进仍然是一项重大挑战。造成这种情况的原因是使用了不适当的性能指标，缺乏与基线传统设计的比较，以及缺乏结合信噪比和分辨率的性能指标。另一个问题是不同的已发布平面透镜设计使用不同的一阶参数，因此无法进行比较。在这项工作中，我们提出了一个整体性能指标，可以比较不同类型的平面透镜，即使它们的一阶光学参数不相同。我们将此指标应用于已发布的几个消色差平面透镜设计，并将它们与等效的传统平面透镜进行比较，我们认为这是消色差平面透镜性能的下限。我们发现所研究的消色差平面透镜的性能并没有超过传统衍射透镜的性能。该指标的使用为消色差平面透镜领域的未来发展铺平了道路，这将显示出经过验证的进展。我们将此指标应用于已发布的几个消色差平面透镜设计，并将它们与等效的传统平面透镜进行比较，我们认为这是消色差平面透镜性能的下限。我们发现所研究的消色差平面透镜的性能并没有超过传统衍射透镜的性能。该指标的使用为消色差平面透镜领域的未来发展铺平了道路，这将显示出经过验证的进展。我们将此指标应用于已发布的几个消色差平面透镜设计，并将它们与等效的传统平面透镜进行比较，我们认为这是消色差平面透镜性能的下限。我们发现所研究的消色差平面透镜的性能并没有超过传统衍射透镜的性能。该指标的使用为消色差平面透镜领域的未来发展铺平了道路，这将显示出经过验证的进展。