A True Assessment of Flat Lenses for Broadband Imaging Applications

TL;DR

This paper introduces a new performance metric for flat lenses, enabling fair comparison with conventional lenses and demonstrating that current achromatic flat lenses do not outperform traditional designs in imaging quality.

Contribution

The paper proposes a novel metric for evaluating flat lens performance, facilitating accurate comparisons and highlighting the lack of true imaging improvements in existing achromatic flat lens designs.

Findings

Current achromatic flat lenses do not outperform conventional lenses in imaging quality.

The new metric allows for fair comparison across different flat lens designs.

Published flat lens designs show no significant improvement over traditional lenses.

Abstract

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, an actual improvement in imaging performance relative to conventional (non-chromatically corrected) flat lenses has not. 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. In this work we present a 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. Use of this metric paves the way for future developments in the field of achromatic flat lenses, which will display proven progress.