Contrary to widespread belief, the Fresnel zone plate outperforms the metalens at high NA

TL;DR

Rigorous simulations and experiments demonstrate that Fresnel zone plates outperform metalenses at high NA, challenging recent claims and emphasizing the importance of direct comparisons in optical device performance.

Contribution

This study provides the first comprehensive comparison showing FZPs outperform metalenses at high NA, highlighting the importance of orientation and traditional diffractive optics.

Findings

FZPs have higher focusing efficiency than metalenses at high NA.

Efficiency depends on illumination direction, favoring FZPs.

Blazed gratings outperform meta-gratings in efficiency.

Abstract

Rigorous simulations challenge recent claims that metalenses outperform conventional diffractive lenses, such as Fresnel Zone Plates (FZPs), in focusing efficiency at high numerical apertures (NAs). Across various lens diameters, FZPs exhibit a pronounced asymmetry in the shadow effect, leading to significantly higher focusing efficiency when optimally oriented. Extending this analysis, we show that conventional blazed gratings also surpass meta-gratings in efficiency. Since any linear optical element can be decomposed into local gratings, these findings broadly underscore the superiority of blazed structures over binary metastructures. Experimental characterization of an FZP with diameter = 3 mm, focal length = 0.2 mm operating at $\lambda$ = 634 nm confirms the dependence of efficiency on illumination direction. Our results emphasize the need for rigorous, direct comparisons between meta-optics and traditional diffractive optics to ensure accurate performance assessments.