Optimizing the spectral range of diffractive metalenses for polychromatic imaging applications.

Jacob Engelberg,Uriel Levy

doi:10.1364/oe.25.021637

Abstract

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.

Highlights

Dielectric metasurfaces are a subject of extensive research over the years [1,2,3,4,5,6,7,8,9,10,11,12]
The question we address is, can such lenses be used for continuous broad spectrum applications? If so, what is the optimal spectral band that should be used? In particular, we demonstrate and discuss the tradeoff between the two primary performance metrics, resolution and signal-to-noise ratio (SNR), that exists when choosing metalens design parameters
In any optimization task it is necessary to obtain a single number, that represents all relevant performance parameters, for use as the system merit function. This can be achieved by taking the area under the SSNR function, to obtain the average SNR (ASNR)

Summary

Introduction

Dielectric metasurfaces are a subject of extensive research over the years [1,2,3,4,5,6,7,8,9,10,11,12]. Recent work has focused on metalenses as potential candidates for replacing conventional lenses in miniature imaging system [13,14,15,16]. Many imaging systems use broad spectrum illumination In such systems, metalens chromatic aberration is a critical limitation. The larger the spectral range and the aperture of the system, the better the SNR will be This comes at the expense of degraded spatial resolution, as a result of chromatic aberration. We will address this tradeoff and provide guidelines for finding the optimal values for these two free parameters, based on system requirements.

Metalens resolution

Metalens SNR

Optimization method

Simulation results

Findings

Conclusions