The role of refractive index in metalens performance

TL;DR

This paper investigates how the refractive index of materials affects the performance of metalenses, finding that for moderate focal lengths and NA<0.6, material choice has minimal impact on focal spot size and efficiency.

Contribution

It provides a comprehensive analysis of the influence of refractive index on metalens performance using both forward and inverse design methods.

Findings

High refractive index enables shorter focal lengths.

No significant difference in focal spot size for refractive indices 1.25 to 3.5 at moderate NA.

Material choice has limited impact on focusing efficiency at moderate focal lengths.

Abstract

Sub-wavelength diffractive optics, commonly known as metasurfaces, have recently garnered significant attention for their ability to create ultra-thin flat lenses with extremely short focal lengths. Several materials with different refractive indices have been used to create metasurface lenses (metalenses). In this paper, we analyze the role of material refractive indices on the performance of these metalenses. We employ both forward and inverse design methodologies to perform our analysis. We found that, while high refractive index materials allow for extreme reduction of the focal length, for moderate focal lengths and numerical aperture (<0.6), there is no appreciable difference in focal spot-size and focusing efficiency for metalenses made of different materials with refractive indices ranging between n= 1.25 to n=3.5.