Inverse designed metalenses with extended depth of focus

TL;DR

This paper presents an inverse electromagnetic design of silicon nitride metasurface lenses with extended depth of focus, validated through fabrication and characterization, achieving efficiencies comparable to traditional metalenses.

Contribution

It introduces a novel inverse design method for EDOF metasurface lenses with extended focus, validated by fabrication and optical testing.

Findings

Achieved extended depth of focus exceeding traditional lenses

Fabricated silicon nitride metasurface lenses with three focal lengths

Focusing efficiencies comparable to conventional metalenses

Abstract

Extended depth of focus (EDOF) lenses are important for various applications in computational imaging and microscopy. In addition to enabling novel functionalities, EDOF lenses can alleviate the need for stringent alignment requirements for imaging systems. Existing EDOF lenses, however, are often inefficient or produce an asymmetric point spread function (PSF) that blurs images. Inverse design of nanophotonics, including metasurfaces, has generated strong interest in recent years owing to its potential for generating exotic and innovative optical elements, which are generally difficult to model intuitively. Using adjoint optimization-based inverse electromagnetic design, in this paper, we designed a cylindrical metasurface lens operating at ~ 625nm with a depth of focus exceeding that of an ordinary lens. We validated our design by nanofabrication and optical characterization of silicon nitride metasurface lenses (with lateral dimension of 66.66 {\mu}m) with three different focal lengths (66.66 {\mu}m,100 {\mu}m,133.33 {\mu}m). The focusing efficiencies of the fabricated extended depth of focus metasurface lenses are similar to those of traditional metalenses.