Inverse Designed Metalenses with Extended Depth of Focus

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 designs, 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 design based on intuition alone. Using adjoint optimization-based inverse electromagnetic design, in this paper, we designed a cylindrical metasurface lens operating at ∼625 nm 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 a lateral dimension of 66.66 μm) with three different focal lengths (66.66, 100, and 133.33 μm). The focusing efficiencies of the fabricated extended depth of focus metasurface lenses are similar to those of traditional metalenses. Keywords: diffractive optics; dielectric metasurface; extended depth of focus lens; inverse design; cylindrical lens