Computational inverse design for ultra-compact single-piece metalenses free of chromatic and angular aberration

TL;DR

This paper introduces a full-Maxwell topology-optimization approach to design ultra-compact, single-piece multlayer metalenses that focus over wide angles and bandwidths without chromatic or angular aberrations, achieving diffraction-limited performance.

Contribution

It presents the first full-wave, topology-optimized multlayer metalenses with plan-achromatic focusing over wide angles and bandwidths, using approximately 100,000 degrees of freedom.

Findings

Achieves diffraction-limited focusing with Strehl ratio > 0.8

Maintains > 50% focusing efficiency across the spectrum and angles

Demonstrates lens miniaturization while preserving optical performance

Abstract

We present full-Maxwell topology-optimization design of a single-piece multlayer metalens, about 10 wavelengths~$\lambda$ in thickness, that simultaneously focuses over a $60^\circ$ angular range and a 23\% spectral bandwidth without suffering chromatic or angular aberration, a "plan-achromat." At all angles and frequencies it achieves diffraction-limited focusing (Strehl ratio $> 0.8$) and absolute focusing efficiency $> 50$\%. Both 2D and 3D axi-symmetric designs are presented, optimized over $\sim 10^5$ degrees of freedom. We also demonstrate shortening the lens-to-sensor distance while producing the same image as for a longer "virtual" focal length and maintaining plan-achromaticity. These proof-of-concept designs demonstrate the ultra-compact multi-functionality that can be achieved by exploiting the full wave physics of subwavelength designs, and motivate future work on design and fabrication of multi-layer meta-optics.