Coherent all-optical tuning of large-area phase-gradient metasurface

TL;DR

This paper introduces a scalable all-optical coherent control method for large-area phase-gradient metasurfaces, enabling ultrafast, continuous beam steering and tunable optical devices without individual meta-atom actuation.

Contribution

It presents a novel scalable approach combining coherent illumination and optimization algorithms to control large-area metasurfaces, overcoming previous size limitations.

Findings

Achieved continuous beam steering with large-area metasurfaces.

Demonstrated tunable metalenses and axicons using the proposed method.

Validated the approach through numerical simulations.

Abstract

Tunable active metasurfaces have become a major research focus in recent years. Among tuning mechanisms, all-optical coherent control stands out because it requires no material or geometric change, enabling ultrafast, low-energy, interference-based modulation of amplitude, phase, and polarization in ultrathin devices. However, when applied to phase-gradient metasurfaces, coherent control has been limited to small apertures effectively confined to a single Fresnel zone, leading to large divergence and degraded beam quality. Here we propose and numerically validate a scalable method that enables large-area coherent control. The key idea is to use coherent illumination to tune the phase gradient within each Fresnel zone while a direct search algorithm optimizes zone-by-zone parameters to meet system-level targets. Using this principle, we demonstrate continuous tuning of a large-area metasurface for continuous beam-steering without per-meta-atom phase actuation. The same framework applies broadly to continuously tunable phase-gradient optics, including varifocal metalenses, parfocal zoom metalenses, tunable axicons, and related dynamic focusing elements.