Nonlinear chiral response governed by meta-atom rotation

TL;DR

This paper demonstrates that planar metasurfaces with rotated meta-atoms can exhibit strong, tunable nonlinear chiral responses, enabling control over circular dichroism in third-harmonic generation through symmetry and resonance effects.

Contribution

It introduces meta-atom rotation as a novel mechanism to engineer and tune nonlinear chiral responses in planar metasurfaces, simplifying design compared to 3D systems.

Findings

Strong nonlinear chiral response observed in planar metasurfaces.

Swapping of nonlinear chiral channels with different meta-atom rotations.

Resonance and symmetry interplay governs nonlinear chiral behavior.

Abstract

Chiral photonics provides powerful routes for controlling the light handedness, yet nonlinear chiral responses are typically associated with intricate three-dimensional systems. Here, we demonstrate that strong nonlinear chirality can emerge and be precisely tuned in planar metasurfaces. We study free-standing membrane metasurfaces composed of periodic lattices of tilted elliptic holes, which preserve out-of-plane mirror symmetry while breaking all in-plane mirror symmetries through the in-plane rotation of the meta-atoms. We demonstrate that optical resonances play a decisive role in governing the nonlinear chiral response, enabling pronounced circular dichroism in third-harmonic generation even when symmetry is broken only in plane. We experimentally reveal strong nonlinear chiral response from the metasurfaces and a striking swapping of nonlinear chiral channels for complementary meta-atom rotation angles. This behaviour arises from the interplay between lattice symmetry and meta-atom orientation, which controls the symmetry of the resonant modes and the resulting nonlinear selection rules. Our results establish meta-atom rotation as a powerful mechanism for engineering nonlinear chiral responses in planar metasurfaces, opening new opportunities for tunable chiral nonlinear metaphotonics devices.