26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Nonlinear chiral response governed by meta-atom rotation

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Speaker

Dhruv Hariharan (University of Sydney)

Description

Chiral photonics provides powerful routes for controlling the handedness of light, enabling unprecedented control over light-matter interactions and novel optical functionalities. Metasurfaces have emerged as a powerful platform for controlling chiral responses due to their design versatility and capacity for light manipulation on a sub-wavelength scale. In particular, recent works have explored nonlinear metasurfaces as a route for pronounced chiral light-matter interactions. However, these responses tend to arise from intricate three-dimensional systems, requiring complex fabrication techniques and inducing weaker electrical confinement.

I will outline our recent work demonstrating the tunability of strong nonlinear chirality from 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. We experimentally observe nonlinear circular dichroism spanning from -0.8 to 0.8, and a 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.

This work establishes a new paradigm for nonlinear chiral metaphotonics by demonstrating that giant and fully tunable nonlinear circular dichroism can emerge purely from meta-atom rotation in planar dielectric metasurfaces, without relying on intrinsically chiral three-dimensional geometries. These findings challenge the conventional understanding that strong chiral nonlinear responses require structurally chiral architectures and instead identify symmetry engineering in low-loss planar metasurfaces as a powerful and scalable route toward nonlinear chiral functionality. Beyond its fundamental importance, this work introduces a versatile platform for tunable chiral harmonic generation with significant potential for applications in chiral imaging, nonlinear optical information processing and polarisation-encoded photonics.