Symmetry analysis of trimer-based all-dielectric metasurfaces with toroidal dipole modes

TL;DR

This paper investigates the excitation and properties of symmetry-protected toroidal dipole modes in all-dielectric metasurfaces with trimer clusters, combining theoretical analysis, simulations, and experiments to reveal their potential for enhanced light-matter interactions.

Contribution

It introduces a comprehensive symmetry-based framework for understanding and exciting toroidal dipole modes in dielectric metasurfaces, validated by experiments and simulations.

Findings

Toroidal dipole modes appear as quasi-dark states in trimer metasurfaces.

Proper symmetry reduction enables excitation of these modes by linearly polarized light.

Toroidal properties depend mainly on individual trimers, not array periodicity.

Abstract

Herein, we discuss the conditions for excitation of symmetry-protected toroidal dipole modes in all-dielectric metasurfaces composed of trimer or twin-trimer clusters of dielectric disks. Such metasurfaces permit enhanced light-matter interaction due to spatially confined light in resonant systems with a high-quality factor. To describe characteristics of toroidal modes existing in the clusters, we use the magnetic dipole moments approximation, group-theoretical methods, group representation theory, symmetry-adapted linear combination method, and circuit theory. To validate the obtained theoretical results, we fulfill both full-wave numerical simulations and microwave experiments. In particular, we have shown that the toroidal dipole mode appears as a quasi-dark state of the trimer. It can be excited in the metasurface by the field of a linearly polarized wave, providing the symmetry of the trimer is properly reduced. In the metasurface, the properties of the toroidal dipole mode are determined primarily by the parameters of a single trimer and are not a consequence of the periodicity of the array. The coupling of the toroidal dipole modes in the twin-trimers can appear in both bonding and anti-bonding fashion resulting in different orders of the net toroidal dipole moment. Due to the unique field configuration of these modes, the proposed metasurfaces can be considered as a platform for efficient light-matter interaction for enhanced absorption, nonlinear switching, and sensing.