Generalization of the circular dichroism from metallic arrays that support Bloch-like surface plasmon polaritons

TL;DR

This paper develops a theoretical framework to understand and optimize circular dichroism in planar chiral nanohole arrays supporting Bloch-like surface plasmon polaritons, highlighting the roles of geometry and excitation.

Contribution

It introduces an analytical model using temporal coupled mode theory to relate dissymmetry factors to system geometry and excitation, demonstrating how to maximize circular dichroism.

Findings

Dissymmetry factor depends only on polarization angle and phase difference.

Maximum dissymmetry factor of ±2 achievable through array orientation.

Experimental and numerical results confirm the theoretical predictions.

Abstract

The broken mirror symmetry in subwavelength photonic systems has manifested many interesting chiroptical effects such as optical rotation and circular dichroism. When such systems are placed periodically in a lattice form, in addition to intrinsic chirality, extrinsic chirality also takes part, and the overall effect depends not only on the basis and lattice but also the excitation configuration. Here, we study planar chiral nanohole arrays in square lattice that support Bloch-like surface plasmon polaritons (SPPs) and clarify how the system geometry and the excitation contribute to circular dichroism. By using temporal coupled mode theory (CMT), the dissymmetry factor and the scattering matrix of the arrays are analytically formulated. Remarkably, we find the dissymmetry factor depends only on the coupling polarization angle and the in-coupling phase difference between the p- and s-polarizations. Besides, the upper limit of the dissymmetry factor at +/-2 can be reached simply by orienting the lattice of the arrays for properly exciting the Bloch-like SPPs and at the same time making the basis mimic two orthogonal and relatively displaced dipoles, demonstrating the interplay between extrinsic and intrinsic chirality. The models have been verified by numerical simulations and experiments, yielding the dissymmetry factors to be 1.82 and 1.55, respectively, from the proposed dual slot system.