# A Knotted Meta-molecule with 2-D Isotropic Optical Activity Rotating the Incident Polarization by 90{\deg}

## TL;DR

This paper introduces a knotted chiral meta-molecule with 2-D isotropic optical activity that can rotate incident polarization by 90°, independent of the wave's initial polarization, validated experimentally in microwaves.

## Contribution

It presents the first chiral meta-molecule with intrinsic 2-D isotropic optical activity due to its knotted torus structure, enabling polarization rotation regardless of incident polarization.

## Key findings

- Achieved 90° polarization rotation in microwave spectrum
- Demonstrated isotropic optical activity independent of incident polarization
- Proposed structure is the most optically active meta-molecule reported to date

## Abstract

Optical activity is the ability of chiral materials to rotate linearly-polarized (LP) electromagnetic waves. Because of their intrinsic asymmetry, traditional chiral molecules usually lack isotropic performance, or at best only possess a weak form of chirality. Here we introduce a knotted chiral meta-molecule that exhibits optical activity corresponding to a 90{\deg} polarization rotation of the incident waves. More importantly, arising from the continuous multi-fold rotational symmetry of the chiral torus knot structure, the observed polarization rotation behavior is found to be independent of how the incident wave is polarized. In other words, the proposed chiral knot structure possesses two-dimensional (2-D) isotropic optical activity as illustrated in Fig. 1, which has been experimentally validated in the microwave spectrum. The proposed chiral torus knot represents the most optically active meta-molecule reported to date that is intrinsically isotropic to the incident polarization.

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Source: https://tomesphere.com/paper/1908.03254