Perfect Chirality with imperfect polarisation

TL;DR

This paper demonstrates that elliptical dipoles can achieve perfect unidirectional light emission in waveguides, surpassing the limitations of circular dipoles and enabling larger chiral interaction areas with higher efficiency.

Contribution

It introduces the concept of using elliptical dipoles for unidirectional emission, expanding the design space beyond circular dipoles and proposing practical schemes for implementation.

Findings

Elliptical dipoles increase the chiral interaction area by a factor of about 30.

Elliptical dipoles can achieve unidirectional emission for any elliptical polarization.

Proposed schemes enable engineering elliptical transitions in atomic systems and quantum dots.

Abstract

Unidirectional (chiral) emission of light from a circular dipole emitter into a waveguide is only possible at points of perfect circular polarisation (C points), with elliptical polarisations yielding a lower directional contrast. However, there is no need to restrict engineered systems to circular dipoles and with an appropriate choice of dipole unidirectional emission is possible for any elliptical polarization. Using elliptical dipoles, rather than circular, typically increases the size of the area suitable for chiral interactions (in an exemplary mode by a factor $\sim 30$), while simultaneously increasing coupling efficiencies. We propose illustrative schemes to engineer the necessary elliptical transitions in both atomic systems and quantum dots.