Abstract
Unidirectional (chiral) emission of light from a circular dipole emitter into a waveguide is only possible at points of perfect circular polarization (C points), with elliptical polarizations 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 ∼30), while simultaneously increasing coupling efficiencies. We propose illustrative schemes to engineer the necessary elliptical transitions in both atomic systems and quantum dots.
Highlights
Unidirectional 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
The light propagating through these narrow channels has components of transversely rotating (“rolling”) electric fields [4], a consequence of Gauss’ law [5]
In nanofibre based waveguides only elliptical polarisation is practically accessible [12], while nano-beam and photonic crystal structures support circular polarisation at a few accessible locations, but the light field is elliptically polarised over the majority of the mode volume [5, 13, 14]
Summary
In (a) the polarisation is circular so that a dipole matching the helicity of the light phase shifts a passing photon (1), while a dipole of opposite helicity transmits the photon with no phase shift (3). Second [36], with Caesium atoms described with three levels in a Λ-like configuration In both cases there are two relevant optical transitions and in both ideally one transition couples only to the forwards direction, while the other couples only backwards, depicted in Fig.. Conclusion - We propose the engineering of elliptical dipoles in quantum emitters as an approach to building chiral interfaces These strategies offer the two-fold advantage of making far more of the space within a waveguide useful for directional interactions while simultaneously enabling a higher photon collection efficiency. Advanced proposals call for a system with two transitions, each unidirectional but in opposite directions This requires that the opposite circular dipoles are replaced with ellipses stretched along a shared axis.
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