Polarisation control of linear dipole radiation using spin-momentum locking of light

TL;DR

This paper demonstrates that a linear dipole embedded in a nanophotonic environment can emit a full range of polarisation states, including elliptical and circular, by exploiting spin-momentum locking of light.

Contribution

It experimentally shows that linear dipoles can produce arbitrary polarisation states without birefringent components, expanding control over light polarisation at the nanoscale.

Findings

Linear dipoles can emit various elliptical polarisations.

Emission can span the entire Poincare sphere.

Polarisation control is achieved via nanostructure geometry.

Abstract

We experimentally demonstrate that a linear dipole is not restricted to emit linearly polarised light, provided it is embedded in the appropriate nanophotonic environment. We observe emission of various elliptical polarisations by a linear dipole including circularly polarised light, without the need for birefringent components. We further show that the emitted state of polarisation can theoretically span the entire Poincare sphere. The experimental demonstration is based on elongated gold nanoparticles (nanorods) deposited on an optical nanofibre and excited by a free-space laser beam. The light directly collected in the guided mode of the nanofibre is analysed in regard to the azimuthal position and orientation of the nanorods, observed by means of scanning electron microscopy. This work constitutes a demonstration of the mapping between purely geometrical degrees of freedom of a light source and all polarisation states and could open the way to new methods for polarisation control of light sources at the nanoscale.