Controlling circular polarization of light emitted by quantum dots using chiral photonic crystal slab

TL;DR

This paper demonstrates that chiral photonic crystal slabs can induce high degrees of circular polarization in quantum dot emission, with theoretical predictions exceeding 98% and experimental results reaching 81%, by modifying electromagnetic modes.

Contribution

It introduces a novel method to control quantum dot emission polarization using chiral photonic structures without external magnetic fields.

Findings

Predicted circular polarization degree exceeds 98% at resonance.

Experimentally achieved polarization degree is 81%, limited by scattering defects.

Removing unpolarized background estimates polarization as high as 96%.

Abstract

We study the polarization properties of light emitted by quantum dots that are embedded in chiral photonic crystal structures made of achiral planar GaAs waveguides. A modification of the electromagnetic mode structure due to the chiral grating fabricated by partial etching of the wave\-guide layer has been shown to result in a high circular polarization degree $\rho_c$ of the quantum dot emission in the absence of external magnetic field. The physical nature of the phenomenon can be understood in terms of the reciprocity principle taking into account the structural symmetry. At the resonance wavelength, the magnitude of $|\rho_c|$ is predicted to exceed 98%. The experimentally achieved value of $|\rho_c|=81$% is smaller, which is due to the contribution of unpolarized light scattered by grating defects, thus breaking its periodicity. The achieved polarization degree estimated removing the unpolarized nonresonant background from the emission spectra can be estimated to be as high as 96%, close to the theoretical prediction.