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

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 waveguide layer has been shown to result in a high circular polarization degree ρ 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 |ρ c | is predicted to exceed 98%. The experimentally achieved value of |ρ 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.

Optomechanics of Chiral Dielectric Metasurfaces

“…The main peculiarity of our device resides instead in the use of a chiral pattern, with the consequent possibility to enable polarization‐dependent optomechanical effects; moreover, as highlighted above, the choice of a dielectric material (GaAs) allows for almost lossless operation. GaAs has also other advantages: it is easily machinable, it can host active elements, and it has strong nonlinear optical response . Furthermore, being its refractive index similar to that of silicon, the design presented here can be straightforwardly exported to complementary metal‐oxide‐semiconductor (CMOS)‐compatible platforms for eventual integrability with electronics.…”

Photonic bands, superchirality, and inverse design of a chiral minimal metasurface

“…Instead, θ is directly connected with the "chiral" Stokes parameter S 3 . In the following, we will mostly drop the use of θ and will rather define the metasurface functionality referring to the S 3 values of w (1,2) : S (1,2) 3 = ± cos 2θ.…”

“…Notice that in mode B the Poynting vector follows a well-defined direction, witnessing the presence of a traveling wave, while in mode A it "winds up" around the L-shaped inclusion, indicating a localized resonance. (1,2) and v (1,2) identify the polarization states of, respectively, right and left singular vectors of the transmission (Jones) matrix. The metasurface operation is to map the w's into the v's, plus a rescaling described by the singular values (see text for details).…”

Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

“…In particular, chiral photonic structures are known to demonstrate a giant optical activity, several orders of magnitude stronger than natural materials [4][5][6][7][8][9] . Recently, it has been demonstrated that incorporating a chiral photonic structure into a planar GaAs waveguide or a semiconductor microcavity (MC) with embedded lightemitting achiral InAs quantum dots (QD) allows to achieve highly circularly polarized light emission, without applying magnetic field and without the need of thick quarter-waveplates [10][11][12] . The effect is due to the modification of the symmetry and density of environmentally allowed electromagnetic modes relative to that in free space due to the chiral nanostructuring, which, in turn, affects the spontaneous emission rate, directional pattern, and polarization 13,14 .…”

“…To optimize the chiral structures for obtaining a high degree of circular polarization degree (DCP) of light emission we have calculated the frequency dependence of emission in right and left circular polarizations, using the optical scattering matrix and Fourier modal method [10][11][12]18 . In this approximation the emission is calculated actually for homogeneously distributed oscillating point dipoles in the QW plane, which are driven by external excitation and emit incoherently, so that the intensities rather than the electromagnetic fields are summed up at the receiver.…”