Abstract
Chiral optical response is an inherent property of molecules and nanostructures, which cannot be superimposed on their mirror images. In specific cases, optical chirality can be observed also for symmetric structures. This so-called extrinsic chirality requires that the mirror symmetry is broken by the geometry of the structure together with the incident or emission angle of light. From the fabrication point of view, the benefit of extrinsic chirality is that there is no need to induce structural chirality at nanoscale. This paper reports demonstration extrinsic chirality of photoluminescence emission from asymmetrically Au-coated GaAs-AlGaAs-GaAs core-shell nanowires fabricated on silicon by a completely lithography-free self-assembled method. In particular, the extrinsic chirality of PL emission is shown to originate from a strong symmetry breaking of fundamental HE11 waveguide modes due to the presence of the asymmetric Au coating, causing preferential emission of left and right-handed emissions in different directions in the far field.
Highlights
Chiral optical response is an inherent property of molecules and nanostructures, which cannot be superimposed on their mirror images
In the Au-coated NW samples, the extrinsic chiral behavior can observed given a proper orientation of the NW and its Au-coated sides with respect to the light to be absorbed or emitted: the average anisotropy of the structure is in the y-direction, the NW axis is in the z-direction, while the wave-vector of the emitted light lies in xz-plane in such way that k is not parallel with the z-axis
Splitting of left and right-handed polarizations in different directions in the far field was measured by circular polarization dependent detection for different sample tilt angles
Summary
Chiral optical response is an inherent property of molecules and nanostructures, which cannot be superimposed on their mirror images. The chiral PL emission from the GaAs core with linear polarized excitation originates from a strong symmetry breaking of HE11 modes due to the presence of Au on three of the six (111) sidewalls, leading to a preferential directionality of left and right-handed circular polarizations in different angles in the far field. A unique property of this concept is that the intrinsic waveguiding properties of the NWs are modified with the external Au layer to provide extrinsic chirality of light emission They are fabricated with a completely lithography-free, self-assembled technique and potentially allow electrical injection for LED operation by incorporating a PN-junction in the NW, providing a chiral light manipulation platform for applications spanning from quantum information technology to biology and chemistry
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