Giant optical birefringence of semiconductor nanowire metamaterials

TL;DR

This paper reports the creation of semiconductor nanowire metamaterials with unprecedented optical birefringence, surpassing natural and artificial materials, achieved through aligned nanowire arrays with controllable orientation.

Contribution

Demonstration of giant optical birefringence in aligned semiconductor nanowire metamaterials with full control over birefringence orientation.

Findings

Largest optical birefringence to date, Δn=0.80

Birefringence exceeds natural quartz by 75 times

Full control over birefringence orientation via crystallographic growth

Abstract

Semiconductor nanowires exhibit large polarization anisotropy for the absorption and emission of light, making them ideal building blocks for novel photonic metamaterials. Here, we demonstrate that a high density of aligned nanowires exhibits giant optical birefringence, a collective phenomenon observable uniquely for collections of wires. The nanowire material was grown on gallium phosphide (GaP) (111) in the form of vertically standing GaP nanowires. We obtain the largest optical birefringence to date, with a difference between the in-plane and out-of-plane refractive indices of 0.80 and a relative birefringence of 43%. These values exceed by a factor of 75 the natural birefringence of quartz and a by more than a factor of two the highest values reported so far in other artificial materials. By exploiting the specific crystallographic growth directions of the nanowires on the substrate, we further demonstrate full control over the orientation of the optical birefringence effect in the metamaterial.