A vertical hyperbolic metamaterial to enhance the optical spin Hall effect

Abstract

Hyperbolic metamaterials composed of horizontally stacked metal and dielectric multilayer have recently attracted scientific interest as a platform to enhance and observe optical spin Hall effect. However, the large optical spin Hall effect in the horizontal hyperbolic metamaterials always accompanies extremely low efficiency, which obstructs its implementation on practical usage. Reducing the sample thickness to augment the transmission causes diminishment of the optical spin Hall effect. Here, we demonstrate that a vertical hyperbolic metamaterial can enhance the optical spin Hall effect by several orders of magnitude in comparison to that of its horizontal counterpart. Under the same conditions of material combinations and total thickness, the enhancement, which is incident angle-dependent, can be higher than 800-fold when the incident angle is 5°, and 5000-fold when the incident angle is 1°. As a proof of concept, we fabricate a large-scale gold nano-grating by nanoimprint lithography and observe the enhancement of optical spin Hall effect experimentally, which agree well with the simulated result. The gigantic optical spin Hall effect in a vertical hyperbolic metamaterial will offers a venue for helicity-dependent control of optical devices such as filters, sensors, switches and beam splitters.