Observation of Enhanced Optical Spin Hall Effect in a Vertical Hyperbolic Metamaterial

Abstract

Hyperbolic metamaterials, horizontally stacked metal and dielectric multilayer, have recently been studied as a platform to observe optical spin Hall effect. However, the large optical spin Hall effect in the horizontal hyperbolic metamaterials accompanies extremely low transmission, which obstructs its practical applications. Reducing the sample thickness to augment the transmission causes diminishment of the optical spin Hall effect. In this Article, 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 degrees. As a proof of concept, we fabricate a large-scale gold nanograting by nanoimprint lithography and observe the optical spin Hall effect experimentally, which agrees well with the simulated result. The gigantic optical spin Hall effect in a vertical hyperbolic metamaterial will enable helicity-dependent control of optical devices including filters, sensors, switches, and beam splitters.