Observation of enhanced optical spin Hall effect in a vertical hyperbolic metamaterial

TL;DR

This paper demonstrates that vertical hyperbolic metamaterials significantly enhance the optical spin Hall effect compared to horizontal structures, enabling improved control of optical devices with practical transmission levels.

Contribution

The study introduces a vertical hyperbolic metamaterial design that amplifies the optical spin Hall shift by several orders of magnitude, overcoming limitations of horizontal structures.

Findings

Shift enhancement exceeds 800-fold at 5 degrees incident angle.

Shift enhancement exceeds 5000-fold at 1 degree incident angle.

Experimental measurements agree with simulations, confirming the effect.

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 shift. In this letter, we demonstrate that a vertical hyperbolic metamaterial can enhance the shift by several orders of magnitude in comparison to the shift of its horizontal counterpart. Under the same conditions of material combinations and total thickness, the shift enhancement, which is incident angle-dependent, can be higher than 800-fold when the incident angle is 5 degree, and 5000-fold when the incident angle is 1 degree. As a proof of concept, we fabricate a large-scale gold nano-grating by nanoimprint lithography and measure the helicity-dependent shift by Stokes polarimetry setup, 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.