Spin-Orbit Coupling for Optical Vortex Generation in van der Waals Materials

TL;DR

This paper demonstrates a novel method to generate optical vortex beams using van der Waals materials, leveraging their high birefringence and spin-orbit coupling to create efficient, compact, and fabrication-free vortex generators for integrated photonics.

Contribution

The study introduces the use of van der Waals materials for spin-orbit coupling-based vortex generation, enabling high-efficiency, ultra-thin, fabrication-free optical vortex devices.

Findings

Optical vortices generated with 8-um-thick hBN crystal.

Generation of vortex beams in 320-nm-thick MoS2 with 0.09 efficiency.

Potential for ultra-compact, fabrication-free vortex generators.

Abstract

An optical vortex beam has attracted significant attention across diverse applications, including optical manipulation, phase-contrast microscopy, optical communication, and quantum photonics. To utilize vortex generators for integrated photonics, researchers have developed ultra-compact vortex generators using fork gratings, metasurfaces, and integrated microcombs. However, those devices depend on costly, time-consuming nanofabrication and are constrained by the low signal-to-noise ratio due to the fabrication error. As an alternative maneuver, spin-orbit coupling has emerged as a method to obtain the vortex beam by converting spin angular momentum (SAM) without nanostructures. Here, we demonstrate the creation of an optical vortex beam using van der Waals (vdW) materials. The significantly high birefringence of vdW materials allows generations of optical vortex beams with high efficiency in a sub-wavelength thickness. In this work, we utilize an 8-um-thick hexagonal boron nitride (hBN) crystal for the creation of optical vortices carrying topological charges of +2 and -2. We also present the generation of an optical vortex beam in a 320-nm-thick MoS2 crystal with a conversion efficiency of 0.09. This study paves the way for fabrication-less and ultra-compact optical vortex generators, which can be applied for integrated photonics and large-scale vortex generator arrays.