Generating far-field orbital angular momenta from near-field optical chirality

TL;DR

This paper presents a method to generate and control far-field orbital angular momentum (OAM) beams using nanostructured chiral membranes, revealing the underlying OAM selection rules and their experimental validation.

Contribution

It introduces a novel approach to tailor far-field OAM indices via nanostructure design and elucidates the OAM selection rules imposed by a central aperture.

Findings

Nanostructures on both sides of a membrane couple light into chiral near fields.

Vortex beams with specific OAM indices can be transmitted through a central aperture.

OAM summation rules are derived and confirmed experimentally.

Abstract

We demonstrate that nanostructures carefully designed on both sides of a thin suspended metallic membrane couple light into a chiral near field and transmit vortex beams through a central aperture that connects the two sides of the membrane. We show how far-field orbital angular momentum (OAM) indices can be tailored through nanostructure designs. We reveal the crucial importance of OAM selection rules imposed by the central aperture and derive OAM summation rules in perfect agreement with experimental data.