Manipulation of Orbital Angular Momentum Spectrum Using Shape-Tailored Metasurfaces

TL;DR

This paper introduces a universal, broadband method for manipulating the orbital angular momentum spectrum of vortex beams using shape-tailored metasurfaces, enabling high-purity and wideband OAM spectrum control.

Contribution

It presents a novel amplitude-modulation scheme with shape-tailored metasurfaces for wideband OAM spectrum manipulation, advancing beyond current broadband amplitude control limitations.

Findings

The rotating meta-atoms on a triangular lattice reduce coupling distortion.

A universal relation links metasurface shape to vortex beam spectrum.

Experimental demonstration of broadband and comb-like OAM spectra.

Abstract

Vortex beams carrying orbital angular momentum (OAM) have been widely applied in various electromagnetic, optical, and quantum systems. A tailored OAM spectrum composed of several specific modes as expected holds a promise for expanding the degrees of freedom of the systems. However, such a broadband high-purity tailored spectrum is difficult to be achieved by the present devices, where the broadband amplitude manipulation has not been explored yet. In this work, inspired by the envelope-modulation theory, an elegant and universal way to manipulate the OAM spectrum in wide bandwidth is proposed by using a shape-tailored metasurface. Firstly, the rotating meta-atoms on a triangular lattice are proved to have smaller coupling distortion than that on a square lattice, and this behavior is critical for high-purity vortex spectrum generation by the Pancharatnam-Berry-based metasurfaces. Secondly, a universal modulation relation is established between the spatial arrangement of metasurfaces and the generated vortex beams. Finally, the broadband modulated OAM spectra and the comb-like OAM spectra are theoretically and experimentally demonstrated by the shape-tailored metasurfaces. The proposed amplitude-modulation scheme offers a novel concept and engineering route to manipulate the OAM spectrum in wide bandwidth, which could promote the development of OAM-based applications.