Local topological charge analysis of electromagnetic vortex beam based on empirical mode decomposition

TL;DR

This paper introduces an empirical mode decomposition-based method to analyze local topological charges of electromagnetic vortex beams, overcoming Fourier transform limitations for high-resolution, local mode, and amplitude analysis in divergent and imperfect beams.

Contribution

It presents a novel EMD-based approach for local topological charge analysis, providing high azimuthal resolution and mode amplitude information for electromagnetic vortex beams.

Findings

The EMD method accurately identifies local topological charges.

Simulation and experiments validate the effectiveness of the approach.

The method improves resolution over traditional Fourier-based techniques.

Abstract

The topological charge of an electromagnetic vortex beam depends on its wavefront helicity. For mixed vortex beams composed of several different coaxial vortices, the topological charge spectrum can be obtained by Fourier transform. However, the vortex beam is generally divergent and imperfect. It makes it significant to investigate the local topological charges, especially in radio frequency regime. Fourier transform based methods are restrained by the uncertainty principle and cannot achieve high angular resolution and mode resolution simultaneously. In this letter, an analysis method for local topological charges of vortex beams is presented based on the empirical mode decomposition (EMD). From EMD, the intrinsic mode functions (IMFs) can be obtained to construct the bases of the electromagnetic wave, and each local topological charge can be respectively defined. With this method the local value achieves both high resolution of azimuth angle and topological charge, meanwhile the amplitudes of each OAM modes are presented as well. The simulation and experimental results confirm the validity of the EMD based method.