Annular Channel Eigenmodes: A Physical-Layer Approach to Suppressing OAM Modal Crosstalk

TL;DR

This paper introduces Annular Channel Eigenmodes (ACEs), a new physical-layer method that significantly reduces modal crosstalk in OAM-based communication systems by optimizing energy confinement within annular channels.

Contribution

The paper presents ACEs as a novel, rigorously derived set of optimal beams that improve spatial isolation and crosstalk suppression in OAM multiplexing.

Findings

ACEs suppress modal crosstalk to nearly -30 dB, outperforming POVs at -16 dB.

Crosstalk suppression with ACEs improves exponentially with channel width.

Experimental results show a 36% increase in energy confinement using ACEs.

Abstract

Modal crosstalk is a fundamental limitation for orbital angular momentum (OAM)-based spatial-division multiplexing. Here, we introduce Annular Channel Eigenmodes (ACEs) - rigorously derived as the optimal band-limited solution for maximizing energy concentration within distinct annular channels. This approach reformulates the design as a Hermitian eigenvalue problem, efficiently yielding optimal beams that are physically isolated in space. Numerical simulations demonstrate that under identical conditions, conventional Gaussian-enveloped perfect optical vortices (POVs) exhibit an average modal crosstalk of -16 dB, whereas ACEs suppress crosstalk to nearly -30 dB. Moreover, the crosstalk suppression of ACEs continues to improve exponentially with increasing channel width, while that of POVs saturates at a fundamental limit. We experimentally generated ACEs and confirmed a 36% enhancement in energy confinement relative to POVs. ACEs thus provide a physically robust basis for high-fidelity, high-density OAM communications.