# Vortex Waves and Channel Capacity: Hopes and Reality

## TL;DR

This paper critically examines claims that vortex waves can increase free space channel capacity, demonstrating that fundamental electromagnetic principles limit their effectiveness and that OAM does not enhance degrees of freedom.

## Contribution

The paper provides a theoretical refutation of the idea that vortex waves can increase channel capacity by showing fundamental electromagnetic constraints.

## Key findings

- Vortex waves do not increase the degrees of freedom of electromagnetic fields.
- The over-quadratic power decay of OAM beams is not fundamental to channel capacity.
- Fundamental properties of Maxwellian fields limit the potential of vortex waves.

## Abstract

Several recent contributions have envisioned the possibility of increasing currently exploitable maximum channel capacity of a free space link, both at optical and radio frequencies, by using vortex waves, i.e. carrying Orbital Angular Momentum (OAM). Our objective is to disprove these claims by showing that they are in contradiction with very fundamental properties of Maxwellian fields. We demonstrate that the Degrees of Freedom (DoF) of the field cannot be increased by the helical phase structure of electromagnetic vortex waves beyond what can be done without invoking this property. We also show that the often-advocated over-quadratic power decay of OAM beams with distance does not play any fundamental role in the determination of the channel DoF.