Physical meaning of the deviation scale under arbitrary turbulence strengths of optical orbital angular momentum

TL;DR

This paper clarifies the physical origin of the deviation scale in optical orbital angular momentum propagation under turbulence, linking intensity modulation, vortex splitting, and vortex-antivortex pair generation, beyond Rytov variance predictions.

Contribution

It provides a physical interpretation of the deviation scale using the multiple phase screen approach, highlighting the role of intensity modulation and vortex dynamics in turbulence.

Findings

Deviation scale relates to vortex splitting and vortex-antivortex pair formation.

Deviation only significant when phase disruption exceeds certain thresholds.

Rytov variance alone cannot predict the appearance of the deviation scale.

Abstract

The recently so-called deviation scale [C. M. Mabena et al., Phys. Rev. A 99, 013828 (2019)] bridges the connection between the result of the infinitesimal propagation equation (IPE) prediction and that of the single phase screen (SPS) approximation. Thanks to the multiple phase screen (MPS) approach, in this paper we elaborate the physical meaning of the deviation scale: the spatial accumulation of slight intensity modulation of incident orbital angular momentum (OAM) carrying beam splits the original vortex into multiple individual vortices with a topological charge (TC) of +1 and re-generates the vortex-antivortex pairs with a TC of +1 and with a TC of -1, leading to a significant deviation between these two different results only when the disruption of this compound effect on the phase distribution of the incident OAM-carrying beam becomes more significant. Other than that, we also show that the appearance of the deviation scale cannot be predicted only by the Rytov variance, which can be predicted through the vortex-splitting ratio of the received optical field alone or with the help of the normalized propagation distance.