Propagation dynamics and crosstalk of orbital angular momentum beams influenced by a supersonic wind-induced environmental disturbance

Abstract

Near field airflow induced by wind is an important factor influencing vortex beams propagation under airborne optical communication, and the cross-talk among different orbital angular momentum (OAM) modes occurs in OAM-based optical communication. In this paper, the propagation of vortex beams through a supersonic wind-induced random environment is investigated. The wind-induced phase model is firstly validated by wind tunnel experiment, with the phase model, vortex beams propagation under supersonic wind condition is analyzed, and the spiral spectrum distortion is discussed in detail. It is demonstrated that the larger wind velocity and boundary-layer thickness leads to the enhanced distortion and spiral spectrum expansion of OAM beams. The behavior of multiplexed vortex beams influenced by supersonic wind is also studied, and the effect of the topological charge interval is given. Our results may provide a powerful tool to estimate the effect of a random airflow environment on OAM-based communication performance under airborne condition.

Ghost Imaging Through a Supersonic Wind‐Induced Environment Under Weak Illumination

“…where S(x, y, z j ) is the random phase modulation due to the supersonic wind disturbance and Δz = z j − z j−1 denotes the length of one propagation step. From our previous work, [23] the phase of wind-induced random environment can be approximately constructed from the average phase difference which is described as:…”

“…For beams propagation in supersonic wind environment with one step, the light field can be expressed as [ 27,28 ] : $$$$\begin{equation}A\left( {x,y,{z}_j} \right){\mathrm{ = }}\exp \left( { - \frac{i}{{2k}}\nabla _ \bot ^2\Delta z} \right)\exp \left[ {iS\left( {x,y,{z}_j} \right)} \right]A\left( {x,y,{z}_{j - 1}} \right)\end{equation}$$$$where $$S(x,y,{z}_j)$$ is the random phase modulation due to the supersonic wind disturbance and $$\Delta z = {z}_j - {z}_{j - 1}$$ denotes the length of one propagation step. From our previous work, [ 23 ] the phase of wind‐induced random environment can be approximately constructed from the average phase difference which is described as: $$$$\begin{equation}S=1.7\times {{10}^{-5}}\times \frac{2\pi {{\delta }^{*}}{{\rho }_{0}}}{\lambda \sin (\beta ){{\rho }_{SL}}}{{M}^{2}}\end{equation}$$$$where $${\delta }^*$$ is the displacement boundary‐layer thickness ($$\delta /{\delta }^* = q$$, δ is the boundary‐layer thickness and q is a constant), …”

“…[20][21][22] For GI under wind-induced environment, the propagation of random source is influenced by the random airflow, and the imaging quality is degraded due to additional noise to detected signal. [23] In addition, the detected optical signal is very weak under airborne condition because of long-distance imaging, and the imaging quality is influenced by both the airflow and detector noise, as a result, investigation on GI through a random environment induced by wind under low light detection is significant for applications in airborne remote sensing. To the best of our knowledge, GI influenced by the random airflow under low light detection has not been reported yet.…”