Optimized multiemitter beams for free-space optical communications through turbulent atmosphere

Area of Science:

• Optical engineering
• Free-space optical communication
• Atmospheric turbulence

Background:

• Scintillations, or intensity fluctuations, degrade performance in free-space optical (FSO) communication links.
• Spatial coherence of laser beams is a critical factor influencing scintillation levels.
• Partially coherent beams offer a potential method to mitigate these atmospheric effects.

Purpose of the Study:

• To experimentally investigate the scintillation reduction capabilities of a specific type of partially coherent beam in simulated atmospheric turbulence.
• To quantify the relationship between constituent beam separation and scintillation index.
• To validate theoretical models for partially coherent beam propagation through turbulence.

Main Methods:

• A scaled model of an FSO communication link was established.
• The beam was constructed from multiple, mutually incoherent, partially overlapping fundamental Gaussian beams.
• Atmospheric turbulence was simulated using a random phase screen with Kolmogorov statistics.
• The scintillation index was measured at the detector for varying degrees of turbulence and beam separations.

Main Results:

• An optimal separation distance between constituent beams was identified that minimizes the scintillation index.
• Substantial scintillation reduction was observed at this optimum, outperforming a single Gaussian beam.
• The scintillation reduction factor increased with a higher number of constituent beams.
• Experimental results for weak-to-intermediate turbulence aligned well with Rytov approximation predictions.

Conclusions:

• Partially coherent beams are effective in reducing scintillations in FSO communication.
• The proposed multi-beam configuration offers a practical approach to enhance link stability.
• Further research can explore advanced partially coherent beam types and their performance in diverse atmospheric conditions.