Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications.

Area of Science:

• Optical Communications
• Quantum Optics
• Fluid Dynamics

Background:

• Underwater optical communication systems face capacity limitations.
• Spatial multiplexing using orbital angular momentum (OAM) offers a potential solution.
• Environmental factors like turbidity and turbulence degrade optical signal quality.

Purpose of the Study:

• To enhance underwater optical communication capacity by multiplexing multiple OAM beams.
• To investigate the impact of environmental factors on OAM beam transmission.
• To demonstrate mitigation strategies for signal degradation.

Main Methods:

• Multiplexing and transmitting four green OAM beams through a single aperture.
• Utilizing two data generation techniques: 1064 nm for 10 Gbit/s/beam and 520 nm for 1 Gbit/s/beam.
• Investigating the effects of scattering, water current, and thermal gradient-induced turbulence.

Main Results:

• Achieved a 40 Gbit/s link capacity by multiplexing four green OAM beams.
• Identified thermal gradients as the primary cause of signal distortion and turbidity as the main cause of signal loss.
• Demonstrated mitigation of inter-channel crosstalk using multi-channel equalization processing.

Conclusions:

• Spatial multiplexing of OAM beams is a viable strategy for increasing underwater optical communication capacity.
• Thermal gradients and turbidity pose significant challenges to OAM-based underwater communication systems.
• Multi-channel equalization can effectively mitigate crosstalk induced by thermal gradients.