Turbulence-resistant high-capacity free-space optical communications using OAM mode group multiplexing

Area of Science:

• Optical Communications
• Free-Space Optics
• Photonics

Background:

• Orbital angular momentum (OAM) offers high-capacity free-space optical (FSO) communication potential.
• Atmospheric turbulence degrades OAM-based FSO links through power fluctuations and crosstalk.

Purpose of the Study:

• To propose and demonstrate a novel OAM mode-group multiplexing (OAM-MGM) scheme with transmitter mode diversity.
• To enhance the reliability of FSO communication systems under atmospheric turbulence.

Main Methods:

• Experimental demonstration of an FSO system using OAM-MGM.
• Transmission of two OAM groups with a 144 Gbit/s discrete multi-tone (DMT) signal.
• Testing under varying turbulence strengths (D/r0 = 1, 2, and 4).

Main Results:

• Achieved bit-error-rate (BER) below 3.8 × 10^-3 for turbulence strengths D/r0 of 1 and 2.
• Reduced system interruption probability from 28% to 4% under moderate turbulence (D/r0 = 2) compared to conventional systems.
• Demonstrated the scheme without adding extra system complexity.

Conclusions:

• The proposed OAM-MGM scheme effectively increases the reliability of OAM-based FSO communication systems.
• Transmitter mode diversity in OAM-MGM mitigates the adverse effects of atmospheric turbulence.
• OAM-MGM is a promising technique for robust high-capacity FSO links.