Orbital angular momentum mode diversity gain in optical communication.

Area of Science:

• Optical communications
• Wireless communication technologies
• Signal processing

Background:

• Vortex beams with orbital angular momentum (OAM) offer enhanced multiplexing for increased communication capacity.
• Turbulence noise causes signal fading, degrading performance and potentially interrupting communication in OAM systems.

Purpose of the Study:

• To propose and investigate a diversity gain strategy for mitigating signal fading in OAM multiplexing communication.
• To optimize diversity efficiency and communication capacity through gain combination and channel assignment.

Main Methods:

• Signals were endowed with distinct channel matrices and superposed using designed channel weights for optimal diversity gain.
• Turbulence noise was equalized to mitigate signal fading.
• Multiplexed channels were assigned for diversity and multiplexing based on bit-error rate and outage probability.

Main Results:

• Demonstrated a 6-channel multiplexing communication system transmitting 24 Gbit/s QPSK-OFDM signals using 3 OAM modes for diversity gain.
• Achieved a significant decrease in bit-error rate from 1.41 × 10⁻² to 1.63 × 10⁻⁴ at -14 dBm after applying diversity gain.
• Successfully suppressed an 86.7% outage probability.

Conclusions:

• The proposed diversity gain strategy effectively mitigates signal fading in OAM multiplexing communication.
• The method optimizes the tradeoff between turbulence noise tolerance and communication capacity.
• This approach enhances the reliability and performance of high-capacity optical wireless communication systems.