Photon-counting-based underwater wireless optical communication employing orbital angular momentum multiplexing

Area of Science:

• Underwater wireless optical communication (UWOC)
• Optical physics
• Information theory

Background:

• UWOC systems offer high speed, low latency, and security for underwater applications.
• Signal attenuation in water channels remains a significant challenge, limiting UWOC system performance.
• Advanced modulation and detection techniques are needed to overcome these limitations.

Purpose of the Study:

• To experimentally demonstrate an orbital angular momentum (OAM) multiplexing UWOC system utilizing photon-counting detection.
• To analyze bit error rate (BER) and photon-counting statistics with a theoretical model.
• To implement signal processing for demodulating OAM states at the single-photon level.

Main Methods:

• A single-photon counting module was employed for signal reception.
• A theoretical model was developed to fit the experimental system and analyze BER and photon-counting statistics.
• Field-programmable gate array (FPGA) programming was used for signal processing and OAM state demodulation.

Main Results:

• A 2-OAM multiplexed UWOC link was successfully established over a 9-meter water channel.
• On-off keying modulation achieved a BER of 1.26×10^-3 at 20 Mbps.
• 2-pulse position modulation achieved a BER of 3.17×10^-4 at 10 Mbps, both below the FEC threshold.
• A total transmission loss of 37 dB was recorded, equivalent to 283 m of Jerlov I type seawater attenuation.

Conclusions:

• The demonstrated photon-counting based OAM multiplexing UWOC system effectively overcomes water channel attenuation.
• The system achieves high-capacity and reliable underwater communication below the FEC threshold.
• This verified scheme is crucial for advancing long-range and high-capacity UWOC applications.