Long-reach underwater wireless optical communication with relaxed link alignment enabled by optical combination and...

Area of Science:

• Optical Engineering
• Underwater Communication Systems
• Photonics

Background:

• Underwater wireless optical communication (UWOC) faces challenges in transmission distance and alignment.
• Existing UWOC systems require precise optical alignment, limiting practical applications.
• High data rates over extended distances in underwater environments remain a significant hurdle.

Purpose of the Study:

• To extend the transmission distance of UWOC systems.
• To relax the strict alignment requirements for UWOC.
• To improve the robustness and applicability of UWOC through advanced detection and diversity techniques.

Main Methods:

• Design and implementation of a novel UWOC system.
• Utilizing a 3x1 fiber combiner for signal aggregation.
• Employing a high-sensitive multi-pixel photon counter (MPPC) as the primary detector.
• Investigating diversity reception technologies with dual MPPC detectors.

Main Results:

• Successfully achieved 50m and 100m transmission distances in a 50m swimming pool (24 attenuation lengths).
• Demonstrated data rates of 16.78 Mbps at 50m and 8.39 Mbps at 100m.
• Maximal ratio combining (MRC) extended misalignment tolerance to 9m offset at 50m, significantly outperforming single MPPC detection (6m offset).

Conclusions:

• The developed UWOC system effectively extends transmission distance and relaxes alignment constraints.
• The use of fiber combiners and MPPCs offers a viable solution for robust underwater optical communication.
• Diversity reception techniques, particularly MRC, significantly enhance the system's tolerance to misalignment, paving the way for more reliable UWOC deployments.