The connectivity of undersea sensors and airborne nodes across the water–air interface has been long sought. This study designs a free-space wireless laser communications system that yields a high net data rate of 850 Mbit/s when perfectly aligned. This system can also be used for an extended coverage of 1963 cm² at the receiver while sustaining a net data rate of 9 Mbit/s over 10 m. The utility of this system was verified for direct communications across the water–air interface in a canal of the Red Sea based on a pre-aligned link as well as a diving pool under a mobile signal-searching mode. The canal deployment measured a real-time data rate of 87 Mbit/s when pre-aligned in turbid water over 50 min, which confirms the system robustness in harsh water environments. In the pool deployment, a drone configured with a photodetector flew over the surface of the water and recorded the underwater signals without a structure-assisted alignment. Using a four-quadrature amplitude-modulated orthogonal frequency-division multiplexing (4-QAM-OFDM) modulation scheme provided a net data rate of 44 Mbit/s over a 2.3-m underwater and 3.5-m air link. The results validated the link stability and mitigated problems that arise from misalignment and mobility in harsh environments, which paves the way for future field applications.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): BAS/1/1614-01-01, GEN/1/6607-01-01, KCR/1/2081-01-01, KCR/1/4114-01-01, FCC/1/1973-27-01
Acknowledgements: This work was supported by the King Abdullah University of Science and Technology (KAUST), BAS/1/1614-01-01, KCR/1/2081-01-01, KCR/1/4114-01- 01, GEN/1/6607-01-01, and FCC/1/1973-27-01. The authors also thank Mr. Nabeel M. Moamenah and the team at Residential & Facilities Operations, KAUST, for providing support for the Red Sea canal deployment.