Underwater Free-Space Optical Power Transfer: An Enabling Technology for Remote Underwater Intervention

This paper describes the research and development of underwater free-space optical power transfer (uFSO-PT) technology at Johns Hopkins University Applied Physics Laboratory (JHU-APL). Smart and autonomous underwater intervention for future, low-cost, safe, ultra-deep offshore operation desires a set of tools that are highly efficient and capable of providing new abilities. For example, resident autonomous underwater vehicles (AUVs) equipped with the optical transmitter would be able (i) to charge batteries of undersea sensors such as wellhead sensors and telemetry of well-monitoring systems and (ii) to turn on and off switches remotely without docking/latching to its target assets. This allows the assets to function for an extended period of time performing power and energy-demanding tasks without requiring expensive services from the water surface during inclement weather for its replacement, recharging, or switching. uFSO-PT technology enables the remote power transfer capability. It can serve as a remote battery charger for AUVs and other underwater assets supported by AUVs as well as currently used remotely operated underwater vehicles (ROVs). The successful bench- top laboratory demonstration of uFSO-PT has been made in this study by charging on-board batteries of a commercial AUV. Off-the-shelf blue light-emitting diodes (LEDs) were assembled to produce a 225W optical power transmitter and a standard optical tranducer was used to convert the optical beam to electrical power necessary to charge the batteries. The transmission distance can reach up to 10 meters and it varies according to the wavelength of the light, the type of seawater, and operational depth. The performance of the technology met the initial expectation and the analysis of the data from the experiment has identified science and technology (S&T) gaps to be filled in order to achieve the full potential of uFSO-PT.