High speed wireless communication has proven elusive in subsea environments due to the inherent bandwidth limitations of acoustics and range limitations of other transmission modalities. A truly connected subsea system necessitates a high-speed, resilient architecture that can enable the integration of new sensor technologies and edge analytics and allow closed-loop monitoring and control of subsea operations for integrity monitoring and optimization. Like terrestrial Internet of Things applications, the realization of this "digital subsea" vision requires the application of high speed, point-to-point wireless technologies to complement rather than replace "hard-wired" communications such as optical fiber or acoustic systems. This work addresses the development of ULTRA (Underwater LASER Telemetry and Remote Access), an ultra-long range underwater laser communications system for use in critical points of the subsea communications architecture to increase reliability, operational flexibility, and reduce communication system maintenance associated with physical subsea connections.
To demonstrate the data capacity and range of ULTRA, a subscale laboratory point-to-point wireless laser communication system was constructed with the flexibility to transmit through either air or water. The test system used power and modulation frequencies for air, fresh water, and different qualities of seawater. Optical and RF encoding methodologies were implemented to facilitate and characterize data transmission through the various media. The laboratory experiment used a subscale, filtered, and attenuated 5 mW blue-green laser in a 22-meter folded path configuration to demonstrate real-time data transmission at 312 Megabit per Second (Mbps) data rate using single channel Quadrature Phase Shift Keying (QPSK) modulation. A field prototype ULTRA system will use an unattenuated 5 mW laser that can reach approximately 280-meter range at 312 Mbps in clear conditions, which are typical of deepwater subsea. The selection of laser power and data rate are considered operational tradeoffs in environments where underwater vehicles operate. The extended range of ULTRA can enable various use cases to greatly augment subsea data communications capacity to enable the "Digital Subsea".