Optical Modem Technology for Seafloor Observatories

Regional cabled observatories will bring broadband Internet to the seafloor around areas that include hydrothermal vent sites and other scientifically interesting features. The ideal platform for exploring these sites in response to episodic events is a remotely-piloted, autonomous underwater vehicle (AUV) that is capable of sending back high-quality video or other high-rate sensor data. The combined requirement of remote command/control and high data rates argues for a bi-directional optical communications link capable of streaming data at 1-10 Mbit per second rates. In this paper, we present a preliminary design for an optical modem system based on an omnidirectional source and receiver. The functional requirements and system constraints driven by use case scenarios are first reviewed. This is followed by a discussion of the optical transmission properties of seawater and the resulting impact on detection in high-rate communications, including coding considerations. A link budget and the data rate versus range relationship are developed. Validation results in a test tank and in the ocean will then be reviewed