Underwater Free-Space Optical Communication Using Smart Transmitters and Receivers

The number of unmanned vehicles and devices deployed underwater is rapidly increasing. Present underwater systems are acoustic and have relatively limited bandwidth. Underwater free-space optical communication is poised to augment acoustic communication underwater, and to provide high-bandwidth, short-range wireless links. Most underwater optical systems are point to point links with relatively strict pointing and tracking requirements. New communication strategies and networking protocols have the potential to greatly expand the capability to communicate between multiple mobile underwater platforms in water of varying quality.;In this research, compact smart transmitters and receivers for underwater free-space optical communications are demonstrated. The receivers have a segmented wide field of view and are capable of estimating angle of arrival of signals. The transmitters are highly directional with individually addressable light emitting diodes for electronic switched beam steering, and can estimate water quality from the backscattered light collected by a co-located receiver. Together, they form enabling technologies for non-traditional networking schemes in swarms of unmanned vehicles underwater.;Some of the contributions of this dissertation that can be leveraged to improve the performance of underwater free-space optical communication systems are:;1. The use of smart transmitters and receivers to show that strict pointing and tracking requirements typically associated with underwater free-space optical communication can be relaxed. This is a benefit to power and volume limited underwater vehicles.;2. The use of segmented field of view and electronic beam steering that enable the ability to obtain angle of arrival information. This information used with code division multiple access techniques allow the relative position and pose between systems to be obtained, as well as identify the platforms. This allows improved ability to communicate in the presence of other optical signals in a multi-platform environment.;3. Estimation of water quality from backscatter measurements to provide information about the underwater optical channel and to provide information for the system to adapt to a changing environment.;4. Some circuit implementations of how to implement smart transmitters and receivers, including a new digital to analog converter based bias-tee that shows an improved method of driving multiple diode lasers and light emitting diodes at high currents.