Short Range Underwater Optical Communication Links

Abstract

The future tactical ocean environment will be increasingly complicated. In addition to traditional communication links there will be a proliferation of unmanned vehicles in space, in the air, on the surface, and underwater. To effectively utilize these systems improvements in underwater communication systems are needed. Since radio waves do not propagate in sea water, and acoustic communication systems are relatively low bandwidth the possibility of high speed underwater optical communication systems are considered.

In traditional communication systems, constructing a link budget is often relatively straight forward. In the case of underwater optical systems the variations in the optical properties of ocean water lead to interesting problems when considering the feasibility and reliability of underwater optical links. The main focus of this thesis is to understand how to construct an underwater link budget which includes the effects of scattering and absorption of realistic ocean water.

The secondary focus of the thesis was to construct LED based optical communication systems. This required understanding the behavior of Gallium Nitride LEDs operated under intense electrical pulsing conditions. An optical FM wireless system was constructed for transmitting speech. An LED based Ethernet compatible digital communications system that was capable of operating at 10 Mbps was also constructed and packaged for underwater operation.