An adaptive data rate controller (ADRC) for the through cloud, undersea laser communications channel

The decades-old VLF radio system used to communicate with submerged submarines is limited to a few 10´s of bits per second, and the submarine must surface to respond. If radio cannot be used for reasons of covertness, the submarine is silenced. QinetiQ North America (QNA) is developing for DARPA an Adaptive Data Rate Controller (ADRC) for a Submarine Laser Communications (SLC) system utilizing wavelengths in the blue-green window of seawater. This SLC system can link a submarine at speed and depth with an aircraft above the clouds at data rates up to megabits per second during both day and night. The high peak power and monochromaticity of a laser, along with a very narrow-band optical filter, significantly improves rejection of solar background, and thus maximizes communication depth.