Remote, aerial, translayer, nonlinear downlink underwater acoustic communication.

Abstract

The nonlinear mechanism for optical to acoustic energy conversion is explored for optoacoustic communication from an in-air platform to a submerged platform. This downlink communication can provide a bell ringer function and transmission of text and data. The nonlinear conversion mechanism, also known as the nonlinear optoacoustic regime where focused laser energy is converted to sound at the air-water interface, involves a phase change of the water medium through evaporation and vaporization leading to plasma production. The nonlinear conversion mechanism provides a more efficient, i.e., higher source level, controllable method for producing underwater acoustic signals. A means of deterministically controlling the spectrum of the underwater acoustic signal has been investigated and demonstrated by varying the laser-pulse repetition rate to provide M-ary frequency shift keyed signaling. This physics-based conversion process provides a methodology for providing low probability of intercept signals whose information is embedded in noiselike signals. These laser generated signals can then be used in a frequency hopped spread spectrum technique with the use of the proper receiver structures to take advantage of the frequency diversity and periodicity inherent in this type of signal structure that could also be used to combat frequency selective fading in underwater acoustic channels.