Simulation, Modeling, and Design of Underwater Optical Communication Systems

Underwater free-space optical communications has the potential to provide high speed, low latency communications for undersea vehicles and sensors. This thesis describes the design and validation of a Monte Carlo numerical simulation tool for underwater optical communications systems. The simulation tool can also be used more generally for other systems that require calculations of the underwater light-field. The program, named Photonator, was validated experimentally in a laboratory tank where the absorption and scattering was controlled by the addition of Maalox to vary the water conditions from open ocean to turbid harbor water. These results were also compared with custom blue/green light emitting diode and laser transmitters and receivers that allowed the wavelength and field-of-view (FOV) to be controlled.;An emphasis was placed on understanding the requirements of point-to-point underwater communication links. Results are presented for on and off-axis received power for a series of receiver apertures and fields-of-view. Also presented are the scattering histograms at the receiver and the temporal bandwidth of each communication link. A two-term exponential power loss model is developed and compared with the simulated outputs to agreement within 30% over twelve orders of magnitude power loss. This type of power loss model is useful in constructing link budgets which are more accurate than the usual Beer's law assumption in water environments where scattering is appreciable.;Several results are presented that are of interest to the underwater optical systems designer: 1. The simulations and experiments show that the power gain from FOV and aperture changes of an optical system are independent in highly turbid waters. 2. A power-law relationship between FOV and received power is shown for turbid water environments for fields-of-view up to 45 degrees. 3. A systematic series of simulations show how the scattering orders at the receiver evolve as water quality is varied which provides a physical underpinning to understanding temporal dispersion of underwater pulses. 4. A systematic series of simulations shows how the temporal bandwidth of underwater optical communication systems varies strongly with the receiver field of view, but weakly with aperture size.