Beam wander due to optical turbulence in water (Conference Presentation)

Abstract

Optical methods to communicate or sense in the ocean environment can be effected inhomogeneities in the index of refraction called optical turbulence. Beam wander introduced by optical turbulence is of particular interest for optical means relying on the propagation of a well-defined laser beam such as free space communication and laser line scan. Here we present a comprehensive study of beam propagation simulations, lab experiments, and field measurements of laser beams propagating through varying degrees of optical turbulence. For the computational part of the investigation a true end to end simulation was performed. Starting with a CFD simulation of Rayleigh–Benard convection the temperature fields where converted to index of refraction phase screens which then where used to simulate the propagation of a focused Gaussian laser beam via the split-step Fourier method. Lab experiments where conducted using the same parameters as in the simulation using a good quality TEM00 beam and a CCD camera to record data. For the field experiments a Telescoping Ridged Underwater Sensor Structure (TRUSS) was equipped with a transmitter and a receiver capable of analyzing a multitude of laser beams simultaneously. The TRUSS was deployed in the Bahamas to record beam wander under weak optical turbulence conditions above and stronger optical turbulence conditions inside the thermocline. The data from the experimental and lab experiments are compared and the strength of the optical turbulence in terms of the structure parameter Cn2 are extracted. We also extract Cn2 from the TRUSS experiments and in doing so provide, for the first time, a quantitative estimate for the strength of optical turbulence in the ocean.