Propagation of modulated optical beams carrying orbital angular momentum in turbid water.

The attenuation and temporal dispersion of beams with and without orbital angular momentum (OAM) underwater are investigated in a controlled laboratory water tank environment. Both spherical polystyrene beads and a commercial antacid are used to determine the effect of scattering particle size and shape on the results. Varying concentrations of the scattering agents were used to study the propagation of light in both minimally scattered and multiply scattered regimes (over 20 attenuation lengths). To study temporal dispersion, a custom diode seeded fiber amplified laser source is used to modulate beams up to 1 GHz, and diffractive spiral phase plates are used to compare performance over different spatial modes. We observe an increase in received signal with increasing OAM order (|m|=0, 8, and 16) under multiple scattering conditions. Initial experimental results suggest that this variation is dependent on particle shape and size. We do not observe any dependency of OAM order on temporal dispersion.