Properties of focused Laguerre–Gaussian beam propagating in anisotropic ocean turbulence

We analyze the properties of a focused Laguerre–Gaussian (LG) beam propagating through anisotropic ocean turbulence based on the Huygens–Fresnel principle. Under the Rytov approximation theory, we derive the analytical formula of the channel capacity of the focused LG beam in the anisotropic ocean turbulence, and analyze the relationship between the capacity and the light source parameters as well as the turbulent ocean parameters. It is found that the focusing mirror can greatly enhance the channel capacity of the system at the geometric focal plane in oceanic turbulence. The results also demonstrate that the communication link can obtain high channel capacity by adopting longer beam wavelength, greater initial beam waist radius, and larger number of transmission channels. Further, the capacity of the system increases with the decrease of the mean squared temperature dissipation rate, temperature-salinity contribution ratio and turbulence outer scale factor, and with the increase of the kinetic energy dissipation rate per unit mass of fluid, turbulence inner scale factor and anisotropy factor. Compared to a Hankel–Bessel beam with diffraction-free characteristics and unfocused LG beam, the focused LG beam shows superior anti-turbulence interference properties, which provide a theoretical reference for research and development of underwater optical communication links using focused LG beams.