Channel capacity of focused hypergeometric-Gaussian type-II beams in ocean turbulence

The channel capacity of the hypergeometric-Gaussian type-II (HyGG-II) beam propagating in ocean turbulence is investigated in this work. A method of utilizing a focusing mirror to enhance the channel capacity is further proposed. Comparison among focused HyGG-II beam, unfocused HyGG-II beam and Laguerre Gaussian beam is also carried out. The results indicate that the employment of focusing mirrors is effective in enhancing the channel capacity, however, the corresponding transmission distance range is restricted to about 100 m. Optimal enhancement is observed near the convergence point of the HyGG-II beam focused by mirrors. By increasing the wavelength and adjusting the focal length of the focusing mirror or the waist radius of the HyGG-II beam, the channel capacity can be further improved. Moreover, when the HyGG-II beam is transmitted in oceanic turbulence characterized by a smaller dissipation rate of kinetic energy per unit mass and a larger dissipation rate of mean-squared temperature, the enhancement effect of the focusing mirrors on the channel capacity is more pronounced. Compared with Laguerre Gaussian beams, HyGG-II beams exhibit superior channel capacity at the same transmission distance, no matter whether focusing mirrors are used. The findings can serve as a reference for designing underwater wireless optical communication systems based on the HyGG-II-beam.