Underwater Bessel-like beams with enlarged depth of focus based on fiber microaxicon

Underwater optical wireless communication, which is useful for oceanography, environmental monitoring, and underwater surveillance, suffers the limit of the absorption attenuation and Mie-Rayleigh scattering of the lights. Here, Bessel-like beams generated by a fiber microaxicon is utilized for underwater wireless propagation. Underwater, the cone angle for generating Bessel-like beams starts from 46, which is smaller than that in air for Bessel-like beams. When the cone angle of the fiber microaxicons is about 140, the depth of focus underwater, which is four times as long as the depth of focus in air, has enlarged about 28 m, 36.12 m, and 50.7 m for 470 nm, 520 nm, and 632 nm visible lights. The transmission distance of the Bessel beams for visible lights has been simulated by using Henyey-Greenstein-Rayleigh phase function methods and spectral absorption by bio-optical model due to Monte Carlo methods. The results show that the propagation distance could reach 4000 m, which overcome the limit of the Mie-Rayleigh scattering and absorption attenuation underwater.