Search

Consider the evolution of the wander and M2-factor of Mathieu Gaussian-Schell beam in turbulent ocean. We develop models for wander and M2-factor of this beam based the theory of wigner distribution function. The influences of the oceanic parameters on the wander and M2-factor are discussed in detail. It is found that as the propagation distance, the dissipation rate of temperature variance, the eddy diffusivity ratio and ratio of temperature and salinity contributions to the refractive-index spectrum increases, both M2-factor and beam wander increase; but M2-factor and beam wander increase with the decreasing of initial beam width, the kinetic energy per unit mass of fluid. However, as the variation of ellipticity factor and OAM quantum number increase, the evolution of M2-factor and beam wander are some complexes. The influences of coherent width of light source and wavelength on the M2-factor and beam wander are negligible. Our results are helpful in the design of an optical communication system in an oceanic environment.

By developing new wave structure function of a beam waves, we derive the transmitting probability of signal vortex modes in oceanic turbulence based on Rytov approximation theory. Applying this transmitting probability of signal vortex modes, we study the influence of oceanic turbulence on the transmittance of the vortex modes carried by Mathieu-Gaussian beam. This model shows the transmitting probability of Mathieu-Gaussian beam with narrow initial beam width, long wavelength, and small ellipticity parameter is higher than the transmitting probability of the signal vortex modes in case of the beam with wide initial beam width, short wavelength, and great ellipticity parameter. Furthermore, when Mathieu-Gaussian beam has a suitable semi-cone angle, the effect of weak-turbulence channel on the transmitting probability of signal vortex modes with different topological charge can be ignored. Mathieu-Gaussian beam is a more suitable carrier for high information channel of underwater wireless optical communication than Laguerre-Gaussian beam.

The long-term beamwidth and quivering of modified Bessel Gaussian Schell vortex beam in oceanic turbulence are derived based on the extended Huygens-Fresnel principle. With the help of these models, we analyze the effect of vortex beam and turbulence parameters on long-term beamwidth and beam quivering. We find that modified Bessel Gaussian Schell vortex beam has smaller beam quivering when beam has higher orbital angular momentum quantum number, larger beam waist, larger width parameter, longer wavelength and lower coherent length. We also find that turbulence of large temperature-salinity contribution ratio, large inner scale of turbulence, large outer scale of turbulence and small rate of dissipation of the kinetic energy per unit mass of fluid is more likely to cause beam quivering. The variation trends of long-term beamwidth with beam parameters are opposite to that of beam quivering.

By developing the spatial coherence radius of a collimated Gaussian beam, we derive the normalized received probability of orbital angular momentum (OAM) modes of the random finite energy frozen wave (FW) in anisotropic weak seawater turbulence based on Rytov theory. We investigate the influences of seawater turbulence and beam parameters on the normalized received probability of OAM modes. This study concludes that the normalized received probability of signal OAM modes increases as the anisotropic factor of the seawater turbulence increases. The rate of dissipation of kinetic energy per unit mass of fluid and the inner scale of turbulence but the normalized received probability of signal OAM modes decreases as the increase of temperature-salinity contribution ratio and the dissipation rate of the mean-squared temperature. For the smaller received diameter of the receiver, larger transverse size and longer signal wavelength, the signal OAM modes achieve the higher normalized received probability. The normalized received probability of signal OAM modes is independent of the quantum number of OAM modes in weak seawater turbulence. The security of signal transmission can be enhanced by designing the position and interval of signals that can be detected along the optical path.

By analyzing the construction features of a Lommel Gaussian-Schell beam and the beam wander for Gaussian beams, we derive the closed-from approximations expression for the wander of Lommel Gaussian-Schell beam through unstable stratification and weak ocean-turbulence. Turbulence conditions with a smaller outer- and inner-scale of turbulence usually cause smaller beam wander. There is a extremum value βex of the beam paraxial coefficient corresponding to the maximum beam wander for given parameters of turbulence and beam. We can utilize larger beam waist, longer wavelength, higher quantum number of orbital angular momentum and larger asymmetry factor, meanwhile, avoid extremum value βex to reduce the beam wander. The influence of salinity fluctuations of turbulent ocean on beam wander is greater than temperature fluctuations. Under the assumption of unit diffusivity ratio, the beam wander is either underestimated or overestimated. Keywords: Beam wander, Lommel Gaussian-Schell, Turbulent ocean

We propose a model of the fiber coupling efficiency for a partially coherent collimating laser beam propagating through turbulent biological tissue to fiber. By studying the influence of link parameters on fiber coupling efficiency, we find that there are optimal focal length and transmitting beam radius for specific turbulent tissue. We also find that a larger characteristic length and small length-scale factor, or smaller fractal dimension and strength coefficient of refractive-index fluctuation will lead to larger fiber coupling efficiency. In order to improve the fiber coupling efficiency, we recommend select the optimum focal length, moderate transmitting beam radius, lower aperture diameter of the coupling lens, longer wavelength and higher coherent degree of light source. 2000 MSC: 41A05, 41A10, 65D05, Keywords: Fiber coupling efficiency, Biological tissue, Turbulence, Optimum parameter, Laser beam