Study On Echo Scattering Characteristics Of Vortex Beam Through Rough Surface In Ocean Turbulence

The scattering characteristics of light echoes field are one of the key technologies for the integration of underwater laser communication and detection in the future.A typical vortex beam with the properties of hollowed light intensity distribution,phase spiral,and orbital angular momentum(OAM)orthogonality is the Laguerre Gaussian(LG)beam.Compared with Gaussian beam,it can carry more information,which is conducive to suppressing the ocean turbulence effect in the transmission process.This thesis mainly explores the echo scattering characteristics of vortex beams through Gaussian random rough surfaces in ocean turbulence,as follows:(1)Based on the research of the scattering characteristics of vortex beams passing through rough surfaces,a two-way propagation model of LG beams passing through Gaussian random rough surfaces in ocean turbulence was established.Analyzed the effects of different topological charges,ocean turbulence intensity,and different roughness parameters on the optical field intensity at the receiving end.It was discovered that when topological charges increase,speckle particle size at the receiving end drops but light intensity declines as ocean turbulence intensity and roughness increase.(2)Using the generalized Huygens Fresnel diffraction principle and the phase perturbation mechanism of ocean turbulence,an analytical expression for the average intensity of LG beams scattered by Gaussian random rough surfaces in ocean turbulence was derived,and the autocorrelation function of the echo intensity at the receiving end was further calculated.The influence of wavelength and waist radius of LG beam on the autocorrelation function of echo intensity was explored.Research has found that the stronger the ocean turbulence and the rougher the rough surface,the smaller the autocorrelation function of the echo light field,and the smaller the average size of the echo speckle particles.(3)The theoretical expression of the complex degree of coherence of the echo light field was derived and numerical simulations were conducted to explore the effects of light source parameters,ocean turbulence intensity,and roughness parameters on the complex degree of coherence of the echo light field.It is discovered that the influence of the rough surface on the complex degree of coherence of the light field can be ignored in comparison to the influence of the ocean turbulence when the coherence length of the rough surface is greater than the coherence length of the beam propagating in the ocean turbulence.The complex degree of coherence is influenced by both the ocean turbulence and the rough surface when the coherence length of the rough surface is smaller than the coherence length of the beam propagating in the ocean turbulence.The root mean square roughness of the rough surface has no effect on the complex degree of coherence of the echo light field.Underwater target identification technology has a theoretical foundation due to the analytical expression for the scattering light field of LG beams over rough surfaces in ocean turbulence and the theoretical expression for the complex degree of coherence of the echo light field derived in this thesis...