Uplink And Downlink Transmission Characteristics Of Blue-Green Laguerre-Gaussian Beam In Atmosphere-Ocean Cross Medium

About 70%of the earth is covered by the sea.At present,most underwater communication technologies use acoustic waves as carriers.But acoustic waves have shortcomings such as low bandwidth and poor confidentiality.With the rapid development of new-generation communication technology,the Laguerre-Gaussian beam has many advantages such as large information capacity,strong anti-interference,and high security.This thesis provides a theoretical basis for the blue-green Laguerre-Gaussian beam to realize uplink and downlink transmission across the atmosphere-ocean interface and optical communication experiments.The main research contents are as follows:1.Using the power spectrum inversion method to simulate atmospheric turbulence.Analyze the influence of atmospheric refractive index structure constant on atmospheric turbulence intensity.Using linear filtering method to simulate the dynamic sea surface under the JONS WAP sea spectrum,and compare the sea surface height fluctuations under different wind speeds.Based on the power spectrum inversion method,simulate ocean turbulence and study the effects of kinetic energy dissipation rate and mean square temperature dissipation rate on the intensity of ocean turbulence.2.The distribution characteristics of orbital angular momentum of the Laguerre-Gaussian beam in atmospheric turbulence and ocean turbulence are studied.The effects of wavelength,propagation path,and atmospheric turbulence intensity on the spiral spectrum of the LaguerreGaussian beam are analyzed in detail in the atmosphere.The effects of wavelength and ocean turbulence intensity on the spiral spectrum of the Laguerre-Gaussian beam are analyzed in detail in the ocean.3.Build the downlink propagation model of the blue-green Laguerre-Gaussian beam from the atmosphere to the ocean.The influence of different atmospheric turbulence intensity,sea surface with different wind speeds,ocean turbulence intensity,and different transmission distance on the transmission characteristics of blue-green Laguerre-Gaussian beam downward across the medium is studied.Discuss the difference between the vertical and oblique downward transmission of the atmosphere-ocean across media.4.Based on the total reflection and transmission of blue-green beams through the sea surface,the propagation characteristics and transmission scattering of the blue-green Laguerre-Gaussian beam through the sea surface are studied.The results show that the increase of atmospheric refractive index structure constant leads to the increase of atmospheric turbulence intensity above the sea surface.The increase in wind speed leads to greater fluctuations in sea surface height.The decrease of energy dissipation rate of ocean turbulent flow or the increase of mean square temperature dissipation rate lead to the increase of ocean turbulence intensity.The transmission quality of long wavelength LaguerreGaussian beams in atmospheric turbulence and ocean turbulence is better than that of short wavelength beams.The downlink transmission performance of blue-green Laguerre-Gaussian beams in atmospheric turbulence will be significantly better than that of uplink transmission.The greater the intensity of atmospheric turbulence or ocean turbulence,the more serious the spiral spectrum expansion of blue-green Laguerre-Gaussian beams,and the impact of ocean turbulence on beams is more serious than that of atmospheric turbulence.When the blue-green LaguerreGaussian beam propagates downlink across the atmosphere-ocean,the intensity attenuation and phase distortion are directly proportional to the intensity of atmospheric turbulence,sea surface wind speed and ocean turbulence.The increase of sea surface wind speed leads to serious phase distortion of the Laguerre-Gaussian beam,and the increase of transmission distance leads to the gradual degradation of the dark hollow distribution and the rotation distortion of the phase of the Laguerre-Gaussian beam.Compared with the vertical transmission of blue-green LaguerreGaussian beams,the oblique transmission quality is worse.The phase distortion of blue-green Laguerre-Gaussian beams propagating uplink on the sea surface is more serious than that propagating downlink.Compared with the uplink transmission and the downlink transmission,the wind speed has a greater impact on the scattering transmission coefficient during the uplink transmission.Compared to the sea surface wind region and wind speed,the wind speed will have a greater impact on the scattering transmission coefficient.