Effects Of Oceanic Turbulence On Propagation Of Vortex Pulsed Beams

With the development of technology and economy,terrestrial resources can no longer satisfy the expanding global demand for resources,and marine exploration became commonplace.Compared with the ocean traditional acoustic communication,the underwater wireless optical communication system(UWOCS)has the advantages of high channel capacity,low delay and high security.The UWOCS can satisfy the demands of constructing a long-distance secure underwater sensing system and communication network with high-speed bulk data.Especially,the information carrier of UWOCS adopts vortex beam,which has larger channel capacity,better anti-diffraction ability and higher security.However,the spiral phase structure of vortex beam is vulnerable to turbulent disturbances in ocean turbulence,resulting in attenuation effects such as fluctuations in transmitted signal intensity,beam drift,expansion and jitter,thus reducing the communication performance of UWOCS.Hence,it is an important scientific research topic to study the interaction between continuous or pulsed vortex beam and oceanic turbulence,improve the anti-turbulence disturbance ability of vortex pulse beam,and effectively optimize the communication performance of UWOCS.The main innovations of this thesis are as follows:1.A new vortex pulse beam vortex X-waves and localized Lommel-Gaussian vortex beams are introduced into UWOCS research.The interaction between the new vortex pulse beam in UWOCS and oceanic turbulence is being investigated.Based on the optical field of vortex X-waves and localized Lommel-Gaussian vortex beams and the power spectrum of refractive index fluctuation in oceanic turbulence,the correlation equations are respectively derived by Rytov approximation,thus the propagation model of new vortex pulse beam in ocean turbulence are established,and the research of vortex X-waves and localized Lommel-Gaussian vortex beams is advanced.2.To study the inhibitory effect of turbulence on the propagation of vortex X-waves and localized Lommel-Gaussian vortex beams in the ocean,we obtain the analytical expressions of probability density of vortex X-waves and localized Lommel-Gaussian vortex beams by using the correlation equation.The detection probability and channel capacity models of vortex X-waves and localized Lommel-Gaussian vortex beams propagating in ocean turbulence are established,and the influences of oceanic turbulence and beam source parameters on channel capacity are studied.3.Effects of unstable stratification and anisotropic general ocean turbulence on temproal broadening of vortex pulsed beams.Theoretical and experimental explorations have demonstrated that there are unstable stratified turbulence layers in general ocean turbulence due to wind mixing and atmospheric heat exchange.Meanwhile,the general ocean turbulence is anisotropic due to the periodic rotation of the earth.Anisotropy and unstable stratification are introduced in the study of temporal broadening for vortex pulse beam propagation in general ocean turbulence.Using the Rytov approximation and the temporal-moment method,temporal broadening model for propagation of vortex pulse beam in general ocean turbulence is established.It is found that the temporal broadening changes of vortex pulse beam propagating in stable stratified ocean turbulence are significantly different from those in unstable stratified ocean turbulence.In conclusion,the main objective of this thesis is to study the propagation characteristics of vortex pulse beams in ocean turbulent channel.By establishing the correlation function of vortex pulse beams propagation in oceanic turbulence,the effects of ocean turbulence and beam source parameters on the UWOCS based on vortex pulse beam are analyzed by probability density,detection probability,channel capacity and temporal broadening,which provided a reference for studying the propagation of vortex pulse beam in oceanic turbulence.