Propagation Of Stochastic Electromagnetic Beams In Oceanic Turbulence

The coherence and polarization are two closely related aspects in statistical optics, which play an important role on properties of the beam transmission. After the unified theory of coherence and polarization was presented by Wolf in 2003, the theory of partially coherent light was generalized from scalar to vector and closely linked with the polarization of the optical field. It has not only enriched the theory of optics, but also brought new insights into many aspects in statistical optics. The development has important applications, such as tracking, remote sensing, and optical communication. In recent years a lot of papers have appeared on polarization changes of beams propagating through optical turbulence. The best two examples of naturally optical turbulence are atmosphere and ocean. Both media have been explored to some extent, however atmospheric turbulence has received much more attention and is believed to be better understood. Atmospheric optical turbulence is primarily caused by fluctuating temperature, oceanic turbulence is induced by temperature and salinity fluctuations. The two power spectral have been separately measured a fairly long time ago but only recently have been analytically combined and creating a comprehensive model for the ocean. This model is a combination of both salinity and temperature fluctuation.Recently the interest in optical underwater communications, imaging and sensing appeared and it has become important to investigate how oceanic turbulence affects stochastic electromagnetic beams. But compared with the turbulent atmosphere, light propagating through oceanic turbulence is a relatively unexplored topic. In this dissertation, we investigate various properties of stochastic electromagnetic beams on propagation through oceanic turbulence, and derived some meaningful results.The dissertation is divided into five chapters:Chapter 1:After analyzing the situation and trend at home and abroad, we emphasize the motivation and significance of this dissertation. Then we introduce the fundamental method and the theoretical basis used in our work. Finally, some current research keypoints on this field are summarized and analyzed, such as the spectral degree of cross-polarization and three-dimensional stochastic electromagnetic beams.Chapter 2:On the basis of the extended Huygens-Fresnel principle, an analytical propagation expression for the elements of the cross-spectral density matrix of a stochastic electromagnetic beam through oceanic turbulence is derived. From this formula the spectral density, the spectral degree of coherence, the spectral degree of polarization, the orientation angle and the degree of ellipticity of such a beam on propagation are determined. Some numerical calculations are illustrated relating to the electromagnetic Gaussian Schell-model beams propagating through the oceanic turbulence. The results indicate that the spectral degree of coherence of stochastic electromagnetic beams tends to zero with the increasing of propagation distance through the oceanic turbulence. It is also found that the changes in the statistical properties of the anisotropic source on propagation are qualitatively different from that of the isotropic source.Chapter 3:In this chapter, we investigate the characteristics of astigmatic stochastic electromagnetic beams through oceanic turbulence. Taking the electromagnetic Gaussian Schell-model (GSM) beam as an example, the analytic expressions for the spectral density and the spectral degree of polarization of the beam propagating the oceanic turbulence are derived. It is indicated that the spectral density along the z-axis of the GSM beam in the oceanic turbulence is severely influenced by the source correlation properties, as well as by the sea-related parameters. We show that the characteristics of the spectral density along the x-axis, y-axis and z-axis of astigmatic electromagnetic GSM beams passing through the oceanic turbulence are qualitatively different. Furthermore, we find that as the astigmatic coefficient becomes larger, the maximum value of the spectral density along the z-axis increases rapidly and the point take the maximum value become closer to the source plane. Finally, the results have shown that different strengths of astigmatism have different effects on the spectral degree of polarization.Chapter 4:Taking the Gaussian Schell-model (GSM) beam as a typical example of partially coherent beams, closed-form expressions for the mean squared beam width, power in the bucket (PIB),βparameter, and Strehl ratio characterizing the beam quality of partially coherent beams propagating through the oceanic turbulence are derived and illustrated both theoretically and numerically. It is shown that turbulence results in degradation of the beam quality and partially coherent beams are less affected by the oceanic turbulence than the fully coherent ones.Chapter 5:We outline the work already done and discuss plans for future work.