海气湍流信道中的光束偏振起伏

发布时间：2018-11-03 18:26

【摘要】：无线光通信作为当今通讯领域新兴的一门技术,具有设备轻便,保密性好,传输信息量大等特点,已成为当今学者研究的热点。光的偏振,在经典及量子领域都有其重要应用价值。由于光的偏振态能够储存信息,就可利用此特性实现无线光通信。然而,光束在大气中传输时不可避免的会遭受恶劣天气及湍流等因素的干扰,使得无线光通信性能的稳定性受到影响。所以研究光束在湍流信道中的传输问题不仅具有理论意义,而且对自由空间量子通信系统的设计也有重要指导作用。工作内容如下:本文主要探讨了高斯-谢尔光束传输在海气湍流信道环境下的偏振起伏问题。通过应用广义惠更斯-菲涅尔积分和Rytov近似等方法,建立了光束传输在海气湍流信道下的偏振模型,并且导出了球面波的横向相干长度。另外,基于交叉谱密度矩阵,建立了高斯-谢尔电磁光束的平均偏振度模型。最后,通过数值模拟详细的分析了高斯-谢尔光束传输在海气柯尔莫哥诺夫与非柯尔莫哥诺夫湍流信道下的偏振起伏特性,并且对比了光束传输在海气与陆气信道之间的偏振起伏差异,得出了如下结论:1.高斯-谢尔光束传输在海气柯尔莫哥诺夫湍流信道时,偏振度会随着光子数目和光源相干宽度的增加而增加。通过对比海气与陆气柯尔莫哥诺夫湍流信道下的偏振度差异,发现光束在海气湍流信道中传播时受到的湍流衰减效应相比陆气信道要明显,也就是说在海气湍流信道中的退偏效应较强。2.高斯-谢尔光束在海气非柯尔莫哥诺夫湍流信道传输时,研究发现湍流内尺度的增大有助于我们获得较大的球面波横向相干长度和较高的偏振度,并且湍流外尺度对偏振度的影响可以被忽略,通过引入各向异性因子分析得到:不论在海气或是陆气湍流信道环境下,湍流的各向异性程度越高,偏振度越强。3.利用交叉谱密度矩阵,建立了高斯-谢尔电磁光束传输在陆气与海气湍流信道中的平均偏振度模型。平均偏振度会随非柯尔莫哥诺夫谱指数的增加而增加,并且高斯-谢尔电磁光束配置数值较小的δ_(yy)、δ_(xx)、A_x与较大A_y参数时,能够减少光束在大气湍流中传播时受到的干扰。也就是说,通过选取特定参数可以实现较高质量的偏振通信。
[Abstract]:As a new technology in the field of communication, wireless optical communication has the characteristics of portable equipment, good confidentiality and large amount of transmission information. Polarization of light has important application value in classical and quantum fields. Since the polarization state of light can store information, wireless optical communication can be realized by using this characteristic. However, the stability of wireless optical communication is affected by the interference of bad weather and turbulence when the beam propagates in the atmosphere. Therefore, the study of beam propagation in turbulent channels has not only theoretical significance, but also plays an important role in guiding the design of quantum communication systems in free space. The main work is as follows: in this paper, the polarization fluctuation of Gauss-Schell beam propagation in air-sea turbulent channel is discussed. By using the generalized Huygens-Fresnel integral and the Rytov approximation, the polarization model of beam propagation in air-sea turbulent channel is established, and the transverse coherent length of spherical wave is derived. In addition, based on the cross spectral density matrix, an average polarization model of Gaussian Schell electromagnetic beam is established. Finally, the polarization fluctuation characteristics of Gauss-Schell beam propagating in the turbulent channel between Kormogorov and non-Kolmogorov at sea and air are analyzed in detail by numerical simulation. The difference of polarization fluctuation between sea and land air channel is compared, and the following conclusions are obtained: 1. The degree of polarization increases with the increase of the number of photons and the coherent width of the light source when the Gaussian Schell beam propagates in the Kelmogorov turbulent channel. By comparing the polarization difference between the sea and the land atmosphere in Kolmogorov turbulent channel, it is found that the turbulent attenuation effect of the beam propagating in the sea and air turbulence channel is more obvious than that in the land air channel. That is to say, the depolarization effect in the air-sea turbulent channel is strong. 2. 2. When the Gaussian Schell beam propagates in a non-Kolmogorov turbulent channel at sea and air, it is found that the increase of the internal scale of turbulence can help us to obtain larger transverse coherent length and higher degree of polarization of spherical waves. The influence of the external scale of turbulence on the degree of polarization can be neglected. By introducing anisotropy factor analysis, it is concluded that the higher the degree of anisotropy of turbulence is, the stronger the degree of polarization is. Based on the cross spectral density matrix, an average degree of polarization model of Gauss-Schell electromagnetic beam propagation in land-air and sea-air turbulent channels is established. The average degree of polarization increases with the increase of the non-Kolmogorov spectral exponent, and the Gauss-Schell electromagnetic beam has a smaller 未 _ (yy), 未 _ (xx), _ Ax and a larger ASP _ y parameter. It can reduce the interference of light beam propagating in atmospheric turbulence. That is to say, high quality polarization communication can be achieved by selecting specific parameters.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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