拉盖尔—高斯光束湍流大气传播特性

发布时间：2018-05-03 09:03

  本文选题：自由空间光通信 + 大气湍流　； 参考：《中南民族大学》2015年硕士论文

【摘要】：近年来,轨道角动量已成为自由空间光通信(free-space-optical-communication,FSO)领域内的研究热点,并取得了较快进展。利用OAM光束进行信息交换、复用,并以此为基础,与其他传统复用技术相结合,可大幅度提高光通信数据传输容量和光谱效率。然而OAM光束在大气空间传播时,由于湍流的作用,会引起一系列湍流效应,如误码率增加、光强波动以及FSO系统信道容量降低。因为任意拓扑荷轨道角动量的光束都可以通过具有螺旋相位波前的拉盖尔—高斯光束(LG)线性组合表示,因此对此类光束的研究可以归为对LG光束的研究。本论文重点研究LG光束在大气的传播过程中特性变化情况,分析有无湍流的性能差异。首先,基于傅里叶光学理论推导出涡旋光束的菲涅尔衍射积分的角谱形式;然后采用分谐波的方法改进Monte-Carlo大气相位屏;据此利用MATLAB工具对LG在湍流大气中的传播进行建模分析,获得其传播特性。通过数值分析讨论光束光强和相位分布与湍流、OAM值、距离之间的关系,利用桶中功率(Power In Bucket,简称PIB)评估LG光束与高斯光束、点光源三者的抗湍流能力,研究结果表明,LG光束在大气湍流中的传播特性与无湍流条件相比差异较大:在湍流中传播时,当增加LG光束的传播距离,会降低光束的聚焦能力,光束有明显扩散;光束本身特有环状光强分布和螺旋相位分布受湍流作用而发生严重畸变,畸变的程度与OAM值的大小、湍流强度、传播距离均紧密相关。最后,通过对比PIB曲线,还发现携带不同OAM值的LG光束的抗湍流能力具有明显的差异。本文利用傅里叶光学,结合“光束分步传播法”和相位屏法,设计了一套现实可行的MATLAB理论分析与数值仿真方法,并推导出具体角谱形式的光束衍射模型及其对应的抽样限制条件,从而获取最精确的仿真结果;明确了LG光束与湍流的关系。这些方法和结论对较全面地了解OAM光束大气通信特性具有重要意义,可为OAM光通信系统仿真及其应用领域的深入研究提供思路和理论参考。
[Abstract]:In recent years orbital angular momentum has become a research hotspot in free-space-optical-communication FSOs and has made rapid progress. The data transmission capacity and spectral efficiency of optical communication can be greatly improved by using OAM beams for information exchange and multiplexing and combining with other traditional multiplexing techniques. However, when the OAM beam propagates in atmospheric space, it will cause a series of turbulent effects due to turbulence, such as the increase of bit error rate, the fluctuation of light intensity and the decrease of channel capacity in FSO system. Since beams with arbitrary topological charged orbital angular momentum can be expressed by a linear combination of Laguerre- beams with helical phase wavefront, the study of such beams can be classified as the study of LG beams. In this paper, the characteristics of LG beams propagating in the atmosphere are studied, and the performance difference of turbulence is analyzed. Firstly, based on Fourier optics theory, the angular spectrum of Fresnel diffraction integral of vortex beam is derived, then the phase screen of Monte-Carlo atmosphere is improved by subharmonic method. Based on this, LG propagation in turbulent atmosphere is modeled and analyzed by using MATLAB tool. To obtain its propagation characteristics. The relationship between the intensity and phase distribution of the beam and the value and distance of the turbulence is discussed. The anti-turbulence ability of LG beam, Gao Si beam and point light source is evaluated by using the power in bucket Bucket. The results show that the propagation characteristics of LG beams in atmospheric turbulence are different from those without turbulence. When the propagation distance of LG beams in turbulence is increased, the focusing ability of LG beams will be reduced and the beam diffusion will be obvious. The intensity distribution and helical phase distribution of the beam itself are distorted by turbulence, and the degree of distortion is closely related to the magnitude of OAM value, turbulence intensity and propagation distance. Finally, by comparing the PIB curves, it is found that the anti-turbulence ability of LG beams with different OAM values is obviously different. In this paper, a set of practical MATLAB theory analysis and numerical simulation method is designed by using Fourier optics, combining with "beam step propagation method" and "phase screen method". The beam diffraction model in the form of angular spectrum and its corresponding sampling limiting conditions are derived to obtain the most accurate simulation results, and the relationship between LG beam and turbulence is clarified. These methods and conclusions are of great significance in understanding the atmospheric communication characteristics of OAM beams, and can provide a theoretical reference for the further study of the simulation of OAM optical communication systems and their applications.
【学位授予单位】：中南民族大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN929.1
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本文编号：1837877