自适应光学在自由空间光通信大气补偿中的应用研究

发布时间：2019-03-23 19:58

【摘要】：自由空间光通信（FSO）是一种新型的无线通信方式，它包括很多的应用领域。例如：深空、中轨道、地面站之间的FSO通信，在某些情况下还可以利用其进行卫星与地面站之间的通信，在一般情况下又把地面站之间的激光通信称为大气激光通信。自由空间光通信之所以会受到越来越多国家学者们的关注，主要是由于FSO通信有着以下的几个优点：FSO通信技术能够提供相当高的传输速率，不亚于光纤的传输速率，甚至在某些情况下，FSO通信的最高速率已经可以达到5.6Gb/s，，最远可传送4.5km；FSO通信技术没有频谱的限制，对于频谱资源的分配与普通射频无线通信相比有着很大的优势。在FSO通信技术的发展中也存在着很多问题，在可见光在传输中，一个限制通信质量和通信距离的瓶颈就是大气衰减和光强起伏。大气吸收和散射会导致激光强度严重衰减，大气湍流会导致大气闪烁、光束漂移、到达角起伏和波前畸变等效应。为了克服大气湍流的影响、实现有效的信道补偿，需要进行大量的实验研究和理论探索。自适应光学（AO）在FSO通信技术中的使用受到了越来越多人的重视。组合变形镜（CDM）在自适应光学中的使用是有先例的，但是不同于之前提过的基于变形镜冲程考虑的CDM的使用，本文提出的CDM的使用主要考虑变形镜本身的参数特征以及结构设计。考虑到不同的变形镜结构参数对于不同类型的波前畸变的补偿效果存在很大不同，本文考虑让两个变形镜各自补偿不同部分的波前畸变，从而达到最优的补偿效果。同时给出了一种两变形镜之间的解耦合算法—限定校正算法。传统的PID控制算法在AO系统或者自由空间光通信系统中的使用有一些缺陷或者限制：PID参数整定技术还不够成熟，在一般实际情况下还依赖于现场操作者的经验。在一些需要高精度高要求的场合，比如对于可见光通信大气通信系统，这是不可取的。而且，在某些强湍流的情况下波前传感设备的性能会急剧下降，这时基于智能优化控制算法的无波前传感的AO系统就变得很有意义。本文研究基于随机并行梯度下降（SPGD）算法，模拟退火（SA）算法，改进型人工鱼群（MAFS）算法，改进型混合蛙跳（MSFL）算法等优化算法的AO控制系统，仿真结果表明它们对波前畸变有较好的补偿效果，接收端光耦合效率有明显的提高。仿真结果表明，本论文所提出的CDM以及智能仿生优化算法可以在AO系统或者FSO系统中取得较好的效果，这些优化算法可以通过较少的迭代循环达到很好的最终收敛值，从而有效地改善了整个FSO通信系统的通信质量。
[Abstract]:Free space optical communication (FSO) is a new type of wireless communication, which includes many applications. For example, FSO communication between deep space, medium orbit and earth station can be used to communicate between satellite and ground station in some cases. In general, laser communication between ground stations is called atmospheric laser communication. The reason why free space optical communication has attracted more and more attention is that FSO communication has the following advantages: FSO communication technology can provide a fairly high transmission rate, no less than the transmission rate of optical fiber. Even in some cases, the maximum rate of FSO communication can already reach 5.6 GB / s, and it can transmit 4.5 km as far as possible. FSO communication technology does not have the limitation of spectrum, and it has great advantages over the common radio frequency radio communication in the allocation of spectrum resources. There are also many problems in the development of FSO communication technology. In the transmission of visible light, a bottleneck limiting the communication quality and communication distance is atmospheric attenuation and light intensity fluctuation. Atmospheric absorption and scattering will lead to serious attenuation of laser intensity, atmospheric turbulence will lead to atmospheric scintillation, beam drift, angle-of-arrival fluctuation and wavefront distortion. In order to overcome the influence of atmospheric turbulence and realize effective channel compensation, a lot of experimental research and theoretical exploration are needed. More and more people pay attention to the application of adaptive optical (AO) in FSO communication technology. There is a precedent for the use of composite deformable mirror (CDM) in adaptive optics, but is different from the use of CDM based on deformable mirror stroke considerations. The use of CDM in this paper mainly considers the parameter characteristics and structural design of the deformable mirror itself. Considering that different structural parameters of deformable mirror have different compensation effects for different types of wavefront distortion, this paper considers that the two deformable mirrors can compensate the wavefront distortion of different parts respectively, so that the optimal compensation effect can be achieved. At the same time, a de-coupling algorithm between two deformable mirrors, the finite correction algorithm, is presented. There are some defects or limitations in the use of traditional PID control algorithms in AO systems or free space optical communication systems: the PID parameter tuning technique is not mature enough, and in general, it depends on the experience of field operators. This is not desirable in situations where high precision and high requirements are required, such as for visible-light atmospheric communication systems. In addition, the performance of wavefront sensing equipment will decrease sharply under some strong turbulence conditions, so the AO system without wavefront sensing based on intelligent optimal control algorithm becomes meaningful. In this paper, the AO control system based on random parallel gradient descent (SPGD) algorithm, simulated annealing (SA) algorithm, improved artificial fish group (MAFS) algorithm, improved hybrid frog jump (MSFL) algorithm and other optimization algorithms is studied. The simulation results show that they have a good compensation effect on wavefront distortion, and the optical coupling efficiency of the receiver is improved obviously. Simulation results show that the CDM and intelligent bionic optimization algorithms proposed in this paper can achieve better results in AO or FSO systems. These algorithms can achieve good convergence values by less iterative cycles. Thus, the communication quality of the whole FSO communication system is improved effectively.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.1

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