提高空间光通信系统耦合效率的研究

发布时间：2018-03-19 03:01

本文选题：光纤耦合　切入点：自由空间光通信　出处：《中国科学院大学(中国科学院光电技术研究所)》2017年硕士论文　论文类型：学位论文

【摘要】：随着空间通信技术在社会服务、科学应用等方面发挥着越来越重的作用,传统微波通信已经难以满足一些通信链路的需求,而自由空间光通信技术的通信容量大、传输速率快、抗干扰能力强,已经成为了通信领域的研究热点。同时,为了提高通信链路的传输速率与探测灵敏度,基于光纤通信技术的自由空间光通信系统也得到了广泛的研究与应用。对于上述空间光通信系统来说,首先需要将接收到的空间光束耦合进单模光纤中。然而,空间光束到单模光纤地耦合总是十分困难,其主要受到两方面的限制:单模光纤纤芯尺寸小,对准误差、热效应等因素会造成聚焦光斑无法精确对准单模光纤;空间光束传输质量极易受到大气湍流效应影响,光束波前相位畸变严重。以上因素都会导致通信系统的误码率增加,严重影响通信链路的正常工作。因此,保证空间光束高效地耦合进单模光纤是空间光通信系统中的关键技术之一。自适应光学技术能够对大气湍流扰动所造成的波前畸变进行实时测量和校正,有效改善光束传输特性。但是,平台振动、系统噪声等因素的存在,仍会导致聚焦光斑随机偏移单模光纤,光纤耦合效率有待进一步的提高。为了充分发挥自适应光学技术的优势,提高空间光通信系统的耦合效率与稳定性,在系统中引入校正机构结合自适应光学技术构成二级校正系统是十分必要的。本文首先以空间光束耦合单模光纤的理论模型为基础,仿真分析了静态对准误差以及随机抖动对单模光纤耦合效率的影响,结果表明:两者的存在会引起严重的耦合损耗,为了获得较高的耦合效率,必须对其进行补偿。然后对不同湍流强度时耦合效率的变化情况展开了研究,根据结果可知:湍流强度越强,通信系统的光纤耦合效率衰减越严重,需要对更高阶的像差进行校正才能改善耦合效率。利用AO技术对湍流效应影响进行补偿实验,实验结果表明,AO技术能够有效缓解湍流效应,校正波前畸变,光束传输质量得到改善。为了进一步改善自适应光学系统中的光纤耦合效率,针对单模光纤耦合方案展开了研究:将模拟退火算法与随机并行梯度下降算法应用于光纤耦合方案,分别对两种算法的基本原理以及在改善光纤耦合效率上的应用流程展开了讨论,通过数值仿真对比分析了两者对耦合效率的优化情况以及收敛速度;在此基础上,提出了一种基于光栅螺旋扫描与随机并行梯度下降算法的单模光纤耦合方案,并针对随机抖动情况仿真分析了耦合效率的优化迭代过程与收敛效果。仿真结果表明:通过设定最佳扫描步长,光栅螺旋扫描算法能够有效的校正初始对准误差,校正成功概率高于99%,并且校正后的残余初始偏移集中在0.5μm 6.5μm范围内,耦合效率得到初步改善;开启SPGD控制算法后,聚焦光斑与光纤间的随机横向偏移得到校正,耦合效率能够有效提升至0.81,接近无湍流情况下的理论极限。根据上述方案搭建了相关的软硬件实验平台,实验结果表明,该单模光纤耦合方案可以有效校正横向偏移误差,光纤耦合功率能够快速收敛到极值。
[Abstract]:With the development of space communication technology in the service of society, plays a more and more important role in scientific applications, traditional microwave communication has been difficult to meet the needs of some communication link, and communication capacity of free space optical communication technology, fast transmission speed, strong anti-interference ability, has become a hot research field in communication. At the same time. In order to improve the transmission rate and the detection sensitivity of the communication link, free space optical communication system of optical fiber communication technology has been widely studied and applied. Based on the space optical communication system, first of all need to be received by the space beam coupled into a single-mode fiber. However, the beam space to single mode fiber coupling is always very difficult and it is constrained by two aspects: single-mode fiber core size, alignment error, thermal effect and other factors will cause the focal spot of inexact quasi monomode fiber Space; beam quality is extremely easy to be influenced by the effects of atmospheric turbulence, the beam wavefront distortion is serious. These factors will lead to the error rate of communication system increase, seriously affect the normal work of the communication link. Therefore, to ensure the efficient coupling of spatial beam into a single-mode fiber is one of the key technologies of space optical communication system. Adaptive optics technology the atmospheric turbulence wavefront distortion caused by the real-time measurement and correction, effectively improve the beam transmission characteristics. However, the vibration, noise and other factors, will lead to the focused spot random offset single-mode optical fiber, optical fiber coupling efficiency to be further improved. In order to give full play to the advantages of adaptive optics technology, improve coupling efficiency and the stability of space optical communication system, introducing the correction mechanism combined with two order correction adaptive optical system technology in the system The system is very necessary. In this paper, a theoretical model of spatial beam coupling single-mode fiber based on the simulation analysis of static alignment error and the influence of random jitter on single-mode fiber coupling efficiency. The results showed that the presence of both will cause the coupling loss is serious, in order to obtain high coupling efficiency, the compensation is necessary. Then the change of coupling efficiency when different turbulence intensity was studied. According to the results, the turbulence intensity is stronger, the coupling efficiency of the fiber communication system's attenuation is more serious, the need for more high order aberration in correction can improve the coupling efficiency. The influences of the turbulence compensation experiment using AO technology, the experimental results show that AO technology can effectively alleviate the effect of turbulence wavefront distortion, beam quality improved. In order to further improve the fiber coupling efficiency in adaptive optical system According to the rate of single mode fiber coupling scheme is studied: simulated annealing algorithm and stochastic parallel gradient descent algorithm is applied to the optical fiber coupling scheme, respectively. The basic principle of the two kinds of algorithm and application in improving the process of fiber coupling efficiency is discussed, through numerical simulation, comparative analysis of the optimization of the coupling efficiency of both convergence and speed; on this basis, puts forward a raster spiral scanning with stochastic parallel gradient descent algorithm based on single-mode fiber coupling scheme, and analyses the iterative process of optimization and the convergence effect of the coupling efficiency for random jitter simulation. The simulation results show that by setting the optimal scanning step, raster spiral scanning algorithm can effectively correct the initial alignment error the correction of the probability of success is higher than 99%, and the initial residual offset correction after concentrated in 0.5 m 6.5 m range, coupling effect The rate of initial improvement; open SPGD control algorithm, spot and fiber between random transverse offset correction, which can effectively improve the coupling efficiency to 0.81, close to the theoretical limit of non turbulent condition. According to the hardware experimental platform has been set up. The experimental results show that the single-mode fiber coupling scheme can effectively the transverse offset error correction, fiber coupled power can quickly converge to the extreme.

【学位授予单位】：中国科学院大学(中国科学院光电技术研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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