量子通信光学地面站ATP关键技术研究

发布时间：2018-03-13 03:16

本文选题：量子通信　切入点：量子密钥分发　出处：《中国科学院研究生院（光电技术研究所）》2014年博士论文　论文类型：学位论文

【摘要】：量子密钥分发是量子通信中发展最为迅速、最为成熟的技术，具有量子力学基本原理保证的绝对安全性。受到光纤的损耗影响以及单光子探测器的特性限制，基于光纤的量子密钥分发距离已基本达到了极限。受地球曲率和远距离可视等条件的限制，地对地自由空间量子密钥分发也很难实现更远的距离，因此人们将目光投向卫星平台，通过建立卫星平台与光学地面站之间的高稳定低损耗量子信道，可实现超远距离的量子密钥分发。通过卫星中继，将有可能实现覆盖全球的量子通信网络，这也是目前国际公认的最为可行的方案之一。高稳定低损耗量子信道的构建依赖于光学地面站和星载载荷的持续跟踪和对准，要求光学地面站ATP系统的跟踪精度要达到几微弧度，同时量子编码的特殊性又要求ATP系统具有高的偏振保持能力。本文正是在这样的背景需求下，开展星地量子通信系统中光学地面站捕获跟踪瞄准(ATP)关键技术的研究，旨在地面站ATP系统设计、理论仿真分析和技术验证等方面有所突破，为量子通信光学地面站的研制奠定技术基础。论文对量子通信光学地面站和ATP技术的国内外发展现状进行了回顾与分析，指出了ATP系统要实现高稳定低损耗量子信道所面临的技术难点：偏振保持技术、大动态范围高精度跟踪技术和高效耦合接收技术。对星地量子通信系统进行了全面的分析，确定了星地链路建立流程。系统分析了整个通信链路的链路裕量，并以此确定了ATP系统的接收口径、跟踪精度等关键技术指标。分析了大气信道对ATP性能的影响，重点分析了大气湍流导致的到达角起伏效应，并指出该效应是影响ATP系统精度的主要扰动源，同时从到达角起伏的幅值和频率分析，整个ATP系统闭环带宽要达到70Hz～100Hz。分析了光束偏振对比度变化对通信误码率的影响，并推导出星地全链路偏振对比度要优于100：1，对应地面站ATP系统的偏振对比度要优于250:1。从光学元件对偏振对比度的影响展开分析，提出了通过单镜片高保偏设计加工、光学元件小角度入射和改变光学元件间的空间布局关系等措施可以提高ATP系统的偏振对比度。在传统复合轴ATP系统跟踪方法的基础上，提出了实现大动态范围和高精度跟踪的新方法——双快速偏转反射镜串联的复合轴跟踪方法，并以偏振对比度和跟踪精度的双重约束完成了整个ATP系统的设计，针对两个FSM互相耦合问题，提出了相应的解耦策略。开展了提高ATP系统跟踪精度及光纤耦合效率的方法研究，建立了随机并行梯度下降（SPGD）算法的理论框架，分析该算法用于提高成像质量、进而提高跟踪精度的可行性；提出了利用SPGD算法提高量子通信光纤耦合效率的方法，通过仿真分析，，进一步表明SPGD优化算法可以提高光纤通信的耦合效率和远场光斑质量。给出了单模光纤最优的耦合效率与光纤耦合几何参量a、大气湍流强度r0、波前校正器单元数N的关系；并指出采用多模光纤的耦合效率与其芯径尺寸密切相关，提高耦合效率应优先考虑增加光纤芯径，其次考虑增加校正器单元数，为实现具有SPGD优化功能的ATP系统分析设计提供了参考。为了验证ATP系统跟踪策略的可行性，建立了700mmATP系统实验平台，通过水平50km和96km两个链路开展了多次信标光跟踪实验，验证了强湍流条件下的ATP系统跟踪策略。同时还开展了100km量子纠缠分发实验和96km量子密钥分发实验，实验中ATP系统均采用双FSM实现了复合轴闭环跟踪。研制了一套ATP后光路系统，对该系统的各项指标进行了室内测试，测试结果表明其偏振对比度优于300：1，接收效率为34％@850nm。并将该系统与国家天文台的1m天文望远镜主光路进行集成，完成了外场工作条件下的跟踪精度测试，跟踪精度优于5urad。建立了SPGD算法静态像差补偿实验系统，望远镜系统的静态像差校正后，光斑的分布形态也有明显改善。为了进一步测试SPGD算法对跟踪精度的优化效果，开展了3km水平链路校正实验，结果表明：SPGD系统闭环后，远场光斑的脱靶量方差明显减小。
[Abstract]:Quantum key distribution is the most rapid development of quantum communication, the most mature technology, has the absolute safety guarantee the basic principle of quantum mechanics. The characteristics and effect of fiber loss by single photon detectors, optical fiber quantum key distribution distance has basically reached the limit. Based on the earth curvature and distance visual conditions limit surface free space quantum key distribution is also difficult to achieve greater distances, so people will look to the satellite platform, through the establishment of high stability and low loss of quantum channel between the satellite platform and optical ground station, can realize quantum key distribution via satellite. The ultra long distance relay, it will be possible to achieve the global quantum communication network at present, it is internationally recognized as one of the most feasible scheme. High stability and construction of low loss of quantum channel dependent optical ground station and satellite Keep track of load and alignment requirements of optical ground station ATP, the tracking accuracy of the system to achieve a few radian, the particularity of quantum encoding and ATP system with high polarization maintaining capability. In this situation, to carry out satellite quantum communication system optical ground station acquisition tracking and pointing (Research on the key technology of ATP), the design of ATP system to the ground station, a breakthrough in theory analysis and simulation verification technology etc, lay the technical foundation for developing quantum communication optical ground station.
The development of quantum communication optical ground station and ATP technology at home and abroad were reviewed and analyzed, pointed out the technical difficulties faced by ATP system to achieve high stability and low loss of quantum channel: polarization maintaining technology, large dynamic range and high accuracy tracking technology and efficient coupling receiving technology.
The satellite quantum communication system were analyzed, the satellite link establishment process. System analysis of link margin entire communication link, and in order to determine the aperture of the ATP system, the key technical indicators tracking precision etc. This paper analyzes the effects of atmospheric channel on the performance of ATP, focuses on the analysis of the atmospheric turbulence induced the angle of arrival fluctuation effect, and points out the effect of the precision of ATP the main disturbance sources, and from the angle of arrival fluctuation amplitude and frequency analysis, the ATP loop bandwidth to reach 70Hz ~ 100Hz.
Analysis of the impact of changes in the polarization contrast on BER, and deduced the satellite link full polarization contrast is better than 100:1 and polarization contrast ATP system corresponding to ground station is better than 250:1. from the optical component of polarization contrast analysis, put forward by single lens with high polarization maintaining optical design and processing. Element of small incident angle and change the optical element between the spatial distribution of the relationship between measures can increase the polarization contrast of the ATP system.
Based on the traditional ATP system compound axis tracking method, is proposed to achieve high dynamic range and high precision tracking of the new method of fast steering mirror series compound axis tracking method, and the dual constraints of polarization contrast tracking accuracy and completed the design of the ATP system for two FSM coupling problem and put forward the corresponding control strategy.
Research on methods to improve the tracking accuracy and the fiber coupling efficiency of ATP system, established the stochastic parallel gradient descent (SPGD) algorithm for the analysis of the theoretical framework, improve the image quality of the algorithm, and the feasibility of improving the tracking accuracy of the proposed method; improve the fiber coupling efficiency of quantum communication using SPGD algorithm, through the simulation analysis, further show that SPGD optimization algorithm can improve the coupling efficiency of optical fiber communication and the far field of laser beam is given. The coupling efficiency of fiber coupling with single-mode fiber geometric parameters of the optimal a, atmospheric turbulence intensity R0, relationship between the wave front corrector unit number N; and that the coupling efficiency of multimode fiber with core diameter should be closely related to improve coupling efficiency give priority to increase the fiber core diameter, then consider increasing the number for the corrector unit, with the analysis of design ATP SPGD system optimization function The reference.
In order to verify the feasibility of the tracking strategy of ATP system, established the 700mmATP system platform, the levels of 50km and 96km two link to carry out a number of beacon tracking experiments verify the tracking system ATP the strong turbulence condition strategy. Also launched 100km quantum entanglement distribution experiment and 96km quantum key distribution system ATP in the experiment using FSM to achieve the dual compound axis closed loop tracking.
Developed a ATP optical path system, each index of the system was tested. The test results show that the polarization contrast is better than 300:1, and the receiving efficiency of 34%@850nm. system and the National Astronomical Observatory of 1m telescope main light path integration, complete tracking precision testing field working condition, tracking precision better than 5urad.
A SPGD algorithm for static aberration compensation experiment system, the static aberrations of the telescope system after correction, the distribution of the spot is improved obviously. In order to further test the SPGD algorithm on tracking accuracy of the optimization effect, to carry out the 3km link level calibration experiment, the results show that the SPGD closed loop system, the far field spot miss distance variance decreases obviously.

【学位授予单位】：中国科学院研究生院（光电技术研究所）
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN918;O413

【参考文献】