星间激光通讯中的精跟踪研究

星间激光通讯中，精跟踪起着十分重要的作用，而精密偏转镜(FSM)是精跟踪系统中最为关键的部件.基于光学矢量反射定律，推导得到了FSM的精确光学特性，这一特性为精跟踪控制系统提供了精确的理论依据.设计了基于FSM精确光学特性的精跟踪控制系统，对系统整定所用的单纯形法进行了两点重要改进，并对所设计的精跟踪系统进行了数字模拟，由此实现了对FSM的精确控制，提高了精跟踪系统的精确性；将光学衍射超分辨原理应用到星间激光通讯中.利用三区位相光瞳滤波器的超分辨性能，改变光学系统的点扩散函数，从而改变接收端焦平面上的光强分布.由此减小接收衍射光斑的大小，提高系统的光学分辨能力，从而提高精跟踪系统的精确性. 关键词： 星间激光通讯 精跟踪 精密偏转镜(FSM) 超分辨 光瞳滤波器     

Secure key distribution over a 500 km long link using a Raman ultra‐long fiber laser

In traditional communication systems the transmission medium is considered as a given characteristic of the channel, which does not depend on the properties of the transmitter and the receiver. Recent experimental demonstrations of the feasibility of extending the laser cavity over the whole communication link connecting the two parties, forming an ultra‐long fiber laser (UFL), have raised groundbreaking possibilities in communication and particularly in secure communications. Here, a 500 km long secure key distribution link based on Raman gain UFL is demonstrated. An error‐free distribution of a random key with an average rate of 100 bps between the users is demonstrated and the key is shown to be unrecoverable to an eavesdropper employing either time or frequency domain passive attacks.     

基于半波片的偏振跟踪理论分析

分析了卫星量子密钥分配中采用半波片进行偏振跟踪的原理，通过旋转半波片实现对偏振“零”方向的跟踪.针对BB84协议和B92协议，给出了三组共轭基六个光子偏振态的变换关系式，分析了基于偏振跟踪的量子密钥编码原理. 关键词： 量子密钥分配 偏振跟踪 半波片     

Space-to-Ground Quantum Key Distribution Using a Small-Sized Payload on Tiangong-2 Space Lab

Quantum technology establishes a foundation for secure communication via quantum key distribution(QKD). In the last two decades, the rapid development of QKD makes a global quantum communication network feasible. In order to construct this network, it is economical to consider small-sized and low-cost QKD payloads, which can be assembled on satellites with different sizes, such as space stations. Here we report an experimental demonstration of space-to-ground QKD using a small-sized payload, from Tiangong-2 space lab to Nanshan ground station. The 57.9-kg payload integrates a tracking system, a QKD transmitter along with modules for synchronization, and a laser communication transmitter. In the space lab,a 50 MHz vacuum+weak decoy-state optical source is sent through a reflective telescope with an aperture of 200 mm. On the ground station, a telescope with an aperture of 1200 mm collects the signal photons. A stable and high-transmittance communication channel is set up with a high-precision bidirectional tracking system, a polarization compensation module, and a synchronization system.When the quantum link is successfully established,we obtain a key rate over 100 bps with a communication distance up to 719 km. Together with our recent development of QKD in daylight,the present demonstration paves the way towards a practical satellite-constellation-based global quantum secure network with small-sized QKD payloads.     

基于多处理器的视频跟踪系统研究

传统视频跟踪系统的目标检测环节常采用手动指定或使用单处理器运算来确定跟踪目标,这种方法耗费人力且检测速度慢。针对此问题提出了一种改进的图像分割方法,该方法采用多处理器系统构架,并行处理分割区域,增加了检测目标的速度,并且在后续目标跟踪环节中,各处理器根据任务划分,协同处理跟踪任务。实验结果表明基于多处理器系统构架的视频跟踪系统能够实现快速自动检测与跟踪目标,系统加速比为2．066,处理器效率为51．65％。     

深空光通信中图像信标的捕获和跟踪

用激光进行深空探测科学数据回传,上行信标光衰减严重,不能提供足够高的跟踪速率,因此常采用自然天体图像作为信标。对该信标的捕获和跟踪是深空光通信链路成功建立和保持的关键。在航天器上存储一幅目标天体图像做参考,利用该图像和探测图像的相关性对该信标进行捕获,理论分析和仿真结果都表明,可以精确地确定光通信天线的初始对准方向,使跟瞄系统进入跟踪模式。基于离散傅里叶变换和极大似然方法对信标的平移进行计算,需要解一个非线性方程组,线性近似计算结果表明平移量总误差在0.5个像素以内,X方向的平移误差为3.3%,Y方向的平移误差为2.7%,可以满足深空通信的要求,因而是一种可行的方案。     

Agile protection based on network coding against key link failures

In order to provide cost-efficient and rapid protection against the key link failures dynamically, an intelligent p-cycle protection strategy based on network coding is proposed. Data units are combined from different links using network coding method at the on-cycle nodes, and then they are transmitted downstream for recovering data units lost due to failures. Under static traffic, an integer linear program (ILP) is formulated to provision the optimal p-cycles. Furthermore, according to the dynamic variation of the link importance degree, a heuristic cycle construction algorithm for generating, extending and contracting p-cycle is introduced to achieve intelligent and self-adaptive protection. The key of the proposed protection strategy is how to set the key link as a straddling link of the p-cycle as possible. The experiments demonstrate that the proposed strategy can guarantee instantaneous recovery of data units upon the failure of a key link with a low blocking rate and resource cost.     

Geometrical Optics Restricted Eavesdropping Analysis of Satellite-to-Satellite Secret Key Distillation

Traditionally, the study of quantum key distribution (QKD) assumes an omnipotent eavesdropper that is only limited by the laws of physics. However, this is not the case for specific application scenarios such as the QKD over a free-space link. In this invited paper, we introduce the geometrical optics restricted eavesdropping model for secret key distillation security analysis and apply to a few scenarios common in satellite-to-satellite applications.     

基于高准确度搜索运动目标关键帧的智能跟踪算法

分析了目标在不同运动阶段所呈现的不同成像特征,为了增加跟踪的鲁棒性,提出了一种基于高准确度搜索运动目标关键帧的智能跟踪算法,并搭建了实验平台,进行了相关实验.实验结果和某靶场试验中实际应用结果表明,该算法准确度高,鲁棒性好、成功率高.     

舰炮跟踪雷达干扰试验环境构建条件分析

针对舰炮跟踪雷达复杂电磁环境下试验鉴定考核需求,在分析武器装备使用过程中面临的典型干扰环境的基础上,结合典型跟踪雷达技术特点,分析外场抗干扰飞行试验方案制定中应着重考虑的问题,作为典型实例,通过计算机仿真重点分析了干扰源方向对准对干扰效果产生的影响,理论分析及仿真结果对舰炮跟踪雷达抗干扰试验的环境构建具有一定的指导意义。     

空间激光通信及其关键技术

通信领域中激光通信技术由于自身的优越性得到了广泛的应用。通过将空间激光通信与微波通信比较，介绍空间激光通信的优点：大容量、低功耗及体积小、质量轻等。叙述空间激光通信的基本原理。重点阐述空间激光通信系统大功率光源技术、高灵敏度抗干扰光信号接收技术、通信链路的快速及精确的捕获、跟踪和瞄准技术等关键技术。激光通信可广泛应用于军事、经济等各个领域，必将有广阔的发展前景。     

光纤耦合对量子密钥分配系统光子探测的影响

借助量子密码术和卫星可以实现全球性的保密通信网络。但使用现有的单光子探测模块搭建星地量子密钥分配(QKD)系统,接收端就面临着空间光-多模光纤耦合的技术挑战。空间光-多模光纤耦合条件对星地量子密钥分配系统的跟瞄精度提出了严格要求。理论分析和定量计算表明,跟瞄精度ε与光束发散角θdiv的比值ε/dθiv≤0.5时,星地量子密钥分配系统的光子探测概率较高,系统可以正常工作;ε/dθiv≤0.1时,系统处于量子密钥产生速率为几kb/s的更理想状况。采用短波长更有利于满足空间光-多模光纤耦合条件,同时有利于系统获得更高的密钥产生速率。     

星-地量子密钥分发链路持续时间分析与仿真

链路持续时间是影响卫星量子密钥分发量子比特率的重要参数.文章分析了影响星-地单光子和纠缠光子量子密钥分发链路持续时间的若干因素,并且进行了数值仿真研究.结果表明,随着轨道高度的增加或者地面最小通信仰角的减小,单光子和纠缠光子链路的持续时间有较大的改善;单光子链路时地面站同卫星星下点轨迹间的距离和纠缠光子链路时两地面站之间的距离也均是影响链路持续时间的重要参数;纠缠光子链路持续时间的影响因素较单光子链路更为复杂,其最终决定于卫星星下点轨迹同两地面站之间的位置关系.     

导引头性能可视化数据获取方法

目前,制导武器系统导引性能评估主要采用室内仿真和实弹射击方法。但是,受模拟条件的限制,室内仿真存在目标瞬变作用机理描述不足及过程复现可信度低等难题;而外场实弹射击则存在试验样本量有限,目标环境设定单一且射击条件无法保证一致性的问题,难以全面考核出武器系统对环境和干扰的适应性。针对这一问题,提出了一种介于室内仿真与外场实弹试验之间的中间验证考核方法,在接近真实复杂战场环境条件下,构建了制导武器系统的可视化动态测试平台,获取导引头探测、识别和跟踪目标过程的同步、实时可视化观瞄图像,提取目标信息并实现导引性能评估。这种方法在靶场环境下针对实际靶标目标进行静态、动态跟踪试验,能够为激光、毫米波、电视以及红外等不同制导模式的导引头系统进行集成试验与测试,可为室内仿真提供目标背景的直接驱动数据,提升仿真逼真度; 同时,也可多次重复考核导引环节的关键能力,弥补实弹射击试验数量的不足,为武器系统研制过程提供了一种全新的测试验证手段     

基于泊松分布单光子源的量子误码率的分析

在自由空间量子密钥分配中,单光子源采用具有泊松分布的高度衰减激光脉冲,量子密码术协议采用BB84和B92协议。通过引入量子信道传输率、单光子捕获概率、测量因子和数据筛选因子,建立了量子误码率理论模型,给出了量子误码率的表达式。对于自由空间量子信道,引起量子误码率的主要因素是光学元件、探测器暗噪声和空间光学环境,并对这些因素进行了分析。针对低轨卫星_地面站间链路,进行了量子误码率的数值仿真研究。结果表明,在低轨卫星_地面站间进行量子密钥分配是可行的,限制自由空间量子密钥分配链路距离的主要因素是探测器暗噪声和空间光学环境。     

面向经纬仪图像序列的关键帧提取算法

将传统的关键帧提取算法应用于经纬仪图像序列时,关键帧序列中会包含大量的非稳定跟踪图像帧。为了在关键帧提取过程中更好地保留目标稳定跟踪测量信息,该文在分析了经纬仪图像序列的特点后,构建了一种基于局部极大值的经纬仪图像序列关键帧提取算法。该算法首先计算图像序列的帧间差分,然后使用汉宁窗函数对帧间差分进行平滑,最后基于平滑后的帧间差分局部极大值来提取关键帧。实验结果表明:提出的算法相对于传统的帧间差分强度排序方法能更好地保留目标的跟踪测量信息,提取的关键帧在整个跟踪测量图像序列中分布更为均匀,包含的场景信息更为丰富。     

Machine-vision-based acquisition,pointing, and tracking system for underwater wireless optical communications

Due to the proliferation of underwater vehicles and sensors, underwater wireless optical communication(UWOC) is a key enabler for ocean exploration with a strong reliance on short-range bandwidth-intensive communications. A stable optical link is of primary importance for UWOC. A compact, low-power, and low-cost acquisition, pointing, and tracking(APT) system is proposed and experimentally demonstrated to realign the optical link within 0.04 s, even when the UWOC transmitter and receiver are in relative motion. The system successfully achieves rapid auto-alignment through a 4 m tap water channel with a relatively large number of bubbles. Furthermore, the required minimum illumination value is measured to be as low as7.1 lx, implying that the proposed APT scheme is robust to dim underwater environments. Meanwhile, mobility experiments are performed to verify the performance of the APT system. The proposed system can rapidly and automatically align moving targets in complex and unstable underwater environments, which can potentially boost the practical applications of UWOC.     

The queueing model for quantum key distribution network

This paper develops a QKD (quantum key distribution)-based queueing model to investigate the data delay on QKD link and network, especially that based on trusted relays. It shows the mean packet delay performance of the QKD system. Furthermore, it proposes a key buffering policy which could effectively improve the delay performance in practice. The results will be helpful for quality of service in practical QKD systems.     

一种导引头性能可视化评估方法

激光制导、微波制导的导引头由于不具备可视化功能,在实际环境中进行性能考核时,导引头是否成功截获指定目标、截获目标后的稳定跟踪过程是否正常以及在稳定跟踪过程中出现的问题都不易得到及时、准确的定位和分析。文中设计的可视化评估系统可有效解决上述问题,通过加装可见光成像系统同步伴随导引头运动的方法,将导引头搜索、跟踪目标的过程清晰成像,直观显示导引头的整个工作过程,同时利用图像跟踪系统和图像存储系统保存关键性能参数,试验完成后对导引头的输出参数及跟踪性能进行验证及处理,进而对导引头的性能参数进行分析和评估;通过动态跟踪或加载干扰源试验验证,该方法能利用可视化系统可靠同步跟随不可视导引头的运动,并对导引头跟踪过程进行定性观察及定量分析。该方法不仅可以克服室内仿真环境不太真实的缺点,又可进行多次重复性研究,性价比高,为导引头性能评估提供一种比较适用的研究手段。     

基于光电振荡器的宽带射频下转换及在高清视频传输的应用

以无压缩全高清视频的光载无线传输为背景,通过研究宽带射频光子下转换技术,从而构建全高清视频的实时传输系统,其中下转换系统主要基于光电振荡器实现.由于光电振荡器的注入锁定,光微波信号中的载波信号被提取出来,并反馈至调制器,与宽带光微波信号混频,在光域实现信号下转换.实验论证了载频为10GHz,码率大于2Gb/s的信号下转换和有线无线传输.利用天线和光纤实现了距离为0.5m的无线分发和距离为10km的有线传输.本文还成功实现了1.5Gb/s无压缩高清视频信号的实时传输.实验结果表明,该系统具有大带宽、抗电磁干扰等优点,同时利用光电振荡器的自动相位跟踪技术,无须外加锁相等操作.整个下转换系统简单稳定,为高清视频的有线无线传输提供了论证和演示平台.