临近空间相干激光通信链路外差效率分析

临近空间相干激光通信链路是天地一体化高速通信网络节点间连接的重要链路。围绕外差效率这一表征大气湍流扰动后信号光和本振光相干合成的指标,推导了非均匀湍流路径上的外差效率理论表达式,并结合大气折射率结构常数廓线,开展了临近空间-地面、临近空间-临近空间和临近空间-低轨卫星三类临近空间相干激光通信链路的外差效率仿真。仿真结果表明：临近空间-低轨卫星链路可以忽略大气对外差效率的影响;如果临近空间-临近空间链路距离大于500 km或是临近空间-地面链路天顶角大于60,外差效率将小于50%,有必要采用自适应光学技术进行补偿。     

空地激光通信链路功率与通信性能分析与仿真

分析了空地激光通信系统中主要器件和信道对通信光功率的影响,并根据接收探测器的信噪比和通信误码率公式,建立了空地激光通信仿真系统.分析了在误码率优于10-7条件下,不同地面大气能见度所对应的最高通信速率;以及要实现通信速率为1.5 GHz,误码率优于10-7时需要的最小发射功率和最长通信距离.结果表明,当发射功率越大时,地面大气能见度对误码率的影响越明显.     

机载激光通信链路中光场二阶特性的分析计算

为了评估大气湍流对机载激光通信系统的影响,理论分析和数值计算了机载激光通信链路中传输光场的二阶特性,包括接收光斑尺寸、光斑偏移量、光束相干半径、光束到达角起伏。计算结果表明:大气湍流对空间激光通信系统的影响主要在低空对流层,并随着机载平台高度的增加而降低。由于受到低空大折射率结构常数的影响,上行链路的接收光斑尺寸、光斑漂移量比下行链路大。下行链路光束到达角抖动比上行链路大,其值为若干rad。提出的模型及计算结果,可以为机载激光通信系统设计及性能评估提供参考。     

星间相干激光通信中反射镜面形畸变状态下通信性能的研究

单个激光波长受卫星相干光通信系统中反射镜的影响,其波前将会发生不可预期的变化。研究了波前在单个反射镜面形畸变下的变化,并分析了它对卫星相干光通信效率的影响。仿真结果表明,畸变位置处的峰谷值是影响激光波前的主要因数,而畸变的大小对链路性能的影响却有限。     

大气激光通信的实验测量

设计了大气激光通信信道测量系统，利用此系统在不同气象条件下进行了近地视距实验测量并采集了不同天气条件下的实验数据，详细分析讨论了所得实验数据并进行了误差分析．同时实验中获得了大量数据，为进一步完善大气激光信道模型提供了有力的依据．     

大气信道对星地链路激光通信的影响

星地链路激光通信系统的运行不可避免地要受到湍流大气等随机介质的影响,从而可导致卫星接收信息误码或通信中断。基于Born近似和弱起伏下的Rytov近似,分析推导了激光光束从发射机经湍流大气斜程到达接收机(或目标)时的光场变化。采用McGlamery算法,对Kolmogorov功率谱下的大气湍流随机相位屏进行了数值模拟,进而在模拟的相位屏和惠更斯-菲涅尔原理基础上,将主要适用于模拟平面波相位波前的McGlamery算法推广应用到了高斯光束的光场模拟。研究表明:大气信道段对星地链路激光通信系统有着极为重要的影响,也间接说明了McGlamery算法对准直激光光束相位波前模拟的适用性。     

空间激光通信中湍流信道光束传输仿真

对大气光信道特性的研究是空间激光通信研究的重要组成部分。首先以大气湍流理论为基础,阐述了激光在大气中传输时受到的大气湍流的影响和分析方法。接着重点对近年来应用日益广泛的空间激光通信的数值仿真方法进行了综述。不仅介绍了基本传输方程及其求解方法,还对采用数值方法模拟光波在随机介质中传播的若干关键技术进行了分析。最后结合现有的研究成果,说明了数值方法在空间激光通信中的应用。     

大气激光通信链路的性能仿真

大气衰减和大气湍流严重影响着大气激光通信的链路质量。建立了大气信道的激光通信链路模型，研究了衰减信道和湍流信道中光链路的传输影响，对最大通信速率、链路功率余量和误码率进行了分析和计算。结果表明，大气湍流严重影响系统误码率，当大气闪烁指数斫是0．07时，可达到的最小误码率为10^-9。分析结果可为系统设计提供参考依据。     

大气激光通信的实验测量(英文)

设计了大气激光通信信道测量系统,利用此系统在不同气象条件下进行了近地视距实验测量并采集了不同天气条件下的实验数据,详细分析讨论了所得实验数据并进行了误差分析.同时实验中获得了大量数据,为进一步完善大气激光信道模型提供了有力的依据.     

Retrodiction for coherent communication with homodyne or heterodyne detection

Previous work on the retrodictive theory of direct detection is extended to cover the homodyne detection of coherent optical signal states and . The retrodictive input state probabilities are obtained by the application of Bayes' theorem to the corresponding predictive distributions, based on the probability operator measure (POM) elements for the homodyne process. Results are derived for the retrodictive information on the complex amplitude of the signal field obtainable from the difference photocount statistics of both 4-port and 8-port balanced homodyne detection schemes. The local oscillator is usually assumed much stronger than the signal but the case of equal strengths in 4-port detection is also considered. The calculated probability distributions and error rates are illustrated numerically for values of signal and local oscillator strengths that extend from the classical to the quantum regimes.     

Research on heterodyne efficiency of laser Doppler velocimeter

Heterodyne efficiency is a very important factor in a laser Doppler velocimeter (LDV). Gaussian-Airy mode is put forward to analyze the heterodyne efficiency. And the calculate formulas and results of simulation of heterodyne efficiency are given. The results of numerical analysis show that heterodyne efficiency of LDV depends on the parameters—x₀, A, θ and x_a. Heterodyne efficiency can reach 81.45%, when x₀ = 3.59, A = 5.04 and θ = x_a = 0. At last, the antenna theorem of LDV is derived, and a defocused telescope system is used to adjust the waist's position and radius of the reference beam to match the signal beam.     

Analysis of signal-to-noise ratio and heterodyne efficiency for reference-beam laser Doppler velocimeter

Heterodyne efficiency is a very important factor in a laser Doppler velocimeter (LDV). Gaussian-Airy mode is put forward to analyze the heterodyne efficiency. By studying the distribution of the optical field, the mathematic expression and simulation results of heterodyne efficiency are given under the conditions of both exact match and mismatch. The results of numerical analysis show that heterodyne efficiency of LDV depends on Gaussian beam's parameter Q, detector's parameter X₀, angle of collimation mismatching θ_a, parameter of offset mismatching X_a and the radius of curvature of the reference beam on the detector R(z). Heterodyne efficiency can reach 83.39% when Q=4.15×10^?7, X₀=6.1×10^?7, θ_a=X_a=0, R(z)=∞. But it declines to 0.5 when Fθ_a enhances to 0.28. It decreases with the increment of the offset X_a and the diminishment of the radius of curvature R(z). Results of experiment are in good accordance with the theoretical analysis.     

振动对星间相干激光通信的影响

针对星间相干激光通信中卫星平台的振动造成发射天线和接收天线的瞄准角误差，使系统信号信噪比下降，误码率 (BER)增加，该文以瑞利分布作为振动造成的瞄准角误差模型，结合高斯本振光和艾里信号光外差检测模型，以PSK零差通信体制为例分析卫星振动对系统的瞬时误码率和平均误码率的影响，给出误码率仿真计算结果。指出接收天线瞄准角误差对星间光通信质量影响很大，在瞄准角误差的标准偏差σ小于1μrad范围内，系统误码率小于10^-6。     

Research on tunable local laser used in ground-to-satellite coherent laser communication

In order to realize homodyne reception and Doppler frequency shift tracking in ground-to-satellite coherent laser communication, a local laser is experimentally demonstrated in this Letter. It is realized based on modulationsideband injection locking, and has a 10 GHz tuning range, a 1 THz/s tuning rate, a 5 k Hz linewidth, and 16 m W of output power. When applied to a Costas loop in a coherent laser communication system, the local laser can achieve ?5 GHz Doppler frequency shift tracking with a 20 MHz/s frequency shift rate, which is sufficient for the ground-to-satellite coherent laser communication.     

镜面热变形对空地激光通信链路性能的影响

 低轨卫星在轨运行热环境条件下,不能有效释放热应力的反射镜面将产生热变形,镜面法向偏转可达百μrad量级;经其反射的光束将产生较大的指向偏差,严重影响空地激光通信链路的系统性能。对空地激光通信星上端机目前常用的压板法镜体固定方式进行的分析表明：镜体释放热应力后的法向角度偏差可减小近3个数量级,对由于热变形带来的光束指向偏差能进行很好地抑制,减轻对系统性能的影响。     

镜面热变形对空地激光通信链路性能的影响

低轨卫星在轨运行热环境条件下,不能有效释放热应力的反射镜面将产生热变形,镜面法向偏转可达百μrad量级;经其反射的光束将产生较大的指向偏差,严重影响空地激光通信链路的系统性能。对空地激光通信星上端机目前常用的压板法镜体固定方式进行的分析表明：镜体释放热应力后的法向角度偏差可减小近3个数量级,对由于热变形带来的光束指向偏差能进行很好地抑制,减轻对系统性能的影响。     

自由空间宽谱部分相干光通信系统

大气湍流对自由空间光通信系统所造成的影响是不可忽略的，为了减弱湍流对空间光通信系统带来的影响，实验搭建了一套通信距离为900 m的真实大气信道宽谱部分相干光通信系统。系统采用皮秒脉冲泵浦高非线性光纤产生超连续谱并滤波得到部分相干宽谱脉冲，对其调制后完成通信。在测试过程中，实验专门设置了一条参考链路，保证了测试环境的一致性。实验结果表明，在中等湍流条件下，系统光强闪烁指数为0.035 8，相比窄线宽通信系统提升了23%，最低探测灵敏度达到了-23.35 dBm，相比窄线宽通信系统提升了42%。与窄线宽激光通信系统相比，宽谱部分相干光通信系统可以明显降低湍流引起的光功率抖动，并提升自由空间光通信系统通信性能。     

Influence of satellite vibration on optical communication performance for intersatellite laser links

For intersatellite laser links, vibration-induced pointing jitter severely influences the communication quality as a result of intensity fluctuation. In this paper the probability density function of normalized intensity at the receiver is derived in the presence of pointing jitter taking consideration of bias error. Accordingly, the scintillation index is developed to identify the impact of bias error on intensity fluctuation. Furthermore the bit error rate (BER) is obtained as a function of the beam divergence angle and vibration variance. Qualitative analysis is also given, and the numerical simulation is carried out for demonstration. Results suggested that bias error has a significant detrimental impact on optical terminals which should be considered in system design. This work can benefit the intersatellite optical system design.