光通信 激光通信

TN929.1 2006043570大气湍流对空间光耦合至单模光纤的影响=Influence ofat mospheric turbulence on coupling space light into singlemode fiber[刊,中]/向劲松(电子科技大学物理电子学院四川,成都(610054)) ,陈彦…∥强激光与粒子束.—200618(3) .—377-380根据弱湍理论,考虑湍流强度闪烁、孔径平均效应、湍流波前畸变及耦合系统跟踪误差的影响,导出了空间光到单模光纤的平均耦合效率及耦合功率起伏方差模型。根据Hufnagel-Valley 5/7折射率结构模型,对下行连接及上行连接的平均耦合效率及耦合功率起伏进行了研究。仿真结果表明,对于…     

上下行传输孔径接收光强起伏特性分析

为了研究地星上行和星地下行激光链路孔径内接收光强信号的典型特征,基于大气湍流理论和位相屏方法,计算了短波和中波红外激光在特定大气相干长度条件下,孔径内接收激光功率与总功率的比值及起伏情况。根据统计结果讨论了上下行大气通道传播特性的差异,结果表明相同外界条件下,直径50 cm孔径内接收的下行激光信号强度大于上行激光信号强度1个数量级以上,其信号的起伏程度也低于上行激光;中等湍流下,下行激光孔径接收光强的概率分布函数服从对数正态分布,最大概率接收功率比与无湍流条件下的功率比值一致,分别为0.42%(1.315 m)和 0.26%(3.8 m)。     

大气湍流中空间光至单模光纤耦合的跟踪算法

 通过模拟湍流波前的振幅起伏及相位起伏，研究了采用CCD探测器的湍流波前倾斜校正系统的空间光到单模光纤耦合功率的衰落特性，对CCD图像的跟踪算法进行了研究。仿真结果表明，在接收孔径直径与Fried 参数的比值较大时，采用质心跟踪算法的倾斜校正系统的性能很差，耦合光功率会产生严重衰落。提出了一种高斯模板匹配的倾斜校正跟踪算法，在湍流较强时，可以有效地降低耦合光功率的衰落深度，并且可以避免采用质心算法可能出现的大孔径接收性能低于小孔径的不利情况。     

各向异性海洋湍流DHPIM无线光通信性能分析

水下无线光通信系统易受由折射率波动起伏引起的海洋湍流的影响,造成光强闪烁、光束漂移、光束扩展和波前畸变等效应,从而使光信号产生衰落,导致通信质量降低及通信性能恶化.利用扩展的惠更斯-菲涅耳原理和渐近Rytov理论分别导出有限尺寸探测器的平均接收光功率和辐照度通量方差,研究了Gamma-Gamma湍流信道模型下双头脉冲间...     

激光大气闪烁饱和的孔径平均效应

理论分析了湍流介质中一定孔径内光强起伏（闪烁）的频谱特征，在6.8km的大气传播距离上同时测量了激光在针孔和φ260mm孔径内的闪烁，根据两者功率谱特征的对比分析结果以及两者闪烁均方差间的关系，指出孔径平均效应可以在一定程度上消除激光大气闪烁的饱和效应，从而可以利用孔径平均效应在临界强起伏条件下测量湍流强度。     

逆向传输标定法校正自适应光学非共光路像差

自适应光学系统可以抑制大气湍流所产生的波前畸变，波前探测支路和光纤耦合支路之间存在的非共光路像差会导致自适应光学系统闭环后其耦合功率未能有效提升。采用逆向传输标定法由耦合光纤端到波前传感器进行反向传输，将波前传感器采集相对应的波前信息折算到自适应光学系统并实现闭环控制。结果表明：采用逆向传输标定法，数值仿真的耦合效率由27.31%提升至68.14%；静态环境实验的耦合效率由9.04%提升至45.21%；湍流环境实验的耦合效率由19.72%提升至36.93%；复杂环境实验的耦合效率由3.87%提升至7.52%。该方案简单而切实可行，易于在工程上推广应用。     

非科尔莫戈罗夫湍流情况下光学波前的到达角起伏方差分析

引入非科尔莫戈罗夫 (Kolmogorov)湍流情况下的归一化相位空间功率谱 ,针对 G倾斜和Z倾斜两种情形 ,分别推导了非科尔莫戈罗夫湍流情况下光学波前的到达角起伏方差与相位空间功率谱指数下降因子β和归一化大气湍流相干长度ρ0 之间的关系。结果表明 ,对于 2 <β <4 ,非科尔莫戈罗夫湍流情况下光学波前的到达角起伏方差随着β的增加而增大 ,β相同时 ,G倾斜方差总是小于 Z倾斜方差。     

孔径平均效应对采用相位补偿技术的空间相干光通信系统误码率的影响

基于大气湍流影响下的空间相干光通信系统模型和孔径平均效应的平面波模型,通过数值模拟研究了弱光强波动条件下孔径平均效应以及大气湍流内外尺度对相干光通信系统误码率和接收孔径直径最优值的影响。研究结果表明:孔径平均效应能够有效减小相干光通信系统的误码率,改善系统性能;原始信噪比越高,传输距离越短,波长越长,相位补偿模式的J值越大,接收孔径直径越接近最优值,孔径平均效应对误码率的改善效果越明显;孔径平均效应会影响接收孔径直径的最优值,相位补偿模式的J值越大,影响越明显;系统误码率和接收孔径直径最优值会随着大气湍流内尺度的增大而相应增大,随着大气湍流外尺度的减小而相应减小。研究结果将为空间相干光通信系统设计提供必要的理论依据。     

大气湍流中部分相干光束角反射器的回波光强特性

根据广义的Huygens-Fresnel原理和修正Von Karmon谱模型,推导出了部分相干高斯-谢尔模型(GSM)光束上行传输时的平均光强解析式;获得了GSM光束经角反射器回波后下行传输到接收端的平均光强表达式,并对其进行归一化处理;分析了GSM光束在上行-下行传输过程中平均光强的变化,且发射端和接收端在同一高度。数值分析结果表明:在大气湍流双程斜路径传输中,准直光束受湍流的影响比聚焦光束小;接收端在轴归一化光强随角反射器半径的增大先增大,最终趋于定值;在轴归一化光强随湍流外尺度增大几乎无变化,随湍流内尺度的增大而减小。     

大气风速对大气传输光束相位特性的影响

采用功率谱反演法构建湍流相位屏,通过横向平移相位屏的方法模拟大气风速引起的湍流时间变化,进而模拟分析了包括时间进程的激光大气传输特性,从波前相位功率谱密度的角度,定量分析了大气风速引起的激光束在大气湍流中传输时的相位特性变化。在此基础上,采用影响函数模拟变形镜对畸变波前的校正作用,对激光束经大气湍流传输后的自适应校正效果进行了预估,分析了大气风速对校正效果的影响。结果表明,大气风速对边界层湍流中光束相位特性的影响很小,然而,对于自由大气湍流中的传输光束,大气风速越大,波前相位畸变程度越大,畸变波前中高频相位比例也越大;环状光束的校正效果受大气风速的影响比平顶光束更小,并且,随着环状光束阶数的增大,校正效果所受影响逐渐减小;在一定相位畸变范围内,畸变程度越大的环状光束的相位校正效果受大气风速的影响越小。     

Reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links with spatial diversity

In the scenario of first laser communication relay satellite being launched into geostationary earth orbit, we evaluate the reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links in presence of turbulence and various weather conditions using spatial diversity technique. In channel modeling, Beer Lambert Law incorporates the weather effects. The log-normal probability density function (pdf) models weak turbulence and gamma–gamma pdf moderate to strong turbulence. Using the combined channel state pdf, bit error rate (BER) expressions are derived for on-off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) schemes. From the BER plots, we evaluate the minimum average received power required to achieve a desired BER for all three schemes for different channel conditions. Subsequently, minimum transmitter power requirement is evaluated for both uplink and downlink using the range equation. It is observed that presence of moderate, light and thin fog cause additional power requirement. Also, among the three schemes, M-PPM scheme requires the least transmitter power, followed by M-DPPM and OOK schemes. Further, it is seen that the transmitter diversity or multiple input single output technique reduces the uplink minimum transmitter power requirement, whereas for downlink aperture averaging and receiver diversity or single input multiple output techniques can achieve the same. The power requirement for uplink is 8–10 dB more as compared to downlink in presence of turbulence and various weather conditions.     

上行链路大气波前畸变对剪切光束成像技术的影响

剪切光束成像（sheared-beam imaging,SBI）技术是一种利用三束剪切相干激光照明的非传统成像技术,该技术通过探测器阵列接收目标反射回波的散斑图进行计算成像,在对远距离暗弱目标高分辨率成像方面有着独特的优势.大气湍流引起的光束波前畸变是影响SBI成像质量的一个关键因素,因此本文从湍流引起的激光波前畸变对目标频谱信息提取的影响入手,建立了光束波前畸变对成像影响的理论模型.利用多层相位屏模型模拟了近地25 km大气对SBI光束传输的影响.通过计算机仿真,得到了不同激光发射孔径和不同成像距离时SBI的成像结果.仿真结果表明,选取合适的发射孔径尺寸可以有效缓解湍流对光束波前质量的影响,从而提升成像质量.在Hutchin的研究基础上,对孔径选择范围的已有研究成果进行了扩展与深化.给出了SBI系统发射孔径尺寸选取的建议,为SBI对不同高度目标成像的像质差异分析提供了参考.     

Aperture averaging of optical scintillations: power fluctuations and the temporal spectrum

Using a recently developed theory of scintillation that is valid under all fluctuation conditions, including the focussing and saturation regimes, we develop general models for predicting power fluctuations (or aperture averaging) over finite-size collecting apertures. Inner-scale effects are introduced using a modified atmospheric spectrum for refractive-index fluctuations that includes a high-wavenumber bump. Where comparisons can be made, these models of aperture averaging are in good agreement with previous asymptotic models and experimental data. In addition to the aperture-averaging factor, we calculate the temporal spectrum associated with power fluctuations over various aperture sizes and conditions of turbulence. These later results clearly show the transfer of power distribution from high to low frequencies as the size of the collecting aperture is increased. The transfer of power is more pronounced in the saturation regime where high frequencies (fastest fluctuations) can be averaged out even for relatively small apertures.     

部分相干涡旋光束通过大气湍流上行和下行传输的比较研究

基于广义惠更斯-菲涅耳原理,以高斯-谢尔模型(GSM)涡旋光束作为典型的部分相干涡旋光束,推导出GSM涡旋光束通过大气湍流斜程传输的平均光强、均方根束宽和交叉谱密度函数的解析表达式,并用以研究了大气湍流中上行和下行对GSM涡旋光束传输和对相干涡旋的影响.结果表明,在相同条件下,GSM涡旋光束下行传输受大气湍流的影响要小于上行传输,下行传输时相干涡旋拓扑电荷守恒距离要长于上行传输.对所得结果做了物理解释. 关键词： 部分相干涡旋光束 相干涡旋 大气湍流 上行和下行传输     

Effect of non-Kolmogorov turbulence on beam spreading in satellite laser communication

In the past half a century, satellite laser communication has caught the attention of scientists due to its distinct advantages in comparison with conventional satellite microwave communication. For ground-to-satellite and satellite-to-ground data links, the atmosphere is a part of the communication channel; thus, atmospheric turbulence severely degrades the performance of satellite laser communication systems. In general, the Kolmogorov turbulence model is used to study the effect of atmosphere turbulence on satellite laser communications since it has been confirmed by numerous direct measurements of temperature and humidity fluctuations in the atmospheric boundary layer. However, increasing experimental evidence and theoretical investigations have shown that the Kolmogorov theory is sometimes inadequate to describe atmospheric statistics properly, in particular, in some domains of the atmosphere. We analyze the joint influence of Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the spot size associated with the uplink and downlink propagation channels for a satellite laser communication system in the geosynchronous orbit, using a power spectrum of non-Kolmogorov turbulence with power law ?5 that describes the refractiveindex fluctuations in the atmosphere above 6 km and considering the combined power spectrum of Kolmogorov and non-Kolmogorov turbulence. Before this analysis, we study the joint influence of the Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams.     

Numerical simulation of super-continuum laser propagation in turbulent atmosphere

Considering the atmospheric extinction and turbulence effects,we investigate the propagation performances of supercontinuum laser sources in atmospheric turbulence statistically by using the numerical simulation method,and the differences in propagation properties between the super-continuum(SC)laser and its pump laser are also analyzed.It is found that the propagation characteristics of super-continuum laser are almost similar to those of the pump laser.The degradation of source coherence degree may cause the relative beam spreading and scintillation indexes to decrease at different propagation distances or different turbulence strengths.The root-mean-square value of beam wandering is insensitive to the variation of source correlation length,and less aperture averaging occurs when the laser source becomes less coherent.Additionally,from the point of view of beam wandering,the SC laser has no advantage over the pump laser.Although the pump laser can bring about a bigger aperture average,the SC laser has a lower scintillation which may be due to the multiple wavelength homogenization effects on intensity fluctuations.This would be the most important virtue of the SC laser that can be utilized to improve the performance of laser engineering.     

21元分立式变形反射镜

来自远处目标的光波通过大气以后,由于大气湍流将使波面发生随机起伏,导致望远镜分辨率下降,而且口径越大,湍流效应越明显。为获得接近衍射极限的分辨率,就需要采用自适应光学技术对波面误差进行实时校正。而自适应光学系统之所以具有能动可控的特点,关键之一是它具有能控制光程的元件——变形镜。本文将从空间域的观点出发,讨论21元变开镜的最佳影响函数,机械耦合的确定及其滤波函数,并估算21元变形镜对大气湍流的补偿效果。     

Angle of Arrival Fluctuations for Optical Waves Propagating Through Joint Moderate to Strong Atmospheric Turbulence

Satellite laser communication has gained wide attention both at home and abroad. The pointing, acquisition, and tracking (PAT) technology is the kernel of satellite laser communication systems, and the atmospheric layer is a part of the communication channel for satellite-to-ground links. Thus, angle of arrival (AOA) fluctuations caused by atmospheric turbulence inevitably influence long-distance satellite laser communication. Therefore, it is very important to analyze the impact of AOA fluctuations in satellite laser communication systems. According to the actual situation of satellite-to-ground links, a joint atmospheric turbulence power spectrum model is defined that includes Kolmogorov turbulence from the ground to 6 km in portions of the troposphere and non-Kolmogorov turbulence above 6 km in the stratosphere. Based on the extended Rytov theory, we derive the large-scale and small-scale variances of AOA fluctuations propagating in the uplink and downlink channels for a satellite laser communication system and analyze the influence of large zenith angle variations on the AOA fluctuations. It has long been a focus of concern that the expressions for the AOA variance obtained must be concise and of closed form.     

基于拉盖尔-高斯光束的单光子捕获概率研究

单光子源通常采用基于高斯光束的高度衰减激光脉冲,假设激光束具有初始高斯时域脉冲波形和TEM01模拉盖尔-高斯空域分布.基于折射率起伏的Rytov近似和修正von Karman谱模型,研究了大气湍流对星地量子通信单光子捕获概率的影响;建立了上行信道和下行信道的单光子捕获概率理论模型;针对低轨卫星-地面站间激光链路,对单光子捕获概率进行了分析.结果表明:上行信道的单光子捕获概率强烈依赖于地面折射率结构常数C2n(0),且随着C2n(0)的增加而减小;然而,下行信道的单光子捕获概率并不依赖于C2n(0),即大气湍流对其没有影响.