排序方式: 共有39条查询结果,搜索用时 422 毫秒
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大气光通信中大气闪烁时间平滑效应研究 总被引:4,自引:1,他引:3
利用大气闪烁的时间平滑效应,增加光电探测器曝光时间是克服大气闪烁对大气光通信的瞄准、捕获、跟踪链路影响的有效途径之一.基于科尔莫戈罗夫谱,导出了弱湍流起伏区无限平面波和球面波的大气闪烁时间平滑因子的一般表达式,并且用几何光学近似得到了在大孔径和小孔径接收情况下的时间平滑因子近似表达式.在孔径远大于菲涅耳区尺度时,平面波和球面波的时间平滑因子的近似表达式与精确表达式的误差分别小于6%和3%.分析结果表明,孔径越小,时间平滑效应越显著,并且菲涅耳区尺度对时间平滑效应影响的程度也随着孔径的增加而减弱. 相似文献
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深空光通信中的图像信标捕获技术 总被引:1,自引:0,他引:1
为实现深空光通信链路建立过程中精确的对准,提出了一种深空光通信系统扩展信标的捕获方案。该方案以可视地球图像作为信标,在航天器上存储一幅信标图像作为参考图像,采用天线扫描的方式在各点对所瞄准的区域成像,利用像素扫描的方式,使参考图像和实际探测图像进行相关,在天线扫描完成以后,找出相关性最大的位置,即可认为在该点捕获到地球图像。在计算两图像相关系数的过程中,由于傅里叶梅林变换幅度谱具有伸缩及旋转不变性,因此利用傅里叶梅林变换即可消除两图像相关系数因为旋转和伸缩的影响。利用蒙特卡罗方法随机产生1000个视场,仿真结果表明,3σ内正确捕获到信标图像的概率为99.6%,表明这是一种可行的方法。 相似文献
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分析了温度梯度和均匀温度对潜望式激光通信终端反射镜形变的影响,利用椭圆域上的Zerni-ke多项式对椭圆反射镜的波前进行拟合,计算由于热形变导致的波前畸变误差,给出了星间激光通信终端反射镜均方根值、发射光束瞄准误差、接收端光强随温度梯度和均匀温度的变化关系。结果表明:温度梯度对反射镜的影响只是引起峰值光强的漂移和少许下降,当温度梯度为14℃/m时瞄准误差达2.1μrad。均匀温度会引起接收端的光强分布变化,从而导致很大的瞄准误差和光强衰减,当均匀温度与参考温度的差值小于0.6℃时,由波前畸变误差引起的瞄准误差小于1μrad,当差值大于0.6℃时,瞄准误差突然增大到几μrad,接收端光强分布发生变化,此时反射镜热形变引起的像散项对光强分布起重要作用。 相似文献
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Further analysis of scintillation index for a laser beam propagating through moderate-to-strong non-Kolmogorov turbulence based on generalized effective atmospheric spectral model 下载免费PDF全文
A new expression of the scintillation index(SI) for a Gaussian-beam wave propagating through moderate-to-strong non-Kolmogorov turbulence is derived, using a generalized effective atmospheric spectrum and the extended Rytov approximation theory. Finite inner and outer scale parameters and high wave number "bump" are considered in the spectrum with a generalized spectral power law in the range of 3–4, instead of the fixed classical Kolmogorov power law of 11/3. The obtained SI expression is then used to analyze the effects of the spectral power law and the inner scale and outer scale on SI under various non-Kolmogorov fluctuation conditions. These results will be useful in future investigations of optical wave propagation through atmospheric turbulence. 相似文献
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Study on irradiation-induced defects in GaAs/AlGaAs core–shell nanowires via photoluminescence technique 下载免费PDF全文
To gain a physical insight into the radiation effect on nanowires(NWs), the time resolved photoluminescence(TRPL)technique is used to investigate the carrier dynamic behaviors in GaAs/AlGaAs core–shell NWs before and after 1-MeV proton irradiation with fluences ranging from 1.0 × 10~(12) cm~(-2) to 3.0 × 10~(13) cm~(-2). It is found that the degradations of spectral peak intensity and minority carrier lifetime show similar trends against irradiation fluence, which is closely related to the displacement defects induced by irradiation. We also find that the proton irradiation-induced defects behave as Shockley–Read–Hall(SRH) recombination center trapping free carriers. Finally, the defect concentration could be estimated through measuring the minority carrier lifetime. 相似文献
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实际星地光通信系统的发射光束为高斯型的情况下,跟瞄误差和大气闪烁是星地激光链路中的主要信道噪声源。在结合两者对系统性能影响的前提下,对星地激光通信链路进行了理论分析和模型建立。基于该模型对星地激光链路中光束发散角与跟瞄误差之比的优化选择问题进行了研究。结果表明:对于上行链路,在不同误码率需求下都存在一个光束发散角与跟瞄误差的最佳比值,使得上行链路余量最大;对于下行链路,在不同误码率要求下均存在一个光束发散角与跟瞄误差的最佳比值,使得下行发射光功率的需求最小。利用最优化方法和最小二乘法拟合,得到星地激光链路中光束发散角与跟瞄误差的最佳比值和系统误码率的经验公式。 相似文献
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Based on the modified spectrum, the analytic expressions for the
variance and normalized covariance of angle-of-arrival (AOA)
fluctuations are presented, which are applicable to the weak and
strong regimes. The experimental data of AOA fluctuations validate
the new derived expressions in weak and strong regimes. The results
show that the receiving aperture D, outer scale and cell scale
larger than the scattering disc S contribute significantly to the
AOA fluctuations, and contributions from the small-scale turbulence
are negligible. For the case of 4S/D\ll 1, the receiving aperture
dominates low-pass filtering effects and the new displacement
variances are in good agreement with the results from the
old weak-fluctuation theory. For the case of 4S/D\gg 1, the scattering disc dominates the low-pass
filtering effects and the new displacement variances depart from the
results from the old
weak-fluctuation theory. 相似文献
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