Chen Chunyi, Yang Huamin, Zhou Zhou, Zhang Weizhi, Kavehrad Mohsen, Tong Shoufeng, Wang Tianshu
Opt Express. 2013 Dec 2;21(24):29731-43. doi: 10.1364/OE.21.029731.
The temporal covariance function of irradiance-flux fluctua-tions for Gaussian Schell-model (GSM) beams propagating in atmospheric turbulence is theoretically formulated by making use of the method of effective beam parameters. Based on this formulation, new expressions for the root-mean-square (RMS) bandwidth of the irradiance-flux temporal spectrum due to GSM beams passing through atmospheric turbulence are derived. With the help of these expressions, the temporal fade statistics of the irradiance flux in free-space optical (FSO) communication systems, using spatially partially coherent sources, impaired by atmospheric turbulence are further calculated. Results show that with a given receiver aperture size, the use of a spatially partially coherent source can reduce both the fractional fade time and average fade duration of the received light signal; however, when atmospheric turbulence grows strong, the reduction in the fractional fade time becomes insignificant for both large and small receiver apertures and in the average fade duration turns inconsiderable for small receiver apertures. It is also illustrated that if the receiver aperture size is fixed, changing the transverse correlation length of the source from a larger value to a smaller one can reduce the average fade frequency of the received light signal only when a threshold parameter in decibels greater than the critical threshold level is specified.
利用有效光束参数法，从理论上推导了高斯谢尔模型（GSM）光束在大气湍流中传输时辐照度 - 通量涨落的时间协方差函数。基于此公式，得出了由于GSM光束通过大气湍流导致的辐照度 - 通量时间谱均方根（RMS）带宽的新表达式。借助这些表达式，进一步计算了在受大气湍流影响的自由空间光（FSO）通信系统中，使用空间部分相干源时辐照度通量的时间衰落统计特性。结果表明，在给定接收孔径大小的情况下，使用空间部分相干源可以减少接收光信号的衰落分数时间和平均衰落持续时间；然而，当大气湍流变强时，对于大、小接收孔径，衰落分数时间的减少变得不显著，对于小接收孔径，平均衰落持续时间的减少变得微不足道。还表明，如果接收孔径大小固定，仅当以分贝为单位的阈值参数大于临界阈值水平时，将源的横向相关长度从较大值更改为较小值才能降低接收光信号的平均衰落频率。
