A mathematical model of the effect of random pointing errors on the mixing efficiency of heterodyne detection is established, and the effect of angle-of-arrival fluctuation on the mixing efficiency of heterodyne detection is investigated. The results show that the average mixing efficiency is significantly affected by the angle-of-arrival fluctuation in the outer scale. The larger the obscuration ratio and receiving aperture of the optical system, the lower the average mixing efficiency is. The closer the value of $D/r_0$ is to 0.79, the closer the bit error rate of heterodyne detection is to $1\times {10}^{-9}$ under weak turbulence.

A mathematical model considering the effects of amplitude and phase random fluctuations on the signal-to-noise ratio (SNR) of heterodyne detection was established, and the effects of irradiance and phase fluctuations on the performance of heterodyne detection were investigated. The results show that the inner scale of turbulence significantly affects the SNR. The first 20 Zernike modes have a greater effect on the SNR of the heterodyne detection system. The SNR is affected more significantly by phase fluctuations than by irradiance fluctuations. The SNR decreases by four orders of magnitude because of amplitude and phase fluctuations.

By analyzing the effect of the degree of polarization (DoP) of the partially coherent Gaussian Schell-model (GSM) beam on a heterodyne system of an uplink path and a downlink path, we developed an innovative and noteworthy theory according to which σ_sy (signal beam waist radius in the y direction component) and δ_Syy (coherence length of the signal beam in the yy direction component) had a more significant impact on heterodyne efficiency and DoP than the turbulence term on uplink and downlink paths. Namely, the DoP and heterodyne efficiency of an uplink path are higher than that of a downlink path when σ_sy > 0.02 m or δ_Syy ≥ 0.03 m. This innovative rule provides an efficient way for increasing the heterodyne efficiency of a signal beam propagating along an uplink or a downlink path channel in satellite-ground communication links in free-space optical heterodyne detection communication.

Partially coherent optical vortices have been applicated widely to reduce the influence of atmospheric turbulence, especially for free-space optical (FSO) communication. Furthermore, the beam array is an effective way to increase the power of the light source, and can increase the propagation distance of the FSO communication system. Herein, we innovatively report evolution properties of the radial phased-locked partially coherent vortex (RPLPCV) beam array in non-Kolmogorov turbulence. The analytical expressions for the cross-spectral density and the average intensity of an RPLPCV beam array propagated through non-Kolmogorov turbulence are obtained. The numerical results reveal that the intensity distribution of the RPLPCV array propagated in the non-Kolmogorov turbulence is gradually converted to a standard Gaussian distribution. In addition, the larger the radial radius, radial number and waist radius are, the smaller the coherence length is. Moreover, the longer the wavelength is, the shorter the propagation distance required for the intensity distribution of the RPLPCV beam array to be converted into a Gaussian distribution in the non-Kolmogorov turbulence. The research in this paper provides a theoretical reference for the selection of light sources and the suppression of turbulence effects in wireless optical communication.

涡旋光束轨道角动量(Orbital Angular Momentum, OAM)模式的识别属于OAM复用通信系统中的关键技术之一. 本文以高阶拉盖尔-高斯(Laguerre-Gaussian, LG)光束为研究对象, 提出了一种基于卷积神经网络(Convolutional Neural Network, CNN)的高阶涡旋光束叠加态OAM模式识别方法. 将经大气湍流传输后的高阶LG光束叠加态强度图像作为基础训练CNN模型, 在给定训练数据的情况下, 可以准确高效地对不同条件下高阶LG光束叠加态的OAM模式进行分类与识别. 重点讨论了不同大气湍流强度、传输距离、光束截面完整程度和模式间隔对OAM模式识别准确率的影响. 研究结果表明, CNN能够在强大气湍流环境下以高于99%的准确率对固定的OAM模式集进行分类和识别. 本研究成果为大气湍流环境中叠加涡旋光束的智能解码和解复用提供了新思路.