大口径投影光学系统采用低成本、大口径菲涅耳透镜制作, 可将远场散斑强度分布投影到CCD成像探测器上。通过CCD图像处理, 能够对给定孔径上的接收功率、闪烁指数进行量化评估; 在接收孔径足够大、保障散斑不会因为光束漂移效应而脱离菲涅耳透镜的条件下, 该系统还可以对光束漂移和特征半径进行量化评估。同时讨论了CCD像元响应非均匀性误差及其影响、CCD辐照响应函数和图像几何投影系数的定标方法。实验表明, 系统能够对激光大气传输过程中的远场散斑特征参数进行监测。特别对自由空间激光通信系统而言, 可以为大气衰减和多种大气湍流效应综合作用下的中值电平慢衰落研究和检测阈值优化设计提供实验数据支撑。

In order to systematically evaluate the characteristic parameters of far field speckle in the real atmosphere condition and analyze the influence of laser atmospheric propagation on the optoelectronic system, a monitoring method is presented using large aperture projection optics. The projection optics is made of low cost and large aperture Fresnel lens, which can project the irradiance distribution of far field speckle on the CCD detector. The receiving power and scintillation index on a certain aperture can be evaluated through CCD imaging process. The beam wander and beam radius can also be evaluated under the condition that the receiving aperture is large enough and the speckle would not leave the Fresnel lens because of the beam wander effect. The error of CCD pixel response non-uniformity and its influence and the calibration of CCD irradiance response function and image geometric projection coefficient are discussed. The experiments show that this system is feasible for the monitoring of far field speckle characteristic parameters in the laser atmospheric propagation. Especially for the free space optical communication, it can prove experiment data support on the slow fading research of median level and optimal design of detection threshold under the complex influence of atmospheric extinction and various kinds of turbulence effects.