直视合成孔径激光成像雷达双面反射棱镜旋转发射装置内发射场的空间波前特性研究

Research on Spatial Wave-Front Characteristics of the Inner Optical Fields of the Transmitter with Double-Face Rotatable Reflectors in Down-Looking Synthetic Aperture Imaging Ladar

直视合成孔径激光成像雷达(SAIL)中,在发射端主镜的后焦面,两个同轴反向扫描正交偏振发射光束需要具有空间抛物波前相位波前差。采用自差接收探测和相位复数化处理,在交轨向产生与目标点横向位置成正比的线性项调制,在顺轨向产生与目标点纵向位置成中心的二次项相位历程,成像原理分别采用傅里叶变换和匹配滤波聚焦成像。提出了一种新的双面反射镜旋转发射结构,实现了同轴正交偏振的双光束,在交轨向对远场目标反向扫描且速率相同,同时通过柱面镜控制顺轨向光束相位变化。基于傅里叶光学理论和数学近似,理论分析和公式推导双面反射镜的放置位置对内发射光场分布的影响。建立了物理模型,数值模拟正交偏振双光束在发射端衍射到内发射场物理过程,给出光场强度和相位分布,并且和解析分析结果作对比,给出误差分析和结论。

In down-looking synthetic aperture imaging ladar （SAIL）, spatial parabolic wave-front phase differences are requested for two coaxial reverse scanned polarization-orthogonal beams at the rear focal plane of inner optical fields of the transmitter. Using self-heterodyne detection and phase complex-value processing, this kind of SAIL generates a linear phase modulation proportional to the lateral distance in the orthogonal direction, and a parabolic phase history concerted in longitudinal position of the target point in the travel direction, based on the imaging principles of Fourier transformation focus and two-order phase matched filtering, respectively. The novel rotatable structure with double-face reflectors is proposed, in order to make two coaxial polarization-orthogonal beams scan far field target with different directions and the same angular rate in the orthogonal direction. And then, cylinder lens is employed in one of polarization branches to control phase change of the travel direction beam. According to the theory of Fourier optics and mathematical approximation, the effect of the positions of double-face rotatable reflectors on the distribution of inner optical field is studied by theoretical analysis and formula derivation. Under physical model constructed, the diffraction of two coaxial polarization-orthogonal beams from laser to inner optical fields is simulated numerically. The comparison results of amplitude and wave-front phase distribution between the discrete simulation and formula analysis are given, and finally, error analysis and conclusions are obtained.