【作者】 郑春艳；

【导师】 吴健；

【作者基本信息】 电子科技大学 ， 光学， 2012， 博士

【摘要】 液晶光栅作为一种光学相控阵被应用在激光雷达、卫星通信等系统中，可以实现激光束的灵活偏转。而要对定向光束的质量进行控制，就需要对液晶光栅相控阵的波前进行测试，分析其波前畸变的情况。要正确的测量出液晶光栅的特殊的剧烈变化的波前轮廓，就需要了解其波前分布误差对器件性能也即是对光栅衍射场的影响情况。为此，本文分析了影响液晶光栅波前轮廓的误差来源，把液晶光栅相控阵的波前误差分成周期型和非周期型两种，利用傅里叶级数分解及角谱衍射理论得出了不同类型波前误差对光栅衍射场的影响，并进行了仿真分析。根据波前误差的不同类型提出了针对性的波前测量方法，对这些方法进行了理论和仿真分析。对波前误差为周期型的情况，提出可通过测试各衍射级次的近场光强来近似反演液晶光栅后表面处（也可称为出口端面）的光场分布，从而求出波前分布。对波前误差为非周期型的情况，提出两种测试方法。一种是直接测量液晶光栅出口端面的波前分布。一种是测量闪耀级次的衍射光场，用逆衍射运算来反演液晶光栅出口端面的波前误差分布。提出采用新型四边形结构的径向剪切干涉光路来测量液晶光栅相控阵的波前，给出了适合于不同频率范围波前的三种测量方法：自载波调制法，固定载波调制法及单一衍射级反演法。研制出口径10mm×10mm的剪切干涉仪，并与商用WYKO干涉仪进行比对测试，对同一块平面样板测出的波前之差的峰谷(Peak ToValley,简称P-V)值小于/20，均方根值（Root Mean Squares,简称RMS）小于/200。用该剪切干涉仪测量了液晶光栅的静态相位分布、电压-相移特性及偏转光束波前，为液晶光栅器件的性能分析及加载电压方案提供了依据。提出基于4f系统的Mach-Zehnder共轭移相干涉法测试液晶光栅出口端面波前。用研制的10mm×10mm口径Mach-Zehnder共轭移相干涉仪测量出了不同周期液晶光栅的波前分布，由测试结果计算出的远场光强分布与实测远场分布基本一致，说明了测试结果的准确性。更多还原

【Abstract】 Liquid-crystal grating, as a kind of optical phased array, has been used in laserradar system, satellite communication system and other photoelectric systems to realizeagile beam steering. In order to control directional beam quality, the wavefront of liquidcrystal grating phased array needs to be tested and the wavefront distortion needs to beanalysised.To properly test the special dramaticly-changed wavefront contour of the liquidcrystal grating, the impact of the wavefront distribution on device performance, or onthe grating diffraction field, needs to be understood. This paper analyzes the errorsources of liquid crystal grating wavefront contour and divides the wavefront errors ofliquid crystal grating phased array into two types: periodic and non-periodic. Using theFourier series decomposition and angular spectrum diffraction theory, the influence ofdifferent types of wavefront errors on grating diffraction field has been calculated, andthe simulation analysis has been done.According to the different types of wavefront errors, different wavefront measuringmethods have been proposed. And theoretical analysis and computer simulation aboutthese methods have been done. For periodic wavefront error, optical field distribution ofthe back surface of liquid crystal grating (also known as the exit end of liquid crystalgrating) can be restructured approximately by testing the near-field intensities of all thediffraction orders, and thus the wavefront distribution is obtained from it. Fornon-periodic wavefront error, two kinds of test methods have been proposed. one isgetting wavefront distribution through directly measuring optical field distribution ofthe exit end of liquid crystal grating. The other is gaining wavefront error distributionthrough measuring optical field distribution of the blazed order and the inversediffraction propagation calculation.Measuring the wavefront of liquid crystal grating phased array by means of thenovel quadrilateral radial shearing interference light path has been proposed. And threekinds of measuring methods suitable for different frequency range wavefronts havebeen given: the own carrier modulation, fixed carrier modulation and a single diffraction order inversion. A10mm×10mm aperture radial shearing interferometer hasbeen developed. Using this interferometer and a commercial WYKO interferometertesting the same plane optical element, the difference of test results is less than λ/20forpeak to valley (P-V) value and less than/200for root mean square (RMS) value. Staticphase distribution of liquid crystal grating, voltage-phase shift characteristics and thewavefront of deflection beam have been measured utilizing this shearing interferometer,which provide a basis for performance analysis and voltage load scheme of liquidcrystal grating device.Mach-Zehnder conjugate phase shifting interferometry based on4f system hasbeen advanced to measure the wavefront of the exit end of liquid crystal grating. Thewavefronts of different periodic liquid crystal gratings have been tested with a10mm x10mm aperture Mach-Zehnder conjugate phase shifting interferometer. The far fieldintensity distributions of diffraction fields of liquid crystal gratings calculated from theresults are the same as the far field distributions measurement, which proves theaccuracy of test results.更多还原