【作者】 吕清花；

【导师】 朱晓； 许忠保；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2013， 博士

【摘要】 普通点对点的成像系统不足之处就是当物面和像面不共轭时，图像迅速模糊。光学成像系统景深延拓则意味能包含更多的物方信息，在工业生产和科学研究中有着广泛的应用前景，长期以来倍受研究者关注。本论文研究利用“0/π”二元相位模板实现光学系统景深延拓的成像技术。本论文的主要研究工作如下：从频谱的角度分析了普通衍射受限成像系统离焦时光学传递函数的计算方法，给出了光学传递函数（OTF）曲线与离焦量的变化关系，分析了随着离焦量的增大，在通频带内会出现相位反转和调制传递函数（MTF）曲线过零点现象，从而导致图像高频细节部分被截止，图像出现模糊。为此提出了利用“0/π”二元相位模板实现通频带内相位的调制，提升截止频率并实现通频带内无零点。结合筒长无限显微镜，设计了大景深显微成像系统。将点扩散函数按照归一化光瞳函数的孔径展开，通过分别设置0.1和0.05的对比度，利用0.1和0.01步距相结合的粗搜索和精搜索结合的算法，寻找最大截止频率对应的最佳二元相位模板参数，并从理论上分析了π相位的正、负相位误差对MTF曲线的影响。运用ZEMAX软件，设计了筒长无限显微系统，并通过优化得到最佳系统结构参数。分析了点扩散函数和调制传递函数在不同离焦参数，即不同物距变化量下的变化情况，并给出了分辨率板和字符仿真成像结果，比较了在相同物距变化量下，施加相位模板前后的图像清晰度。研究了利用液晶空间光调制器实现“”二元相位板模拟的可行性。通过分析空间光调制器实现纯相位调制的原理，设计了利用干涉法测量相位变化的光路图，并提出了利用二元峰-峰值计算相位移动量的算法，通过两组不同偏振角的相位调制实验，得到了相位调制度与输入图像灰度值之间的关系，确定出选取液晶空间光调制器前、后偏振片的角度分别为40°和160°，灰度值设为190时，可得到π相位调制。根据理论计算和仿真的“”二元相位模板的最佳半径参数，运用液晶空间光调制器模拟“0/π”二元相位模板，并加入到4f系统中，分别对圆孔、双缝、二维光栅字和字符进行成像实验。ZEMAX仿真结果和实际成像实验结果表明，“0/π”二元相位模板能有效延拓景深，即使不采用图像处理，也具有较好的离焦不变性和高分辨率。更多还原

【Abstract】 Lens imaging system is based on point-to-point imaging, and it has an obviousdisadvantage that when the object and image planes are not in conjugate position, theresultant image is rapidly blurred. An optical imaging system with extended depth of fieldmeans it can include more information of the object，and it can be widely used in mostfields such as: industry manufacture and scientific research. Therefore, it has been anactive research topic to extend the depth-of-field of optical imaging systems. The aim ofthis thesis is to present a0/πbinary phase mask and prove it can extend the depth offield of imaging systems.The main research works are as follows:The method of calculating the OTF (Optical Transfer Function) of a general defocusdiffraction-limited imaging system is analyzed in terms of frequency spectrum. Therelationship between the OTF and the defocus value is given with some curves. With theincreases of the defocus value, there will appear the phase inversion and amplitudezero-crossing phenomenon in the pass-band, which cut off the high-frequency detail partsof the image. Therefore a binary phase mask is introduced in the pass-band, toenhance the cut-off frequency and keep no zero-crossings within the pass band.A micro-imaging system with a large depth of field is designed through adding a0, binary phase mask into the infinite tube length microscope. The PSF (Point SpreadFunction) is expanded with the normalize pupil function. A searching algorithm, combinedby global rough search and local careful search, is used to seek an optimal pupil mask thatprovides the largest spatial cut-off frequency band in certain desired contrast values5%and10%. The effect for MTF curves by the positive and negative manufacture errors ofphase is analyzed.Using the optical design software ZEMAX, an infinite tube length micro imaging system with the binary phase mask is arranged and optimal parameters are acquired afterseveral optimizations. The MTFs (modulation transfer function) curves and the normalizePSFs of the imaging system corresponding to the different defocus values (i.e.differentobject distance) are analyzed. Imaging results for the objects of letters, resolution and chipsare compared in the cases of without and with the mask for the same defocus position.A liquid crystal spatial light modulator is proposed to simulate the0/πbinaryphase mask, and it is feasible method affirmed by the theoretic analyzing. An interferenceoptical system is designed for measuring phase shift, and a method is presented to calculatethe phase shift in terms of the peak-to-peak values of the interference fringes. Twoexperimental results show the relationship between the image gray value and the phasedepth, and the π phase shift can be obtained in the case of angles polarizer φ1=40°,φ2=160°and gray value190.According the theoretic calculation and ZEMAX simulated results, the SLM,simulating the optimal binary phase mask, insert the4f optical system which instead of theinfinite tube length microscope. Imaging experiments are performed with the objects ofcircle, dual slit,2-D grating words and letters.ZEMAX simulation results and imaging experiments show that binary phasemask can effectively extend the depth of field of the imaging system, which has a highresolution in a long frequency band and can obtain clear images without anypost-processing.更多还原