【作者】 翟中生；

【导师】 赵斌；

【作者基本信息】 华中科技大学 ， 测试计量技术及仪器， 2008， 博士

【摘要】 大景深光学成像系统具有更大的成像空间,不需要进行机械调焦和用于三维显示等优点,长期以来倍受研究者关注。本文根据无衍射光具有线焦的特性,将其应用于成像系统中以增大光学系统的景深。本文的主要研究工作及创新如下:研究了轴锥镜在不同光源下所产生光场的光学特性,建立了其理论数学模型。基于平行单色光照射轴锥镜的衍射特性,推导了轴上点产生的发散、会聚球面波照射轴锥镜的衍射特性。同时根据光源的光谱特性,建立了准单色光和复色光照射轴锥镜的衍射图样。分析了两束无衍射光的干涉理论。利用两小孔产生两束相干的无衍射光,依据单束倾斜平行光照射轴锥镜的衍射场,分析出这两束无衍射光产生的干涉场为每束无衍射光的无衍射场的线性叠加,即为两个零阶贝塞尔函数的叠加。根据暗条纹的计算公式,推导出干涉条纹的轨迹为双曲线。设计并研制了三种常用的大景深成像原理实验装置。利用轴锥镜能产生无衍射光的特性,分析了将其应用到成像系统中增大景深的原理。根据应用的不同,分别设计了大景深1:1成像系统、显微成像系统和望远成像系统。以设计的1:1成像系统为例,推导了无衍射光大景深成像系统的点扩散函数的形式和变化规律,重点分析了点扩散函数中心光斑的变化规律,这个变化规律为系统所成的像的变化原因以及进行图像复原提供了理论依据。还从光学传递函数、分辨率、对比度和景深等方面对成像系统进行了深入的理论分析。介绍了四种常用的图像复原方法:维纳滤波,约束最小二乘方,Lucy-Richardson法和盲复原法,并比较了这四种方法对无衍射光成像系统的恢复结果。针对无衍射光成像系统的成像特性,提出了多幅图像叠加法。由于无衍射光成像系统的点扩散函数扩散较开,使得所成的像对比度很低,图像细节淹没在大量噪声中,为了提高图像的对比度和清晰度,提出了这种有效的算法。用设计的成像系统分别对字符、图案和空间连续的物体进行了成像实验。成像实验表明,本文设计的三种基于无衍射光大景深成像系统比普通光学系统有更大的景深,因此,本文提出的方法能有效的增大非相干成像系统的景深。更多还原

【Abstract】 An optical imaging system with large depth of field has features of greater imaging space, without requiring mechanical focusing and displaying 3-D objects. Therefore, it has been an active research topic to extend the depth-of-field of optical imaging systems. The non-diffracting beam has the characteristics of focal segment, so it can be used to extend the depth-of-field of an imaging system.The main research and innovations are as follows:The diffracting patterns produced by the axicon in different light illuminating are analyzed, and the mathematical models of these patterns are theoretically established. Based on the diffraction pattern of the axicon in monochromatic parallel light illumination, the diffraction patterns of the axicon illuminated by converging and diverging waves produced by an axis point are derived. Moreover, the diffraction patterns of the aixcon illuminated by quasi-monochromatic light and polychromatic light are presented based on their spectrum characteristics.The interference pattern of two non-diffracting beams is analyzed. Two non-diffracting beams are gene rated when an axicon is illuminated by two coherent beams, which are produced by two pinholes illuminated by a monochromatic wave. Based on the non-diffracting property of an axicon in oblique illumination, the interference field is the linear superposition of each non-diffracting field of non-diffracting beam, namely the interference intensity is the sum of the two zero-order Bessel functions. The locus of inte rfe rence f ringes is analyzed to be hyperbola according to the formula of dark fringe.Three common large depth of field imaging systems are designed and produced. The axcion can produce a non-diffracting beam, and it is used to extend depth of field of optical imaging system, and the theorem of this method is analyzed in this paper. According to the different applications, three optical systems with large depth of field 1:1 imaging system, microscopic imaging system and telescopic imaging system are designed.The form and characteristics of the point spread function (PSF) of the designed imaging systems are derived based on the 1:1 imaging system. The changing rule of the point spread function centre spot is analyzed, and the rule gives the reason of the changing of the images quality, and provides a theoretical basis for image restoration. The imaging system is analyzed theoretically from OTF (optical transfer function), resolution, contrast and depth of field.Four tranditional image restoration methods: wiener filtering, constrained least squares filtering, Lucy-Richardson algorithm and blind deconvolution are introduced, and the experimental results used these four methods are compared. A multiple images superposition algorism is introduced based on the properties of the pictures imaged by the designed optical system. Since the PSF except the center spot spreads out on the full image, which makes the contrast be lower, and makes the details of image immerse in large noise. In order to improve the contrast and definition of the image, this effective algorism is presented.Imaging experiments were steped to use the designed three imaging systems to image with the objects of letter, pattern and space continuous object. Experimental results show that these three imaging systems, designed based on the non-diffracting beam, have larger depth of field than ordinary optical systems. Therefore, the performed experiments validate the effect and feasibility of non-diffracting beam for imaging with extending depth of field.更多还原