分数域滤波的分数傅里叶变换光学成像性能分析

将分数域滤波同光学成像相结合,提出了一种基于Lohmann Ⅰ型的带有滤波孔径的两级联分数傅里叶变换光学成像系统.根据分数傅里叶变换和菲涅耳衍射之间的关系以及分数傅里叶变换的分数阶可加性,结合分数域滤波分析了分数傅里叶变换光学成像的基本理论.以点扩散函数和调制传递函数作为评价成像质量的准则,详细分析了不同分数阶光学系统...     

提高微细图形光刻分辨力的相移滤波技术研究

详细研究了提高投影成像光刻分辨力的相移滤波技术的基本理论,给出了理论模型,进行了模拟计算.对不同掩模图形设计制作的不同优化滤波器进行光刻对比实验并取得实验结果.研究表明,相移滤波能显著提高部分相干成像系统光刻分辨力和增大焦深,同时能提高光能利用率,有利于提高光刻生产率,是一种有效提高光刻分辨力和焦深的波前工程技术.     

分辨力增强技术的频谱分析

离轴照明和衰减型相移掩模作为重要的分辨力增强技术,不仅可以提高光刻的分辨力,同时还可以改善成像焦深,扩大光刻工艺窗口,实现65~32 nm分辨成像。从频谱的角度分析了离轴照明和衰减型相移掩模对成像系统交叉传递函数和像场空间频率分布的影响,研究这两种技术的物理光学本质,由此进一步优化光学成像系统设计、分辨力增强技术和确定设备使用的参量。对分辨力增强技术的频谱分析研究表明,分辨力增强技术通过调整像场频谱分布,改善了光学光刻的图形质量。对于65 nm密集图形,离轴照明和相移掩模结合后可以使成像衬比度最高达到0.948,工艺窗口在5%曝光范围内焦深达到0.51μm。     

一种新型投影曝光调焦方法

为研究大面积激光投影光刻的调焦,利用Zemax光学设计软件模拟离焦对光程差（OPD）和调制传递函数（MTF）的影响,分析二者对投影曝光图形质量的影响,给出系统最大的离焦量值。提出一种利用显微镜的调焦方法,分析此方法的调焦误差主要来自于显微镜景深,根据景深表达式和系统最大离焦量值,选择一款景深不大于系统最大离焦量的显微镜来构建调焦系统,并基于该调焦系统进行光刻实验。实验结果表明:利用该方法对投影成像光刻进行调焦,无论是否离焦,边缘视场与中心视场的MTF均有差异,分辨率也有差异,但这种差异不影响光刻图形的质量。     

基于数字微反射镜灰度光刻的成像模型

在深入探讨DMD(Digital Mirror Device)灰度图形传递的特点基础上,把曝光量分布作为分析数字光刻成像的物理量,建立了数字灰度光刻的成像模型.以制作微米量级微透镜为例,通过模拟分析,讨论了数字光刻过程中DMD的工作方式、成像系统参量对抗蚀剂曝光量分布的影响,揭示了数字灰度光刻成像机理,为开展数字光刻实验研究提供了理论根据.     

入射光束角度及强度偏差对多光束干涉光刻结果的影响

建立了多光束干涉光刻干涉场内光强分布的数学模型,仿真计算了双光束、三光束、四光束干涉曝光情况下,入射光束存在角度偏差以及各入射光强不同时的干涉图样,并与理想状态的模拟结果进行对比.结果表明:光束入射角度偏差主要影响干涉图样的形状和周期;入射光的光强不同是降低图形对比度的主要因素.利用402nm波长激光光源进行多光束干涉光刻实验.设定激光器输出功率32mW,每两束光夹角为16°,通过控制曝光、显影工艺,双光束干涉光刻产生周期为1.4μm的光栅、点阵和孔阵结构,三光束干涉光刻产生周期为1.7μm的六边形图形阵列.该模型可为利用干涉光刻技术制备微细周期结构,提高光刻图形质量,提供一定的理论参考.     

可模式识别的水声成像方法

提出一种在自由环境中可以进行模式识别的水声成像方法。利用角域滤波将空间不同入射方向的平面波在阵元域中进行分离,在成像扇面内按要求设计一系列角域带通滤波器,这些滤波器的输出就是从角通带内入射的平面波在阵元域中的快拍数据,可以实现要求输入为阵元域特性数据的目标识别和底质分类等专用的模式识别算法,角域滤波器输出的平面波快拍数据的幅度作为像素值进行水声成像。采用角域滤波的方法可以进行水声成像得到所需要的声图,并且每个像素对应着相应点目标远场平面波入射到接收阵时所产生的快拍数据。仿真和实验数据处理结果表明,采用角域滤波和利用常规波束形成所得到的声图是一样的,并且两种成像方法具有相同的稳健性。      

具有存储功能的衍射图像光刻系统的研制

研制了一种在衍射光变图像器件上进行信息存储的新型数字化激光光刻系统。采用空间光调制器作图形自动输入,双远心投影成像系统在光刻记录面上缩微图形。通过光栅干涉光学头对记录面上的微图形进行干涉调制,使微图形上产生干涉条纹,条纹空间频率范围为500-1200lp／mm。在光刻胶干版上的存储实验表明,在衍射光变图像上的单角度存储信息密度大于3．7Mbit／cm^2。改变干涉条纹取向、条纹间隔和需要存储的图形,光刻系统可实现信息的旋转复用存储。上述光刻系统将会在防伪和衍射光变图像器件制造领域有良好应用。     

用多项式近似逆滤波函数实现场曲修正

根据光电成像系统传递函数,确定逆滤波函数对获得图像进行反降质恢复.将连续逆滤波函数按泰勒级数展开,用多项式近似表示.对逆滤波函数的多项式作反傅里叶变换,得到图像恢复在空间域中的近似运算表达,即图像信号及其各阶导数的线性组合,而不是复杂的反卷积操作.该方法特别适合空间移变系统的图像恢复.详细分析了这种方法的原理,推导了运算公式,并给出了对场曲图像处理的结果.     

非接触式光刻中的微透镜阵列系统

本文介绍一种供非接触式光刻使用的由三片微透镜陈阵叠合成1：1成像多孔径微小光学光刻曝光系统。针对大面积光刻，可以获得良好的分辨率和较大的焦深。本文还介绍了这种微透镜阵列的制作方法。     

用全息透镜记录多重分数傅里叶变换全息图

提出一种全息透镜记录多重分数傅里叶变换全息图的新方法，它能在三维空间不同位置和不同方向上分别再现所记录的多个物体的图象，分析了利用全息透镜记录多重分数傅里叶变换全息图的原理及特点，制作了多重分数傅里叶变换全息图，并获得了满意的再现结果。     

分数傅里叶变换啁啾滤波

针对常规傅里叶变换所不能解决的啁啾噪声滤除问题，利用Wigner分布函数分析分数傅里叶变换的空域和频域特性，提出在分数傅里叶变换域进行啁啾滤波的方法。并将该方法应用到图像处理中，对分数傅里叶变换滤除一维和二维图像的啁啾噪声进行了计算机仿真，获得了满意的效果，结果表明该方法在图像处理中的有效性。     

Optical image encryption using fractional Fourier transform and chaos

We propose a new method for image encryption using fractional Fourier transform and chaos theory. Random phase masks are generated using iterative chaos functions. The input image is combined with the first random phase mask at the object plane and is then transformed using the fractional Fourier transform. After the first fractional Fourier transform, the second random phase mask, again generated by using the chaos functions, is used at the fractional plane. The second fractional Fourier transform operation is then carried out to obtain the encrypted image. Three types of chaos functions have been used: the logistic map, the tent map and the Kaplan–Yorke map. The mean square error and the signal-to-noise ratio between the decrypted image and the input image for the correct order and the incorrect order of the fractional Fourier transform have been calculated. The computer simulations are presented to verify the validity of the proposed technique.     

规范光学分数傅里叶变换下的光学传递函数

基于规范光学分数傅里叶变换,从光学传递函数概念出发,根据菲涅耳衍射、夫琅和费衍射定义,应用线性系统理论,分别给出了菲涅耳与夫琅和费衍射系统在规范分数傅里叶变换下的光学传递函数数学表达式。证明了其具有分数傅里叶变换的级联性,指出常规傅里叶变换下的光学传递函数为分数传递函数的特例。所得结果对光学分数傅里叶变换在信息处理、像质评价等方面的应用具有实用价值。     

Fast imaging algorithm for DMD-based photolithography with partially coherent illumination

In the paper, the characteristic of imaging with digital micro-mirror device (DMD) illuminated by a partially coherent light is discussed using Abbe's method. When a mask is sampled by DMD, the intensity in the substrate is modulated by sinc function and cut off by pupil function, according to oblique illumination theory and Fourier transform property of exponential function, a fast partially coherent imaging algorithm for DMD-based dynamic projection photolithography is proposed to combine Hopkins's method with Abbe's method. In the algorithm, the transmission cross coefficient (TCC) matrix of DMD projection photolithography is constructed as two-matrix multiplication according to illuminate source points. The new development presented in this paper utilizes matrix multiplication technique to speed up the computation of TCC matrix by tenfold on an average, which is beneficial to real time mask shift and mask optimization in DMD-based gray-tone photolithography.     

Fractional Gabor transform

A fractional Gabor transform (FRGT) is proposed. This new transform is a generalization of the conventional Gabor transform (GT) based on the Fourier transform to the windowed fractional Fourier transform (FRFT). The FRGT provides analyses of signals in both the real space and the FRFT frequency domain simultaneously. The space-FRFT frequency pattern can be rotated as the fractional order changes. The FRGT has an additional freedom, compared with the conventional GT, i.e., the transform order. The FRGT may offer a useful tool for guiding optimal filter design in the FRFT domain in signal processing.     

Coincidence fractional Fourier transform with a stochastic electromagnetic Gaussian Schell-model beam

Based on classical theory of optical coherence and polarization, coincidence fractional Fourier transform (FRT) with a stochastic electromagnetic Gaussian Schell-model (EGSM) beam is investigated. Dependences of the quality and visibility of the coincidence FRT pattern of an object on the degree of polarization and correlation coefficients of the EGSM beam are studied numerically. It is shown that the quality and visibility of the coincidence FRT pattern of an object are determined by the polarization and coherence of the EGSM beam together.     

Second-order fractional Fourier transform with incoherent radiation

Based on the coherent optical theory, we extend the fractional Fourier transform of first-order correlation to a fractional Fourier transform of second-order correlation. An optical system for implementing a second-order fractional Fourier transform was designed. As a numerical example, we investigate the second-order fractional Fourier transform for a single slit.     

Computation of the cascaded optical fractional Fourier transform under different variable scales

A simple but effective method for calculating the cascading of the multiple stages of optical fractional Fourier transform was proposed. Unlike the previous methods for solving the problems of cascading the optical fractional Fourier transform, we did not change the structures of the optical setups proposed by Lohmann but calculate the cascaded optical fractional Fourier transform with modified transform orders obtained by our method. Computer-simulation and experimental results were presented and a good agreement between them was obtained.