基于数字闪耀光栅的位相全息图光电再现优化

针对利用液晶空间光调制器（LC-SLM）进行全息图光电再现过程中,再现像面存在多级衍射像造成单一像能量利用率低的问题,提出了一种在位相全息图中加载数字闪耀光栅的方法,以提高全息图光电再现中单一衍射像的衍射效率.分析了闪耀光栅作为衍射光学元件的特性及其对光波进行位相调制的原理,并阐述了在LC-SLM中加载数字闪耀光栅对位相全息图光电再现时像面能量分布的影响.搭建了基于LC-SLM的位相全息图光电再现实验系统.理论分析表明：在其他条件不变的情况下,加载竖直（或水平）槽向周期为2 pixels的数字闪耀光栅可使 关键词： 全息光电再现 位相全息图 数字闪耀光栅 液晶空间光调制器     

基于液晶光阀非线性变换的实时光学相关识别

提出了一种高鉴别能力的实时光学相关器，它采用液晶光阀作为实时输入器件，并利用其非线性变换特性对图像微分预处理，全息记录材料采用光折变晶体，且使用全取球面波作参考光。所给出的实验结果表明，该光学相关具有鉴别能力高，实时性和灵活性强，以及结构２紧凑的特点。     

Fast phase retrieval in slightly off-axis digital holography

In this study, three efficient algorithms are proposed for fast phase retrieval in slightly off-axis digital holography using spectrum cropping, spatial multiplexing, and complex encoding. In the first algorithm, the real spectral order of the subtracted hologram is filtered and cropped, and the number of pixels is decreased in the subsequent retrieval operations. In the second algorithm, two sequential subtracted holograms are digitally phase shifted and spatial multiplexed into one synthetic hologram, and thus only one inverse Fourier transformation is then required. In the third algorithm, two sequential subtracted holograms are encoded separately into the real part and the imaginary part of a complex hologram. Two cross-correlations can be used to reconstruct the phase, thereby improving the utilization of the spectrum. The three new algorithms speed up our previously proposed retrieval method with the assistance of specimen-free holograms. Our experiments demonstrated the validity and improved time requirements of the proposed methods.     

数字化合成全息图自动记录系统研究

从合成全息术的编码原理出发,采用了液晶空间光调制器、步进电机控制的可移动狭缝和一维移动平台等设备以及计算机数字多媒体技术、软件编程技术设计出一套数字化合成全息自动记录系统。该系统能够改善传统全息图手工制作效率低、操作不准确产生误差等缺陷,提高了合成具有视差、动感、颜色以及不同景深等特殊效果全息图的自动化水平。实际应用该系统合成了含有40幅照片信息的全息图。     

数字合成彩虹全息图

提出了一种利用现代计算机技术制作全息图的新方法。数字彩虹全息图是计算机技术、数字图像处理技术应用到传统的合成全息图制作技术中的一种全息图。把用数码设备采集到的图像或利用计算机生成的图像作为全息拍摄的“物”,突破了传统全息只能拍摄实物的限制,实现了全息图制作的数字化。实验结果表明了该方法的可行性。同时也讨论了该方法的优越性及在实际应用中的重要意义。     

Studies on aperture synthesis in digital Fresnel holography

Aperture synthesis can improve image resolution in digital holography by increasing the numerical aperture of the system. In this paper, we show that both the lateral resolution and image field of view can be enhanced at the same time using a more general Fresnel holography setup and hologram stitching. The impact of aperture synthesis on the lateral resolution is investigated both theoretically and experimentally. In the experiment, the synthesis is executed by moving the compact digital holographic system in two directions. Nine holograms are recorded and stitched into one hologram. The reconstruction results show that expanding aperture improves the lateral resolution. The lensless Fresnel holography used in this paper is demonstrated to have the ability to provide a larger numerical aperture and can compress the object spectrum in recording process.     

Recording and reconstruction of digital Gabor hologram

This paper looks at some as yet undisclosed observations in the recording and reconstruction of digital Gabor hologram. Small particles on the specimen plane diffract the illuminating spherical wave to form the object wave which interferes with the un-diffracted reference to form the in-line hologram. The interference is similar to that between two spherical wavefronts. It is shown that resolution enhancement can be achieved in the recording process through the use of wavefronts with different curvature. Numerical reconstruction of this hologram with a conjugate of the illuminating (reference) wave provides the in-focus real image at the object plane. It is exemplified that the proper choice of the reconstruction wavefront can optically magnify the reconstructed image enabling one to better visualize the resolution enhancement. Both theoretical analysis and experimental confirmation are provided for these observations.     

Vertical-bandwidth-limited digital holography

Optical scanning holography (OSH) is a promising technique to acquire a big-size digital hologram. However, the acquisition speed is limited by the mechanical scanner. In this Letter we apply the OSH in conjunction with an anisotropic low-pass filtering pupil to acquire vertical-bandwidth-limited (VBL) holograms. The size and the acquisition time of the VBL hologram can be reduced by one order of magnitude while the horizontal resolution remains the same as the conventional scanning hologram. The VBL hologram can be coded as an off-axis hologram without any postfiltering. Meanwhile, the full horizontal bandwidth of the displaying device can be capitalized.     

基于Matlab的计算全息图的制作与数字再现的研究

 应用Matlab语言,结合博奇型计算全息的编码方法,利用计算机分别绘制了菲涅耳全息图和傅里叶变换全息图,实现了计算全息图的快速制作,讨论了制作计算全息图的原理、方法和步骤。利用CGH技术和数字全息技术所生成的全息图再现出原始图像,完成了全息图的数字重现,实现了整个全息记录和再现过程的计算机模拟。与传统的编程语言和绘图方法相比较,该算法在实现上更加简单和快捷,并且带有一系列提高计算全息图质量的措施,有效地消除了零级像和孪生像的影响,获得了清晰的数字再现图像。     

基于希尔伯特-黄变换方法的同轴粒子全息图中粒子轴向位置提取方法

在颗粒的数字全息中,传统方法应用数值再现反演计算得到颗粒的相关信息,其中再现的判焦过程中存在繁琐费时的缺点.本文提出了一种基于希尔伯特-黄变换方法的同轴粒子全息图分析方法.将粒子同轴全息图沿中心往外得到的单个粒子径向强度分布作为初始信号,根据希尔伯特-黄变换方法中的经验模态分解首先将信号分解成几个本征模态函数,通过分析第一本征模态函数的希尔伯特谱,由拉依达法则剔除部分奇异点后做最小二乘线性回归分析,得到粒子的空间位置.该方法不需要对全息图进行重建,由信号自身构建基函数,有很强的适应性.理论模拟和实验证明,该方法计算速度快,准确度高,有望应用于全息图的实时在线分析.     

基于液晶空间光调制器的全息显示

在传统的纯相位全息显示系统中, 一般基于快速傅里叶变换(FFT)算法来计算相位全息图, 在FFT的计算中需要遵循Nyquist采样定理, 因此, 重建图像的尺寸往往受限于空间光调制器的固定采样率. 这个限制可以通过卷积算法或者两步菲涅耳衍射算法来解决, 但是需要使用多个FFT的计算, 导致计算量增大. 鉴于此, 提出了一种基于透镜的纯相位全息图计算方法. 在全息图的计算中, 通过透镜的成像原理建立一个采样率可变的虚拟全息面, 通过调节相应的距离参数使得在全息图的计算中可以任意调节原始图像的采样率, 摆脱了传统方法中液晶空间光调制器带宽积对重建图像尺寸的限制, 并且这种算法只需使用一次FFT就能达到变采样率的衍射计算, 大幅提高了全息图的计算速度. 数值模拟及光学实验结果证明了此方法可以在全息显示光学系统中清晰地重建不同尺寸的图像. 同时该系统可以有效地消除由空间光调制器的像素化结构带来的零级衍射.     

结合线性回归的离轴数字全息去载波相位恢复算法

为实现仅用一幅离轴数字全息图便能直接恢复相位,提出一种利用空间载波相移技术(spatial carrier phase shift, SCPS)和线性回归相结合的离轴数字全息去载波相位恢复算法.首先,利用SCPS将一幅离轴数字全息图分为四幅含有载波相移的全息图,其中载波相移由沿行、列两个方向的正交载波所引入;然后,将四幅载波相移全息图作为输入,将所求物体相位和两个正交的载波作为未知量,结合最小二乘法和线性回归同时求出载波和相位信息.相较于已有的去载波技术,本算法无需背景全息图作为参考,便可准确地去除载波,实现高质量的相位重建.本文结合数值仿真和具体实验结果验证本算法的有效性和优越性.     

基于数字全息干涉的实时微振动检测

基于数字全息理论的方法,构建了一套微振动实时测量的实验系统。通过运用基于全息干涉图像的振动快速解算算法,直接从记录的全息图中提取振动信息,实现对振动物体振幅值进行实时测量。该系统的接收光为散射光,使得测量角度不受被测物体结构的影响。通过测量由标准正弦波驱动的被测物微振动情况,对该实验系统进行了实验验证,实验结果表明,该系统能够实时测量微振动的振幅值（算法处理时间约为0.11 ms）,在550～2700 Hz频段内被测物的振幅较为稳定,系统稳定性误差为1.66%,真实地反映了其振动情况。     

Reconstruction of digital hologram of small particles on arbitrarily tilted plane using digital holography

Digital holographic off-axis geometry is presented for the reconstruction of the digital hologram of small particles in an arbitrarily tilted plane. A single hologram is sufficient to obtain a well focused clear image. We can't obtain clear images of small particles in the case of plane tilted to the detector plane by ordinary reconstruction method because of the rotation of the hologram plane. Rotational transformation based on coordinate rotation in Fourier space makes it possible to reconstruct holographic images on any plane in the object space. The reconstruction of digital hologram is based on the plane wave expansion of the diffracted wave fields, using Fourier optics and the two-axis rotation of the wave vectors. With this method, the object-to-hologram distance can be any small distance because the minimum distance requirement does not apply.     

An approach for sensing marine plankton using digital holographic imaging

The goal of this paper is to use digital holographic imaging for sensing marine plankton in recording sampling volume. The process stage of this approach includes: wavefront recording using in-line holographic recording set up and numerical reconstruction using Fresnel approximation and convolution algorithm. So, by capturing hologram of marine plankton and reconstructing hologram, the recorded optical field of marine plankton is retrieved. Digital holographic imaging is an extremely powerful technique for the study of marine plankton fields as it allows instantaneous, noninvasive, high-resolution recording of substantial volumes. Finally, this paper presents that it is possible for digital holographic imaging system to sense marine plankton according to laboratory results.     

数字全息图取样模型的简化研究

数字全息研究领域目前存在两种不同的数字全息图取样模型.按照这两种模型进行研究时, 不但涉及较复杂的数学运算, 在许多情况下还会导致不同的研究结果, 不便于理论分析及实际应用.基于对数字全息图记录的物理过程分析及电荷藕合器件(charge coupled device, CCD)几何结构的研究, 本文将这两种取样模型简化为相同的数学表达式. 利用数字全息图的余弦级数展开及取样定理对简化模型的研究表明, 简化模型不但具有清晰的物理意义, 而且可以方便地为应用研究服务. 基于简化模型对物光波通过光学系统到达CCD的数字全息记录系统进行了研究, 导出得到实验证实的波前重建表达式. 关键词： 数字全息 波前重建 相干光成像     

Potential of digital holography in particle measurement

This paper describes the potential power of digital holography in particle measurement and its expected development in the near future. In digital holography, image reconstruction is carried out numerically on a computer using observed hologram patterns and some quantitative information can be derived from the reconstructed images. In this paper, the basic concept and procedure of digital in-line holography are shown mainly for particle depth measurement and the performance test results obtained in numerical simulations and experiments are demonstrated to examine the potential of the present method.     

Effect of intensity quantization level in parallel phase-shifting digital holography

Parallel phase-shifting digital holography (PPSDH) enables the instantaneous recording of three-dimensional fields. The three-dimensional field can be reconstructed using a computer by numerical scalar wave propagation. In PPSDH, we record a space-division multiplexed hologram that includes the required phase retardation in the spatial distribution of the reference wave and then interpolate the data at blanked pixels for each phase retardation to obtain the complex amplitude distribution of an object wave. The recorded quality of the multiplexed hologram influences the reconstruction quality. In this study, we investigate the effect of the intensity quantization of a multiplexed hologram on the reconstruction quality. We compare the influence of intensity quantization in PPSDH with that in the conventional phase-shifting method. Random noise is also added to the multiplexed hologram. The required intensity quantization level is helpful for selecting a digital image sensor.     

数字全息周期像的产生机理及在抑制零级衍射上的应用

在数字全息成像中, 利用CCD的RGB模式采样全息图时, 全息重构像会出现特定的周期性分布. 本文从理论和实验上详细研究了这种周期像产生的机理、分布特性和应用. 研究结果显示, 由于CCD的光谱滤镜会使全息图的RGB三个单色采样阵列出现部分像素信号的缺失, 因此, 需要通过特定的demosaicing数学算法对缺失的像素信号进行重建以形成完整的单色采样阵列, 这是数字全息再现像周期分布产生的根源. 而基于demosaicing算法的采样阵列重建会在全息图频谱中引入调制函数, 导致物体再现像和零级衍射斑的周期分布差异. 本文揭示了全息图的RGB采样、demosaicing算法与全息重构像周期性之间的内在关联. 最后, 讨论了结合空间移位和图像形态学技术, 利用重构像的周期性抑制零级衍射斑的应用. 所有理论与实验研究结果完全一致. 关键词： 数字全息 图像周期性 零级斑抑制     

Elimination of zero-order and conjugate images in off-axis digital holography

In this paper, a new digital method has been developed for eliminating the zero-order and conjugate image in off-axis digital holography. The method consists of filtering the spatial frequencies associated with these undesired terms (the zero-order and conjugate images) in the computed Fourier transform plane of the hologram multiplied with computer simulated original reference wave (written as (RI_h)). An important conclusion is that, without the need for additional shift-spectrum process, the spectrum of real image always appears in the center of the spectrum plane and never shifts. This brings us some convenient to design a filtering window. The theoretical analysis and the corresponding simulation and experiment results are given. As the zero-order and conjugate image are eliminated, both the contrast and brightness of the real image are enhanced and the image quality is improved. Meanwhile, the process of designing a filtering window is simple and convenient.