Elimination of zero-order diffraction in digital off-axis holography

A simple experimental method of eliminating zero-order diffraction in the reconstructed image of off-axis digital holography is presented. Holographic diffraction grating acting as a beam splitter, an off-axis holography system is formed. The holograms of object with different recording parameters are obtained by adjusting the reflecting mirror in the recording optical system to vary the incidence orientation of the object beam in CCD to introduce a phase shift. The zero-order image can be eliminated by numerically processing the holograms of object with different recording parameters. The theoretical analyses have been done in detail and the experimental results are also given. The zero-order image eliminated, the area of reconstructed image increases remarkably, the image quality can then be significantly improved and the better resolution obtained. The experimental results show that the method presented in this paper is feasible, simple in optical system and easy in operation and data processing.     

Heterodyne shearing interferometers using diffractive filters with rotational symmetry

Spiral fringe computer-generated holograms are used to advantage as elements in shearing interferometers. Several different functions can be incorporated in these filters. A heterodyne system is achieved by rotating one of these filters. Constant radial and constant azimuthal shear arrangements are described. These are particularly suited for optical data processing in polar coordinates.     

Effect of aberrations in formation of holographic lateral shear interferograms under high measurement sensitivity

Analysis of the effect of aberrations of a system for recording and optical processing of holograms, as well as of inhomogeneities in hologram bases, on fringe distortion is performed for different methods of holographic shearing interferometry. Different dependences of the degree of fringe distortion in lateral shear interferograms on the measurement sensitivity are revealed. A method of excluding aberrations in formation of shear interferograms is proposed for the cases of single-and double-exposure holograms. Experimental results are reported.     

Some basic experiments on the optical resolution of sampled microwave holograms

Sampling the field of a physically large microwave hologram space enables subsequent optical reconstruction of the original object space existing in various environments. It is shown fundamentally how the required resolution is related to the sample frequency. The recording of some basic microwave holograms is described, and the resultant patterns are shown. Optical reconstructions of two-point objects indicate the resolution capability of the holograms. Sampling in the prescribed manner yields optical reconstructions of the object points, but random sampling with the same number of measurements does not yield a reconstruction of the object.     

Rotation- and size-invariant object identification system using the liquid crystal on silicon device

We propose a shape discrimination technique using the optical matched spatial filter, which gives an identical result against randomly scattered objects of the same shape but different rotation and scale change. The main idea in this study is to apply optical coordinate transformation, which transforms rotation and scale change including a linear shift into translation, not to the objects themselves but to their Fourier spectra. Thus, rotation and scale change as well as the linear shift can be processed with the same optical matched spatial filter. In addition, we built a two-wavelength system for simultaneous processing of the optical matched spatial filter and optical coordinate transformation. In this system, both Fourier transform and the coordinate transformation were implemented merely by displaying computer-generated holograms (CGH) on the liquid crystal on silicon (LCOS) devices, resulting in a compact lensless system.     

超短脉冲激光电子学全息选通透过散射介质成象系统的噪音分析

本文详细分析了超短脉冲激光电子学全息选通透过散射介质成象系统的噪音因素,其噪音来源主要有电子学全息图的记录过程、再现过程以及CCD自身的噪音、系统光学元件产生的噪音等等,提出了相应的噪音处理措施.     

一种消除数字离轴全息零级像的实验方法

提出一种消除数字离轴全息零级像的实验方法.这种方法是将全息衍射光栅作为分光元件,形成数字离轴全息记录系统,通过调节记录光路系统中平面镜,改变物光波到达CCD的入射方向而引入相移,从而得到不同记录参数的全息图.再通过对不同记录参数全息图的数字处理,即可达到零级像消除的目的,并对这种方法进行了理论分析和实验验证.给出了利用这种方法获得的实验结果.实验结果证明了该方案的可行性,并且具有光路系统简单、操作和处理容易等特点.     

Imaging of rotating objects by means of synthesized optical holograms

A scheme is presented for producing optical holograms of rotating objects by illuminating the object by a single-frequency coherent laser beam. Along one axis, the synthesis takes place due to rotation of the object; along the other axis, the hologram is synthesized by the coherent radiation field generated by a long linear optical antenna. Numerical simulation shows that reliable discrimination of object images from the accompanying background is possible, for point objects, using a single hologram recorded at one angular position and, for extended flat objects or thin cylinder-like objects, using holograms recorded at two or three angular positions. If the holograms are synthesized in the presence of normally distributed random phase noise, the quality of the reconstructed images of rotating objects remains sufficiently high for root-mean-square noise amplitudes exceeding π/2 and reaching the limiting value 2π/3.     

超短脉冲激光电子学全息选通透过散射介质成象系统的噪音分析

本文详细分析了超短脉冲激光电子学全息选通透过散射介质成象系统的噪音因素，其噪音来源主要有电子学全息图的记录过程、再现过程以及ＣＣＤ自身的噪音、系统光学元件产生的噪音等等，提出了相应的噪音处理措施．     

Digital spatially incoherent Fresnel holography

We present a new method for recording digital holograms under incoherent illumination. Light is reflected from a 3D object, propagates through a diffractive optical element (DOE), and is recorded by a digital camera. Three holograms are recorded sequentially, each for a different phase factor of the DOE. The three holograms are superposed in the computer, such that the result is a complex-valued Fresnel hologram. When this hologram is reconstructed in the computer, the 3D properties of the object are revealed.     

Enhancement of sensitivity of measurements of the holographic lateral-shear interferometry in studies of fast processes

The possibility of enhancing the sensitivity of measurements upon visualization of temporal variations of a phase object by means of optical processing of the holographic lateral-shear interferograms, without the necessity of detecting the original holographic interferograms under nonlinear conditions, is considered. In rewriting the original holographic interferogram, it is advisable to change the orientation of the holographic fringes and to record the secondary holograms under nonlinear conditions. The proposed method for increasing the sensitivity of measurements was used to visualize variations of thickness of a polymethyl methacrylate plate in the course of its thermal treatment.     

Incoherent recovering of the spatial resolution in digital holography

We report on a technique to recover the spatial resolution of digitally recorded and reconstructed holograms of large objects. Due to the high-contrast speckle noise diminishes the spatial resolution in coherent imaging systems our proposal is based on the reduction of the contrast of it. This aim is achieved through the superposition on an intensity basis of digitally reconstructed holograms of the same static scene. We show a theoretical justification of the procedure and experimentally-obtained results of applying the technique with digitally reconstructed holograms of an object with very poor optical contrast.     

Study of the parameters of a difference image in the presence of a linear phase shift

The spatial filtering in the localization range of the holographic lateral shearing interferograms of a solid object shows that the effect of the subtraction of the compared original data arrays is realized in the presence of a filtering aperture in the center of a dark fringe [1, 2]. Methods for the holographic subtraction of the images involving the detection and spatial filtering in the Fourier plane of the optical system are proposed and realized in [3–5]. Thus, the difference data can be reconstructed with a narrow (unexpanded) laser beam. However, a relatively high level of speckle noise in the difference image is caused by the spatial filtering with a small aperture (laser beam) in the minimum of the superposition field in the Fourier hologram plane. The detection of double-exposed Fourier holograms with a linear phase shift and the effect of the size of the filtering reconstructing beam on the resolution of the difference image are studied. In addition, the application of the multiple exposure for the broadening of the interference maxima is analyzed.     

Extraction of object position from in-line holograms by using single wavelet coefficient

A novel digital method for tracking position of objects from in-line holograms by using single wavelet coefficient is proposed. In the proposed method, a wavelet transform is used to analyze the holograms. An axial position of the object being studied is determined by using a real value of a resultant wavelet coefficient appears at a center position of interference fringes. A feasibility of this method is experimentally verified by analyzing holograms of an optical fiber.     

Control of the tuning of reference fringes in the interference pattern of changes in the object state in the optical processing of holograms and photographic images with the same spatial carrier

The condition of obtaining undistorted reference fringes when processing a pair of superimposed holograms or photographic images with a constant carrier frequency of bands due to their relative rotation or tilt is obtained. It is shown that the degree of fringe distortion is determined by the combined action of aberrations and the value of the parameter being measured. The technique of an arbitrary tuning of reference fringes is described, which makes it possible to eliminate the relative shift of holograms or photographic images. Experimental results obtained by the optical processing of photographic images of projected fringes are presented.     

Synthesis of multifrequency optical holograms of rotating objects

A two-channel system for synthesizing two-dimensional complex multifrequency optical holograms of rotating objects was developed. In the object irradiation (longitudinal) direction, a hologram is synthesized due to multifrequency laser radiation, and in the transverse direction, the synthesis is provided by object rotation. The object image is reconstructed in the plane coinciding with the plane of its rotation. The resolution of the synthesized hologram in the longitudinal direction is determined by the frequency bandwidth of the laser radiation, and in the transverse direction, the resolution is determined by the initial laser-radiation frequency and the angle of object rotation during the time of hologram synthesis. Using a digital simulation, the degree of isoplanarity of the multifrequency system for synthesizing holograms of rotating objects and its noise immunity under conditions of phase noises were analyzed.     

Cutoff Wavelength Measurement for Single Mode Optical Fibers with Computer-generated Matched Filter

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二步合成平板周视彩虹全息术

提出一种将物光波前先分解记录，再合成的二步平板周视彩虹全息术。波前的分解记录与合成彩虹全息图是分别通过转动物体和干板来实现的。记录这种周视全息图，不需要大孔径和其它特殊光学元件，即可获得周视半径大的无象差立体再现象。该方法可直接用于模压全息图母板的制作。     

基于空间光调制器的非相干数字全息单次曝光研究

菲涅耳非相干相关全息术(Fresnel incoherent correlation holography,FINCH)利用在空间光调制器(spatial light modulator,SLM)上加载双透镜模式对同一物点光分束自相干,并通过改变加载的相位因子得到不同的相移全息图.本系统利用SLM可分区编码调制特性,将FINCH成像中SLM上分三次加载的0°,120°,240°相位双透镜掩模各提取1/3组成一幅复合相移模式加载,并研究了三种相位分布方式对FINCH成像质量的影响.结果表明:三个相位在SLM上分布间隔越大,再现像越清晰.在此基础上,提出了一种新的掩模加载方式,在SLM加载透镜阵列,每一个相位因子对应一个双透镜,具有一个光轴.实验表明,通过这种加载方式,通过SLM后形成的三个相移图能够一次在电荷耦合器上记录,并且三个相移图不重叠,然后通过MATLAB编程计算将不同相移角度的全息图分别提取出来,通过三步相移计算合成一幅包含有物光波的复值全息图,最后通过数值再现算法重建待测样品.此系统可用于对光源相干性较低的实时成像系统,也为微小形变测量、动态物体的观测提供了新方法,为非相干数字全息术的发展提供了新思路.     

Low-complexity compression of holograms based on delta modulation

Past research has demonstrated that hologram of a real world object can be acquired by scanning it with a single two-dimensional optical scan. The technology commonly referred to as optical scanning holography (OSH), have found important applications such as in microscopy, pattern recognition, 3D holographic display, and optical remote sensing. As holograms are often employed to capture three dimensional objects with high resolution, large amount of data is required to represent them. In this paper we propose a method for compressing holograms based on Delta modulation. Specifically, we apply our proposed method for holograms captured by OSH. Experimental evaluation reveals that our proposed approach is capable of attaining a compression ratio of 64 times, and still preserves favorable fidelity on the reconstructed images. In addition, both the encoding and decoding processes of the proposed method are very low in complexity, hence enabling real-time operation.