Storage of binary electrical signals in one-dimensional holograms with extremely narrow tracks

A report is given on the results of an experiment in which binary data stored in sequentially superimposed one-dimensional holograms with extremely narrow tracks were recorded on a transported recording medium. The width of the holograms was reduced to 3 μm. Since the results obtained show the optical signal-to-noise ratio of the reconstructed image points to be only slightly inferior to that with holograms with 100 μm wide tracks, the method used can be expected to yield an areal bit density greater than 10⁷ bits/cm².     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

基于螺旋相位调制的非相干全息点扩散函数研究

分析了菲涅耳非相干相关全息(Fresnel incoherent correlation holography,FINCH)系统中纯相位空间光调制器(spatial light modulator,SLM)加载螺旋相位掩模时的点扩散函数.以氙灯为照明光源搭建了FINCH系统,电荷耦合器记录的点源全息图与点扩散函数模拟结果一致.采用该系统分别在SLM上加载双透镜掩模和螺旋相位调制双透镜掩模两种情况下对分辨率板和非染色洋葱细胞成像,给出了成像对比结果.结果表明:采用螺旋相位调制的FINCH系统可以在几乎不牺牲分辨率的情况下提高图像的边缘对比度;同样,对相位物体也可以实现图像的边缘提取和识别.该方法在实时监测活细胞的分裂、形变等方面具有重要应用前景.     

Illumination-angle-scanning digital interference holography for optical section imaging

We propose and experimentally demonstrate a new (to our knowledge) digital holographic method to reconstruct section images of objects with wavelength-dependent reflectivity. A number of holograms of an object are taken as the illumination angle of the laser beam with a specific wavelength is changed in regular intervals. The complex object fields reconstructed from the holograms are numerically superposed to show the image of a sliced section of the object, whose position and thickness can be chosen arbitrarily. By changing the wavelength of the illumination beam, wavelength-dependent section images can be obtained with our method.     

环形光栅光学扫描全息术的研究

为了充分利用光学扫描全息系统的分辨率,提出了用环形光栅扫描物体的光学扫描全是术。其优点是：可以用非相干光源记录扫描全息图,系统为单光路,从而可以提高系统的稳定性。阐明了环形光栅光学扫描全息术的基本原理,并给出了实验结果。     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

用Stokes参量法实现数字同轴偏振全息的研究

提出了一种基于Stokes参量的数字同轴偏振全息方法.在实验中用一束线偏振光和一束椭圆偏振光作为参考光, 分别与物光进行干涉,通过拍摄在两个相互垂直方向上的全息图,计算出物光在这两个方向的振幅和相位信息, 从而得到物光的Stokes参量和物体的全偏振信息,实现对各向异性物体偏振态空间分布的图像重建. 实验结果表明,该方法可用于物体的全偏振特性的测量.这种方法在求出物光Stokes参量的同时, 也可消除零级像和共轭像的干扰,因此也可用于同轴或离轴全息.     

全视差合成全息图的激光直写拍摄

为了实现可白光下再现的全视差拼接合成全息图,结合图像处理技术、合成全息图的原理,提出一种激光直写拍摄技术.实验得到了具有57°的较大观察视场的数字合成全息图,并实现了1×1m2大面积拼接.     

Optical encryption of gray-level image using on-axis and 2-f digital holography with two-step phase-shifting method

In this paper we propose an encryption/decryption technique of gray-level image information using an on-axis 2-f digital holographic optical encrypting system with two-step phase-shifting method. This technique reduces the number of holograms in phase-shifting digital holography and minimizes the setup of the encryption system more than multistep phase-shifting technique. We are able to get the complete decrypted image by controlling the K-ratio which is defined as the reference beam intensity versus the object beam intensity. We remove the DC-term of the phase-shifting digital hologram to reconstruct and decrypt the original image information. Simulation results show that the proposed method can be used for encryption and decryption of a 256 gray-level image. Also, the result shows some errors of the decrypted image according to K-ratio.     

水窗波段同轴X射线全息成像及其数字重现

水窗波段同轴Ｘ射线全息成像及其数字重现张玉火亘蒋诗平付绍军张新夷（中国科学技术大学国家同步辐射实验室，合肥２３００２９）陈建文徐至展陈敏（中国科学院上海光学精密机械研究所，上海２０１８００）水窗波段软Ｘ射线对生物样品成像时，不需要电子显微镜观察时那样...     

A method of image plane multiplex holography

A method for making image plane multiplex holograms is described. These exhibit the full 3-D imagery of conventional multiplex holograms, but can be made without the use of coherent light. A similarity to lenticular photography is noted; this similarity is then utilized in devising methods for constructing image plane multiplex holograms.     

Method for eliminating zero-order diffraction in lensless Fourier transform digital holography

A method to induce phase shifting in lensless Fourier of digital holography system is presented. In this method, by computer simulation and theoretical analysis on the technology to eliminate the influence of zero-order diffraction in force, it can be found that, a reference light induced in a random non-2π integral number of phase shifting shooting to get the second hologram, and wave reconstruction can be got by the difference value image of the two holograms. And, the method of different digital holography record system with different phase shifting should be used. In this paper, theoretical analyses have been done in detail to discuss the problems that exist in the unsuitable phase-shifting methods. Furthermore, some experiments have been done to prove the reliability of this method. This method can significantly improve the image quality and give better resolution of the reconstructed image.     

Transformation properties of dynamic χ<Superscript>(2)</Superscript> holograms generating at the difference frequency

The transformation properties of dynamic χ⁽²⁾ holograms generating at the difference frequency are analyzed as applied to the position and scales of reconstructed images. Some regularities are established for the spatial localization and scales of images for different combinations of frequencies and positions of the reference and object point sources, involved in the formation of a holographic image. The formation of amplitude transparency images, reconstructed by dynamic χ⁽²⁾ holograms with a decrease or conservation of the object beam frequency, and their transformations are experimentally demonstrated.     

Optical retrieval of encrypted digital holograms for secure real-time display

Secure data transmission by use of encrypted digital holograms and an optical retrieval system for secure real-time display are proposed. Original images are encrypted by a double-random phase encryption technique and then are recorded as digital holograms in a CCD, together with a reference plane wave. This digital hologram of the encrypted image can be transmitted to receivers via any conventional electronic or digital communication channels. The decryption key is also recorded as a digital hologram. At the receiver, the original image can be retrieved by an optical correlation-based reconstruction process. Both encryption and retrieval can be performed by all-optical means, and thus a real-time secure display can be implemented. We demonstrate the proposed system numerically and experimentally.     

Superphotons and Natural Holograms

The first observation of natural holograms and their main properties are described. Perfect colored, in real time, holograms of any objects illuminated by usual lamps or by Sun's radiation can be obtained using CdS crystal platelets grown from vapor phase. The new state of electromagnetic field that is linear superposition of multipole waves with the same frequency but with different values of angular momenta (superphoton) is discovered. Superphotons possess many unusual properties such as great penetrative ability, high directionability and possibility to create holograms. The latter permit, particularly, to take images of Sun and other stars and planets using transformation of multipole waves into usual visible light, to obtain essential reducing noise at image processing and rising efficiency of solar batteries. Also, we have observed some effects of adaptive optics.     

Disturbance-free digital holographic microscopy via a micro-phase-step approach

This work proposes a cost-effective, simple, micro-phase-step (MPS) method for suppressing the zero-order diffraction and conjugate-image interferences that are caused during digital holographic microscopic image reconstruction. The proposed MPS method replaces the conventional phase modulation approach; it uses a rotatable cover glass that enables smooth modification of the incidence angle and the optical path of the reference beam. This setup allows the phase step to be accurately estimated by shifting the reference wave phase more freely close to π/2, at which the background noise can be suppressed more effectively. In the proposed MPS method, the optimal conditions for suppressing conjugate-image interference are identified using a relatively moderate intensity distribution and suppression of noise in the numerically reconstructed object wave-field. In addition, the proposed method mitigates the effect of disturbances that are caused by environmental factors, such as minor vibrations and small changes in temperature and humidity. Importantly, only two holograms are required to satisfy the objective of image reconstruction. The results in this work reveal that even with intentional interference caused by minor vibrations, conjugate-image interference can still be suppressed by determining the phase deviation between the two original holograms.     

Cross-talk free image encryption and watermarking by digital holography and random composition

In previous image watermarking methods an encoded host image and a watermark image are usually directly added, consequently the two images have cross-talk in the decryption step. To eliminate this effect, we propose a novel method based on digital holography, in which all the image pixels of the two sets of holograms resulted from two hidden images are rearranged and integrated into one set of composite holograms with a random scattering matrix (RSM). In decryption the use of this matrix can ensure the exact retrieval of each hologram, and then the perfect reconstruction of each image without cross-talk noise can be achieved. The feasibility of this method and its robustness against occlusion and additional noise are verified by computer simulations with phase-shifting interferometry and double random-phase encoding technique. This approach is suitable for both two- and three-dimensional images, and the additional RSM as a key provides a much higher level of security.     

Single-shot polarization-imaging digital holography based on simultaneous phase-shifting interferometry

We propose single-shot digital holography which is capable of simultaneously capturing both the information of multiple phase-shifted holograms and the distribution of the polarization. In this technique, a single image sensor records both the information required for phase-shifting interferometry and that of the polarization states of objects using an array of polarizers. The essence of the technique is the capability of imaging the distribution of the polarization of three-dimensional objects with a single-shot exposure by using the space-division multiplexing of holograms. The validity of the proposed technique was confirmed by the preliminary experiments.