Interferometric moiré pattern encoded security holograms with concealed phase object

This paper describes an interferometry-based scheme for concealing phase objects in a security hologram. The decoding process is based on geometrical moiré technique and requires a key for hologram authenticity verification. Decoding process is straightforward and could be carried out in white light, making it suitable for validation of security holograms. The method is described and experimental results are presented.     

Dual beam encoded extended fractional Fourier transform security hologram with in-built repositioning

This paper describes a simple method for making dual beam encoded extended fractional Fourier transform (EFRT) security holograms. The hologram possesses different stages of encoding so that security features are concealed and remain invisible to the counterfeiter. These concealed and encoded anticounterfeit security features in the security hologram can only be read through a key hologram. Key hologram also facilitates in-built repositioning of security hologram. The method of fabrication, the principle of reconstruction and the experimental results are presented.      

计算机制彩虹全息图的新算法

提出利用查表方法进行数字彩虹全息的计算方法.根据彩虹全息的基元全息图为线全息图的特点,找出物点与其线全息图的一一对应关系,建立空间点阵物点的线全息物光分布数据表.在对实际物体进行计算时,根据物点的位置,在数据表中找到与之对应的物光分布,并将这些分布进行叠加,从而形成实际物体被狭缝限制的物光分布,最后引入参考光计算其彩虹全息图.本方法充分利用了线全息图的性质,使得计算量大大减小,同时提高了计算速度.     

A new theta modulation multiplexing scheme for computer-generated holograms

In this paper, a new theta modulation multiplexing scheme for producing multiplexed computer-generated holograms (CGHs) is proposed. Under this scheme, normal Lohmann-type CGHs are individually modulated by gratings with different orientations and then superimposed to form a single hologram. The proposed method results in a higher storage capacity without the increase of hologram space. Theoretical analysis and experimental results are presented.     

单波长编码计算机制彩色彩虹全息图的研究

提出计算机制三维物体彩色全息图的新方法.通过理论分析表明，在满足一定的条件下，三个不同原色的点光源所产生的全息图光栅结构和距全息图不同距离的三个同色物点的光产生的全息图光栅结构是等价的.根据这一原理并参照彩虹全息技术，研究了物体三原色信息光分布的编码方法和全息图的算法，用单波长计算实现彩色全息图的制作，同时，较为完满地解决了全息图叠加和色串扰问题.实验结果证明了该方法的可行性及有效性.     

UHU adhesive holograms replication

It is possible to apply a new recording material with high diffraction efficiency (of the order of 82.3%) to replicate computer phase or analogical holograms. This material is the all purpose adhesive UHU^®. It is constituted by some components of polyvinyl, nitrates and some solvent agents; it is easily applied to any substrate. We record this material with heat generation by hand rubbing, using a mask (Kodalith^® films) manufactured with lithographic techniques. The holographic replication is excellent on the new material UHU^® adhesive, showing a phase modulation for refraction index and relief. This modulation is determined by the cured polymers process induced by friction, as pressure and temperature, with an anaerobic reaction.For copy of conventional holograms at high frequencies (holographic ranges), the diffraction efficiency parameter is in the neighborhood of 19.1% at first order or more, depending on diffraction efficiency of the pattern of the hologram. The hologram is elaborated in the absence of any development process and does not need to have carefully controlled conditions of the environment. Following this process, the hologram is obtained at standard atmospheric conditions of pressure and temperature.     

Characteristics in optimization of CGH for array generator

A method of simulated annealing in optimization of a computer generated holo-gram(CGH)is presented.The characteristics of energy in annealing curve are analyzed.Thecooling schedule such as giving an initial temperature,the temperature function,the numberof interactions and stopping criterion are discussed.As an example,an optimization of phaserelief kinoform,a CGH with multiple phase levels,is implemented.     

Hologravure as a computer-generated and laser engraved scratch hologram

We presented “hologravure” as the generalization of a scratch hologram, generated by computer from a three-dimensional (3D) model by using an appropriate software, and laser-drawing with a conventional engraver-laser system. For making this type of computer-generated hologram, neither diffractive optics, nor mask pattern or photo-reduction of a transparency onto a high resolution film plate is needed. The shape of a 3D virtual object is encoded in a two-dimensional (2D) multiple circular-scratch drawing. A computer program was created for generating the holograms. Hologravures representing several 3D models are engraved on different materials, and the quality of the lines traced by the CO₂ laser is considered. Sheets of acrylic, polycarbonate, glass and thermo-resistant pieces of acetate were tested. Reconstructed images of all this computer-generated and laser engraved holograms and also of computer assisted and hand-drawn scratch holograms, synthesized by means of the same software are shown.     

Phase-only stereoscopic hologram calculation based on Gerchberg–Saxton iterative algorithm

A phase-only computer-generated holography(CGH) calculation method for stereoscopic holography is proposed in this paper.The two-dimensional(2D) perspective projection views of the three-dimensional(3D) object are generated by the computer graphics rendering techniques.Based on these views,a phase-only hologram is calculated by using the Gerchberg–Saxton(GS) iterative algorithm.Comparing with the non-iterative algorithm in the conventional stereoscopic holography,the proposed method improves the holographic image quality,especially for the phase-only hologram encoded from the complex distribution.Both simulation and optical experiment results demonstrate that our proposed method can give higher quality reconstruction comparing with the traditional method.     

点阵全息图衍射效率的测量

提出了测量点阵全息图衍射效率的测试方法和相应的光学系统,其优点在于巧妙让零级与正负二级不能进入聚光系统,只有正负一级可以被记录,并且这种测试方法不受被测点干涉条纹方向变化的影响。并给了几种点阵全息防伪标识的测试结果。     

Concealed moiré pattern encoded security holograms readable by a key hologram

This paper describes a novel method of incorporating concealed coding features in security holograms in the form of moiré patterns, which need an encoded key hologram to decode them. These concealed codes in the holograms are in turn recorded with an encoded feature, so that these remain invisible to the counterfeiters thereby enhancing the anti-counterfeiting ability of security holograms. These security features, which are specific kinds of moiré patterns, can only be decoded by using an encoded key hologram in the final reading process. Though these type of security holograms are quite suitable for visual inspection, they possess high degree of anti-counterfeit ability and also do not require expensive reading machines. They can also be used as security codes for better protection against counterfeiting embossed holograms. Two different recording schemes for the formation of such security holograms and typical experimental results have been presented.     

复数滤波器在数字全息图处理中的应用

数字全息图在微电路检测、粒度分析、透明场测量等小孔径、小视场对象测量和细胞观测等显微测量方面有着广泛的应用前景。根据离轴数字全息图的频谱特点,提出采用复数滤波器,利用计算机及相关算法对离轴数字全息图进行滤波,消除其零级及共轭像,同时可以得到全息图的相位分布。讨论了复数滤波器的设计方法,给出了实验结果。为数字全息图的压缩、再现和相息图制作提供了方便。     

Interferometric key readable security holograms with secrete-codes

A new method is described to create secrete-codes in the security holograms for enhancing their anti-counterfeiting characteristics. To imitate these codes is difficult as pure phase objects having complex phase distribution function are used to modulate the object beam that is recorded in conjunction with an encoded interferometric reference beam derived from a key hologram. Lloyd’s folding mirror interferometer is used to convert phase variations of the reconstructed wave-front into an intensity pattern for hologram authenticity verification. Creating the secrete-codes through an interferometric reference beam from the key hologram facilitates a multi-stage authenticity verification as well as easy repositioning of the security hologram through a specific Moiré pattern generated during the verification process.      

Full-view rainbow-reflection holograms

A simple method of recording full-view rainbow-reflection holograms on a single flat plate is described: only one white-light illuminating source is required in the reconstruction process. The hologram can be viewed from opposite sides, where each side of a three-dimensional object, with its original spatial relationship, is displayed in bright colours.     

纯位相信息自聚焦计算全息匹配滤波器

本文介绍一种用计算全息方法制作的纯位相信息自聚焦匹配滤波器。它在编码时取滤波函数的振幅为１,仅对位相进行编码;并通过对傅里叶谱加入二次位相因子代替傅里叶透镜,使其具有自聚焦功能。与常规的方法（光学全息法或计算全息法）所获得的匹配滤波器相比较,具有原理上更合理,滤波器的制作和匹配光路更简单,也更容易实现匹配等特点。所得到的匹配实验结果也很清晰,这与理论是完全符合的。     

余弦二值编码纯相位全息图的数字微镜器件显示

分析了采用错误减算法的迭代过程,在已知物波函数傅里叶谱的振幅和物波函数振幅的情况下恢复出纯相位的物波函数,最大限度地保留物波的振幅及相位信息.提出采用余弦二值编码生成二值全息图,即全息图的透射率函数取0或1.二值全息图通过数字微镜器件全息显示系统进行了重构显示,重构效果很好.理论分析了数字微镜器件的衍射效率,表明其最大衍射效率仅和微镜之间的间隔尺寸与微镜边长之比有关.余弦二值编码方法从理论上消除了零级衍射,可以制作像素较多的全息图.     

Review of Fresnel incoherent correlation holography with linear and non-linear correlations

Fresnel incoherent correlation holography(FINCH) is a well-established incoherent imaging technique. In FINCH, three selfinterference holograms are recorded with calculated phase differences between the two interfering, differently modulated object waves and projected into a complex hologram. The object is reconstructed without the twin image and bias terms by a numerical Fresnel back propagation of the complex hologram. A modified approach to implement FINCH by a single camera shot by pre-calibrating the system involving recording of the point spread function library and reconstruction by a nonlinear cross correlation has been introduced recently. The expression of the imaging characteristics from the modulation functions in original FINCH and the modified approach by pre-calibration in spatial and polarization multiplexing schemes are reviewed. The study reveals that a reconstructing function completely independent of the function of the phase mask is required for the faithful expression of the characteristics of the modulating function in image reconstruction. In the polarization multiplexing method by non-linear cross correlation, a partial expression was observed, while in the spatial multiplexing method by non-linear cross correlation, the imaging characteristics converged towards a uniform behavior.     

Improved phase hologram design for generating symmetric light spots and its application for laser writing of waveguides

The improved method for calculation of a phase hologram and its application to laser writing of waveguides with a spatial light modulator are presented. It was found that the amplitude and phase distributions of light spots generated by a phase hologram can be distorted compared to those of a focused single beam. The distortion of light spots could be reduced by adding a simple constraint, in which light intensities around a light spot should be as small as possible, to the conventional calculation method of a phase hologram. It was also demonstrated that the improved calculation method can be considered essential for laser writing of waveguides.     

用双计算全息图检测凹非球面

为实现对凹非球面的高精度检测,提出并设计了一种二元纯相位型双计算全息图.设计的双计算全息图由主全息和对准全息两部分组成,分别用于检测非球面和精确定位主全息.介绍了双计算全息图的工作原理及其设计方法,并给出了一个检测Φ140、F/2抛物面反射镜的双计算全息图设计实例,实验得到的均方根(RMS)误差为0.062λ.通过分析对准全息的误差,推导出主全息的条纹位置畸变误差,最后计算出其综合误差为0.06A.为验证实验结果的可靠性,将其与平面镜自准直检测结果(ERMS=0.062A)比较,结果二者吻合良好.     

Computer-Generated Image Holograms for 3D-Display

Computer-generated image holograms are particularly useful for 3D-display applications. We discuss the properties of the reconstructions obtained with this hologram type. Conditions are given which must be fulfilled to ensure a disturbance free reconstruction. A new efficient algorithm is presented which implements the hidden surface effect for synthetic image holograms.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.