Grid-based computer-generated holograms synthesizing for holographic three-dimensional display

To reduce the computing time of composite computer-generated holograms （CGHs） gen- eration based upon the angular projection algorithm for holographic three-dimensional （3D） display, a grid-based holographic display （ GHD ） scheme was designed. The grid computing technology was applied to numerically process the different angular projections of an object in distributed-parallel manner to create the corresponding CGHs. The whole treatment of a projection was regarded as a job executed on the grid node machine. The number of jobs which were submitted to grid nodes, therefore, was equal to that of the projections of the object. A Condor-based grid testbed was constructed to verify the feasibility of the GHD scheme, and a graphical user interface （GUI） program and several service modules were developed for it. A 3D terrain model as an example was processed on the testbed. The result showed that the scheme was feasible and able to improve the execution elficiency greatly.

基于自由曲面光学元件的大视场光学成像系统

面向机载探测系统大视场光学成像的需求,开展了大视场光学成像系统光学设计、自由曲面光学元件超精密加工、形位误差同步检测以及系统集成与成像实验研究。首先,采用视场扩展法进行大视场自由曲面离轴反射光学系统的设计;其次,进行铝合金自由曲面反射镜纳米精度加工和高频抑制工艺探索,并实现了基于计算全息元件的自由曲面形位高精度检测;最后,进行了光学系统的装调集成与成像实验。结果表明,系统的视场角为30°×5°,全视场光学传递函数值大于0.7,接近衍射极限,最大像元均方根半径为2.075μm,自由曲面光学元件的面形精度均方根(Root Mean Square,RMS)值优于20 nm,位置精度优于1μm,装配集成后能够满足大视场高分辨的场景使用要求,同时具备稳定可靠和快响制造等特点。

三次位相传播中的波像差及在CGH中衍射级次的分离

设计了利用计算全息图(CGH)作为零位补偿器来检测三次位相板的光学系统,最重要的两个理论问题是三次位相在空间传播过程中产生的波像差的具体形式和经过CGH衍射后衍射级次的分离。本文推导了三次位相在传播过程中产生高阶像差的理论公式,并由公式得出高阶项随着传播距离的增大而增大的结论。讨论了检测光波经过CGH衍射后衍射级次分离的理论过程。设计了一个用CGH检测三次位相板的系统作为例证,通过在CGH位相方程中引入高阶项四次项和五次项,使得残余波像差从原来的0.75λ降至0.007λ。实验得到的传播过程中的波像差及衍射级次的分离,都与理论推导相吻合。

Use of Virtual Medium in Designing of the CGH Wave Front Generator for Aspheric Testing

Design method and procedures of computer-generated hologram （CGH） used for aspheric test are in- troduced in detail. For CGH phase calculation, virtual medium which has zero refractive index at given wavelength is used to model ideal aspheric wavefront. Reflective Fresnel zones located in a ring area concentric to the CGH structure is designed to reduce or eliminate alignment errors. Substrate figure error, pattern distortion, etching and duty cycle variations that influence the reconstructed wavefront are quantitatively analyzed in theory and corresponding error equations are obtained to guide the tolerance distribution during CGH fabricating. A design example is given and the uncertainty of t achieves λ20.

用于柱面镜面形检测的CGH的设计与误差分析

现代X射线掠入射成像式望远镜是由大量的圆柱面超薄玻璃镜面经压制成圆锥面组成的准Wolter-I型望远镜。为了完成超薄玻璃圆柱面的检测,设计了适用于干涉检测的计算全息图(CGH)。结合CGH的设计制作过程,分析了CGH的基底面形误差、刻蚀占空比误差、刻蚀位置误差、刻蚀深度等误差,并对占空比、刻蚀深度的参数做了具体的分析,通过对制作误差的分析选择了制作参数。采用设计制作的CGH和ZYGO干涉仪实现了X射线望远镜用柱面镜的检测,检测结果达到了柱面镜的使用要求。

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.

Computer-generated image hologram

We investigate the computer-generated hologram with full parallax and which can be reconstructed with white light. The object of the hologram is processed from three-dimensional computer graphics polygon data and has shaded surface for hidden surface removal. The optically reconstructed image from the printed hologram is evaluated.

Computer-generated holograms for 3D display(Invited Paper)

We have been studying various types of computer-generated holograms for three-dimensional （3D） displays both for a real-time holographic video display and a hard copy, or a printed hologram. For the hard copy output, we have developed a direct fringe printer, which is achieved to print over 100 gigapixels computer-generated hologram with 0.44μm pitch. In this paper, we introduce our recent progresses on the rainbow hologram, the cylindrical holograms, and the disk hologram for 3D display.

Full-color and less-speckled modified Gerchberg–Saxton algorithm computer-generated hologram floating in a dual-parabolic projection system

This Letter proposes to apply full-color computer-generated holograms to the virtual image projection system so that the viewers can comfortably view floating images. Regarding the spatial division and distribution operation,a modified Gerchberg–Saxton algorithm is used for acquiring the phase infographics, which are input into the spatial light modulator for the reconstructed projection. Such a virtual image projection system could reach the vertical angle of view of 15°–75° and the horizontal angle of view 360°, and the mixed-light modulating proportion contains a 3 m W red light laser, a 2 m W green light laser, and a 2.6 m W blue light laser to achieve the full-color mixed-light proportion with a speckle contrast of 6.65%. The relative diffraction efficiency and root mean square error of the reconstructed image are 95.3% and 0.0524, respectively.

Real-time gradation-expressible amplitude-modulationtype electroholography based on binary-weighted computer-generated hologram

In amplitude-modulation-type electroholography, the binary-weighted computer-generated hologram(BW-CGH) facilitates the gradation-expressible reconstruction of three-dimensional(3 D) objects. To realize real-time gradation-expressible electroholography, we propose an efficient and high-speed method for calculating bit planes consisting of BW-CGHs. The proposed method is implemented on a multiple graphics processing unit(GPU) cluster system comprising 13 GPUs. The proposed BW-CGH method realizes eight-gradation-expressible electroholography at approximately the same calculation speed as that of conventional electroholography based on binary computer-generated holograms. Consequently, we were able to successfully reconstruct a real-time electroholographic 3 D video comprising approximately 180,000 points expressed in eight gradations at 30 frames per second.

Color representation method using RGB color binary-weighted computer-generated holograms

We propose a method for color electroholography using a simple red-green-blue （RGB） gradation representa- tion method without controlling the respective brightness of tile reference RGB-colored lights. The proposed method uses RGB multiple bit planes comprising RGB binary-weighted computer-generated holograms with various light transmittanees. The object points of a given three-dimensional （3D） object are assigned to RGB nmltiple bit planes according to their RGB gradation levels. The RGB multiple bit planes are sequentially displayed in a tim-division-multiplexe- manner. Consequently, the proposed method yields a color gradation representation of a reconstructed 3D object.

Computer-Generated Holograms for Recording Multiple-Phase-Shifte Fiber Bragg Grating Corrugations

A new method of fabricating multiple-phase-shifts fiber Bragg grating by CGHsis proposed . The authors present an example of such CGH by which a section multiple-phase-shiftefiber Bragg grating with twoπ/2 phase shifts and grating length L = 21.2 μm was produced. Theauthors describe the production process and finally give an example of a reconstructed fiber gratingwith two phase-shifts.

离轴非球面的计算全息图高精度检测技术

为了实现离轴非球面高精度定位、光路对准及面形检验,提出了一种使用计算全息图(CGH)技术实现离轴非球面高精度光学检测的方法。将被检非球面倾斜平移后作为轴上自由曲面进行CGH补偿检测设计,从而减小了检测光路的相对口径和CGH所需补偿像差,提高了CGH检测精度。使用自行开发的CGH专用设计计算软件,设计完成的CGH同时具有非球面检验、检测光路对准、被检非球面基准定位等多项功能。采用该方法设计(设计精度优于λ/10 000rms)并制作CGH对面形精度优于λ/50rms的离轴非球面进行了检测,误差分析表明,其检测精度优于λ/100,与传统null-lens方法的检测结果精确吻合。实验表明,采用该CGH可同时实现离轴非球面位置高精度定位、CGH与干涉仪对准以及离轴非球面高精度面形检验。

真实场景的三维视频采集及显示

提出了一种真实场景三维视频采集及彩色显示的方法.设计了一种采用条纹投影的实时三维成像系统及采用液晶空间光调制器的实时全息彩色三维显示系统.在三维成像系统中采用π相移正弦条纹与编码图案结合实现绝对相位测量,从而可以测量孤立物体.同时对采用数字微镜的投影仪进行改造,实现高速投影,并与高速摄像机配合实现三维视频采集.首先利用实时三维成像系统同时获取三维场景的彩色强度像和距离像;然后根据这些三维成像数据,设计和制作计算菲涅耳全息图;最后在实时全息彩色三维显示系统中再现.三维信息的采集和显示速度达到了60帧每秒.

迂回相位编码的傅里叶变换计算全息图及其再现

光学全息图直接利用光学干涉法在记录介质上记录物光波和参考光波叠加后形成的干涉图样 ,而采用计算全息 (CGH)的方法可不借助参考光直接记录物光波的复振幅信息。如果对迂回相位编码的全息图再进行一次逆的快速傅里叶变换 ,则可由计算机模拟完成物光波的全息图再现。试验结果也验证了该方法的可行性。

三维物体的计算全息的快速算法

提出了一种新的三维物体全息图的快速算法,根据点光源在全息面上的复振幅是中心对称的特性,加速得到阵列采样的全息数据,还快速得到了不同深度的主全息数据.该算法通过主深度主全息数据按比例缩放得到其他深度主全息数据,在同一深度上点全息数据由同深度主全息数据平移得到.分析和实验结果表明,改进后的算法能够减少计算量,提高计算速度,得到深度主全息数据的速度提高了5倍左右.

多重计算全息水印技术

为了增强水印安全性,用三维物体作为水印信息嵌入载体,提出了一种基于层析法的多重计算全息数字水印技术。该方法用层析技术得到三维物体的菲涅尔(Fresnel)全息图;利用Arnold变换对全息图进行置乱加密,置乱后的图像作为待嵌入水印;选择离散余弦变换(DCT)作为嵌入与提取算法;将Arnold变换次数与三维物体每层的衍射距离作为加密密钥。数字仿真与实验结果显示,当密钥正确时,从水印中提取的全息图的再现结果与直接再现全息图的结果一致,可以再现出三维物体相应层次的信息;密钥错误时,从水印中提取的全息图的再现结果无法识别,水印提取失败。实验结果证明了水印嵌入及提取算法的正确性,表明提出的方法可以实现水印信息的立体化和多重化,具有较高的安全性和易于实现等优点。

三维物体空间再现技术中的全息图计算

在简要论述三维物体计算全息技术理论的基础上,对具有代表性的三维物体全息计算方法的原理和技术要点进行了重点论述。采用层析法、菲涅耳波带法、多视角投影合成全息法等3种方法进行了三维物体全息图的计算,并利用LCR-2500空间光调制器及650 nm的150 mW半导体激光器对层析法计算的三维物体全息图进行了光电再现,对其它两种方法获得的三维物体全息图进行了数值再现,并对3种计算方法各自的特点和局限性进行了具体的分析。在对目前三维物体计算全息技术中存在的硬件和算法等关键问题进行分析的基础上,讨论了提高三维物体计算全息图效率和质量的有效途径。

彩虹全息标识的计算全息加密

提出了一种利用计算全息实现对彩虹全息图的加密，利用全息干涉对信息解码的新防伪方法．将计算全息和普通的彩虹全息合成在一张全息图上．通常情况下只能看到普通的彩虹全息标识图，用另外一张计算全息图解码后，在其干涉图样中可再现出用于加密的图象信息．该方法可在不增加原有设备和条件的情况下，大大提高彩虹全息图的防伪力度．

大偏离度非球面检测畸变校正方法

在高数值孔径(NA)投影光刻物镜中,随着数值孔径的增加,非球面的偏离度越来越大。对这种大偏离度非球面进行亚纳米量级的检测,一直是光学检测的一大难题。本文首先对一偏离度超过500μm的偶次高次非球面进行了计算全息图(Computer-Generated Hologram,CGH)设计,设计出了满足高精度面形检测和刻蚀加工要求的CGH。然后,针对此设计方案,定量分析了CGH的成像畸变及畸变对像差分析的影响。分析结果表明,不同径向位置的成像倍率偏差(畸变)最大达到了2.7∶1,并且由于畸变的存在,低阶像差衍生出了明显的高阶像差。最后,针对用CGH检测大偏离度非球面时出现的成像畸变,提出了采用光线追迹与最小二乘法相结合的成像畸变的校正方法,并通过实验验证了此方法的准确性。实验结果表明,畸变校正之后相对剩余残差小于0.2%,可以满足高精度非球面检测加工的要求。