A full‐color eyewear display using planar waveguides with reflection volume holograms

Abstract— A full‐color eyewear display with over 85% see‐through transmittance with a 16° horizontal field of view was developed. Very low color crosstalk, less than 0.008 Δu′v′ uniformity, and 120% NTSC color gamut were achieved. Waveguides with two in‐ and out‐coupling reflection volume hologram elements enabled a simple configuration that has an optical engine beside the user's temples. The reflection volume hologram elements used on the waveguides realized a small thickness of 1.4 mm for each waveguide, and an out‐coupling reflection volume hologram used as an optical combiner contributed a high see‐through transmittance of 85% due to its wavelength selectivity. However, there are technical challenges in achieving a reasonable screen size and quality color images with optics that utilize holographic waveguides because holograms have large chromatic dispersions compared to conventional optical elements such as lenses and mirrors. Approaches to overcome these issues are described.     

Fast optimization of computer-generated holograms using conjugate gradient

Holographic display, as an ideal three-dimensional (3D) display method, can provide a realistic stereo-perception sense, and is expected to be used in the next generation of augmented reality (AR) prototypes without complex optical devices. While holographic 3D displays have been proposed in the past decades, high-quality holographic reconstructed images have always relied on well-designed generation algorithms, and it is still a challenge to obtain an accurate phase profile fast. In this work, we utilize a first-order optimization algorithm to optimize the phase profile using the conjugate gradient direction instead of the steepest gradient direction to update the phase parameters. We validate this proposed method by comparing the current widely used stochastic gradient method and the wirtinger holography method. The simulation and experimental results illustrate the superiority of the proposed method, which can achieve faster optimization with the same quality metrics.     

Structural Studies of DNA–Cationic Lipid Complexes Confined in Lithographically Patterned Microchannel Arrays

We have used lithographically patterned microchannel arrays with channel widths ranging from 1 to 20 m, fabricated using electron beam lithography and reactive ion etching, in structural studies of DNA–cationic lipid complexes in confinement. Various techniques have been developed for loading these DNA–membrane complexes into the microchannels or to form the complexes in situ by sequentially depositing DNA and lipid solutions into the microchannels. Optical microscopy studies indicate that such complex formation is strongly influenced by the periodic channel structure even at channel widths much larger than the persistent length of the DNA molecules. Preliminary x-ray diffraction experiments conducted at Stanford Synchrotron Radiation Laboratory (SSRL) yielded only a weak signal from the lipid bilayers in the complexes. The use of a microfocused x-ray beam produced by the newly developed Bragg–Fresnel optics at a third-generation synchrotron facility may dramatically increase the signal-to-noise ratio and allow observation of orientational as well as positional ordering of DNA molecules induced by the microchannels. Structural control of the DNA–membrane complexes has a broad range of potential applications in gene probe technology and as mesoscopic biomolecular composites.     

The evaluation of speckle contrast with variable speckle generator

Abstract— While laser projection has many advantages, there is a problem with speckle patterns generated as a result of interference of the laser beam and results in bad effects to observers. In 2010, a variable speckle generator, which produces an angular shift of incident light to the screen and generates variable speckle patterns, was suggested. In this study, the performance of a variable speckle generator by using a volume phase holographic beam shaper and scanning mirror was investigated in detail by evaluating both the objective and subjective speckle contrast. The morphology of the speckle pattern was also investigated when the variable speckle generator was activated. With a scanning VPH beam shaper, the objective speckle was effectively reduced because each point of the VPH beam shaper generated different speckle patterns and coherency among each pattern disappeared by using the scan process. On the other hand, subjective speckle was also dramatically reduced by changing the incident angle on the screen, which resulted in generating variable subjective speckle. It was also shown that the speckle reduction rate by using a variable speckle generator did not depend on the coherent length of a laser by evaluating the normalized speckle contrast against the angular shift on the screen.     

基于菲涅耳变换的图像加密算法

针对相位截断加密算法无法抵御信息泄露问题,文章提出了一种基于相位截断菲涅耳变换与随机振幅掩模的加密算法,以抵御信息泄露问题;算法首先将原彩色图像分为3个独立的颜色通道,在对其进行菲涅耳变换后加入随机振幅掩模通道,将4个通道分别进行菲涅耳衍射截断处理;算法通过级联处理不仅提高了秘钥与密文间的关联性,还消除了信息泄露的风险;通过仿真试验与结果分析可知,本算法不仅在波长与自由空间传播错误距离参数、密文噪声、遮挡污染、密文泄露以及不同攻击等情况下有较好的鲁棒性,还解决了信息泄露问题。     

真实感眩光效果实时绘制

针对现有眩光效果绘制方法的真实感和速度问题,提出一种基于GPU的真实感眩光效果绘制方法.首先根据光圈和镜头生成带有随机镜头噪声的二维衍射光栅图像;其次考虑夫琅禾费和菲涅耳2种不同的衍射效果,利用预存算法系数的快速傅里叶变换模拟衍射效果的光学过程,并通过衍射效果的光谱模型实现真实感绘制,同时利用2个独立的一维高斯卷积核加速实现bloom效果;再通过随机小角度旋转和混合操作进行真实感增强;最后采用实时光线跟踪渲染框架,在三维场景中实现了真实感眩光效果的实时绘制.该方法的主要步骤采用CUDA实现,充分利用了GPU强大的并行计算能力并兼顾考虑存储器优化策略.实验结果表明,文中方法绘制结果具有较强的真实感和实时性.     

利用相位光栅的衍射检测啁啾飞秒激光脉冲

分析了一种0ˉπ相位光栅在啁啾飞秒激光脉冲照射下的菲涅耳衍射.通过选择相位光栅的结构,可以使衍射光的±1级分量最大.提取±1级衍射分量,并通过两反射镜将这束光在远处干涉.当飞秒激光脉冲的宽度一定时干涉条纹的强度与飞秒激光脉冲的啁啾系数有关.通过检测干涉条纹的强度,可以间接测量飞秒激光脉冲的啁啾系数.     

一种用于版权保护的随机相位量化编码方法

基于传统的随机相位编码技术，提出了一种新的相息图量化编码方法。该方法采用条码编码技术和数制转换原理，将编码得到相息图的高阶量化信息映射为二值矩阵，并进一步打印制作成二值的防伪标签，不但可以实现文本内容的自动录入，同时也提高了传统随机相位编码技术解码图像的信噪比。计算机仿真与光学扫描实验表明，该方法具有认证过程相对简单、解码图像信噪比高、成本低和防伪性能好等优点。     

Optical dual self functions

A recipe to construct the exact dual self-Fourier-Fresnel-transform functions is shown, where the Dirac comb function and transformable even periodic function are used. The mathematical proof and examples are given Then this kind of self-transform function is extended to the feasible optical dual self-transform functions.     

Holographic digital Fourier microscopy for selective imaging of biological tissue

We present an application of digital Fourier holography for selective imaging of scatterers with different sizes in turbid media such as biological tissues. A combination of Fourier holography and high‐resolution digital recording, digital Fourier microscopy (DFM) permits crucial flexibility in applying filtering to highlight scatterers of interest in the tissue. The high‐resolution digital hologram is a result of the collation of Fourier holographic frames to form a large‐size composite hologram. It is expected that DFM has an improved signal‐to‐noise ratio as compared to conventional direct digital imaging, e.g., phase microscopy, as applied to imaging of small‐size objects. The demonstration of the Fourier filtering capacity of DFM using a biological phantom represents the main focus of this article. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 253–258, 2004; Published online inWiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20031