计算全息用于激光显示艺术

计算全息用于激光显示艺术可以显示有意义的图像,例如字符、人头像、生肖图像等.本文介绍两种新型反射型计算全息图,效率约30%,并能承受强激光照射.     

Moiré effects in computer-generated holograms

Moiré patterns are generated on a computer digital printout when a mathematical sampling grid is superimposed over a two-dimensional function to be plotted. The appearance of these Moiré effects in the computer-generated zone plates takes the form of additional zone-plate patterns if the incremental sampling grid is rectangular.     

新型四通道计算全息图

提出了一种新的制作四通道计算全息的方法,它在双通道计算全息的基础上通过在一个抽样单元中放置两个宽度和高度均可变化的矩形,实现在u方向和v方向各记录两个物体的信息,从而可以一次性记录四个物体.该方法已经在实验中得到了印证,文中给出了相应的原理和实验结果.     

干涉型计算机全息图检测非球面

本文从离轴参考束全息图的基本方程出发,介绍了干涉型计算全息图。分析了宽条纹和窄条纹干涉型全息图的特点并给出了检验结果。指出了波差近似计算公式的适用范围。给出了三组实际检验结果。实验表明,(-1,0)和(0, 1)级波面的干涉图是相同的,并给出了解释。     

计算机全息术在非球面检验中的应用

本文根据Lohmann关于计算机全息术的一般理论阐明了干涉条纹型计算机全息图的原理;对Sirohi等人的计算方法进行了改进,提高了计算精度,而计算时间略有缩短;还制成了一个用于检验抛物面镜(f=1021毫米、2r_o=214毫米)的计算机全息图,再现波面的精度(方均根误差)达到1/20波长,并且已将此计算机全息图用于抛物面镜的检验,显示出了被验元件的面形缺陷.     

利用计算全息产生的拉盖尔-高斯光束旋转微粒

分析了采用计算全息再现拉盖尔-高斯(Laguerre-Gaussian,LG)光束光场的原理。将计算全息法生成的全息图载入空间光调制器(spatial light modulator,SLM),在全息光镊平台上生成了LG光束。对吸收性氧化铜(CuO)微粒进行了系列旋转操纵实验。实验发现单个微粒既可以被光学漩涡捕获在暗中空区域绕固定轴旋转,又可以被囚禁在光强最大值处绕轨道旋转;还实现了多个微粒的绕轨道旋转。通过实验观察和测量,得出了微粒旋转的周期与激光功率和角向指数的变化关系。所得结果对光致旋转微粒的精确操控具有一定的指导作用。     

Lossless compression of continuous-tone images

In this paper, we survey some of the recent advances in lossless compression of continuous-tone images. The modeling paradigms underlying the state-of-the-art algorithms, and the principles guiding their design, are discussed in a unified manner. The algorithms are described and experimentally compared     

Halftone to continuous-tone conversion of error-diffusion codedimages

Considers the problem of reconstructing a continuous-tone (contone) image from its halftoned version, where the halftoning process is done by error diffusion. The authors present an iterative nonlinear decoding algorithm for halftone-to-contone conversion and show simulation results that compare the performance of the algorithm to that of conventional linear low-pass filtering. They find that the new technique results in subjectively superior reconstruction. As there is a natural relationship between error diffusion and SigmaDelta modulation, the reconstruction algorithm can also be applied to the decoding problem for SigmaDelta modulators.     

Data re-ordering technique for lossless LZW continuous-tone imagecompression

A data re-ordering technique is proposed to enhance the compression performance of lossless LZW image compression over continuous-tone images. The proposed scheme incurs few overheads and functions as a preprocessing stage prior to actual compression. The compression performance is increased by an average of 18% for continuous-tone test images compared with the popular GIF compressor     

Acoustic holograms

The letter describes a method of reconstructing a holographic image by electronic means, thus avoiding the multiple images produced owing to ambiguity of angle.     

用计算机产生全息图

本文叙述了用计算机产生全息图的原理和方法,同时给出了制作全息图的全过程和实验结果.     

A sampled computer-generated binary hologram

A simple way of recording computer-generated holograms is reported. It involves recording the sign of the amplitude (hence the word binary) on computer printer paper. Also the resolution attained during reconstruction of a hologram is discussed and compared with the theoretical limit.     

平面合成彩虹全息图

提出一种记录平面合成彩虹全息图的空间分割记录方法.利用这种方法得到的彩虹全息图不仅可以在白光下再现一动态图象,而且可以用常规方法进行模压复制.文中描述了这种方法的基本原理、实验装置及结果.     

Lossless compression of continuous-tone images via contextselection, quantization, and modeling

Context modeling is an extensively studied paradigm for lossless compression of continuous-tone images. However, without careful algorithm design, high-order Markovian modeling of continuous-tone images is too expensive in both computational time and space to be practical. Furthermore, the exponential growth of the number of modeling states in the order of a Markov model can quickly lead to the problem of context dilution; that is, an image may not have enough samples for good estimates of conditional probabilities associated with the modeling states. New techniques for context modeling of DPCM errors are introduced that can exploit context-dependent DPCM error structures to the benefit of compression. New algorithmic techniques of forming and quantizing modeling contexts are also developed to alleviate the problem of context dilution and reduce both time and space complexities. By innovative formation, quantization, and use of modeling contexts, the proposed lossless image coder has a highly competitive compression performance and yet remains practical.     

Single-step digital backpropagation for nonlinearity mitigation

Nonlinearity mitigation based on the enhanced split-step Fourier method (ESSFM) for the implementation of low-complexity digital backpropagation (DBP) is investigated and experimentally demonstrated. After reviewing the main computational aspects of DBP and of the conventional split-step Fourier method (SSFM), the ESSFM for dual-polarization signals is introduced. Computational complexity, latency, and power consumption of DBP based on the SSFM and ESSFM algorithms are estimated and compared. Effective low-complexity nonlinearity mitigation in a 112 Gb/s polarization-multiplexed QPSK system is experimentally demonstrated by using a single-step DBP based on the ESSFM. The proposed DBP implementation requires only a single step of the ESSFM algorithm to achieve a transmission distance of 3200 km over a dispersion-unmanaged link. In comparison, a conventional DBP implementation requires 20 steps of the SSFM algorithm to achieve the same performance. An analysis of the computational complexity and structure of the two algorithms reveals that the overall complexity and power consumption of DBP are reduced by a factor of 16 with respect to a conventional implementation, while the computation time is reduced by a factor of 20. Similar complexity reductions can be obtained at longer distances if higher error probabilities are acceptable. The results indicate that the proposed algorithm enables a practical and effective implementation of DBP in real-time optical receivers, with only a moderate increase in the computational complexity, power consumption, and latency with respect to a simple feed-forward equalizer for bulk dispersion compensation.     

Single-step creation of localized Delaunay triangulations

A localized Delaunay triangulation owns the following interesting properties for sensor and wireless ad hoc networks: it can be built with localized information, the communication cost imposed by control information is limited, and it supports geographical routing algorithms that offer guaranteed convergence. This paper presents two localized algorithms, fast localized Delaunay triangulation 1 (FLDT1) and fast localized Delaunay triangulation 2 (FLDT2), that build a graph called planar localized Delaunay triangulation, PLDel, known to be a good spanner of the Unit Disk Graph, UDG. Our algorithms improve previous algorithms with similar theoretical bounds in the following aspects: unlike previous work, FLDT1 and FLDT2 build PLDel in a single communication step, maintaining a communication cost of O(n log n), which is within a constant of the optimal. Additionally, we show that FLDT1 is more robust than previous triangulation algorithms, because it does not require the strict UDG connectivity model to work. The small signaling cost of our algorithms allows us to improve routing performance, by efficiently using the PLDel graph instead of sparser graphs, like the Gabriel or the Relative Neighborhood graphs.     

全视场彩虹-反射全息图

提出了一种摄制全视场彩虹—反射全息图的简单方法。通过在被记录物体的侧后方放置一反射镜来完成全视场记录。该法减少了曝光次数及所需主全息图的数目,也不需精细地对准调节装置。     

透射全息图的反射象成因分析

本文从实验结果出发,比已有的文献更全面地分析了透射全息图的反射象的成因。