基于空间角度复用和双随机相位的多图像光学加密方法

提出了基于空间角度复用和双随机相位的多图像光学加密新方法.加密过程中,首先将原始图像进行随机相位调制和不同距离的菲涅耳衍射;其次,将携带调制后图像的参考光与携带随机相位且具有不同立体角的参考光相干叠加,产生干涉条纹;最后,将不同方向的干涉条纹叠加形成复合加密图像.解密为加密的逆过程,将复合加密图像置于空间滤波和菲涅耳衍射系统中,经过不同相位密钥解调和正确距离的菲涅耳衍射完成解密,得到多幅解密图像.该方法可以同时对多幅图像进行高效的加密,计算简单、安全可靠、抗噪声能力强.利用相关系数评估了该方法的加密效果,并通过仿真实验验证了该方法的有效性和安全性.     

基于联合变换相关和相移干涉的图像加密

提出了一种在联合变换相关器结构中引入三步相移干涉和二元置乱技术的图像加密方法.用纯相位空间光调制器同时调制原始图像和两个随机相位掩模,利用三步相移技术分别将图像信息和主密钥加密为全息图,并用CCD在输出面上接收,再利用二元置乱技术置乱图像信息的全息图.在获得置乱密钥和附加密钥的情况下,可以通过一定的算法快速、清晰的重建原始图像.用计算机仿真验证了它的可行性和有效性.     

基于计算全息和θ调制的彩色图像加密方法

提出了一种基于计算全息和θ调制的彩色图像光学加密新方法.该方法利用彩色三基色原理和计算全息编码技术,首先将彩色图像的红、绿、蓝三基色分量进行随机相位调制和菲涅耳衍射变换,然后经过θ调制后进行图像叠加并编码为计算全息图,即加密过程是将一幅彩色图像加密为一幅实值的二元计算全息图,得到单幅密文.解密为加密的逆过程,首先将加密的计算全息图置于空间滤波和菲涅耳衍射系统中,经过相位密钥解调和基于滤光片的滤波器滤波,最后通过正确距离的菲涅耳衍射完成解密,得到彩色明文图像.计算机模拟结果证明了该方法的有效性和可行性.     

基于压缩全息和空分复用的多彩色图像加密

针对现有光学加密方法进行彩色图像加密时加密容量低、解密图像失真度高等问题,提出一种基于压缩全息和空分复用的多彩色图像加密方法.在光学加密阶段,结合改进的Mach-Zehnder干涉仪与空分复用技术,通过不同的随机相位掩膜对多幅彩色图像进行同时加密,仅需单次曝光即可得到由多幅彩色图像加密的全息图.在解密过程中,由于记录全息图的过程可建模为压缩感知过程,使用两步迭代收缩/阈值算法即可求解.实验结果表明,提出的加密系统加密容量大,解密重建图像质量高,结合压缩感知理论,有效地消除了同轴全息中平方场项对解密重建性能的影响,解密图像平均峰值信噪比仅下降约2～5dB;密钥安全性高,随机相位掩膜与传播距离均起到密钥的作用,在随机相位掩膜错误或传播距离仅偏移0.25%时,便无法解密出原始彩色图像;且对噪声与遮挡性攻击具有良好的鲁棒性,解密重建性能随噪声增大下降趋势缓慢,加密全息图80%信息受到遮挡性攻击时,仍可取得良好的解密重建结果.     

基于光学扫描全息密码术的多图像并行加密

对光学扫描全息术中的双光瞳做出改进,提出对多图像并行加密和任意层图像再现的新方法.将其中一个光瞳设置成环形光瞳,另一个光瞳处插入随机相位板,干涉形成环形随机相位板,实现对多层图像的快速扫描和并行加密,扫描信号通过计算机合成为加密全息图,在数字全息再现的过程中进行解密,实现对任意层图像的精准重建.该方法快捷高效、安全可靠,抗噪声能力强.利用相关系数评估了该方法的加密效果,并通过仿真实验验证了该方法的有效性和安全性.     

双随机相位加密系统的已知明文攻击

运用密码分析学的方法对双随机相位加密系统进行了初步的安全性分析.研究结果表明，该系统属于线性的对称分组密码系统，线性性质为其安全性留下隐患.在已知明文攻击下，攻击者可通过常规的相位恢复算法获得4-f系统输入平面的随机相位函数密钥，继而可轻易推出频谱平面的随机相位函数密钥，从而攻破此密码系统. 关键词： 光学信息安全 双随机相位加密 密码分析学 已知明文攻击     

一种基于随机相位板复用的光学多二值图像加密系统

利用随机相位板复用提出了一种基于干涉原理的光学多二值图像加密系统。该系统加密过程采用数字方法,解密过程既可以采用数字方法也可以采用光学方法。利用该方法可将多幅图像信息解析地隐藏于两个纯相位板中。解密时,通过分束镜将两个随机相位板的衍射场进行相干叠加形成干涉场,利用专用密钥对此干涉场进行调制,即可在输出平面上恢复出与该专用密钥对应的原始图像,此图像可以采用CCD等图像传感器件直接记录。该方法加密过程无需迭代,非常省时,且解密系统易于物理实现。利用相关系数评估了系统的加密容量,计算机模拟结果证实了该方法的有效性。     

基于自适应模拟退火算法的光学模式转换技术

模式转换技术是光学模分复用系统的关键技术之一,用于实现任意模式之间的相互转换,是模分复用系统实现信道接入、交换及分插复用的基础。采用纯相位空间光调制的方式实现光学模式转换,通过改变加载于空间光调制器上的相位全息图,控制不同模式的产生。对相位全息图产生算法进行了改进,采用自适应的模拟退火算法,结合图形处理器并行计算,与传统的模拟退火算法相比,运算效率提升7倍以上。并搭建了模式转换系统实验平台,得到的实验结果验证了算法的有效性。     

基于多混沌系统的双图像光学加密算法

为了扩展双图像光学加密算法的密钥空间,克服双随机相位加密系统中随机相位掩模作为密钥难于存储、传输和重构的问题,突破传统图像加密的研究思路,提出了一种基于多混沌系统的双图像加密算法,构造了光学加密系统。系统增加混沌系统参数作为密钥,利用混沌加密密钥空间大和图像置乱隐藏性好的特点,构建基于Logistic混沌映射的图像置乱算法,利用Kent混沌映射生成的伪随机序列构造出一对随机相位掩模,分别放置在分数傅里叶变换光学装置的两端,图像经加密系统变换后得到密文。数值仿真结果表明,算法的密钥敏感性极高,能够有效地对抗统计攻击,具有较高的安全性。     

基于混合相位掩码与Gyrator小波变换的光学图像加密算法

为了提高密文的安全性,设计了基于混合相位掩码与Gyrator小波变换的光学图像加密算法。基于Logistic映射,利用明文像素对其迭代,生成一个随机相位掩码,引入Fresnel波带与Hilbert相位函数,获取二者对应的相位掩码,通过对这三个相位掩码进行组合,形成一个混合相位掩码,对输入明文进行调制处理;联合Gyrator变换与小波变换,构建Gyrator小波变换机制,根据明文像素迭代Logistic映射所输出的混沌序列来计算其旋转角度,获取明文Gyrator频谱对应的4个子带;对这些子带进行位置复用,借助幅度-相位截断技术,获取相应的密文与相位信息,而相位信息则视为解密密钥,以准确复原明文。实验数据表明:与当前非对称光学加密机制相比,所提算法具有更高的密文安全性与抗明文攻击能力。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.