基于空间光调制器的非相干数字全息单次曝光研究

菲涅耳非相干相关全息术(Fresnel incoherent correlation holography,FINCH)利用在空间光调制器(spatial light modulator,SLM)上加载双透镜模式对同一物点光分束自相干,并通过改变加载的相位因子得到不同的相移全息图.本系统利用SLM可分区编码调制特性,将FINCH成像中SLM上分三次加载的0°,120°,240°相位双透镜掩模各提取1/3组成一幅复合相移模式加载,并研究了三种相位分布方式对FINCH成像质量的影响.结果表明:三个相位在SLM上分布间隔越大,再现像越清晰.在此基础上,提出了一种新的掩模加载方式,在SLM加载透镜阵列,每一个相位因子对应一个双透镜,具有一个光轴.实验表明,通过这种加载方式,通过SLM后形成的三个相移图能够一次在电荷耦合器上记录,并且三个相移图不重叠,然后通过MATLAB编程计算将不同相移角度的全息图分别提取出来,通过三步相移计算合成一幅包含有物光波的复值全息图,最后通过数值再现算法重建待测样品.此系统可用于对光源相干性较低的实时成像系统,也为微小形变测量、动态物体的观测提供了新方法,为非相干数字全息术的发展提供了新思路.     

菲涅耳非相干数字全息大视场研究

菲涅尔非相干相关全息术(Fresnel incoherent correlation holography, FINCH)通过空间光调制器(spatial light modulator, SLM)将来自物点的光波分解为曲率半径不同的两束自相干光,干涉条纹由CCD记录.由于受限于SLM与CCD的像素数目及像素尺寸, FINCH技术与光学全息术相比记录视场要小得多.本文通过对FINCH系统的记录过程进行理论分析,给出了SLM所能记录的视场角,说明通过调控加载在SLM上的双透镜光轴中心,能够扩大SLM的有效直径从而将SLM的有效记录范围增大2.77倍,有效扩大了系统的记录视场.搭建了非相干光反射式数字全息记录系统并对理论分析进行了实验验证,结果表明:在SLM上依次加载不同光轴中心位置的双透镜掩模进行FINCH记录及再现,将得到的各子图像拼接融合可以得到高分辨率大视场图像,为菲涅尔非相干全息术在高分辨大视场显微成像的进一步应用提供了有力支撑.     

利用电光相位调制和交叉相位调制制作时间透镜的实验及仿真分析

对时间成像理论进行简要研究. 利用电光相位调制器进行光脉冲压缩实验,并分别对基于电光相位调制和交叉相位调制的时间透镜组成的时间成像系统进行了仿真和讨论. 实验结果表明,基于电光相位调制的时间透镜组成的时间成像系统可以有效压缩光脉冲,但是该系统受到了孔径限制,压缩系数较小,分辨率较低. 进一步的仿真分析结果表明,基于交叉相位调制的时间透镜组成的时间成像系统不受孔径限制,能够获得更大的压缩系数和更高的分辨率,但是该系统的实现难度较大. 关键词： 光脉冲压缩 时间透镜 电光相位调制 交叉相位调制     

图像传感器像素化效应对菲涅耳非相干关联全息分辨率的影响

作为复光场显微成像的一种新技术,菲涅耳非相干关联全息术(Fresnel incoherent correlation holography,FINCH)因其非相干光记录的特点在近年来受到关注.FINCH作为一种新型非相干全息系统,如何设计光路实现其最佳的分辨率是一个关键问题.然而,针对这个问题的讨论,目前已有文献存在不同的观点,有关FINCH最佳分辨率的成像条件仍有待研究.全息图有效孔径大小是决定全息成像系统分辨率的重要因素,在FINCH系统中,全息记录距离的变化则会引起全息图有效孔径发生变化,全息图的有效孔径大小不仅与光路各元件的孔径有关,还与相干光波相互干涉叠加区域的面积以及图像传感器的像素间距等因素有关.本文基于波动光学理论,结合FINCH全息图的波带结构特征,研究了FINCH全息图的有效孔径.研究发现数字全息记录相机的像素化特性是影响FINCH成像分辨率的决定性因素,并进一步通过数值模拟和光学实验验证了理论分析结果:全息图记录距离(Z_h)等于空间光调制器加载的衍射透镜焦距(f_d)时,FINCH系统的再现像将会达到最佳横向分辨率,且分辨率随成像距离|Z_h-f_d|的增大而降低.     

循环-托普利兹块相位掩模可压缩双透镜成像

压缩成像是压缩传感理论的重要应用领域之一,可以用比Nyquist测量数目少的测量值捕获充分信息重建稀疏或可压缩图像.在研究现有的压缩成像方法的基础上,给出一种新的循环-托普利兹块相位掩模矩阵可压缩双透镜成像方法.模拟实验结果表明新的相位掩模矩阵成像方法可以在欠采样的情况下有效地获得图像信息来重建原始图像.新方法的研究为...     

基于径向希尔伯特变换的图像边缘增强特性研究

研究了基于螺旋相位频谱滤波器滤波的径向希尔伯特变换对不同边缘分布图像的增强特性.给出了拓扑荷n=1的有限孔径螺旋相位滤波器点扩散函数的解析表达式,并利用圆孔、汉字和人像等三幅不同边缘分布密度的图像进行了边缘增强的模拟计算.结果表明,基于螺旋相位频谱滤波的径向希尔伯特变换会使边缘增强图像具有立体浮雕效果,并且随着输入图像的边缘分布密度变大,立体浮雕效果会越显著.通过理论分析得出,这一现象是由螺旋相位滤波器点扩散函数中的次极大分布与输入图像边缘卷积引起的.这一结论为图像的信息处理提供了一些有利的手段.     

基于相位差异法的简易光学系统的图像复原方法

简易光学系统因系统结构简单而存在严重像差,导致所成图像出现模糊、失真等问题.对简易光学系统的成像特性进行分析,在已知光学系统焦距和光瞳孔径的条件下,建立含有像差的点扩散函数模型和图像复原模型,根据焦面和离焦面图像以及精确的离焦量,无需点扩散函数的先验信息,采用相位差异法对简易光学系统所成图像进行重构.实验结果表明:单透镜、双透镜和三透镜系统复原图像质量评价指标提升率分别达到24.96%、24.80%和42.04%,重构后图像质量均有明显提升.     

利用维纳滤波改善声透镜光声成像系统的分辨率

为了克服衍射效应对光声成像系统分辨率的限制,需要采用逆卷积方法进行图像反演.从理论上分析了声透镜成像原理,模拟仿真了声透镜的点扩展函数对声透镜成像系统分辨率的影响和维纳滤波解卷积方法复原光声成像的过程,并利用自搭建的声透镜光声成像系统进行了深入的实验研究,得到了物平面上相距4 mm和3 mm的两个黑胶带点的直接成像光声...     

基于径向希尔伯特变换的图像边缘增强特性研究

研究了基于螺旋相位频谱滤波器滤波的径向希尔伯特变换对不同边缘分布图像的增强特性.给出了拓扑荷n=1的有限孔径螺旋相位滤波器点扩散函数的解析表达式,并利用圆孔、汉字和人像等三幅不同边缘分布密度的图像进行了边缘增强的模拟计算.结果表明,基于螺旋相位频谱滤波的径向希尔伯特变换会使边缘增强图像具有立体浮雕效果,并且随着输入图像...     

螺旋光子筛用于相衬成像的模拟研究

为了提高螺旋波带片用于相衬成像的分辨率和成像对比度,因此本文将螺旋波带片的透光环带替换为透光微孔,以类-贝塞尔函数作为螺旋光子筛透过率的振幅调制窗函数设计了一种螺旋光子筛.在相同的特征尺寸下,螺旋光子筛比螺旋波带片具有更大的数值孔径,因此分辨率更高.同时基于光瞳切趾原理,经过类-贝塞尔振幅调制窗函数对螺旋光子筛透光微孔的分布进行调制,螺旋光子筛的成像对比度将高于螺旋波带片.通过数值计算和仿真分析表明:螺旋光子筛的点扩展函数主瓣宽度相对于螺旋波带片更窄,旁瓣幅值也相对更低.在相衬成像中,螺旋光子筛不仅能够消除螺旋波带片对圆盘状位相物体成像时图像的"浮雕"效应而且能够更为清晰地分辨出位相跳变更为密集的周期矩形条状物体.因此,螺旋光子筛用于相衬成像中将具有更高的成像分辨率和成像对比度,其在医学领域将具有广阔的运用前景.     

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.     

Incoherent digital holographic spectral imaging with high accuracy of image pixel registration

Fresnel incoherent correlation holography(FINCH) is a unique three-dimensional(3 D) imaging technique which has the advantages of scanning-free,high resolution,and easy matching with existing mature optical systems.In this article,an incoherent digital holographic spectral imaging method with high accuracy of spectral reconstruction based on liquid crystal tunable filter(LCTF) and FINCH is proposed.Using the programmable characteristics of spatial light modulator(SLM),a series of phase masks,none of whose focal lengths changes with wavelength,is designed and made.For each wavelength of LCTF output,SLM calls three phase masks with different phase constants at the corresponding wavelength,and CCD records three holograms.The spectral images obtained by this method have a constant magnification,which can achieve pixel-level image registration,restrain image registration errors,and improve spectral reconstruction accuracy.The results show that this method can not only obtain the 3 D spatial information and spectral information of the object simultaneously,but also have high accuracy of spectral reconstruction and excellent color reproducibility.     

基于位相变更的非相干数字全息自适应成像

菲涅耳非相干数字全息作为一种非扫描的三维成像技术具有其独特的优势,但其成像过程中会受到各种像差的影响,导致成像分辨率、再现像的质量降低.为了解决这一问题,可以结合适当的自适应光学技术对波前像差进行探测和校正.位相变更是一种基于两幅具有已知位相差的强度图像实现波前探测和像差校正的技术.本文发展了基于位相变更的非相干数字全息自适应成像技术,不需要引入引导星,利用全息记录过程中的两幅相移全息图,实现波前像差的探测.本文给出了所发展技术的数值仿真和实验结果,结合位相变更算法求解出系统像差的位相分布,将像差的共轭位相加载到光瞳面上,在全息图记录的同时校正像差,从而提高重建像的质量.     

Digital spatially incoherent Fresnel holography

We present a new method for recording digital holograms under incoherent illumination. Light is reflected from a 3D object, propagates through a diffractive optical element (DOE), and is recorded by a digital camera. Three holograms are recorded sequentially, each for a different phase factor of the DOE. The three holograms are superposed in the computer, such that the result is a complex-valued Fresnel hologram. When this hologram is reconstructed in the computer, the 3D properties of the object are revealed.     

Selective edge enhancement in three-dimensional vortex imaging with incoherent light

We demonstrate a new imaging method enabling a selective edge contrast enhancement of three-dimensional amplitude objects with spatially incoherent light. The imaging process is achieved in a spiral modification of Fresnel incoherent correlation holography and uses a vortex impulse response function. The correlation recordings of the object are acquired in a one-way interferometer with the wavefront division carried out by a spatial light modulator. Two different methods based on applying a helical reference wave in the hologram recording and a digital spiral phase modulation in image reconstruction are proposed for edge enhancement of amplitude objects. Results of both isotropic and anisotropic spiral imaging are demonstrated in experiments using an LED as an incoherent source of light.     

Multiple information encryption by user-image-based gyrator transform hologram

A novel multiple information encryption by user-image-based gyrator transform hologram is proposed. In encryption process, each channel of the user image is phase encoded, modulated by random phase function and then gyrator transformed to get the gyrator spectrum of user image. Subsequently, each channel of the secret image is normalized, phase encoded, multiplied by modulated user image, and then gyrator transformed to obtain the gyrator spectrum of secret image. The encrypted digital hologram is recorded by the interference between the gyrator spectrum of user image and the spherical wave function. Similarly, the digital hologram for decryption is recorded by the interference between the gyrator spectrum of secret image and the spherical wave function. The multiple encrypted digital holograms are multiplexed into a final encoded hologram and the corresponding digital holograms for decryption are multiplexed into a final hologram for decryption. The wavelength and radius of the spherical wave function, and angle of gyrator transform are all essential keys for decryption. The proposed system has two main features. First, the encrypted hologram has no information about secret image. Second, the hologram for decryption used as identification key. Consequently the two marked security layers of information protection are achieved. The proposal can be realized by optoelectronic system. Numerical simulation results demonstrate the feasibility and security of the proposed technique.     

Deterministic phase encoding encryption in single shot digital holography

We demonstrate a deterministic phase-encoded encryption system based on the digital holography and adopted a lenticular lens array (LLA) sheet as a phase modulator. In the proposed scheme the holographic patterns of encrypted images are captured digitally by a digital CCD. This work also adopt a novel, simple and effective technique that is used to suppress numerically the major blurring caused by the zero-order image in the numerical reconstruction. The decryption key is acquired as a digital hologram, called the key hologram. Therefore, the retrieval of the original information can be achieved by multiplying the encrypted hologram with a numerical generated phase-encoded wave. The storage and transmission of all holograms can be carried out by all-digital means. Simulation and experimental results demonstrate that the proposed approach can be operated in single procedure only and represent the satisfactory decrypted image. Finally, rotating and shifting the LLA is applied to investigate the tolerance of decryption to demonstrate the feasibility in the holographic encryption, as well as can also be used to provide the higher security.