基于数字闪耀光栅的位相全息图光电再现优化

针对利用液晶空间光调制器（LC-SLM）进行全息图光电再现过程中,再现像面存在多级衍射像造成单一像能量利用率低的问题,提出了一种在位相全息图中加载数字闪耀光栅的方法,以提高全息图光电再现中单一衍射像的衍射效率.分析了闪耀光栅作为衍射光学元件的特性及其对光波进行位相调制的原理,并阐述了在LC-SLM中加载数字闪耀光栅对位相全息图光电再现时像面能量分布的影响.搭建了基于LC-SLM的位相全息图光电再现实验系统.理论分析表明：在其他条件不变的情况下,加载竖直（或水平）槽向周期为2 pixels的数字闪耀光栅可使 关键词： 全息光电再现 位相全息图 数字闪耀光栅 液晶空间光调制器     

液晶空间光调制器相位调制特性的快速测量与标定方法

为提高液晶空间光调制器（LC-SLM）在波前相位调制中的精度,提出了一种能对LC-SLM实现快速标定的数字全息测量方法。该方法仅需在成像面上采集单幅数字全息图像,就能实时测量LC-SLM在特定波长下的相位调制特性,系统结构简单,且无需经过复杂的衍射传播计算,测量效率较高。在不改变光路结构的情况下利用Twyman-Green干涉法开展对比实验,进一步验证了数字全息法在测量精度方面的优势。实验结果表明,LC-SLM在标准光波波长（633 nm）下的相位调制范围为0～6.185 rad,利用反插值法校正相位响应的非线性特性使得非线性误差降低到2.45%,有效提升了器件的线性驱动精度。最后,针对LC-SLM的波长响应特性,建立了相位-波长调制修正系数模型,对LC-SLM在非标准光波波长（670 nm）下的实际相位调制范围进行了修正,探究了该器件在双波长干涉测量系统中用于相位校正的可行性。     

基于纯位相液晶空间光调制器的可变焦透镜的实现

提出一种基于纯位相液晶空间光调制器(LC-SLM)实现变焦透镜的方法。根据液晶空间光调制器的位相调制原理,以相息图控制LC-SLM来调制入射光波,并衍射产生透镜波面,改变相息图的衍射距离,可实现变焦位相菲涅耳透镜的功能。分析衍射孔径、衍射距离、相息图位相阶数等参数对变焦位相菲涅耳透镜的影响,并以点光源相息图为例对该方法的可行性进行了实验验证。实验结果表明:通过改变计算衍射距离,提出的方法可得到焦距不同的透镜,且易于控制,为三维扫描显示的实现提供了可行性依据。     

空间调制线偏振光谱测量的误差影响仿真分析

通过理论推导,给出了1/4波片复合双折射光楔偏振片型空间调制结构的误差矩阵,并在空间调制相位为0及0.5π的位置分别计算了理想像面光强受器件误差的影响程度。1/4波片的延迟量误差是将入射光斯托克斯参量的V分量引入调制光强中的主要原因,在调制相位为0.5π的位置,当延迟量误差为0.02π时,其调制系数为0.0314。在给定的器件误差范围内,入射斯托克斯参量具有同样的Q、U分量时,V=0.2会使得U分量测量偏差控制在0.45%内的概率从V=0时的80%左右下降到6%。利用计算机仿真分析得到了线偏振度测量偏差随入射条件的变化,在所有误差取误差范围内的最大值且入射光的V分量小于0.04时,在仪器未定标的条件下,线偏振度的相对测量偏差可以控制在0.5%以内。     

Mask相位法校准液晶空间光调制器的相位调制特性

提出Mask相位法校准出厂标定波长在532 nm的液晶空间光调制器(LC-SLM)在561 nm处的相位调制特性曲线.首先基于傅里叶光学模拟计算得出棋盘型二维相位光栅相位对比度与零级衍射光斑光强之间的对应关系,然后搭建实验光路测量计算机所发灰度图所对应的零级衍射光斑光强值.根据前面两组结果最后得到相位延迟量与计算机灰度...     

三维场景相息图的白光再现研究

讨论了相息图白光再现的可行性,得到采用在相息图和观察者之间加入狭缝的方法可实现相息图的白光再现的结论.提出了一种通过对彩虹全息图进行复数滤波来制作相息图的方法.根据彩虹全息图中物光的频谱宽度设计有限脉冲响应数字滤波器.对该滤波器进行移频,得到与通带位置物光的频谱位置一致的复系数带通滤波器.对全息图进行空域滤波,去除共轭像和零级,求出调制后物光的位相分布,制作场景相息图.实验观察到了经过此方法制作的相息图在白光下的再现像,表明本文的理论分析正确,所提出的方法可行.     

KNSBN：Co晶体自泵浦位相共轭特性的研究

本文报道在两块不同尺寸的KNSBN:Co晶体中实现了自泵浦位相共轭输出,通过实验验证了位相共轭反射率与入射角、入射位置以及波长有关,并给出各自的实验曲线.保持激光器工作波长为514.5nm不变,在大块晶体中可得到高达73.0%的位相共轭反射率.文章还给出共轭光的形成时间随系统光强变化关系的实验曲线,并指出自泵浦形成时透射光强和晶体表面反射光强的时间变化特性,解释了自泵浦形成的阈值特性.     

数字微镜器件闪耀特性及其在全息显示中的应用

为了提高数字微镜器件的空间光调制性能,发挥其在全息显示和三维重构等方面的作用,研究了数字微镜器件的闪耀特性.结合数字微镜器件的物理结构,利用反射光栅理论分析了数字微镜器件的闪耀规律,进行了理论计算与实验修正,得出了其存在四个相对闪耀状态的结论,而通常实验所要求的24°角入射,为出现相对闪耀状态的最小入射角.据此,可在全息显示中选择恰当的入射角,改变数字微镜器件的闪耀状态,增强全息再现的视觉效果.以傅里叶变换全息为例进行了具体应用研究,通过再现光入射角的调节,可实现闪耀级次的调整,并增强了再现的视觉效果.实验表明,分析结果是正确的.     

彩色全息图的计算机产生和数字再现

提出了一种基于色彩合成以及菲涅尔衍射原理,用计算机产生全息图并用数字方法再现彩色全息图的方法。该方法的第一步是将物体的彩色RGB图像分离为三基色强度图,再利用博奇编码的方法制成修正离轴参考光分色计算机全息图;第二步是分别对分色全息图在频域进行调制以实现用原参考光真实再现原始物光波。通过滤波消除零级衍射及共轭像的影响,获得了所需要的实像并提高了像质。提供的实验是选用一幅RGB图像作为原始物体,给出了用博奇编码法制成的全息图以及最后经色彩合成获得的再现像。结果表明,该方法能使各分色全息图的再现像准确重合,解决了在色彩合成时容易出现的色串扰问题。     

RGB三波段消光法测量细微颗粒粒度分布研究

提出了采用彩色相机RGB信号实现三波段消光法测量微米级颗粒粒度分布的方法。当一束平行白光入射到弥散细微颗粒时,测量不同波长的透射光强信号,用多波长消光法理论反演可以测得被测弥散细微颗粒粒度。当用彩色相机拍摄透射光,得到的图像实际是RGB三个波段的透射光信号,该信号与相机的RGB响应曲线、光源光谱特性、被测颗粒粒径及颗粒浓度有关。对RGB三波段信号用消光法理论进行分析和反演计算,可以得到细微颗粒的粒度分布。通过数值模拟与实验验证,表明用彩色相机RGB三波段消光法可以测量亚微米到3 mm大小的颗粒粒度分布。将该方法与图像法颗粒粒度测量相结合,可以将彩色相机测量颗粒粒度的范围拓展到从亚微米到数百微米。     

A Color Holographic Reconstruction System by Time Division Multiplexing with Reference Lights of Laser

3D-TV systems by holography technique have been studied in the world. In this paper, we report a color holographic reconstruction system by time division multiplexing method with reference lights of laser. The method can reconstruct a color holographic image by switching reference lights of red, green and blue colors at certain intervals. We can observe a color holographic image using red and green lasers as the reference lights, a high minute liquid crystal display (LCD) panel as a spatial light modulator (SLM) and electro-shutters as the shuttering device of the laser lights in the optical system. This approach has some advantages. Namely, the structure of the optical system can be simple and the number of LCD panels in the optical system can be decreased.     

Computer-generated kinoforms of real-existing full-color 3D objects using pure-phase look-up-table method

A computational method based on pure-phase look-up-table (LUT) is proposed for generating kinoforms of full-color real-existing three-dimensional (3D) objects. The principle of the pure-phase LUT method is described. 3D depth as well as color information of a full-color 3D object is obtained by the full-color 3D profile measurement approach based on binocular vision. The obtained full-color 3D data is decomposed into red (R), green (G), and blue (B) channels, and kinoforms of each channel are calculated from the depth map and color information of the corresponding channel using the pure-phase LUT method. In order to reduce the speckle noise of reconstructed full-color 3D image, sequential kinoforms of each color channel are generated by adding dynamic-pseudorandom phase factor into the object domain. Numerical reconstruction and optical reconstruction with a phase-only spatial light modulator (SLM) show that, with the proposed method, full-color holographic 3D display of real-existing full-color 3D objects is available.     

Transmission type twisted nematic liquid crystal display for three gray-level phase-modulated holographic data storage systems

Gray-level data pages enhance the storage capacity of holographic data storage systems. A balanced three gray-scale data page in phase mode produces a homogenized Fourier spectrum which is regarded to be necessary for suitable exploitation of the holographic recording medium. A commercially available transmission type twisted nematic liquid crystal display has been characterized for use as a phase spatial light modulator with phase modulation in the range 0–3π/2 at 532 nm wavelength, such that it may be used for holographic data storage with binary as well as three gray-level phase-modulated data pages. Experimental results of the phase and amplitude modulation characteristics of the SLM, Fourier plane homogeneity, and recording of phase-modulated binary, three gray-level data pages and their reconstruction with a real-time holographic interferometric method are presented.     

Color holographic display based on azo-dye-doped liquid crystal (Invited Paper)

A multiplexed holographic display video has been achieved by using a passive azo-dye-doped liquid crystal （LC） cell. Holograms formed in this cell can be refreshed in the order of several milliseconds. By angular multiplexing technique, dynamically multiplexed holographic videos are realized. Moreover, the reconstructed RGB images are merged into a color image, which illustrates the possibility of a color holographic three-dimensional （3D） display by holographic multiplexing of the LC cell.     

液晶相息图用于光学检测

根据液晶的动态响应和位相调制特性,研究了一种利用液晶显示器进行光学检测的检测方法.实验中,把液晶显示器改造为纯位相的空间光调制器,并测定了它的位相调制特性.实验测得：改造后的液晶显示器可实现1 λ(λ=632.8 nm)的调制量.通过引入相息图的方法,实现了液晶空间光调制器的大位相调制量.并产生了调制量为3.4 λ的球面波.最后,利用液晶显示器检测了凸透镜的前表面.检测结果发现,干涉条纹为平行直条纹且PV值为0.32λ.     

Holographic imaging of full-color real-existing three-dimensional objects with computer-generated sequential kinoforms

We propose a computational method for generating sequential kinoforms of real-existing full-color threedimensional (3D) objects and realizing high-quality 3D imaging.The depth map and color information are obtained using non-contact full-color 3D measurement system based on binocular vision.The obtained full-color 3D data are decomposed into multiple slices with RGB channels.Sequential kinoforms of each channel are calculated and reconstructed using a Fresnel-diffraction-based algorithm called the dynamicpseudorandom-phase tomographic computer holography (DPP-TCH).Color dispersion introduced by different wavelengths is well compensated by zero-padding operation in the red and green channels of object slices.Numerical reconstruction results show that the speckle noise and color-dispersion are well suppressed and that high-quality full-color holographic 3D imaging is feasible.The method is useful for improving the 3D image quality in holographic displays with pixelated phase-type spatial light modulators (SLMs).     

液晶空间光调制器相位调制测量及波前校正

提供了一种简单且精度较好的测量液晶空间光调制器相位调制特性的方法,即相位与电压(灰度)之间的关系。采用数字波面移相干涉仪,由干涉仪直接给出不同灰度对应的相位差,从而得到液晶空间光调制器的相位调制曲线。利用液晶空间光调制器实现了波前校正。由干涉仪作波前测试,对待校正的畸变波前进行泽尼克多项式描述,根据液晶空间光调制器的相位与灰度的关系,产生相应的灰度图,获得畸变波前的共轭波前,从而完成静态波前的校正,使相关参数如PV值、RMS值和Strehl比值得到了改善。     

Display method with compensation of the spatial frequency response of a liquid crystal spatial light modulator for holographic femtosecond laser processing

Liquid crystal spatial light modulators, which are widely used as display devices for computer-generated holograms, have modulation characteristics that depend on spatial frequency. We describe a method for displaying a computer-generated hologram on a liquid crystal spatial light modulator with compensation of its spatial frequency response. Using this method, we demonstrate a binary phase grating with smaller dependence on the spatial frequency. We also demonstrate application of the display method to holographic femtosecond laser processing.     

基于液晶空间光调制器的全息显示

在传统的纯相位全息显示系统中, 一般基于快速傅里叶变换(FFT)算法来计算相位全息图, 在FFT的计算中需要遵循Nyquist采样定理, 因此, 重建图像的尺寸往往受限于空间光调制器的固定采样率. 这个限制可以通过卷积算法或者两步菲涅耳衍射算法来解决, 但是需要使用多个FFT的计算, 导致计算量增大. 鉴于此, 提出了一种基于透镜的纯相位全息图计算方法. 在全息图的计算中, 通过透镜的成像原理建立一个采样率可变的虚拟全息面, 通过调节相应的距离参数使得在全息图的计算中可以任意调节原始图像的采样率, 摆脱了传统方法中液晶空间光调制器带宽积对重建图像尺寸的限制, 并且这种算法只需使用一次FFT就能达到变采样率的衍射计算, 大幅提高了全息图的计算速度. 数值模拟及光学实验结果证明了此方法可以在全息显示光学系统中清晰地重建不同尺寸的图像. 同时该系统可以有效地消除由空间光调制器的像素化结构带来的零级衍射.     

Optical holographic memory using angular-rotationally phase-coded multiplexing in a LiNbO3:Fe crystal

We propose a new holographic memory scheme based on random-phase-coded multiplexing in a photorefractive LiNbO₃:Fe crystal. Experimental results show that rotating a diffuser placed as a random-phase modulator in the path of the reference beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this rotational multiplexing with angular multiplexing offers further data-storage possibilities. The advantage of using post-image versus pre-image phase modulation of the object beam is demonstrated. Received: 15 August 2000 / Published online: 10 January 2001