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For a recording medium such as dichromated gelatin, a quasi-Fourier transform holographic memory is preferred over the exact Fourier transform. We proceed here with angular multiplexing and consider undesired reconstructed waves such as cross-talk noise, and show that the signal-to-noise ratio is 33 dB for 20 angular multiplexed elements in 25 μm thickness of the recording medium. We also study the energy coupling between gratings to standardize the diffraction efficiency of each multiplexed grating. 相似文献
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The effect of nonlinearity of a photosensitive medium response on the diffraction properties of thick phase holograms is analyzed on the basis of coupled-wave equations. It is shown that, for a typical dependence of the refractive index on the exposure, the response nonlinearity lowers the diffraction efficiency of a hologram illuminated by an s-polarized light. For the p polarization of the reading beam, the response nonlinearity reduces the hologram efficiency when the angle between the beams diffracted into the zero and second orders (into the minus first and first orders) is smaller than 90°, increases the efficiency for angles larger than 90°, and hardly affects the diffraction efficiency when this angle is close to 90°. The results for p polarization are obtained, to the best of our knowledge, for the first time. The analysis of angular selectivity of the gratings has shown that the effect of nonlinearity becomes particularly important for light waves incident on the hologram at angles close to the Bragg one. It is also found that, for any thickness of the photosensitive medium, there exists an optimum value of the maximum change in the refractive index, for which the diffraction efficiency may be close to 100% in a wide range of exposures. In this case, the nonlinearity for s polarization stabilizes, to some extent, the dependence of the diffraction efficiency on the exposure. 相似文献
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可擦写俘精酸酐/PMMA薄膜的全息记录特性研究 总被引:10,自引:10,他引:0
对一种新型可擦写有机光致变色材料-吡咯俘精酸酐的光全息记录特性进行了实验研究.用涂布法制成厚度约10 μm 的吡咯俘精酸酐/PMMA聚合物薄膜.样品无色态吸收峰在373 nm处,经紫外光照射发色后,变为呈色态,其吸收峰移动到626 nm处,呈色态在氦氖激光照射下可以重返为无色态.无色态和呈色态在室温下都是稳定的.以呈色态吡咯俘精酸酐/PMMA薄膜作为记录材料,以氦氖激光作为记录光,分别建立了双光束干涉衍射记录装置和四波耦合实验系统.实验测得该薄膜的空间分辨率至少可以达到1680 lines/mm,一级衍射效率大于2%,全息记录中的最佳曝光量约为1 J/cm2.实验测量了衍射效率与曝光量的特性曲线,分析了衍射光强度和光斑模式随曝光时间的变化关系. 相似文献
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为设计基于多路复用体全息光栅的角度放大器, 建立了多路复用角度放大器(MAM)模型, 从效率均衡性和角度分布均匀性两个方面归纳了其设计规则; 研究了光刻过程中的误差对MAM性能的影响; 分析了实际发散光束对MAM性能的影响. 研究表明:控制光栅空间频率和光栅倾斜角可以实现需要的MAM角度分布, 控制光栅厚度和折射率调制深度可以实现MAM最佳衍射效率; MAM最大复用路数不超过10路; 增大光栅倾角或者记录光与工作光波长之比有利于抑制参考光角度误差带来的MAM出射角分布误差, 减小光栅厚度有利于抑制厚度误差与折射率调制深度误差对衍射效率的影响; 当远场发散角大于光栅角半宽时, 最佳衍射效率下降到50%以下且角度选择曲线失去局部最小值; 增大空间频率或者光栅厚度可以减小所需的折射率调制深度, 增多MAM可复用路数, 但是不利于效率均衡性设计和抑制发散光束的影响. 相似文献
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为设计基于多路复用体全息光栅的角度放大器, 建立了多路复用角度放大器(MAM)模型, 从效率均衡性和角度分布均匀性两个方面归纳了其设计规则; 研究了光刻过程中的误差对MAM性能的影响; 分析了实际发散光束对MAM性能的影响. 研究表明:控制光栅空间频率和光栅倾斜角可以实现需要的MAM角度分布, 控制光栅厚度和折射率调制深度可以实现MAM最佳衍射效率; MAM最大复用路数不超过10路; 增大光栅倾角或者记录光与工作光波长之比有利于抑制参考光角度误差带来的MAM出射角分布误差, 减小光栅厚度有利于抑制厚度误差 相似文献
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For reflection geometry hologram storage in LiNbO3:Fe, we have shown that the diffraction efficiency increases with doping level and thickness of storage material monotonically. When the acute angle between reference and z-axis is large enough for getting a relative small Bragg angle that is needed for angle multiplexing, smaller angle does good to diffraction efficiency after thermal fixing. And for absorption coefficient, there is an appropriate value responding to optimal diffraction efficiency after thermal fixing and we develop a theoretical model that predicts achievable diffraction efficiency after thermal fixing as a function of crystal thickness, doping level, acute angle between reference and z-axis and absorption coefficient. We compare this model with experiment results and get a good agreement. 相似文献
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The dependence of the maximal diffraction efficiency of a volume reflection hologram recorded in a cubic optically active
photorefractive piezocrystal on the crystal thickness is investigated. The theoretical analysis is fulfilled on the basis
of the coupled wave equations in a static grating approximation taking into account the linear electro-optic, inverse piezoelectric,
and photoelastic effects. The optimal cuts of the crystals with various thickness for which the maximal diffraction efficiency
of the reflection hologram can be attained are determined. It is shown that the optical activity of the crystal is responsible
for a variety of the optimal cuts corresponding to different crystal thicknesses. Effect of the crystal on the dependence
of the maximal diffraction efficiency of the reflection hologram on a crystal cut is discussed. 相似文献
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梯形介质膜光栅衍射特性分析 总被引:3,自引:1,他引:2
基于严格耦合波理论建立了梯形介质膜光栅的衍射机理模型,利用该模型讨论了底角为70°的梯形介质膜光栅-1级的衍射行为.通过对梯形介质膜光栅的占空比、槽深和剩余厚度的优化,设计了应用于1053 nm和51.2°角度入射的梯形介质膜光栅.对于顶层为HfO2的介质膜光栅,当槽深为200 nm,剩余厚度为100 nm,占空比为0.35时.其衍射效率优于99.5%,而对于顶层为SiO2的梯形光栅,为获得99.5%的衍射效率.其槽深为800 nm,剩余厚度为320 nm.而且,获得同样的衍射效率,顶层为HfO2的梯形光栅具有更宽的光谱特性.数值计算表明,严格耦合波理论模型对梯形介质膜光栅衍射效率的计算具有很好的收敛性和稳定性. 相似文献
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The quality of images recorded on photothermoplastic media (PTPMs) with various thicknesses of the thermoplastic layer is investigated. It is found that the potential of a corona-forming electrode initiating deformations on a PTPM surface and the diffraction efficiency, corresponding to the additional maxima in its dependence on the spatial frequency, increase with decreasing thickness of the thermoplastic layer, in contrast to the diffraction efficiency at the resonance frequency. It is shown that the frequencies corresponding to additional maxima in the dependence of the diffraction efficiency on the spatial frequency are preferable for application as the carrier frequency for raster-scan recording and as the center carrier frequency for holographic image recording on PTPMs in order to reach a higher diffraction efficiency, image contrast, and signal-to-noise ratio than those attainable at the resonance frequency. An anomalous relation between the resolution and sensitivity of PTPMs is found under the suggested recording conditions and carrier frequencies. It is shown that both the resolution and the sensitivity of PTPMs increase with decreasing thickness of the thermoplastic layer. 相似文献
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耦合波理论是分析光折变晶体的基本方法,由耦合波理论可以得到光折变晶体的衍射效率具有角度选择性。针对这一结论,利用Cu:KNSBN晶体中的双光束耦合,从理论和实验两个角度做了分析,实验结果和理论分析基本吻合。结果表明,对于一定厚度的Cu∶KNSBN晶体,双光束的写入角存在着一个最佳值,使得Cu:KNSBN晶体的衍射效率最大。 相似文献
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T. Kubota 《Optics Communications》1976,16(3):347-349
The profile of the hologram grating is described considerating the absorption of the recording medium and its diffraction efficiency is calculated for special cases using the coupled wave theory. The maximum diffraction efficiency obtainable is not affected by the absorption of the recording medium in the case of transmission holograms, while it decreases with increasing absorption in the case of absorptive reflection holograms. 相似文献
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We have studied the anisotropic diffraction properties of the stratified volume holographic gratings recorded in photorefractive media using the anisotropic coupled wave theory. It is shown that the diffraction efficiency of such system exhibit the uniform periodic Bragg selectivity properties. In addition the dependence of the stratified volume holographic optical elements (SVHOEs) diffraction properties on the buffer-layer thickness, grating-layer thickness, number of modulation layers, and total thickness of system are discussed in detail. 相似文献
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Based on numerical modeling of metallized diffraction gratings with multilayer insulator coatings, the diffraction efficiency of such gratings is investigated, assuming that the initial profile of the metallized grat-ing is not reproduced in the course of sequential deposition of coating layers. From comparison of experimental and calculated data, it is concluded that the initial grating relief is subject to considerable smoothing. The new nontraditional range of the optimum values of layer thicknesses, which provides a high diffraction efficiency in the operating wavelength range of 1.06 μm, is suggested. The stability of the diffraction efficiency with respect to random errors in the thickness of insulator layers deposited is investigated numerically. 相似文献
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The diffraction efficiency of M holograms superimposed in the volume of the recording medium is proportional to 1/M(2). We present a method, based on nondestructive localized holograms in a doubly doped LiNbO(3) crystal, that allows us to also record M holograms in the same volume without an exposure schedule or a diffraction efficiency that has 1/M dependence. We compare experimentally the final diffraction efficiency obtained with the localized and distributed recording methods. 相似文献