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Optical memories implemented with photorefractive media 总被引:2,自引:0,他引:2
We consider holographic optical data storage systems implemented with photorefractive media. Our viewpoint emphasizes the close interaction between materials and device issues. First we discuss our current understanding of photorefractive physics as it pertains to the holographic data storage problem. Then we consider architecture issues, including angular, phase-encoded, and wavelength-multiplexing techniques, and several approaches to increasing the signal-to-noise ratio of the recordings. Finally, we discuss materials issues related to crystal growth and how crystal quality impacts the performance of data storage systems. Both bulk and fibre crystal growth techniques are reviewed. 相似文献
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In this paper, we review recent progress of research on the photorefractive effect of ferroelectric liquid crystals. The photorefractive effect is a phenomenon that forms a dynamic hologram in a material. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon is applicable to a wide range of devices related to diffraction optics including 3D displays, optical amplification, optical tomography, novelty filters, and phase conjugate wave generators. Ferroelectric liquid crystals are considered as a candidate for practical photorefractive materials. A refractive index grating formation time of 8–10 ms and a large gain coefficient are easily obtained in photorefractive ferroelectric liquid crystals. 相似文献
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Multilayer volume holographic optical memory 总被引:3,自引:0,他引:3
We demonstrate a scheme for volume holographic storage based on the features of shift selectivity of a speckle reference-wave hologram. The proposed recording method permits more-efficient use of the recording medium and yields greater storage density than spherical or plane-wave reference beams. Experimental results of multiple hologram storage and replay in a photorefractive crystal of iron-doped lithium niobate are presented. The mechanisms of lateral and longitudinal shift selectivity are described theoretically and shown to agree with experimental measurements. 相似文献
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Chi Ching Chang Gu Liang Chen Wen Kuei Young Ching Yang Lin Hon Fai Yau 《Optical Review》2007,14(4):214-218
This work presents a novel optical holographic encrypted data storage approach based on a phase encoding multiplexed scheme.
In the proposed data storage scheme, patterns to be encrypted are stored holographically in a photorefractive LiNbO3:Fe crystal using a lenticular lens array (LLA) sheet phase-encoded multiplexing. Experimental results reveal that rotating
an LLA placed as a phase modulator in the path of the reference beam is a simple but effective method of increasing the phase
addresses for holographic memory in a crystal. Combining this rotational multiplexing with two-axis rotating multiplexing
provides further data storage and data encryption capacity. 相似文献
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共光轴体全息存储是体全息存储技术实用化的一个发展方向。为了选择合适的参数以搭建基于晶体的透射式共光轴体全息存储系统,对该系统的存储容量、串扰特性和晶体在共光轴存储结构中的存储特性等进行了研究。从理论上分析了共光轴体全息存储系统的存储密度、物镜的参数、空间光调制器的像素尺寸、有效像素数目和移位复用间隔等之间的关系,给出了点扩展函数表达式的物理解释,并根据点扩展函数分析了系统的串扰特性,优化了存储偏振光方向以使晶体表现出最大的动态范围。根据分析优化结果搭建了基于LiNbO3晶体的透射式共光轴体全息存储实验系统,实现了高分辨图像的记录与再现。与传统的双轴系统相比,所搭建的共光轴系统具有光路结构紧凑的特点。 相似文献
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Photorefractive response time and photorefractive sensitivity are two important parameters characterizing photorefractive materials. We study theoretically the effect of the grating spacing on these parameters at large modulation depth in the absence and presence of an applied electric field for some of the most promising photorefractive materials, namely, LiNbO3, KNSBN, SPS, BGO, and GaAs. We find that the response time increases with increasing grating spacing for LiNbO3 and KNSBN, whereas the response time decreases with increasing grating spacing for SPS, BGO, and GaAs. The photorefractive sensitivity is mainly affected by the mobility–lifetime product in the presence of an applied electric field. 相似文献
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掺Ce,Fe系列LiNbO3晶体光折变效应光存储特性 总被引:9,自引:4,他引:5
研究了系列Ce:Fe掺杂以及不同后处理态(生长态、还原态和氧化态)铌酸锂晶体的透过率光谱和光折变全息存储特性。实验结果表明单掺Ce铌酸锂晶体具有较好的图像存储质量和较宽的透过率光谱范围,二波耦合增益相对较低;高掺杂铌酸锂样品的透过率光谱范围较窄,光折变二波耦合增益较低。晶体的后处理对铌酸锂样品的光折变特性影响明显,双掺Ce:Fe还原态铌酸锂晶体具有较高的二波耦合增益;氧化态样品具有较大的透过率光谱范围;还原态样品具有较大的光折变二波耦合增益特性。实验结果还表明在同种样品中难于同时获得大的二波耦合增益和图像存储质量。 相似文献
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A general theory of the two-beam coupling between a pump beam and a signal beam in photorefractive materials is presented. The coupled wave equations describing the non-linear two beam coupling are derived, based on Maxwell's wave equation. The coupled equation for the intensities of the two beams in the photorefractive crystals with the absorbing properties have been derived analytically. The intensity of the signal beam increases with the increasing crystal thickness, reaches a maximum and then decreases. The influence of energy beam coupling coefficient, oscillation frequency shift, crystal thickness, absorption coefficient and the input beam intensity ratio on the signal beam intensity have been studied in details. The effect of the photoconductivity of the materials on the intensities of the two beams in both the co-directional as well as contra-directional two beam coupling cases have been studied. 相似文献
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Photoconductive dependence of two-beam coupling between the pump beam and the signal beam in photorefractive materials have been analyzed in case of non-degenerate wave mixing under the undepleted pump approximation method. During the two-wave mixing in photorefractive materials, steady state amplification of the signal beam and oscillation characteristics of a single unidirectional ring resonator has been studied. The domination of the two-beam coupling gain over the combined absorption and resonator losses such as Fresnel reflections from the crystal and imperfect mirrors builds up unidirectional oscillation. The buildup of such an oscillation leads to a saturation of the gain, which can be explained in terms of the photorefractive phase-shift. The existence of this phase-shift between the photorefractive index grating and the illumination intensity pattern, which is of characteristic of the photorefractive effect, leads to an energy transfer between the two beams. For a single unidirectional ring resonators, the effects of photoconductivity of the materials, two-beam energy coupling coefficient, dielectric constant, crystal thickness, and material's absorption coefficient on amplification of the two-beam coupling gain and photorefractive phase-shifts of the signal beam have also been studied in detail. It has been found that amplification of the signal beam and phase-shift can be enhanced by taking the photorefractive crystal having higher photoconductivity and lower dielectric constant, which improves performance of the resonators. 相似文献
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In practice, decrypting a random-phase encrypted volume holographic data storage system is impossible unless the original random-phase plate for the encryption is available. However, this study demonstrates that under certain conditions, ways are available that can decrypt an encrypted photorefractive LiNbO3 crystal holographic storage system. In addition to presenting experimental results that show the efficacy of this decryption approach, problems and difficulties in the experiments are discussed. 相似文献
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We propose a method of near-field recording in a space that is quite apart from the original source (generator) of optical near fields. The method is based on the recently developed technique of near-field holography. Experiments based on our method have shown that near fields that originate from sub-diffraction-limit-sized objects can be stored in a photorefractive crystal 2 mm apart from the crystal surface, resulting in the retrieval of sub-diffraction-limit-sized spots. This means that our scheme can provide a method for multilayer (stackwise) near-field storage and, thus, contribute to a significant enhancement of the storage capacity of near-field optical memory. 相似文献
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The optical storage properties of LiTaO3:Fe are investigated and compared with those of the isomorphous compound LiNbO3:Fe. Absorption, photocurrent, photoconductivity and holographic measurements are reported. In the case of photovoltaic writing
similar results for LiTaO3- and LiNbO3-crystals are obtained. However, in the case of photoconductive writing using external electric fields LiTaO3:Fe-crystals yield much better results due to large photoconductivity values. Considering the recording sensitivity and the
extremely large storage time LiTaO3:Fe turns out to be one of the most promising materials for photorefractive storage of volume phase holograms. 相似文献
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The correct determination of the spatial phase shift ?(p) in photorefractive materials is crucial to the proper characterization of novel materials. It is shown that the grating translation techniques commonly used for the measurement of ?(p) need to be reevaluated for high-gain materials. Strong energy and phase coupling leads to nonuniform slanted gratings, which result in an apparent dependence of the phase shift of the beam ratio and the optical polarization. A revised theory is presented, and analytical solutions are obtained for the special case of ?(p)?pi/2 . Numerical solutions for arbitrary ?(p) are in good agreement with measurements in a photorefractive polymer. 相似文献
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Intensity-independent self-trapping of optical beams in photorefractive crystals was found recently. But we show that due to the existence of dark conductivity in some photorefractive materials or coherent and non-coherent background irradiance, the self-trapping of weak optical beams in photorefractive materials, such as SBN, becomes intensity dependent. The threshold condition of the applied external de electric field for self-trapping is determined as function of the material parameters as well as the initial transverse sizes and relative intensities of the beams. 相似文献
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In this paper, the fundamental characteristics of the photorefractive effect, both in bulk crystals and waveguides, as well as some of the most important photorefractive materials, their properties, and applications, are reviewed. In the last section, we report some experimental considerations on diffracted power from holograms written in pure LiNbO3 and Fe:LiNbO3 crystals and waveguides. 相似文献