超大容量光学体全自存储技术与材料的研究动态

结合国内外发展动态以LiNbO3晶体为主说明了光学体全息存储材料具有超大容量、数据传输快、并行计算、按页存储和内容寻址等优点，详细介绍了光学体全息存储的原理及技术特点，以实验中的数据为基础指出：抑制串扰噪声和改进双掺和三掺铌酸锂晶体的存储性能应成为今后研究的主攻方向。     

Ce:Eu:SBN晶体的生长和全息存储性能研究

在SBN中掺进0.1%(质量分数)CeO2和0.1%(质量分数)Eu2O3,以Czochralski技术生长CeEuSBN晶体,在空气中退火24h,退火温度为1300℃.测试CeEuSBN晶体的住相共轭反射率和响应时间.CeEuSBN晶体最大位相共轭反射率(R=92%)和响应时间(38s),以CeEuSBN晶体作为存储元件和位相共轭镜(阈值,增益反馈系统)进行全息关联存储实验.系统具有实时处理、反复使用、成像质量好、信噪比高等优点.CeEuSBN晶体是比SBN晶体全息存储性能更好的晶体.     

激光全息法制备三维光子晶体的研究进展

三维光子晶体作为一种光子带隙材料,在光学器件、化学生物传感以及信息传输和存储等方面具有广泛的潜在应用价值。激光全息法制备光子晶体具有均匀性好、无缺陷、成本低廉等优点。综述了激光全息法制备三维光子晶体的理论及实验方面的研究进展,并阐述了各种方法的代表性工作以及各自的优缺点。     

全息光子晶体的理论分析

提出用光学全息的方法来制作光子晶体，并且从理论上推导出光子晶体的周期结构，验证了光学全息方法实现光子晶体的可行性。     

新型三维存储材料及应用

通过实施双掺杂工程,既控制光折变晶体中的光折变敏感中心(即施主中心),又控制其中的电子陷阱中心,优化双掺LN晶体的光折变存储特性,得到了优良的光存储材料,同时,利用光折变全息记录以及全光固定光栅技术,研制成三维全息存储器原型。具体研究成果如下: (1)首次在国际上发现光强阈值效应,打破了国际上传统的“与光强无关”的概念,同时,首次提出最佳写入光强的概念;首次发现高掺镁晶体的紫外光折变增强效应,打破了国际上的“掺镁抗光折变”的概念的绝对化;建立了国际上较为完善的晶体缺     

超高密度光存储技术的现状和今后的发展

文章综述了光存储领域的研究进展 ,主要包括体全息存储、近场光学存储和双光子双稳态存储技术 .在介绍各种存储技术发展现状的同时 ,分析了各自的优势和存在的问题 .从整个光存储学科发展的角度给出了未来的趋势 .     

交变极化改善重掺Zn：Cu：Fe：LiNbO3晶体光折变性能及体全息存储特性研究

生长了Zn：Cu：Fe：LiNbO3晶体，对晶体进行了多次交变极化，有效的提高了Zn：Cu：Fe：LiNbO3晶体的光折变性能，使得Zn：Cu：Fe：LiNbO3晶体的响应速度大大加快，散射噪声减小，体全息存储图像质量得到较大改善。     

吲哚俘精酸酐实现三值偏振全息光学存储器

针对三值光计算机需要直接存储线偏振光束的问题,利用光致各向异性材料吲哚俘精酸酐对偏振态敏感的特性,提出了一种基于吲哚俘精酸酐/PMMA 薄膜的三值偏振全息数字存储方法,并建立了相应的光学存储器模型.该存储器系统采用He-Ne 激光器为记录和读出光源,以双层液晶和偏振器为核心的编码器作为三值数据的输入部件,以双CCD 为核心的解码器作为数据输出器件,采用傅里叶变换全息记录的方法,在吲哚俘精酸酐/PMMA薄膜上实现三值数字光学存储.该存储器系统可望实现直接并行存储用光束的正交线偏振态和无光态表示的三值数字信息,以及以页面为单位的并行寻址和读写操作.     

Mg:Sc:Fe:LiNbO_3晶体缺陷结构和全息存储性能

采用提拉法,从Li/Nb变化(0.94,1.05,1.20,1.38)的熔体中生长出Mg:Sc:Fe:LiNbO_3晶体。Li/Nb=1.05的晶体OH~-振动吸收峰在3504cm~(-1)处出现的主吸收峰,且在3466cm~(-1)、3481m~(-1)处有两附加峰。Li/Nb=1.38的晶体OH~-振动吸收峰在3535 cm~(-1)处出现附加吸收峰。红外光谱结果表示Li/Nb=1.05的晶体是近化学剂量比的,且Sc掺质优先于Mg掺质达到阈值浓度。采用透射光斑畸变法测得Mg:Sc:Fe:LiNbO_3晶体(Li/Nb=1.05)的抗光损伤能力为2.0×10~4W/cm~2,比Fe:LiNbO_3提高了三个数量级。采用波长为632.8nm的He—Ne激光器作为光源,通过二波耦合方法测试晶体全息存储性能。实验结果表明:随着Li/Nb的增加,晶体的写入时间缩短,晶体的衍射效率降低,光折变灵敏度增加,动态范围减少。在一系列晶体中,Mg:Sc:Fe:LiNbO_3晶体(Li/Nb=1.05)更加适合作为全息存储介质。     

在多工位炉上CeO2:Bi12SiO20单晶生长的研究(Ⅱ)——空间生长实验部分

掺CeBi12SiO20单晶在神舟3号(SZ-3)飞船上成功地进行了空间生长,得到晶体尺寸为φ10mm×40mm.将空间生长的晶体和地面生长晶体对比发现空间生长晶体的外观同地面生长晶体有明显差异.分析测试空间和地面晶体的X射线摇摆曲线、吸收曲线和喇曼光谱,结果表明空间生长掺CeBSO晶体的结构完整性优于地面生长的晶体,掺Ce对BSO晶体光学性能的影响空间制备晶体要大于地面制备的晶体     

Pr:Fe:LiNbO3晶体光折变性能的研究

在Fe∶LiNbO3中掺进Pr6011生长Pr∶Fe∶LiNbO3晶体。对晶体进行氧化－还原处理。测试晶体的指数增益系数、衍射效率、响应时间、光电导和信噪比。测试结果Pr∶Fe∶LiNbO3晶体的响应时间缩短,信噪比提高,克服了Fe∶LiNbO3响应时间长,光电导和信噪低的缺点。以Pr∶Fe∶LiNbO3晶体作为存储元件实现了全息关联存储。     

双掺杂LiNbO3晶体的生长及其实时图象微分的研究

采用Ｃｚｏｃｈｒａｌｓｋｉ Ｚｎ：Ｆｅ：ＬｎＮｂＯ３晶体和Ｃｅ：Ｎｄ：ＬｉＮｂＯ３晶体。测试了晶体的抗光致散射能力、衍射效率和响应时间。以双掺杂ＬｉＮｂＯ３晶体作为全息记录材料,Ｃｅ：Ｃｕ：ＫＮＳＢＮ晶体构成自泵浦位相共轭镜,进行了实时图象边缘增强的研究,并探讨了不同的记录晶体对实验结果的影响。     

Absorption characteristic and nonvolatile holographic recording in LiNbO3:Cr:Cu crystals

The absorption characteristic of lithium niobate crystals doped with chromium and copper (Cr and Cu) is investigated. We find that there are two apparent absorption bands for LiNbO3:Cr:Cu crystal doped with 0.14 wt.% Cr2O3 and 0.011 wt.% CuO; one is around 480 nm, and the other is around 660 nm. With a decrease in the doping composition of Cr and an increase in the doping composition of Cu, no apparent absorption band in the shorter wavelength range exists. The higher the doping level of Cr, the larger the absorbance around 660 nm. Although a 633 nm red light is located in the absorption band around 660 nm, the absorption at 633 nm does not help the photorefractive process; i.e., unlike other doubly doped crystals, for example, LiNbO3:Fe:Mn crystal, a nonvolatile holographic recording can be realized by a 633 nm red light as the recording light and a 390 nm UV light as the sensitizing light. For LiNbO3:Cr:Cu crystals, by changing the recording light from a 633 nm red light to a 514 nm green light, sensitizing with a 390 nm UV light and a 488 nm blue light, respectively, a nonvolatile holographic recording can be realized. Doping the appropriate Cr (for example, NCr = 2.795 x 10(25) m(-3) and NCr/NCu = 1) benefits the improvement of holographic recording properties.     

Nonvolatile holographic storage of near-stoichiometric LiNbO3:Cu:Ce with green light

The nonvolatile holographic storage of a near-stoichiometric LiNbO(3):Cu:Ce crystal with green light was investigated. With an increase in composition, improved nonvolatile holographic performance was obtained. The sensitivity S? of the near-stoichiometric LN(49.57):Cu:Ce crystal is 1 order of magnitude larger than the congruent crystal. And according to our research, Ce ions should be the deep centers of the LiNbO(3):Cu:Ce crystal.     

Storage density of shift-multiplexed holographic memory

The storage density of shift-multiplexed holographic memory is calculated and compared with experimentally achieved densities by use of photorefractive and write-once materials. We consider holographic selectivity as well as the recording material's dynamic range (M/#) and required diffraction efficiencies in formulating the calculations of storage densities, thereby taking into account all major factors limiting the raw storage density achievable with shift-multiplexed holographic storage systems. We show that the M/# is the key factor in limiting storage densities rather than the recording material's thickness for organic materials in which the scatter is relatively high. A storage density of 100 bits/mum(2) is experimentally demonstrated by use of a 1-mm-thick LiNbO(3) crystal as the recording medium.     

Orthogonal polarization simultaneous readout for volume holograms with hybrid angle and polarization multiplexing in LiNbO(3)

The orthogonal polarization simultaneous readout technique in a hybrid-multiplexed memory using angular multiplexing and polarization multiplexing is presented. Twenty holograms were hybrid multiplexed in a single LiNbO(3) crystal with ten angular positions for angular multiplexing. In each angular position of the holographic memory, two images with orthogonal polarization are multiplexed in the same spatial location inside the LiNbO(3) via polarization multiplexing. These two orthogonally polarized images can be reconstructed simultaneously with a linear polarization reading beam, but they can be separated with a polarization beam splitter, and accordingly each can be viewed independently. The exposure schedule for holographic storage using the proposed hybrid-multiplexing technique is derived.     

Threshold effects for resistance to optical damage and nonvolatile holographic storage properties in In:Mn:Fe:LiNbO3 crystals

The threshold concentration for In2O3 was found in In:Mn:Fe:LiNbO3 crystals by measurement of the infrared spectra of the crystals. The resistance of the In:Mn:Fe:LiNbO3 crystals to optical damage is characterized by changes in photoinduced birefringence as well as by distortion of the transmitted beam pattern. The resistance increases remarkably when the concentration of In2O3 exceeds its threshold. The resistance to optical damage of a In(3.0 mol. %):Mn:Fe:LiNbO3 crystal is 2 orders of magnitude higher that of a Mn:Fe:LiNbO3 crystal. The dependence of defects on the resistance to optical damage of the In:Mn:Fe:LiNbO3 crystals is discussed in detail. Nonvolatile holographic storage was achieved for all crystals, and the sensitivity of the In(3.0 mol. %):Mn:Fe:LiNbO3 crystal is much higher than that of the others.     

Thermal fixing of 10,000 Holograms in LiNbO3:Fe

We discuss thermal fixing as a solution to the volatility problem in holographic storage systems that use photorefractive materials such as LiNbO(3):Fe. We present a systematic study to characterize the effect of thermal fixing on the error performance of a large-scale holographic memory. We introduce a novel, to our knowledge, incremental fixing schedule to improve the overall system fixing efficiency. We thermally fixed 10,000 holograms in a 90 degrees -geometry setup by using this new schedule. All the fixed holograms were retrieved with no errors.     

Optimal recording wavelength for maximum diffraction efficiency of thermal fixing in LiNbO3:Fe

Optimal recording wavelength for maximum diffraction efficiency of thermal fixing in LiNbO(3):Fe crystal is investigated. Holographic gratings are recorded using three typical recording wavelengths including 488, 514, and 633 nm. Optimal switching from recording to thermal fixing is taken into consideration. The fixed holograms are developed by an original recording setup. Diffraction efficiencies of recording and thermal fixing are measured by a two-wave coupling technique. The theoretical and experimental results are analyzed and compared. With a blue beam, the nonvolatile hologram with maximum fixing efficiency is achieved. This work can obtain high persistent diffraction of the nonvolatile holographic storage in LiNbO(3):Fe crystals.     

Effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals

The effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals is investigated experimentally. The results show that the dopant composition ratio affects the recording sensitivity and fixed diffraction efficiency by altering the UV light absorption characteristics of the crystals during nonvolatile, holographic recording. Increasing the dopant composition ratio of Cu and Ce leads to an increase in the absorption of UV light and further to an increase in the recording sensitivity and fixed diffraction efficiency. The UV light absorption characteristics of LiNbO3:Cu:Ce crystals and their roles in nonvolatile holographic recording are theoretically analyzed. The theoretical results are consistent with those of the experiments.