【作者】 石宏新；

【导师】 孙秀冬；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2010， 博士

【摘要】 光学体全息数据存储器以其存储容量大、数据传输速率高、信息寻址速度快等优点,在现代信息存储技术竞争中显示出巨大的优势和良好的发展前景。理想的体全息存储材料应具有高折效率调制度、低噪声、高记录灵敏度以及较大的动态范围。铌酸锂(LiNbO3)晶体因其良好的光折变性能而成为体全息数据存储的首选记录材料。然而,LiNbO3晶体存在的响应时间长、散射噪声强等缺点从不同程度上制约了光学体全息数据存储的发展。因此,改善和优化LiNbO3晶体的光折变特性,进而提高体全息存储器的整体性能已成为目前体全息数据存储领域的重要研究课题之一。本文以新型双掺Hf:Fe:LiNbO3晶体为研究对象,从其微观缺陷结构出发,详细研究了Hf:Fe:LiNbO3晶体在488nm波长下的光折变特性,并以该材料为记录介质设计和搭建了基于光学滤波的快速相关识别系统,进行了边缘增强图像的光学相关识别研究。通过红外OH-吸收光谱、紫外-可见吸收光谱、ICP-AES分析以及拉曼光谱等光谱分析手段,详细研究了Hf:Fe:LiNbO3晶体的缺陷结构以及掺杂离子在晶体中的占位情况。分析结果表明,Hf4+离子掺杂浓度低于其阈值浓度时,Hf4+离子占据NbLi4+的锂位,当Hf4+离子掺杂浓度达到阈值浓度后,Hf4+离子开始进入正常的铌位。在所有样品中,Fe2+/3+离子一直占据正常的锂位。采用光斑畸变和光致双折射变化两种方法,针对Hf:Fe:LiNbO3晶体在488nm波长下的抗光损伤性能进行了系统研究。研究结果表明,在同成分Hf:Fe:LiNbO3晶体中,当Hf4+离子掺杂浓度为其阈值浓度(4.0mol.%)时,晶体的抗光损伤能力最强。对Hf4+离子掺杂浓度为1.0mol.%和4.0mol.%的晶体,晶体的抗光损伤能力随晶体内[Li]/[Nb]比变化呈现不同的规律。当Hf4+离子掺杂浓度为1.0mol.%时,晶体抗光损伤能力随[Li]/[Nb]比的增加而增强;当Hf4+离子掺杂浓度为4.0mol.%时,晶体抗光损伤能力随[Li]/[Nb]比的增加而减弱。基于二波耦合实验光路,对Hf:Fe:LiNbO3晶体在488nm波长下的光折变性能进行了详细研究。研究结果表明,随着Hf4+离子掺杂浓度的增加,晶体的光折变性能减弱,当Hf4+离子掺杂浓度超过阈值浓度后,晶体的光折变性能增强。对[Li]/[Nb]比变化的Hf:Fe:LiNbO3晶体,晶体的光折变性能改变与晶体内Hf4+离子掺杂浓度有关。对Hf4+离子掺杂浓度为1.0mol.%的晶体,晶体的光折变性能随[Li]/[Nb]比的增加而减弱。对Hf4+离子掺杂浓度为4.0mol.%的晶体,晶体的光折变性能随[Li]/[Nb]比的增加而增强。此外,通过对实验中所用记录光强进行优化,可以进一步提高晶体的光折变特性。利用光学高通滤波的方法实现了目标图像的边缘特征提取,并从理论和实验两方面研究了图像边缘增强对光学相关识别结果的影响。以Hf:Fe:LiNbO3晶体为记录介质,设计并搭建了基于光学滤波的快速相关识别系统。理论分析和实验结果均表明,与未经光学滤波的图像相比,经光学滤波后的边缘增强图像的相关识别准确率得到了明显提高。更多还原

【Abstract】 Optical volume holographic data storage is the promising storage technique because of its high data storage density, high transfer speed, fast parallel access, and so on. Ideal volume holographic storage material should have high refractive index modulation, low scattering noise, high recording sensitivity and large dynamic range. Lithium niobate (LiNbO3) crystal has become a preferred holographic storage material because of its well-known photorefractive performance. However, LiNbO3 crystal exhibits the relatively low response speed and strong light-induced scattering, which limit the application of LiNbO3 crystal in volume holographic storage. So, improving and optimizing the photorefractive performance of LiNbO3 crystal have become one of important research subjects in volume holographic storage. In this thesis, a series of co-doped Hf:Fe:LiNbO3 crystals were grown and investigated. Based on the defect structure, the photorefractive properties of Hf:Fe:LiNbO3 crystals at 488nm wavelength were investigated in detail. The optical filtering correlation recognition system was designed and built up using Hf:Fe:LiNbO3 crystals as the recording materials, and the optical correlation recognition results of edge-enhanced images were investigated.The defect structures and occupied sites of Hf:Fe:LiNbO3 crystals were investigated detailedly by using infrared OH- absorption spectra, UV-Visible absorption spectra, ICP-AES analysis and Raman spectra. From the analytical results, its can be seen that Hf4+ ions take priority of replacing the antisite NbLi4+ defects when Hf4+ doping concentration is below its threshold concentration. While, when Hf4+ doping concentration exceeds its threshold concentration, Hf4+ ions begin to occupy the normal Nb sites. In our samples, Fe2+/3+ ions always occupy the normal Li sites.The optical damage resistance ability of Hf:Fe:LiNbO3 crystals was studied at 488nm wavelength by using the transmitted light spot distortion method as well as the photo-induced birefringence change method. The experimental results show that for congruent Hf:Fe:LiNbO3 crystals, the optical damage resistance ability of the crystal is the strongest when Hf4+ doping concentration is its threshold concentration (4.0mol.%). For Hf:Fe:LiNbO3 crystals with Hf4+ doping concentrations of 1.0mol.% and 4.0mol.%, the influence of the [Li]/[Nb] ratio on the optical damage resistance ability of crystals is different. When Hf4+ doping concentration is 1.0mol.%, the optical damage resistance ability of the crystals enhances remarkably with the [Li]/[Nb] ratio increasing. While, when Hf4+ doping concentration is 4.0mol.%, the optical damage resistance ability of the crystals decreases with the increase of the [Li]/[Nb] ratio.The photorefractive properties of Hf:Fe:LiNbO3 crystals were investigated experimentally at 488nm wavelength by using two-wave coupling experiment. The experimental results show that the photorefractive properties of the crystals descend with the increase of Hf4+ doping concentration. While, when Hf4+ doping concentration exceeds its threshold concentration, the photorefractive properties of the crystals return to increase. For Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios, the photorefractive properties of crystals is related to Hf4+ doping concentration. When Hf4+ doping concentration is 1.0mol.%, the photorefractive properties of the crystals descend with the [Li]/[Nb] ratio increasing. While, when Hf4+ doping concentration is 4.0mol.%, the photorefractive properties of the crystals enhance with the increase of the [Li]/[Nb] ratio. In addition, by optimizing the recording light intensity, preferable photorefractive properties can be obtained.Edge feature extraction of target images was achieved by using optical high-pass filtering method, and the influence of image edge enhancement on optical correlation recognition results was investigated theoretically and experimentally. The optical filtering correlation recognition system was designed and built up using Hf:Fe:LiNbO3 crystals as the recording materials. Theoretical analysis and experimental results show that the recognition rate of edge-enhanced images has a remarkable improvement compared with those of the original images.更多还原