【作者】 宫德维；

【导师】 周忠祥；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2007， 博士

【摘要】 光折变效应（photorefractive effect）是贝尔实验室的Ashkin等人于1966年发现的一种光学效应。他们将激光束聚焦在铁电材料（LiNbO₃和LiTaO₃）上进行光倍频实验时发现材料的折射率会发生改变。随着研究的深入,人们发现这种效应在全息数据存储与处理方面有着重要的应用价值。本文对光折变材料的高阶衍射特性进行了深入研究,从Raman-Nath衍射理论出发,给出小角度入射下二波耦合中的折射率最大变化值与衍射光相对强度的关系。给出存在和不存在相位转移时,不同波长的探测光在正入射和斜入射情况下各阶衍射光的衍射角度及相对光强分布。在忽略吸收的情况下,给出二波耦合各阶衍射光的强度分布。从理论上解释了高阶衍射光强度发生震荡的原因,在实验上验证了薄光折变材料在小角度二波耦合中形成的光栅衍射为Raman-Nath衍射。利用光折变聚合物(PVK:5CB:C₆₀)样品实现小角度全息存储实验,分别给出了样品置于焦平面前、焦平面后、焦平面上三种情况下的实验结果。实验结果表明信号光图像的高阶衍射图像相对于信号光图像分别被放大、缩小和旋转。利用掺杂甲基红（MR）的液晶（5CB）样品,实现了小角度存储实验,并记录了永久光栅,用不同波长的探测光垂直样品表面入射,再现了高阶衍射图像。建立了光折变材料中小角度二波耦合存储及再现高阶衍射理论,理论与实验符合很好,表明了光折变高阶衍射用于图像处理是可行的。观察到了高阶衍射图像的叠加、耦合及高阶衍射光与入射光之间的耦合。从光折变材料的高阶衍射特性出发设计了一种全新的光折变高阶衍射分束器。利用He-Ne激光器通过小角度二波耦合方法在光折变晶体LiNbO₃上制作了一维光折变高阶衍射分束器,利用半导体激光器通过小角度多波耦合方法在光折变聚合物材料上制作了二维光折变高阶衍射分束器。利用三种不同波长（632.8 nm, 432.0 nm和488.0 nm）携带图像信息的入射光进行了分束实验,给出了不同波长下的分束实验结果,实验表明高阶衍射分束器可以把携带图像信息的入射光分成多个等大且等间距的出射光,实验效果良好,并对不同波长入射光的分束结果进行了比较。对分束器置于焦平面前、焦平面后及焦平面上的分束结果进行了研究,并在理论上讨论了高阶衍射光束的光强分布和位置分布。讨论了光折变材料厚度和读出光的入射角度对高阶衍射光强度分布的影响,理论和实验结果都表明光折变高阶衍射分束器是一种实用的光学分束器。提出了旋转柱面透镜相位编码复用全息存储方法。从理论和实验两方面分析了这种方法的交扰问题,给出了柱面透镜旋转最小角度的实验值,提出了一种减小柱面透镜旋转角度提高存储密度与相关识别准确度的方法,实验验证了这种方法的正确性。实验上把旋转柱面透镜相位编码复用与角度复用结合,在Zn:Fe:LiNbO₃晶体的同一位置存储了36幅全息图,并进行了相关识别,识别率达到100%。同其它相位编码复用技术相比,旋转柱面透镜相位编码全息存储的优点是在存储的同时实现相关识别。最后,讨论了高阶衍射光在相关识别中的应用。更多还原

【Abstract】 Photorefractive effect was discovered in 1966 by A. Ashkin et al in Bell Laboratory when frequency double experiments was done with the inorganic crystals LiNbO₃ and LiTaO₃. The refractive index of the crystal was changed by the incident light. After analyzing it more deeply, the Photorefractive effect is recognized to be significant for holographic data storage and information process.In this thesis, we study the higher-order diffraction properties of photorefractive materials. The relationship between the changes of refractive index and diffraction light intensity is given. The maximum variation of the refractive index versus the relative intensity of diffraction light is discussed using Raman-Nath theory in two-wave coupling experiment at small incident angle With and without the phase transfer, the distributions of diffraction light intensity and angle position are presented when the probe light illuminates the photorefractive materials with different input angles and wavelengths. In two-wave coupling, the intensity of higher-order diffraction is derived with ignoring the absorption. The fluctuation of higher-order diffraction intensity is discussed theoretically. In thin photorefractive materials, it is confirmed experimentally that the diffraction of higher-order diffraction is belong to Raman-Nath diffraction in two-wave coupling at small incident angle.In PVK:5CB:C₆₀, the holographic storage results were given with small input angle when the film was placed behind the focal plane, in front of the focal plane and in the focal plane. It is found that higher-order diffraction images were amplified, reduced and rotated images compared with signal image. The permanent grating was recorded in MR doped 5CB at small incident angle. The higher-order diffraction images were reconstructed when different wavelength probe light input with direction perpendicular to the surface of the sample. A theory of higher-order diffraction images storage and reconstruction is developed. The theory is in good agreement with the experimental results. It is proved that higher-order diffraction images can be used in optical image processing. The superposition of higher-order diffraction images, the energy transfer between the higher-order diffraction images, the energy transfer between higher-order diffraction lights and incident beams were observed. A photorefractive higher-order diffraction optical beam splitter has been designed based on the higher-order diffraction of photorefractive materials. The one-dimension splitter was produced by two-wave coupling in photorefractive crystal at a small incident angle with He-Ne laser. The two-dimension splitter was produced by four-wave coupling in photorefractive polymer at a small incident angle with semiconductor laser. Three different wavelength signal lights （632.8 nm, 532.0 nm and 488.0 nm） were split into multi-output beams by the splitter. The experimental results indicate that the splitter can split signal beam into several diffraction beams with equal size and distance very well. We discuss the position and intensity distribution of higher-order diffraction beams when the film was placed in front of the focal plane, behind the focal plane and in the focal plane. The effect of photorefractive material thickness and the incident angle on the higher-order diffraction beam position and intensity distribution are discussed. The theoretical and experimental results show that the photorefractive higher-order diffraction optical beam splitter can provide a practical way to split the signal beam.A new phase-code multiplexed holographic storage method has been realized by using a rotated cylindrical-collimating lens system. The cross-talk is discussed theoretically and experimentally. The minimum value of angular selectivity is given experimentally. A method is proposed and the experimental results testified the validity to decrease the angular selectivity and increase the correlation accuracy. In Zn:Fe:LiNbO₃ （0.03 wt. % Fe, 3 mol. % Zn）, 36 holograms have been successfully stored with phase-coded and angular multiplexing. The correlation recognition was finished for 36 holograms. The correlation accuracy was 100%. The advantage of rotationally phase-code multiplexed storage is used for correlation recognition, but the other phase-code multiplexed storage can’t realize correlation recognition. Finally, the using of higher-order diffraction in correlation recognition was discussed.更多还原