中心对称光折变晶体中平移空间光孤子研究

发布时间：2018-03-15 06:14

本文选题：中心对称晶体　切入点：b轴偏压　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：光折变空间孤子具有在低功率、短时间内形成且能稳定传播的特性,在光纤通信、光波导等方面也存在着较大的应用价值,因而其一直是科研人员研究的热门课题。本文将在实验中平移中心对称光折变晶体钽铌酸钾使其产生空间光孤子,并对此在理论上进行分析。鉴于此,本文的主要工作如下:首先,综述了光折变空间孤子的相关研究,重点介绍了国内外关于中心对称光折变晶体中空间光孤子的研究进展。其次,简述了钽铌酸钾晶体的结构特点、物理性质及其相关应用。钽铌酸钾晶体在室温下具有较强的二次电光效应;晶体加压后会由光学各向同性体变为各向异性体,折射率椭球由一个球体变成椭球体。据此,推导了不同轴向偏压的立方相钽铌酸钾折射率变化An的表达式和晶体光轴的变化;重点分析了 b轴偏压下晶体折射率变化及折射率椭球方程的数学表达式,分析了施加电场前后晶体折射率曲面、晶体折射率椭球方程的变化情况。再次,通过在偏压条件下相对平移晶体的方式,增强了晶体的光折变效应,实验研究了钽铌酸钾晶体中空间光孤子的传播特性。(1)观测了外电场条件对对光束传播形态的影响,实验结果表明:当只给晶体施加电压时,光束会出现短暂的自聚焦现象,随后便又恢复到自散焦状态;当给晶体施加不同的电压时,光束的自聚焦程度会随着电压值的不断增加而加强。(2)采用控制变量法进行了外电场、平移两个外势场下的对比实验,结果表明:只有在外电场作用下进行实验,才有可能通过平移的方法使晶体中形成稳定的空间光孤子。(3)观测了平移条件对晶体内光束传播形态的影响,实验结果表明:外电场作用下,移动晶体可以使晶体内光束发生自聚焦现象并有自陷成亮空间孤子的趋势;晶体移动的速度越大,光束的自聚焦效应越明显;从外形上看,伴随着移动速度的增加,晶体内光束会逐渐变细。若晶体在特定的速度下平移,改变给其施加的电压值,光束的传播行为也会发生相类似的变化效果。最后,根据文献及相关理论分析,修正了平移机制下中心对称光折变晶体中的空间电荷场理论模型。利用模型,理论上分析了晶体平移导致空间光孤子现象形成的原因;数值求解了新模型理论下光束传播的波动方程;模拟了光束在不同平移速度下的传播行为及其演化过程。
[Abstract]:Photorefractive spatial solitons have the characteristics of low power, short time formation and stable propagation. They also have great application value in optical fiber communication, optical waveguide and so on. In this paper, we will translate the center symmetry photorefractive crystal potassium tantalum niobate to produce spatial optical soliton, and analyze it theoretically. The main work of this paper is as follows: firstly, the research on photorefractive spatial solitons is reviewed, and the research progress of spatial solitons in centrosymmetric photorefractive crystals at home and abroad is introduced. The structure, physical properties and related applications of potassium tantalum niobate crystals are briefly described. Potassium tantalum niobate crystals have a strong secondary electro-optic effect at room temperature. The refractive index ellipsoid changed from a sphere to an ellipsoid. Based on this, the expression of refractive index change an of cubic phase potassium tantalum niobate with different axial bias and the change of optical axis of crystal were derived. The mathematical expressions of refractive index change and refractive index ellipsoid equation under b axis bias are analyzed, and the change of crystal refractive index surface and refractive index ellipsoid equation before and after application of electric field are analyzed. The photorefractive effect of the crystal is enhanced by the relative translation of the crystal at bias voltage. The propagation characteristics of spatial soliton in potassium tantalum niobate crystal are experimentally studied. The effect of external electric field on the beam propagation morphology is observed. The experimental results show that when only the voltage is applied to the crystal, the beam will appear a transient self-focusing phenomenon, and then return to the self-defocusing state, and when different voltages are applied to the crystal, The self-focusing degree of the beam will be strengthened with the increasing of the voltage. (2) the control variable method is used to carry out the experiment of the external electric field, and the results show that the experiment is carried out only under the action of the external electric field. It is possible to form a stable spatial soliton in the crystal by the method of translation. The effect of the translational condition on the propagation morphology of the beam in the crystal is observed. The experimental results show that: under the action of the external electric field, The moving crystal can cause the self-focusing of the beam in the crystal and has the tendency of self-trapping into the bright spatial soliton. The faster the crystal moves, the more obvious the self-focusing effect of the beam is. The beam in the crystal will gradually become thinner. If the crystal moves at a specific velocity and changes the voltage applied to it, the propagation behavior of the beam will have a similar effect. Finally, according to the literature and related theoretical analysis, The theoretical model of space charge field in centrosymmetric photorefractive crystals with translational mechanism is modified. By using the model, the causes of spatial soliton phenomena caused by crystal translation are analyzed theoretically. The wave equation of beam propagation under the new model theory is numerically solved, and the propagation behavior and evolution process of the beam at different translational velocities are simulated.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O734

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