多光束耦合对光折变晶体中光束传播特性影响的研究

发布时间：2018-05-19 18:51

本文选题：光束传播特性 + 多光束耦合　；参考：《山东大学》2017年硕士论文

【摘要】：光折变晶体因具有优良的电光性能而被广泛地应用于光电子技术领域。改善和提高晶体材料的光折变性能有利于提高其潜在的应用价值。多年来,人们在改善和提高晶体材料光折变性能方面做了大量工作,如对晶体掺杂、施加外电场、改变背景光强度、改变温度及对晶体进行相对平移操作等。但是,有关频率不同但沿相同的传播轨迹导入晶体的多束光对晶体光折变性能影响的研究基本没有。基于此,本文主要在无偏压条件下,研究当频率不同但传播轨迹相同的多束光导入晶体时,其对晶体光折变性能的影响。主要研究内容如下:1.综述了改善和提高晶体材料光折变性能的研究进展。改善晶体材料光折变性能的方法有很多,如向晶体中掺入光折变敏感杂质能提高晶体光折变性能;对晶体施加外电场使晶体内部形成非均匀屏蔽,可以改变晶体形成的空间电荷场;对晶体施加背景光并改变背景光强度可改变晶体中迁移载流子的密度,影响晶体中形成的空间电荷场,进而影响晶体光折变性能;改变环境温度可影响晶体内部载流子的迁移速度,进而影响晶体中形成的空间电荷场;晶体被相对平移是在晶体内引入了附加场,改变了晶体中空间电荷场的分布。2.在无偏压条件下,实验研究了当掺铁铌酸锂晶体中存在频率不同但传播轨迹相同的双光束时,其光折变性能的变化。根据实验要求,合理搭建了实验平台,并在实验中,保持信号光(目标光束即研究对象)的光强不变。首先,通入信号光,当晶体的折射率变化达到饱和时,信号光束呈自散焦状态。其次,沿相同的传播轨迹导入另一束光(在文中被称为辅助光,并通过斩波器控制其脉冲频率),信号光束由自散焦向自聚焦转变。然后,分别改变辅助光的脉冲频率、光强进行对比实验,发现脉冲频率或光强越大,信号光束的自聚焦程度越大。最后,移去辅助光,信号光恢复到自散焦状态。实验研究表明:当掺铁铌酸锂晶体中存在频率不同但传播轨迹相同的双光束时,晶体的光折变性能发生改变。3.理论探讨并通过数值法模拟了频率不同但传播轨迹相同的多束光对晶体中光束传播特性的影响。理论研究了等效附加场、等效暗辐射对晶体中空间电荷场的影响,并尝试对空间电荷场的表达式进行了推导。修正了非线性波动方程,确定了相关参数,并对其数值求解。通过数值法模拟了在双光束耦合条件下,掺铁铌酸锂晶体中信号光束的传播特性。理论分析及数值模拟的结果进一步佐证了实验结果。
[Abstract]:Photorefractive crystals are widely used in the field of optoelectronics due to their excellent electro-optic properties. Improving and improving the photorefractive properties of crystal materials is beneficial to its potential application value. Over the years, a great deal of work has been done to improve the photorefractive properties of crystal materials, such as doping crystal, applying external electric field, changing the intensity of background light, changing temperature and performing relative translation operation on crystal. However, there is no study on the effect of multi-beam light on the photorefractive properties of crystals with different frequencies but along the same propagation path. Based on this, the effect of multi-beam light with different frequency but the same propagating path on the photorefractive properties of the crystal is studied under the condition of no bias voltage. The main research contents are as follows: 1. The progress in improving and improving the photorefractive properties of crystal materials is reviewed. There are many ways to improve the photorefractive properties of crystal materials, such as the incorporation of photorefractive sensitive impurities into the crystals can improve the photorefractive properties of the crystals, and the application of an external electric field to the crystals causes the formation of non-uniform shielding inside the crystals. The space charge field formed by the crystal can be changed by adding background light and changing the intensity of the background light, which can change the density of the carrier migration in the crystal, affect the space charge field formed in the crystal, and then affect the photorefractive property of the crystal. Changing the ambient temperature can affect the transport speed of carriers in the crystal, and then affect the space charge field formed in the crystal, and the relative translation of the crystal is the introduction of additional field in the crystal, which changes the distribution of the space charge field in the crystal. Under the condition of no bias voltage, the photorefractive properties of lithium iron doped lithium niobate crystals with different frequencies and the same propagation path have been studied experimentally. According to the requirements of the experiment, a reasonable experimental platform is set up, and in the experiment, the intensity of the signal light (the target beam is the object of study) is kept constant. Firstly, when the refractive index of the crystal reaches saturation, the signal beam is self-defocusing. Secondly, another beam is introduced along the same path of propagation (called auxiliary light in this paper, and its pulse frequency is controlled by chopper, and the signal beam changes from self-defocusing to self-focusing). Then, the pulse frequency of the auxiliary light is changed, and the intensity of the light is compared. It is found that the greater the pulse frequency or intensity, the greater the self-focusing degree of the signal beam. Finally, the auxiliary light is removed and the signal light returns to self-defocusing. The experimental results show that the photorefractive property of lithium niobate doped with iron is changed when there are two beams with different frequencies but the same propagation path. The effects of multiple beams with different frequencies but the same propagating trajectory on the propagation characteristics of the beams in the crystal are investigated and simulated by numerical method. The effect of the equivalent additional field and the equivalent dark radiation on the space charge field in the crystal is studied theoretically, and the expression of the space charge field is derived. The nonlinear wave equation is modified and the relevant parameters are determined and solved numerically. The propagation characteristics of signal beams in Fe-doped lithium niobate crystals are simulated numerically under the condition of double beam coupling. The theoretical analysis and numerical simulation results further support the experimental results.
【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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