摘要
光折变晶体在光学图像处理、光学数据存储、光互连以及在光学计算机中
都具有潜在的应用前景，目前人们已经并仍在不断研制各类实用的光折变非线性
光学器件，如体全息实时存储器、像放大器、相位共轭器等。大多数与光折变晶
体有关的应用都涉及到光波的耦合特性。本文主要就SBN:61:Cr的光折变二波耦
合特性，从理论和实验上进行了详细的研究。
首先根据带输运模型，讨论了两束相干平面光波作用下SBN晶体内折射率
栅的建立过程，推导出了二波耦合方程的稳态解，从理论上得出SBN晶体中的
二波耦合过程将伴随着极强的能量转移。由所给出的吸收特性曲线得出SBN:61:Cr
晶体在He-Ne激光照射下应表现出更为优良的光折变特性。其次，给出了两种掺
杂浓度的SBN:61:Cr晶体中进行二波耦合实验所观察到的现象和结果：（1）.二波
耦合存在一最佳耦合角，在掺杂浓度分别为1000ppm和2000ppm的SBN:61:Cr
晶体中测得最佳耦合角分别约为20°和27°。指出最佳耦合角的存在是有效电光系
数和空间电荷场矛盾作用的结果，并计算出了最佳耦合角的取值范围。（2）.测得
二波耦合的稳态响应时间不超过0.8s，且随双光束夹角增大而逐渐减小，文中对
此进行了解释。（3）.测量了二波耦合与入射总光强的变化关系。（4）.观察到二
波耦合过程中所表现出的不同能量转移特性，信号光呈现双稳态变化趋势。对不
同实验过程中信号光不同的衰减趋势进行了说明。（5）.分析了实验中可能产生误
差的因素，分析了数据采集系统对实验数据的影响。发现光电探测器件的非线性
问题，提出三种解决方法，并采用“后处理方法”对实验数据作了修正。（6）讨
论了晶体表面内反射对二波耦合的影响，得出表面内反射实际上增大了二波耦合
的相互作用距离，有利于光波之间的能量转移。本文最后简单提及了光折变二波
耦合的一些应用，提出将二波耦合应用于光纤通信过程信号的加载与拾取、在光
纤通信系统中作为光信号的中继放大，以及利用二波耦合在光折变晶体中制作波
导阵列等设想。
二波耦合实验结果显示，掺杂浓度较高的SBN:61:Cr晶体在He-Ne激光照
射下表现出了优良的光折变特性。
Photorefractive crystals have many potential applications in optical image processing, optical data storage, optical interconnection, and optical computers. People developed many kinds of photorefractive nonlinear optical devices, such as volume holograph timing memorizers, optical image amplifiers and phase conjugation devices. Most of these applications have relations with beam-coupling in photorefractive crystals. The theories and experiments of the two-beam coupling in Cr-doped SBN:6 1 crystal is investigated detailedly in this thesis.
Based on the band transport model, the formation of refractive index grating is discussed firstly. The steady solutions of two-beam coupling equations are deduced, and the conclusion is that the two-beam coupling process accompanies the energy transfer. From the absorption curves of various SBN crystals, we deduce that SBN:61 :Cr crystals should show great photorefractive properties by being irradiated with a He-Ne laser. We carry out two-beam coupling experiments in two SBN:61 :Cr crystals, and obtain the following results and phenomena: (1). There exists certain external beam crossing angle 20pcak at which the steady coupling coefficient F reaches the maximum. The values are approximately 200 and 27~ for l000ppm and 2000ppm SBN:Cr crystals, respectively. We point out that the existence of 20peak is the interactional result of the efficient electric-optic coefficient and the spatial electric field, and the range of the 2Opeak is calculated. (2). The steady coupling response time r is less than 0.8 sec, which is decreased as the increasing of 20, and a reasonable explanation is given out. (3). We also measured the relation of Fand the total beam intensity J~. (4). The different process of the energy transfer, the bistable state of the signal beam intensity and its different attenuation process are observed. The rational explanations are also presented. (5). The factors that can bring errors are briefly analyzed to minimize their influence. Three methods are provided to resolve the non-linearity of the optic-electric detectors, and the 損ost-disposal?method is applied to correct the experimental data. (6). The inside reflection of beams on the crystal?s surface is discussed. The conclusion is the inside reflection actually enhances the energy transfer through increasing the interactive length of the two beams. In the last part, some new applications are presented. The experiment results show that SBN:6l :Cr crystals have large coupling gains under the irradiation
of He-Ne laser.
引文
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