全息聚合物分散液晶Bragg光栅的机理研究与性能优化

【作者】 蒲海辉；

【导师】 刘建华；

【作者基本信息】 复旦大学 ， 光学工程， 2010， 硕士

【摘要】 聚合物单体由于光敏感性好、折射率调制度大和分辨率高等优点在全息聚合物光栅、光了晶体和光相位调制器等器件中得到广泛的应用。在形成器件的过程中,单体的扩散能力和聚合能力对器件的性能具有很大的影响。因此,如何确定单体的扩散速率和聚合速率系数在优化器件性能方面至关重要。所以提出一种方法可通用的并且便利的确定不同条件下单体的扩散速率和聚合速率系数就成了一项重要的任务。另外,在衡量全息聚合物分散液晶Bragg体光栅的性能时,高的衍射效率、低的阈值和关闭电压和快的效应速度是必要的参考指标。因而,本论文的工作主要围绕以下两个方面：1.理论上,根据Zhao和Mouroulis的一维反应扩散模型并结合严格的双波耦合理论推导出扩散速率系数和聚合速率系数的解析表达式。用该表达式确定扩散速率系数和聚合速率系数不仅与理论预测的参数范围符合很好,而且对于同一条件多次重复实验取得的数据一致性也很好,说明了该方法的可行性。之后,我们根据隐性中心差分方法对一维反应扩散模型进行求解,通过人为改变衰减系数,模拟光栅衍射效率建立过程。由于后聚合效应,我们将模拟分为聚合和后聚合两个过程,并对衰减系数加以区别。模拟结果显示,在适当选择衰减系数后,模拟曲线与实验实时记录曲线匹配很好。更进一步,修正一维反应扩散模型,将反应对光强的依赖性修正为其对活性单体浓度和寿命的依赖性,从而理论上给予后聚合效应很好的解释；2.实验上,利用后聚合效应,通过优化曝光时间制得衍射效率为96%的光栅,并通过在配方中引入紫外固化胶NOA65将光栅的阈值电压和关闭电压分别降至1.5V/μm和3.5V/μm。响应时间下降沿和上升沿经测量分别为153ms和250ms。最后通过光学偏光显微镜和共聚焦显微镜对液晶分了的排列取向定性的进行了分析研究。更多还原

【Abstract】 Good photon sensitivity, large index modulation and high resolution make monomer in a number of applications such as holographic polymer grating, photonic crystal and light phase modulator. In fabrication of such devices, diffusablity and reaction of monomer have a great effect on the performance of devices. Hence, how to determine the diffusion and reaction coefficients is of significance on the improvement of devices performance. Thus, it is desirable to determine the diffusion and reaction coefficients of monomer universally under convenient conditions. Besides, high diffraction efficiency, low threshold and turn-off voltages and fast response time are necessary gauges to evaluate the holographic polymer dispersed liquid crystal Bragg volume grating. Therefore, this article can be summarized into the following two sides:1. Theoretically, analytical expressions of diffusion and reaction coefficients were derived according to Zhao and Mouroulis’s one dimensional diffusion-reaction model and in combination with two-wave coupling theory. Small discrepancies among parameters values determined in multiple experiments under same condition and good agreement with theoretical prediction suggested the feasibility of this method. Thereafter, simulations of the build-up of grating diffraction efficiency were conducted by adjusting the decay constants through solving the finite difference equations under implicit scheme. Taking post curing into account, decay constants were specific for curing and post curing processes. The results showed great agreement between the simulated curves and experimental real-time traces. Moreover, the one dimensional diffusion-reaction model was revised by introducing the radicals’ concentration and lives instead of the reaction dependence on recording beam intensity, which interpreted theoretically the post curing very well.2. Experimentally, grating with diffraction efficiency as high as 96% was fabricated by optimizing the recording time making use of post curing effect. In addition, threshold and turn-off voltages of the grating were reduced to 1.5 V/μm and 3.5 V/μm respectively by means of introducing some amount of NOA65 into the recipe. Response times of the up and down slopes were measured to be 250ms and 153 ms respectively. In the end, alignment of liquid crystal molecules was investigated through optically polarized microscope and confocal microscope.更多还原