【作者】 董毅；

【导师】 侯学元； 于晓强；

【作者基本信息】 山东大学 ， 光学工程， 2008， 博士

【摘要】 波导光栅在集成光学发展中扮演着重要的角色,提供了一种将光耦合输入或输出波导的便捷方式,这种十分具有吸引力的耦合方式可以有效减小光学系统、波导及电子器件的体积和重量。聚合物体波导光栅与表面浮雕光栅不同,前者通常位于波导层内。在这个位置,导模特别是零阶导模的振幅最大,导波光与光栅作用更强烈,因此有望获得更高的耦合效率。同时,体波导光栅还具有制备工艺简单、波导表面平整等优点。因此,制备可以实际应用的具有较高分辨率的聚合物体波导光栅受到各国研究者的重视。迄今,聚合物体波导光栅的制备方法基本上属于物理方法,并没有在材料内部引发本质性的化学变化,因此所制备的器件的长期稳定性难以保证。利用双光子引发光聚合反应可以在材料内部引起本质性的化学变化,致使材料折射率发生永久性变化,这种技术为制备体波导光栅带来了极大的便利。本文研究了体波导光栅耦合器的泄漏特性并提出利用双光子引发光聚合反应制备体波导光栅的新方法。主要取得以下几个方面的进展:基于等效传输线理论和微扰理论分析了体波导光栅的导波特性。体波导光栅做输入输出耦合器时,泄漏参数是一个重要的因子,它决定了进入光栅各衍射级中能量的大小。本文从理论上推导了泄漏参数同体波导光栅结构参数如光栅常数、光栅高度以及折射率调制深度之间的函数关系。数值计算的结果有助于设计具有较高耦合效率的体波导光栅。利用棱镜耦合法测量了由三元材料体系构成的聚合物平面波导的光传输模式和传输损耗。通过控制聚合物材料体系溶液的浓度,可以得到高质量的单模、双模和多模波导。利用光纤扫描的方法测量了聚合物薄膜波导TE和TM偏振模式的光传输损耗,分别只有0.38dB/cm和0.41dB/cm。首次证实双光子聚合反应能够在三元材料体系构造的固态聚合物薄膜中实现。根据双光子吸收上转换荧光的特点,给出了飞秒脉冲激光经高数值孔径显微物镜聚焦后正好位于波导层中的判据。研究了体波导光栅制备过程中加工系统的性能参数包括平台震动、扫描速度等对体波导光栅质量的影响。利用相衬显微镜研究了制备的体波导光栅,并利用原子力显微镜对体波导光栅的表面形貌进行了研究。随着入射光功率的增加,体波导光栅表面会出现明显的表面浮雕结构。经分析,这种结构是由于材料的膨胀而不是烧蚀引起的。实验测得体波导光栅的折射率调制深度达5.7×10^-3。研究了表面无形变的体波导光栅的输入耦合特性,实现了He-Ne光的输入耦合,最高耦合效率达11%。针对棱镜耦合测试系统对波导硬度及光洁度要求较高的缺点,提出了利用体波导光栅测量聚合物波导的厚度和折射率的新方法。更多还原

【Abstract】 Waveguide grating structures have been playing an important role in the development of integrated optics. They provide a means of coupling light into or out of waveguide. This attractive coupling method reduces the size and weight of optical systems, integrated waveguides and electronic components to form photoelectric systems. In contrast to surface relief gratings, volume index grating is usually positioned inside the guided wave layer. In this position, the amplitude of the guided mode, especially fundamental mode, reaches a maximum and the interaction between guided mode and volume index grating is expected to be very strong. Therefore, a higher coupling efficiency can be achieved. Volume gratings have many advantages over their competitors, such as simpler fabrication method and smoother surface. Unfortunately, it seems to be very difficult to produce stable high-resolution volume index gratings in polymeric planar waveguide for practical application. At present, most methods utilize basically physical change of materials, and do not induce natural chemical change within the material. So it is very difficult to guarantee the long-term stability of the gratings. The two-photon initiated polymerization as a technique for the direct fabrication induces essential chemical processes and results in a permanent change of the refractive index of materials. This technique will achieve the flexibility of one-step fabricating gratings and be helpful for further procedures in integrated optics. The purposes of this dissertation are to study the coupling characteristics of volume waveguide gratings and to propose a novel method for fabricating volume waveguide gratings using two-photon initiated photo-polymerization. The main research content and achievements are shown as following.Basing upon equivalent transmission line method, a perturbation analysis on the guiding properties of volume waveguide gratings is presented. The leakage parameter is important for volume gratings used as input or output couplers. The leakage parameter, which influences the leakage energy into the diffracted orders scattered by the grating, is achieved as functions of the structure parameters of the volume grating, for example, grating period and thickness of the waveguide and index modulation. We provide an analysis in quality for the variation of the grating parameters. The result enables one to predict the changes of a with the parameter variation in coupling performance. It is therefore useful for design of volume waveguide gratings.By using the prism-in coupling method, the transmission modes have been obtained, and the optical transmission losses of guided modes have been measured at 632.8nm for the polymer film waveguides. By controlling the concentration of resin solution, waveguides of different guided modes can be achieved. The optical loss of the fundamental mode is 0.38dB cm^-1 for TE polarization and 0.41dB cm^-1 for TM polarization, respectively.This thesis first reports the existence of two-photon initiated photopolymerization in solid polymer waveguide film. Criterion of the laser beam focused by a high numerical aperture objective just lying in the waveguide film is presented. Influence of the system performance including the shake of the translator and the scanning speed on the quality of volume gratings is studied.The fabricated volume waveguide gratings were illustrated with a phase-contrast optical microscope. The surface topography of the grating samples was investigated by an atom force microscope. Characteristic microstructure simultaneously appears on the surface of the polymer film with increased incident power during the two-photon initiated photopolymerization. It is confirmed that the stable morphological change is attributed to material swelling.The corresponding index modulation depth of volume grating reaches 5.7×10^-3. The input coupling characteristic of volume waveguide grating without surface morphology is investigated. We successfully demonstrated the implementation of input coupling by the volume waveguide grating at the wavelength of 632.8nm. The measured coupling efficiency was about 11%. Also a simple approach to measure the refractive index and thickness of the polymeric waveguide film is presented.更多还原