【作者】 吕明双；

【导师】 冯德军；

【作者基本信息】 山东大学 ， 物理电子学， 2009， 硕士

【摘要】 光纤光栅是利用掺杂光纤的光敏效应,在光纤的纤芯中因激光曝光、离子注入、电弧放电或激光热效应刻写等因素形成的一类折射率周期性调制结构,是一种新型光纤光子器件。光纤光栅具有与光纤完全兼容、反射特性好、附加损耗小、体积小、成本低等特点,同时对外界温度、应力、应变的变化具有较好的响应特性,因此在光纤通信和光纤传感领域已经并将继续得到广泛应用。在实际的应用中也需要根据滤波器的要求设计出合适的光纤光栅器件,这涉及到光栅的参数重构理论。本文以啁啾光纤光栅的特性为核心,对啁啾光纤光栅的切趾、参数重构、调谐技术进行了理论和实验研究,主要内容有:1.简要介绍了光纤光栅的发展历史、光纤材料的光敏性、光纤光栅的分类,对光纤光栅的写入技术进行了总结。2.介绍了光纤光栅常用的理论分析方法,在折射率调制模型的基础上,利用光场对本征模的展开式以及本征模的正交关系,推导出光纤光栅的耦合模方程。在给定的边界条件下,得出了均匀布拉格光栅的反射特性公式,分析了光栅长度、折射率调制深度对反射特性的影响;对于啁啾光纤光栅,利用矩阵传输法将整个光栅离散为多个均匀布拉格光栅的级联从而得到啁啾光栅的反射特性,对光栅长度、啁啾系数、折射率调制深度等因素的影响进行了详细分析。3.针对对称切趾严重降低反射带宽的问题,仿真分析了非对称切趾在展宽带宽和抑制时延波动方面的优势。以啁啾光纤光栅为例,讨论了在光栅两端进行不同比例的切趾时反射带宽和时延纹波的变化情况,通过仿真提出了一个相对合理的切趾比例值。综合来看,需要在反射带宽和群时延纹波之间根据实际需要进行折衷考虑。长波长端30%切趾、短波长端20%切趾是个比较合适的方案。4.对光纤光栅参数重构的相关理论进行了介绍,给出了离散层析算法的基本原理和步骤。通过耦合模方程和矩阵传输法有效近似得到了耦合系数与光栅折射率分布之间的关系以及离散层析算法的迭代公式。运用此算法对无色散FBG滤波器和用于色散补偿的CFBG滤波器进行了仿真。此外将算法应用于斜边滤波器的设计,重构了三角光谱光纤光栅,得到了有效的结果。5.提出了一种新的压杆调谐机构,利用该机构可以实现波长调谐和带宽调谐。压杆的推进量由步进电机精确控制,将光纤光栅粘贴在压杆的中点处,获得了中心波长在35.43nm(1532.94nm-1568.37nm)范围内的双向调谐。将光纤光栅粘贴在压杆的四分之一处,通过压应变和拉应变可以实现12.6nm的带宽调谐。最后一章总结概括了论文的主要工作以及下一步需要继续研究的方向。更多还原

【Abstract】 As a new kind of optical device, the fiber grating is a fiber structure that the refractive index of the core is modulated periodically. Based on the photosensitivity of Ge-doped fiber, fiber gratings can be fabricated by successive laser exposure of single mode fiber to UV light beam, excimer laser, femtosecond laser, CO2 laser. Also, they can be inscribed by ion implantation technique, arc discharge method, HF etching technique. Because of the excellent characteristics, such as good compatibility to fiber, fine reflectivity performance, low insertion loss, small volume, low cost and high sensitivity to the changes of environmental temperature, stress and strain, fiber gratings have been and will be used in fiber communication and fiber sensing domain extensively. In actual applications, we always need to design proper fiber grating devices to meet the special demands of filters, which is related to fiber grating synthesis algorithm.The thesis pays more attention to the characteristics of chirped fiber Bragg gratings. Apodization technique, parameters reconstruction algorithm and grating tuning technique of chirped fiber grating are theoretically and experimentally studied.The main contents are as follows:1. The development history of fiber gratings, photosensitivity of fiber materials and the sorts of grating are briefly introduced. And write techniques of fiber grating are summarized in chapter 1.2. Common analysis theories of fiber gratings is introduced. Based on index modulation model, the coupled mode equations are derived by eigenmode expansion of light field. By the given boundary conditions, the reflectivity formula of uniform fiber Bragg grating is obtained. The influences of grating length and index modulation depth on uniform Bragg grating are analyzed. Reflection characteristics of chirped fiber Bragg grating are described by transfer matrix method which divides the grating into many uniform gratings. The influences of grating length, chirp parameter and index modulation depth on chirped fiber grating are demonstrated in detail in chapter 2. 3. Symmetric apodization of fiber grating can seriously reduce the bandwidth of reflection spectrum. In chapter 3, we show the advantages of asymmetric apodization of fiber grating in broadening reflection bandwidth and reducing time delay ripples. We take chirped fiber Bragg grating as an example to discuss the changes of reflection bandwidth and time delay ripples when the two ends of grating have different apodization ratios. A reasonable apodization ratio is presented after sufficient simulations. To sum up, we should take a compromise consideration between reflection bandwidth and time delay ripples in apodization design process. 30% apodization on long wavelength end and 20% apodization on short wavelength end is a proper scheme when design a CFBG for dispersion compensation.4. Theories of fiber grating parameters reconstruction are introduced. Especially, basic principles and computation steps of discrete layer peeling algorithm are demonstrated. We get the relationship of coupling coefficients and fiber index distribution by taking an effective approximation of coupled mode equation and transfer matrix. Finally, we apply this algorithm to synthesizing three kinds of special fiber grating filters, dispersionless FBG filter, CFBG filter for dispersion compensation and triangular spectrum FBG. Results show its effectiveness in synthesizing process.5. A new grating tuning mechanism is presented. Based on elastic compression bar, the mechanism can realize both wavelength tuning and bandwidth tuning. By attaching the fiber grating to the middle of the compression bar, the center wavelength tunes 35.43nm bidirectionally. When attached it to the quarter part of bar, 12.6nm bandwidth tuning is realized.In the end, we summarize the main work of the thesis and predict the direction for further study.更多还原