摘要光纤光栅以其诸多优点，在通信和传感领域都发挥着巨大的作用。光纤光栅的研究深入与其制作工艺的不断改进密不可分，飞秒激光的逐点写入法，为其发展提供了新的可能。然而目前飞秒激光刻写技术并不成熟，其制造的光栅折射率分布较为复杂，通过对其光谱的模拟仿真将有利于我们对相关实验现象的理解。81858

介绍光纤光栅的发展历程，叙述光纤光栅不同分类方式以及其在不同领域中的相应作用，重点叙述飞秒激光逐点写入技术的国内外的研究成果和发展现状。

2。阐述了光纤光栅的基本理论，利用耦合模理论和传输矩阵模型，借助软件对不同种类的光栅进行仿真研究，同时探究了不同参数对于光纤光栅反射谱和时延特性的影响。

3。在实验过程中发现采用飞秒激光逐点刻写法制造出的光纤光栅出现了正交的偏模以及双折射的现象。通过COMSOL建模仿真，我们得出这一现象源于光栅折射率调制区域非圆对称，同时无论仿真分析还是实验现象都表明飞秒激光降低了折射率调制区域的有效折射率。并且结合耦合模理论，研究了椭圆率，折射率调制区域面积大小及轴向偏移对这种现象的影响。

毕业论文关键词 飞秒激光布拉格光纤光栅耦合模双折射 COMSOL建模

毕业设计说明书外文摘要

Title Simulation Study of the Spectral Characteristic ofPoint-by-point Fiber Bragg Gratings Induced by Femtosecond Laser 

Abstract Fiber grating has been widely used in the fields of fiber communication and fiber sensing on account of its wonderful characteristics。 The development of fiber gratings has a close relation to the improvement of the manufacturing technology, and the gratings inscribed with femtosecond laser using the point-by-point technique provide a new possible way。 But at present, this technology is far from mature。 The refractive index modulations in gratings fabricated by this way is more complex。 And it will help us understand the related experimental phenomena better by thesimulation study of the spectral characteristic and the following content of research are included:

1。The development process of the fiber gratings were reviewed。 Different kinds of fiber gratings and its applications in different fields were introduced。 The overseas and domestic research status of the point-by-point inscribing technology with femtosecond laser is summarized in detail。

2。This paper introduced the basic theory of fiber gratings。 Analysis model was establishedbased on Couple-mode Theory and Transfer Matrix Theory。 We simulate the action of different kinds of fiber gratings with MATLAB and study the effect of the grating length,depth of modulation ,chirp degree and apodization to the reflection andpropagation delay。

3。Fiber Bragg gratings inscribed with a femtosecond laser using the point-by-point technique have polarization dependent grating strength and exhibit birefringence。 We found this result from the elliptical shape of the refractive index modulations and the effective modal index is lower than that of the pristine fiber。 At last, we explored the dependence of the birefringence on the size, ellipticity , axial deviation of the index modulation region。

KeywordsFiber Bragg gratings Couple-mode TheoryTransfer Matrix birefringence

目 次

1引言

1。1 光纤光栅发展概况 1

1。2 光纤光栅的分类 2

1。3 光纤光栅的应用5

1。4 飞秒激光刻写光栅技术简介及研究现状6

2光纤光栅的基本理论 

2。1 光栅衍射的谐振波长… 9

2。2 耦合模理论… 10

2。3 光纤布拉格光栅的耦合模理论11

2。4 光纤布拉格光栅的耦合模理论12