亚波长MIM等离激元波导中光波的传播与调控

发布时间：2018-04-01 00:08

本文选题：表面等离激元　切入点：U型金属开口谐振环　出处：《淮北师范大学》2015年硕士论文

【摘要】：表面等离极化激元（SPPs）是一种沿着金属和介质之间的界面传播的，由自由电子和电磁场相互作用产生的电子疏密波。它具有一系列的独特光学性质，例如局域电场增强，对电磁波的亚波长束缚，非线性增强等等。由于spp沿着金属和介质之间的界面传播，在金属和介质上纵向传播的时候SPPs会呈指数衰减，因此，设计合适的金属微结构可实现对电磁波的调控。因其独特的性能而被广泛应用于增强透射，负折射率材料，，超分辨率成像，生物传感等方面。随着超构材料的加工和制备技术以及理论数值模拟分析手段的发展，越来越多的亚波长等离激元器件得到理论上的分析和实验上的验证。和传统的，受到衍射极限限制的光学器件相比，等离激元器件在尺寸上可以达到亚波长的微纳量级。在这些器件中，对表面等离激元波起到束缚和引导作用的是各种类型的波导，例如金属纳米阵列结构，矩形槽波导，异质结构波导，V型槽波导，MIM波导等。在众多波导中，MIM波导由于更好的束缚效果，模式尺寸小，传输损耗小和易于加工等优点而得到了众人广泛的研究，理论上研究MIM波导的传输特性以及对其进行调控具有重要意义。本文设计了基于MIM波导的周期型微纳光学器件，通过数值分析的方法来讨论这些结构的电磁波传播特性。本文的主要工作和研究成果可以简单归结如下： 1、首先在MIM波导中加入单个U型开口金属谐振环，研究金属开口环和波导的各参数对结构的透光性造成的影响，经过探究发现，波导的共振波长随着开口金属谐振环臂长增大而呈现红移现象；若增宽MIM波导，则波导中的共振趋于一个恒定的共振。 2、在波导中再次加入一个谐振环形成一字排列双谐振环结构。经过数值分析，发现结构中两耦合共振会呈现出对称模式和反对称模式。随着两个谐振环间距逐渐增大，两个透射谷逐渐重合在一起，直至形成一个透射谷。 3、将结构做成周期排列的U型金属开口环，发现周期型MIM波导的透射光谱呈现出了两个带隙，随后我们探究了波导各参数对带隙的影响：减小谐振环的排列周期可以使布拉格带隙向短波长蓝移；若增加谐振环的臂长，两个透射禁带会呈现一同向短波长蓝移的性质；增大MIM波导的宽度可以使两个带隙的宽度变窄。 4、随后我们针对周期型MIM波导进行了改变，做成了一大一小双U型谐振环排列的周期结构。通过对结构的透射光谱分析，我们发现：在该结构中也出现了双带隙，局域共振带隙会随着长U型谐振环的臂长增长而向长波长红移；改变短U型谐振环的底部宽度可以使左侧带隙的线宽变宽，并使两个带隙共同出现了蓝移现象；改变波导中的空气介质宽度会使两个带隙向高频波段略微移动，同时缩短带隙宽度。 5、最后设计了一种滤波器，可以通过调节竖直空气波导的位置来调节结构在1400nm波段的透光性能，也可通过改变空气波导的长度来调节该滤波器的透射极小位置。通过对以上结构的分析，希望可以对以后的二维亚波长金属微纳器件的设计提供参考。
[Abstract]:This paper designs a kind of periodic micro - nano optical device based on MIM waveguide , which is widely used in enhancing transmission , negative refractive index material , super - resolution imaging and biosensing .

The main work and research results of this paper can be summarized as follows :

1 . Firstly , a single U - shaped open metal resonant ring is added to MIM waveguide to study the influence of the parameters of metal opening ring and waveguide on the light transmission of the structure , and it is found that the resonant wavelength of the waveguide exhibits a red shift phenomenon with the increase of the arm length of the opening metal resonant ring ;
If the MIM waveguide is widened , resonance in the waveguide tends to be a constant resonance .

2 . A resonant ring is added to the waveguide to form a double resonant ring structure . After numerical analysis , two coupling resonances in the structure are found to exhibit a symmetric mode and an anti - symmetric mode . As the spacing of the two resonant rings gradually increases , the two transmission valleys are gradually brought together until a transmission valley is formed .

3 . It is found that the transmission spectrum of the periodic MIM waveguide shows two band gaps , and then we investigate the influence of the parameters of the waveguide on the band gap : to reduce the arrangement period of the resonant ring , the Bragg band gap can be shifted to the short wavelength blue shift ;
If the arm length of the resonant ring is increased , the two transmission forbidden bands will show the properties of the blue shift with the short wavelength together ;
increasing the width of the mim waveguide may narrow the width of the two band gaps .

4 . The periodic structure of a small double U - shaped resonant ring is formed by changing the periodic MIM waveguide . Through the transmission spectrum analysis of the structure , we have found that in this structure , a double band gap is also present , and the local resonance band gap will shift to the long wavelength red with the increase of the arm length of the long U - shaped resonant ring ;
changing the width of the bottom of the short U - shaped resonant ring can widen the line width of the left side band gap and cause the blue shift phenomenon to be common in the two band gaps ;
changing the width of the air medium in the waveguide causes the two band gaps to move slightly toward the high frequency band while reducing the band gap width .

5 . Finally , a filter is designed , which can adjust the transmission energy of the structure in the 1400 nm wavelength band by adjusting the position of the vertical air waveguide , and the transmission minimum position of the filter can be adjusted by changing the length of the air waveguide .

Through the analysis of the above structure , it is hoped that the design of the later two - dimensional sub - wavelength metal micro - nano device can be referenced .

【学位授予单位】：淮北师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN252

【参考文献】