平面次波長對掌性週期結構的分析與設計

Analysis and Design of Periodic Subwavelength Planar Chiral Structures

李維懿(Wei-Yi Li)

指導教授 ： 陳瑞琳

國立臺灣大學/工學院/應用力學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.00437

摘要

在電磁波的研究領域當中，次波長週期結構一直是一個重要的議題。因為其結構呈現週期性排列時，具有可調式共振，以及等效介質材料的特性，所以其在設計元件時具有高度的自由度，且可建構出天然材料中不存在的物理特性，例如負磁導係數、負折射率、特殊非等向性，其被稱為超常材料。次波長週期材料源自大自然的素材，在天然材料的微觀的世界中，經常可以觀察到原子的排列影響材料巨觀的物理特性。由於次波長週期材料的多樣性，其已經被廣泛的運用在各個領域中，如天線系統、雷達吸波器、波導控制器。於本文中利用次波長結構的高自由度設計偏振片，偏振片經常被使用於光學技術與儀器，光為電磁波的一種，光傳播時其電磁波會往四面八方震動，當光通過偏振片時，偏振片只允許往某一方向振盪的電磁波通過，其他電磁波將被偏振片反射或吸收。不眩光檯燈與太陽眼鏡均利用偏振片使眼睛只接收到單一振盪方向的電磁波。液晶螢幕為利用偏振片與電壓改變液晶排列方向，以控制光線的亮暗。3D電影為使用兩台投影機放映，且投影機鏡頭皆放置偏振片，觀賞者也須配戴偏振片眼鏡，使得左右眼接收到不同投影機的影像，藉此產生立體的假象。然而上述的偏振片均為限制某一方向振盪的電磁波通過。
本篇論文著重於設計不同的次波長週期結構，使得線性偏振波通過此結構能夠產生偏轉，並且利用結構的改變控制其穿透電磁波偏轉的角度，而不是由反射與吸收。並藉由共振模態同時增強穿透與穿透電磁波的偏轉。且找出達到全穿透時，所產生的共振模態；與穿透電磁波偏轉時，所顯現的物理現象。並且致力於全穿透與電磁波的偏轉能夠同時地發生，使得入射波的能量不反射與吸收。本文共振模態著力於Lorentzian共振、布拉格共振(Bragg resonance)、表面電漿共振(surface plasmon resonance)與波導模態共振(guided mode resonance)。

關鍵字

對掌性 ； 對映體 ； 偏振旋轉角 ； 橢圓率 ； 振幅 ； 相位

並列摘要

In electromagnetic science, subwavelength periodic structure is always an important issue. Caused by periodic arrangement of structures, structures themselves are equipped with tunable resonance and effective dielectric material. With these properties, the design objects possess high degrees of freedom which can create physical characteristics that can’t be found in nature material, including negative permeability, negative index of refraction, special anisotropic material, etc. This concept derived from the arrangement of atoms in the microscopic world influences the macroscopic physical properties. Subwavelength periodic structure has been widely applied to different fields owing to its diversity, such as antenna, radar receiver and guided wave controller. In this thesis, that utilizing the property of high degrees of freedom in subwavelength periodic structure to design for polarizers are often used in optical devices and technology. Light is one form of electromagnetic waves. When light travels, electromagnetic wave oscillations propagate in all directions. However, electromagnetic wave oscillations propagate only in a direction after passing through polarizers. Electromagnetic wave oscillation in other directions will be reflected or absorbed by polarizers. Polarizing light and sunglasses let eyes only receive electromagnetic wave oscillations in a direction by polarizers. An LCD controls intensity of lights by polarization rotation and voltage change for liquid crystals. The 3D film is screened by two projectors, with the polarizer is placed in front of the projector lens. The viewer must wear polarized glasses to create illusion of 3D. Indeed, the basic functions of above mentioned polarizers are to confine the electromagnetic wave oscillations in a direction passing through polarizers.
This thesis focuses on the design for different subwavelength periodic structures making the passing linearly polarized light rotate. And it can control the angle of rotation of electromagnetic wave by changes in the structure instead of by reflection and absorption. Resonant modes can enhance both transmission and artificial optical activity. When they attain full transmission or optical activity, resonant modes can be found. Besides, we also work to reach full transmission and rotate polarization direction of electromagnetic wave at the same time which can prevent incident wave energy from wasting on reflection and absorption. This thesis is devoted to the study of Lorentzian resonance, Bragg resonance, surface plasmon resonance, and guided mode resonance.

並列關鍵字

chirality ； enantiomers ； rotation angle of polarization ； ellipticity ； magnitude ； phase

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