異常光學穿透現象於兆赫波段之研究

Abstract

本論文針對近年來相當熱門的一個研究主題－異常光學穿透 (EOT) 現象－在兆赫波段上進行深入的物理探討。目前已知的是在金屬上週期性排列的孔洞會造成EOT，但此現象的物理機制仍在爭論中，而在THz波段，一些導電性好金屬可視為完美導體，因此表面電漿子理論在此波段的解釋並不適當。

第一個部分為理論推導，我們將整個系統的電磁場做模態展開，此電磁場滿足馬克斯威爾方程式及其所推演出的荷姆霍茲方程式，計算的結果與實驗結果十分穩合。此結果排除了表面電漿子理論在此波段的解釋。

第二個部分我們探討孔洞的形狀大小對穿透頻譜的影響。結果顯示：1) 孔洞的面積愈小絕對穿透效率愈高，2) 孔洞的寬長比會對頻譜造成非單調的紅移現象，3) 孔洞和晶格的對稱性關係亦會對頻譜造成顯著的影響，這些特性可以為日後的兆赫波微光學元件應用提供一個新的指引。

This thesis studies the physical origin of a very popular research theme, extraordinary optical transmission (EOT) phenomenon, in THz region. It is known that 2D periodic metal hole arrays can cause EOT; however, the real physical mechanism of this phenomenon is under debate. In THz region, good conductors can be seen as perfect electric conductor and therefore the explanation based on theory of surface plasmon ploariton (SPP) is improper. The first part of this thesis is theoretical formalism. We expand the EM fields of the system by eigenfunctions of Helmholtz’s equations in each sub-system, and then match the boundary condition obeying Maxwell’s equations. The simulation results match very well with experiment results, and so that we can exclude the SPP effect in THz region. In the second part we investigate the influence of hole shape and size on transmission spectrum. It is shown that, 1) the smaller the hole area, the higher the absolute transmission efficiency, 2) the aspect ratio of holes can cause shift in the peak transmission spectrum non-monotonously, and 3) the symmetry difference between hole and unit cell also has influence on transmission spectrum. These properties can be taken as a guide for future micro-optic THz device.