光通過次波長狹縫後所產生之現象在近幾年引起許多的注意，其中光線通過次波長孔洞所產生之異常穿透現象更已被研究數年之久。根據法國Ebbesen研究團隊所發表之研究中提出，在次波長結構下，光線穿透一於出射面上有週期性結構環繞之孔洞後，可產生強度增強二至三階之「指向性」現象，且穿透結構後之光線，發散角可降至二至三度。此次波長結構之聚焦現象可被廣泛的應用在許多光學元件上，以及資料儲存、近場光學顯微鏡等領域。
　　在許多所發表過之研究中，激發金屬表面電漿以達到次波長聚焦現象之光源皆為平面光源。在此篇論文中，入射光源之特性將被研究及探討。經由改變光源之物理特性，穿透光強增強後進而使聚焦現象之強度隨之提升，且光源位置亦將影響所需輸入之光源特性及聚焦現象。透過模擬可找出提升聚焦現象光強所需之光源特性間關係。在本文中所使用之模擬軟體為「OptiFDTD 6.0」，為一以有限時域差分法為理論基礎作進行計算模擬之套裝軟體。

　Light transmission through a sub-wavelength slit has drawn much interest recently, and the phenomenon of extraordinary optical transmission through a sub-wavelength aperture has been studied over the years. According to the researches published by Ebbesen et al.[1998,2002], the “directional beaming” phenomenon has shown that the transmittance of light penetrating sub-wavelength slits surrounded by periodic corrugation on the exit side can be enhanced to 2~3 orders, and the divergence of the diffraction can be lowered to 2~3 degrees. The sub-wavelength slit structures can be used in many optical devices such as light emission, data storage, and near-field microscopy.
　Most of the published researches use plane wave as their incident light source to excite the surface plasmon in the metallic structure to achieve enhanced transmission through the aperture. In this thesis, the light source of this sub-wavelength focusing phenomenon will be studied. By changing the light beam properties, the focusing phenomenon will have enhancement in their intensity, and the light source position will also affect the focusing intensity. The beam properties which can achieve better focusing phenomenon will be found out. All numerical simulations and analysis of these structures will be performed by the package of “OptiFDTD 6.0” which is based on the theory of the finite-difference time-domain (FDTD) method.

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