複合式奈米孔洞搭配表面微結構

Abstract

隨著光學儲存技術的進步,大量的光學儲存容量需求也與日俱增.這個需求也驅使著研究方向朝著有高儲存密度的微小光點發展.通常是使用開口端微小的奈米探針把光於近場範圍內侷限在超越繞射極限的奈米尺度內.這種方法的最大缺陷就是出光強度太弱不利於應用.Bethe對於尺度遠小於入射波長的奈米孔洞提供了清楚的物理圖像.穿透孔洞的光強度與孔洞尺寸的四次方成正比,也就是說穿過小尺度孔洞的微小光點通常都是非常微弱的. 然而Bethe的理論孔洞建立在不符合實際的數學假設上:厚度可以忽略的完美金屬薄膜.實際的條件是違反這個假設.因此,奈米孔洞的光穿透增益是可能產生的此論文中由以下三種機制來探討奈米孔洞的特性:(1)表面結構決定的攫取光子機制(2)由金屬厚度決定的能量傳輸機制(3)出光面幾何結構所決定的光場分布. 由以上三個面向的討論,我們提出了改良的複合式奈米孔洞結構,同時具備了光穿透增益以及微小光點的特性.此外,我們在孔洞周圍的表面制作微結構來提供水平方向的動量以激發自由電子的集體震盪,由此進一步增強光穿透之增益.我們提出的改良結構與原始的方型奈米孔洞比較,可以提高光穿透增益到達兩百倍左右.

As the development of optical data storage, the demand for higher data storage capacity inspires researchers to produce the tiny and intense light spot. The nano-probe is widely used to confine the input light into the small area at the near field. The main issue lies in its low throughput. The Bethe’s formula provides a clear physical insight to the nano-aperture. When the aperture size on an infinitely thin and perfectly conducting film is much smaller than the incident wavelength, the transmission of the circular aperture is ~ (d/λ)4. The mechanism of nano-aperture is divided into three parts: (1) photon capture ability determined by the entrance geometry, (2) energy transportation influenced by the film thickness, and (3) the exit radiance distribution. Based on the prior literature, we designed a composite aperture to keep the intense throughput and the tiny spot at the same time. The metal surface in the vicinity of the aperture is corrugated to supply horizontal momentum and induce the “extended surface plasmonic resonance”, which results in the further enhancement of the transmission. Our proposed corrugated composite aperture was able to enhance power throughput by ~200X compared with the comparable square aperture.