基於金屬孔洞陣列之廣域電漿子透鏡

Broadband Plasmonic Lens Based on Metallic Nanohole Arrays

周彥宇(Yen-Yu Chou)

指導教授 ： 李有璋

中原大學/工學院/機械工程研究所/博士(2016年)

https://doi.org/10.6840/cycu201600831

摘要

輕薄的光學元件是光學系統微小化中重要的一環，並且為各式電子產品當前的發展趨勢。如何在尺寸縮小的同時，維持甚至於提升元件性能也成為近年各國研究單位努力克服的目標。電漿子透鏡藉由金屬奈米結構達到聚焦效果，其鏡面為平面、表面也不需要有複雜的三維浮雕結構，因此可進一步微小化透鏡尺寸，適用於微光學系統中。本論文以表面具有金屬洞狀結構陣列的石英基板進行電漿子透鏡開發，利用有限時域差分法(Finite difference time domain, FDTD)探討結構各項幾何變數(結構週期、結構直徑、金屬層厚度、透鏡尺寸)以及入射光條件(偏振方向、入射光斑尺寸)等參數對於穿透頻譜以及透鏡性能之影響。結果顯示，金屬洞狀結構具有多波長的聚焦功能，λ=400 nm～800 nm的入射光皆能於空間中產生聚焦點，其焦距取決於入射光的波長以及照射範圍；越小的波長或是越大的入射光斑皆會造成焦距增加。聚焦點的強度則與電漿子透鏡的穿透率成正比；當以共振波長入射時，異常光穿透現象將使穿透率大幅上升，進而提高聚焦強度。此外，當入射波長小於結構週期時，金屬孔洞會於空間中產生泰伯效應，將泰伯距離內的能量加總後，發現其強度分佈不論是圖形、週期、排列都與金屬洞狀結構相同；若將其應用於微影技術中，將可改善曝光製程中光罩的損壞與汙染問題。除了以數值分析模擬電漿子透鏡外，本論文同時開發膠體微影技術，以分散聚合法製備球徑為500 nm的聚苯乙烯球，並利用氣液介面沉降法以六角最密堆積的方式將聚苯乙烯球排列於基板表面；後續由氧電漿蝕刻縮小球徑，金屬蒸鍍後將表面聚苯乙烯球移除，即可完成電漿子透鏡製作。

關鍵字

表面電漿子 ； 繞射光學 ； 次波長結構 ； 有限時域差分法

並列摘要

Planar focusing lenses based on metallic structures have been attracting considerable attention as a means of miniaturizing optical systems. Most plasmonic lenses cause the convergence of transmitted light onto a small hot-spot through a metal pattern with a specific and precise geometry to create a curved phase front. Recently, a novel type of plasmonic lens based on patches of circular nanoholes have been reported, wherein light is focused using optical diffraction in conjunction with surface plasmon resonance (SPR), which is not a consequence of phase-front engineering. The advantage is the precision associated with the design and fabrication of the nanoholes is far less stringent.
This thesis used finite-difference time-domain (FDTD) method to investigate various geometry-related Al nanoholes as well as factors associated with the incident light to adjust the quality of the focused spot. Simulation results demonstrate that the planar plasmonic lens has the focusing characteristic across the entire visible range from 400 nm to 800 nm, and the focal length of plasmonic lenses is dominated by the wavelength and beam size of the incident light. When the light with SPR wavelength illuminated onto the palsmonic lens, the intensity of the focused spot can be significantly enhanced due to the extraordinary optical transmission (EOT) phenomenon. Moreover, the Talbot effect was occurring when the wavelength of incident light is shorter than the period of nanohole structures. Integrating the transmitted intensity by a nanoholes over a distance of one Talbot period, one can obtain an intensity distribution that is identical with a metal pattern, which can be applied to the non-contact photolithography technique. Finally, the planar plasmonic focusing lens was fabricated by using a rapid and low cost polystyrene (PS) sphere lithography in conjunction with thermal evaporation process to fabricate Al nanoholes on a quartz substrate.

並列關鍵字

Surface plasmons ； Diffractive optics ； Subwavelength structures ； Finite difference time domain

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