微小化多層金屬寬頻超材料完美吸收器

Abstract

在此篇論文中，我們提出了一個結構非常簡單的多金屬層超材料完美吸收器，設計了一個厚度僅221nm，吸收的波長落在400nm到700nm之間。相較於過去的超材料完美吸收器使用電漿激發達成，在這篇論文裡面，我們利用超薄金屬膜來達成一個範圍的寬頻吸收，此外，利用我們所設計的平面結構，有機會達到更寬頻的波長吸收，並且在製程方面，也不需要經過顯影蝕刻的步驟，非常適合用於大面積的光子晶體設計。此物理特性是利用電磁場的穿透與吸收，在不同的波長範圍要設計不同金屬層。每一層不同金屬厚度的調整，可以在真空的狀態中得到一個完美的阻抗匹配，在此實驗中，我們選用了鈦(Ti)、鎳(Ni)、鋁(Al)來呈現，並且也觀察到了阻抗匹配的結果。利用不同的金屬，此吸收範圍一定可以更寬，並且再利用這個平面結構擴展大面積的光子晶體，我相信此篇論文的設計觀點對於未來在實現超材料完美吸收器與其應用上能有所幫助。

An extremely simple multiple-metal metamaterial perfect absorber (MPA) has been proposed in this project. The dimension of the proposed design, for the visible wavelength range from 400 nm to 700 nm, is only 221 nm. Even if the plasmonic excitation is absent in this proposal, our design has dimension comparable to the past effort of MPAs using plasmonics. An unity broadband absorption can be achieved with ultra-thin metallic films. In addition, the wavelength scalability is possible using our design, and the fully-planar, simple configuration facilitates large-area photonic design without the need of lithography and etching. The physics are the field penetration and the field absorption for the photons at different wavelength ranges using different metallic layers. It showed that the adjustment of the individual layer thickness was critical to attain a perfect wave impedance matching to vacuum. The titanium (Ti), nickel (Ni), and aluminum (Al) triple-metal configuration are used to demonstrate the concept experimentally, and a close match to the theoretical result is observed. The absorption band can be further widened with more stacking layers with various metals. It is believed that the proposed design is very promising in the aspects of simple processing, scalable for large-area, and broadband unity absorption. Thus, it improves the future implementation of metamaterial perfect absorbers and facilitates a wide range of relevant applications.