可選擇極化方向之超寬頻吸收器

Abstract

超材料完美吸收器在近幾年來，受到各界高度的注目，是相當熱門的研究題材，但是至今都尚未出現，可選擇吸收特定極化方向的寬頻吸收器。在此篇論文中，我們將以半導體製造常見的鋁，做為屏蔽橫向電波（Transverse electric wave）的金屬線結構，由於電磁波必須符合邊界條件，以及利用完美導體的特性，延金屬切向方向電場為零，垂直方向電場不連續量正比於表面電荷密度，將此結構結合在平面型交疊層完美吸收器上，達到選擇完美吸收橫向磁波（Transverse magnetic wave）的效果。我們使用鈦以及二氧化矽堆疊成堆疊成十六對的平面交疊層結構，上方在做出三百奈米厚的鋁線，藉由控制鋁線的寬度、週期以及以及介電材料（二氧化矽）的厚度等等，可以透過幾何材料的改變，影響元件對於電磁波的吸收響應。理論計算出波段從1.98微米至11.74微米，可以達到良好的選擇極化方向電磁波吸收效果，橫向電波（Transverse electric wave）吸收小於0.04，橫向磁波（Transverse magnetic wave）＞0.95。除模擬之外，我們也在國家奈米元件實驗室製作出元件，其量測結果符合模擬所預期之行為。

In recent years ,a ultra-broadband perfect absorber has been widely researched ,but ultra-broadband absorber with polarization selectivity has not been implemented in the past. In this work , we propose a structure of polarization-selectivity metamaterial perfect absorber(PS-MPA).The aluminum wire grid is intergrated on top of metal-dielectric stacking. The aluminum can be considered nearly perfect conductor , and we can impose boundary condition on metal grids. The transverse electric(TE) wave is blocked by aluminum wire grid, because of the metal mirror.The transverse magnetic wave can passed the aluminum wire grid since the normal electric field can be supported by the surface charge density at the metal surface, and full absorption of the TM wave is accomplished by the metal-dielectric stacking beneath. Our structure is made of 16-pairs Ti/SiO2 stacking and 300 nm thick aluminum(Al) wire grid .Additionally, the property of wavelength scalability can be achieved by adjusting the dielectric thickness (tSiO2) , the wire grid period (P) and height (t). Theoretical calculation using rigorously coupled wave analysis demonstrates the wavelength selectivity from λ = 1.98μm to λ = 11.74μm where the TE absorption is <0.04 while TM absorption is >0.95. The experimental result demonstrated the feasibility of proposed structure, and the measured result fully supports the previous calculation.