孔洞型金屬次波長週期結構之異常光學穿透與吸收

Abstract

在電磁領域研究當中，次波長意指結構之特徵長度小於入射電磁波波長，而當結構呈現週期排列時，則具有可調式共振以及等效介質材料特性，可建構出自然界材料不具有的物理性質，稱為超常材料，例如負磁導係數、負折射率、特殊非等向性、以及特殊非均勻性等，此想法源自於微觀中原子排列會影響巨觀材料之特性，利用此觀念於人造原子排列即是次波長週期結構。當運用於微波波段時，稱為頻率選擇表面，在頻率響應上具有帶通、帶斥的特性，可作為天線系統之反射器、濾波器、雷達罩、雷達吸收器、波導控制器。在光波段中除了可濾波的光柵外，近年來熱門的研究課題─光子晶體，可用於光顯示、光萃取、光吸收、光通訊、光儲存、光感應、以及光成像等。此外，近期許多學者利用超常材料共振達異常穿透、異常吸收、光捕捉以及對掌性結構於改變電磁波偏振模式，甚至利用轉換光學理論(Transformation Optics)達到光學隱形之效果，其多樣特性已成許多學者投入研究之因素。 本篇論文著重於利用電磁理論進行共振模態之分析與機制探討，共振形式如Lorentzian共振、Bragg共振、表面電漿共振、Fabry-Perot共振、波導模態共振、Fano共振等，電磁理論包含電磁場形式與強度、表面電荷、引發之電流、能量密度與通量等物理量，引用之材料包含完美導體、真實金屬以及介電質材料，結構幾何參數包含一維與二維排列、晶格大小、孔洞型與貼片型以及其幾何形狀、結構厚度與多層排列等，了解各項機制之後，便可用於設計擇頻穿透、反射、吸收等光學元件。

In electromagnetic science, subwavelength structure means that characteristic length of the structure is smaller than incident electromagnetic wavelength. While the arrangements of the structures are period, the structures have tunable resonance and effective dielectric material. These characters can build some materials that are not found in nature. We can call these artificial structures as meta-materials, just like negative permeability, negative refraction index, some special anisotropic and inhomogeneous materials. These ideals derive from the arrangements of atoms in microscopic that will influence the physical properties in macroscopic. In microwave band, we usually name sub-wavelength periodic structures as frequency selective surface. Because they possess band-pass and band-stop identities, what are often used to be filters, reflectors, radar receivers or guided wave controllers. In optical band, they are not only used to be optical gratings but also popular researches about photonic crystals. they can be applied to optical displayers, optical extractors, optical storages, optical sensors...etc. Recently, many scholars use the resonance of meta-materials to attain extraordinary transmission, extraordinary absorption, optical capture and chiral structures...etc. Even a new research is about using optical transformation theorem to achieve optical invisible. This thesis emphasize using electromagnetic theorem to explore and analyze the mechanism of resonance modes. they include Lorentzian resonance, Bragg resonance, surface plasmon resonance, Fabry-Perot resonance, guided mode resonance and Fano resonance. Electromagnetic theorems include the patterns and magnitude of electromagnetic field, surface bounded charges, induced currents, time average power flow. Materials we used include perfectly electric conductors, real metals, dielectric materials. Parameters we used include one dimension slits, two dimension holes, lattice constant, shape of holes, thickness of layers and multi-layers. After knowing every mechanisms, we can use them to design frequency selective transmission, reflection and absorption devices.