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標題: | 由雙曲線超常材料包覆之圓柱電漿子波導 Cylindrical Plasmonic Waveguides Cladded by Hyperbolic Metamaterials |
作者: | Ming-Chih Tsai 蔡旻志 |
指導教授: | 陳瑞琳 |
關鍵字: | 電漿子波導,超常材料,傳播距離,模態面積,品質因數, Plasmonic Waveguide,Metamaterial,Propagation Length,Mode Area,Figure of Merit, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 光由於繞射極限無法在次波長結構中傳播,所以傳統介電波導如光纖無法在奈米尺度下運作。電漿子波導則透過等效波長較短的表面電漿子,可使光以表面波形式在次波長結構中傳播,進而運用在光子積體電路中。然而電漿子波導卻因為金屬的損耗而限制了傳播距離。混合式電漿子波導則結合了傳統介電波導與電漿子波導的特性,得到一種折衷的性能。另一方面,異向性材料被用於波導中來控制波傳不同方向的光動量,本研究使用具有強烈異向特性的雙曲線超常材料來設計與分析一種新型的圓柱電漿子波導,形成一種由雙曲線超常材料包覆之圓柱電漿子波導,或簡稱為金屬–介電–雙曲線圓柱波導。此種新型波導具有混合式電漿子波導的概念,其在電磁場高度侷限的需求下仍擁有良好的傳播距離。
在本研究中,我們使用解析方法來分析這種金屬–介電–雙曲線圓柱波導:先由電磁波理論推導出三層異向性圓柱波導的解析形式色散關係;再利用色散關係逐一求得波導橫磁模態之傳播常數、傳播距離、模態面積以及品質因數。透過觀察品質因數的變化趨勢,得知金屬–介電–雙曲線圓柱波導的電磁場呈高度侷限(接近等向性的金屬–介電–金屬圓柱波導)。然而其傳播損耗將會大幅減小,因此擁有相對較長的傳播距離。舉例來說,當波導結構尺寸在400奈米左右,金屬選用銀及介電選用氧化鋅,經調變適當的結構幾何及材料組成之後,此種金屬–介電–雙曲線圓柱波導在波長1.55微米下,可以同時具有非常小的模態面積(接近銀–氧化鋅–銀圓柱波導)以及比舊有金屬–介電–金屬圓柱波導長上將近兩倍的傳播距離。 Conventional dielectric waveguides, such as optical fiber, cannot operate at the nanoscale due to the diffraction limit that light cannot be guided within the subwavelength structures. Plasmonic waveguides (PWs), guiding surface plasmon-polaritons (SPPs)––a form of surface waves which have smaller effective wavelength at the same frequency, make light can propagate in subwavelength dimensions and have been used in photonic integrated circuits. However, the propagation length of SPPs in PWs are limited due to the losses of metal. Hybrid plasmonic waveguides (HPWs) combine the advantages of the dielectric waveguides and the PWs, which have a balanced performance between high confinement and long-range propagation. On the other hand, anisotropic material has been used to control the optical momentum of waves in different directions. In this study, we propose and analyze a new design of cylindrical PWs based on strongly anisotropic media––hyperbolic metamaterial, that is, cylindrical PWs cladded by hyperbolic metamaterials or metal–dielectric–hyperbolic (MDH) cylindrical waveguides. This new type of waveguides has similar function as the HPWs with high field confinement and the long propagation length. We analytically solve the basic properties of the MDH cylindrical waveguides: First, we derive the dispersion equation of three-layer anisotropic cylindrical waveguides based on Maxwell’s equations. Second, the propagation constant, propagation length, mode area and the figure of merit (FOM) of the transverse magnetic modes are obtained from the dispersion relation. Through observing the trend of the FOM, we found the MDH cylindrical waveguides have high field confinement which approximates to the isotropic metal–dielectric–metal (MDM) cylindrical waveguides. Nevertheless, the propagation losses will be sharply reduced, which leads to the longer propagation length. For example, for the case of Ag–ZnO–hyperbolic cylindrical waveguides with the size around 400 nm at wavelength, it perform both extremely small mode area that approximates to the Ag–ZnO–Ag cylindrical waveguides and better propagation length which is almost twice longer than that of the MDM cases. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/51061 |
DOI: | 10.6342/NTU201600357 |
全文授權: | 有償授權 |
顯示於系所單位: | 應用力學研究所 |
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