以三維有限時域差分數值模型分析正立方體介電質奈米天線

Abstract

在本論文中，我們利用C程式語言發展了三維有限時域差分法，並且透過訊息傳遞介面協定，開發具有平行化功能以減少數值運算時間。本研究的主要目的是研究正立方體介電質奈米天線的散射特性，以及產生單向散射光的機制。首先，我們計算總散射截面和其輻射圖。然後我們分析了偶極共振的波長和廣義Kerker條件。另外，為了進一步增加散射光的指向性，我們考慮兩個正立方體奈米天線排列在不同方向。儘管可以通過增加奈米天線的間距來增強散射光的指向性，但是散射光的旁波瓣的數量和強度將同時增加。我們還考慮在行進光方向排列的正立方體奈米天線群，由於繞射光柵效應，它可以增強方向性並同時消除不需要的旁波瓣。最後，我們研究了可用於旋轉散射光方向的不對稱奈米天線。由於在不對稱奈米天線中激發的電偶極共振之間的干涉，散射光的方向可以被旋轉到遠離入射波方向的右側或左側方向。

In this thesis, we develop a parallelized three-dimensional (3-D) finite-difference time-domain (FDTD) numerical simulator by using the message passing interface (MPI) library code in C language. The main purpose of this research is to analyze the scattering properties of all-dielectric cubic nano-antennas, and the mechanism to produce unidirectional scattering. First, the total scattering cross-section and the radiation patterns are calculated. Then we analyze the wavelengths of the dipole resonances and the generalized Kerker's condition. Moreover, to further increase the directionality of the scattered light, we consider the double nanocubes. Although the directionality of the scattered light can be enhanced by increasing the gap size between the nanocubes, the number and the intensity of the side lobes will be increased at the same time. We also consider a linear chain of nanocubes aligned in z direction, which can enhance the directionality and eliminate the unwanted side lobes simultaneously due to the diffraction grating effect. Finally, the asymmetric nanoparticles which can be utilized to switch the direction of scattered light are studied in detail. Because of the interference between the electric and magnetic dipole resonances stimulated simultaneously in each of the asymmetric nanoparticles, the direction of scattered light can be tuned to either right or left away from the incident wave direction.