以三維時域有限差分法研究多種奈米金屬結構

Abstract

時域有限差分法已被廣泛應用在光電電磁模擬上。本篇論文中，我們使用C++語言發展了三維時域有限差分法的模擬器，並透過訊息傳遞介面協定發展平行化功能以減少運算時間。 我們的研究主要在分析多種奈米金屬結構在入射一道光波後的間隙場增強量。一開始我們先模擬以一道寬頻平面波正向射入單個的多段轉折奈米天線，計算得在波長0.3微米到4.0微米間的天線間隙的場增強量及相對應的共振波長。然後將天線臂長等比例的拉長並研究不同天線臂長對其頻譜所造成的影響，發現天線臂長與共振波長呈現正線性關係。第二部分，我們研究討論等長天線臂長但不同轉折比例的多段轉折天線以及U型天線，並且將多段轉折天線與新型結構的奈米天線進行比較。透過比較間隙場增強量的結果，我們發現當多段轉折天線在x軸上有較大的比例時，會得到較大的間隙場增強量。因此我們接著研究了天線長度對線性偶極天線的影響，發現偶極天線的長度與其共振波長呈現正線性關係，且隨著偶極天線的長度拉長，會得到較大的間隙場增強量。

The finite-difference time-domain (FDTD) method has been widely used in computational electromagnetics. In this thesis, we develop a parallelized three-dimensional (3-D) FDTD simulator in C++ language and use the message passing interface (MPI) protocol in order to reduce the simulation time. The main topic of this research is to analyze the gap-field enhancement of several nano metal structures under incident optical waves. We first simulate the single Multi-Bent-Section Nano-Antennas (MBSNAs) by applying a broadband normally incident plane wave to get their responses for the electric-field enhancement and resonant wavelengths in the antenna gap from the wavelength range of 0.3 um to 4.0 um. Then the antenna arm length of the MBSNAs are proportionally elongated and the influence of the varied antenna arm length is studied. We find that the antenna arm length has positive linear relationship with the resonant wavelength. In the second part, the MBSNA(1)'s and U-shaped nano-antennas with different proportions of the bent section with the same total antenna length are investigated. Then we study modified nano-antennas and compare with the MBSNA(1). With the results from comparing the gap-field enhancement values, we find that the MBSNA(1) with the larger proportion of x-direction component has the higher value of gap enhancement. So after that, the influence of the antenna length of the linear dipole antenna is studied.