本研究應用轉換光學，在電磁有限時域差分模擬方法中產生非均勻網格，以提升模擬效率。在此研究中，我們以光穿透單一金屬次波長孔洞為例子，設計出以精細網格解析孔洞附近之電磁場，同時以粗糙網格解析孔洞以外區域之物理座標，再使用多層線性函數或線性-非線性函數將此座標轉換為均勻的數值座標。為了比較差異性，我們從事完美金屬導體及有電漿子效應的理論分析以及均勻網格光電模擬的穿透頻譜。我們發現非均勻網格下之模擬結果皆與之相符，而計算資源最多能顯著地節省約96%。更甚者，我們可以設計出更精細的網格，以得到更為精確的結果。根據分析，本方法所需計算資源隨著解析度增加的速度遠小於均勻網格。基於此，我們相信本方法對電漿子學模擬研究具有幫助。

We propose a transformation-optics method to generate non-uniform grids in FDTD simulations in order to enhance the computation efficiency. Fine cells are designed to be around the aperture while coarse cells are in other areas. We define mapping functions to transform non-uniform physical coordinate into uniform numerical coordinate. For the purpose of demonstration, we simulate the light transmission through a rectangular subwavelength aperture in a metal film in order to obtain the transmission spectrum. The transmission spectrums for the film being PEC or plasmonic material are compared with that of analytical theory. We show that the simulation of non-uniform grids is sufficient accurate, and for the best case the computational cost can be reduced to 4%. Furthermore, we can design finer grids to obtain more accurate transmission spectrum. The increasing rate of the computational cost due to higher cell resolution can be up to three orders lower in comparison with the uniform numerical coordinate. These results indicate that the method should be helpful for the FDTD simulation study in plasmonics.

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