光子晶體是由兩個或是多個不同折射率物質的人造週期性介質堆疊，光子晶體存在著光子能隙，光子能隙廣泛應用在光子晶體元件上，在這篇論文我們首先探討一維三元光子晶體能隙增寬，其中每一個週期是由兩個介電質夾著金屬層的三元結構，我們將要討論兩個主題，首先探討增加金屬層會強烈地擴大光子晶體能隙，相較於沒有添加金屬層的光子晶體(介電質-介電質-光子晶體)
接著我們探討有效電漿頻率在三元結構中，我們發現有效電漿頻率隨著金屬層厚度的增大而增加，以上所有的分析是依據Abeles theory,這是個在處理多層介質系統中簡練確切的方法。

A photonic crystal (PC) is an artificial medium with a periodic structure stacked by alternating two or more different materials with distinct refractive indices. It is known that there exist some photonic band gaps (PBGs) in a PC. Wide PBGs are usually needed in photonic applications.
In this thesis, we investigate the band gap extension for a one-dimensional ternary PC, in which each period is made of a metal layer sandwiched by two dielectric layers. Two topics will be studied. First, it can be seen that the addition of metal layer will strongly enhance the PBG compared to that without metal layer, i.e., the dielectric-dielectric photonic crystal (DDPC).
Next, we investigate the effective plasma frequency for such a ternary MDPC. We find that the effective plasma frequency increases with the increase in the thickness of the metal layer. All the above analyses are made based on the Abeles theory which is an elegant method in dealing with the multilayer system.

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