Abbas Mohammed Nadhim, Chang Yia-Chung, Shih M H
Research Centre for Applied Sciences, Academia Sinica, Taipei 115, Taiwan.
Opt Express. 2010 Feb 1;18(3):2509-14. doi: 10.1364/OE.18.002509.
It is shown that asymmetric T-shaped plasmonic gratings can display plasmon-polariton band structures with wide range of band gaps and tunable group velocities. A structure gap is introduced in the post of Tshaped plasmonic gratings and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We obtained variation of energy band gap ranging from 0.4 eV to 0.0323 eV by changing the size of the structure gap from 0 to 250 nm. The plasmon-polariton band structures were obtained by using Rigorous Coupled Wave Analysis. We studied the difference between symmetric and asymmetric T-shaped gratings and found that the symmetric structure has a momentum gap in the photonic band structure, which can be avoided in the asymmetric structure. Furthermore, by varying the post and spacer (made of SiO2) thicknesses we can tune the energy band gap from 0.1 eV to 0.148 eV and from 0.183 eV to 0.19 eV, respectively. In this device, we obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap.
结果表明，非对称T形等离子体光栅可呈现具有宽范围带隙和可调群速度的等离子体极化激元能带结构。在T形等离子体光栅的柱体中引入了一个结构间隙，发现该间隙的大小在控制等离子体极化激元带隙和群速度方面起着重要作用。通过将结构间隙的大小从0改变到250 nm，我们获得了从0.4 eV到0.0323 eV的能带隙变化。利用严格耦合波分析获得了等离子体极化激元能带结构。我们研究了对称和非对称T形光栅之间的差异，发现对称结构在光子能带结构中有一个动量间隙，而在非对称结构中可以避免。此外，通过改变柱体和间隔层（由SiO2制成）的厚度，我们可以分别将能带隙从0.1 eV调谐到0.148 eV以及从0.183 eV调谐到0.19 eV。在该器件中，我们获得了可调群速度，其范围比真空中的光速小一到几个数量级。这种非对称T形等离子体光栅有望应用于基于表面等离子体极化激元（SPP）的光学器件，如滤波器、波导、分束器和激光器，特别是对于需要大光子带隙的应用。
