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为了提高对远场方向性调控的灵活性,提出双蝶形银纳米光天线,基于时域有限差分的方法研究了天线不同结构与尺寸的变化对远场方向性产生的影响。研究发现,由于局域表面等离激元的存在,偶极子源垂直放置于双蝶形银结构下表面一定距离时,远场方向图出现明显的旁瓣。天线长度的增加是方向图出现旁瓣的关键因素。天线臂之间夹缝的减小,使远场方向图中旁瓣增大,同时主瓣增益增大。天线厚度的增加使远场方向图出现旁瓣,主瓣增益先增大后减小。结果表明,双蝶形银纳米光天线能够改变与其相耦合的偶极子源的辐射方向性。
In order to improve the flexibility of directional modulation in the far field, a double-butterfly silver nano-optical antenna is proposed. Based on the finite-difference time-domain method, the influence of different antenna structure and size changes on the far-field directivity is studied. It is found that due to the presence of local surface plasmon polaritons, the dipole source is placed vertically at a distance from the lower surface of the double-butterfly silver structure, and obvious sidelobes appear in the far-field pattern. The increase of the antenna length is the key factor of the side lobe in the pattern. The reduction of the nip between the antenna arms increases the side lobe in the far-field pattern and increases the gain of the main lobe. With the increase of antenna thickness, the far-field pattern appears side-lobe and the gain of the main lobe increases first and then decreases. The results show that the double-butterfly silver nano-optical antenna can change the radiation direction of the dipole source coupled with it.