表面等离子体激元透镜设计及其数值计算

Design and numerical simulation of plasmon polariton nanolens

提出了一种新的表面等离子体激元透镜的设计方案,该方案通过在两个亚波长小孔的外表面放置电介质光栅实现对入射光束的有效会聚。利用遗传算法研究了波导中表面等离子体激元的色散关系,结果表明,通过调节亚波长小孔的宽度和介电常数可以有效地调控有效折射率,从而实现对亚波长金属平板波导结构中表面等离子体激元传播特性的调控。利用时域有限差分方法(FDTD)结合完美匹配层(PML)边界条件数值模拟了此结构中的光场分布,讨论了光栅周期数对成像特性的影响,从而深入理解了纳米聚焦效应的物理机制。结果显示,随着表面光栅数的增多,焦距和焦斑大小都在增加。光栅数从5增加至11时,焦距由1.715μm增大至2.325μm,焦斑大小由0.615μm增大至1.715μm,这一结构有可能被用作未来集成光路中的纳米聚焦器件。

A novel plasmon polariton nanolens formed by two subwavelength metal slits surrounded by surface dielectric gratings is proposed and demonstrated numerically.The dispersion characteristics of surface plasmon polaritons （SPPs） in a metal waveguide are studied by using genetic algorithm,which shows that the effective index can be adjusted effectively by changing the widths and dielectric constants of these slits,and the propagation of SPPs can be controlled further.By combining the Finite-difference Time-domain （FDTD） method with Perfect-matching Layer （PML） absorbing boundary conditions,the distribution of optical field in the lens structure is simulated and the effect of number of surface gratings on imaging characteristics is discussed.Experiments show that the focal length and width are increased with the increase of number of the surface gratings.When the number of the surface gratings increases from 5 to 11,the focal length increases from 1.715 μm to 2.325 μm and the focal width increases from 0.615 μm to 1.715 μm.Results show that this lens structure can be availabe for the future integrated optics.