阶梯型纳米孔径的近场光学局域增强特性研究

提出一种高分辨力与高通光效率兼备的阶梯型纳米孔径设计方法 ,孔径的尺寸从膜层的入射表面向出射表面呈阶梯型逐渐减小 ,直到在膜层的出射表面形成一个亚波长的小孔。采用三维时域有限差分 (FDTD)方法对方形阶梯型纳米孔径及三角形阶梯型纳米孔径进行了数值模拟计算。结果表明 ,由于近场光学很强的局域场增强效应 ,其通光效率与输出光强极大值在具有相同近场光斑尺寸情况下 ,较普通的非阶梯型纳米孔径提高了两个数量级 ,甚至更高 ,有效地提高了输出光功率。采用四台阶三角形阶梯型纳米孔径 ,当光斑半峰全宽为 97nm× 74nm时 ,出射光强极大值达到 10 4 9.76 ,较入射光增强了 10 0 0倍 ,而通光效率大于 1,达到 1.6 7。这种阶梯型纳米孔径可以直接作为纳米孔径激光器的出射孔径提高其输出光功率 ,也可以作为独立的光学屏对入射光进行整形得到具有高输出功率的亚波长尺度光源 ,在纳米尺度光学成像、光谱探测、数据存储、光刻、光学操作等近场光学应用领域具有潜在的应用前景。

Research on Near-Field Local Enhancement Properties of Step-Shaped Nano-Aperture

A novel kind of step-shaped nano-aperture with high resolution and high power throughput is proposed. The step-shaped nano-aperture's size is gradually reduced from the incident surface to the exit surface until a sub-wavelength aperture is formed on the exit surface. The step-shaped square aperture and the step-shaped triangle aperture have been numerically simulated by the method of 3-D finite-difference time-domain (FDTD). The calculation results reveal that the light intensity peak and the power throughput of the step-shaped aperture are increased by about 100 times or more in comparison with those of the ordinary non-step-shaped nano-aperture with a comparable light spot size due to the near-field optical local enhancement effect. For step-shaped triangle aperture with four steps, when the full-width at half-maximum (FWHM) of light spot is 97 nm×74 nm, the peak intensity reaches 1049.76 (1000 times of the incident light intensity) and the power throughput is 1.67. This kind of step-shaped nano-aperture can be directly used as an exit aperture of nano-aperture semiconductor lasers or as an unattached shield, to produce a sub-wavelength light source with high transmission. It is possible to be used in near-field optical applications such as near-field super-resolution imaging, high-density optical data storage, nano-photolithograhy, manipulation, and so on.