Finitte-Difference Time-Domain Studies on Optical Transmission through Planar Nano-Apertures in a Metal Film

Abstract

The finite-difference time-domain (FDTD) method is employed to numerically study the transmission characteristics of an Hshaped nano-aperture in a metal film in the optical frequency range. It is demonstrated that the fundamental TE 10 mode concentrated in the gap between the two ridges of the H-shaped aperture provides a high transmission efficiency above unity and the size of the gap determines the sub-wavelength resolution. Fabry-Perot-like resonance is observed. Localized surface plasmon (LSP) is excited on the edges of the aperture in a silver film but has a negative effect on the signal contrast and field concentration, while aluminum acts similar to an ideal conductor if the film thickness is several times larger than the finite skin depth. In addition, it is shown that two other ridged apertures, C-shaped and bowtie-shaped apertures, can also be used to achieve a sub-wavelength resolution in the near field with a transmission efficiency above unity and a high contrast.

Resonant Transmission of a Rectangular Waveguide Probe with H-type Small Aperture

“…이와 같은 투과 공진 현상을 이용하여 파장에 비 해 매우 작은 개구를 이용하여 만들어진 근접장 탐 침(Near-field Probe)은 근접장 마이크로파 현미경, 나 노 현미경, 나노 리소그래피(nano-lithography) 등에 활용되고 있다 [2], [8]～ [10] . 여기서 근접장 마이크로파 현미경은 피측정 물체를 비파과적으로 조사하여 이 미지를 얻을 수 있으며, 간략한 구성은 그림 1과 같 다 [9] .…”

Experimental verification of electromagnetic scattering via two-dimensional periodic array of small resonant apertures

“…Recently, a lot of research has studied methods for increasing the transmission efficiency of a small aperture by modifying its geometrical shape like C-shape, H-shape or bow-tie-shape in the design area of a nano-scale optical probe, i.e., in the design area of a near-field scanning optical microscope (NSOM) probe, for near-field optical applications such as optical data storage, nano-lithography, and nano-microscopy [3,4,5,6,7,8,9].…”

“…The reason for choosing the small circular aperture with a ridge is that the circular aperture with a ridge is an optimized small aperture structure for nano-aperture and NSOM probe from the viewpoint of both transmission efficiency and spatial confinement and is essentially the same structure as H-shaped or C-shaped aperture which has been found to be the above optimum structure for the nano-aperture [3,4] or waveguide aperture coupling [12]. Furthermore, the resonant transmission through the single small resonant aperture and its array has drawn concern and interest from the EMC [13] community as well as optics [14] society.…”

Optical nanolithography with λ/15 resolution using bowtie aperture array

“…However, the transmitted light of the aperture is subjected to strong divergence. The light emerging from the exit plane is only collimated within tens of nanometers, beyond which it diverges quickly and its intensity decreases significantly [11,12]. Therefore, a precise distance control between the aperture and the recording material (i.e., the photoresist) is required to achieve stable and repeatable sub-diffraction lithography patterns [6,10,13].…”