Obtaining super resolution light spot using surface plasmon assisted sharp ridge nanoaperture

Finite difference time domain computations is used to study surface plasmon (SP) excitation around C- and H-shaped ridge nanoapertures made in silver film. The SP enhances optical transmission, in addition to the transmission mechanism of the waveguide propagation mode and Fabry-Pérot-like resonance. However, the near-field collimation of ridge aperture is found completely destroyed. On the other hand, using a bowtie-shaped aperture with sharp ridges made in silver, the loss of near-field collimation can be recovered. A super resolution optical spot with full width half magnitude as small as 12nm×16nm is achieved due to the resonant SP excitation localized at the tips of bowtie. Much higher field enhancement is also obtained compared to the bowtie aperture made in chromium.