Greatly enhanced power throughput from a "C"-shaped metallic nano-aperture for near field optical applications

Abstract

Summary form only given. Metal apertures with sizes down to 100 nm can provide deep sub-wavelength optical resolution in the near field region and are proposed for various applications such as ultra-high density optical data storage, nano-structure sensors et al. Unfortunately, the power throughputs from these nano-apertures are typically very low and this power deficiency problem hinders the practical use of the apertures. To overcome this problem, we investigate how the power throughput changes when we change the aperture geometry, using a numerical finite difference time-domain (FDTD) method. To testify the simulation result, we carried out experiments in the microwave frequency range. The microwave wavelength is 5 cm, which is 50,000 times the incident light wavelength in the simulation. The apertures are fabricated in a 0.5 mm thick copper plate. An intuitive understanding for the power throughput enhancement from the "C"-aperture can be achieved by considering the "C"-aperture as a short "ridge-waveguide", which has the unique property that its cutoff wavelength is much larger than twice the size of the waveguide. This simple understanding has been investigated to be quantitatively valid by comparing the cutoff wavelength of the ridge-waveguide and the resonance wavelength of the "C"-aperture.