Investigation of nano lithography and optical waveguides based on surface plasmonics

Abstract

We have for the first time exactly measured the variation of the refractive index of gold film as a function of film thickness from 16 nm to 70 nm using the surface plasmon resonance method at telecommunication wavelengths. The measured thicknesses using the surface plasmon resonance technique are in good agreement with those measured by the ellipsometry and the values listed in the literature. These results can be applied to devices utilizing the thin film optics. We have also theoretically studied the propagation characteristics of the surface plasmon polaritons waveguide along a gold stripe through method of line calculation and experimentally investigated the long-range surface plasmon polaritons and the linearly tapered long-range surface plasmon polaritons waveguide with 10-nm-thick gold stripes embedded in a polymer, at 1550 nm wavelength. The lowest insertion loss of linearly tapered long-range surface plasmon polaritons waveguide was $\sim$4.3 dB and this value is improved by $\sim$0.7 dB than that of the straight long-range surface plasmon polaritons waveguides. Finally, we studied the improvement of resolution of optical images created by a silver superlens as a function of silver thickness which is originated from the antisymmetric mode of the surface plasmon. The antisymmetric mode has a large propagation wave vector and a small electric field. As the thickness of the silver superlens decreases, the propagation wave vector of the antisymmetric mode increases and the silver lens yields enhanced resolution. A chromium grating with various period was imaged with good contrast through the finite-difference time-domain simulation. Double slit of 40 nm width separated by a 60 nm gap were clearly imaged as the thickness of silver lens decreases. It is demonstrated that enhanced super-resolution can be obtained through the decrease of the thickness of silver lens using the antisymmetric mode of the surface plasmon.