Enhanced and Resonant Transmission of Light through Dielectric-filled Subwavelength Waveguides*

We analyze transmission of light through dielectric-filled subwavelength waveguides in a metal using both analytical and numerical methods. Our analysis revealed that a propagating mode can in principle exist in a waveguide of arbitrarily small size when a certain relationship between the dielectric constants of the metallic cladding and filling material is satisfied. Transmission through a subwavelength aperture of finite length can be further enhanced when the length is such that Fabry-P\'{e}rot-like resonances are excited. Strong, localized near-field intensity at the exit can be achieved with this mechanism for aperture diameters down to $\sim \lambda $/20. We will describe potential applications of this resonantly enhanced transmission phenomenon in near-field scanning optical microscopy and single-molecule spectroscopy.