Properties of three-dimensional plasmonic slot waveguides

We investigate the properties of the modes supported by three-dimensional subwavelength plasmonic slot waveguides. We show that the fundamental mode supported by a symmetric plasmonic slot waveguide, composed of a subwavelength slot in a thin metallic film embedded in an infinite homogeneous dielectric, is always a bound mode. Its modal fields are highly confined over a wavelength range extending from zero frequency to the ultraviolet. We then show that for an asymmetric plasmonic slot waveguide, in which the surrounding dielectric media above and below the metal film are different, there always exists a cutoff wavelength above which the mode becomes leaky.