Modes Of Sub-wavelength Surface Plasmonic Slot Waveguides

The concept of "Integrated Optics" was proposed by Miller in Bell Laboratories, which raised the curtain on the age of the study of the integration of photonic devices. In the past a few decades, the theories and the fabrication technology of integrated photonic devices have been developed greatly. And then the Integrated Optics is moving in the direction of higher integration which is similar to the electronic integrated circuits. We must design the nanostructure waveguide to achieve this goal. Metal waveguides based on surface plasmon can break the diffraction limit which can be a promising approach for Integrated Optics.We investigate the properties of the modes which are supported by 3-D sub-wavelength plasmonic slot waveguides, which is composed of a sub-wavelength slot in a thin metallic film embedded in an infinite homogeneous dielectric. There is always an abound mode for any combination of operating wavelength and waveguide parameters. Its modal fields are highly confined over a wavelength range 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 may exist a cutoff slot width and/or a cutoff metal film thickness above which the mode becomes leaky, and there always exists a cutoff wavelength above which the mode becomes leaky. We investigate the effect of variations of the parameters of the symmetric and asymmetric plasmonic slot waveguides. We also consider another plasmonic waveguide, such as the slot waveguide, in which the two metal film regions that form the slot have a finite width, and a plasmonic strip waveguide, which is formed between a metallic strip and a metallic substrate. We show that for a specific modal size, the fundamental mode of the standard plasmonic slot waveguide has a larger propagation length compared with the corresponding modes of these plasmonic waveguides.