Novel metal-dielectric structures for guiding ultra-long-range surface plasmon-polaritons at optical frequencies

Abstract

It is well known that propagation ranges of surface plasmon-polaritons supported by thin metal films are significantly limited by losses due to the concentration of a portion of the mode's energy within the metal. Propagation distances may be increased by using lower frequency light or thinner metal films. Implementation of these techniques is limited, however, and may not always be desirable. A layered structure, which allows for propagation ranges to be increased while holding the wavelength of the light and film thickness constant has been proposed. The surface plasmon-polariton guide consists of a metal film surrounded above and below by a thin, low index of refraction dielectric layer. When set in a dielectric cladding of higher index of refraction, the thickness of the inner dielectric layer may be increased up to a cutoff to achieve dramatic extension in propagation range. The effects of adjustment to parameters of the guide, such as the dielectric cladding index of refraction, metal film thickness and wavelength are discussed. Due to the fact that propagation distance and mode confinement are closely related, these two properties are investigated together, and the merits of the guide are discussed.