The optical properties of SPPs at a metal–dielectric interface inspire a new group of waveguides made of insulating and conducting materials. These novel waveguides are often called plasmonic waveguides or SPP waveguides. Conventional dielectric waveguides guide light by using the refractive index difference between cladding and core media. However, SPP waveguides, such as metal-insulator-metal (MIM) and insulator-metal-insulator (IMI) waveguides, guide wave modes at the interface between a metal and a dielectric medium. The permittivity of the constituted media are opposite signs. The main advantage of plasmonic waveguides is the confinement of wave energy within a small spatial cavity. Plasmonic waveguides can guide either long- or short-range SPP waves. The structure and transverse core dimensions determine the working condition.
The wave confinement performed by plasmonic waveguides has
motivated extensive research into photon integration. Plasmonic waveguides with various geometries have been proposed and investigated, furthering the development of integrated plasmonic devices.
This chapter discusses the elementary structures of plasmonic waveguides and their guiding modes, especially regarding the manipulation of propagation modes. The suitable trade-off between mode confinement and propagation length are analyzed. The compromises of these features are discussed under specified applications. Finally, from the perspective of the effective index method (EIM), the mode effective index and propagation lengths are investigated in a few SPP waveguides.
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