ABSTRACT
A trench in a metal can be considered as a complex coupled assembly of stripe and wedge plasmonic waveguides. The plasmonic modes of the GW are only the 2 first Transverse Magnetic (TM) modes, while all other modes are either oscillatory or evanescent. The dramatic change in the modal characteristics stems from the fact that as the metal becomes thicker, the TM polarized single surface plasmons on both sides of the metal detach. Symmetric trench structures can be used to guide plasmons for long distances – similar and even better than thin metal stripes. When the metal is thicker than the skin depth the internal metal walls are contributing additional types of modes which are confined predominantly within the trench and have field polarization of plasmons of the inner vertical walls. Trench waveguides are shown to be superior compared to their complimentary stripe structures both at the micrometer and nanometer regime.
