ABSTRACT

Propagation of plasmonic modes within dielectric voids embedded in metal layers is a favorable method of constructing plasmonic based nanocircuitry. In these structures – the metal cladding is providing the guiding mechanism and the tight confinement, while the dielectric core can be used for light-matter interactions for the realization of switches, modulators, nonlinear elements and for ultrasensitive probing. While the generic ID plasmonic gap structure (MIM) can be solved in closed form to exhibit explicitly the merits of the plamonic modes – the 2D version of such waveguides – slots, trenches and channels, is by far more complex. This complexity stems from the fact that, in contrary to regular dielectric cladded waveguides, each metal-dielectric ingredient of the waveguide is a guide of surface plasmon polariton by itself. This includes flat interfaces as well as metallic wedges. A trench in a metal can be considered as a complex coupled assembly (“hybridization”) of stripe and wedge plasmonic waveguides. Trench waveguide modes are studied here by mode-solving methods and the issue of structural symmetry and its significance for cutoff at nano dimensions is emphasized. Experimental measurements of modal field intensities of trench waveguides is presented and validating the theoretical considerations. As a conclusion we show that trench/slot waveguides are the favorable means to launch long propagating plamonic waves either millimeters long for micrometers wide trenches or tens of micrometers for nanometers wide trenches. The embedded mechanism in most cases is due to coupled edge (wedge) guiding – which has no parallel in regular dielectric waveguides.