This chapter investigates the use of subwavelength scatterers and corrugations in a metal as efficient, localized sources of surface plasmon polaritons propagating for several micrometers at the dielectric/metal interface. Plasmonics, with its ability to confine and guide electromagnetic waves in subwavelength metallo-dielectric structures, promises to be a valuable alternative to the implementation of compact, fast and power-efficient optical integrated networks. The chapter presents a design study for three-dimensional plasmonic vias and modulators, and investigate several schemes for coupling light into such devices, evaluating their power efficiency. It demonstrates that essential building blocks for all-optical computation and networks, such as logic elements and modulators. In all-optical modulators, two different light beams are generally employed: one of the two beams is used to copy information onto the other at a different wavelength. The chapter discusses a multilayer metal/dielectric stack which defines two horizontal dielectric waveguides, separated from each other by a 150-nm-thick layer of silver cladding.