Chapter 2 - Metal strip and wire waveguides for surface plasmon polaritons

Abstract

This chapter discusses the metal strip and wire waveguides for surface plasmon polaritons (SPP). SPPs are propagating waves of resonant longitudinal electron oscillations at the interface between a metal and a dielectric, which are coupled to a light field. SPP waveguides are fabricated by vacuum evaporation of thin gold or silver films with a thickness of typically 50–100 nm on a transparent substrate. It is found that for the efficient coupling of light to SPPs and vice versa, the SPP dispersion relation has to be considered. Wave vector matching between light and SPPs can be achieved by the Kretschmann method. The local coupling of light to SPPs can rely as well on light scattering at nanoscale surface structures. The scattered light exhibits a wave vector distribution according to the spatial Fourier spectrum determined by the structure geometry. For waveguides with a width equal to a few times the SPP wavelength, the most efficient mirrors are obtained assuming that the SPP mode wave-vector modulus is practically equal to that of the incident light wave. The waveguiding and routing capabilities of SPP strip waveguides might complement the existing SPP sensor concepts that mainly rely on functionalized gold surfaces.