Keywords: surface plasmons, enhanced optical transmission, electromagnetics, nanostructured thin films, optical filters, metallic multilayers, nanotechnology
Plasmon-enhanced optical transmission of nanostructured metallic multilayers
Surface plasmons (SPs) – charge oscillations on metallo-dielectric interfaces – offer the possibility of controlling light at a scale much smaller than its wavelength, even down to the nanometre scale for visible wavelengths. Experiments have been performed to study the influence of SPs on the optical transmission of metallic multilayers in which one of the layers has been patterned at the nanometre scale to excite localised and extended SP modes. Films with linear gratings or two-dimensional hole arrays have been studied, and exceptionally-high transmission levels (up to 39%) are measured for these otherwise-opaque systems. The transmission resonances can be designed to be much narrower than for an equivalent Fabry-Perot filter, and can be tuned with geometrical parameters (film thicknesses and/or grating dimensions) or illuminations conditions (angle of incidence or polarisation). The measured dispersion of the transmission maxima agrees with the theoretical dispersion of extended surface plasmon polariton (SPP) modes on a planar metal film, which strongly suggests that the excitation of these SPP modes is responsible for the transmission features. This is further supported by rigorous electromagnetic simulations.