Low-frequency surface plasmon polaritons propagating along a metal film with periodic cut-through slits in symmetric or asymmetric environments.

Surface plasmon polaritons (SPPs) propagating along a perfectly electric conducting film with an array of cut-through slits are studied analytically, and both the symmetric and asymmetric dielectric environments of the film are considered. Such a film structure, whether its substrate and superstrate are the same or different, may support a series of SPP modes, whose dispersion relations can be tailored by the film geometry. There exists a fundamental mode without any cutoff in the symmetric film structure, whereas all modes in the asymmetric structure have cutoffs, meaning that even the lowest-order mode can only exist when the film thickness is larger than a certain value. Moreover, for both types of symmetric and asymmetric film structures, the SPP bands do not overlap each other in the frequency domain, so the single-mode propagation is available for each mode. The fields of SPP modes are often highly confined to the structured film when the frequency approaches the asymptotic frequency. [ABSTRACT FROM AUTHOR]