Tunable plasmonic metamaterials based on fractal geometry

Surface plasmon polaritons (SPPs) are elementary electromagnetic (EM) excitations bounded at a metal/dielectric interface. Due to two important features - local field enhancement and subwavelength resolution capability - of the SPP, it has attracted considerable attention recently and many SPP-based applications were proposed or demonstrated. However, for a natural material, its plasmon frequency (
_p
omega) is fixed by electron density. This restriction limits the aforementioned SPP-based applications to a wider frequency regime. In this talk, we show that a metallic plate with subwavelength fractal-shaped slits supports SPpsilas with omega
_p
tuned efficiently by the geometry of the fractal structure. We derive effective-medium models to describe such tunable plasmonic metamaterials, and found that the latter can mimic plasmonic metals in frequency regimes beyond the (fixed) plasmon frequencies of natural metals (gold, silver, etc.). We show that our plasmonic metamaterials possess many applications. As one example, we show that one can use it to focus light sources with subwavelength imaging abilities and enhanced field strengths. Finite-difference-time-domain (FDTD) simulations are performed to design realistic structures and verify all predicted phenomena.