We present a theoretical study of the dispersion relation of surface plasmon resonances of mesoscopic metal-dielectric-metal microspheres. These are spherically symmetric Bragg resonators comprising thin, alternating layers of dielectric and metal shells around spherical metal cores. By analyzing the solutions to Maxwell's equations, we obtain a simple geometric condition for which the system exhibits a band of surface plasmon modes whose resonant frequencies are weakly dependent on the multipole number. Using a modified Mie calculation, we
investigate the effect of this flat-dispersion band on the absorption and scattering cross-sections of the layered particle. We find that a large number of modes belonging to this band can be excited simultaneously by a plane wave, thus enhancing the absorption cross-section. Moreover, we observe a narrow transmission resonance due to the metallodielectric shells behaving as a transparent coating in a narrow spectral range. We demonstrate that the enhanced absorption and transmission of the sphere are geometrically tunable over the entire visible range.
We present an analytical study of surface plasmon polariton (SPP) propagation about a circular bend formed by the interface between a metal and a dielectric with the metal occupying the inner volume. It is shown that in the short wavelength limit, the problem is essentially analogous to scattering from a 1D finite potential well, with standard expressions for the transmittance and reflectance. In certain cases, we find that propagation on nonplanar interfaces may result in lower losses than on flat surfaces, contrary to expectation. We also show that the same approach is valid when the metal occupies the outer volume, such that in the 1D approximation SPPs propagating around such bends do not radiate. An upper bound for the transmittance, valid even when our approximation breaks down, is also derived. This is found to depend nonmonotonically on the bend radius, allowing increased transmission with decreasing radius. We further present a numerical study using the finite-
difference time-domain method and show that it is consistent with theoretical predictions. We also show that the introduction of a microcavity plasmon resonator could significantly enhance the transmission.