A multiplicity of exceptional compound plasmon-polariton waves

The propagation of compound plasmon-polariton (CPP) waves was investigated for the canonical boundary-value problem involving a metal film sandwiched between a homogeneous uniaxial dielectric material and a periodically nonhomogeneous isotropic dielectric material. Attention was focused upon exceptional CPP waves whose decay in the uniaxial dielectric material is governed by the product of a linear and an exponential function of distance from the uniaxial dielectric/metal interface. For physically realistic constitutive-parameter values, up to three exceptional CPP waves were found to exist, each with different propagation directions and with different wavenumbers, in each quadrant of the interface plane. The number of exceptional CPP waves, and their natures, were found to be sensitive to the period of the nonhomogeneous material, the thickness of the metal, as well as the constitutive properties of all three materials involved.