Properties of plasmon-polariton waveguide on silver nanowires

Abstract

In this paper we examine properties of plasmon-polariton waveguide made of five rows of silver nanorods arranged in the hexagonal lattice. Electromagnetic wave illuminating metal structures generates surface plasmons. In nanoscale structures plasmons locally enhance near field and light propagates in modes confined below the diffraction limit. We present results of simulations using Finite Difference Time Domain (FDTD) method, which illustrate guiding visible light in the examined waveguide. We calculate modal properties of the waveguide. Propagation of two groups of modes with different symmetry with respect to the waveguide axis is observed. When the monochromatic light source is located on the waveguide axis both groups of modes are excited independently due to source symmetry. We assess that in the symmetric mode wavelengths longer than 500 nm are guided. For the antisymmetric mode that value is equal 450 nm. For off-axis illumination modes propagate together and form a snake-like beat pattern. Interference of modes from the first and second Brillouin zones (BZ) is also observed for a few wavelengths. To analyze the dispersion properties of the waveguide we assume Bloch type and absorbing boundary conditions in a single cell of the waveguide and make calculations on complex fields. FDTD equations work as a sieve that extracts modes with a given wavenumber from the initial field distribution. Then the guided frequency is found from spectrum. Group and phase velocities of modes are obtained from the dispersion relations.