In recent years a lot of attention has been paid to metal nanoscale structures because of new phenomena and
potential applications in waveguide and antenna techniques. Especially in the optical region new effects arise
based on plasmon resonances. It is known that in the optical region some noble metals behave like free-electron
plasma with low losses. In this study field propagation in nanoporous metal structures is considered. We consider
propagation in regular arrays of pores in metal in the presence of an interface. Although the field is decaying
outside the pores, these inclusions are so close to each other that there is interaction with the neighboring pores.
In addition the metal-insulator interface causes coupling. Near the plasmonic resonance these interactions are
strong enough, and there exist guided wave modes along the array. Properties of these modes are investigated.
The allowed frequency range where the guided modes exist depends on the geometry, i.e., on the size of the pores
and on the distance between them. In such structures there exist three propagating modes, two transversely and
one longitudinally polarized. The transversely polarized fields propagate as forward waves and the longitudinally
polarized fields form a backward wave. When the chain of pores is far from the interface, the two transversely
polarized modes become decoupled and have the same dispersion due to degeneracy.