Resonant tunneling between two continua

We consider the tunneling between two monomode continua through a monomode structure with the symmetry of two orthogonal mirror planes. We derive in c losed farm the conditions for selective transfer of a single propagating st ate from one continuum to the other, leaving all other neighbor states unaf fected. We illustrate the results of this analysis by analytical solutions for a simple structure made out of one-dimensional photonic waveguides. The se theoretical results are confirmed by experiments using coaxial cables. [ S0163-1829(99)16735-3].