Guided modes and light trapping in the negative-refractive-index slab waveguides

We derive mathematical criteria for a pair of guided modes which have the same parity, mutually parallel wave vectors along the guiding direction of the waveguide, but opposite directions of optical power flow in a negative-index slab waveguide using a graphical method. It is also proven that the so-called light trap mode corresponds to the degenerate mode of this pair. We also propose a waveguide structure in which guided light waves can be trapped via tunneling through thin metamaterial clad layers. This trap is temporary since the trapped light tunnels out completely after a short time.