An active optical multi-channel switch

We present the theoretical results on using the spontaneous emission which is induced from a two-level atom embedded in a photonic crystal with two bands and one forbidden gap. It is shown that the emission field from the atom is composed of two parts, one is a localized field, which always exists, and the other is one or two propagating modes. The emission of the propagating mode depends on the gap size and the relative position of the upper-level of the atom with respect to the edges of the two bands. The propagating modes have a sudden jump from zero to a certain value when the gap or the related position of the upper level changes. This jump can be used to design an active optical two-channel or four-channel switch. Due to the localized field being within a few dozen atoms, the switch can be designed in a few micrometers.