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 localizedfield being within a few dozen atoms,the switch can be designed in a few micrometers.