Evanescently coupled interface states in the gap between two Bragg reflectors.
Interface states are known to exist at the surface of an appropriately structured Bragg reflector. If such reflectors are present on the surfaces of two prisms separated by a narrow gap, the evanescently coupled interface states can interact to produce a pair of very narrow transmission lines, the separation of which can be adjusted by varying the size of the gap between the two prisms. Thus, although only a single cavity is involved, the spectral properties of the system are similar to those of a dual-cavity photonic microstructure. In addition to other potential applications, we propose that such a structure could form the basis of an adjustable beat-frequency emitter in the terahertz regime.