Figure shows a photonic band gap (indicated by white regions) as a function of wavelength for bulk material with periodic layers The physical effects involved in optical coupling in periodic structures which allow for photonic band gaps are explained. A simple model to do this is used, since this allows us to establish some general principles for the operation of such devices. The choice of parameters, with respect to the band gap, is investigated which will allow the device to operate suitably.

S. Tomljenovic-Hanic and A. Ankiewicz, 'Wavelength splitting in photonic band-gap structures with multiple defects', Optics Communications, 237/4-6, (2004), pp 351-355.