Photonic band-gap (PBG) versus effective refractive index: a case study of dielectric nanocavities

This paper answers the fundamental computational question: can one use the effective refractive index concept and analyze the performance of PBG structures? It is clarified that (a) when the lattice constant is of the order of the dielectric wavelength and the PBG structure operates inside the band-gap, the structure cannot be modeled using the effective refractive index and (b) for the frequencies outside the band-gap and where the lattice constant is small compared to the wavelength, the effective refractive index can almost model the PBG structure. In addition, it is shown that the PBG structure can properly localize the EM waves in a defect region, and a high Q nanocavity structure can be designed.