Photonic bandgap analysis based on the dynamical diffraction theory and its application to multilayer structures

Photonic band gap Crystals (PhC) are usually analyzed using the analogy between photon propagation in artificial periodic structures and electron wave propagation in real crystals. The forbidden band of photons is regarded as equivalent to the energy gap that electrons experience in crystals because of the periodic potential.On the other hand, electron propagation and electromagnetic wave diffraction in periodic solids, respectively developed into band-theory and Dynamical Diffraction Theory (DDT), are formally identical. It appears therefore natural to perform an analysis of the features of an electromagnetic phenomenon, as the PBG, in analogy to the most direct antecedent electromagnetic theory, the DDT, that historically has also represented the direct reference for the derivation of the band-theory of electrons.In this communication, we introduce an analysis of the features of PhCs in analogy with the DDT, underlining the differences between DDT classical application to the x-ray diffraction from real crystals and that from artificial crystals at optical wavelengths. In particular, the high contrast of material refractive indices in PhC makes inapplicable some approximations generally used in x-ray diffraction analysis. Moreover, we discuss in which cases DDT has to be generalized in order to overcome such limitations.