Localized modes in defective multilayer structures

In this paper, we investigate the localized surface modes in a defective multilayer structure. We show that the defective multilayer structure can support two different kinds of localized modes, depending on the position and the thickness of the defect layer. In one kind, the modes are localized at the interface between the multilayer structure and a homogeneous medium (the so-called surface modes). While, in the other one, the modes are localized at the defect layer (defect-localized modes). We reveal that in the presence of the defect layer, the dispersion curve of the surface modes are pushed to the lower (upper) edge of the photonic band gap when the homogeneous medium is a left-handed (right-handed) material. Therefore, the existence regions of the surface modes are restricted due to the defect layer. Moreover, the effect of defect on the energy flow velocity of the surface modes is discussed.