Wave classification and resonant excitations in lossy metal–dielectric multilayers

Loss-induced optical Bloch waves are investigated in a metal–dielectric semi-infinite multilayer placed over a substrate. In addition to the well-known classification of the electromagnetic waves into forward and backward waves, the electrostatics-based sub-classification elucidates one-level finer details of the wave nature. For this purpose, a hypothetical process is devised by continuously varying the signal velocity. As a result, a given electromagnetic wave turns out to be related to a certain electrostatic state. By this way, the metal's material loss is found to play an essential role in inducing depthwise energy flows, although it has the usual detrimental role in wave attenuation. Depending on the wave direction, normal and inverted reflection peaks on resonant excitations are illustrated.