Electromagnetic unidirectionality in magnetic photonic crystals

We study the effect of electromagnetic unidirectionality, which can occur in magnetic photonic crystals under certain conditions. A unidirectional periodic medium, being perfectly transparent for an electromagnetic wave of certain frequency, "freezes" the radiation of the same frequency propagating in the opposite direction. One of the most remarkable manifestations of the unidirectionality is that while the incident radiation can enter the unidirectional slab in either direction with little or even no reflectance, it cannot escape from there getting trapped inside the periodic medium in the form of the coherent frozen mode. Having entered the slab, the wave slows down dramatically and its amplitude increases enormously, creating unique conditions for nonlinear phenomena. Such a behavior is an extreme manifestation of the spectral nonreciprocity, which can only occur in gyrotropic photonic crystals. Unidirectional photonic crystals can be made of common ferro- or ferrimagnetic materials alternated with anisotropic dielectric components. A key requirement for the property of unidirectionality is the proper spatial arrangement of the constitutive components.