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We call a photonic crystal tunable if its spectrum can be altered by an external electric or magnetic field. One of the two constitutive components of the proposed periodic composite structure has either electric permittivity or magnetic permeability dependent on the external electric or magnetic field. Consequently, the electromagnetic spectrum of the photonic crystal can be altered over a wide range by the external quasistationary uniform field. The tunable photonic crystal exhibits some useful features reminiscent of those accompanying the well-known electronic topological phase transitions in metals. Thorough theoretical analysis of a two-dimensional tetragonal periodical structure is undertaken. This specific periodic structure exhibits the most important features of a tunable photonic crystal.
Figotin et al. (Sun,) studied this question.