Hyperbolic dispersion and plasmon-polariton gap induced by off-diagonal anisotropy in photonic heterostructures

The influence of the optical axis orientation on the features of the plasmon-polariton (PP) gap in photonic heterostructures is investigated. To this end a one-dimensional layered system embedded in vacuum and formed by stacking alternate layers of anisotropic metamaterial and air is thoroughly analyzed. Within the formalism of Maxwell's equations and transfer matrix techniques we show the existence of the PP-gap at normal incidence. Furthermore, by tuning the frequency of the incident wave in the neighborhood of this gap, the otherwise usual elliptic dispersion relation, becomes hyperbolic.