Linear guided waves and solitons sustained by hyperbolic metamaterials under strong optic axis and magnetooptic control

Abstract

A very recent paper [1] focuses on linear hyperbolic metamaterials. The latter have uniaxial symmetry and are the basis of elegant outcomes concerning a new generalized theory about their structural topology. The broad assertion, developed here, is that the current hyperbolic metamaterial world is only partially served by investigations that incorporate only some limited version of anisotropy. It is emphasised that a strong emphasis must be placed upon the orientation of the optic axis, which can, for example, be at a polar angle θ to the z-axis and possess a projection angle φ to x-axis in the (x,y) plane. These are significant elements in the optical properties of uniaxial hyperbolic metamaterials. Indeed, it is shown that, quite differently from conventional anisotropic waveguides, for a hyperbolic metamaterial, a critical angle exists for which the guided waves are homogeneous for all the values of the polar angle. This remarkable effect facilitates the achievement of propagating modes in meta-waveguides and leads to resulting structures that are more tolerant to optic axis misalignment. It is shown, using graphene as an example, that tilting the optic axis of a uniaxial metamaterial produces beautiful new effects in the linear domain [2]. Both leaky and surface waves are supported. Critical orientation angles are derived for the optic axis. In more detail, for the linear domain, it is the propagation of TM-polarized surface waves and leaky waves for a finite-thickness slab of hyperbolic metamaterial, with the optic axis, tilted with respect to slab interfaces, that is fully investigated, for the first time‥ It is only in the low frequency range that backward waves occur. For an optic axis perpendicular to the slab interfaces, the hyperbolic nature of the metamaterial is destroyed above a certain frequency window. For a tilted optic axis mode, changes occur at lower frequencies and a negative permittivity is maintained.