Ghost resonance in anisotropic materials: negative refractive index and evanescent field enhancement in lossless media

Abstract

We show that dielectric waveguides formed by materials with strong optical anisotropy support electromagnetic waves that combine the properties of propagating and evanescent fields. These "ghost waves"are created in tangent bifurcations that "annihilate"pairs of positive- and negative-index modes and represent the optical analogue of the "ghost orbits"in the quantum theory of nonintegrable dynamical systems. Ghost waves can be resonantly coupled to the incident evanescent field, which then grows exponentially through the anisotropic media - as in the case of negative index materials. As ghost waves are supported by transparent dielectric media, the proposed approach to electromagnetic field enhancement is free from the "curse"of material loss that is inherent to conventional negative index composites.