Figure 1: -Space topology. (a) The isofrequency contour for an isotropic dielectric is a sphere. For extraordinary waves in an extremely anisotropic uniaxial medium, the isofrequency contour becomes a hyperboloid which supports waves with unbounded wavevectors, in stark contrast to an isotropic medium. (b) A type 1 HMM has one component of the dielectric tensor negative and and supports low-and high-waves. (c) A type 2 HMM has two components of the dielectric tensor negative and and only supports high- waves.