Analysis of a hyperprism for exciting high-k modes and subdiffraction imaging

We study the effect of resonances on the ability of prisms made of hyperbolic metamaterials in the canalization regime (such as wire array media) to couple evanescent high spatial frequencies (high-$k$ modes) to low spatial frequencies that propagate in the far-field zone. Using simple analytical models, we calculate the far-field propagation from the hyperprism. The resonant nature of the metal wire segments within the prism yields a transmission function identical to that of a grating, but with periodicity proportional to the wavelength, making the hyperprism function like a nondispersive grating. Numerically compensating the effect of resonances allows the hyperprism to be used as a one-dimensional imaging device able to resolve feature sizes below the diffraction limit if the host medium has a low refractive index. Furthermore, the hyperprism enables coupling of propagating plane waves to a range of high-$k$ modes that can be increased by increasing the angle of the prism. We quantify how this tunable, nondispersive excitation of high-$k$ modes opens up possibilities for new experimental approaches for coupling to plasmonic systems and for increased axial resolution in total internal reflection imaging, in particular in the terahertz spectrum.