Collimation effects controlled by near-zero refractive indices in highly anisotropic dielectric photonic crystals: Simulation and experiment

We demonstrate that 2D photonic crystals (PhCs), composed of dielectric rods and organized in rectangular lattices with precisely determined lattice constants, can support, at both TM and TE polarization of incident waves, unidirectional wave propagation with near-zero refractive indices (NZRIs) along short sides of unit cells. Wave propagation along the orthogonal direction, i.e., along long sides of unit cells, is fully suppressed that results in collimation of incident divergent waves. We show that the observed promising collimation effect is correlated with flat equi-frequency contours of PhCs, while operating frequency corresponds to the lower edge of the 2nd transmission band of the crystal media. For experimental verification of the simulation results, obtained by using full-wave electromagnetic solvers, we have recorded wave patterns beyond PhC fragment designed for operating frequency in the microwave range. Fabricated samples were composed of ceramic dielectric rods with mm-size diameters. The samples were illuminated by divergent TM polarized electromagnetic waves. Obtained results extend perspectives of low-loss artificial anisotropic media with NZRI properties for microwave and photonic applications.