Flat lens achieved by all-dielectric photonic crystal with near-zero refractive index

We realize double zero-refractive-index material by dielectric photonic crystals (PCs) with hexagonal lattice at the frequencies near the degenerated Dirac point. We demonstrate such PC can be used as a flat lens which has matched impedance to the air and low loss. The performance of the lens is verified by good near-field imaging both theoretically and experimentally. Further, the zero-refractive-index PC is extended to the plane wave generator and concave lens at terahertz frequencies. Our design provides potential for practical applications of wave manipulation.