Strong optical transport of a square-lattice photonic crystal due to the self-collimation effect and negative refraction effect

We investigate the optical transport properties of a square-lattice photonic crystal structure formed by air holes in a dielectric background with concave interface. A strong focusing beam of a point source is formed while a good-quality focus of a plane wave can also be formed by the photonic crystal structure. The focusing properties of the photonic crystal structure show that the self-collimation effect mainly occurs inside the photonic crystal region whereas the negative refraction effect occurs near the concave interface. A high efficiency of manipulation of the light propagation is realized. Contributions to the wave transport inside the photonic crystal region are different for the spatial frequencies in different zones because higher spatial frequencies are generated, mainly arising from the periodic potential of the finite photonic crystal structure.