Luneburg and flat lens based on graded photonic crystal

•Square-lattice graded photonicphotonic crystals employed for designing Luneburg and Flat Lens is presented.•The structures of the flat lens are optimized.•The influence of imperfect gradient on the focusing characteristics is also analyzed.

Square-lattice graded photonic crystals employed for designing Luneburg and Flat Lens is presented. Comparable simulation of the Luneburg lens with TE and TM polarizations predicts that TM lens possesses of enlarged transmission bandwidth and strengthened focusing ability, in comparison with TE lens. As a typical simplified counterpart, the evolution of focusing intensity and numerical aperture of the flat lens is achieved. What is more, those Luneburg and Flat Lens can withstand imperfect gradients in structure design. This will provide a guidance to produce a high quality focusing lens with small size, short focal length and large numerical aperture applied in the integrated photonic devices.