Flat focusing mirrors with two-dimensional chirped photonic crystals

Flat focusing mirrors without any optical axis have been investigated by two-dimensional chirped photonic crystals. The principle of flat focusing mirror is similar to Veselago flat lens, which allows the beam focusing in the near field. The key idea of 2D chirped PhCs is to provide anomalous diffraction that can restrain a beam spreading and even focus a divergent beam upon reflection. Different focusing phenomena of the three 2D PhCs are shown in this paper and importantly, all of them have transversal invariance (lack of an optical axis).