Optimize design super collimation in square lattice two-dimensional photonic crystals

The plane wave expansion (PWE) method was used to get the three-dimensional band diagram and equifrequency surface (EFS). From the EFS the maximum flatness half width (MFHW) and its position were got. The relation between MFHW and filling fraction Pf, dielectric ratio εb/εa were given in order to get the optimal structure we employ in this paper. Then the maximum super collimation was given by beam propagation method (BPM).