(a) Schematic diagram illustrating the scattering of an incident wave by a square photonic potential barrier. (b) A square photonic potential barrier constructed by a PC sandwich structure. Both PC1 and PC2 are square lattice dielectric photonic crystals, but with different length scales ( and ). The PC1 and PC2 domains have a thickness of and , respectively. The length scale change induces a rigid band shift of the conical dispersion. Adapted from .