Figure 4

EFCs for the CH structure, the “ + ”-shaped (CS) structure and free space. The wave vectors kx and ky are normalized, and the cell models are shown here. The three EFCs have identical incident wave vectors ki (green solid arrow), but the refracted wave vectors kr (dotted arrows) vary. Because the wave directions must be normal to the EFCs, the directions of the group velocities (solid arrows) also vary.