Diffraction engineering with braided modes in photonic crystal waveguide arrays

We consider discrete diffraction in coupled photonic crystal waveguides in a hexagonal lattice. We show that in these structures the (discrete) diffraction coefficient depends strongly on frequency and can even change sign. This behavior does not occur in photonic crystal waveguides in square lattices. This behavior is interesting in its own right and has intriguing consequences for the propagation of discrete spatial solitons.