A paper recently published in Optics Express has described how varying the orientation of a unit cell in a photonic crystal has provided a new way of controlling the path of a light beam. In "Tight control of light beams in photonic crystals with spatially-variant lattice orientation", infra-red light of one polarisation was shown to propagate through sharp bends, whilst the other polarisation passed in a straight line through the photonic crystal. The unit cell was designed for self-collimation using the plane wave expansion method before the spatial variation of the lattice was introduced. The resulting structure was simulated using FDTD code. Unlike standard graded index materials, which rely on refraction, these new photonic crystals rely on diffraction to achieve control light.