The light control performance of photonic crystals is closely related to their lattice constant, which typically requires the lattice constant to be in the same order of magnitude as the working wavelength. In crystal materials, the photonic crystal structure is formed by the periodic arrangement of units with different dielectric constants than the crystal itself in space, and its lattice constant depends on the size of the unit and the gap between adjacent units.
Click here for original story, Fabrication of nanoscale photonic crystals with an ultrafast laser
Source: Phys.org