Fig. 1. Schematic of Hilbert fractal structure. (a) Schematic of third-order Hilbert fractal curve structure; (b) a partial mask schematic of the positive space structure of Hilbert fractal superlattice

Fig. 2. Schematic of periodic superlattice structure masks with different shapes. (a) Square; (b) regular hexagon; (c) regular hexagon rotated by 30°

Fig. 3. Simulation and experimental (inset) diagrams of periodic superlattice structure diffraction with different shapes. (a) Square; (b) regular hexagon; (c) regular hexagon rotated by 30°

Fig. 4. Hilbert fractal diffraction diagrams. (a) Experimental diffraction diagram; (b) simulated diffraction diagram; (c) enlarged diagram of central part

Fig. 5. Experimental diagrams of fractal structure diffraction. (a) Hilbert fractal; (b) H-fractal^[22]