Ring-shaped two-dimensional photonic crystal structures showing large higher-order stop-bands

Large absolute higher-order stop-bands are realized in two-dimensional photonic crystals of a square lattice with ring-shaped features using a real-valued genetic algorithm. The idea of the photonic crystals with ring-shaped features comes from the phenomenon of formation of the Arago spot in the middle of circular patterns in the process of optical lithography. As a result of the optimization, two structures showing large absolute higher-order stop-bands are obtained. The maximum absolute bandwidth of the higher-order band-gaps for the obtained structures is 0.1646(2πc/a), which is larger than the so far reported values for higher-order bands.