A two-dimensional photonic crystal with six large bandgaps formed by a hexagonal lattice of anisotropic cylinders

The plane-wave expansion method is used to calculate the band structure of a two-dimensional photonic crystal formed by a hexagonal structure of anisotropic cylinders. Two cylindrical inclusions in the unit cell have two different radii, R₁ and R₂ (R₁<R₂). By reducing the symmetry of the structure and choosing appropriately parameters R₂ and s=R₁/R₂ (s<1), we obtain six large complete bandgaps, among which three are over 0.05 \omega_e (where \omega_\rm e=\frac2\pi ca) in the high region of the normalized frequency (however, one of these over 0.065 \omega_e is not stable). There are two other stable complete bandgaps in the low-frequency region.