Investigating the slow light in a 2D heterostructure photonic crystal composed of circular rods and holes in the square lattices

This theoretical work proposed a two-dimensional heterostructure of photonic crystal and investigated it for slow light applications. The structure includes two photonic crystals: circular Ge rods in the air background and circular holes in the Ge background. It is assumed that both of the crystals have square lattices. The band structures of the individual photonic crystals were studied to choose appropriate rod and hole radii to achieve common photonic band gaps. The effect of the possible combinations of the rod and hole radii was investigated on the group indices, bandwidths, and group index-bandwidth products. The optimum rod and hole radii were achieved. Moreover, the effect of displacements of the rods relative to the hole cylinders was studied, and the optimum displacement was calculated to achieve a high group index-bandwidth product value.