Nearly flat donor and acceptor bands of two-dimensional photonic crystals with periodic vacancy defects

We have calculated the photonic band structures of two-dimensional triangular photonic crystals with periodic vacancy defects formed by removing air holes or dielectric rods. We found that both periodic donor and acceptor defects can create nearly flat, angle-independent, extremely narrow impurity bands in the photonic band gaps. We also showed that the center frequency and the linewidth of the impurity bands can be controlled by using the period (doping density) and the size of the defects. These properties of periodic vacancy defects can be useful for angle-independent band-pass and band-stop filters.