Figure 7

(a,b) Ewald constructions of a triangular PhC for different modes, while (c,d) Ewald constructions of a quasi-period PhC for different modes. The red circle describes the extraction cone. The blue arrow describes a guided mode. The yellow arrows and green arrows describe the harmonic falling in the extraction cone. It is more potential for a guided mode to satisfy the Bragg diffraction condition in a quasi-period PhC structure than that in an exact PhC structure.