Mini-stop bands in single-defect photonic crystal waveguides

We numerically study single-defect photonic crystal waveguides obtained from a triangular lattice of air holes in a dielectric background. It is found that, for medium-high air filling ratios, the transmission has very small values in narrow frequency regions lying inside the photonic band gap - the so-called mini-stop bands. Two types of mini-stop bands are shown to exist; one of which is due to the multimode nature of the waveguide. Their dependence on the length of the waveguide and on the air filling ratio is presented.