Coupling into slow-mode photonic crystal waveguides

We study efficient injectors for coupling light from z-invariant ridge waveguides into slow Bloch modes of single-row defect photonic crystal waveguides. Two-dimensional vectorial computations performed with a Bloch mode theory approach predict that very high efficiencies $(>90\%)$ can be achieved for injector lengths of only a few wavelengths in length, even for small group velocities in the range of $c∕100–c∕400$. This result suggests that photonic crystal devices operating with slow waves can be interfaced with classical waveguides without sacrificing compactness.