Systematic investigation of misalignment effects at junctions between feeder waveguide and photonic crystal channel waveguide

The coupling between two different guiding elements, a ridge waveguide and a photonic crystal channel waveguide (obtained by a single line defect in the crystal), is investigated both computationally and experimentally. The study concentrates on the effects that different widths for the ridge waveguide, as well as positions with respect to the channel waveguide, have on the coupling efficiency--thus allowing the assessment of the sensitivity to drift effects that can occur in fabrication--and the optimal design parameters. Characterization of devices fabricated in GaAs/AlGaAs epitaxial waveguide material shows good overall agreement with the simulated trends for all the configurations of the junction considered. On the other hand, the trends from experiments also demonstrate reduced dependency of transmission on mismatch, by comparison with simulations. Finally, the configuration, which allows optimum coupling and transmission (98%), is found to be verified by both simulation and characterization.