Cavities without confinement barrier in incommensurate photonic crystal superlattices

We design and fabricate cavities without confinement barrier by combining two incommensurate photonic crystal superlattice waveguides. A resonant mode with a high quality factor shows up in the pass band of waveguides. The experimental measurement confirms the theoretical prediction of coexistence of localized cavity mode and continuous waveguide mode with high coupling efficiency in the same frequency and space regime, which is more like the conventional Anderson localization within photonic band gaps in disordered structures.