Analyses of mode coupling in joined parallel phononic crystal waveguides

In this paper, we present an analysis of coupling effects in joined parallel phononic crystal waveguides. The finite difference time domain (FDTD) method with periodic boundary condition is adopted to analyze the band gaps and dispersion relation of phononic waveguides. The defect modes of a single phononic waveguide are analyzed and first discussed to serve as a basis for a joined waveguides system. Then, the dispersion relation and displacement field of supermodes of joined waveguides are calculated and discussed. Both displacement pattern and transmission coefficient of the defect modes are calculated. To transfer the power from one waveguide to another, the coupling lengths are evaluated by numerical experiments and can be understood by the concept of beat length. Finally, we analyze an elastic waveguide coupler and demonstrate that the coupler can potentially be employed as a power switch of the acoustic wave.