Effects of interference on couplings in three optical waveguides

In the interaction of a coupled, three-optical-waveguide system, it is shown that, even when there is no direct coupling between two phase-matched waveguides, the high-efficiency coupling between them can be established by the indirect coupling through the third phase-mismatched waveguide. It is also shown that the coupling between the two phase-matched waveguides, having direct coupling, can be effectively vanished by introducing the third phase-mismatched waveguide.