Figure 1
Mode diagram for orthogonality and orthogonality breaking.
The green, black and red arrows denote the longitudinal wavenumbers of the fundamental, first and second modes, respectively. The length of each arrow indicates the magnitude of the corresponding wavenumber. The small images above the arrows depict the field distributions of the different transverse modes at the cross section. The vertical ordinate represents the frequency. f1 and f2 are the cutoffs for the first and second modes, respectively and the purple cylinders represent the investigated waveguide. The purple lines indicate the wavenumbers of the periodic corrugations. (a) No interference occurs among the different modes in a straight duct because of their orthogonality. The left-hand side shows the incident waves and the right-hand side depicts the output waves. (b) Mode-interaction diagram for orthogonality breaking: incident fundamental modes (left) and mode interactions in the periodic waveguide (right). (c) A three-mode interaction to induce single-mode transparency: two-mode interaction diagrams (left), the interaction-coupling process (middle) and the interaction diagram of the fundamental mode, the first mode and the single remaining second mode (right).
