Coupled propagation of acoustic topological states

Abstract We theoretically and experimentally investigate the coupled propagation of two pseudospin states in an acoustic topological heterostructure. Within the framework of coupled-mode theory, the heterostructure is mapped onto a two-waveguide model, in which the two pseudospin topological states serve as guiding modes. The propagation constants of the individual topological states and the coupling strength between them are quantitatively extracted from the projected band structures of supercells. When the two topological states are decoupled, acoustic energy remains confined to the excited topological interface. When the two topological states are coupled, acoustic energy undergoes Bloch oscillation between two topological interfaces. Notably, the energy-transfer coefficient of the Bloch oscillation can be tuned by introducing interface detuning. Owing to the frequency dispersion of the coupling strength, the heterostructure can function as a wavelength-selective demultiplexer. This work establishes a generalized coupled-mode framework for the quantitative analysis and flexible manipulation of topological-state coupling, offering new insights into the design of topologically protected acoustic devices with controllable multichannel functionalities.