Experimental demonstration of mode-division multiplexing and demultiplexing for acoustic waves

Underwater communication has garnered significant attention due to its pivotal role in the offshore development, with recent efforts particularly focused on enhancing information capacity. Here, we investigate the mode-division multiplexing and demultiplexing of acoustic waves in a coupled waveguide array. First, we theoretically derive the two-dimensional field distribution required for generating supermode propagation. The results demonstrate that the number of acoustic supermodes corresponds precisely to the number of waveguides. Subsequently, we design a 3 × 2 waveguide array and validate the plane wave-like propagation characteristics of acoustic supermodes. Remarkably, supermode propagation exhibits broadband stability, which can be effectively multiplexed with the excitation frequency to significantly enhance communication information capacity. Furthermore, by leveraging the multimode interference effect, we simultaneously achieve the demultiplexing and multiplexing of acoustic supermodes through the introduction of a phase onto the excitation mode. Finally, we demonstrate the data transmission capability by encoding four English letters, and the encoded information can be directly recognized in the output sound intensity without additional decoding operations. Capitalizing on the benefits of mode diversity and the high fidelity of the supermode propagation, our proposed approach holds great potential for advancing high-fidelity signal transmission in complex acoustic networks and underwater communication systems.