Pressure-Independent Acoustic-Vortex Communication With Enhanced-Capacity and Cryptographic Information by Free-Flooded Metasurfaces

Structured vortex beams have driven significant advances in multiplexing communication technologies and have been demonstrated experimentally in optics, electromagnetics, and airborne acoustics. However, the strong vibroacoustic coupling and high hydrostatic pressure hamper the experimental enhancement of acoustic information capacity in underwater communication via passively modulating coaxial beams. Here, we report the experimental realization of simultaneous information capacity enhancement and hybrid physical-computational camouflage in underwater free-space pressure-independent acoustic-vortex communication. Two inverse-designed free-flooded metasurfaces, with hydrostatically resilient stability and customized wave scattering characteristics, synthesize and demodulate experimentally coaxial vortex beams of different topological charges, enabling physically encrypted, port-to-port information transfer. A computational-mask encryption scheme further digitally conceals a plaintext image within two ciphertext bitstreams. Transmission of these ciphertexts through the synthesized hetero-order vortex beams experimentally confirms physical-computational anti-eavesdropping capabilities of the system. Our research charts an unprecedented path toward high-capacity, highly secure underwater acoustic communication technologies in the deep ocean.