Dual-function acoustic-to-optical transducers for underwater encrypted communication and subwavelength distance measurement.

The development of next-generation communication networks with integrated multifunctional capabilities across diverse environments-spanning space, air, land, and sea-requires efficient transduction between disparate information carriers. While substantial progress has been made in transducers for terrestrial applications, devices that unify sensing and communication in underwater environments remain in their infancy. We present an experimental demonstration of a dual-function acoustic-to-optical transducer, enabling simultaneous underwater encrypted communication and distance measurement. Specifically, the transducer efficiently converts underwater acoustic signals into single photons for transmission through optical fibers over distances of up to 50 kilometers. Concurrently, we achieve deep subwavelength precision in distance measurement, reaching an accuracy of 1/250 of the acoustic wavelength, while maintaining robust communication performance. Furthermore, we implement coincidence counting-based encryption to embed acoustic information within noisy optical fiber networks. This work represents a notable step toward next-generation network architectures that seamlessly integrate sensing and communication across heterogeneous media.