Article Dans Une Revue Proceedings of the National Academy of Sciences of the United States of America Année : 2017

High-speed acoustic communication by multiplexing orbital angular momentum

Résumé

Long-range acoustic communication is crucial to underwater applications such as collection of scientific data from benthic stations, ocean geology, and remote control of offshore industrial activities. However, the transmission rate of acoustic communication is always limited by the narrow-frequency bandwidth of the acoustic waves because of the large attenuation for high-frequency sound in water. Here, we demonstrate a high-throughput communication approach using the orbital angular momentum (OAM) of acoustic vortex beams with one order enhancement of the data transmission rate at a single frequency. The topological charges of OAM provide in-trinsically orthogonal channels, offering a unique ability to multi-plex data transmission within a single acoustic beam generated by a transducer array, drastically increasing the information channels and capacity of acoustic communication. A high spectral efficiency of 8.0 ± 0.4 (bit/s)/Hz in acoustic communication has been achieved using topological charges between −4 and +4 without applying other communication modulation techniques. Such OAM is a completely independent degree of freedom which can be readily integrated with other state-of-the-art communication modulation techniques like quadrature amplitude modulation (QAM) and phase-shift keying (PSK). Information multiplexing through OAM opens a dimension for acoustic communication, providing a data transmission rate that is critical for underwater applications. high-speed acoustic communication | high spectral efficiency | orbital angular momentum | multiplexing | demultiplexing W ith the increasing amount of human activities underwater including unmanned vehicle exploration, offshore industrial applications, and remote ocean environment monitoring, the development of underwater communication has become essential. The intrinsic strong absorption of microwave and mid-and far-infrared radiations by water molecules limits the propagation distance of radio frequencies to mere centimeters (1-4), making rf wireless communication approaches impossible. On the other hand, optical waves are scattered by objects in the ocean such as small particles, debris, and marine life due to the shorter wavelengths, limiting the range of optical communication underwater to be within just 200 m (5-7). Presently, acoustic waves are the only option for long-range (over 200 m) underwater communications. However, the applicable band-width of acoustic waves is limited within 20 kHz because the higher damping loss of high-frequency acoustic waves in water reduces the propagation distance to less than a kilometer range (8). Such a low carrier frequency limits drastically the spectral bandwidth and data rate accessible for data transmission. Although spectral efficiency has been improved through recent advanced communication technologies such as differential phase-shift keying (PSK) and quadrature amplitude modulation (QAM), the number of available data transmission channels remains tied to the low carrier frequency (9-13). We propose to overcome such a fundamental limitation in acoustic communication by using additional spatial degrees of freedom for data transmission, such as orbital angular momentum (OAM) of the information-carrying wave whose wavefront has helical patterns (i.e., vortex beams). This spatial degree of freedom increases the data transmission capacity, which is given by the product of the available frequency bandwidth and number of modes used for communication, at the same frequency band. In optics and microwaves, vortex or helical beams with different OAM topological charges are generated by spatial light modu-lator, metasurfaces, or parity-time symmetric ring resonator and multiplexed through beam splitters or spin-orbital coupling to demonstrate a significant increase of data transmission capability (14-19). For acoustics, the underwater propagation of vortex beams with single topological charge was demonstrated with active phase arrays (20, 21). Passive acoustic phase modulation structures were proposed to generate single-charge vortex beams (22-25). These acoustic vortex beams were used to develop acoustic tweezers, and screwdrivers for particle trapping, levita-tion, and manipulations (26-30). However, information encoding through multiple OAM channels multiplexing/demultiplexing remains unexplored. Here, we demonstrate that the data transmission rate can be dramatically enhanced at a single frequency modulation by using the spatial degree of freedom OAM of acoustic vortex beams. The proposed high-throughput acoustic communications with OAM multiplexing are experimentally demonstrated in air here due to the facility limitations in underwater acoustics, but this technique can be readily extended to underwater applications because the wave physics in air and underwater are the same for low-frequency acoustics below Significance Acoustic communication is critical for underwater application such as deep-ocean scientific explorations and offshore industrial controls. This is because other techniques using electromagnetic waves are difficult for underwater applications due to the strong absorption of water. Optical communication, on the other hand, suffers from the light scattering, making long-range underwater optical communication very challenging. Therefore, using acoustic waves to transmit information is currently the dominant technique for underwater applications. However, the low-frequency bandwidth available limits the data transmission rate and information capacity. We propose and experimentally demonstrate an approach using the orbital angular momentum (OAM) of acoustic vortex beams, which provides an independent channel that enhances the data transmission rate. This OAM multiplexing method will significantly impact future underwater communications.

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hal-02145716 , version 1 (03-06-2019)

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Chengzhi Shi, Marc Dubois, Yuan Wang, Xiang Zhang. High-speed acoustic communication by multiplexing orbital angular momentum. Proceedings of the National Academy of Sciences of the United States of America, 2017, 114 (28), pp.7250-7253. ⟨10.1073/pnas.1704450114⟩. ⟨hal-02145716⟩
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