Light-Based Communication Connects Air, Land, Sea

A team of researchers from Nanjing University of Posts and Telecommunications has demonstrated a prototype mobile all-light communications network, paving the way for seamless connectivity across air, land, and underwater environments, even when communication nodes are on a moving vehicle. The advance could enable uninterrupted data exchange in dynamic and challenging settings for navigation, emergency response, research, and commercial operations.

According to research team leader Yongjin Wang, the network combines different light sources to allow uninterrupted connectivity while at the same time dynamically aligning optical paths between moving nodes. “This enables two-way real-time data transmission, ensuring reliable communication and data exchange within and across networks, regardless of the environment,” he said.

The research demonstrated how two prototype communication apparatuses separately deployed on two moving vehicles can establish bidirectional light transmission between moving network nodes across air and underwater environments.

“Our new wireless optical communication system could enable continuous connectivity for essential mobile nodes like drones, vehicles and ships,” said Wang. “This could transform the way mobile networks operate.”

The new work builds on previous experiments in which the researchers demonstrated all-light communication based on fixed communication nodes.

Researchers have demonstrated a prototype all-light communication network that can achieve seamless connectivity across air, land, and underwater environments, even when communication nodes are on moving vehicles. The laboratory where they tested the vehicle-mounted system is pictured. Courtesy of Nanjing University of Posts and Telecommunications/Yongjin Wang.

“In this work, we solve the challenging issue of dynamic optical path alignment to achieve mobile full-duplex light communication,” said Wang. “We also provide a new network architecture that ensures even and accurate comprehensive connectivity across all its parts while simultaneously supporting fast, two-way data exchange.”

The new system combines mobile green light communication under the transmission control protocol/internet protocol (TCP/IP) scheme with blue laser communication for data exchange between underwater vehicles. The researchers also used a deep UV light communication system for "solar-blind" wireless data transmission that does not suffer from interference from solar radiation and an 850-nm laser diode communication system to receive data. All the communication systems were connected in series via ethernet switches that provide access to various terminals, including sensors and personal computers.

To establish bidirectional light transmission across air and underwater environments between moving network nodes, optical alignment is required among the various communication systems. The researchers accomplished this by building an image identification module and a full-duplex light communication module that are packaged together and fixed on a three-axis gimbal stabilizer.

The image identification module captures images of the light coming from the other communication systems and provides real-time feedback signals to control the three-axis gimbal stabilizer. This allows the setup to dynamically maintain the optical path alignment between the two light communication ends, making mobile bidirectional data transmission under the TCP/IP scheme possible. The researchers also developed a complete mapping network architecture to enable seamless and balanced data flow between all nodes, ensuring real-time, bidirectional data transmission so that information can be sent and received simultaneously without delays or data loss.

The researchers demonstrated their new network by developing two green-light communication devices with image identification modules that were each mounted on a three-axis gimbal stabilizer and installed on separate moving vehicles.

During tests carried out on an outdoor lawn at night and during full sunlight as well as with an indoor water tank, the researchers demonstrated bidirectional light transmission between mobile network nodes across air and underwater environments with a maximum modulation bandwidth of 4 Mbps, which is fast enough for video and audio transmission. The system was also able to transmit video communication seamlessly across both environments and provide internet access through a Wi-Fi modem.

Next, the researchers want to establish an all-light communication network that fuses wired modes with wireless moving and fixed nodes and light sources with different wavelengths. They would also like to eventually combine mobile all-light communication with radio, sonar, and gas communication technologies to establish a future communication network.

“In the future, we could combine on-chip light communication with free-space light communication to create an all-light interconnection communication network, which could transmit and receive data across space and chip environments for seamless connectivity,” said Wang. “Such sophisticated all-light interconnection networks could be used to develop advanced information processing and computing systems.”

The research was published in Optics Express (www.doi.org/10.1364/OE.543730).