Researchers have developed a prototype all-light communication system that can achieve seamless connectivity across air, land and underwater environments. The picture shows the laboratory where the research team tested the vehicle-mounted system. [Image: Yongwin Wang, Nanjing University of Posts and Telecommunications]
Users of mobile communication systems may operate them in all sorts of circumstances: on rainy days, in bright sunshine, on mountaintops, in moving vehicles and even underwater. Running the system on light signals instead of radio waves has benefits but also introduces more challenges, such as optical path alignment and atmospheric attenuation of different wavelengths.
Now, researchers in China have reportedly designed a prototype all-light communication system that spans the spectrum from deep ultraviolet to near-infrared (Opt. Express, doi:10.1364/OE.543730). The proof-of-concept mobile devices achieve full-duplex light communication of up to 4 Mbps under varying conditions, including outdoors at night, outdoors in full sunlight and submersed in a water tank.
The push toward light communication
Light-based communication systems have distinct advantages over their radio-frequency counterparts. For example, light signals don’t require licensing, are immune to electromagnetic interference and can transmit at high data rates. The downsides are that fog and air pollution can interfere with or disperse light signals, and that bright sunlight can muddle outdoor transmissions.
In designing their system, researchers from the Nanjing University of Posts and Telecommunications employed a combination of optical technologies developed for fixed communication nodes. First, they outfitted two robotic vehicles with full-duplex green-light transmitters and receivers operating under Transmission Control Protocol/Internet Protocol (TCP/IP) standards. The devices used a 520-nm green lamp as the optical source and an avalanche photodiode and an image identification module at the receiving end.
Changing the injection current modulated the light intensity and shifted the emission peak of the signal. A three-axis gimbal stabilizer on each robot, controlled by real-time feedback signals from the image identification module, kept the optics and electronics in alignment with each other.
Increasing versatility
They demonstrated bidirectional light transmission between mobile network modes in these environments with a maximum modulation bandwidth of 4 Mbps—fast enough for video and audio transmission.
For sunny days, the Nanjing team switched to 275-nm deep-ultraviolet communication devices connected to the rest of the system via ethernet switches. Complementing the green- and deep-UV modes were a full-duplex blue laser communication system (450-nm wavelength) and a system with 850-nm laser diodes.
The researchers tested their system on an outdoor lawn at night, in full sunlight and in an indoor water tank. They demonstrated bidirectional light transmission between mobile network modes in these environments with a maximum modulation bandwidth of 4 Mbps—fast enough for video and audio transmission.
“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,” lead author Yongwin Wang said in a press statement.