Solar cells enable high-data-rate underwater wireless communications

While solar cells are typically designed to convert light into electricity, the researchers showed that they could also be used to allow for high-data-rate underwater wireless optical communications. The new method, which uses a series of solar cells as detectors, could provide a cost-effective, low-energy way to transmit data underwater.

Solar cells enable high-data-rate underwater wireless communications
The use of solar cell arrays as detectors in underwater wireless optical communication systems can achieve high data rates.

Researchers have shown that high data rates can be achieved by using solar arrays as detectors in underwater wireless optical communication systems. Image source: Xu Jing, Zhejiang University
“Efficient underwater communication is urgently needed to meet the growing need for underwater data exchange in marine conservation activities around the world. For example, in coral reef conservation efforts, data links are needed to transfer data from divers, human-crewed submarines, underwater sensors. And wireless Human autonomous underwater vehicles are transmitted to surface ships that support their work,” said Xu Jing, head of the research team from Zhejiang University in China.
In the journal Optics Letters, Xu and colleagues report laboratory experiments using a series of commercially available solar cells to create an optimized lensless system for high-speed optical inspection underwater. Solar cells offer a larger detection area than photodiodes traditionally used as detectors in wireless visual communications. “To the best of our knowledge, we demonstrate the highest bandwidth achieved by a commercial silicon solar panel optical communication system with a large detection area,” Xu said. “This type of system can even exchange data and generate electricity with one device.”

Optimizing solar cells for communications

Light-based underwater wireless communications have higher speeds, lower latency, and less power consumption than radio or sound waves. However, most long-distance high-speed optical systems are not suitable for underwater implementation. They require strict alignment between the transmitter that emits light and the receiver that detects the incoming light signal. [Underwater acoustic communication]

Solar cells enable high-data-rate underwater wireless communications
Light-Based Underwater Wireless Communication Has Higher Speed, Lower Latency, and Less Power

The researchers tested the detector, made of a 3×3 solar cell array, in a 7-meter-long tank that simulates an underwater passage. Mirrors are used to extend the path length of the optical signal. Image source: Xu Jing, Zhejiang University
Since solar cells detect light from large areas and convert it into electrical signals, using them as detectors can alleviate the transmitter-receiver alignment requirements in underwater wireless communication systems. However, high bandwidth is difficult because solar cells are optimized for energy harvesting rather than communication. Until now, implementing high-speed links using off-the-shelf silicon solar cells required complex modulation schemes and algorithms, which required significant computational resources to consume additional power and generate high processing delays. By modeling and simulating the connected solar cells, the research team optimized the peripheral circuit and significantly improved the performance of the solar cell-based detector.

underwater test

The researchers tested the new design in a 7-meter-long tank that simulates an underwater channel, using a 3-by-3 solar cell array to create a 3.4-by-3.4-centimeter detection area. Mirrors were used to extend the path length of the optical signal, creating a transmission distance of 35 meters. The system exhibits reliable stability, low power consumption, and high performance. As the size of the solar array increases from 1×1 to 3×3, the -20-dB bandwidth increases from 4.4 MHz to 24.2 MHz. Despite using a simple modulation scheme, the new system shows a higher detection bandwidth than reported in other studies using commercial silicon solar cells with large detection areas as detectors – which results in higher data rates. Applying a reverse bias voltage of 90 V further increased the bandwidth, allowing them to achieve a -20-dB bandwidth of 63.4 MHz. This bandwidth enables a 35 m/150 Mbps underwater wireless optical link using the simplest form of amplitude-shift keying modulation.
“Because solar cells are mass-produced, the proposed scheme is very cost-effective,” Xu said. “Besides the underwater world, this type of detector can also be used for visible light communication, which is a wireless communication, Using visible light from LEDs and other sources to transmit data over long distances.” The researchers plan to study its performance under weak light signals next to optimize the system for practical use in underwater communications. This will show how well it works in muddy water and motion. They also make the system more practical by vital fine-tuning parameters such as the number of solar cells in the array and the required reverse bias voltage.

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