Researchers use solar cells to achieve fast underwater wireless
communication
Optimized approach simplifies underwater optical data links; could enable devices that transmit data and produce power

Date:
February 16, 2022
Source:
Optica
Summary:
Researchers have shown that solar cells can be used to achieve
underwater wireless optical communication with high data rates. The
new approach - - which used an array of series-connected solar
cells as detectors - - could offer a cost-effective, low-energy
way to transmit data underwater.



FULL STORY ========================================================================== Although solar cells are typically designed to turn light into power, researchers have shown that they can also be used to achieve underwater wireless optical communication with high data rates. The new approach
-- which used an array of series-connected solar cells as detectors --
could offer a cost-effective, low-energy way to transmit data underwater.


========================================================================== "There is a critical need for efficient underwater communication to meet
the increasing demands of underwater data exchange in worldwide ocean protection activities," said research team leader Jing Xu from Zhejiang University in China. For example, in coral reef conservation efforts,
data links are necessary to transmit data from divers, manned submarines, underwater sensors and unmanned autonomous underwater vehicles to surface
ships supporting their work.

In the Optica Publishing Group journal Optics Letters, Xu and colleagues
report on laboratory experiments in which they used an array of
commercially available solar cells to create an optimized lens-free
system for high-speed optical detection underwater. Solar cells offer
a much larger detection area than the photodiodes traditionally used as detectors in wireless optical communication.

"To the best of our knowledge, we demonstrated the highest bandwidth ever achieved for a commercial silicon solar panel-based optical communication system with a large detection area," said Xu. "This type of system
could even allow data exchange and power generation with one device." Optimizing solar cells for communication Compared to using radio or
acoustic waves, light-based underwater wireless communication exhibits
higher speed, lower latency and requires less power.

However, most long-distance high-speed optical systems are not practical
for underwater implementation because they require strict alignment
between the transmitter emitting the light and the receiver that detects
the incoming light signal.



========================================================================== Because solar cells detect light from a large area and convert
it to an electrical signal, using them as detectors can ease the transmitter-receiver alignment requirement in an underwater wireless communication system. However, it has been difficult to achieve high
bandwidth because solar cells are optimized for energy harvesting rather
than communication.

"Until now, achieving high-speed links using off-the-shelf silicon
solar cells has required complex modulation schemes and algorithms,
which need intense computing resources that use extra power and create
a high processing latency," said Xu. "Using modeling and simulation
of connected solar cells, we optimized the peripheral circuit, which significantly improved the performance of our solar cell-based detector." Underwater testing The researchers tested the new design, which used a
3x3 solar array to create a detection area of 3.4 x 3.4 centimeters, in
a 7-meter-long water tank that emulated an underwater channel. Mirrors
were used to extend the pathlength of the optical signal, creating a transmission distance of 35 meters. The system showed reliable stability,
low power consumption and high performance. As the size of the solar
array increases from 1x1 to 3x3, the ?20-dB bandwidth increases from
4.4 MHz to 24.2 MHz.

Even though a simple modulation scheme was used, the new system exhibited
a much higher detection bandwidth -- which leads to a higher data rate --
than has been reported in other studies using commercial silicon solar
cells with a large detection area as detectors. Applying a reverse
bias voltage of 90 V boosted the bandwidth further, allowing them
to achieve a ?20-dB bandwidth of 63.4 MHz. This bandwidth enabled 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 quite cost effective," said Xu. "Beyond the underwater world, this type of detector
could also be used in visible light communication, a type of wireless communication that uses visible light from LEDs and other sources to
transmit data across distances." To optimize the system for real-world applications in underwater communication, the researchers plan to next
study its performance with weak optical signals.

This will show how well it works in muddy water and with movement. They
are also working to make the system more practical by fine tuning key parameters like the number of solar cells in the array and the required
reverse bias voltage.

========================================================================== Story Source: Materials provided by Optica. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Zhijian Tong, Xingqi Yang, Hao Zhang, Yizhan Dai, Xiao Chen,
Jing Xu.

Series-connected solar array for high-speed underwater
wireless optical links. Optics Letters, 2022; 47 (5): 1013 DOI:
10.1364/OL.449466 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220216112218.htm

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