Radio waves do not travel well through water, so devices such as ROVS (Remote Operated Vehicles) must be tethered to their operator via a communications cable. According to a new study, however, solar panels could soon enable practical work underwater based on light communications.
First, various groups have used pulses of laser light to transmit data underwater. The functionality of such systems has however been limited because the emitter which emits the light must be precisely aligned with the photodiode which receives it. Due to this limitation, the two units must be located fairly close to each other.
Solar cells, on the other hand, are designed to collect incoming light scattered from a wide area. Unfortunately, however, they are much better at funneling that light into an electrical circuit than at converting it to a data signal. A team from the Chinese University of Zhejiang now claims to have corrected this shortcoming.
“Until now, achieving high-speed links using off-the-shelf silicon solar cells has required complex modulation schemes and algorithms, which require intense computing resources that use additional power and create high processing latency,” said lead scientist Prof. Jing Xu. “Using [computer] modeling and simulation of connected solar cells, we optimized the peripheral circuit, which significantly improved the performance of our solar cell-based detector.”
The resulting configuration incorporated a 3 x 3 array of linked solar cells, creating a detection area of 3.4 x 3.4 cm (1.3 inches). This array was placed at one end of a 7-meter (22.9 ft) long water tank, at the other end of which was a laser diode. However, a series of mirrors inside the tank forced the laser light to travel a total of 35 meters (114.8 ft) to get from the diode to the solar panel.
In testing, the system reportedly exhibited reliable stability, low power consumption, and much higher sensing bandwidth than reported in previous studies that used commercial solar cells for the same purpose. Specifically, the scientists managed to achieve a -20 dB bandwidth of 63.4 MHz, which enabled an underwater wireless optical link of 35 meters/150 Mbps (megabits per second).
Xu and his colleagues now plan to study the setup’s effectiveness in detecting faint optical signals, similar to what it should work with in muddy or otherwise murky water.
The research is described in a recently published article in the journal Optical letters.
Source: Optica via EurekAlert