Solar cells used to boost wireless underwater communications
Radio waves don't travel well through water, which is why devices such as ROVS (remotely operated vehicles) have to be linked to their operator via a communications cable. According to a new study, however, solar panels may soon allow for practical underwater light-based communications.
First of all, various groups have already used pulses of laser light to transmit data underwater. The functionality of such systems has been limited, though, due to the fact that the transmitter which emits the light has to be precisely aligned with the photodiode that receives it. Because of this limitation, the two units have to be located quite close to one another.
Solar cells, on the other hand, are designed to gather scattered incoming light from a wide area. Unfortunately, however, they're much better at channelling that light into an electrical circuit than they are at converting it into a data signal. A team from China's Zhejiang University now claims to have addressed that shortcoming.
"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 the lead scientist, Prof. Jing Xu. "Using [computer] modelling and simulation of connected solar cells, we optimized the peripheral circuit, which significantly improved the performance of our solar cell-based detector."
The resulting setup incorporated a 3 x 3 array of linked solar cells, creating a 3.4 x 3.4-cm (1.3-in) detection area. That 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. A series of mirrors within the tank, however, caused the laser light to have to travel a total of 35 meters (114.8 ft) to get from the diode to the solar array.
When tested, the system reportedly exhibited reliable stability, low power consumption, and a much higher detection bandwidth than has been reported in previous studies which used commercial solar cells for the same purpose. More specifically, the scientists managed to achieve a -20-dB bandwidth of 63.4 MHz, which enabled a 35-meter/150-Mbps (megabits per second) underwater wireless optical link.
Xu and colleagues now plan on studying how effective the setup is at detecting weak optical signals, similar to those that it would have to work with in muddy or otherwise murky water.
The research is described in a paper that was recently published in the journal Optics Letters.