Researchers from Sejong University have developed a new system to transmit power over 30 meters using infrared light wirelessly.

During laboratory tests, researchers demonstrated that the new system could transfer 400 mW of light power. For now, this amount of power is enough for charging sensors; however, further progress could mean enough high levels to charge mobile phones in various public places.

The research has been published in Optics Express.

"The ability to power devices wirelessly could eliminate the need to carry around power cables for our phones or tablets," said research team leader Jinyong Ha from Sejong University in South Korea. "It could also power various sensors such as those in Internet of Things (IoT) devices and sensors used for monitoring processes in manufacturing plants."

Up to now, a couple of methods have been studied to transfer power over long ranges wirelessly; however, it wasn't that easy to send enough power in a safe way. Therefore the researchers worked on a novel method called distributed laser charging. According to the press release, this method provides safe high-power illumination with less light loss.

Distributed laser charging works almost like traditional lasers; however, the optical components of the laser cavity are not integrated into one device but are separated into a transmitter and receiver.

When two are in the line of sight, a laser cavity is created between the transmitter and receiver over the air. This allows the system to deliver light-based power. When a barrier cuts the transmitter-receiver line of sight, the system switches to power-safe mode and maintains hazard-free power delivery in the air.

While developing the new system, researchers used an erbium-doped fiber amplifier optical power source with a central wavelength of 1550 nm. This wavelength is harmless to human eyes or skin at the power used as it's at a safe point on the spectrum.

"While most other approaches require the receiving device to be in a special charging cradle or to be stationary, distributed laser charging enables self-alignment without tracking processes as long as the transmitter and receiver are in the line of sight of each other," said Ha. "It also automatically shifts to a safe low power delivery mode if an object or a person blocks the line of sight."

The researchers set a transmitter and a receiver 30 meters (98 feet) apart to see how the system worked. The transmitter was made of the erbium-doped fiber amplifier optical source. At the same time, the receiver consisted of a retroreflector, a photovoltaic cell converting the optical signal to electrical power, and an LED capable of illuminating while power is being delivered. The 10-by-10 millimeter receiver is small enough to be integrated into devices.

The results revealed that a single-channel wireless optical power transfer system could create an optical power of 400 mW with a channel linewidth of 1 nm over a distance of 30 meters.

"Using the laser charging system to replace power cords in factories could save on maintenance and replacement costs," said Ha. "This could be particularly useful in harsh environments where electrical connections can cause interference or pose a fire hazard."