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Using Infrared Light to Safely Transfer High Power Levels

Visualize a smartphone automatically starting to charge as users enter an airport or grocery shop. Thanks to a new wireless laser charging technology that resolves some of the issues that have impeded earlier attempts to create secure and practical on-the-go charging systems, this might become a reality one day.

Researchers created a new system that uses infrared light to safely transfer high levels of power over distances of up to 30 meters.

Researchers created a new system that uses infrared light to safely transfer high levels of power over distances of up to 30 meters. This type of long-range optical wireless power transfer system could enable real-time power transmission to fixed and mobile receivers. Image Credit: Jinyong Ha, Sejong University

The researchers explain their innovative method, which employs infrared light to securely transfer huge levels of power, in the Optica Publishing Group journal Optics Express.

According to laboratory studies, it was capable of transferring 400 mW of light power up to 30 m. With future advancement, this power could be boosted to levels required to charge mobile devices. It is adequate for charging sensors.

The ability to power devices wirelessly could eliminate the need to carry around power cables for our phones or tablets. It could also power various sensors such as those in the Internet of Things (IoT) devices and sensors used for monitoring processes in manufacturing plants.

Jinyong Ha, Study Team Leader, Sejong University, South Korea

Long-distance wireless power transfer has been researched using a variety of methods, however it has been challenging to reliably transmit enough power across meter-level distances. The researchers developed distributed laser charging, which has recently received increasing attention for this application because it offers secure high-power illumination with less light loss, to get around this problem.

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. It also automatically shifts to a safe low power delivery mode if an object or a person blocks the line of sight.

Jinyong Ha, Study Team Leader, Sejong University, South Korea

Going the Distance

Distributed laser charge functions similarly to a conventional laser, except the optical parts of the laser cavity are split into a transmitter and a receiver rather than being combined into one unit. The device may provide light-based power when the transmitter and receiver are in sight of each other because a laser cavity is created between them over the air or free space.

To achieve hazard-free power distribution in the air, the system automatically shifts to a power-safe mode whenever an obstruction blocks the transmitter-receiver line of sight.

Researchers employed an optical power source with an erbium-doped fiber amplifier and a core wavelength of 1550 nm in the novel system. At the power levels utilized, this wavelength range is in the safest part of the spectrum and does not harm the skin or eyes in humans. A wavelength division-multiplexing filter, another essential component, produced a narrowband beam with optical strength that was appropriate for open space propagation.

In the receiver unit, we incorporated a spherical ball lens retroreflector to facilitate 360-degree transmitter-receiver alignment, which maximized the power transfer efficiency. We experimentally observed that the system’s overall performance depended on the refractive index of the ball lens, with a 2.003 refractive index being the most effective,” said Ha.

Laboratory Testing

The scientists separated a transmitter and a receiver by 30 m to show how the system worked. The receiver unit featured a retroreflector, a photovoltaic cell that transforms the optical signal into electrical power, and an LED that glows when power is being given.

The transmitter was made of the erbium-doped fiber amplifier optical source. It would be simple to include this receiver, which measures roughly 10 by 10, into gadgets and sensors.

According to the experimental findings, a single-channel wireless optical power transfer system is capable of transmitting 400 mW of optical power over a 30-meter distance with a 1-nm channel linewidth.

This was turned by the photovoltaic to electrical power of 85 mW. The scientists also demonstrated how, when the sight line was broken by a human hand, the device switched immediately to a safe power transfer mode. The transmitter generated a very low-intensity light in this mode that posed no danger to people.

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

Jinyong Ha, Study Team Leader, Sejong University, South Korea

Scientists are working to make the technology more useful now. For instance, the solar cell’s efficiency could be raised to more effectively convert light into electrical power. Additionally, they want to figure out how to charge numerous receivers at once using the technology.

The Ministry of Science and ICT of the Korean government provided funding for the Institute of Information and Communications Technology Planning & Evaluation grant, which supports this effort.

Journal Reference

Javed, N., et al. (2022) Long-range wireless optical power transfer system using an EDFA. Optics Express.


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