“From the inception of the wireless system... I saw that this new art of applied electricity would be of greater benefit to the human race than any other scientific discovery, for it virtually eliminates distance."

Nikola Tesla, 1926

Laser beams are most often used in communications, precision cutting, or even science fiction weapons. But NTT and Mitsubishi Heavy Industries (MHI) have been looking into a quite different, intriguing possibility: transmitting usable amounts of electricity through the air via lasers.

Power Through the Air

Earlier this year, the two companies carried out a demonstration at Nanki-Shirahama Airport in Wakayama Prefecture, Japan, where they succeeded in delivering more than 150 watts of power across a distance of one kilometre. That may sound relatively modest compared to the output of a household socket, yet for wireless power transmission under real atmospheric conditions it was the most efficient experiment of its kind ever reported. And it's just the beginning.

Nikola Tesla and the World Wireless System

The idea of wireless power isn't new. Serbian-American engineer and inventor Nikola Tesla experimented with it more than a century ago, even going so far as to propose a "World Wireless System" and creating the Wardenclyffe Tower (also known as the Tesla Tower) prototype on Long Island, New York, in 1901. Since that time, researchers have studied the possibility of sending electricity without cables for many decades.

You Can Aim Lasers

Two main approaches have emerged: microwaves and lasers. Microwave systems have reached practical use in certain areas, but lasers offer the benefit of very high directivity: in other words, they can be aimed precisely. That makes them well suited to long-distance applications where compact equipment is needed. The challenge for lasers, however, is that air is not a stable medium. Heat, wind, and turbulence can disrupt the beam, creating uneven patterns of light. When that happens, solar panels or other photovoltaic receivers find it impossible to convert the energy they receive efficiently.

NTT and MHI think they can do better.

NTT designed the transmitting optics for the joint demonstration, while MHI focused on the receiving side. On the transmission end, NTT researchers used a diffractive optical element, a patterned piece of glass that reshapes the laser light before it leaves the system. The design ensures that when the beam travels through the atmosphere, the different parts overlap in such a way that the intensity at the target becomes more uniform. MHI’s contribution was to deal with what happens at the receiver. They built a homogenizer that diffuses hot spots in the incoming light, and added electronic circuits that stabilise the output from the solar cells, even when turbulence causes fluctuations.

World-Record Efficiency

In the Wakayama experiment, the system transmitted just over a kilowatt of laser power. At the receiving booth, located a kilometre away and only about a metre above ground level, the photovoltaic array converted the laser light into 152 watts of usable electricity. The resulting efficiency of 15 percent may seem low compared with a wired connection, but it was actually a world record level of efficiency. The demonstration also ran for 30 minutes continuously, showing that the setup has the potential to operate stably. It's not just something cooked up in the laboratory.

The Future is Wireless

NTT and MHI's achievement shows a huge level of potential for the future. In places where cables are impossible to install quickly—think of disaster zones, isolated islands, or mountainous regions—the ability to “point and send” power could be life-saving. Imagine an earthquake has cut off an area’s power grid. Instead of waiting days for infrastructure repair, an emergency team could rapidly set up a transmitter on safe ground and beam electricity to a hospital or shelter. In the same way, power could be sent to mobile platforms. Drones that are currently weakened by their dependence on limited battery life could stay airborne far longer if recharged by a laser beam. Meanwhile, High Altitude Platform Stations, or HAPS, which operate like mobile phone towers in the stratosphere, could also receive sustained power without the need for heavy fuel or oversized batteries. And looking further ahead, space applications ranging from lunar exploration to satellites are now thinkable.

The experiment is only a first step. But it's a step that would probably have thrilled Nikola Tesla. By developing photovoltaic receivers tailored to specific laser wavelengths, efficiency could be pushed even higher. By using more powerful laser sources, the system could deliver even greater amounts of electricity.

Power From Light

Fundamentally, it's proof that wireless power transmission at the kilometre scale can work in outdoor conditions. Until now, we've been used to having electricity traveling through copper and aluminium wires. Let's get ready for it to travel through beams of light.

Innovating a Sustainable Future for People and Planet

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Daniel O'Connor

Daniel O'Connor joined the NTT Group in 1999 when he began work as the Public Relations Manager of NTT Europe. While in London, he liaised with the local press, created the company's intranet site, wrote technical copy for industry magazines and managed exhibition stands from initial design to finished displays.

Later seconded to the headquarters of NTT Communications in Tokyo, he contributed to the company's first-ever winning of global telecoms awards and the digitalisation of internal company information exchange.

Since 2015 Daniel has created content for the Group's Global Leadership Institute, the One NTT Network and is currently working with NTT R&D teams to grow public understanding of the cutting-edge research undertaken by the NTT Group.