TOKYO – September 17, 2025 – NTT, Inc. (Headquarters: Chiyoda, Tokyo; President and CEO: Akira Shimada; hereinafter “NTT”) and Mitsubishi Heavy Industries, Ltd. (Headquarters: Chiyoda, Tokyo; President and CEO: Eisaku Ito; hereinafter “MHI”) conducted an optical wireless power transmission experiment using laser beam to wirelessly transmit energy 1 kilometer away. By irradiating laser beam with an optical power of 1 kW, we succeeded in receiving 152 W of electric power 1 kilometer away. This marks the world’s highest efficiency of an optical wireless power transmission using a silicon photoelectric conversion element(Note2) in an environment with strong atmospheric turbulence.
This result demonstrates the feasibility of delivering power to distant sites. In the future, it is expected to be applied to on-demand power transmission to remote islands and disaster-stricken areas where power cables cannot be installed.
This achievement was published in the British magazine Electronics Letters on August 5, 2025.
Figure 1 Schematic diagram of optical wireless power transmission system
Background
In recent years, wireless power transmission technologies for devices such as smartphones, wearable devices, drones, and electric vehicles, which can supply electricity without using cables, have garnered increasing attention. There are two types of wireless power transmission systems: one uses microwaves and the other uses laser beams. Microwave wireless power transmission is already in practical use and its use is expanding. On the other hand, optical wireless power transmission using laser beam has not been put into practical use, but it is expected to realize compact long-distance wireless power transmission on the order of kilometers by taking advantage of the high directivity of laser beam (Figure 1).
Future prospects envision the development of next-generation infrastructure capable of supplying power and expanding communication coverage in situations and regions where electricity or communication networks are unavailable, such as during disasters, in remote islands, mountainous areas, or at sea. This includes delivering power precisely to specific areas or moving platforms such as drones. Achieving such highly accurate and long-distance power delivery requires laser-based wireless power transmission that takes advantage of its strong directionality.
Challenges of existing technologies and achievements of this experiment
The efficiency of optical wireless power transmission technology is generally low, and improvement of efficiency is an issue for practical use. One of the reasons for this is that when long-distance laser beam propagates, especially in the atmosphere, the intensity distribution becomes uneven, and the efficiency of converting laser beam into electric power in the photoelectric conversion element becomes low.
In this experiment, we combined NTT’s beam shaping technology with MHI’s light receiving technology to improve the efficiency of laser wireless power transmission. We conducted a long-distance optical wireless power transmission experiment in an outdoor environment using long-distance flat beam shaping technology that shape the beam at the transmission side to achieve uniform beam intensity after 1 kilometer propagation, and output current leveling technology that suppresses the influence of atmospheric fluctuations with a homogenizer and leveling circuits on the receiving side.
From January to February 2025, we conducted an optical wireless power transmission experiment on the runway at the Nanki-Shirahama Airport in Shirahama Town, Nishimuro District, Wakayama Prefecture (Figure 2). A transmission booth equipped with an optical system for emitting laser beam was installed at one end of the runway, and a reception booth containing a light-receiving panel was placed 1 kilometer away.
During transmission, the optical axis of the laser was set at a low height of approximately 1meter above the ground and aligned horizontally. As a result, the beam was strongly affected by ground heating and wind, and the experiment was conducted under conditions with strong atmospheric turbulence.
Inside the transmission booth, a laser beam with an optical power of 1035 W was generated. Using a diffractive optical element (DOE)(Note3), the beam was shaped to create a uniform intensity distribution at a distance of 1 kilometer. In addition, a beam steering mirror was used to precisely direct the shaped beam toward the receiving panel. The beam exited through the aperture of the transmission booth and propagated across 1 kilometer of open space, ultimately reaching the reception booth.
During propagation, atmospheric turbulence caused fluctuations in the beam’s intensity, creating hot spots. These were diffused by a homogenizer in the reception booth, resulting in a uniform beam being irradiated onto the receiving panel. The laser beam was then efficiently converted into electrical power (Figure 3). A silicon-based photoelectric conversion element was adopted for the receiving panel, taking into account both cost and availability.
In this experiment, the average electrical power extracted from the receiving panel was 152 W (Figure 4), corresponding to a wireless power transmission efficiency of 15%, defined as the ratio of received electrical power to transmitted optical power. This result marks the world’s highest optical wireless power transmission efficiency ever demonstrated using a silicon-based photoelectric conversion element under conditions of strong atmospheric turbulence. Furthermore, continuous power delivery was successfully maintained for 30 minutes, confirming the feasibility of long-duration power transmission using this technology.
Figure 2 Scene of the experiment
- From a safety perspective, the optical transmission system and the receiving panel were each installed inside booths to prevent accidental exposure to high-power laser beams and the scattering of reflected light.
Figure 3 Schematic diagram of experimental system
Figure 4 Power from the light-receiving panel
Technical highlights
- Long-distance flat beam shaping technology
To improve photoelectric conversion efficiency, it is necessary to make the intensity distribution of the beam incident on the photoelectric conversion element uniform.In this study, we proposed a beam shaping method that enables intensity uniformity after long-distance propagation. In this approach, the outer part of the beam is transformed into a ring-shaped pattern using the effect of an axicon lens(Note4). The central part of the beam is phase-modulated to expand through the effect of a concave lens. As the beam propagates, the ring-shaped beam and the expanded central beam gradually overlap, resulting in a uniform intensity distribution at the target location, as shown in Figure 5.
For the experiment, we optimized the beam design to achieve the desired intensity profile at a distance of 1 kilometer. The beam shaping was implemented using a diffractive optical element, which improved the uniformity of the beam intensity at the target position located 1 kilometer away.
Figure 5 Image of beam shaping
- Output current leveling technology
As the laser beam propagates through the atmosphere, it is affected by atmospheric turbulence, which disturbs the intensity distribution. Although the flat-beam shaping technique described above can uniform the intensity distribution, strong turbulence can still cause the formation of high-intensity spots, as shown in Figure 6.To address this issue, we placed a beam homogenizer in front of the light-receiving panel. The homogenizer diffuses high-intensity spots so that the beam is uniformly irradiated onto the panel. In addition, leveling circuits were connected to each photoelectric conversion element on the receiving panel. These circuits help suppress fluctuations in output current caused by atmospheric turbulence and contribute to stabilizing the overall power output.
These two technologies make it possible to achieve beam uniformity in kilometer-order transmission, which was difficult with conventional beam shaping methods, and to stabilize output in outdoor environments. As a result, stable power supply to remote locations such as isolated islands and disaster-affected areas is expected to become feasible.
Figure 6 Image of beam pattern after atmospheric propagation and diffusion effect by homogenizer
Role of each company
NTT: Design and implementation of transmission optics such as beam shaping techniques
MHI: Design and implementation of photodetector optics such as photodetector panels, homogenizers, and leveling circuits
Future developments
This technology enables the efficient and stable transmission of energy over long distances even under atmospheric turbulence. In this experiment, silicon was used as the photovoltaic conversion element. However, by employing photovoltaic devices specifically designed to match the wavelength of the laser light, even higher power transfer efficiency can be expected. In addition, the use of laser light sources with higher output power would make it possible to supply larger amounts of electricity.
As a result, flexible and rapid power delivery can be achieved in remote areas such as disaster-stricken regions and remote islands, where the installation of power cables has traditionally been difficult. Beyond terrestrial applications, a wide range of new use cases can also be envisioned based on this technology (Figure 7). Notably, the high directivity and low divergence of laser beams allow for the design of compact and lightweight receiving devices. This is a major advantage for mobile platforms that face strict limitations in weight and payload capacity.
For example, by combining this technology with beam steering techniques, it becomes possible to deliver power wirelessly to drones in flight. This avoids operational constraints such as landing for battery replacement or the use of tethered power supply cables, enabling long-duration and long-distance continuous operation. Such capabilities can enhance disaster-area monitoring as well as wide-area communication relay in mountainous or maritime regions, applications that were previously difficult to realize.
In addition, potential applications in space are anticipated, including power delivery to mobile platforms such as HAPS (High Altitude Platform Station)(Note5), which falls within the scope of NTT’s space brand, NTT C89(Note6). Looking further ahead, the technology could be applied to power space data centers and lunar rovers, as well as to space solar power systems in which electricity is transmitted from geostationary satellites to the ground via laser. These applications represent areas with strong potential for market expansion.
Through the collaboration between NTT and MHI, we have realized the world’s most efficient laser wireless power transfer technology under conditions strongly affected by atmospheric fluctuations. This achievement represents a significant step toward building an innovative technological foundation that can meet a wide range of societal needs, from disaster response to space development.
Figure 7 Use case of the technology
[Glossary]
- 1Efficiency:
The ratio of the electrical power extracted by the receiving panel to the optical power emitted by the laser. - 2Photoelectric conversion element:
A semiconductor device that converts light into electricity. Semiconductors generate electromotive force when light is shone on them due to the photoelectric effect. Adjusting the semiconductor composition allows control of the bandgap, which determines the wavelengths of light that can be efficiently used for power generation. Solar cells are also a type of photovoltaic cell. A photoelectric conversion panel is formed by connecting multiple of these cells. - 3Diffractive optical element:
An optical element that can control the intensity and phase of a beam by using the diffraction phenomenon of light by performing fine processing on a surface of the wavelength of light. - 4Axicon lens:
A conical lens capable of producing a Bessel beam, a ring-shaped beam or a non-diffracting beam. - 5HAPS (High Altitude Platform Station):
Unmanned aerial vehicle operated in the stratosphere. It is expected to serve as a base station for applications such as communications and related infrastructure. - 6NTT C89:
The brand name of the space business that NTT Group companies are engaged in. We will contribute to the development of the space industry by encouraging business expansion and further market development in the space business field.
https://group.ntt/en/aerospace/
https://group.ntt/en/magazine/blog/ntt_c89/
About NTT
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