Tokyo, – NEC Corporation has successfully achieved Japan’s longest terrestrial wireless optical communication (*), or free-space optical (FSO) communication, over a distance of more than 10 km. In addition, NEC has successfully conducted FSO communications between an observation deck at TOKYO SKYTREE®, the tallest structure in Japan, and a location on the ground approximately 3 km away, representing a significant change in elevation.
Elevation difference test conducted with TOKYO SKYTREE
FSO is a wireless communication method that enables high-speed and high-capacity communication compared to radio waves. It transmits and receives light beams without using physical paths such as optical fibers. Additionally, it has high directionality and does not spread beams, resulting in low risk of interception by third parties, reduced interference and congestion in communication, and no need for radio wave usage permits.
These newly developed technologies are expected to be utilized for communications in locations and regions where it is difficult to install optical fiber, and for communications between ships at sea and the land. In addition, it is expected that the technologies will be used as an alternative or emergency communication method in the event of a disaster when wired communication networks become damaged, making communications difficult, as well as for highly confidential short- and medium-range communications related to national security.
Conventionally, one of the challenges for FSO communications has been overcoming the negative impact on stable communications from atmospheric turbulence, such as heat haze, that increase with distance, and it has been difficult to grasp atmospheric turbulence that differs between different elevations.
NEC has now successfully achieved communication over a distance of more than 10 km and communications at different elevations with FSO communication by applying its capture and tracking technology developed for its communication systems and long-distance optical communication technology used in satellites.
Overview and Results of the Demonstration Experiment
① Long-Distance Test
- (1)Location: Nasushiobara City, Tochigi Prefecture, Japan
- (2)Period: January–February 2025
- (3)Content: NEC conducted a communication demonstration between a pair of FSO communication devices located more than 10 km apart in Nasushiobara City, Tochigi Prefecture. As a result, NEC confirmed that automatic capture and tracking of bidirectional optical beams functioned correctly even over long distances, enabling communication.
② Elevation Difference Test
- (1)Location: TOKYO SKYTREE, Sumida Ward, Tokyo, Japan
- (2)Period: March 2025
- (3)Content: NEC conducted a demonstration of FSO communication between the rooftop of a TOKYO SKYTREE observation deck, which is 350 meters above ground level, and a point on the ground approximately 3 km away. As a result, NEC confirmed that communication was possible and also measured the effects on communications from atmospheric turbulence due to elevation differences.
NEC will advance technological development based on the success of this demonstration, aiming to improve communication quality and reduce the device size from approximately 2 m³ to about 1% of the current size, so that it can be carried by one person, with plans to commercialize it by 2028. Furthermore, by combining quantum cryptography communication technology—which is expected to be applied to national-level critical infrastructure systems—with FSO communication technology, NEC aims to develop free-space quantum key distribution technology in the future, thereby enabling more secure communication. NEC also aims to apply this technology to communications between ground and satellites while continuing to advance its efforts to provide networks tailored to the diverse needs of its customers.
