SoftBank Corp. and Toshiba Digital Solutions Successfully
Demonstrate QKD Operation with Optical Wireless Communications

- Advancing Toward Urban QKD Secure Networks that Combine Optical Wireless and Optical Fiber Technologies -

March 19, 2024
SoftBank Corp.
Toshiba Digital Solutions Corporation

SoftBank Corp. (“SoftBank”) and Toshiba Digital Solutions Corporation (“Toshiba Digital Solutions”) have announced that they have successfully demonstrated the integration of Quantum Key Distribution technology (“QKD”) with optical wireless communications (“optical wireless”), marking a step forward in enabling the deployment and expansion of urban QKD networks. The breakthrough, achieved by deploying Toshiba Digital Solutions' QKD system in SoftBank's optical wireless test environment, shows how a QKD network can be deployed by combining optical wireless technologies and optical fiber technologies, providing a new, cost effective and timely method for deploying QKD secure networks in urban environments. 

■ Background
Cybersecurity is of paramount importance in various fields that include national security, financial services, and personal data protection. However, rapid advances in quantum computing and cryptographic decryption algorithms are raising deep concerns about the vulnerability of conventional data encryption. QKD, a secure communications mechanism grounded in the principles of quantum mechanics, safeguards critical data with cryptographic keys that are theoretically impossible to eavesdrop on or decipher. SoftBank and Toshiba Digital Solutions are collaborating in realizing quantum-secure networks for 6G, and have already conducted proof-of-concept experiments using QKD for inter-site Virtual Private Network (VPN) communications*.

QKD applies quantum mechanics to generate a shared secret key (“symmetric key”) between the sender and receiver of data and transmits the information via photons (particles of light). Typical urban QKD networks require optical fibers to connect sites. This may limit the implementation of QKD on sites where new optical fiber installation is physically difficult or requires significant amount of time, such as between buildings in urban areas or across public roads. SoftBank and Toshiba Digital Solutions have taken on this challenge by investigating the combination of optical wireless technologies and optical fiber technologies.

■ Demonstration Overview and Future Outlook
The demonstration successfully validated the operational and functional effectiveness of a QKD network combining optical wireless technologies and optical fiber technologies. This was done by deploying Toshiba Digital Solutions’ QKD system in SoftBank's optical wireless test equipment. 

In the operation demonstration, SoftBank and Toshiba Digital Solutions were able to confirm that stable key generation is possible without changing the QKD system for optical fibers, even when optical wireless is combined in the middle of the photon transmission path. In addition, in the performance evaluation, the companies were able to grasp the amount of optical attenuation of the entire transmission line where the encryption key can be generated. Further analysis of these findings will enable the delineation of requirements for wireless devices and the design of network connections necessary for seamless operation of a combined optical wireless QKD system. Such insights are anticipated to substantially advance the design and implementation of QKD secure networks that integrate both technologies. 

By installing optical wireless devices on building rooftops, etc. it will be possible to deploy QKD without the need for dedicated or new optical fiber installations, enabling rapid deployment. SoftBank and Toshiba Digital Solutions remain committed to advancing research and development efforts that will enhance the scalability of QKD secure networks, such as extending the range of optical wireless transmission to expand network coverage.

Configuration of optical wireless QKD operation demonstration
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