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Use of single fiber achieved through quantum encryption key technology and data wavelength multiplexing



Quantum encryption key distribution is a cryptographic technology which ensures data security by utilizing the quantum mechanical properties of photons. In the past, encryption keys made of ultra-weak photons were transmitted through dedicated fiber instead of fiber that transmits optical communication data equivalent to about one million photons per bit. The Cambridge Research Laboratory (CRL) of Toshiba Research Europe succeeded in transmitting optical communication data and encryption keys at the same time through a single fiber by multiplexing encryption key photons having a different wavelength from that of optical communication data. The achievement was published in Physical Review X (November 20, 2012), an on-line version of Physical Review, the most prestigious publication in the U.S. physics community.

Challenges faced by conventional technologies

Conventionally, quantum encryption keys are sent through dedicated fiber to keep their quantum state and protect them from disturbance. Transmitting encryption keys together with optical communication data in a single fiber causes scattered light to affect the photons and lose their quantum state. To avoid this trouble, at least two fiber lines are needed, one for encryption keys and the other for optical communication, which makes this technique more costly than others. CRL therefore designed a technology for wavelength multiplexing of optical communication data and encryption keys, as well as a technology to obtain quantum information from ultra-weak photons by controlling the photon detector timing. Specifically, the photon detection time is limited to as short as 50 picoseconds in coordination with the arrival of an encryption key to suppress the noise caused by strong optical signals. Using this technology, we succeeded in sending a 1 megabit encryption key through a 35 km-long fiber. The 1 megabit data, which is 1000 to 100,000 times the volume of data that had been sent via wavelength multiplexing in the past, was a world record.


We have been working on wavelength multiplexing of encryption keys, clock signals and optical communication data, and plan to increase the volume of optical communication data for wavelength multiplexing and establish an encryption system which is more effective and practical than other systems.