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Telecoms fibers carry key 87 km

15 Nov 2002

Mitsubishi Electric sends a quantum key over 87 km of optical fiber smashing the previous record by 20 km.

Mitsubishi Electric of Japan claims to have sent a cryptographic key made up of single photons over 87 km of optical fiber, a new world-record. The experiment was carried out at 1550 nm.

The company says this is a significant step towards realizing a practical integrated quantum cryptography system that promises totally secure data transmission.

Development of quantum cryptography systems operating at this crucial telecoms wavelength, and also 1300 nm, has been hampered in recent years by inefficient single-photon detectors. But Mitsubishi says it has concentrated on developing a detector with a low dark-count probability to overcome the problem.

The company says its system has a bit rate of 7.2 bps; a quantum bit error rate of 7.6% and contains optics that can compensate for phase and polarization fluctuations. It is unclear if the company developed speciality fiber to perform this experiment.

Mitsubishi now plans to enhance the performance of the single-photon detector and increase the bit rate. Its goal is to develop a user-friendly and compact system that is attractive as a commercial product.

The previous record of 67 km at 1550 nm was held by a team of swiss researchers who successfully exchanged a quantum key over a fiber link between Geneva and Lausanne. As in this case, the key was sent in the form of single photons allowing any eavesdropper to be detected.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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