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Optical Fiber Communication Conference

97-km QKD field trial using PLC-based one-way interferometers, SSPDs and WDM synchronization

Akihiro Tanaka, Mikio Fujiwara, Sae Woo Nam, Yoshihiro Nambu, Seigo Takahashi, Wakako Maeda, K. Yoshino, Shigehito Miki, Burm Baek, Zhen Wang, Akio Tajima, Akihisa Tomita, Masahide Sasaki

Published Feb 1, 2008• 2 citations
Publisher

Abstract

The world's fastest BB84 QKD through a 97-km installed fiber was demonstrated using PLC-based interferometers, SSPDs and WDM synchronization. By suppressing nonlinear crosstalk induced by the multiplexed clock, QBER of 2.8% was obtained after 97-km transmission.
DOI
10.1109/ofc.2008.4528716

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We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour stable key generation at a high sifted key rate of 2.4 kbps and a low quantum bit error rate (QBER) of 2.9%. The asymptotic secure key rate was estimated to be 0.78- 0.82 kbps from the transmission data with the decoy method of average photon numbers 0, 0.15, and 0.4 photons/pulse.
We developed a one-way quantum key distribution (QKD) system based upon a planar lightwave circuit (PLC) interferometer. This interferometer is expected to be free from the backscattering inherent in commercially available two-way QKD systems and phase drift without active compensation. A key distribution experiment with spools of standard telecom fiber showed that the bit error rate was as low as 6% for a 100-km key distribution using an attenuated laser pulse with a mean photon number of 0.1 and was determined solely by the detector noise. This clearly demonstrates the advantages of our PLC-based one-way QKD system over two-way QKD systems for long distance key distribution.
We developed a one-way quantum key distribution (QKD) system based upon a planar lightwave circuit (PLC) interferometer. This interferometer is expected to be free from the backscattering inherent in commercially available two-way QKD systems and phase drift without active compensation. A key distribution experiment with spools of standard telecom fiber showed that the bit error rate was as low as 6% for a 100-km key distribution using an attenuated laser pulse with a mean photon number of 0.1 and was determined solely by the detector noise. This clearly demonstrates the advantages of our PLC-based one-way QKD system over two-way QKD systems for long distance key distribution.
Quantum key distribution (QKD) systems can generate unconditionally secure common keys between remote users. Improvements of QKD performance, particularly in key generation rate, have been required to meet current network traffic. A high-speed QKD system should be equipped with low-loss receivers with high visibility, highly efficient photon detectors with small dark count probability. A solution to these issues is to employ planar lightwave circuit (PLC) interferometers, single photon detection circuits and modules, together with multi-wavelength channels transmission using wavelength division multiplexing (WDM) technique.
One of our major target is quantum key distribution (QKD,) which is closest to the practical use. Though QKD can be performed only with current technology, there still remain many thing to be improved. One of the most important devices that determine the system performance is photon detectors. It limits the transmission distance in optical fiber communication wavelength. A photon detector combining the two avalanche photon diodes (APD) has been demonstrated for qubit discrimination in 1550 nm. Spikes accompanied with the signals in gated-mode were canceled by balanced output from the two APDs. The balanced APD photon detector shows very low dark count rate (2x10-7) counts/pulse) with 10 % detection efficiency. We have also developed a highly stable interferometer on a planer-lightwave-circuit (PLC.) We have achieved single-photon interference over 150 km using time-division interferometers for quantum cryptography, which were composed of the two integrated-optic asymmetric Mach-Zehnder interferometers, and the balanced gated-mode photon detectors. The observed visibility was more than 80 % after 150-km transmission, which refers to a quantum bit error rate of less than 10 %. We will also describe temperature insensible QKD system and high speed (100 bps) key transmission over 40 km fiber.