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IEEE/LEOS Summer Topical Meetings

Sagnac Quantum Key Distribution Using Novel Polarization-Insensitive Phase Modulators Based On Frequency Shift

Leilei Huang, Bing Qi, R. Mong, Li Qian, Hoi‐Kwong Lo

Published Sep 22, 2006• 1 citation
Publisher

Abstract

We demonstrate a stable Sagnac quantum key distribution implementing BB84 phase-encoding protocol based on acousto-optic frequency shifters. The quantum bit error rate remains 4-6.5% for at least one hour without recalibration or feedback control.
DOI
10.1109/leosst.2006.1693999

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In this paper, we propose a polarization-insensitive phase modulation scheme based on frequency modulation of light waves using either one or a pair of acousto-optic modulators. A stable Sagnac quantum key distribution (QKD) system employing this technique is also proposed. The interference visibility for a 40km and a 10km fiber loop is 96% and 99% respectively, at single-photon level. We ran standard BB84 QKD protocol in a simplified Sagnac setup (40km fiber loop) continuously for one hour and the measured quantum bit error rate stayed within 2%-5% range.
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In polarization-encoding quantum key distribution (QKD) systems, achieving high-speed, robust, and low-error polarization modulation helps to increase the secure key rate (SKR). Moreover, the advanced QKD protocols place higher demands on the system’s photon preparation capability, which implies providing additional polarization states for practical implementation. Here, we redesign the Sagnac interferometer and utilize the non-reciprocity of the lithium niobate modulator to eliminate the reverse modulation that limits the modulation speed. The proposed scheme enables high-speed, robust, and low-error modulation with arbitrary polarization states. The average bit error rate (BER) for the 10 min measurement is 0.2332% with a system repetition frequency of 16.5 GHz.