| 摘要 |
PROBLEM TO BE SOLVED: To provide a quantum encryption key delivery system capable of stably supplying an encryption key independently of fluctuation of polarization condition. SOLUTION: In one embodiment of this invention, a transmitter 310 transmits optical pulse sequence, on which differential phase shift modulation is performed. This optical pulse sequence is set by an attenuator 316 so that an average number of photon per a pulse is less than one. A receiver 330 receives the optical pulse sequence from the transmitter 310 through an optical transmission path 320 wherein polarization condition changes, and detects photon of each pulse in response to a modulation phase difference. This receiver separates photon of each pulse into two polarized light components orthogonal to each other, and converts one of the polarized light components to the other polarized light components, and synthesizes them with a predetermined time difference so as to detect photon by using one polarized light components. With this structure, the receiver 320 stably detects photon independently of fluctuation of polarization condition in the optical transmission path 320, and can generate an encryption key. COPYRIGHT: (C)2009,JPO&INPIT
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