Patent ID: 7869599

Claim:
A quantum cryptography key distributing system comprising: an optical fiber; a transmission unit which is connected with said optical fiber, generates a transmission optical pulse signal from an optical pulse signal based on a first data in synchronism with an optical clock signal and transmits said transmission optical pulse signal to a reception unit via said optical fiber, wherein polarization of said transmission optical pulse signal is different from that of said optical pulse signal, and optical pulses reflected in the transmission unit are modulated in the reception unit; and said reception unit which is connected with said optical fiber, transmits said optical pulse signal to said transmission unit via said optical fiber, phase-modulates a part of said transmission optical pulse signal based on a second data in synchronism with said optical clock signal, and detects a reception data corresponding to said first data based on said transmission optical pulse signal in synchronism with said optical clock signal, such that phase synchronization is established in addition to the clock synchronization, wherein the quantum cryptography key distribution system is configured such that the phase synchronization is established by a reception unit-transmission unit-reception unit loop.