Development of integrated quantum key distribution system over 25 km

Development of integrated quantum key distribution system over 25 km
QKD 시스템; 25 Km; 양자키; 키분배
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Recently, quantum key distribution (QKD) system has been highly noticed since it can guarantee an unconditional secure communication channel based on the fundamental laws of quantum mechanics [1]. There are two types of QKD system. One is the one way system that can generate higher key rate. The other is the plug and play system that may provide more stable operation in the harsh environment condition [2]. We have successfully developed the size-efficient plug and play QKD system of which size is 43 x 36 x 16㎤. This is automatically operated by the integrated controller. Our system shows that the sifted key rate is over 1kbps and Quantum Bit Error Rate (QBER) is less than 5% in the case of that the Bob and Alice is connected by the 25km optical fiber. To realize the integrated system we have designed main controller using Field-Programmable Gate Array (FPGA) of which clock frequency is 200MHz. The compact single photon detector module that is operated in the temperature of under -45℃ is also developed. To get 1kbps key rate we use pulse trains consisted of 140 pulses of which width is 5 ns. We realize a 1550nm single photon level laser using a 2MHz operated laser diode and optical attenuator. To reduce negative effects of back scattering noise the optimized algorithm is proposed and implemented in FPGA. In addition, Bob and Alice are synchronized well by the customized operation without an additional auxiliary light beam [3]. In the near future, we will adopt a low after pulse noise single photon detector the integrator method [4]. With this detector, we expect higher quantum key rate and decrease QBER in our QKD system.
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