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We have demonstrated a polarization encoded, fiber-based quantum key distribution system operating at 850 nm in the B92 protocol. With a quantum bit transmission rate i.e. optical pulse driving frequency of 625 MHz and a mean photon number of 0.1, we achieved a sifted-key rate of 2.09 Mbit/s over 1 km optical fiber. The quantum bit error rate is 3.2%. After error collection and privacy amplification a net key rate of 1.7 Mbit/s is obtained. That is sufficient for one-time-pad encryption of streaming video. Moreover, we studied various limitations for higher speed quantum key distribution systems. The results show that the dead time of the Silicon Avalanche Photo Diodes limits the possible sifted-key rate if one does not consider the error rate. The timing jitters in the system, particularly the data-dependent part of the jitter, limits the quantum bit error rate and thus prevent the generation of higher sifted-key rate.
fiber optics communications, optical communication, photon counting, polarization-maintaining, quantum detectors