This paper presents the principles and experimental results of an optical fiber QKD system operating at 1550 nm, and using the BB84 protocol with QPSK signals. Our experimental setup consists of a time-multiplexed super-homodyne configuration using P.I.N detectors in a differential scheme as an alternative to avalanche photon counting. Transmission over 11km of optical fiber has been done using this detection scheme and major relevant characteristics such as noise, quantum efficiency and bit error rate (BER) are reported.
We present the integration of the optical and electronic subsystems of a BB84-QKD fiber link. A high speed FPGA MODEM generates the random QPSK sequences for a fiber-optic delayed self-homodyne scheme using APD detectors.
IntroductionIn fiber-optic quantum key distribution (QKD) at telecommunications wavelengths, QPSK encoding of Alice's Qbits constitutes an attractive modulation format [1, 2] since it could be detected in differential interferometric schemes that need only one fiber, thus relaxing the requirements in phase and polarization stability and providing a more reliable long distance QKD link, and at the same time simplifies the system's integration and control.
We present a QKD system with fainted pulses using self-homodyne coherent detection in optical fibers at 1543nm. BB84 protocol key is encoded in the optical phase using a twoelectrode Mach-Zehnder modulator, producing a QPSK modulation.
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