  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.

Optics