Homodyne QPSK Detection for Quantum Key Distribution
  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. 
M. B. Costa e Silva, Q. Xu, S. Agnolini, P. Gallion, F. J. Mendieta