Two-photocurrent devices
  Heterodyne, eight-port homodyne and six-port homodyne detectors belong to the class of two-photocurrent devices. Their full equivalence in probing radiation field has been proved both for ideal and not fully efficient photodetectors. The output probability distribution has been also evaluated for a generic probe mode. 
Matteo G. A. Paris (Arbeitsgruppe 'Nichtklassiche Strahlung' der   Max-Planck-Gesellschaft)