Heterodyne and photon-counting receivers for optical communications.

The relative performance of an optical heterodyne receiver and a photon-counting receiver are compared. These conditions under which the two types of systems perform equally well are defined. Background noise is shown to be an almost negligible consideration. Detector noise is seen to be a much more severe problem. It is concluded that for wavelengths below 1 micro, photon-counting reception is preferred because of the availability of photoemissive detectors. For wavelengths greater than 3 micro detector noise considerations are so severe that it is unlikely that photon counting will be competitive with heterodyne detection. The type of detection preferred in the 1-3 microrange is shown to be a matter of detector development.