Detection Experiment of Decision Errors Caused by Quantum Noise in an Optical Signal System

Decision errors caused by quantum noise in an optical signal system have been experimentally detected. Such an experiment is necessary in order to facilitate the development of a future advanced zero-error optical communication system. The apparatus consisted of two low dark-count photoelectron multiplying tube detectors which were used to detect two separate polarization components (X; Y ) of manually controlled static binary polarization shift keying (PolSK) signals. With this system, events of the output state (0, 0) (the error events caused by quantum noise) were observed. Undesired error events for zeroerror communication were also observed. Such events are caused by external noise such as polarization beam splitter leaks or darkcount (current) noise. However, the number of these error events was reduced by the suppression of polarization beam splitter leak noise.