An optical communication system including repeaters (5-1 to 5-n) which return a preamble signal to a receive line (2) as soon as it detects a carrier on a transmit line (1) of a single line optical bus (1,2,6). Therefore, transmission equipment (7-1 to 7-m) can confirm data transmission quickly because the time delay between data transmission and its confirmation is decreased. The repeater (5-1 to 5-n) also monitors a time delay associated with the return through a return loop (6) of the transmitted data, and produces and transmits a failure signal when the time delay is longer than a predetermined value. The system also includes an optical transceiver (10-1 to 10-m) connected between the optical bus and the transmission equipment (7-1 to 7-m) which converts optical signals into electrical signals and vice versa and also adds the preamble signal to the front of data to be transmitted.
