Abstract: An optical transmission system according to the present invention includes a connection confirming circuit 106 for confirming connection of an input data signal, a test signal generator 105 for generating a test signal, and a switching device 107 on a transmitter side. The switching device 107 selectively generates the input data signal from an output terminal in the case where the input data signal is detected by the connection confirming circuit 106, and the test signal when the input data signal is not detected. An output of the switching device 107 is connected to an optical transmitter TX. On a receiver side, there is provided a determination circuit for receiving an optical signal from a transmission path and detecting the test signal to determine transmission characteristics of the transmission path on the basis of the test signal.

Abstract: To effectively collecting information necessary for maintenance of the optical transmission system from each optical repeater equipment, in an optical transmission system of the wavelength division multiplexing type according to this invention, a repeater unit 210-1 in optical repeater equipment 200 detects the wavelengths of optical signals .lambda.1 to .lambda.q', the directions of optical signals, the transmission line ID Nos., and so on by using an optical couplers 211, 219, demultiplexers 212, 213, O/E converters 214-1.about.p, 215-1.about.q, and local oscillators 216-1.about.p, 217-1.about.q, and a supervisory control signal, including information about the detection results and a light amplifier 218, is sent to optical terminal equipment 100.