Path monitoring in optical communication systems

摘要

An optical communication line having optical fibre amplifiers including a pump laser can be configured to suppress the transmission of optical signals, for example when used as a duplicate line for redundancy, by reducing the power of the pump laser. In order that the portion of the line downstream of the amplifier can be monitored for fibre breaks causing only negligible crosstalk with a parallel working line and with the elimination the risk of mistaking reflections from a working line for light emitted by the standby amplifier, light emitted by the standby amplifier is modulated by a low frequency control tone. Preferably the pump laser current is modulated by a low frequency signal. The modulated laser light causes modulation of the ASE generated in the amplifier to create a control tone. Monitoring means disposed at the end of the optical line detect this control tone and use this as the criteria for a functional connection downstream of the amplifier.