Optical communication system monitor

摘要

The system comprises optical repeaters 16a to 16n, each including two optical amplifiers 17a to 17n and 18a to 18n, inserted in an optical fibre transmission link having up 12a to 12n and down 13a to 13n side channels. The monitor supervises the condition of the optical transmission link using a supervisory signal from one of transmission stations 22a, 23b superimposed (e.g. modulated) on the traffic signal. Each repeater has a conducting loopback circuit Aa to An which attenuates and returns part of a signal on one channel onto the other channel, so that a plurality of supervisory signals are returned. The supervisory signals can be distinguished at the transmission station.