Ring transmission system that detects presence/absence of each optical carrier

摘要

A signal transmission system has a number of wave division multiplex optical carriers linking a number of switching units arranged in a closed ring network. The carriers are amplified to compensate for loss and attenuation, but the ring gain of each carrier must be less than unity to prevent unwanted signal oscillation. An automatic gain control arrangement is operative for each optical carrier which is detected as being present at a switching unit, and the gain control is disabled for each carrier which is detected as being absent.