Supervisory system for an optical transmission system

摘要

An optical transmission system comprises optically amplified forward and return paths 15a, 15b between a local station 11 and a remote stations 13. Each amplifier 17 of the forward path has an attenuated loopback coupling its output to the return path. Frequency modulated supervisory signals generated at the local station are returned via the loopbacks. These signals are analysed e.g. by Fourier analysis to obtain a measure of the performance of each amplifier. The system may also be employed for the location of fibre breaks.