A repeater node for an optical transmission system provides amplification
of optical signals and uses a modulated pump signal to transfer status
information about the repeater node to a control system via an optical
supervisory signal. The pump signal supplied by a pump source to an
optical amplifier is modulated with one or more tones that are indicative
of status in the repeater node. In a transmission fiber coupled to the
output of the optical amplifier, the modulation of the pump signal is
transferred to the supervisory signal of the optical transmission system
as a result of Raman effect. More specifically, the pump wavelength and
the supervisory signal wavelength are such that the modulated tone on the
shorter wavelength pump signal is transferred to the longer wavelength
supervisory signal. The tone can then be extracted from the supervisory
signal and processed at another node in the system.