Patent ID: 7146100

Claim:
A repeater for conducting Raman amplification on an optical signal propagating in a transmission line, comprising: a Raman excitation light production/answer signal superimposition unit for modulating an answer signal to a monitor control command, included in an optical signal from a first terminal station through an up-direction line, into a Raman excitation light for the Raman amplification and for supplying the modulated Raman excitation light to a transmission line fiber of a down-direction line on a second terminal station side to produce a first reply signal for said down-direction line by superimposing said answer signal on an optical signal passing through said down-direction line on said second terminal station side; and an answer signal production unit for producing a second reply signal to said monitor control command in a case in which an optical signal is not inputted through said second terminal station side down-direction line.