Patent ID: 8031395

Claim:
An optical transmission system comprising a plurality of nodes on first and second transmission lines corresponding to an uplink and a downlink, and with each node equipped with a Raman amplifying device for Raman-amplifying each main signal light transmitted on the first and second transmission lines, wherein the Raman amplifying device comprising: a pump light generating section that generates backward Raman pump light for Raman-amplifying the main signal light transmitted on the first optical transmission line, and provides the backward Raman pump light to the first optical transmission line; a pump light modulating section that modulates the backward Raman pump light generated by the pump light generating section to thereby transmit a pilot signal for confirming a connection state of the first optical transmission line from a first node positioned on a downstream side of the first optical transmission line to a second node positioned on an upstream side of the first optical transmission line; a modulated-component detecting section that receives backward Raman pump light propagating on the second optical transmission line, and detects whether a modulated component corresponding to a response signal indicating that the pilot signal transmitted from the first node to the first optical transmission line is received by the second node is included in the received backward Raman pump light; and a pump light controlling section that controls a power of the backward Raman pump light generated in the pump light generating section to a normal operation level when a modulated component corresponding to the response signal is detected by the modulated-component detecting section, and controls a power of the backward Raman pump light generated in the pump light generating section to a safe level when a modulated component corresponding to the response signal is not detected by the modulated-component detecting section.