Patent ID: 6907157

Claim:
A method comprising: providing an optical fiber transmission line for transmitting signal light; providing a Raman repeater having a pumping source for supplying pump light propagating in a direction opposite to the direction of propagation of said signal light to said optical fiber transmission line, said pumping source comprises first and second laser diodes for respectively outputting first and second pump lights having different wavelengths; providing a terminal device having a pumping source for supplying pump light propagating in the opposite direction to the propagation direction of said signal light to said optical fiber transmission line, at one end of said optical fiber transmission line, said pumping source comprises first and second laser diodes for respectively outputting first and second pump lights having different wavelengths; transmitting a control signal to said Raman repeater by said pump light from said terminal device; and controlling said Raman repeater by said control signal transmitted; said transmitting comprises modulating said first and second pump lights in said terminal device by first and second frequency components different from each other, respectively; and said controlling comprises the converting said pump light from said terminal device into an electrical signal and detecting said first and second frequency components according to said electrical signal.