Patent ID: 7835067

Claim:
A Raman amplifier for amplifying signal light that includes communication information from an upstream station by using a transmission line fiber, and for receiving the amplified signal light, comprising: a pump light source to supply pump light to the transmission line fiber toward the upstream station; a signal light monitoring unit to measure an intensity of the received signal light; a target calculating unit to calculate a corresponding intensity of amplified spontaneous scattering light from a required Raman gain by using a correlation between a Raman gain and an intensity of amplified spontaneous scattering light that occurs with Raman amplification, and to calculate a target light intensity for a total intensity of the amplified spontaneous scattering light and the amplified signal light from the obtained intensity of amplified spontaneous scattering light and an intensity of the amplified signal light; and a pump light controlling unit to control the intensity of the pump light output from the pump light source so that the intensity of light measured by the signal light monitoring unit becomes equivalent to the target light intensity calculated by the target calculating unit.