Patent ID: 8879145

Claim:
A Raman amplifier comprising: a pump-light generator configured to supply pump light to a transmission optical fiber; a measurement circuit configured to measure a relationship between power of the pump light and power of noise output from the transmission optical fiber with respect to a range from first pump-light power to second pump-light power that is higher than the first pump-light power; a signal detector configured to monitor a supervisory signal transmitted from a transmission equipment provided at a transmitting end of the transmission optical fiber in output light of the transmission optical fiber; and a decision unit configured to decide a state of the transmission optical fiber according to a monitoring result provided by the signal detector, wherein when the supervisory signal is detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the measurement circuit measures the relationship while increasing the power of the pump light from the first pump-light power to the second pump-light power, and when the supervisory signal is not detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the measurement circuit measures the relationship while decreasing the power of the pump light from the second pump-light power to the first pump-light power.