Optical amplification device and light amplification method

1. An optical amplification device comprising:

a demultiplexer demultiplexing an optical wavelength multiplexed signal to be input into a first optical wavelength multiplexed signal having a first wavelength band and a second optical wavelength multiplexed signal having a second wavelength band located in a longer wavelength band than the first wavelength band;

a first optical amplifier amplifying the first optical wavelength multiplexed signal;

an excitation light controller controlling excitation light that amplifies the first optical wavelength multiplexed signal in the first optical amplifier;

a second optical amplifier amplifying the second optical wavelength multiplexed signal; and

a multiplexer multiplexing the amplified first optical wavelength multiplexed signal and the amplified second optical wavelength multiplexed signal, and outputting the multiplexed optical wavelength multiplexed signal to a Raman amplifier, wherein

the first optical amplifier adjusts intensity of light of the first optical wavelength multiplexed signal in such a way that intensity of light in the second wavelength band is compensated for by a Raman effect in the Raman amplifier,

the first optical amplifier causes, when loss in an optical fiber through which the optical wavelength multiplexed signal to be input passes increases, an amplification factor of the first optical wavelength multiplexed signal to be larger than a setting in a normal condition, and

the excitation light controller controls the excitation light of the first optical amplifier, based on a control signal received from a monitoring device when loss in the optical fiber through which the optical wavelength multiplexed signal to be input passes increases.

2. An optical transmission system comprising:

a plurality of the optical amplification devices according to claim 1 ; and

an optical fiber that connects between the optical amplification devices and amplifies a passing optical signal by a Raman effect, wherein

the first optical amplifier of the optical amplification device in which loss increases in the optical fiber in a previous stage adjusts an amplification factor of the first optical wavelength multiplexed signal, and intensity of light in the second wavelength band is compensated for by a Raman effect of the optical fiber in a subsequent stage.

3. The optical amplification device according to claim 1 , further comprising:

an optical receiver receiving the control signal as an optical signal of the first wavelength band.

4. The optical amplification device according to claim 1 , wherein

the first optical amplifier includes an optical attenuator that attenuates intensity of an optical signal after amplification, and

adjusts intensity of the first optical wavelength multiplexed signal to be output by an attenuation amount by the optical attenuator.

5. The optical amplification device according to claim 4 , further comprising:

an optical receiver receiving the control signal to be multiplexed into the first optical wavelength multiplexed signal; and

an attenuation controller controlling an attenuation amount of the optical attenuator, based on the control signal received by the optical receiver.

6. An optical amplification method comprising:

demultiplexing an optical wavelength multiplexed signal to be input into a first optical wavelength multiplexed signal having a first wavelength band and a second optical wavelength multiplexed signal having a second wavelength band located in a longer wavelength band than the first wavelength band;

adjusting an amplification factor of the first optical wavelength multiplexed signal in a first optical amplifier in such a way that intensity of light in the second wavelength band is compensated for by a Raman effect in a Raman amplifier;

amplifying the first optical wavelength multiplexed signal in the first optical amplifier, by using an adjusted amplification factor;

controlling excitation light that amplifies the first optical wavelength multiplexed signal in the first optical amplifier;

amplifying the second optical wavelength multiplexed signal in a second optical amplifier; and

multiplexing the amplified first optical wavelength multiplexed signal and the amplified second optical wavelength multiplexed signal, and outputting the multiplexed optical wavelength multiplexed signal to the Raman amplifier, wherein the method further comprises

causing, when loss in an optical fiber through which the optical wavelength multiplexed signal to be input passes increases, the amplification factor of the first optical wavelength multiplexed signal to be larger than a setting in a normal condition, and

controlling the excitation light of the first optical amplifier, based on a control signal received from a monitoring device when loss in the optical fiber through which the optical wavelength multiplexed signal to be input passes increases.

7. The optical amplification method according to claim 6 , further comprising:

adjusting the amplification factor of the first optical wavelength multiplexed signal in the first optical amplifier, based on the control signal to be multiplexed into the first optical wavelength multiplexed signal.