Communication system, communication device, and communication method

1. A communication system comprising:

a transmitter that combines and transmits a first signal light and a dummy light having a wavelength different from the first signal light;

a first amplifier that amplifies a light transmitted by the transmitter to a constant power;

a communication device that separates the dummy light from the light amplified by the first amplifier, has a variable transmittance and allows the separated dummy light to pass through, and combines and transmits the passed dummy light and a second signal light having a wavelength different from the dummy light;

a second amplifier that amplifies a light transmitted by the communication device to a constant power;

a receiver that receives the second signal light included in the light amplified by the second amplifier; and

a controller that controls the transmittance.

2. The communication system according to claim 1 , wherein the controller controls the power of the first signal light combined by the transmitter.

3. The communication system according to claim 2 , wherein the controller obtains reception quality information indicating the reception quality of the first signal light, and controls the power of the dummy light based on the obtained reception quality information.

4. The communication system according to claim 1 , wherein

the communication device includes an optical filter that allows the separated dummy light to pass through and of which transmittance differs according to wavelength of light, and

the controller controls the wavelength of the dummy light combined by the transmitter.

5. The communication system according to claim 4 , wherein the optical filter has characteristics where the transmittance with respect to wavelength periodically changes in a wavelength band of the dummy light.

6. The communication system according to claim 4 , wherein

the optical filter is a variable optical filter of which transmittance characteristics with respect to the wavelength of a light that passes therethrough is variable, and

the controller controls the characteristics of the variable optical filter.

7. The communication system according to claim 1 , wherein

the communication device includes an optical variable attenuator that allows the separated dummy light to pass through and of which attenuation amount is variable, and

the controller controls the attenuation amount of the optical variable attenuator.

8. The communication system according to claim 1 , wherein the communication device is an add/drop device that

includes an inserting unit that inserts the first signal light included in the light amplified by the first amplifier into another optical line, and a branching unit that branches the second signal light from the optical line, and

combines the second signal light branched by the branching unit and the dummy light.

9. The communication system according to claim 1 , wherein the transmitter and the receiver are provided in a single communication device.

10. The communication system according to claim 1 , wherein the communication device is a communication device provided on the bottom of sea.

11. The communication system according to claim 1 , wherein the controller obtains reception quality information indicating the reception quality of the second signal light, and controls the transmittance based on the obtained reception quality information.

12. A communication device that transmits/receives a light to/from other communication device, wherein the other communication device

separates a dummy light from a transmitted light in which a first signal light and the dummy light having a wavelength different from the first signal light are combined,

has a variable transmittance and allows the separated dummy light to pass through, and

combines and transmits the passed dummy light and a second signal light having a wavelength different from the dummy light, the communication device comprising:

a transmitter that combines the first signal light and the dummy light and transmits the combined light to the other communication device via a first amplifier that amplifies light to a constant power;

a receiver that receives the second signal light included in a light transmitted by the other communication device via a second amplifier that amplifies light to a constant power; and

a controller that controls the transmittance.

13. A communication device that transmits/receives a light to/from another communication device that includes a transmitter that transmits a light in which a first signal light and a dummy light having a wavelength different from the first signal light are combined, the communication device comprising:

a separator that separates the dummy light from a light transmitted by the other communication device via a first amplifier that amplifies light to a constant power;

a transmission unit that has a variable transmittance and allows the dummy light separated by the separator to pass through; and

a combiner that combines the dummy light that has passed through the transmission unit and a second signal light having a wavelength different from the dummy light, wherein

the communication device transmits the light combined by the combiner to the other communication device via a second amplifier that amplifies light to a constant power.

14. A communication method comprising:

transmitting a light in which a first signal light and a dummy light having a wavelength different from the first signal light are combined via a first amplifier that amplifies light to a constant power;

separating the dummy light from the light transmitted via the first amplifier;

allowing the separated dummy light to pass through according to a variable transmittance;

combining the passed dummy light and a second signal light having a wavelength different from the dummy light;

transmitting the combined light via a second amplifier that amplifies light to a constant power;

receiving the second signal light included in the light transmitted via the second amplifier; and

controlling the transmittance.