Optical communication system, transmission station, and method of optical communication

1. An optical communication system comprising:

a transmission station having

a plurality of optical transmitters, including an optical transmitter that transmits light having a first wavelength different from a second wavelength,

a switch that delivers the light of wavelengths transmitted by the optical transmitters by allowing the light to pass therethrough,

a wavelength controller that performs control to change the first wavelength of the light transmitted by the optical transmitter to a third wavelength between the first wavelength and the second wavelength, and

a switch controller that causes the switch to allow the light of the first wavelength and the third wavelength transmitted from the optical transmitter to pass through the switch and causes the switch to limit the wavelength of the light allowed to pass through to the third wavelength when the wavelength controller performs control to change the wavelength of the light transmitted by the optical transmitter;

a plurality of optical receivers; and

a splitter that splits the light transmitted by the optical transmitter to the plurality of optical receivers, wherein

the optical transmitter includes a variable-wavelength light source capable of transmitting the light of the first wavelength and the third wavelength,

a first optical receiver of the plurality of optical receivers includes:

a first optical filter having a first transmission band including the first and third wavelengths; and

a first receiving unit that receives the light having passed through the first optical filter, and

a second optical receiver of the plurality of optical receivers includes:

a second optical filter having a second transmission band including the second and third wavelengths; and

a second receiving unit that receives the light having passed through the second optical filter.

2. The optical communication system according to claim 1 , wherein

the plurality of optical receivers are provided in a plurality of reception stations, respectively,

two of the plurality of reception stations each include:

a first reception-station-side transmitter that transmits the light of a fourth wavelength to the transmission station; and

a second reception-station-side transmitter that transmits the light of a fifth wavelength to the transmission station, and

the transmission station further includes a transmission-station-side receiver that receives the light of the fourth wavelength transmitted from the first reception-station-side transmitter and the light of the fifth wavelength transmitted from the second reception-station-side transmitter.

3. The optical communication system according to claim 1 , further comprising:

a first wireless transmission point that wirelessly transmits a signal received by the first receiving unit; and

a second wireless transmission point that wirelessly transmits a signal received by the second receiving unit,

wherein the first and second wireless transmission points perform the wireless transmission in cooperation.

4. The optical communication system according to claim 1 , wherein the wavelength controller selects the optical transmitter from a plurality of candidates based on a communication state between the plurality of optical receivers and the plurality of candidates including a first transmission-station-side optical transmitter that transmits the light of neighboring wavelengths adjacent to a short-wavelength side of the second wavelength and a second transmission-station-side optical transmitter that transmits the light of neighboring wavelengths adjacent to a long-wavelength side of the second wavelength.

5. The optical communication system according to claim 4 , wherein the communication state includes a communication amount between each of the plurality of candidate transmission-station-side optical transmitters and a corresponding optical receiver.

6. The optical communication system according to claim 4 , wherein the communication state includes the number of the optical receivers with which each of the plurality of candidate transmission-station-side optical transmitters communicates.

7. A transmission station, connected to a splitter that splits light received from the transmission station to a plurality of optical receivers, comprising:

a plurality of optical transmitters, including an optical transmitter connected to the splitter, wherein the optical transmitter includes a variable-wavelength light source capable of transmitting the light of a first wavelength, different from a second wavelength, and the light of a third wavelength between the first wavelength and the second wavelength;

a wavelength controller that performs control to change the wavelength of the light transmitted by the optical transmitter from the first wavelength to the third wavelength;

a switch that delivers the light of wavelengths transmitted by the transmission-station-side optical transmitters by allowing the light to pass therethrough; and

a switch controller that causes the switch to allow the light of the first and third wavelengths transmitted from the optical transmitter to pass through the switch and causes the switch to limit the wavelength of the light allowed to pass through to the third wavelength when the wavelength controller performs control to change the wavelength of the light transmitted by the optical transmitter, wherein

the light of the first and third wavelengths is receivable by a first optical receiver among the plurality of optical receivers, and

the light of the second and third wavelengths is receivable by a second optical receiver among the plurality of optical receivers.

8. The transmission station according to claim 7 , wherein the wavelength controller selects the optical transmitter from a plurality of candidates based on a communication state between the plurality of optical receivers and the plurality of candidates including a first transmission-station-side optical transmitter that transmits the light of neighboring wavelengths adjacent to a short-wavelength side of the second wavelength and a second transmission-station-side optical transmitter that transmits the light of neighboring wavelengths adjacent to a long-wavelength side of the second wavelength.

9. The transmission station according to claim 8 , wherein the communication state includes a communication amount between each of the plurality of candidate transmission-station-side optical transmitters and a corresponding optical receiver.

10. The transmission station according to claim 8 , wherein the communication state includes the number of the optical receivers with which each of the plurality of candidate transmission-station-side optical transmitters communicates.

11. The transmission station according to claim 7 , wherein

the plurality of optical receivers are provided in a plurality of reception stations, respectively,

two of the plurality of reception stations each include:

a first reception-station-side transmitter that transmits the light of a fourth wavelength to the transmission station; and

a second reception-station-side transmitter that transmits the light of a fifth wavelength, and

the transmission station further includes a transmission-station-side receiver that receives the light of the fourth wavelength transmitted from a first reception-station-side transmitter provided in any one of the plurality of reception stations and the light of the fifth wavelength transmitted from the second reception-station-side transmitter provided in any one of the plurality of reception stations.

12. A method of optical communication comprising:

performing control to change a wavelength of light transmitted by an optical transmitter in a transmission station from a first wavelength, different from a second wavelength, to a third wavelength between the first wavelength and the second wavelength;

selectively transmitting the light of the first wavelength and the light of the third wavelength from the optical transmitter, including

delivering the light of the first and third wavelengths transmitted by the optical transmitter by allowing the light to pass through the transmission station, and

limiting the wavelength of the light allowed to pass through the transmission station to the third wavelength when the control to change the wavelength of the light transmitted by the optical transmitter is performed;

splitting the light transmitted from the optical transmitter to a plurality of optical receivers using a splitter;

receiving, at a first optical receiver among the plurality of optical receivers, the light that passed through a first optical filter having a first transmission band including the first wavelength and the third wavelength; and

receiving, at a second optical receiver among the plurality of optical receivers, the light that passed through a second optical filter having a second transmission band including the second wavelength and the third wavelength.

13. The method of optical communication according to claim 12 , wherein

the optical transmitter is one of a plurality of transmission-station-side optical transmitters provided in the transmission station,

the method further comprises selecting the optical transmitter from a plurality of candidates based on a communication state between the plurality of optical receivers, the plurality of candidates including a first transmission-station-side optical transmitter that transmits the light of neighboring wavelengths adjacent to a short-wavelength side of the second wavelength and a second transmission-station-side optical transmitter that transmits the light of neighboring wavelengths adjacent to a long-wavelength side of the second wavelength.

14. The method of optical communication according to claim 13 , wherein the communication state includes a communication amount between each of the plurality of candidate transmission-station-side optical transmitters and a corresponding optical receiver.

15. The method of optical communication according to claim 13 , wherein the communication state includes the number of the optical receivers with which each of the plurality of candidate transmission-station-side optical transmitters communicates.