Optical communication apparatus and frequency control method

1. An optical communication apparatus that receives a frequency multiplexed signal in which a plurality of optical signals are frequency multiplexed and in which each of the optical signals includes a plurality of multiplexed subcarriers, the optical communication apparatus comprising:

a plurality of transceivers, each of the transceivers corresponding to a respective one of the plurality of optical signals and configured to perform a reception process on a band which is a processing target and in which a corresponding one of the optical signals is included, and to calculate a frequency offset amount between a frequency of local light and a carrier frequency of the corresponding one of the optical signals and calculate a carrier frequency interval that is a frequency interval between the frequency of the local light and a carrier frequency of an optical signal adjacent to the corresponding one of the optical signals; and

a frequency controller configured to calculate an adjustment amount on a basis of the calculated frequency offset amount and the calculated carrier frequency interval and to transmit the calculated adjustment amount to an optical communication apparatus that is a source of the optical signals, the transmitted adjustment amount being used by the source optical communication apparatus to adjust the carrier frequencies of the optical signals.

2. The optical communication apparatus according to claim 1 , wherein each of the transceivers comprises:

a coherent receiver to perform coherent detection on the processing target band to convert the corresponding one of the optical signals into an electric signal; and

a digital signal processor to perform digital signal processing on the electric signal to calculate the frequency offset amount and the carrier frequency interval.

3. The optical communication apparatus according to claim 2 , wherein the digital signal processor calculates the carrier frequency interval on a basis of a signal component of a part of the optical signal adjacent to the corresponding one of the optical signals, the signal component of the part of the optical signal being included in the electric signal.

4. The optical communication apparatus according to claim 3 , wherein the digital signal processor calculates, on a basis of the signal component of the optical signal adjacent to the corresponding one of the optical signals, a frequency interval between the frequency of the local light and a subcarrier located at an end portion of the optical signal adjacent to the corresponding one of the optical signals, the end portion being on a side closer to the corresponding one of the optical signals, and calculates, on a basis of the calculated frequency interval and a predetermined frequency interval between adjacent subcarriers, the carrier frequency interval.

5. A frequency control method in an optical communication system that comprises a first optical communication apparatus including a plurality of first transceivers capable of transmitting a frequency multiplexed signal in which a plurality of optical signals are frequency multiplexed and in which each of the optical signals includes a plurality of multiplexed subcarriers and a second optical communication apparatus including a plurality of second transceivers to receive the optical signals transmitted from the first transceivers, each of the second transceivers corresponding to a respective one of the optical signals, the method comprising:

generating and transmitting the optical signals of different frequencies;

performing a reception process on a band which is a processing target and in which a corresponding one of the transmitted optical signals is included;

calculating a frequency offset amount between a frequency of local light and a carrier frequency of the corresponding one of the optical signals;

calculating a carrier frequency interval that is a frequency interval between the frequency of the local light and a carrier frequency of an optical signal adjacent to the corresponding one of the optical signals;

calculating, on a basis of the calculated frequency offset amount and the calculated carrier frequency interval, a frequency compensation amount for the optical signals transmitted by the first transceivers; and

adjusting, on a basis of the calculated frequency compensation amount, frequencies of the optical signals transmitted by the first transceivers.

6. A control circuit of an optical communication apparatus that receives a frequency multiplexed signal in which a plurality of optical signals are frequency multiplexed and in which each of the optical signals includes a plurality of multiplexed subcarriers, wherein

the optical communication apparatus comprises

a plurality of transceivers, each of the transceivers corresponding to a respective one of the plurality of optical signals and configured to perform a reception process on a band which is a processing target and in which a corresponding one of the optical signals is included, and to calculate a frequency offset amount between a frequency of local light and a carrier frequency of the corresponding one of the optical signals and calculate a carrier frequency interval that is a frequency interval between the frequency of the local light and a carrier frequency of an optical signal adjacent to the corresponding one of the optical signals, and

the control circuit is configured to calculate an adjustment amount on a basis of the calculated frequency offset amount and the calculated carrier frequency interval and to transmit the calculated adjustment amount to an optical communication apparatus that is a source of the optical signals, the transmitted adjustment amount being used by the source optical communication apparatus to adjust the carrier frequencies of the optical signals.

7. A non-transitory computer-readable recording medium of an optical communication apparatus that receives a frequency multiplexed signal in which a plurality of optical signals are frequency multiplexed and in which each of the optical signals includes a plurality of multiplexed subcarriers, the optical communication apparatus comprising a plurality of transceivers, each of the transceivers corresponding to a respective one of the plurality of optical signals and configured to perform a reception process on a band which is a processing target and in which a corresponding one of the optical signals is included, and to calculate a frequency offset amount between a frequency of local light and a carrier frequency of the corresponding one of the optical signals and calculate a carrier frequency interval that is a frequency interval between the frequency of the local light and a carrier frequency of an optical signal adjacent to the corresponding one of the optical signals, the recording medium storing therein a program for causing a processor to execute:

a process of calculating an adjustment amount on a basis of the calculated frequency offset amount and the calculated carrier frequency interval and transmitting the calculated adjustment amount to an optical communication apparatus that is a source of the optical signals, the transmitted adjustment amount being used by the source optical communication apparatus to adjust the carrier frequencies of the optical signals.