Signal processing device and transmission device

1. A signal processing device comprising:

a memory; and

a processor coupled to the memory and configured to:

compensate an electric field signal representing an electric field component in an optical signal input from a transmission channel for an optical frequency offset between light sources on a transmission side and a reception side of the optical signal based on a compensation value;

calculate an estimated value of the optical frequency offset from data having a fixed pattern in the electric field signal;

generate a plurality of candidates for the compensation value from the estimated value;

calculate power of the optical signal compensated for the optical frequency offset based on each of the plurality of candidates; and

select an initial value of the compensation value from the plurality of candidates based on the power of the optical signal.

2. The signal processing device according to claim 1 , wherein the processor generates the plurality of candidates for the compensation value by shifting the estimated value within a range according to accuracy of a center frequency of each of the light sources on the transmission side and the reception side of the optical signal.

3. The signal processing device according to claim 1 , wherein the processor selects the candidate having the highest power of the optical signal among the plurality of candidates.

4. The signal processing device according to claim 1 , wherein the processor is configured to:

perform adaptive equalization on the electric field signal in accordance with filter coefficients to compensate for degradation caused in the optical signal in the transmission channel; and

set initial values of the filter coefficients according to the initial value of the compensation value.

5. A transmission device comprising:

a first light source configured to output local oscillation light; and

an optical transmitter coupled to the first light source and configured to:

convert an optical signal input from a transmission channel into an electric signal by detecting the optical signal with the local oscillation light and receive the electric signal;

convert the electric signal into an electric field signal representing an electric field component in the optical signal; and

compensate the electric field signal for an optical frequency offset between the first light source and a second light source on a transmission side of the optical signal based on a compensation value;

calculate an estimated value of the optical frequency offset from data having a fixed pattern in the electric field signal;

generate a plurality of candidates for the compensation value from the estimated value;

calculate power of the optical signal compensated for the optical frequency offset based on each of the plurality of candidates; and

select an initial value of the compensation value from the plurality of candidates based on the power of the optical signal.

6. The transmission device according to claim 5 , wherein the optical transmitter generates the plurality of candidates for the compensation value by shifting the estimated value within a range according to accuracy of a center frequency of each of the light sources on the transmission side and the reception side of the optical signal.

7. The transmission device according to claim 5 , wherein the optical transmitter selects the candidate having the highest power of the optical signal among the plurality of candidates.

8. The transmission device according to claim 5 , wherein the optical transmitter is configured to:

perform adaptive equalization on the electric field signal in accordance with filter coefficients to compensate for degradation caused in the optical signal in the transmission channel; and

set initial values of the filter coefficients according to the initial value of the compensation value.