Optical signal reception apparatus, optical communication system, and method of generating compensation signal of optical signal reception apparatus

An optical communication system comprising:

• an optical signal transmission apparatus configured to transmit an optical signal on which polarization multiplexing and multi-value modulation are performed;
• and
• an optical signal reception apparatus configured to process the optical signal,
• wherein the optical signal reception apparatus includes:
• an optical front end configured to generate a plurality of output light beams by causing the optical signal and a local light beam to interfere with each other;
• a signal conversion unit configured to generate a plurality of digital signals by photoelectrically converting and further analog-digital converting each of the plurality of output light beams;
• a frequency difference compensation unit configured to generate a carrier recovery signal by compensating for a frequency difference between the local light beam and the optical signal with respect to the plurality of digital signals;
• a first symbol determination unit configured to determine a symbol position of the carrier recovery signal in accordance with a signal arrangement of the multi-value modulation;
• a second symbol determination unit configured to determine the symbol position of the carrier recovery signal in accordance with a signal arrangement in which the number of multi-values of the multi-value modulation is reduced;
• and
• a compensation signal generation unit configured to generate a compensation signal in the frequency difference compensation unit,
• wherein the compensation signal generation unit is configured to temporarily generate the compensation signal using a determination result of the second symbol determination unit, and then to regularly generate the compensation signal using a determination result of the first symbol determination unit, and
• wherein the compensation signal generation unit is configured to temporarily generate the compensation signal using a symbol position indicated by the determination result of the second symbol determination unit and a differential value of a difference in an angle of deviation on a complex representation of the carrier recovery signal.

A method of generating a compensation signal of an optical signal reception apparatus in a frequency difference compensation unit, the optical signal reception apparatus including an optical front end, a signal conversion unit, a frequency, difference compensation unit, a first symbol determination unit, a second symbol determination unit and a compensation signal generation unit, wherein the method comprises:

• generating, by the optical front end, a plurality of output light beams by causing an optical signal on which polarization multiplexing and multi-value modulation are performed and a local light beam to interfere with each other;
• generating, by the signal conversion unit, a plurality of digital signals by photoelectrically converting and further analog-digital converting each of the plurality of output light beams;
• generating, by the frequency difference compensation unit, a carrier recovery signal by compensating for a frequency difference between the local light beam and the optical signal with respect to the plurality of digital signals;
• determining, by the first symbol determination unit a symbol position of the carrier recovery signal in accordance with a signal arrangement of the multi-value modulation;
• determining, by the second symbol determination unit, the symbol position of the carrier recovery signal in accordance with a signal arrangement in which the number of multi-values of the multi-value modulation is reduced;
• temporarily generating, by the compensation signal generation unit, the compensation signal using a determination result of the second symbol determination unit, and then regularly generating the compensation signal using a determination result of the first symbol determination unit;
• and
• temporarily generating, by the compensation signal generation unit, the compensation signal using a symbol position indicated by the determination result of the second symbol determination unit and a differential value of a difference in an angle of deviation on a complex representation of the carrier recovery signal.