Optical relay apparatus, optical transmission system, and optical relay method

An optical transmission system comprising a plurality of optical relay apparatuses, wherein the plurality of optical relay apparatuses comprise:

• a coherent optical reception front-end unit configured to coherently detect an input optical signal to be input from the optical relay apparatus in a preceding stage, based on local oscillation light, and to output the coherently detected first analog electric signal;
• a coherent optical transmission front-end unit configured to coherently modulate a second analog electric signal acquired by turning around the first analog electric signal, based on transmission light, and to output the coherently modulated output optical signal to the optical relay apparatus in a next stage;
• and
• an analog compensator configured to perform analog signal processing on the first analog electric signal in such a way as to compensate for signal quality according to a signal characteristic between an input of the coherent optical reception front-end unit and an output of the coherent optical transmission front-end unit, and thereby generate the second analog electric signal,
• wherein the analog compensator comprises:
• an analog signal processor configured to perform the analog signal processing;
• a monitor configured to monitor a signal characteristic of any of the input optical signal, the first analog electric signal, the second analog electric signal, and the output optical signal;
• and
• a controller configured to control an operation of the analog signal processing, based on a result of the monitoring.

An optical relay method in an optical relay apparatus including a coherent optical reception front-end unit and a coherent optical transmission front-end unit, the optical relay method comprising:

• by the coherent optical reception front-end unit, coherently detecting an input optical signal to be input, based on local oscillation light, and outputting the coherently detected first analog electric signal;
• by the coherent optical transmission front-end unit, coherently modulating a second analog electric signal acquired by turning around the first analog electric signal, based on transmission light, and outputting the coherently modulated output optical signal;
• performing analog signal processing on the first analog electric signal in such a way as to compensate for signal quality according to a signal characteristic between an input of the coherent optical reception front-end unit and an output of the coherent optical transmission front-end unit, thereby generating the second analog electric signal;
• monitoring a signal characteristic of any of the input optical signal, the first analog electric signal, the second analog electric signal, and the output optical signal;
• and
• controlling an operation of the analog signal processing, based on a result of the monitoring.