Optical transmission system and transmission quality monitoring method

A transmission quality monitoring method comprising:

• in which a plurality of optical transmitters converting an input signal into a frequency modulation signal through frequency modulation conversion processing;
• in which the plurality of optical transmitters multiplexing monitoring signals, which are different in frequency from each other among the plurality of optical transmitters and are not frequency modulated, with the frequency modulation signal that is frequency modulated;
• in which the plurality of optical transmitters converting the frequency modulation signal that is an electric signal in which the monitoring signals are multiplexed, into optical signals having different wavelengths among the plurality of optical transmitters;
• in which a relay device acquiring a combined signal obtained by combining the optical signals having the different wavelengths from each other and converting the combined signal into an electric signal;
• and
• in which the relay device measuring transmission quality of the plurality of monitoring signals with different frequencies included in the electric signal.

An optical transmitter comprising:

• a frequency modulation converter configured to convert an input signal into a frequency modulation signal through frequency modulation conversion processing;
• a multiplexer configured to multiplex monitoring signals which are different in frequency from each other among a plurality of optical transmitters and are not frequency modulated, with the frequency modulation signal that is frequency modulated;
• and
• an optical modulator configured to convert the frequency modulation signal that is an electric signal in which the monitoring signals are multiplexed, into optical signals having different wavelengths among the plurality of optical transmitters.