Optical transmitter, optical transmission device, and transmission method

An optical transmission device comprising:

• optical transmitters, each including
• a signal-processing circuit configured to perform signal processing on a first transmission signal and output a second transmission signal,
• an optical modulator configured to modulate input light with the second transmission signal and to output an optical signal, and
• a control circuit configured to output a control signal for controlling a carrier frequency of the optical signal to the signal-processing circuit;
• and
• a multiplexer configured to multiplex optical signals output from the optical transmitters, the optical transmitters being configured to output the optical signals having carrier frequencies that are different from each other,
• wherein the signal-processing circuit includes
• a map-adjustment circuit configured to adjust a map position of the second transmission signal onto a complex plane, based on the control signal and a modulation format, and
• a phase-rotation circuit configured to apply, on the complex plane, rotation of a phase of the carrier frequency corresponding to the control signal to the second transmission signal at the adjusted map position.