Optical transmitter, optical transmission device, and mapping method

An optical transmission device comprising:

• an optical transmitter configured to comprise
• a signal-process circuit configured to execute signal-process for a transmission signal,
• an optical modulator configured to modulate light input by the transmission signal output from the signal-process circuit, and 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-process circuit, wherein
• the signal-process circuit comprises
• a phase-rotation circuit configured to apply phase rotation of the carrier frequency on a complex plane according to the control signal, to the transmission signal,
• a map-adjustment circuit configured to determine scale factor for a map according to an angle of the phase rotation, and
• a modulation-format-map circuit configured to map the transmission signal on the complex plane based on a modulation format and the scale factor;
• and
• a multiplexer configured to include the plurality of optical transmitters and combine optical signals that are respectively output from the plurality of the optical transmitters, wherein
• the phase-rotation circuit is configured to rotate, on the complex plane, the phase of the carrier frequency mapped based on the scale factor.

A mapping method causing an optical transmitter to execute processing, the processing comprising:

• obtaining an amount of phase rotation on a complex plane according to a carrier frequency drift of a transmission signal;
• determining scale factor for adjusting map, on the complex plane, the transmission signal according to the phase-rotation amount;
• and
• mapping the transmission signal on the complex plane based on a modulation format and the scale factor.