Transmitter and bias adjustment method

A transmitter comprising:

• an optical modulator configured to modulate continuous wave light by any one of a plurality of modulation schemes according to a drive signal;
• a driver circuit configured to generate the drive signal based on information data;
• a deviation identification signal generation circuit configured to generate a signal value in accordance with a deviation of a bias voltage of the optical modulator by amplifying a signal value of a dither signal extracted from a modulated signal output from the optical modulator by a factor set for each of the plurality of modulation schemes so as to generate a uniform signal value;
• and
• a bias controller configured to generate a bias value at which a center of a variation range from a maximum value to a minimum value of the drive signal corresponds to transmission characteristics of the optical modulator according to one predetermined adjustment method by using the signal value generated by the deviation identification signal generation circuit,
• wherein the optical modulator operates with a bias voltage adjusted based on the bias value.