Patent ID: 7257332

Claim:
An optical transmitter comprising: an amplitude modulation unit performing amplitude modulation of only a one-side amplitude of a main signal with a low-frequency signal having a predetermined frequency; an optical modulator receiving an input signal generated by the amplitude modulation unit after the one-side amplitude modulation, and modulating an incoming light in response to the received signal in accordance with a predetermined modulation-characteristic curve to output an optical output signal; and an operating point control unit applying a predetermined bias voltage to the optical modulator to control a level of the input signal substantially applied to the modulation-characteristic curve so that the one-side amplitude of the main signal is applied to a minimum portion of the modulation-characteristic curve of the optical modulator; wherein the amplitude modulation unit superimposes a signal, having the predetermined frequency in phase or 180 degrees out of phase with the low-frequency signal, on the input signal generated after the one-side amplitude modulation, so that an opposite-side amplitude of the main signal is canceled.