Patent ID: 8457503

Claim:
An optical transmitter apparatus, comprising: a phase modulator, having a first phase modulation element configured to generate a first modulation signal on a first arm in accordance with a first driving signal, a second phase modulation element for generating a second modulation signal on a second arm in accordance with a second driving signal, and a phase shifter configured to provide a phase difference between the first arm and the second arm, which generates a phase-modulated signal by combining the first and second modulation signals; an intensity modulator configured to perform intensity modulation on the phase-modulated signal output from the phase modulator; a photodetector configured to generate a power signal representing a power of an AC component of an optical signal output from the intensity modulator; first and second amplifiers configured to amplify the first and second drive signals; a gain adjuster configured to generate a gain adjusting signal adjusting again of the first and second amplifiers; a first superimposer configured to superimpose a first low-frequency signal on the gain adjusting signal; a first detector configured to perform synchronous detection on the power signal by using the first low-frequency signal; a phase adjuster configured to generate a phase adjusting signal to adjust the amount of phase sift of the phase shifter; a second superimposer configured to superimpose a second low-frequency signal on the phase adjusting signal; and a second detector configured to perform synchronous detection on the power signal by using the second low-frequency signal, wherein the gain adjuster adjusts a gain of at least one of the first amplifier and the second amplifier based on a result of the synchronous detection by the first detector, and the phase shift adjuster adjusts the amount of phase shift of the phase shifter based on a result of the synchronous detection by the second detection unit.