Patent ID: 8909067

Claim:
An optical output module comprising: a laser; first phase modulating means for modulating a phase of an optical signal output from the laser based on a first bias voltage in which a first modulation signal is inherent; second phase modulating means for modulating a phase of the optical signal output from the laser based on a second bias voltage in which a second modulation signal is inherent; phase shift means for shifting a phase of the optical signal output from the laser based on a third bias voltage; and bias control means for controlling the third bias voltage, wherein an optical signal of which phase is modulated by the first phase modulating means and an optical signal of which a phase is modulated by the second phase modulating means and of which a phase is shifted by the phase shift means are combined to be a modulated optical signal, and the modulated optical signal is output, wherein the first phase modulating means modulates a phase of the optical signal output from the laser based on the first bias voltage in which the first modulation signal and a first low-frequency signal are inherent, the second phase modulating means modulates a phase of the optical signal output from the laser based on the second bias voltage in which a second low-frequency signal which is a low-frequency signal different from the first low-frequency signal and the second modulation signal are inherent, the optical output module further includes detection means for detecting a first power which is the power of the modulated optical signal at a timing where both of a voltage of the first low-frequency signal and a voltage of the second low-frequency signal are one of positive and negative and a second power which is the power of the modulated optical signal at a timing where one of the voltages of the first low-frequency signal and the second low-frequency signal is positive and the other voltage is negative, and the bias control means controls the third bias voltage so that a difference between the first power and the second power becomes small based on the detection result of the detection means.