Patent ID: 8582981

Claim:
An optical transmitter for generating and transmitting a multiphase modulated signal, comprising: a light source that generates an optical light; a splitter that splits the light received from the light source into a plurality of lights; a plurality of optical paths that each input a respective light split by the splitter; a plurality of phase modulators that each perform phase modulation of a respective light propagating through a corresponding optical path in accordance with a data signal; a first bias supply driver that supplies bias voltages for regulating an operating point of each of the plurality of phase modulators; phase shifters that each impart a predetermined phase difference into the respective light propagating through the corresponding optical paths; a second bias supply driver that supplies bias voltages for phase difference regulation to a side of the phase shifters; a coupler that couples lights output from the corresponding optical paths; a monitor that monitors an output of the coupler; and a bias controller that performs a feedback control of one of more of the first bias supply driver and the second bias supply driver based on said monitoring, where the feedback control corresponds to an output level detected in relation to variation in the bias voltages and an amount of a phase shift imparted from the phase shifters to the lights propagating through the corresponding optical paths is regulated to correspond to the bias voltages for stabilization at an optimal value, and wherein one of the first and second bias supply drivers superimposes a pilot signal on either one of bias voltages being supplied to a side of at least one of the plurality of phase modulators and to the side the phase shifters, the pilot signal having a frequency lower than a frequency of a bit rate of the data signal.