Patent ID: 8670674

Claim:
An optical transmitter comprising: a first modulator that modulates a first optical signal with a first data signal; a second modulator that modulates a second optical signal with a second data signal; a multiplexer that multiplexes the modulated first optical signal and the modulated second optical signal to output a multiplexed signal; a phase difference data generator that generates a phase difference signal corresponding to a phase difference between the modulated first optical signal and the modulated second optical signal from the multiplexed signal; a controller that controls the phase difference between the modulated first optical signal and the modulated second optical signal based on the phase difference signal; and an optical source that produces a light and outputs the produced light to the first and second modulators, wherein the controller calculates a ratio between a rate of change in an optical output power and a rate of a change in a power of a specific frequency component, and adjusts phase of the first and second optical signals in the first and second modulators based on the phase difference data, if the ratio is other than 1.