Patent ID: 8731409

Claim:
A method for controlling a polarization multiplexed optical signal in an optical signal transmitter having a first outer modulator to generate a first modulated optical signal, a second outer modulator to generate a second modulated optical signal, and a combiner to generate a polarization multiplexed optical signal by combining the first and second modulated optical signals, comprising: in a first period, generating a first control parameter for controlling at least one of the first and second outer modulators so as to make a difference between an optical power of the polarization multiplexed optical signal obtained when the first outer modulator is in no emission state and an optical power of the polarization multiplexed optical signal obtained when the second outer modulator is in no emission state approximately zero; generating a second control parameter for controlling at least one of the first and second outer modulators so as to make an optical power of the first modulated optical signal and an optical power of the second modulated optical signal approximately same as each other; and in a second period, correcting the second control parameter based on an error between the first control parameter and the second control parameter, and controlling at least one of the first and second outer modulators by the corrected second control parameter.