Optical signal transmitter and method for controlling polarization multiplexed optical signal

An optical signal transmitter comprising:

• a first light source;
• a first modulator to generate a first modulated optical signal by modulating an optical signal generated by the first light source, the first modulator including a pair of optical paths and a first phase shifter to give a phase difference to the pair of optical paths;
• a second light source;
• a second modulator to generate a second modulated optical signal by modulating an optical signal generated by the second light source, the second modulator including a pair of optical paths and a second phase shifter to give a phase difference to the pair of optical paths;
• a combiner to generate a polarization multiplexed optical signal by combining the first and second modulated optical signals;
• a phase controller to control the phase difference by the first phase shifter to A−Δφ and control the phase difference by the second phase shifter to A+Aφ when the first and second modulators are driven by first and second control data signals respectively;
• and
• a power controller to control at least one of the first and second light sources based on an AC component of the polarization multiplexed optical signal when the first and second modulators are driven by the first and second control data signals respectively;
• wherein a data pattern of the first control data signal is same as the second control data signal or reversed pattern of the second control data signal;
• and
• wherein A is an optimal phase determined according to a modulation scheme of the first and second modulator at a time of data transmission, and Δφ is an arbitrary phase other than zero.

A method for controlling a polarization multiplexed optical signal in an optical signal transmitter including a first modulator having a pair of optical paths and a first phase shifter to give a phase difference to the pair of optical paths to generate a first modulated optical signal;

• a second modulator having a pair of optical paths and a second phase shifter to give a phase difference to the pair of optical paths to generate a second modulated optical signal;
• and a combiner to generate the polarization multiplexed optical signal by combining the first and second modulated optical signals, comprising:
• controlling the phase difference by the first phase shifter to A−Δφ;
• controlling the phase difference by the second phase shifter to A+Δφ;
• generating first and second control data signals as drive signals of the first and second modulators, respectively;
• and
• controlling at least one of the first and second modulators based on an AC component of the polarization multiplexed optical signal generated when the first and second modulators are driven by the first and second control data signals, respectively,
• wherein a data pattern of the first control data signal is same as the second control data signal or reversed pattern of the second control data signal;
• and
• wherein A is an optimal phase determined according to a modulation scheme of the first and second modulator at a time of data transmission, and Δφ is an arbitrary phase other than zero.

A method for controlling a polarization multiplexed optical signal in an optical signal transmitter including a first modulator having a pair of optical paths and a first phase shifter to give a phase difference to the pair of optical paths to generate a first modulated optical signal;

• a second modulator having a pair of optical paths and a second phase shifter to give a phase difference to the pair of optical paths to generate a second modulated optical signal;
• and a combiner to generate the polarization multiplexed optical signal by combining the first and second modulated optical signals, comprising:
• in a first period,
• controlling the phase difference by the first phase shifter to A−Δφ;
• controlling the phase difference by the second phase shifter to A+Δφ;
• generating first and second control data signals as drive signals of the first and second modulators, respectively;
• generating a first control parameter for controlling at least one of the first and second modulators so as to minimize an AC component of the polarization multiplexed optical signal;
• and
• generating a second control parameter for controlling at least one of the first and second modulators so as to make optical powers of the first and second modulated optical signals approximately same as each other,
• wherein a data pattern of the first control data signal is same as the second control data signal or reversed pattern of the second control data signal, and
• wherein A is an optimal phase determined according to a modulation scheme of the first and second modulator at a time of data transmission, and Δφ is an arbitrary phase other than zero, and
• in a second period,
• controlling the phase difference by the first and second phase shifters to A respectively,
• generating first and second transmission data as drive signal of the first and second modulators;
• and
• 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 modulators by the corrected second control parameter.