Optical transmitter and method for controlling the same

An optical transmitter, comprising:

• an IQ modulator provided with children Mach-Zehnder modulators;
• an auto bias control circuit making direct current biases for driving the children Mach-Zehnder modulators converge to values close to null driving points of the children Mach-Zehnder modulators;
• a data selector selecting special driving data including a pair of training patterns between which there is a significant correlation, for driving the children Mach-Zehnder modulators;
• a scan circuit scanning direct current biases for setting quadrature angle of the IQ modulator;
• a monitor photo diode monitoring output of the IQ modulator during scanning direct current biases for setting the quadrature angle;
• a control circuit setting the direct current bias for setting the quadrature angle on the basis of the driving data and results monitored by the monitor photo diode;
• and
• a data switch interchanging the driving data between the children Mach-Zehnder modulators of the IQ modulator, depending on the direct current bias for setting the quadrature angle.

A method for controlling an optical transmitter, comprising the steps of:

• (a) making direct current biases for driving children Mach-Zehnder modulators of an IQ modulator in the optical transmitter converge to values close to null driving points of the children Mach-Zehnder modulators;
• (b) driving the children Mach-Zehnder modulators with special driving data including a pair of training patterns between which there is a significant correlation;
• (c) scanning direct current biases for setting quadrature angle of the IQ modulator;
• (d) monitoring output of the IQ modulator during step (c);
• (e) setting the direct current bias for setting quadrature angle on the basis of the driving data and monitored results in step (d);
• and
• interchanging the driving data between the children Mach-Zehnder modulators of the IQ modulator, depending on the direct current bias for setting the quadrature angle set in step (e),
• wherein the training patterns of step (b) have a correlation selected from strictly positive correlation and strictly negative correlation.

A method for controlling an optical transmitter, comprising the steps of:

• (a) making direct current biases for driving children Mach-Zehnder modulators of an IQ modulator in the optical transmitter converge to values close to null driving points of the children Mach-Zehnder modulators;
• (b) driving the children Mach-Zehnder modulators with special driving data including a pair of training patterns between which there is a significant correlation;
• (c) scanning direct current biases for setting quadrature angle of the IQ modulator;
• (d) monitoring output of the IQ modulator during step (c);
• (e) setting the direct current bias for setting quadrature angle on the basis of the driving data and monitored results in step (d);
• and
• interchanging the driving data between the children Mach-Zehnder modulators of the IQ modulator, depending on the direct current bias for setting the quadrature angle set in step (e),
• wherein both of the children Mach-Zehnder modulators are driven with the same electrical signal generated from binary data to be modulated on optical data.

A method for controlling an optical transmitter, comprising the steps of:

• (a) making direct current biases for driving children Mach-Zehnder modulators of an IQ modulator in the optical transmitter converge to values close to null driving points of the children Mach-Zehnder modulators;
• (b) driving the children Mach-Zehnder modulators with special driving data including a pair of training patterns between which there is a significant correlation;
• (c) scanning direct current biases for setting quadrature angle of the IQ modulator;
• (d) monitoring output of the IQ modulator during step (c);
• (e) setting the direct current bias for setting quadrature angle on the basis of the driving data and monitored results in step (d);
• and
• interchanging the driving data between the children Mach-Zehnder modulators of the IQ modulator, depending on the direct current bias for setting the quadrature angle set in step (e),
• wherein, in step (b), the special driving data includes data generated for pre-equalization.

An optical transmitter, comprising:

• an IQ modulator provided with children Mach-Zehnder modulators;
• an auto bias control circuit making direct current biases for driving the children Mach-Zehnder modulators converge to values close to null driving points of the children Mach-Zehnder modulators;
• a data selector selecting special driving data including a pair of training patterns between which there is a significant correlation, for driving the children Mach-Zehnder modulators;
• a scan circuit scanning direct current biases for setting quadrature angle of the IQ modulator;
• a monitor photo diode monitoring output of the IQ modulator during scanning direct current biases for setting the quadrature angle;
• a control circuit setting the direct current bias for setting the quadrature angle on the basis of the driving data and results monitored by the monitor photo diode;
• and
• a data switch interchanging the driving data between the children Mach-Zehnder modulators of the IQ modulator, depending on the direct current bias for setting the quadrature angle,
• wherein the training patterns have a correlation selected from strictly positive correlation and strictly negative correlation.