BIAS VOLTAGE CONTROL CIRCUIT CORRESPONDING TO MARK RATE FLUCTUATION

摘要

PROBLEM TO BE SOLVED: To stably control a bias voltage by providing the circuit with a control target value selection circuit for matching the inclination of a change in the object value to be controlled changing according to α parameter positive and negative codes and the inclination of a change in the control target value at all times and outputting the control target value even at the time of the α parameter positive and negative code conversion. SOLUTION: A mark rate detecting circuit 3 detects the mark rate of an input electric signal from the opposite phase output of a Mach-Zehnder driving circuit 4. This mark rate detecting circuit 3, a standardization circuit 2 which matches the change width of the control target value and the fluctuation width of the object to be controlled at the time of a mark rate fluctuation and the control target value selection selection circuit 1 for matching the inclination of the change in the object value to be controlled changing according to the αparameter positive and negative codes and the inclination of the change in the control target value at all times are disposed between the Mach-Zehnder driving circuit 4 and a bias voltage control circuit 11. Even if the positive and negative codes of the α parameter are changed by an αparameter positive and negative code conversion input signal, the control target value matching the output value of an average light output detecting circuit 10 of the object to be controlled corresponding to the mark rate is outputted.