| 摘要 |
PURPOSE:To drive a laser diode under a stable and constant high frequency superimposing condition by controlling a sperimposed high frequency current amplitude in response to the temperature change in the differentiation quantum efficiency of the laser diode and applying amplitude limit so that the negative peak of a high frequency current is not below a prescribed positive current. CONSTITUTION:The amplitude of an analog signal current inputted to the laser diode 1 from a laser diode drive circuit 2 is increased/decreased in inversely proportion to the change in the differentiation quantum efficiency. Thus, after a voltage across a monitor resistor 6 is amplified by a differential amplifier 7 and the amplified result is fed to a peak detector 8. A differential amplifier 9 outputs a voltage difference between an output voltage of the peak detector 8 and a reference voltage Vr to a variable attenuator 11, which changes a high frequency current amplitude fed from a high frequency signal generator 4 to the laser diode 1. Thus, the amplitude of a superimposed high frequency optical signal is constant even when the differentiation quantum efficiency is changed. On the other hand, a high frequency amplitude limit circuit 12 clips the peak value of the superimposed high frequency voltage (current) inputted from the variable attenuator 11 so that the peak is not smaller than a prescribed positive clip voltage (current) inputted to a reference voltage (current) input terminal 13. |
