| 摘要 |
PURPOSE:To prevent a photodetector from saturating by detecting the optical output of a semiconductor laser to detect the bottom value of a photodetected pulse, and controlling a DC bias current in response to the difference between the detected value and a reference value. CONSTITUTION:A comparison controlling circuit 11 for detecting the bottom pulse of a photodetected pulse by a photodetector 2 for detecting the optical output of a semiconductor laser 1 to control a DC bias current in response to the difference between the detected value and a reference value is provided. Since the controlling circuit 11 compares the bottom value of the pulse with the reference value, it can set a DC bias value in the degree of slightly larger than an oscillation starting current in response to the difference and can hold the light emission of the laser 1 due to the bias current at the minimum limit. Thus, it can prevent the photodetector 2 from saturating and suppress the current consumption of a drive circuit to a necessary minimum limit. |
