| 摘要 |
PURPOSE:To make a bias current constant and to prevent the entering of the bias current into the light emitting region of laser by providing a diode between the output of a current source whose current is changed in correspondence with the characteristics of the laser and the output of a current source which supplies the bias current. CONSTITUTION:The sinking current of NPN transistor 7 for current switching is set at a value larger than the maximum output current of a laser driving current source 5. Thus, the current which is supplied to a semiconductor laser 4 from the current source 5 becomes always zero when the transistor in ON. The bias current for a laser 4 is a constant value which is imparted from a current source 6. Since a diode 12 is provided, the bias current is not associated with the operation of the transistor 7. Therefore, even if a laser driving current is changed in response to the change in temperature of the laser 4, the bias current becomes constant. In this way, entering of the bias current into the light emitting region of the laser can be prevented. |
