PURPOSE: To prevent a semiconductor laser from being damaged and to prevent the abnormal emission of laser light due to the runaway of an APC circuit by a method wherein driving current of the semiconductor laser is monitored apart from the APC circuit of the semiconductor laser to detect the runaway of the APC circuit and the supply of power to the APC circuit is stopped when the runaway of the APC circuit is detected.
CONSTITUTION: Current is supplied to an APC circuit from a switching circuit 5 when a photo coupler 51 is on. An APC trouble detecting circuit 1 detects current IL which flows in a semiconductor laser chip 21 as voltage across a resistor 44 and it turns off the photo coupler 51 of the switching circuit 5 when the detected value of the voltage is equal to or above a specified value. Power is supplied to the APC trouble detecting circuit 1 from a power supply + Vcc, a different power supply from that of the APC circuit A. And, the voltage across the resistor 44 is converted into a voltage level of the APC trouble detecting circuit 1 by means of an amplifier 11. An A/D converter built-in CPU 12 outputs a signal which turns off the photo coupler 51 when the voltage is equal to or above the specified level. The supply of power to the semiconductor laser is thus controlled.
ISHIDA YASUHIKO
TAKAMIYA MAKOTO
ASHIBA JUN
UEDA SHINJI
KATO SHIGEKI
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