| 摘要 |
PURPOSE:To reduce costs, by detecting the amount of output light from a semiconductor laser by a light detector, comparing the result with a reference signal by a comparator, controlling the counting mode of an up and down counter by the output of the comparator, thereby using the relatively low-speed light detector. CONSTITUTION:A light detector 9 comprising a photodiode outputs a current, which is proportional to the intensity of the laser beam from a semiconductor laser 1. The current is converted into a voltage by an amplifier 11. The voltage is compared with a reference voltage Vref in a comparator 12. The output voltage of the comparator 12 controls the counting mode of an up and down counter 13 based on the relationship of the magnitudes of both input voltages. The output of the up and down counter 13 is converted into an analog quantity by a D/A converter 16. A current, which is proportional to the output, is flowed to the semiconductor laser by a semiconductor driving circuit 8. The current of the semiconductor laser is controlled and maintained so that both inputs to the comparator become always equal. |
