| 摘要 |
PURPOSE:To prevent the degradation of a semiconductor laser to hold a stable characteristic for a long time by providing an integrating capacitor in the output part of a negative feedback voltage of an APC circuit and operating the APC circuit when a transistor TR is turned on. CONSTITUTION:A capacitor C1 is connected to a TR3 of an APC circuit 3. The capacitor C1 integrates the feedback voltage of the emitter of a TR3, and its capacity is selected on a basis of the frequency and the duty ratio of pulses of a pulse generating circuit 1. While a series of pulses are given from the pulse generating circuit 1, the emitter voltage of a TR 2 rises and falls repeatedly in a prescribed range. Consequently, the APC circuit 3 starts the operation immediately when a TR1 is turned on. That is, the APC circuit 3 is operated approximately simultaneously with turn-on to limit the driving current of a laser diode LD because the emitter voltage of the TR3 is held at a certain value, thereby eliminating the overshoot.
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