| 摘要 |
PURPOSE:To perform the measurement of a threshold current value in a short time without measurements of plural times by comparing a voltage signal based on a photoreceived amount with a reference voltage, and measuring a current value flowed to a semiconductor laser of the case that both voltages coincide. CONSTITUTION:When a laser light output from a semiconductor laser LD is received by a photoreceptor PIN, a voltage signal corresponding to the photoreceived amount is output, such a voltage signal is amplified by an amplifier made of an operational amplifier, and output to a voltage comparator 13. The comparator 13 compares the amplified voltage signal with a reference voltage, reduced the current applied to the base side of a transistor TR3 in case of the voltage signal > the reference voltage and rises the current in the reverse case. Accordingly, the voltage signal output from the photoreceptor PIN is applied in advance as a reference voltage to a high speed APC circuit, and the current value detected by a voltage detector 2 in case of applying the pulse voltage to the layer LD becomes a threshold current value. |
