| 摘要 |
PURPOSE:To prevent the destruction of a semiconductor laser due to an abnormal overcurrent such as a high frequency noise by holding the optical output of the semiconductor laser to be constant by means of an automatic output control circuit of two series for exclusive reading use and exclusive writing/ erasing use. CONSTITUTION:At the time of reading or writing/erasing, a light beam emitted from a semiconductor laser 13 is detected by a pin-photodiode 17, is subjected to current/voltage conversion by means of an I/V amplifier 1 or 14 and outputted. A current comparator 2 or 23 compares the output with the reference current of a reference current source 6 or 21 and operates transisters 5, 4 or 20, 18. The current of the laser 13 is controlled through the transister 4 or 18 and a current limiting resistor 8 or directly and an optical power is controlled to be a prescribed constant value. At this time, an input signal 9 or 10 is turned on/off with the frequency of light modulation in the state of turning on or at the time of writing and the capacity possesed by the laser and the resistor 8 form an LPF. Consequently, at the time of reading out data, the destruction of the laser 13 due to abnormal overcurrent such as the noise of super-high frequency is prevented. |
