| 摘要 |
PURPOSE:To obtain necessary emitting power by driving only a first current source, feedback- controlling the first current source by an optical detector at the time of reproducing, switching the first current source to control via a holding circuit and further, overlapping a second driving source at the time of recording or erasing. CONSTITUTION:At the time of the reproducing, a semiconductor laser 1 is emitted and driven only by a constant current source 2 for reproducing. Then, the laser 1 is continuously controlled by a feedback control system, which is composed of an optical detecting circuit 4, a comparator 7 and the constant current source 2 for reproducing, and constant power is kept. At the time of the recording, a switch element 10 is changed-over from the comparator 7 side to a holding circuit 9 side and an output from the circuit 9, which holds a comparing output at the time of the reproducing, goes to be effective. Then, a constant current flows to the semiconductor laser 1 by the constant current source 2 for reproducing. At such a time, a switch 8 is selected to a reference voltage VREf2 side and a current source 3 for recording is driven superimposed on the above-mentioned constant current. At the time of the erasing, a same condition is obtained, however, it is different that the switch 8 is selected to a VREf3 side. Thus, the control of reproducing power can be executed with high accuracy at a high speed and power for recording and erasing can be made stable. |
