| 摘要 |
PURPOSE:To obtain a fixed track space by dividing the laser light into three beams by means of a grating and setting the 0 order beam right above a reproduction track and the + or -1 order beams set by half on the reproduction track in a reproduction mode respectively through distribution of the grating. CONSTITUTION:The laser beam delivered from a semiconductor laser source 201 is divided into three beams, that is, 0 and + or -1 order diffracted beams through a grating 203. These beams are turned toward the track on a disk, and three beam spots are obtained in response to said three diffracted beams. A photodetector 280-2 detects the reflected light sent from the beam spot of the primary diffracted light. A switch 416 is closed at the time of recording, and the output of a constant current source 415 which is equal to the voltage value which increases when the beam comes half over a track is added to the output of a power supply voltage converting circuit 401. Then a tracking mirror 205 is moved in accordance with the difference between the above-mentioned added voltage and the voltage value (output of 402) related to the spot of the other primary diffracted light. |
