| 摘要 |
PURPOSE:To attain the detection of information with a satisfactory level of light quantity and to improve the recording density, by providing a photodetector so that the superposed positions of the 0th-degree light and the 1st-degree light as well as the 1st-degree light and 2nd-degree light are covered at a time. CONSTITUTION:A light source uses an array type semiconductor laser 9 having two luminous points. One of both beams is condensed into a groove or an area between grooves via a collimator lens 10, a beam splitter 11 and a condenser lens 5. While the other beam is condensed to the groove edge. The reflected light sent from the groove edge is led to the photodetectors A6 and B7 for detection of an information signal. While the reflected light sent from the groove or the area between grooves is separated by a knife edge mirror 13 and led to a track error detector 16 and a focus error detector 15. For detection errors, a beam spot condensed into the groove or the area between grooves is used. Thus a track error is detected by a push-pull method in a far field and a focus error is detected by a knife edge method respectively. |
