| 摘要 |
PURPOSE:To obtain accurately a control signal for optical spot without losing magnetooptic information, by providing a photodetector to obtain the control signal leading an optical beam to a prescribed position of a recording medium and a photodetector to obtain an information signal separately. CONSTITUTION:The beam irradiated from a semiconductor laser 11 in a figure is irradiated on a magnetooptic disc 17 in the state of P polarization. The beam reflected on the disc 17 is subjected to the magnetooptic effect in response to the magnetization of a minute state on the disc 17, resulting in that either R<+> or R<-> polarization rotated by the Kerr rotary angle + or -alpha of the magnetic medium is obtained, and the polarization reflected to an information signal photodetector 22 with the polarized characteristic of a beam splitter 18 is increased to the magnetooptic rotary angle beta to be R<+>' and R<->'. Further, the light amount transmitted to a control signal photodetector 21 is about TP times (where: TP is P polarized energy transmission rate) the light amount reaching the beam splitter 18. |
