| 摘要 |
PURPOSE:To control the quantity of light while maintaining characteristics which minimize a quantum noise and to enable accurate recording and reproduction by setting the laser beam, emitted by a laser light source, to the level at which the quantum level becomes minimum. CONSTITUTION:A grating plate 2, a light quantity adjusting plate 3, a polarization beam splitter 4, a collimator lens 6, and an objective 7 are provided between a laser light source 1 and an optical disk 8. Further, a 1st photodetector 5 for light quantity detection is provided on the projection surface of the polarization beam splitter 4 for the reflected light of the laser beam and a 2nd photodetector 10 for servo signal and data detection is provided on the projection surface of the polarization beam splitter 3 for the reflected light. A microcomputer 11 controls the quantity of the laser beam transmitted through the light quantity adjusting plate 3 according to the light quantity detection output from the 1st photodetector 5 and the modulated signal for light quantity control which is supplied through an input terminal 12. |
