| 摘要 |
PURPOSE:To execute focus control which is large in S/N ratio and excellent in accuracy, by obtaining a focus controlling signal from a reflected beam of a beam which has irradiated the front part in the running direction, instead of a focus of the irradiation beam for recording and reproducing. CONSTITUTION:A beam from a laser 1 is converged on a point B on a recording layer 8 of a recording medium running in the direction as indicated with an arrow, through a collimator lens 2, an optical modulator 3, a beam splitter 4, a 1/4 wavelength plate 5, a dichroic mirror 6 and a condensing lens 7, and recording is executed. When reproducing, a reflected ray is reflected by the beam splitter 4, is made incident to a photodetector 9, and a reproducing signal is outputted. On the other hand, a beam from a laser 10 is converged on a point C on the recording layer 8 through a collimator lens 11, a beam splitter 12, a 1/4 wavelength plate 14, the dichroic mirror 6 and the condensing lens 7, and the reflected ray is made incident to a 1/2 split photodiode 14 through the beam splitter 12, and a focus control is executed. The focus control which is large in S/N ratio and excellent in accuracy is executed since it is not influenced by a recorded hole. |
