| 摘要 |
PURPOSE:To attain the miniaturization without deteriorating the focus error detecting sensitivity, by arranging a half mirror at a collected optical path of an optical system where a reflecting light of a light spot irradiated on a recording medium is made incident to a photodetector via a condenser lens. CONSTITUTION:The reflecting light from a disc 4 passes through an objective lens 9 and a 1/4 wavelength plate 8, enters a beam splitter 7, is reflected on a polarized plane 10 and is made incident to the condenser lens 11. The light through the condenser lens 11 is cut by about 1/2 at a knife edge 19, about a half of the remaining semi-circle enters the half mirror 16 through a 1/4 wavelength plate 15, a half of the amount of light only is reflected and returned to the beam splitter 7 through the 1/4 wavelength plate 15 and the condenser lens 11. Since this returned reflecting light is subject to polarization at the 1/4 wavelength plate 15, the light is made incident to the 1st photodetector 17 by being transmitted through the polarized plane 10 to detect the focus error. Further, the light transmitting through the half mirror 16 enters the 2nd photodetector 18 and the tracking error is detected through the detection of change in a distributing amount of light. |
