| 摘要 |
PURPOSE:To improve the sensitivity of position detection by employing simple constitution by shielding the elliptic section of a reflected luminous flux along a cut line approximately parallel with the short axis of this elliptic section in a focus error detector of an optical pickup optical system of an optical disc. CONSTITUTION:A laser beam B0 emitted from a semiconductor laser 1 is converged by a coupling lens 2 and becomes a parallel beam, and its advance direction is changed by a polarizing beam splitter 3, and this beam passes a 1/4 wavelength plate 4 and is condensed as a spot having about 1.0mum diameter toward the center of a track T on an optical disc 6 through an object lens 5. A reflected beam B from the optical disc 6 passes the object lens 5 and has the plane of polarization changed by the 1/4 wavelength plate 4 and is separated from the incident beam B0 by the polarizing beam splitter 3 and is converged by a condenser lens 7. 60-90% elliptic section of this converged reflected beam B in the direction of a long axis l of this section is shielded and received by a track detecting photodetector 8 to detect a track position. 10-40% remainder of the reflected beam B which is not shielded is received by a focus error detecting photodetector 9 succeeding the photodetector 8 to detect the position of the optical disc 6 in the focus direction with high sensitivity. |
