Patent ID: 7881174
Filing Date: 2011-02-01
Classification: G11B

Abstract:
1. An optical pickup apparatus for recording and/or reproducing information on an optical information recording medium including multilayered information recording surfaces, the optical pickup apparatus comprising: a light source; an objective lens for converging a light flux from the light source onto one of the multilayered information recording surfaces; a first optical element comprising a first optical area and a second optical area which are arranged on both sides of an optical axis; a second optical element comprising a third optical area and a fourth optical area which are arranged on both sides of the optical axis; a light-converging element for receiving a main light flux and a secondary light flux and converging the main light flux at a position between the first optical element and the second optical element, the main light flux being a light flux reflected by the one of the multilayered information recording surfaces on which the light flux from the light source is converged and the secondary light flux being a light flux reflected by another of the multilayered information recording surfaces; a polarization splitting optical member for splitting the main light flux and the secondary light flux each emitted from the first optical element and the second optical element; and a photodetector for receiving the main light flux, wherein the optical pickup apparatus records and/or reproduces information by converging the light flux from the light source on the one of the multilayered information recording surfaces through the objective lens, wherein the first optical area and the fourth optical area provide a first polarization direction with the main light flux passing through the first optical area and the fourth optical area, the second optical area and the third optical area provide a first polarization direction with the main light flux passing through the second optical area and the third optical area, the first optical area and the third optical area provide a second polarization direction with the secondary light flux passing through the first optical area and the third optical area, and the second optical area and the fourth optical area provide a second polarization direction with the secondary light flux passing through the second optical area and the fourth optical area, wherein the main light flux passes through the first optical element and is converged between the first optical element and the second optical element by the light-converging element, and the main light flux passes through the second optical element and enters into the photodetector through the polarization splitting optical member, wherein the secondary light flux passes through the first optical element and is not converged between the first optical element and the second optical element by the light-converging element, and the secondary light flux passes through the second optical element and does not enter into the photodetector by being split out by the polarization splitting optical member, and wherein the optical pickup apparatus satisfies a following expression: where m is a magnification when the light flux reflected by the one of the multilayered information recording surfaces is converged by the light-converging element, and NA is a numerical aperture of the objective lens on an optical information recording medium side.