Patent ID: 7283439
Filing Date: 2007-10-16
Classification: G11B

Abstract:
1. An optical disk apparatus comprising: a semiconductor laser; an objective lens for condensing light from said semiconductor laser onto an optical disk; a variable focal point applying mechanism for varying a focus position of light condensed in an optical system; a spherical aberration applying mechanism for applying variable spherical aberration to the light condensed in said optical system; a first optical branching element for branching reflection light reflected from said optical disk from said optical system; a lens for condensing the reflection light branched; and a light receiving element for receiving the light condensed by said lens to convert the light received into an electric signal; wherein, a second optical branching element for further separating the reflection light branched into first luminous flux located in a vicinity of an optical axis and second luminous flux located at a peripheral portion is added to said luminous fluxes to branch and condense on said light receiving element, and said second optical branching element is a diffraction grating and is disposed between said semiconductor laser and said objective lens to work on a luminous flux going toward said objective lens so that plus and minus primary diffraction lights of said luminous flux located at a peripheral portion are diffracted almost in a tangential direction and arranged at both sides of a zero-order light and shifted substantially by a guiding groove in a radial direction on the optical disk, and plus and minus primary diffraction lights of said luminous flux located in a vicinity of an optical axis are diffracted almost in a radial direction.