Patent ID: 7206275
Filing Date: 2007-04-17
Classification: G11B

Abstract:
1. An optical pickup device which selectively records or reproduces data on or from a first optical recording medium, a second optical recording medium having a recording density lower than that of the first optical recording medium, a third optical recording medium having a recording density lower than that of the second optical recording medium, and a combined optical recording medium including appropriately combined and integrally stacked signal surfaces of the first to third optical recording mediums, the device comprising: a first laser light source which emits a first laser light for the first optical recording medium; a second laser light source which emits a second laser light having a wavelength longer than that of the first laser light for the second optical recording medium; a third laser light source which emits a third laser light having a wavelength longer than that of the second laser light for the third optical recording medium; an objective lens whose numerical aperture (NA) is set to 0.75 or more for the first optical recording medium and in which at least one of first and second surfaces turning to a reverse direction each other is formed in a non-spherical surface and which converges the first to third laser lights on the respective signal surfaces of the first to third optical recording mediums; and an aberration correction element in which a circular light-transparent flat portion and annular aperture limiting portions for the third and second laser lights are formed toward an outer circular portion from a central portion in order on an undersurface on the side of the first to third laser light sources and in which a diffraction pattern portion is formed in an inner circular region of an upper surface on the side of the objective lens and in which an outer side of the diffraction pattern portion is formed to be flat, wherein the aberration correction element transmits the first laser light, which is incident thereon in a parallel light state, as such through the light-transparent flat portion and the aperture limiting portions for the second and third laser lights, transmits the first laser light without diffracting the first laser light through the diffraction pattern portion, and allows a 0-order light thereof to be incident upon the objective lens, the aberration correction element interrupts the second laser light, which is incident thereon in the parallel light state, by the aperture limiting portion for the second laser light to limit the numerical aperture into the objective lens to a first predetermined numerical aperture, transmits the second laser light through the light-transparent flat portion and the aperture limiting portion for the third laser light, and thereafter diffracts the second laser light by the diffraction pattern portion so that a 1st order light of the second laser light capable of correcting a spherical aberration with respect to the second laser light that will occur on the objective lens is incident upon the objective lens, and further the aberration correction element interrupts the third laser light, which is incident thereon in a divergent light state, by the aperture limiting portions for the second and third laser lights to limit the numerical aperture into the objective lens to a second predetermined numerical aperture, transmits the third laser light through the light-transparent flat portion, thereafter diffracts the third laser light by the diffraction pattern portion to allow the third laser light to have a larger degree in diffusion that that of the second laser light so that a 1st order light of the third laser light capable of correcting a spherical aberration with respect to the third laser light that will occur on the objective lens is incident upon the objective lens.