Patent ID: 7158467
Filing Date: 2007-01-02
Classification: G02B,G11B

Abstract:
1. An optical pick-up apparatus for conducting recording and/or reproduction information for a plurality of optical information recording mediums having respective protective base boards different in thickness, comprising: a first light source having a wavelength of λ a second light source having a wavelength of λ an optical system to focus a light flux from the first and second light sources on an information recording surface through an optical element including an objective lens, wherein an optical functional surface of the objective lens is divided into at least two concentric optical functional regions having a center on an optical axis so that a light flux having passed through a first region including the optical axis is used for recording and/or reproduction information for both of the first and second optical information recording mediums, and a light flux having passed through a second region positioned around the first region is used mainly for recording and/or reproduction information for the first optical information recording medium, and wherein the second region is provided with a diffractive structure to correct a spherical aberration of a converged light spot on an information recording plane to be regulated in a range where reproduction and/or recording information for the first optical information recording medium can be conducted when the refractive index of the optical element and the wavelength of the first light source vary due to a change of the working temperature of the optical system, wherein when an additional length of an optical path length added by the diffractive structure of the second region is represented by the following optical path difference function φ(h): where h is a height (mm) from the optical axis, b 2 is a 2 i -th order coefficient of the optical path difference function, and λ is a wavelength (mm) of a light flux, the following conditional formula is satisfied: where h