Patent ID: 8526286

Claim:
An optical pick-up apparatus for reproducing information recorded on an optical recording medium or recording information on the optical recording medium comprising: a light source unit generating beams; a diffraction element which diffracts beams which are generated from the light source unit; and an objective lens which focuses a p order diffracted beam which is used for recording and reproducing information among a plurality of diffracted beams which are diffracted by the diffraction element on any one of a plurality of information recording layers which are formed on the optical recording medium, wherein a p±1 order diffracted beam which is not used for recording and reproducing information is focused on a point that is away from the plurality of information recording layers and a surface of the optical recording medium, wherein a difference (f p−1 −f p ) between a focal point (f p−1 ) of the p−1 order diffracted beam and a focal point (f p ) of the p order diffracted beam, and a difference (f p+1 −f p ) between a focal point (f p+1 ) of the p+1 order diffracted beam and the focal point (f p ) of the p order diffracted beam satisfy the following conditional equations: − D max− WD≦f p−1 −f p ≦−D max− s×t 2×Dmax−Dmin+s×t≦f p+1 −f p ≦600 μm, wherein Dmax represents a distance from the surface of the optical recording medium to a deepest information recording layer of the optical recording medium, Dmin represents a distance from the surface of the optical recording medium to a shallowest information layer of the optical recording medium. WD represents a working distance of the objective lens, t represents an absolute value of manufacturing tolerance of the optical recording medium, and s represents a safety factor.