Patent ID: 7567496
Filing Date: 2009-07-28
Classification: G11B

Abstract:
1. An optical pickup device that emits a convergent light to an information recording medium having information signals recorded along a recording track, detects a reflection light of the convergent light from the information recording medium and reads out the information signals, the optical pickup device comprising: a hologram element formed on a plane containing a transit area of the reflection light from the information recording medium; and a light receiving element for detecting the reflection light passing through the hologram element, wherein: the hologram element is divided into eight areas by a first parting line that coincides with a tangential axis extending parallel to a reflection optical axis of the reflection light in optical mapping, a second parting line that coincides with a radial axis running through the reflection optical axis and also intersecting with the recording track at right angles in optical mapping, a third parting line extending parallel to the second parting line and a fourth parting line extending parallel to the second parting line, the third parting line being symmetrical to the fourth parting line about the second parting line; the eight areas of the hologram element are classified into first and second area groups both arranged on one side of the second parting line, each of the first and second area groups consisting of two areas opposing to each other in a diagonal direction about an intersection of the first parting line and either the third parting line or the fourth parting line, and third and fourth area groups both arranged on the other side of the second parting line, each of the third and fourth area groups consisting of two areas opposing to each other in a diagonal direction about an intersection of the first parting line and either the fourth parting line or the third parting line, each of the two areas in one area group partially constituting one group of curves producing one diffraction light having continuous wave surfaces; the first to the fourth area groups are formed so that a direction to divide O-order and ±first-order diffraction lights in each area group substantially coincides with an equivalent direction of the radial axis; the first to the fourth area groups are formed so as to produce two pairs of diffraction-light groups, one pair of diffraction-light group having its diffraction angles to the reflection optical axis different from respective diffraction angles of the other pair of diffraction-light group; the first to the fourth area groups are formed so as to add different lens powers with respect to an equivalent direction of the tangential axis to respective diffraction lights which are included in the same pair of diffraction-light group and whose diffraction angles to the reflection optical axis are equal to each other, thereby producing convergent lights of different convergent angles; the light receiving element is formed so as to contain at least respective transit areas of the two pairs of diffraction-light groups diffracted in substantially the same direction to the reflection optical axis by the first to the fourth area groups if the convergent light emitted to the information recording medium is in an in-focus state; the light receiving element is formed on a plane that is spaced from the hologram element in a direction of the reflection optical axis so as to allow the two pairs of diffraction-light groups to secede from each other spatially under a condition that the convergent light emitted to the information recording medium is in the in-focus state; the plane is positioned between a focal line in the tangential direction of one diffraction light in the two pairs of diffraction-light groups and another focal line in the tangential direction of the other diffraction light in the two pairs of diffraction-light groups; the light receiving element is divided into four light receiving areas by a fifth parting line which is parallel to an equivalent direction of the tangential axis and is positioned at the substantial midpoint of the two pairs of diffraction-light groups and a sixth parting line which is parallel to an equivalent direction of the radial axis while passing through the reflection optical axis, the four light receiving areas producing four light-to-photocurrent converted outputs each proportional to any one of irradiation intensities of the diffraction lights; and the light receiving element is constructed such that if the convergent light emitted to the information recording medium is in the in-focus state, then profile lines in the diffraction-light groups corresponding to the third parting line and the fourth parting line coincide with the second parting line of the light receiving element, whereby the four light receiving areas generate four light-to-photocurrent converted outputs corresponding to components of four quadrants obtained by dividing the reflection light from the information recording medium by the tangential axis and the radial axis.