Patent ID: 6167017
Filing Date: 2000-12-26
Classification: G11B

Abstract:
An optical head assembly comprising:a laser light source;an objective lens for converging light emitted from said laser light source onto a recording surface of an optical recording medium;an optical detector means for detecting the light reflected upon said recording surface;a modulating diffraction grating for splitting said light emitted from said laser light source into a 0th-order beam, a +1st-order beam and a -1st-order beam in a track direction of said recording surface, emitting said three beams toward the center of said track of said recording surface and causing, with respect to said +1st-order beam and -1st-order beam, astigmatisms of different focal points in a direction orthogonal to said track direction; anda light-guiding device for guiding three returning beams reflected from said recording surface to said optical detector means;said optical detector means being equipped with an optical detecting portion for detecting recording signals that receives said 0th-order beam of said three returning beams and an optical detecting portion for detecting tracking errors that detects tracking error signals based on said astigmatisms generated to said +1st-order beam and -1st-order beam of said three returning beams, said astigmatisms having different focal points in said direction orthogonal to said track direction;said optical detecting portion for detecting tracking errors having a first light-receiving portion in which a light-receiving plane is divided in half for receiving the +1st-order beam of said three returning beams and a second light-receiving portion in which a light-receiving plane is divided in half for receiving the -1st-order beam of said three returning beams, the light-receiving result on each of said light-receiving planes being computed to cancel the change in the received intensity of light beam caused by a tracking shift of said objective lens so that said tracking error signals are detected.