Optical head assembly having means for detecting tracking errors based

Abstract

In accordance with the invention, an optical head assembly comprises a laser light source, an objective lens for converging light emitted from the laser light source onto an recording surface of an optical recording medium, an optical detector device for detecting the light reflected upon the recording surface, a modulating diffraction grating for splitting the light emitted from the laser light source into 0th-order beam, +1st-order beam and -1st-order beam in a track direction of the recording surface, emitting the three beams toward the center of the track of the recording surface, and causing, with respect to the +1st-order beam and -1st-order beam, astigmatisms of different focal points in a direction orthogonal to the track direction, and a light-guiding device for guiding three returning beams reflected from the recording surface to the optical detector device. The optical detector means is equipped with an optical detecting portion for detecting recording signals that receives the 0th-order beam of the three returning beams and an optical detecting portion for detecting tracking errors that detects tracking error signals based on the astigmatisms generated to the +1st-order beam and -1st-order beam of the three returning beams, astigmatisms having different focal points in the direction orthogonal to the track direction.