Patent ID: 7643391
Filing Date: 2010-01-05
Classification: G11B

Abstract:
1. An optical head for converging, upon an optical information medium, a beam of light for information recording or regeneration which is emitted from a laser light source, and for receiving the beam of light which is reflected from the optical information medium, the optical information medium having a disk shape and having a first portion and a second portion, the second portion being adjacent to the first portion in a radial direction, and the first portion having a different reflectance ratio than the second portion, the optical head comprising a sensor which detects a tilt or a positional shift of the optical information medium from a predetermined reference, said sensor including: a substrate; a light-source chip element which is disposed on said substrate and irradiates the optical information medium with a divergent beam of light; and a light-receiving region which is disposed on said substrate and receives the divergent beam of light emitted from said light-source chip element after being reflected by the optical information medium, wherein said light-receiving region is divided into a plurality of areas by a division line as a boundary which extends on said light-source chip, the plurality of areas being symmetrical with respect to the division line, and based on a ratio of a quantity of light which each of the areas receives, detects a tilt or a positional shift of the optical information medium, wherein the sensor is disposed so that the division line becomes substantially in parallel with a tangential direction of the optical information medium, wherein a cylindrical element is provided on an optical path between the optical information medium and said light-receiving region, wherein the divergent beam of light has a boundary between a bright part and a dark part reflected by the first portion and the second portion of the optical information medium, and transmits across the cylindrical element, and wherein said cylindrical element is placed in a position that a generating line thereof tilts with respect to the division line at an angle in a range of 40 to 50 degrees so that the boundary between the bright part and the dark part of the divergent beam of light transmitting across the cylindrical element turns about its optical axis at an angle of approximately 90 degrees with respect to the divergent beam of light before transmitting across the cylindrical element.