Abstract: A focusing error detecting apparatus having a first photo-detector of which the light receiving portion is halved to provide first and second light receiving portions asymmetrical with respect to the center of a beam spot of a bundle of incident laser beams, the first photo-detector being located in the optical path ahead of the focusing point of the bundle of the incident laser beams, a second photo-detector of which the light receiving portion is halved to provide first and second light receiving portions asymmetrical with respect to the center of a beam spot of a bundle of incident laser beams, the second photo-detector being located in the optical path behind a focussing point of the bundle of the incident laser beams and a calculating circuit for calculating a difference between a difference of detected outputs from the first and second light receiving portions of the first photo-detector and a difference of detected outputs from the first and second light receiving portions of the second photo-detector,

Abstract: An optical pickup device having a semiconductor laser element mounted on a substrate, a photo detector formed on the substrate to receive a laser beam emitted from the semiconductor laser element and an optical element mounted on the substrate to cover the photo detector to branch the direction of optical path of the laser beam, the optical element having its face opposing the semiconductor laser element formed as an inclined face on which a semitransparent reflection film is deposited. The optical path branching optical element is provided with preventing means by which, of laser beams incident on the optical element, a laser beam reflected and/or scattered within the optical element is prevented from irradiating the photo detector.

Abstract: An optical pickup head comprising a substrate on which a optical sensor is formed, and an optical member adhered on said optical sensor on said substrate by an adhesive and including a semitransmissive reflective film adapted to reflect the light emitting from a laser source and to transmit the light returned from a second medium of a disk, characterized in that the refractive index of said optical member is set so as to be larger than the refractive index of said adhesive.

Abstract: The present invention relates to a focusing detection apparatus (1) for detecting a focusing state of an optical recording medium. So as to achieve compactness and low cost of the focusing detection apparatus (1), focusing detection using two photosensors (33) (34) located in front of and behind a convergent point of a beam (45) reflected by the optical recording medium can be achieved by a single prism (37), and a plurality of optical components (31) (33) (34) (37) are formed integrally and can be arranged on a single surface of a semiconductor substrate (32). The present invention is applicable to an optical head requiring compactness, light weight, and low cost as well as high performance.