Abstract: A position detector includes: light emitting component for irradiating the surface of an object to be measured; two light receiving components for receiving light reflected by the measured surface, a distance from one of the light receiving components to the measured surface as viewed in a direction substantially perpendicular to the surface being different from a distance from the other of the light receiving components to the surface; calculating circuit for calculating a correction quantity for correcting the distances between the light receiving components and the surface, with the correction quantity being calculated on the basis of a difference between the output signals of the light receiving components; and, moving component for correcting the distances between the measured surface and the light receiving components in accordance with the correction quantity. A first embodiment has two light receiving components each spaced at different distances from the surface.

Abstract: An optical head for use with a photomagnetic recording/reproducing device which is small in number of parts, compact in light path, small in overall size, easy to assemble and adjust, small in number of errors in adjustment, and high in reliability. The optical head comprises a prism for splitting a beam of light from an objective lens, and a light receiving element for receiving light from the prism to produce an electric signal from which a servo signal and a reproduction signal are to be produced. The prism has parallel incident and emergent side transmitting faces and first and second parallel reflecting faces. The prism may include first and second optical members of uniaxial crystal adhered to each other with optical axes thereof directed perpendicularly to each other or first and second optical members which define a polarizing splitting face on an interface therebetween.

Abstract: An optical head wherein a required astigmatism can be obtained readily to facilitate production thereof and the linear distance between a face of an information record medium and a light receiving element is reduced to reduce the overall size and weight of the optical head. The optical head comprises a prism having a parallelogram shape in side elevation. The prism has a reflecting/transmitting face extending at an angle of about 45 degrees with respect to an optical axis to the information record face for reflecting light from a light source toward the information record face, first and second reflecting faces extending perpendicularly to the optical axis for successively reflecting light transmitted thereto through the transmitting face, and a transmission face extending in parallel to the reflecting/transmitting face. Light emerging from the transmitting face of the prism is received and converted into an electrical signal by a light receiving element.

Abstract: In a compatible recording and reproducing apparatus which is capable of recording and reproducing information on both a video disk and a digital audio disk, a relative angle between an optical axis of a laser beam emitted from a pickup and the disk is adjusted so as to be suitable for the disk loaded on the apparatus. Further, the movement of the pickup in the radial direction of the disk is regulated in accordance with the difference in the outer diameter of the two kinds of disks. A problem due to the difference of the track pitch in the two kinds of disks is solved by moving the pickup in a direction perpendicular to a radial direction of the disk. In addition, an objective lens for focusing the laser beam on the disk is selected within a predetermined range of an effective numerical aperture in order to simplify an optical system of the apparatus.

Abstract: A focus error detection device to be used in an optical system for recording and/or playing back information, including a light detector made up of four light receiving elements arranged symmetrically with respect to the center of the light detector, a multiplication means for generating a pair of multiplication signal by multiplying output signals of two light receiving elements which are arranged symmetrically with respect to the center of the light detector. The multiplication signals are applied to a subtraction means where the focus error signal is generated by the subtraction between the multiplication signals. Thereby the off-set of the focus error signal which has been caused by the deviation of the position of the center of the light beam from the center of the light detector is by far reduced.

Abstract: A focus error detection device to be used in an optical system for recording and/or playing back information, including a light detector made up of four light receiving elements arranged symmetrically with respect to the center of the light detector, a first operation circuit means connected to the light receiving elements for generating a focus error signal, and a second operation circuit means also connected to the light receiving elements for generating an off-set compensation signal. With this construction, and off-set of the focus error signal due to the deviation of the position of the reflection light beam is by far reduced as compared with the conventional devices.

Abstract: In a video and/or audio disc information reproducing apparatus in which the video and/or audio information carried on a video and/or audio disc is picked up with a beam of light incident on the disc to trace the record track on the disc, an error detecting system comprising optical means to emit a beam of light for tracing the record track and producing a signal-carrying beam of light carrying signals picked up from the record track, beam-splitting means to split the signal-carrying beam into two component beams, light-sensitive transducer means responsive to the component beams and having at least four discrete light-sensitive surfaces separate from one another across a first junction line parallel with a line tangent to the record track and a second junction line parallel with a line perpendicular to the record track, the transducer means being operative to produce a first error signal representative of the difference between the intensities of light incident on the light-sensitive surfaces separate from ea

Abstract: An optical pickup device is placed in a video and/or audio disc player operative to reproduce information recorded in the form of an optical pattern such as a train of pits on a recording disc, in which the direction of light beam emitted from a light source is parallel to the propagation path of light impinging onto and reflected from the recording disc toward a photosensor. A polarization prism is used to deflect the light from the light source toward the recording disc, which prism cooperates with a quarter wave plate to act as a beam splitter.

Abstract: An optical system for use in a signal pickup device of, for example, an optical video and/or audio disc player, comprising a beam splitter prism composed of two component segments forming therebetween a light polarization or semi-reflective mirror plane inclined at the angle of 45 degrees to a predetermined path of light through the prism, each of the component segments having an outwardly curved surface portion through which the path of light extends.