Abstract: The light receiving surface of the light receiving element, which receives reflected light from an information recorded disc, is divided into sections along lines passing through the center of the surface which run parallel to and perpendicular to the direction of tracking and which also run at an angle of 45 degrees to the first two lines. The tracking errors are detected either by a push-pull method or a heterodyne method. The two methods are combined and alternately switched into operation depending on whether information is being written into or read from the information recording disc. The push-pull method uses a pair of opposing, divided light receiving surfaces disposed in the direction of tracking and the heterodyne method uses two pairs of opposing, divided surfaces disposed diagonally or at an angle of 45 degrees to the direction of tracking.

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: An optical magnetic recording system has a magnetic head for generating a magnetic field on a magneto-optical disk, and an optical head including a magnetic actuator is provided for irradiating a laser beam. A field cancellation magnet is attached to the back of the magnetic head for producing a magnetic force so as to cancel a leakage magnetic force of the magnetic actuator which affects recording of information. This positioning of the field cancellation magnet provides better compensation of the leakage field without affecting the modulating field of the magnetic head.

Abstract: An apparatus for detecting a focus error signal in which reflected laser light is split into two optical paths by a polarized light beam splitter while astigmatisms are produced in the laser light by at least one astigmatism generating element, and the two split beams are led so as to be incident upon two quadrant photodetectors, respectively. A focus error signal is obtained as an electrical signal by subtracting the sum of the quantities of light received by one of the diagonal pairs of regions among the quadrant regions of the two photodetectors from the sum of the quantities of light received by the other diagonal pair. An offset component in a focus error signal is removed by, for example, a variable resistor. This arrangement enables cancelling of influence of double refraction in a magnetooptic disk or the like, thereby making the optical head free of the problem of such influence.