Abstract: An optical head for reading a signal recorded along spiral or concentric tracks on an optical disc including a semiconductor laser for emitting a linearly polarized light beam, a polarization prism for transmitting the light beam, an objective lens for projecting the light beam upon the optical disc and for collecting a light beam reflected by the optical disc, a critical angle prism for totally reflecting the light beam reflected by the polarization prism and a light detector for receiving the light beam totally reflected by an optical surface of the critical angle prism. The polarization prism and critical angle prism are integrally coupled with each other to form an assembly of prisms which is rotated to adjust an incident angle of the light beam impinging upon the optical surface of critical angle prism substantially at a critical angle of total reflection.

Abstract: An optical head for reading a signal recorded along spiral or concentric tracks on an optical disc including a semiconductor laser for emitting a linearly polarized light beam, a polarization prism for transmitting the light beam, an objective lens for projecting the light beam upon the optical disc and for collecting a light beam reflected by the optical disc, a critical angle prism for totally reflecting the light beam reflected by the polarization prism and a light detector for receiving the light beam totally reflected by an optical surface of the critical angle prism. The polarization prism and critical angle prism are integrally coupled with each other to form an assembly of prisms which is rotated to adjust an incident angle of the light beam impinging upon the optical surface of critical angle prism substantially at a critical angle of total reflection.

Abstract: A method and an apparatus for detecting a focussing error signal and a tracking error signal of an objective lens with respect to an information track of a video disc on which a reading light spot is focussed by the objective lens includes a detection prism having a reflection surface which is set substantially at a critical angle and a light detector for receiving the light flux reflected by the reflection surface. The light detector is arranged in a far field of the track and having four light receiving regions divided along two orthogonal directions. The focussing error signal is derived as a difference between output signals from the regions aligned in a track direction and the tracking error signal is derived as a difference between output signals from the regions aligned in a direction perpendicular to the track direction. An information signal is obtained as a sum of the output signals from the four regions.

Abstract: A method of separating at least two light beams propagating in the substantially same direction but which propagate with making a small angle therebetween is disclosed, which comprises making one of said light beams incident upon an interface between an isotropic first optical medium having a first refractive index and an isotropic second optical medium having a second refractive index lower than said first refractive index at an incident angle substantially equal to the Brewster angle so that the light beam is substantially totally transmitted through said interface; and making the other light beam incident upon said interface at an incident angle greater than the critical angle so that the light beam is totally reflected by said interface.

Abstract: An objective lens drive device for driving an objective lens comprises an objective lens drive mechanism arranged at both sides of the objective lens for flanking the objective lens in the direction of displacement of the objective lens.

Abstract: In order to derive a focussing error signal of an objective lens with respect to a video disc on which a light beam is focussed by the objective lens, the P-polarized light beam is made incident upon a prism and then upon a thin film which is applied to the prism and has a refractive index higher than that of the prism, and the light beam reflected by a boundary surface between the thin film and the air is detected by a photo-detector having two light receiving regions. The thin film is made of material having a higher refractive index than that of the prism. Between the prism and the thin film there may be interposed at least one additional thin film in such a manner that the lower and higher refractive index thin films are alternately arranged.

Abstract: A method and apparatus for detecting a focussing error signal of an objective lens with respect to a video disc on which a light beam emitted from a laser light source is to be focussed as a light spot by the objective lens. A light flux reflected by the video disc is made incident upon a detection prism surface which is set substantially at a critical angle with respect to a central light ray in the reflected light flux, and two light fluxes which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the central light ray reflected by the reflection surface and perpendicular to the plane of incidence. The focussing error signal is derived as a difference between output signals from the two light receiving regions.

Abstract: An apparatus and method for recording optically an information signal on a disk-like record medium as a spiral track or concentrical tracks by modulating a main beam by the information signal to be recorded and projecting the modulated main beam onto the record medium. In order to obtain a tracking error signal, a sub beam is also projected on the record medium at an edge of an adjacent track which has been previously recorded and the sub beam reflected by the record medium is detected by a light detector to produce the tracking error signal which is then supplied to a high pass filter to remove a low frequency component from the tracking error signal.

Abstract: In a method and apparatus for detecting an information signal and a focussing error signal of an objective lens with respect to a video disc on which main and sub beams emitted from a laser light source are to be focussed as light spots by the objective lens, the main and sub beams reflected by the video disc are made incident as parallel light fluxes upon a detection prism surface which is set substantially at a critical angle with respect to the main beam, but at an angle smaller or larger than the critical angle with respect to the sub beam, and two light fluxes of the reflected main beam which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the main beam reflected by the reflection surface and perpendicular to the plane of incidence.

Abstract: In a method and apparatus of recording optically an information signal on a disc along tracks by projecting a main beam modulated with the information signal onto the rotating disc by means of an objective lens, in order to obtain focussing and tracking error signals, a sub beam inclined with respect to the main beam is also projected onto the disc by means of the objective lens.

Abstract: A method and apparatus for detecting a focussing error signal of an objective lens with respect to a video disc on which a light beam emitted from a laser light source is to be focussed as a light spot by the objective lens. A light flux reflected by the video disc is made incident upon a detection prism surface which is set substantially at a critical angle with respect to peripheral light fluxes reflected by the video disc, and the peripheral light fluxes reflected by the reflection surface are separately received by two light receiving regions which are spaced apart from each other. The focussing error signal is derived as a difference between output signals from the two light receiving regions.