Olympus Optical Company, Ltd.

Kiichi Kato

Masaharu Sakamoto

Kenichi Ito

Tohru Musha

Kunio Yamamiya

Hiroshi Kodama

Shoji Yoshikawa

Nobuhide Matsubayashi

Ken Ohshima

Tsuneo Yanagida

Ken Ohsima

Shozi Yoshikawa

Tuneo Yanagida

Hideyuki Kenjyo

Kimiaki Yamamoto

Haruhiko Takemura

Nobuyuki Kaneko

An opto-magnetic pick-up device for use in an information recording and reproducing device is disclosed. The device comprises a phase difference correcting device capable of correcting the phase difference between the linearly polarized component of the reflected light from the recording medium and a polarized component vertical to the linearly polarized component.

Opto-magnetic pick-up device including phase difference correcting means

In an optical information recording and reproducing apparatus for recording and reproducing information by controlling the focus of an optical system for condensing and projecting lights of a light source onto a recording medium, an offset part produced in case the lights are condensed and projected in a focus servo state in data writing regions in the recording medium and prepit regions which are adjacent to the data writing regions and in which discriminating codes are written is detected in the respective format regions by a format detecting means and an offset fluctuation controlling voltage is impressed on the basis of this detecting signal to inhibit the fluctuation of the offset in the respective regions of different formats.

Optical information recording and reproducing apparatus

In a method of detecting track crossings on an optical disc, a light source irradiates a light beam onto an optical disc having guide tracks in the form of a recess and the light beam is reflected and diffracted into a zero order light beam and positive and negative primary light beams. The light beams are defocused so as to produce interference patterns between the zero light beam and the positive and negative primary light beams. The interference patterns are detected by a four split light detector disposed between two parts of a two split detector. The outputs of the detectors are fed to an adder and to a subtractor for producing a sum signal and a difference signal respectively. The sum signal and difference signal are fed to a phase detector. Defocusing of the light beams is effected by a focusing coil to which is fed the amplified output of an adder of a reference signal controlled by a control circuit.

Method and apparatus for detecting track crossings on an optical disc

A linearly polarized light is projected upon a recording medium of a photomagnetic type; the reflected light is rotated by an appropriate angle through a halfwave plate and split into a reflected light and a transmitted light through a beam splitter having reflection factors of 0 or 100% for p- or s-polarized light in such a way that the beam splitter functions as an analyzer for one of the reflected and transmitted lights. The other of the reflected and transmitted lights is passed through an analyzer. The two lights passed through the beam splitter and the analyzer are detected by two photodetectors separately and applied to a differential amplifier to generate a reproduction signal of high S/N ratio without the use of a half mirror R.sub.p =R.sub.s =50% which is very difficult to manufacture.

Photomagnetic differential reproducing system

An optical disk apparatus has an optical head. The optical head emits a light beam onto an optical disk and forms pits in the optical disk, thereby recording a signal. A detector detects the relative inclination between the optical head and the optical disk and generates a signal corresponding to this relative inclination. A beam intensity correction circuit corrects the intensity of the light beam in accordance with the relative inclination to form proper pits. In one embodiment, the intensity of the light beam is increased when the relative inclination is increased.

Optical disk apparatus with beam energy correction for deviations in

An optical memory device comprises a modulator for modulating a laser beam in accordance with recording data, an objective lens for focusing the output laser beam from the modulator on a recording medium, a photosensor arranged at the conjugate position with the focal point of the objective lens, and a judging circuit for detecting erroneous writing in accordance with an output from the photosensor and a source of the recording data. The photosensor is divided into first and second segments by a line which is perpendicular to a direction corresponding to relative movement of the focused light beam on the recording medium. The difference signal between the outputs from the first and second segments is supplied to the judging circuit.

Optical memory device

An optical recording/reproducing apparatus has a beam emitting device adapted to emit at least two light beams in directions at a minute angle to each other. The light beams are condensed by a condensing member onto slightly separated two points on a disk and reflected by the disk. The light beams from the disk are polarized to a prism by a polarizing device. The prism refracts the light beams from the polarizing device, thereby increasing the relative angle between the light beams. The refracted light beams are converged by a converging lens on a detector.

Optical recording/reproducing apparatus

An optical recording and reproducing apparatus includes a first semiconductor laser for emitting a recording laser beam whose intensity is modulated in accordance with an information signal to be recorded and a second semiconductor laser for emitting a reproducing laser beam having a constant intensity. The recording and reproducing semiconductor lasers are commonly mounted in a supporting member which is mounted on a pick-up plate arranged movably in a radial direction of a rotating optical disc. The recording and reproducing laser beams are composed with each other by means of a substantially parallelogram shaped prism having a reflection surface for reflecting the reproducing laser beam and an optical surface upon which the reproducing laser beam is made incident at an incident angle larger than a critical angle and the recording laser beam is made incident at an incident angle near Brewster's angle. The composed recording and reproducing laser beams are commonly focussed by a single objective lens onto the optical disc in such a manner that the recording laser beam is made incident upon an information track to be formed and the reproducing laser beam is made incident upon a guide track or a previously recorded information track.

Apparatus for recording and reproducing information on an optical disc

An optical memory device comprises a modulator for modulating a laser beam in accordance with recording data, an objective lens for focusing the output light beam from the modulator on a recording medium, a sensor arranged in the far field of the objective lens, and a judging circuit for detecting an erroneous writing operation in accordance with an output from the sensor and the recording data. The sensor has a square detecting surface divided into four segments by lines which form angles of .+-.45.degree. with respect to the direction of relative movement between the recording medium and the focused light beam. The difference between the sums of outputs from two pairs of opposing segments is supplied to the judging circuit.

Optical memory device with means for detecting erroneous data writing

In an optical system for synthesizing a plurality of light beams, a first light beam of parallel light rays emitted from a laser beam source is incident on an inclined face of a right angle prism through the prism. A second light beam of parallel light rays emitted from a laser beam source is incident to the inclined face at a predetermined angle of incidence. The first light beam is emitted to the inclined face at an angle of incidence equal to a critical angle so that the first light beam is totally inflected by the inclined face and transmitted in a predetermined direction. The second light beam is refracted at an angle of refraction substantially equal to the Brewster's angle, and then transmitted in a direction which defines a predetermined angular difference with the predetermined direction of the first light beam. A multi-layered film is formed on the inclined face. The film makes the angle of refraction of the second light beam approach the critical angle, so as to reduce the angular difference from that which would exist in the absence of the film.

Optical system for synthesizing plural light beams

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.

Method and apparatus for detecting focussing and tracking error signals

An input signal containing a base line which fluctuates to a great extent is detected or restored by comparing the input signal with reference levels which are shifted in accordance with the fluctuation of base line. The input signal is sampled at a variable sampling rate and an average of sampled values for a predetermined period is derived to produce a profile signal which resembles accurately the fluctuation of the base line. The profile signal thus obtained is added to upper and lower threshold voltages to produce the reference levels which have been corrected in accordance with the fluctuation of the base line of input signal.

Apparatus for detecting input signal

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.

Light beam separation method

A disc-shaped record medium has a recording surface which is divided into a number of concentric recording regions and has a number of concentric guide tracks formed at boundaries between successive recording regions. A number of concentric or spiral information tracks are formed in an optically readable form in respective recording regions with a constant pitch in reference to respective guide tracks and the guide tracks are also recorded in an optically readable form. In an instance of effecting the recording or reproducing for a certain recording region, the guide track related to the relevant recording region is always read out by a tracking light beam which is controlled to trace the guide track and a recording or reproducing light beam is controlled with reference to the guide track so as to trace the information track precisely. The tracking light beam and the recording or reproducing light beam are focussed by a common objective lens onto the record medium and an inclination angle of the recording or reproducing light beam with respect to the tracking light beam is changed in a stepwise or continuous manner by rotating a swingable mirror arranged in the path of the recording or reproducing light beam. The recording or reproducing light beam is shifted in a radial direction of the record medium disc to trace the concentric or spiral information tracks. In the guide tracks are formed additional signals, such as address signals and synchronizing signals which are used for effecting random access.

Optical information recording and/or reproducing apparatus and optical

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.

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Hachioji, Japan

Kiichi Kato