Abstract: An optical information storage device including a first photodetector for detecting a regenerative signal from reflected light from an optical recording medium, a second photodetector for detecting a tracking error signal and a focusing error signal from the reflected light, and a beam splitter for separating the reflected light into a first beam directed toward the first photodetector and a second beam directed toward the second photodetector. The optical information storage device further includes a phase compensating mechanism provided between the beam splitter and the first photodetector for compensating for a phase difference of the first beam, a Wollaston prism provided between the phase compensating mechanism and the first photodetector for separating the first beam into two beams having orthogonal polarization planes, and a polarization plane rotating mechanism for rotating the polarization plane of the first beam incident on the Wollaston prism.

Abstract: A focusing controller executes an appropriate focus jump even in a multilayer disk having layers of characteristics greatly different from each other. The focusing controller has an optical pickup including an objective lens for converging the light beam and a detector for receiving reflected light from the multilayer recording medium; an error signal generator for generating a focus error signal of the irradiated light beam from a detecting signal of the detector; an actuator for operating the objective lens; and a controller for controlling a focusing position of the light beam by operating the actuator based on the focus error signal. The controller calculates intensities of the reflected lights of two layers based on the detecting signal of the detector, and thus controls the timings of acceleration and deceleration signals of a focus jump between these two layers.

Abstract: A tilt detector and tilt detection method which are capable of detecting a tilt in a radial direction of an optical disc at a high degree of precision and being cost-effective and simple in head part construction.

Abstract: A head unit of a photo detector for irradiating a target area with detection light having a pencil of rays substantially shaped like a belt in transverse section and receiving light reflected in the target area. The head unit includes a belt-like-light generation lens having different light gathering functions relative to two directions orthogonal to each other in the transverse section of the pencil of rays for generating detection light substantially shaped like a belt, a light emission section for emitting the detection light from a first interface of the belt-like-light generation lens through a second interface of the belt-like-light generation lens to the target area, and a light reception section for receiving reflected light incident on the light reception section through the first interface of the belt-like-light generation lens from the second interface.

Abstract: A tilt detection method and tilt detector which can make the size of an optical pickup small, improve an installation efficiency of the pickup and reduce a manufacturing cost of the pickup. A first light receiver and second light receiver output detected results corresponding to the amounts of received light to a comparator, respectively. The comparator detects a difference between output signals from the first and second light receivers and outputs the detected result as a tangential tilt signal. An analog delay element delays an output signal from the comparator for a predetermined period of time corresponding to the rotation of an optical disc by 90° and outputs the delayed result as a radial tilt signal.

Abstract: A near-field optical head which reproduces, with high S/N, information recorded with extreme density and is compact in structure. On an electrode (2) is formed a recording medium (3) that emits a light by applying an electric field. Brought into proximity to a recording medium (3) is a near-field optical head (101) having a slider (31) formed with an inverted cone formed hole such that an apex thereof is rendered as a microscopic aperture (6). A microscopic electrode (5) is formed on a side surface (32) of the inverted cone formed hole. An electric field (9) is applied only to a microscopic region to cause light emission. It is possible at the aperture (6) to detect a light emitted only by the microscopic region.

Abstract: In an optical apparatus comprising a condensing optics (104) for condensing incident light of linearly polarized light (10), an optical splitting element (701) for splitting reflected light reflected by a light reflection member (105) disposed in close proximity of the focal plane of the condensing optics (104) from the incident light, and an optical detection element (704) for detecting a split light beam (12) split by the optical splitting element, an optical rotatory element (103), capable of optically rotating substantially 90° a polarization axis of the linearly polarized light in a region thereof, corresponding to a portion of an effective light beam (11) of the linearly polarized light, available for the condensing optics (104), and also controlling an optical rotatory power thereof by electric signals, is disposed in the optical path of the incident light of the linearly polarized light (10), Further, a linearly polarized light detection element (703) is disposed in the optical path of the split l

Abstract: The magnetic tape processing method and apparatus allow at least one of a laser beam or laser beams in a visible region and a laser beam or laser beams in an ultraviolet region to be incident on a backing layer of a magnetic tape while transporting the magnetic tape in a lengthwise direction of the magnetic tape and process the backing layer by means of the laser beam or laser beams to form recesses on the backing layer. The processed magnetic tape is composed of a base layer, a magnetic layer formed on one surface of the base layer and the backing layer formed on another surface of the base layer and having recesses which are formed by processing the backing layer by means of the laser beam or laser beams.

Abstract: An objective lens for use in an optical pickup apparatus to record or reproduce information in an optical information recording medium, comprises an aspheric surface, wherein the following conditional formula is satisfied: 1.1≦d1/f≦3 where d1 represents axial lens thickness and f represents a focal length.

Abstract: To reduce an effect of reflected light from a layer (or layers) other than a layer to be read upon focus position control when reading a multilayer optical disk in an optical disk drive. In an optical system where a focus error signal is generated by the knife edge method, a photodetector 53 that is divided into four parts is used. Each of two pairs of light detecting elements on the right or left side are formed by division of a detection plane of the photodetector such that the reflected light from a neighboring layer falls half-and-half on that pair of the light detecting elements. Signals from the photodetector are given with alternating polarities in such a way that any adjacent light detecting elements have mutually different polarities and are added up together to form the focus error signal.

Abstract: An optical scanning device for scanning a record carrier directs a radiation beam towards the record carrier. Two detection systems are arranged in the path of the beam reflected by the record carrier, one before and one after the focus of the beam. Output signals of the detection systems represent the intensity distribution of the beam in the plane of each detection system. The output signals are processed to form a signal representing an aberration of the reflected beam. The aberration may be coma or spherical aberration. The aberration signal is used to control a compensation element in the optical path of the radiation beam incident on the record carrier.

Abstract: A system and method for data error recovery uses a plurality of error correction routines in an attempt to provide data that can be used by the end user. In some situations the user is prompted for additional information and in some situations the data is provided with the errors highlighted. This system minimizes the amount of data that is unrecoverable. The system will work with CD discs or other storage media as well as with data lost by communication failures.

Abstract: The digital laser image recorder includes a data manipulation and control system which may provide digital data to a digital light source for conversion to an analog modulated light beam. A scanner may also be provided to direct the light beam toward a writing surface which may be disposed on the interior of a rotatable cylinder. A film handling device operable to deliver sheet film to the writing surface may also deliver sheet film from the writing surface to an associated output tray after writing. In another embodiment, beam shaping optics may be provided to convert the analog modulated light beams to collimated beams of a predetermined size and circular distribution. The beam shaping optics may also incorporate a power control filter to control the intensity of the collimated beams. In yet another embodiment, a shutter may be provided.

Abstract: The focal point detection method detects focal point dislocation of a coupling objective lens in accordance with a light beam passing a 60% to 80% region of a light beam effective diameter, which is centered with respect to an optical axis OZ of a light beam passing through the coupling objective lens, and which is regulated by a numerical aperture of the coupling objective lens. In this manner, focal point dislocation of a converging optical system can be performed without an offset, thereby accurately forming a focal point of the converging optical system on an information recording layer of an optical recording medium.

Abstract: In an optical pickup apparatus provided with a first light source; a second light source; a converging optical system having an objective lens provided with a diffractive section, and an optical detector, the optical detector comprises a central light receiving section to detect a focusing condition and a peripheral light receiving section to detect a tracking error, and when information is reproduced from or recorded in the second optical information recording medium, a reflected light flux of the second light flux reflected from or a transmitted light flux of the second light flux transmitted through the second optical information recording medium is irradiated so as to cover the entire surface of the peripheral light receiving section.

Abstract: An opto-electronic data acquisition and storage system, having a light source for directing light along a predetermined light path, a light sensitive electronic memory, a light absorber, a spatial optical storage device being positioned to receive reflected light and to direct the reflected light to the light sensitive electronic memory and a digital light processor having an array of electronically positioned micro-mirrors each being selectively oriented to a reflecting position to reflect light from the light source along a reflected light path to the spatial optical storage device for data storage and being selectively oriented to reflect light from said source to the light absorber when the reflected light is not intended for storage.

Abstract: In a optical head, a beam is emitted from a light emitting element in which a plurality of light sources are integrally formed, the light sources being able to emit beams having different wave lengths to one another. An optical system converges the beam coming from any one of the light sources onto an optical information storage medium. An optical separator separates a reflected beam coming from the optical information storage medium from the beam coming from the light source. A light receiving element detects light quantities of the reflected beam separated by the optical separator.

Abstract: There is provided a near-field optical memory head for recording and/or reproducing information on a recording medium by utilizing near-field light which is a near-field optical memory head having a compact constitution and is suitable for mass production and array formation. According to the near-field optical memory head 11, in a planar substrate formed by penetrating at least one hole in a shape of an inverted pyramid such that a top portion thereof constitutes a very small aperture 4, a near-field light forming system for forming near-field light at a recording medium 1 and a near-field light detecting system for guiding propagating light 10 provided by interactively operating the formed near-field light with the very small aperture 4 to a light detecting element are integrated.

Abstract: The present invention discloses a multiple-beam holographic optical pick-up head, which has the advantages of the multiple-beam optical pick-up head and the holographic optical pick-up head and can increase the light usage efficiency. This invention uses the property that a polarized diffractive optical element can generate different optical effects for laser beam with different polarizations and places a polarized multiple-beam grating and polarized hologram on the optical path for splitting the incident light toward the disc into multiple reading beams by the multiple-beam grating. The returning laser beams reflected from the disc are diffracted and diverted by the hologram to reach a photodetector. Both the incident and reflective beams are diffracted once only; thus the light usage efficiency can be increased.

Abstract: An SIM (solid immersion mirror) made principally of a light-permeable high-refractive-index medium has a lower surface which is produced by rotating a parabola about a symmetry axis, and an upper surface which is a perpendicular bisector surface of a line segment connecting the vertex and the focus of the parabola. The upper surface has the property of transmitting collimated light incident in a direction perpendicular thereto and reflecting the light reflected from the lower surface. Such a structure of the SIM facilitates the design of the upper surface and the lower surface both of which are reflecting surfaces, and allows the light to be incident on a light focusing point uniformly from therearound, thereby to form a proper light spot at the light focusing point. Additionally, the SIM allows the light to enter the medium through the entire upper surface, to achieve effective use of light.

Abstract: A laser scatterometer used, e.g., to detect defects on memory media, includes a beam block that can be finely adjusted so as to block specular light while maximizing the small angle scattered light that is received by the light detector. The beam block may be adjusted independently of the light detector or may be a masked beam block that is adjusted with the entire light detector. The light source produces a light beam that is focused so as to maximize the spot size on the object being tested while minimizing the spot size at the beam block, which advantageously maximizes the small angle scattered light while decreasing testing time. The large spot size at the object being tested permits detection of large defects. Thus, disks may be quickly tested, e.g., during the burnishing process, to determine if there are any large defects.

Abstract: There is disclosed an optical device in which a first light source for outputting a first wavelength light is apart from a second light source for outputting a second wavelength light by a predetermined distance. An information recording medium is irradiated with the first and second wavelength lights transmitted through a holographic optical element having first and second diffraction areas. The first and second diffraction areas are provided with grating arrangements in which grating axis directions are parallel to each other and grating pitches are different from each other. The first and second wavelength lights reflected by the information recording medium are transmitted through the holographic optical element and diffracted by the first and second diffraction areas.

Abstract: An optical pickup apparatus for reproducing information from or recording onto one of different kinds of optical information recording medium comprises a first light source for emitting first light flux whose wavelength is &lgr;1; a second light source for emitting second light flux whose wavelength is &lgr;2, wherein &lgr;2 is greater than &lgr;1; a converging optical system comprising an objective lens having an optical axis and divided three (first, second and third) portions; and a photo detector. The following conditional formula is satisfied for an amount of the first light flux not less than 30% of the total amount of the first light flux passing the first portion: 0.06≧SC1/f1≧0.

Abstract: A method of manufacturing an optical disc master from a glass substrate includes coating the substrate with a layer of photoresist, and applying an alkali-gel layer atop the photoresist. The coated substrate is then placed in an environment with a higher than normal humidity. The surface of the coated glass is selectively exposed to a beam of a writing laser, the exposure being controlled by digital information to be recorded on the disc. Exposed portions of the coated substrate experience a chemical reaction between the photoresist and the alkali material in the humid environment. Exposed portions are then developed and ablated thereby creating the pits and lands.

Abstract: A method and device for storage and retrieval of digitized information. The digitized information storage device consists of a storage medium, a particle ray source, and control and detection electronics. The particle ray source may consist of an electron, ion, or positron beam, a combination of these sources, or an array of one or more of those. The storage medium may consist of a single layer, possibly a compound material, which is susceptible to a structural phase transition, such as a change in morphology, topography, composition, defect concentration or adsorbing bonding characteristics under the influence of the scanning particle ray at recording parameters. The storage medium may also be comprised of two or more different layers, which are chosen from materials which are not intermixing or alloying and which have distinctly different electron or ion adsorption parameters, secondary electron emission characteristics, as well as thermal and structural properties.

Abstract: The present invention provides a method and an apparatus for detecting a position of a light spot in a light distribution that can include stray light components (e.g. from other lasers, ambient lighting etc.) The apparatus includes a continous response position sensitive detector (CRPSD, e.g. lateral effect photo-iode) for determining a first centroid of the light distribution and a discrete response position sensitive detector (DRPSD, e.g. multiplexed array) for determining a second centroid of the light distribution within a reading window defined about the first centroid and within the light distribution. The second centroid represents the position of the light spot in the light distribution. This multiple stage approach exploits the high resolution and speed offered by traditional CRPSDs together with the accuracy under variable lighting conditions offered by traditional DRPSDs.

Abstract: A daylight operable, scan-free, laser spot locating device for locating a laser spot pointed at an object.

Abstract: An optical transducer according to the invention comprises optical detection means (1) including a first (1A), a second (1B), a third (1C) and a fourth optical detector (1D), such that a first imaginary line (2a) from the third optical detector (1C) to the first optical detector crosses a second imaginary line (2b) from the second optical detector (1B) to the fourth optical detector (1D). The optical detectors generate detection signals (A,B,C,D) in response to an intensity of radiation incident thereon. The optical transducer further comprises signal combination means (4) for generating a first, a second, a third and a second combination signal. The first and the second combination signals (AC+, AC−) are indicative for the sum of the electrical detection signals (A,C) of the first (1A) and the third optical detector (1C).

Abstract: A synchronous light detector for an optical scanning apparatus comprises a cylindrical lens 14 and a light-receiving device 15. The cylindrical lens 14 is disposed between an imaging lens 8 of the optical scanning apparatus and the light-receiving device 15 so as to have a generator direction parallel to a scanning direction of a light beam. The light-receiving surface of the light-receiving device 15 is disposed at a position shifted from a paraxial image point P in the direction orthogonal to the scanning plane of the light beam by a predetermined distance &Dgr; along the optical axis direction of the light-receiving device 15 when the deflecting point of the light beam caused by a polygon mirror 6 is taken as an object point. As a consequence, the synchronous signal of the optical scanning can be detected correctly even when there is a flaw or dirt on the light-receiving surface.

Abstract: In an optical pick-up position detector, an optical pick-up is movable by a motor in radial directions of an optical disk for detecting signals on the optical disk. A driver applies a driving voltage to terminals of the motor for forward or reverse rotation of the motor according to a control signal from a controller. The controller has an input terminal connected to a power supply via a resistor and further has a control terminal for outputting the control signal to the driver according to an electric potential at the input terminal of the controller. A switch is disposed between the input terminal of the controller and one of the terminals of the motor. The switch changes its operating state when the optical pick-up moves to exceed a reference position in a radially inward or outward direction with respect to the optical disk. The switch may be connected to the input terminal of the controller via a diode.

Abstract: A device for measuring focusing characteristics of an optical pickup and/or an optical disc capable of measuring characteristics of focusing states with high accuracy by a simplified circuit. An arithmetic-logic unit 12d controls an offset supplying circuit 23 for applying an offset voltage to a focusing servo control signal. This arithmetic-logic unit 12d detects an error rate of the playback data in such a state in which the focusing position of the laser light is deviated by a pre-set offset amount. The arithmetic-logic unit 12d sequentially varies the offset voltage to repeat the above processing for detecting the error rate. The arithmetic-logic unit 12d approximates the relationship of the error rate to the offset amount by a quadratic curve based on detected data. The offset amount which minimizes the error rate is found from this equation of approximation.

Abstract: The object of the present invention is to provide a tracking pull-in circuit for reducing effect by a defect and enabling securely and promptly pulling in a tracking servo loop. To achieve the above object, the following measures are taken: In tracking pull-in operation for reducing relative moving velocity between a code read beam and a code track executed to pull the code read beam irradiated on an optical disk in a tracking servo circuit for instructing the beam to follow the code track, damping operation is forcedly inhibited in a period in which a defect is detected on the optical disk. Therefore, the wrong discrimination caused by the defect of the direction of relative movement between the code read beam and the record medium is prevented beforehand and damping operation in pulling into the tracking loop can be securely executed.

Abstract: In an optical head including an optical unit consisting of a light source and photosensor, and a main focus servo means to allow an objective lens to focus a light beam emitted from the light source, and further an auxiliary focus servo means provided between the optical unit and objective lens to detect a position of the objective lens, the objective lens staying outside a range in which the main focus servo means provides a significant signal output, is moved into that range based on a detection signal from the auxiliary focus servo means.

Abstract: A process of fabricating a durable data storage medium is disclosed, the durable data storage medium capable of storing, digital or alphanumeric characters as well as graphical shapes or characters. Additionally, a durable data storage medium including a substrate having etched characters therein is disclosed, the substrate characterized as containing detectable residual amounts of ions used in the preparation process.

Abstract: In a disc discrimination device provided with a disc apparatus on which a plurality of types of disc can be loaded, when a disc D is loaded on a turntable, detection light is irradiated from light irradiation means 3 and light receiving means 4 receives the light reflected from a recording surface. Since the distance from the front surface Da of the disc to the recording surface thereof is different depending upon a type of disc, the type of the disc can be discriminated depending upon the difference between the thicknesses of the protective layer of the disc by obtaining the difference between the ranges of the light beam of reflected light {circle around (1)} and {circle around (2)}. Further, the difference between the reflection factors of the light on the recording surface can be determined by the output from addition means 6, whereby many types of disc can be discriminated. With this arrangement, the disc apparatus can promptly and simply discriminate a type of disc loaded thereon.

Abstract: A motion compensation device to compensate for motion of an optical system causing image blur, and having a position detection device to detect a position of a motion compensation optical system relative to a lens barrel. The position detection device includes an LED to emit light, a position sensing device (PSD) to sense light received from the LED and a light screening device having a slit between the LED and PSD. The lens barrel includes a movable tube to which the LED is fixed, and a fixed tube to which the PSD is fixed. During photography, the movable tube moves in the optical axis direction from a collapsed state causing the distance between the LED and the PSD to become long, and causing a light ray emitted from the LED and incident on the slit to form a small angle with a line perpendicular to the center of the slit.

Abstract: An optical pickup for irradiating a light beam onto an information recording medium and receiving a light reflected by the medium, includes a light source for emitting a light beam, and a liquid crystal panel for diffracting the light beam to produce a main beam and a plurality of sub-beams to be irradiated on the medium. The liquid crystal panel included a first area in which a first group of grating patterns with predetermined pitches is formed and a second area in which a second group of grating patterns having the predetermined pitches is formed, and the first group of grating patterns and the second group of grating patterns are arranged on a plane with a gap area formed between the first area and the second area so as to form an integrated grating pattern.

Abstract: A reflected beam 6 is diffracted by regions 7a and 7b of a hologram 71, these diffracted beams are converged or diverged, and ±1-order diffracted beams from each region are received by light-receiving regions 9a+to 9b−arranged apart from the center of the hologram by a distance almost optically equal to the distance between the center point of the hologram and a convergence (focal) point of the 0-order reflected beam. Three signals obtained from three regions of each light-receiving region are calculated to obtain a focus signal, and, at the same time, signals obtained from four regions of each light-receiving region are calculated to obtain a tracking signal, so that, by using both the ±1-order diffracted beams, a focus error signal detected by the SSD method and a tracking error signal detected by the DPD method are simultaneously obtained with high efficiency and high precision.

Abstract: In an optical pickup, a beam splitter is arranged on an optical path between a hologram and a grating. Beam splitter includes a first reflecting surface reflecting part of a beam reflected from a disk, and a second reflecting surface arranged parallel to the first reflecting surface. Part of the beam which is reflected from the disk and passed through hologram is reflected at the first reflecting surface and thereafter reflected by the second reflecting surface of beam splitter, and thereafter directed to optical waveguide device, whereby a signal recorded on the disk is detected (reproduced). The beam which has transmitted through hologram and the first reflecting surface is directed to photodiode and detected as a servo error signal.

Abstract: The light intensity converter comprises a transparent body including opposite first and second curved surfaces. The body is surrounded by an outer peripheral surface extending between the first and second curved surfaces. The body of the converter is arranged such that the incident light is made incident to the body at the first curved surface and emerges from the second curved surface. The incident light diverges in a certain area and converges in another area, by refraction, so that the light intensity distribution of the incident, first curved surface is converted into a different light intensity distribution while the light travels through the converter, and thus exits from the second curved surface.

Abstract: A repeat control apparatus is installed in an information reproducing apparatus. The repeat control apparatus performs a repeat control on a control signal. The control signal includes control information to be used for controlling reproduction of recording information from a recording medium. The control signal is generated by using a light beam reflected by the recording medium. The repeat control apparatus has: a storage device for storing the control signal; a detecting device for detecting a damaged part of the control signal; a generating device for generating a compensation signal to compensate the damaged part of the control signal; a storing control device for storing the compensation signal, instead of the damaged part of the control signal, into the storage device; and a repeat control device for performing the repeat control by using the control signal and the compensation signal stored in the storage device.

Abstract: A semiconductor laser apparatus comprises a semiconductor substrate, a semiconductor laser which is fixed on the semiconductor substrate and a prism having a slanted plane. The prism is placed such that its slanted plane faces a side across from the semiconductor laser. The apparatus also includes an optical detector for monitoring which is formed on the surface of the semiconductor substrate. The surface is covered by the prism. The following are formed on the slanted plane of the prism: a reflection region on which the surface is processed for reflecting a part of an emitted light beam from the semiconductor laser and a transmissive refraction region on which the surface is processed such that the remaining part of the emitted light beam is transmitted and refracted to be guided to a light receiving plane of the optical detector for monitoring.

Abstract: An optical head device capable of stably positioning an information head device even if a distance between the object point and the image point is reduced so as to miniaturize the device can be realized. The optical head device comprises a semiconductor laser emitting a light beam, a lens converging the light beam emitted from the semiconductor laser to a disk and a holding means maintaining the disk at a constant distance from the lens. The optical head device satisfies the following equations 24 and 25: L2=f×L1/(L1−f)  (equation 24) h<L2  (equation 25) wherein f denotes a focal length of the lens, L1 denotes a distance between the semiconductor laser and a first principal point located on the semiconductor laser side of the lens and h denotes a distance between a second principal point located on the disk side of the lens and the disk that is held by the holding means.

Abstract: An optical surface measurement device is disclosed. A beam of light is focused through an optical system into a spot on a sample and the optical system collects light reflected and scattered by the sample forming an image of the illuminated part of the sample on a focus detector. A control system responds to the focus detector moving the optical system to keep the spot in focus on the sample as the sample is tracked past the apparatus. The optical system may be moved as a whole or one of the lenses therein may be moved with respect to the others. Alternatively the movable lens may be set to oscillate and its position is recorded each time focus is achieved. The focus detector has two outputs one of which is larger than the other when the surface of the sample is above the plane focussed by the optical system and the other being larger when it is below. The control system uses both sum and difference signals calculated from those outputs to discriminate the point of focus.

Abstract: A focus servo control system is a system for selectively applying a light beam to a disk on which data is recorded on plurally layered recording surfaces and setting the focus position of the light beam on a selected recording surface of the two-layered recording surfaces based on a signal read from reflected light from the selected recording surface of the plurally layered recording surfaces of the disk and includes a focus error detector for detecting a positional difference between the focus position of the light beam and the selected recording surface of the plurally layered recording surfaces, a sample-hold circuit for sampling and holding an output of the focus error detector, a focus position correcting circuit for correcting the focus position of the light beam based on one of the output of the focus error detector and an output of the sample-hold circuit, a data signal level detector for detecting the signal level relating to data read out from the disk, a comparator for comparing a signal level dete

Abstract: This invention allows photography even when distance measurement is impossible, reduces the number of out-of-focus photographs, and reduces the cost of an apparatus. In this distance measurement apparatus, an object is illuminated with an auxiliary light-emitting unit, and light reflected by the object and transmitted through a pair of optical units spaced apart at a predetermined interval is received by a light-receiving unit. The light-receiving unit outputs two image signals to an arithmetic unit. In the first distance measurement mode, the arithmetic unit and a control unit calculate object distance on the basis of the relative image distance between the two image signals. Also, in the second distance measurement mode, the arithmetic unit and the control unit calculate object distance on the basis of the difference between the light amounts from the object in the illuminated and non-illuminated states with the auxiliary light-emitting unit.

Abstract: To provide an optical head wherein no collimate lens nor object lens is used and photo-detection can be made with more than one reflection beams, the optical head has an optical system (101) comprising a collimate hologram (104) working as a collimate lens, an object hologram (105) working as an object lens, a two-portion Leith-type ring-band-plate hologram (106) for converting plane-wave light from the object hologram (105) into spherical-wave light converging on a pair of photo-detectors (107 and 108). The two-portion Leith-type ring-band-plate hologram (106) has two symmetrical portions each having a carrier component symmetrical to each other and each diffracting the plane-wave light into a part of the spherical light converging on a position which is shifted from a center line of respective one of the two symmetrical portions by a carrier angle of the respective one.

Abstract: An optical pickup device for condensing the light from a light source on a signal recording surface by an objective lens and for detecting the return light from the signal recording surface by a light detection unit is disclosed. The optical pickup device is capable of recording and/or reproducing at least two different sorts of optical recording media. The light beam radiated from a light source is condensed by an objective lens. An aperture varying unit varies the size of an aperture of the objective lens depending upon the sorts of the optical recording media. The return light from the optical recording medium is detected by a light detection unit. The size of the aperture of the objective lens for condensing the light from the light source is varied depending upon the difference in substrate thickness of the different sorts of the optical recording media, thus assuring high-quality recording/reproduction for two or more different sorts of optical recording media.