Abstract: A method for reproducing a hologram includes: irradiating a recording disc with a first reference beam and a second reference beam, both having a parallel light flux, in different directions at a same incident angle to form a hologram having an unslanted grating pattern in which a grating vector is parallel to a light incident surface of the recording disc; irradiating the hologram with the first reference beam or the second reference beam to extract reproduced light; and detecting a position where an intensity of the reproduced light is maximum.

Abstract: A plate body 2, multiple hologram layers 3 are provided in the thickness direction of the plate body 2, and at least one of the multiple hologram layers 3 is formed of spirally continuous hologram bands 4. Erasure areas 4A and 4B and non-erasure areas 4C and 4D of the hologram band 4 are provided in the length direction of the hologram band 4. Non-erasure areas 4E and 4F of the hologram band 4 are formed on both sides in the direction orthogonal to the length direction of the hologram band 4 in the erasure areas 4A and 4B.

Abstract: An optical integrated device includes a light source; a light splitting-and-guiding section that splits a reflected light beam into two end light beams, a connection light beam, and a residual light beam, and guides the two end light beams and the connection light beam in directions different from a direction of the residual light beam; and a light receiving section that receives the two end light beams and the connection light beam with photodetection devices divided, in the tangential direction, into at least two regions within a range in which the connection light beam is incident, receives the residual light beam with photodetection devices divided, in the tangential direction, into regions having widths corresponding to portions on which the two end light beams are incident, and outputs a detection signal in accordance with an amount of light received with each of the photodetection devices.

Abstract: An optical information medium measurement method of the present invention, for measuring a degree of modulation in an optical information medium of a multilayered structure having a plurality of information layers, includes a first step of measuring the modulation degree of each layer of the optical information medium, by use of a measurement optical system, a second step of obtaining a thickness between layers of the optical information medium, a third step of obtaining a reflectance of each layer of the optical information medium, and a fourth step of converting the modulation degree of each layer, the modulation degree being measured in the first step, into a modulation degree at a reference optical system differing from the measurement optical system, based on a value indicative of the thickness between layers, the thickness being obtained in the second step, and a value indicative of the reflectance of each layer, the reflectance being obtained in the third step.

Abstract: A traverse for an optical disc drive comprising a base, a main shaft motor, a pick-up motor and a pick-up head module is provided. The base includes a bottom plate and a plurality of raised mesas. The bottom plate has an opening and the raised mesas connect with the bottom plate. The main shaft motor is disposed on the raised mesas. The pick-up motor is disposed on the bottom plate and the pick-up head module connects with the pick-up motor. The pick-up motor enables the pick-up head module to move inside the opening. Additionally, the present invention also provides an optical disc drive with the said traverse.

Abstract: A method of recording holographic information and an apparatus for recording/reproducing holographic information. The method includes: forming an information layer by recording a hologram on a holographic recording layer of a holographic information storage medium; and fixing the information layer on which the hologram is recorded, by radiating light on the information layer.

Abstract: To accomplish the object, the invention provides a record medium including a plate body 2; multiple hologram layers 3 formed in the thickness direction of the plate body 2; and hologram bands 4 formed in at least one of the multiple hologram layers 3. The hologram band 4 is formed with erasure areas 4A and 4B of the hologram band 4 with no hologram band 4 in the direction orthogonal to the length direction of the hologram band 4.

Abstract: A device for measuring eccentricity of a lens includes a support portion, an eccentricity detector, a driving device, a vacuum absorption device, a clamping device, and a rotatable pole. The support portion includes a plurality of gear teeth and a first through hole. The eccentricity detector is positioned above the lens. The driving device includes a driving mechanism and a motor. The motor rotates the driving mechanism. The vacuum absorption device includes an air pipe and a vacuum generation element. The vacuum generation element is for removing air from the air pipe. The clamping device includes a first clamping element and a second clamping element. The first clamping element cooperates with the second clamping element to locate and fix the lens. The rotatable pole includes a second through hole. The rotatable pole is for supporting the support portion.

Abstract: The present invention relates to a method for operating an optical drive system (12) capable of reproducing/recording information from/to an optical carrier (1), wherein the optical drive system includes a focus controller (PID) for controlling a focus actuator (4), and a focus memory loop (ML) for applying a stored correction signal to the focus actuator (4). The method aims at avoiding impacts between the focussing means (3) and the optical carrier (1), by gradually stopping the focus control loop in response to an event, such as a user initiated ejection of the optical carrier. The gradual stop of the focus control loop is achieved by gradually reducing a memory loop parameter of the focus memory loop (ML), and by gradually reducing a controller parameter of an integrating part (I) of the focus controller (PID). It is an advantage of the invention that the phase of the stored correction signal is synchronized with the angular position of optical carrier (1) during the gradual stopping.

Abstract: [Problems] To provide an optical head and an optical information recorder/reproducer in which a high signal/noise ratio can be attained for an RF signal. [Means of Solving Problems] Reflected light beam from a disc (6) is divided into three light beams, a zero order light beam and ±first order diffraction light beams by a diffraction optical element (7a). Each light beam is further divided into four light beams by a diffraction optical element (8) which is divided into four regions by two lines passing the optical axis of incident light and respectively being parallel with the radial direction and the tangential direction of the disc (6) before being received by a photodetector (10a). Zero order light beam from the diffraction optical element (7a) is used for detecting a track error signal and an RF signal by a phase difference method or a push-pull method, and ±first order diffraction light beams from the diffraction optical element (7a) is used for detecting a focus error signal by a Foucault method.

Abstract: When a method for increasing density by providing a tracking guide such as a land/groove and introducing a plurality of strings of super-resolution pits into one track thereof is applied to a reproduction-dedicated optical disk, there are problems in that the production cost is increased, the structure is complicated, and the space which can be used for a recording pits is narrowed because of the land/groove structure. In the invention, a concept of group tracking is applied. One track is formed by a plurality of pit strings having a size not greater than the optical resolution limit in the radial direction and a size not less than or not greater than the optical resolution limit or only not greater than the optical resolution limit in the tangential direction.

Abstract: A disclosed optical pickup includes an aberration correction unit with a phase shifter surface. On the phase shifter surface, rectangular or staircase-like steps are formed in a concentric manner around an optical axial center, in certain regions where a light beam passes through. The steps have different heights in the optical axial direction. A light beam having a wavelength of 405 nm is directly transmitted through the steps so that a phase difference is applied for correcting spherical aberration that occurs on a first optical recording medium. A light beam that passes through an annular region without any steps is focused on a second optical recording medium. A light beam that passes through an outside region is focused by an object lens on the second optical recording medium, and is not focused on the first optical recording medium.

Abstract: A Viterbi detector includes an ACS circuit that performs addition of a path metric and branch metrics, comparison of the path metric values and path selection based on the result of comparison. The ACS circuit performs a path decision based on the path metric values and the reproduced signal supplied to the Viterbi detector at the time instant that is a specified number of channel clocks earlier during the path selection. The ACS circuit selects a mark-continuing path if the reproduced signal at the time instant that is the specified number of channel clocks earlier has an amplitude corresponding to any mark, and performs path decision based on the path metric values if the reproduced signal does not have the amplitude corresponding to any mark.

Abstract: An optical disk drive, and a method of determining a write strategy thereof. In the method of determining a write strategy of an optical disk drive where a mark and a space are formed on an optical disk by a laser beam to display write information and information is written or reproduced, write quality is evaluated by combining at least two of power- and pulse-based parameters defining a writing multi pulse, and the at least two parameters are changed on a 2-dimensional matrix. The power- and pulse-based parameters indicating specific write quality are determined as strategy parameters, based on evaluated results of the write quality.

Abstract: The present invention relates to a method for detecting a blank area of a power calibration area. The method includes the steps of: selecting a recording test area in the power calibration area; writing the recording test area with multiple stages of normal power and detecting power; forming multiple normal blocks and detecting blocks, wherein each of the detecting blocks includes one unit of unrecorded block and one unit of recorded block; and reading information from the unrecorded blocks of the detecting blocks and thus determining whether the unrecorded blocks of the detecting blocks are blank or not. Once all the unrecorded blocks of the detecting blocks are determined to be blank, it represents that the selected recording test area is totally blank.

Abstract: Disclosed herein are aspects of optical tape technology, tape manufacturing, and tape usage.

Abstract: An optical system for efficiently extracting plural signal beams from a bundle of rays reflected from a multilayer optical disc.

Abstract: An apparatus for detecting burst cutting areas on optical discs includes an optical pickup head, a front-end processing unit, a sync pattern detector, a channel clock recovery device, and a data demodulator. The front-end processing unit generates a BCA signal in response to a radio frequency signal. The sync pattern detector counts the BCA signal according to a reference clock, detects a sync pattern of the BCA signal and outputs a channel bit length counting value. The channel clock recovery device generates a channel clock according to the reference clock and the channel bit length counting value. The data demodulator transfers the BCA signal into a BCA data according to the channel clock. The sync pattern detector continuously counts the B CA signal and continuously outputs a plurality of counting values, so that the sync pattern of the BCA signal can be determined according to at least three sequential counting values.

Abstract: An optical disc apparatus in which processing time is shortened and processing accuracy is ensured upon focus offset processing for plural recording layers. Regarding each of mutually adjacent recording layers, based on a signal based on reflected light from a guide groove formed in a recording surface of the recording layer, a focus offset for an optical system with respect to the guide groove is learned, and based on the learned focus offsets for the respective recording layers, a focus offset for recording or reproduction is calculated and set. In an optical disc having three or more recording layers, a focus offset when the difference between the focus offset and the learned focus offsets for the respective recording layers is a value corresponding to the characteristic of the optical system is set as a focus offset for the respective recording layers or a common focus offset to the respective recording layers.

Abstract: A composition for holographic recording medium, which can be coated in a uniform thickness and enables to simply produce a high definition holographic recording medium is provided. And a holographic medium having a low error rate, high storage capacity, high-performance, high-density, which is produced using the composition for the holographic recording medium, is also provided. The composition comprises a (meth)acrylic acid ester group-containing polymerizable substance, an alicyclic epoxy group-containing cationical polymerizable substance of which is ring-opening polymerized by heat, and a hydroxyl group-containing substance which is reactive with the alicyclic epoxy group-containing cationical polymerizable substance. The holographic recording medium is produced by forming a holographic recording layer on a substrate by applying the composition on the base material and polymerizing the alicyclic epoxy group-containing cationical polymerizable substance and the hydroxyl group-containing substance.

Abstract: The invention provides an optical disk drive. In one embodiment, the optical disk drive comprises a feeding device, a power driver, and a controller. The feeding device comprises a spherical aberration (SA) lens and a stepping motor, wherein the SA lens corrects spherical aberration of a light beam emitted by a pickup head, and the stepping motor moves the SA lens according to a plurality of control signals. The power driver generates the control signals to drive the stepping motor to move the SA lens. The controller directs the power driver to drive the stepping motor to move the SA lens with only stable steps when the SA lens is required to move, so that the stepping motor is in a stable state without inducing step errors after the stepping motor rotates with the stable steps.

Abstract: The present invention relates to a method for checking the quality of a recording on a disk intended to be read with a first wavelength and intended to be recorded with a second wavelength, directly with the second wavelength used by the recording system. According to the invention, the method uses a modified jitter definition when a jitter value of recorded information is measured using light of the first wavelength. A special equalizer takes account of a required asymmetry.

Abstract: When writing on a recordable medium the recorder can encounter write errors. When a write error occurrs the record carrier is discarded. By ignoring write errors in sections of the record carrier comprising unused information, for instance sections of the lead-in or lead-out the record carrier no longer needs to be discarded.

Abstract: An apparatus for accessing data from a disc with a linking area comprises a pick up head, a servo, a processing unit, a position predictor, and a control signal generator. The pick up head reads data from the disc and generates a read signal. The servo controls the pick up head. The processing unit processes the read signal and controls the servo according to a plurality of control signals. The position predictor tracks time position on the disc and generates position information. The control signal generator receives the position information and generates the control signals according to the position information.

Abstract: In holographic recording by the angle multiplexing method, in order to allow a signal beam and a reference beam to sufficiently overlap with each other in a storage medium to decrease as much as possible a wastefully exposed region, which does not contribute to a signal recording, an optical pickup apparatus having a function which can control, for example, a size or a position of an aperture of the reference beam is used. An optical information reproducing apparatus or an optical information recording and reproducing apparatus using the optical pickup apparatus is used.

Abstract: An optical information medium measurement method of the present invention, for measuring a degree of modulation in an optical information medium of a multilayered structure having a plurality of information layers, includes a first step of measuring the modulation degree of each layer of the optical information medium, by use of a measurement optical system, a second step of obtaining a thickness between layers of the optical information medium, a third step of obtaining a reflectance of each layer of the optical information medium, and a fourth step of converting the modulation degree of each layer, the modulation degree being measured in the first step, into a modulation degree at a reference optical system differing from the measurement optical system, based on a value indicative of the thickness between layers, the thickness being obtained in the second step, and a value indicative of the reflectance of each layer, the reflectance being obtained in the third step.

Abstract: There are provided an optical pickup device which can satisfactorily record and/or reproduce information on different kinds of optical information recording medium in spite of compactness, and an objective optical element used for the optical pickup device. The optical functional surface of the objective optical element includes at least two areas of a central area including an optical axis and a peripheral area surrounding the central area. An optical path difference providing structure in the central area is a structure obtained by overlapping a first central basic structure and a second central basic structure which are in a shape of ring-shaped zones divided by step differences, with each other. An optical path difference providing structure in the peripheral area is a structure obtained by overlapping a first peripheral basic structure and a second peripheral basic structure which are in a shape of ring-shaped zones divided by step differences, with each other.

Abstract: An optical pickup and an optical information recording and reproducing device in which spherical aberration correction control after a disc is loaded can be efficiently made in a short time. Before an information recording medium is loaded into a drive, an optical axis direction position of a concave lens is preset to a state so as to optimize a converging spot on a recording surface of a single-layered medium of as a first recording medium or a predetermined layer (first layer having a substrate thickness of 0.1 mm) of a medium having two or more layers to which the recording/reproduction is executed by a laser light source. After the information recording medium is loaded, if it is determined to be a second (third) recording medium to which the recording/reproduction is executed by a laser light source, setting of the optical axis direction position of the concave lens is changed.

Abstract: A signal processing device includes a processing circuit and a signal generating circuit. The processing circuit is implemented for determining a position of at least one defective area on an optical storage medium according to a defect signal, and accordingly recording defect position information of the at least one defective area. The signal generating circuit is coupled to the processing circuit, and implemented for generating an output signal according to at least the recorded defect position information of the at least one defective area.

Abstract: A multilayer optical recording system to record information with light includes a lens unit, a recording medium, and a microscopic drive unit. The lens unit includes a metamaterial lens or a plasmon lens. The metamaterial lens has a first dielectric member in which first microstructures are implanted in a substantially regular manner. The plasmon lens has an aperture. The aperture is a hole or a slit created in a metal film. The microscopic drive unit is configured to adjust a relative position between the lens unit and the recording medium. In addition, the principal plane is placed to be in contact with the lens unit or to have a gap between the principal plane and the lens unit. Furthermore, the second microstructures are arranged periodically in a direction substantially perpendicular to the principal plane of the recording medium.

Abstract: An optical system for reading and recording data on a media includes a laser source for generating a laser beam; an optical subsystem for splitting the laser beam into a reference beam and an object beam; and first and second lens for receiving the reference beam and object beam, respectively, and focusing the reference and object beams at a focal point on the media at which the reference beam and object beam interfere with each other. The reference beam and the object beam have first and second optical path lengths defined from the laser source to the focal point of the media. The optical subsystem is positioned so that an optical path length difference between the first and second optical path lengths is substantially equal to an integer multiple of an interference revival period associated with the reference beam and the object beam, the interference revival period associated with peak values of visibility of the interference versus the optical path difference.

Abstract: In an optical disk including at least a rewritable phase change material and comprising a recording layer having a reflectivity of more than 15%, an address output value as an address pit signal component occupying in a reproduced signal in a non recording state is prescribed to be 0.18 though 0.27 or a numerical aperture of an address pit signal occupying in a reproduced signal in a non recording state is prescribed to be more than 0.3.

Abstract: An optical pickup and an optical information recording and reproducing device in which spherical aberration correction control after a disc is loaded can be efficiently made in a short time. Before an information recording medium is loaded into a drive, an optical axis direction position of a concave lens is preset to a state so as to optimize a converging spot on a recording surface of a single-layered medium of as a first recording medium or a predetermined layer (first layer having a substrate thickness of 0.1 mm) of a medium having two or more layers to which the recording/reproduction is executed by a laser light source. After the information recording medium is loaded, if it is determined to be a second (third) recording medium to which the recording/reproduction is executed by a laser light source, setting of the optical axis direction position of the concave lens is changed.

Abstract: An embodiment generally relates to an optical device suitable for use with an optical medium for the storage and retrieval of data. The optical device includes an illumination means for providing a beam of optical radiation of wavelength ? and an optical path that the beam of optical radiation follows. The optical device also includes a diffractive optical element defined by a plurality of annular sections. The plurality of annular sections having a first material alternately disposed with a plurality of annular sections comprising a second material. The diffractive optical element generates a plurality of focal points and densely accumulated ray points with phase contrast phenomena and the optical medium is positioned at a selected focal point or ray point of the diffractive optical element.

Abstract: The present invention can record sub-data. An optical disk drive (20) controls a laser diode (51), which serves as a light source, according to recording main-data information (Da) based on main data, and thus forms a record mark (RM) along a virtual irradiation line (TL) in an optical disk (100). The optical disk drive (20) shifts a target depth in a focusing direction according to recording sub-data information (Db) based on sub-data, and thus forms the record mark (RM) with the center of the record mark deviated in the focusing direction from the irradiation line (TL).

Abstract: In an optical disc apparatus, whether an unrecorded recording layer without information recorded thereon is included in the multiple recording layers of the optical disc mounted inside the apparatus is judged. then when the unrecorded recording layer is judged to be present, a signal for focus offset adjustment is recorded in a non-user data recording area of the unrecorded recording layer, and reproduction of the recorded focus offset adjusting signal is followed by its quality evaluation, which is further followed by calculation and setup of an appropriate focus offset value based on evaluation results.

Abstract: This disclosure describes thin optical media that may be compliant with conventional DVD drives. Unlike conventional DVDs, however, the described media does not include the non-information bearing “dummy” substrate. Instead, the described media may comprise a single substrate having a thickness of approximately 0.6 millimeters. Depending on the format, reflective layers, information layers, dyes, phase change materials, or other materials may be deposited over the replicated side of the substrates. Furthermore, in accordance with this disclosure, a hard coat layer is also formed over the replicated side of the media in order to provide mechanical integrity to the media. Printable layers, printed layers, lacquer, or other materials may also be added. The elimination of the non-information bearing “dummy” substrate can reduce raw materials, thereby reducing costs and providing a more environmentally friendly optical disk. The hard coat can provide the mechanical protection to the replicated side of the 0.

Abstract: An information recording and reproducing device diffracts by a diffracting means (14) to make laser light separated into a main beam and a sub-beam, irradiates evanescent light in relation to the main beam, by an evanescent light generating means (21), to a track where a recording pit provided on a recording surface of a recording medium is formed and also irradiates evanescent light in relation to the sub-beam to be separated to a track where no recording pit provided on the recording surface of the recording medium is formed. A moving means (210) moves the evanescent light generating means to a direction to change a gap with the recording surface.

Abstract: This optical disk device includes a pickup, an offsetting means, a focus servo means, a layer jump means, and a shift means. The pickup irradiates laser light upon an optical disk having a plurality of recording layers via a correction lens and an objective lens, and detects light reflected back from the optical disk. The offsetting means generates a focus error (FE) signal on the basis of the reflected light, and applies an offset voltage to the focus error signal. The focus servo means performs focusing servo on the basis of the FE signal. And, before layer jumping is executed by the layer jump means, the focus servo means displaces the correction lens to an intermediate position after having adjusted the offset voltage to a balance value. Then the layer jump means performs layer jumping.

Abstract: A servo control signal generation device for discriminating a kind of an optical disk, changing over between top and bottom envelope signals of an RF signal, and generating a defect signal and a mirror signal includes an RF generator for generating the RF signal from reflected light of an optical disk, a disk discriminator for discriminating a kind of the optical disk from the RF signal, and a top envelope generator and a bottom envelope generator respectively for generating the top and bottom envelope signals of the RF signal. If the disk has reflectance after recording which is lower than that before recording, the defect and mirror signals are generated respectively from the top and bottom envelope signals. If the disk has reflectance after recording which is higher than that before recording, the defect and mirror signals are generated respectively from the bottom and top envelope signals.

Abstract: The present invention provides an optical disk apparatus and a focus jump method capable of reliably performing a focus jump by appropriately obtaining the amplitude of a signal such as a focus error signal in a multilayer optical disk. An optical disk includes jump areas which are provided separately from data areas and at which a focus jump is performed. When a focus jump is performed, an optical pickup is moved to the jump area, and the laser power level of the optical pickup is changed and set in accordance with a target layer to which the focus is jumped. A focus position is allowed to reach the target layer by counting the number of times of intersecting with recording layers using a reflected light from the optical disk while performing a focus sweep of an objective lens in the optical pickup.

Abstract: Rotation synchronization detection means is provided which detects a specified rotational phase having a period of one revolution of an optical disk. An output of the rotation synchronization detection means is synchronized with an output of rotation phase detection means for detecting a rotation phase on the basis of a FG signal and thereafter, information of surface vibration component and eccentricity component is memorized in memories before a sleep process in accordance with the output of the rotation phase detection means or a timing until jump is determined in accordance with the output of the rotation phase detection means and during recovery from the sleep status of stopping the disk once, the output of the rotation synchronization detection means is again synchronized with the output of the rotation phase detection means adapted to detect the rotation phase on the basis of the FG signal.

Abstract: A write-once optical recording medium is described, which in addition to the write-once properties also has rewritable properties. The optical recording medium has a recording layer with at least a first recording sublayer and a second recording sublayer for recording information marks by alloying material of the at least first and second recording layers. The materials of the at least first and second recording sublayers are chosen such that the alloyed material is a phase-change material adapted for recording additional data as phase changes of the alloyed material.

Abstract: An optical disc drive (1), capable of handling optical discs (2) with at least two storage layers (61, 62), comprises an axially displaceable objective lens (34) and a focus actuator (52) for controlling the axial position of the objective lens; a control circuit (90) for generating actuator control signals (SQF) for the focus actuator; and a threshold source (98) for providing a threshold level (VT) lower than a supply voltage (Vs) for the focus actuator. The control circuit (90) monitors a focus disturbance signal and delays a layer jump if the absolute value of the focus disturbance signal is too high. Particularly, the control circuit compares the absolute value of the disturbance signals with said threshold level and, if this absolute value is higher than said threshold level, inhibits (83) the layer jump until the absolute value of the disturbance signals becomes lower than said threshold level.

Abstract: An optical recording medium is capable of preventing a back focus at the face thereof and reducing the interference between beams reflected by each recording surface, thereby improving the quality of a servo signal and a reproductive signal. In a disk having (N-1) layers if N is a natural number (more than three), if a cover-layer thickness and intermediate-layer thicknesses are d1, d2, . . . dN, then a difference of 1 ?m or above is set between the sum of di to dj and the sum of dk to dm for arbitrary natural numbers i, j, k, m (i?j?k?m?N). If the refractive indexes are different from a standard value or different for each layer, the thickness of each layer is converted on the basis of the spread width of light according to the thickness.

Abstract: There is provided an optical disc drive including a light axis deviation detection means (13) which detects a light axis deviation amount of an emission light, a tilt correction control means (15) which determines and outputs a tilt correction amount on the basis of an output of the light axis deviation detection means (13), a microcomputer (10B) which corrects an output of the tilt correction control means (15) and a warpage of a disc, and an addition means (16) which adds an output of the microcomputer (10B) and the output of the tilt correction control means (15), wherein a tilt actuator (2-9) is driven by an output of the addition means (16) through a tilt drive means (11) to control a tilt of an objective lens which focuses a light beam on the disc.

Abstract: The present invention provides an optical recording material allows for obtaining excellent recording signal properties even at high-speed recording and is excellent in durability in both a single-sided single layer optical recording medium and a single-sided two-layer optical recording medium having a first recording layer and a second recording layer. The optical recording material contains a cyanine compound having a specific structure and a squarylium compound as dyes for optical recording layers.

Abstract: A disc-shaped information recording medium includes a laminate of recording layers on and from which an information signal can be optically recorded and reproduced from one side of the medium. Data areas are provided in the recording layers, respectively. The information signal can be recorded on and reproduced from the data areas while a laser beam emitted from an optical pickup is applied to the data areas. Optical recording test areas are provided in the recording layers, respectively. A test signal can be recorded on and reproduced from the optical recording test areas to decide optimum power values of the laser beam for signal recording. The test areas are out of overlap as viewed in a direction of propagation of the laser beam.

Abstract: Optical information media containing a magnesium metal layer and a reactive material layer are disclosed. The magnesium metal can react directly with the reactive material layer, or with a chemical evolved from the reactive material layer after application of energy from a source such as a laser.

Abstract: A disc playback apparatus characterized in, when receiving either a fast-forward playback request or a fast-backward playback request, calculating a target address by setting up a position which is close to a position at which information being read from a memory and being played back is stored in a disc as a movement destination of an optical pickup, and moving the optical pickup to the above-mentioned target address.