Abstract: A method of stable focus control for an optical drive is disclosed. When the signal processing circuit of the optical drive detects a focus drop, the rotation speed of the spindle motor is detected and compared to a predetermined rotation speed. When the rotation speed of the spindle motor is faster than the predetermined rotation speed, the spindle motor brakes to re-focus, and the focus servo mechanism is reset from open-loop control to closed-loop control. Thus, the focus point is locked on the optical disk.

Abstract: In an optical pickup device, an objective lens unit includes a first lens, a second lens for converging a light beam which passed through the first lens on an information recording layer of a recording medium, and a second-lens-driving-use actuator for adjusting the distance between the first and second lenses. The second lens has a reflecting section for reflecting an outer part of the light beam which passed through the first lens and reached the second lens. Moreover, the optical pickup device includes a condenser lens, a cylindrical lens and a light receiving element for detecting a reflected light beam reflected by the reflecting section, and a control device for detecting the distance between the first and second lenses according to the result of detection and for controlling the second-lens-driving-use actuator according to the result of detection.

Abstract: An optical sensing head, which is for reading out an optical data memory, has a substrate with a main surface. An edge-emitting laser component is configured on the main surface of the substrate and has irradiation axis oriented essentially parallel to the first main plane. A deflection device is arranged on the main surface of the substrate and deflects the laser radiation in a direction that is essentially perpendicular to the main surface. At least one signal detector is provided for sensing the laser radiation that is reflected by the optical data memory. An optical element guides the deflected laser radiation to the optical data memory and guides reflected laser radiation to the signal detector. The optical element is connected to the substrate by at least one supporting element. The invention also includes a method for fabricating such a sensing head.

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: An optical data-processing apparatus is provided for writing data to a data storage disk or reading data from the disk. The data-processing apparatus includes first and second light splitters. The first splitter splits reflected light from the storage disk into two semicircular rays. The second splitter splits these two semicircular rays into non-biased light and biased light. The data-processing apparatus also includes an optical detector for receiving the non-biased light and the biased light, thereby producing a first signal corresponding to the non-biased light and a second signal corresponding to the biased light. Based on the first and the second signals, a focus error signal and a spherical aberration signal are produced.

Abstract: The invention features a fly height measurement system for measuring fly height of a slider over a storage disc. The fly height measuring system includes a source of light, a slider, a detector module and a processor. The source of light produces light along a light path. The slider includes an objective lens positioned such that light from said source hits the objective lens and is directed toward a surface of a disc. Light propagating from the disc is directed to a detector. The processor estimates the fly height of the slider based on detector module output.

Abstract: A focus controller for focusing a light beam and positioning the focused light beam onto a signal recording layer of a signal recording media is disclosed. The controller comprises a light beam focusing means having a numerical aperture of 0.6 or more; a focus controlling means for positioning the light beam focused by the light beam focusing means onto the signal recording layer of the recording media; and an offset adjusting means for adjusting an offset between the focused light beam positioned by the focus controlling means and the signal recording layer of the recording media.

Abstract: By providing an area of a smaller numerical aperture and an area of a greater numerical aperture on an objective lens, forming holograms of different characteristics corresponding to the respective areas, and using diffracted light beams of the same order of light beams having different wavelengths emitted from two light sources so as to carry out recording to and reproduction from an optical disc, it is possible to carry out recording and reproduction of information signals to and from a plurality of optical recording media of different types while efficiently using the light beams, and to eliminate the problem of a stray light due to an unwanted diffracted light.

Abstract: A disk apparatus performs optical recording onto an optical disk with a record mark by using a light beam modulated in a manner of multi-pulse series, includes. A detection pulse generating part generates a detection pulse to replace the multi-pulse series; and a detection power control part controls the power of the detection pulse to be smaller than the power of the multi-pulse series.

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 information reading and recording apparatus in which recording media having respective recording densities different front each other, such as DVD, CD, CD-R/RW and the like, can be compatibly read and recorded only with a low-cost laser diode for low recording density. A laser beam from the laser diode is passed through a collimator lens via a half mirror, and there is provided a reflecting mirror for introducing the laser beam to one of two objective lenses, from which the laser beam is emitted towards the disk. One of the objective lenses is a lens having a high numerical aperture and the other one is a lens having a low numerical aperture. A super-resolution cut-off filter is disposed immediately before the objective lens having a high numerical aperture so that the objective lens and the super-resolution cut-off filter are placed in the optical path on reading DVD. On reading CD, the other lens is placed in the optical path.

Abstract: A focus error signal which is a differential signal indicative of a difference between a sum of amounts of reflected light detected by photodetector elements A and C of a four-split photodetector, and that of amounts of reflected light detected by photodetector elements B and D is measured. The level of the focus error signal at a timing when the amount of reflected light from the optical disc and detected by the four-split photodetector is at the maximum is set as a reference level. The gains of amplifiers 23 and 24 are individually adjusted so that the maximum and minimum values of the focus error signal are substantially symmetrical about the reference level. According to the configuration, the focus control can be performed by using the balance-adjusted focus error signal, and therefore can be stably conducted.

Abstract: The method of the present invention includes the steps of rotating a molecule having a predetermined structure by applying a first alternating current electromagnetic field to the molecule, wherein the first alternating current electromagnetic field is produced by an electromagnetic field generation means that is set to a predetermined phase, controlling a rotational phase of the molecule by applying a second electromagnetic field to the rotated molecule by an information recording means, detecting a signal using a signal detection means in accordance with a rotation of the molecule having the rotational phase which has been controlled, and outputting a shift between the phase of the first alternating current electromagnetic field and a phase of the detection signal from the signal detection means as information by an information reading means.

Abstract: An optical pickup is provided which is constructed from a single optical integrated device adapted to write data to, and/or read data from, more than one type of optical disc such as CD, DVD and the like. The optical integrated device includes means for selectively providing as output a result of the light detection by one of a plurality of light detecting elements. This selective output means makes it unnecessary to provide added terminals at the optical integrated device. There is also provided an optical disc drive using the optical pickup.

Abstract: An image recording apparatus and method for using the same to generate a high-resolution image of a scene from a plurality of low-resolution images taken by the apparatus. The apparatus includes an array of image sensors and a lens for imaging the scene onto the array of image sensors such that each image sensor receives light from a different portion of the scene. The lens is rotationally symmetric about an optical axis that passes through the array of image sensors. The lens has a symmetric light collection function in which the portion of the scene that is imaged onto each of the image sensors depends only on the distance of the image sensor from the intersection of the optical axis. A plurality of low-resolution images taken at different angles of rotation are combined to form the high-resolution image.

Abstract: An optical pickup comprising: a diffraction grating, a beam splitter and laser beam guiding optical components that change direction of laser beams, which are placed on a light path constituted by a semiconductor laser that emits dual wavelength laser beams and an information recording surface of an optical disk, wherein a wavelength plate is provided on a light path between said diffraction grating and said semiconductor laser so that a laser beam irradiated on the recording surface of said optical disk becomes an elliptically polarized (including circularly polarized) beam or a beam having a polarizing plane that produces an angle of 30-60 degrees relative to a radius direction.

Abstract: A method for detecting and compensating inclination of an objective lens includes the steps of: initially driving an optical disk and detecting a record signal while travelling on the track of the optical disk; checking whether a GFS signal according to the rotation of the optical disk is normally detected; checking a center error signal value outputted from the optical pick-up which reads a record data on the optical disk in case that the GFS signal is abnormally detected; and discriminating inclination of the objective lens on the basis of the checked center error signal value, thereby judging inclination of the objective lens quickly and accurately. In order to discriminate inclination of the objective lens by the optical disk driving apparatus, the GFS signal and the center error signal generated according to the rotation of the optical disk are all taken into consideration, so that the inclination of the objective lens in the optical pick-up is accurately and quickly discriminated.

Abstract: The present invention provides an autofocus system for an imaging system, such as an external drum platesetter. The autofocus system automatically focuses each of a plurality of scan lines produced by an imaging system on a supply of recording material, and includes a control loop with scan line to scan line feedforward of a motor command waveform.

Abstract: The optical pickup of this invention includes a diffraction grating for dividing a light beam emitted from a semiconductor laser into a main beam, a precedent sub beam and a subsequent sub beam; a hologram element for dividing reflected light beams of the main beam, the precedent sub beam and the subsequent sub beam from an optical recording medium respectively into first through eighth main beams, first through eighth precedent sub beams and first through eighth subsequent sub beams; a main beam detector for receiving the first through eighth main beams; a precedent sub beam detector for receiving the first through eighth precedent sub beams; and a subsequent sub beam detector for receiving the first through eighth subsequent sub beams.

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: An optical pick-up device includes a semi-conductor laser as a laser light-emitting device, a collimator lens, a directional control mirror, an objective lens, a light amount detecting device, a reflecting mirror that reflects leakage light of the laser light onto the light amount detecting device, and a light amount adjusting member that adjusts the amount of light incident on the light amount detecting device, provided between the light amount detecting device and the reflecting mirror. The light amount adjusting member may include a rotatably or slidably-supported baffle of which a rotational angle or slide position is changed so as to adjust the amount of the light.

Abstract: An optical head scans the information layer (3) of an optical record carrier (1) by means of a radiation beam (13). Optical aberrations in the beam such as coma and spherical aberration, caused by tilt and thickness variations in the optical disc respectively, are compensated by an aberration compensator (27) arranged in the radiation beam. The tilt or thickness variation is measured by a detector (30) and used to control the aberration compensator. The radiation beam is focused onto the information layer by an objective system (11). A displacement of the objective system in the transverse direction (26) as used for radial tracking of the optical beam, causes a mismatch between the wavefront to be compensated and the wavefront introduced by the aberration compensator (27). The mismatch is reduced by using a position detector (33) for measuring the transverse position of the objective system and using the position signal (34) as input for the control of the aberration compensator.

Abstract: Surface-enhanced Raman optical data storage (SERODS) systems having increased reading and writing speeds, that is, increased data transfer rates, are disclosed. In the various SERODS read and write systems, the surface-enhanced Raman scattering (SERS) data is written and read using a two-dimensional process called parallel signal transfer (PST). The various embodiments utilize laser light beam excitation of the SERODS medium, optical filtering, beam imaging, and two-dimensional light detection. Two- and three-dimensional SERODS media are utilized. The SERODS write systems employ either a different laser or a different level of laser power.

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 method and apparatus for focus control of an optical disk drive is disclosed. The method for focus control in accordance with the present invention changes focus servo loop characteristics when the optical pickup moves rapidly to perform track search operations so that the vibration of the objective lens is effectively attenuated, thereby allowing stable focus control and high-speed access capability.

Abstract: A system, method and apparatus for storing data using an optical medium. The medium is initialized and data is inserted into the medium, read from the medium and reinserted into the medium. Queues, random access storage devices and other similar structures are formed according to this technique.

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: A high-precision displacement measurement device and linear or rotational displacement measurement method using a unit displacement sensor based on a confocal theory. This device is simpler in construction, lower in cost and superior in resolution to other displacement measurement devices, and is capable of measuring a much wider area than other measurement equipment. The present device is adapted to project a spot of light from a light source on an object whose displacement is to be measured and measure a relative displacement of the object from a displacement of the projected light spot.

Abstract: An imaging system is disclosed that includes a first illumination source for producing a first illumination field, a modulation system for modulating the first illumination field, and an optical imaging system for directing the modulated illumination field to an imaging surface along a first optical path. The imaging system includes a second illumination source for producing a second illumination field, an optical assembly, a sensor assembly, and a control assembly. The optical assembly is for directing the second illumination field toward the imaging surface along a second optical path that is different than and non-parallel with the first optical path. The sensor assembly is for receiving a portion of diffuse reflected illumination of the second illumination field from the imaging surface.

Abstract: An optical disk apparatus includes a laser diode, and a light from the laser diode becomes a parallel light by a collimator lens, which is reflected toward an object lens by a reflection mirror, and focused on a disk through the object lens. A reflected light from the disk is incident on a light-receiving sensor via the collimator lens and a polarization beam splitter. A disk tilt or a lens tilt that renders an amplitude of a push-pull signal of the light-receiving sensor maximum at an arbitrary radial location of the disk is detected. Furthermore, in recording or reproducing the signal, a tilt amount of the disk or the lens (inclination angle) in accordance with the radial location as of that time is set.

Abstract: An optical pickup has a semiconductor laser having two laser sources of different wavelengths disposed in the same package, one diffraction grating and one optical detector. A plurality of light reception areas each having four divisional light reception planes of a -character shape are disposed at positions where light beams reflected from an optical disc are applied. A focus error signal is generated by an astigmatism method by using independently these light reception areas and a tracking error signal is generated by a differential phase detection method by using one or both the light reception areas.

Abstract: An optical data-processing apparatus is provided for writing data to a data storage disk or reading data from the disk. The data-processing apparatus includes first and second light splitters. The first splitter splits reflected light from the storage disk into two semicircular rays. The second splitter splits these two semicircular rays into non-biased light and biased light. The data-processing apparatus also includes an optical detector for receiving the non-biased light and the biased light, thereby producing a first signal corresponding to the non-biased light and a second signal corresponding to the biased light. Based on the first and the second signals, a focus error signal and a spherical aberration signal are produced.

Abstract: A phase difference plate (12) converts states of polarization of emergent light form a laser light source (13) and return light form an optical recording medium (5). A diffractive element (21) separates the return light from an optical axis leading from the laser light source (13) to the optical recording medium (5), and guides the return light to a photodetector (14) on the basis of a difference between the states of polarization of the emergent light and the return light. The polarization direction of emergent light from the laser light source (13) is arranged so as to be oriented in the radial direction of the optical recording medium (5) (in the direction of birefringence of the optical recording medium).

Abstract: An imaging system is disclosed including a first illumination source for producing a first illumination field, a modulation system for modulating the first illumination field, and an optical imaging system for directing the modulated illumination field to an imaging surface along a first optical path. In accordance with an embodiment, the imaging system includes a second illumination source for producing a second illumination field, a first sub-assembly, a second sub-assembly and a control assembly. The first sub-assembly is for directing the second illumination field toward the imaging surface along a second optical path that is different than and non-parallel with said first optical path. The first sub-assembly includes a beam splitter sub-assembly that includes a beam splitter and at least one lens. The second sub-assembly is for receiving a portion of the second illumination field from the imaging surface, and includes a lens and a sensor for producing a sensor output signal.

Abstract: A multi-layer imaging medium has a layer that absorbs radiation at a wavelength used by an optical auto-focus system. Spurious reflections are suppressed. The layer transmits radiation at a wavelength used to image the medium. The layer may function as a support layer for the medium. Thermal imaging media may be made according to the invention.

Abstract: An optical disk checkup/measuring apparatus capable of shortening measuring time and of being incorporated into a manufacturing line and has a simple structure includes rotation driving elements (2,3) for driving rotation of an optical disk to be measured (10), a light emitting portion LD for emitting a light beam LF onto the optical disk to be measured (10), an optically detecting portion (D1, D2) for receiving and detecting the light beam LR reflected from the optical disk to be measured (10) and an operation processing portion (4, 5) for processing a signal received and detected by the optically detecting portion (D1, D2) so as to form a specified signal. The light emitting portion is composed of a plurality of light emitting elements LD provided in a radial direction of the optical disk to be measured (10), and the light beams are emitted successively from the light emitting elements LD onto the optical disk to be measured (10).

Abstract: A radial tilt detector for an optical disc includes a first system for measuring a first average velocity vector of a light beam on a recording surface of the optical disc along a focusing direction of the light beam, a second system for measuring a second average velocity vector of the light beam on the recording surface of the optical disc along a radial direction of the optical disc, a third system for calculating a resultant vector of the measured first and second velocity vectors, and a fourth system for calculating the radial tilt angle of the optical disc using the measured first average velocity, the measured second average velocity, and the calculated resultant vector.

Abstract: A polarization hologram lens includes: a first portion, positioned at a center of the hologram lens, on which no grating pattern is formed; and a second portion, positioned at an outer circumferential area of the first portion, on which grating patterns are formed, wherein the grating patterns do not diffract a light beam of a first polarization direction, and wherein the grating patterns diffract a light beam of a second polarization direction perpendicular to the first polarization direction to produce a diverging diffracted light or a converging diffracted light.

Abstract: In an imaging system and method are disclosed, including a first illumination source for producing a first illumination field, a modulation system for modulating the first illumination field, and an optical imaging system for directing the modulated illumination field to an imaging surface. The optical imaging system includes at least one optical lens for directing the modulated illumination field toward the imaging surface along the optical axis of said optical lens. The at least one optical lens includes a first surface facing the modulation system and a second surface facing the imaging surface. The optical imaging system also includes a second illumination source for producing a second illumination field. The second illumination field has a frequency that is different than the frequency of the first illumination field.

Abstract: A laser generates a collimated laser beam which passes through a lens off-axis. The beam is focused at a focal plane on a substrate surface. A first position sensitive detector receives the laser beam reflected from the substrate surface through the lens to generate a first signal proportional to lateral beam offset. A beam splitter may be provided to direct a portion of the laser beam before passing through the lens toward a second position sensitive detector to generate a second signal proportional to laser beam pointing instability. Apparatus computes the difference between the first and second signals, the difference being a defocused error signal. It is preferred that the first position sensitive detector be located at a distance from the lens that is at least twice the lens focal length.

Abstract: A focusing control apparatus includes method for an optical pickup having an objective lens and an aberration correcting unit includes the steps of detecting an amount of focus error of a light beam and an amount of aberration of the reflected light beam to generate a focus error value and an aberration value; controlling a focused position of the objective lens on the basis of the focus error value while adjusting an amount of aberration correction of the aberration correcting unit on the basis of the aberration value, and performing a focus jump from one recording layer to another recording layer after adjusting the amount of aberration correction of the aberration correcting unit for the another recording layer.

Abstract: In a light detecting device for detecting light beams passing through a light-gathering optical system, an aberration detector of the present invention includes photodetectors for forming a light-gathering spot of a first light beam passing near an optical axis, and photodetectors for forming a light-gathering spot of a second light beam passing outside the first light beam. In accordance with detection signals of the detectors, a spherical aberration of the light-gathering optical system can be detected. With this arrangement, a spherical aberration appearing on the light-gathering optical system is precisely detected and corrected in an appropriate manner, so that it is possible to suitably record and reproduce information in a magneto-optical disk.

Abstract: A radiation detector array for radial tracking error detection and focus error detection, including a first plurality of spot detectors (100, 102, 104) for conducting multiple-spot radial tracking error detection, said first plurality of spot detectors including a first spot detector (100) arranged substantially centrally thereof. The array further includes a second spot detector (106) for conducting spot-size focus error detection in combination with said first spot detector.

Abstract: An optical recording and/or reproduction apparatus includes: a light source for emitting a first light beam; an optical system for outputting first and second diffracted light beams and a second light beam; and a controlling section for controlling the optical system, wherein the first and second diffracted light beams interfere with each other to generate interference fringes which extend in a direction substantially perpendicular to a recording layer of an recording medium, the optical recording and/or reproduction apparatus further includes a detection section for detecting the interference fringes reflected by the guiding portion so as to output a detection signal, and the control section controls the optical system based on the detection signal such that the optical spots follow at least either of concave portions and convex portions of the guiding portion.

Abstract: In an optical pickup device, a first light source and a second light source, light emission points of which are not on an identical optical axis, are provided. A first laser light beam and a second laser light beam, wavelengths of which are different from each other, are respectively emitted from the first and second light sources. The first and second laser light-beams reflected from an optical recording medium are diffracted based on different diffraction order, such that the diffracted first and second laser light beams are received by a common light receiving element.

Abstract: An optical head scans the information layer (3) of an optical record carrier (1) by means of a radiation beam (13). Optical aberrations in the beam such as coma and spherical aberration, caused by tilt and thickness variations in the optical disc respectively, are compensated by an aberration compensator (27) arranged in the radiation beam. The tilt or thickness variation is measured by a detector (30) and used to control the aberration compensator. The radiation beam is focused onto the information layer by an objective system (11). A displacement of the objective system in the transverse direction (26) as used for radial tracking of the optical beam, causes a mismatch between the wavefront to be compensated and the wavefront introduced by the aberration compensator (27). The mismatch is reduced by using a position detector (33) for measuring the transverse position of the objective system and using the position signal (34) as input for the control of the aberration compensator.

Abstract: An inner control loop controls the relative position of a surface to be scanned with respect to a focal plane. An outer control loop responds to the location of the surface to be scanned with respect to a focal plane of the scan lens to generate a setpoint for the inner control loop. A sample-and-hold element disposed between the inner and outer control loops is switched by an edge or defect detector. It is preferred that the outer control loop has a time constant in the range of three to ten times longer than that of the inner control loop. The sample-and-hold element provides a gradual state transition upon the occurrence of an edge or a surface defect.

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: Systems and methods for processing light from multiple fields (48, 54, 55) of view without excessive machinery for scanning optical elements. In an exemplary embodiment of the invention, multiple holographic optical elements (41, 42, 43, 44, 45), integrated on a common film (4), diffract and project light from respective fields of view.

Abstract: A radial tilt detector provided in an optical disc recording/reproduction apparatus includes an optical head for projecting a condensed beam of light on a recording surface of an optical disc and receiving a projected beam of light reflected from the recording surface, a focus actuator for focusing the condensed beam and a driver for outputting a drive signal to drive the focus actuator. The detector also includes an acceleration detector for outputting a signal indicative of an acceleration in a direction depending on an optical axis of the light beam, and a radial tilt calculation processor for receiving the acceleration signal and a signal indicative of the distance between the center of the optical disc and the projected position of the light beam on the recording surface where calculating the radial tilt is based on the received signals and the rotation velocity of the optical disc.