Abstract: An apparatus which stabilizes an operation of a disc driver in a mode conversion setting section includes a pickup which reads information from a disc that is inserted into the disc driver, a filter which performs a low-pass filtering of a servo error signal that is generated during an operation of the pickup, a selector which selects one of the servo error signal and the low-pass filtered servo error signal from the filter and outputs the selected servo error signal to drive the pickup using the selected servo error signal, and a control signal generator which generates a signal to control the selector to select the low-pass filtered servo error signal in a mode conversion setting section of the disc driver. Accordingly, a defocus and a detrack can be prevented in the mode conversion setting section of the disc driver.

Abstract: A tracking error detector receives laser light that is irradiated onto tracks on a disc surface and that is reflected from the tracks by using a light-receiving device having divided portions, binarizes signals output from the light-receiving device having divided portions in accordance with the amount of tracking error by using a signal processing circuit including a binarization circuit, and outputs a tracking error signal for tracking control on the basis of a phase difference between the binarized signals. The tracking error detector includes an inter-signal amplitude difference adjustment circuit for determining an amplitude difference between signals output from the light-receiving device, for adjusting the amplitude difference between the signals, the amplitude difference being binarized by the signal processing circuit, for equalizing the phase offset of each of the signals, and for suppressing the phase offset with respect to the tracking error signal.

Abstract: A rewritable optical disk apparatus, optical information recording and reproducing apparatus or the like is allowed to automatically and properly adjust the optical system to the optimum focal condition regardless of the readout signal detector's positional error and the residual aberration in the optical system. The spherical aberration and defocus are coarsely adjusted using the amplitude (PP amplitude) of the tracking error signal and then finely adjusted using the amplitude (RF amplitude) of the readout signal. Since the spherical aberration can properly be adjusted, it is possible to raise the reliability of the readout signal.

Abstract: A visible light characteristic changing layer formed from photosensitive or heat-sensitive material is formed in a location which can be viewed from a part of a label surface of an optical disk. The optical disk is set on a turntable of an optical disk unit while the label surface of the optical disk is directed downward. The optical disk and an optical pickup are moved mutually along the plane of the optical disk. In synchronism with the relative movement, the power of a laser beam output from the optical pickup is modulated in accordance with image data, such as characters or graphic images to be printed, and the laser beam is emitted onto the visible light characteristic changing layer. As a result of the visible light characteristic changing layer being exposed to the laser beam, a visible-light reflectivity of the visible light characteristic changing layer is changed, thereby forming a image corresponding to the image data on the label surface.

Abstract: The method prevents an optical disk from being scraped by an optical apparatus of a pickup head of an optical disc drive is disclosed, it mainly includes: moving the optical apparatus of the pickup head to a detection position in which the laser-light emitted from the pickup head focuses on the optical disk; detecting the first-detection position and setting a movement boundary according to the first-detection position, wherein the movement boundary has a upper boundary and a bottom boundary; preventing the optical apparatus from moving out of the movement boundary. The present method can be implemented without installing any additional apparatus in the original video disc player, and can prevent the optical disk and the inner apparatus of the optical disc drive from being scraped or damaged by the pickup head during a read/write process to increase the service life of the optical disk and the optical disc drive.

Abstract: An optical information recording medium includes a plurality of recording layers, a reflectance of at least one of the plurality of the recording layers in a non-initialized state with respect to a light beam for initialization being smaller than a reflectance of the same in an initialized state with respect to the light beam for initialization. The recording layers are initialized by irradiating, among the plurality of recording layers, the recording layer positioned farther from a light beam irradiation side with the light beam prior to irradiating the recording layer positioned closer to the light beam irradiation side, so that the initialized recording layers have no initialization irregularities.

Abstract: An optical information apparatus of the present invention includes: an optical pick-up head including: a light source; a diffraction unit; a condensing unit; a beam splitter; a photodetector; and a tracking error signal generator. An optical recording medium has tracks arranged substantially at a constant pitch. An average of a pitch is tp. When a main beam is placed on the track, a first sub-beam and a second sub-beam are placed between the tracks.

Abstract: The invention relates to a radial slaving method and to a reproduction device implementing it for optical discs. In an optical head of a conventional reproduction device using a four-quadrant detector with four photodiode is distributed on either side of a direction parallel to the axis of the track, the individual signals of the photodiodes (d1 to d4) are combined in order to obtain read signals along the two diagonals (diag1, diag2) by subtraction (21, 22). A phase comparison signal circuit (100) makes it possible to construct a radial error signal (Sr) by measuring the phase shift of the diagonal read signals. The invention applies in particular to phase discs with slightly phase-shifting marks.

Abstract: The displacement of a pick-up head along the radial direction of an optical disk is detected, and the absolute position of the pick-up head is determined by the accumulation of the displacement, hence the apparatus knows which area on the optical disk the pick-up head currently stays. After obtaining control signals for a motor to drive the pick-up head to move along the radial direction, the apparatus calculates the displacement of the pick-up head during every stroke according the control signals. Afterward, the absolute position is determined by the accumulation of the displacement during all strokes.

Abstract: It is possible to obtain preferable recording characteristic and reproduction characteristic by considering irregularities of unique characteristics of an LD or the like mounted on an information recording and reproduction apparatus as well as characteristics of an optical disc used. In the information recording and reproduction apparatus, a light source such as a laser diode is driven by a laser drive signal so that a laser beam for recording or reproduction is emitted from the light source. Moreover, the laser drive signal is superimposed by a high-frequency signal of a predetermined frequency so as to eliminate effect of the return light from the optical disc. The information recording and reproduction apparatus superimposes the high-frequency signal by using a high-frequency signal level during recording which is different from a high-frequency signal level during reproduction.

Abstract: An optical data processing apparatus reads and/or writes data from/on a data storage medium, in which first and second data storage layer are stacked, by radiating light from the second layer. The processor includes: a light detector including at least one photodetector for generating a light quantity signal; a detecting optical system for guiding first and second reflected light beams from the first and second layers to the light detector; and a signal processor for generating a layer sensing signal from the light quantity signal and determining, by the layer sensing signal, whether the focal spot is now located near the first layer or the second layer. The detecting optical system includes an optical element that produces astigmatism to the first and second reflected beams.

Abstract: An optical disc drive includes: a light source; a focusing section; a focus shifting section for shifting the focal point of light by changing the position of the focusing section perpendicularly to a data storage layer of a given optical disc in accordance with a control signal; a light receiving section for receiving, at multiple areas, the light reflected from the data storage layer and generating light quantity signals; a signal generating section for generating a focus error signal based on the light quantity signals; and a control section for generating the control signal responsive to the focus error signal such that the focal point is transferred to a focus controllable range. The control section generates the control signal such that the focal point is decelerated at a first acceleration and then at a second acceleration. The absolute value of the second acceleration is smaller than that of the first acceleration.

Abstract: It is possible to manage an empty region in a disc partition while satisfying an inhibit matter of the ROM standard not recording a space bit map describer (SBD). The SBD is recorded upon disc initialization and additional recording into the partition is performed by using the SBD regardless of the access type in the device. When ejecting the disc, pointer information to the SBD recorded in the partition describer (PD) is hacked up in the SBD pointer information save file or save data and then the pointer information is erased. Upon disc recognition, the existence of the save file/data is confirmed and the SBD is restored.

Abstract: A drive, a method of operating the drive and a hybrid disc, BD9, comprising the physical layer of a dual layer DVD disc, DVD9, and the application layer of a Blu-ray disc (BD). The disc comprises a reserved area containing a modulation code and a file structure of the application layer and a BD-ROM mark for a copy protection system (CPS) according to the established BD-ROM format. The disc is readable by a conventional DVD drive, but the firmware and specific hardware and software (47,48,49) for detecting the BD-ROM mark is used. In this way, present DVD or BD drives need only firmware upgrades.

Abstract: During manufacturing of optical disks, mastering equipment inserts marks (“high frequency wobble marks” or “HFWMs”) into the wobble of the groove on optical disks to store data. The presence of a HFWM at a zero crossing of the wobble indicates an active bit and the absence of the HFWM indicates an inactive bit. The zero crossing is, for example, a negative zero crossing. A matched filter is used to detect the shape of the HFWMs. If a HFWM is detected during a wobble cycle, an active bit is saved in a register or a memory. If a HFWM is not detected during a wobble cycle, an inactive bit is saved in a register or a memory. The active and inactive bits may be coded bits that must be decoded to data bits. The data bits include information such as a synchronization mark, a sector identification data, and an error detection code.

Abstract: The present invention relates to an apparatus and a corresponding method for determining write strategy parameters for recording data on an optical record carrier (100) and to an apparatus and a corresponding method for determining read parameters for reading data from an optical record carrier (100).

Abstract: A storage system includes a communication port, the mode of operation of which can be dynamically switched by a user between a target mode and an initiator mode. The port may be a Fibre Channel port. The storage system may be a unified storage system operable to provide file-level access and block-level access to stored data.

Abstract: A method and system that provides for execution of a first calibration sequence, such as upon initialization of a system, to establish an operation value, which utilizes an algorithm intended to be exhaustive, and executing a second calibration sequence from time to time, to measure drift in the parameters, and to update the operation value in response to the measured drift. The second calibration sequence utilizes less resources of the communication channel than does the first calibration sequence. In one embodiment, the first calibration sequence for measurement and convergence on the operation value utilizes long calibration patterns, such as codes that are greater than 30 bytes, or pseudorandom bit sequences having lengths of 2N?1 bits, where N is equal to or greater than 7, while the second calibration sequence utilizes short calibration patterns, such as is fixed codes less than 16 bytes, and for example as short as 2 bytes long.

Abstract: A method and system that provides for execution of a first calibration sequence, such as upon initialization of a system, to establish an operation value, which utilizes an algorithm intended to be exhaustive, and executing a second calibration sequence from time to time, to measure drift in the parameter, and to update the operation value in response to the measured drift. The second calibration sequence utilizes less resources of the communication channel than does the first calibration sequence. In one embodiment, the first calibration sequence for measurement and convergence on the operation value utilizes long calibration patterns, such as codes that are greater than 30 bytes, or pseudorandom bit sequences having lengths of 2N?1 bits, where N is equal to or greater than 7, while the second calibration sequence utilizes short calibration patterns, such as fixed codes less than 16 bytes, and for example as short as 2 bytes long.

Abstract: A disk apparatus includes a light emitter that emits a light beam to be reflected on the optical disk, a light detector that detects a reflected light beam that is reflected from the optical disk, the light detector also outputting detection signals based on the amount of the reflected light beam detected, and a controller determines whether the optical disk is a recordable optical disk or not based on the detection signals. The controller also shifts a spot on the light detector at which the reflected light beam is incident by adjusting the focus point of the light beam on the optical disk in the radial direction when the controller determines that the optical disk is not a recordable optical disk. A wobble signal can be detected with high precision at low cost even when the position of the light detector is not balanced in the radial direction.

Abstract: The present invention provides a disk playback device comprising a control circuit 7 for determining an optimum value of offset for a focus error signal based on amplitude values of a tracking error signal or an RF signal fed from an optical head 5, and making an offset adjustment with reference to the optimum value. The control circuit 7, in signal reproduction, approximates the relationship between offset values and the amplitude values to a quadratic curve with reference to three different offset values and three amplitudes at the respective offset values, repeats a calculation of an optimum offset value corresponding to the peak of the quadratic curve, and sets the three different first to third offset values respectively at an optimum value obtained in a previous optimum offset value calculation processing, and second and third offset values set in the previous optimum offset value calculation processing.

Abstract: A layer-jumping control device and method for an optical disc device includes a calculator, a controller, and a driver. The calculator is configured to receive an error-focusing signal, and to determine a peak and a trough of the error-focusing signal. The controller, coupled to the calculator, is configured to process the error-focusing signal to generate a control-focusing signal. The driver, coupled to the controller, is configured to convert the control-focusing signal to a control-driving signal. The device further includes a counter coupled to the calculator, and enables the layer jump when the counter reaches a predetermined value.

Abstract: An optical disc recording and reproducing apparatus permitting a recording test using an external memory, and a method of driving the apparatus is provided. The optical disc recording and reproducing apparatus reads and bypasses test data to be recorded, which is stored in a buffer memory in a compact disc-digital audio (CD-DA) format or a data format similar to the CD-DA format. The bypassed data is directly converted into serial data by a synchronizer without being encoded, and is then used in a write strategy for a write strategy unit.

Abstract: An optical disc includes tracking polarity information. The optical disc includes a clamping area, a lead-in area, a data area, and a burst cutting area (BCA). The BCA is present between the clamping area and the lead-in area and in which information regarding the optical disc is recorded, and the information is read before performing tracking in the data area. Accordingly, it is possible to obtain the tracking polarity information and/or reflectivity information without trial and error and directly record or reproduce user data in a data area of the optical disc.

Abstract: In an optical information reproduction apparatus having optical beam sources having at least two types of wavelengths, an object lens may be damaged by colliding with an information recording medium while driving a focus servo, which is caused by a fake signal generated due to an incompatibility of the wavelength in use with the information recording medium. To solve such a problem, in case the type of the information recording medium is unrecognizable and a focus servo is led in by using the optical beam source having the first wavelength, the focus servo is led in by using the second focus servo lead-in unit which is driven by an output of a near focus point detection unit during an operation of a second focus search unit which renders the object lens move away from the information recording medium.

Abstract: An image forming apparatus includes: a spindle motor (130) for rotating an optical disk (200); an optical pick-up (100) for applying laser light to the optical disk which moves in a radial direction of the optical disk; a stepping motor (140) for transporting the optical pick-up in the radial direction by a predetermined distance every time the optical disk is rotated plural times; a tracking actuator for actuating a position of laser light irradiated from the optical pick-up; a servo circuit (138) for controlling the tracking actuator in such a manner that irradiation loci of the laser light is made different from each other every time the optical disk is rotated plural times; and a data converter (160) for defining intensity of the laser light in accordance with gradation of dots to be arrayed and a total rotation time of the optical disk.

Abstract: An apparatus and method for controlling a focus jump between recoding layers in a high-density multi-layer disk. The apparatus includes: an optical pickup including an objective lens focusing light on the disk, an aberration correcting unit, and a photodetector detecting light reflected from the disk; a signal processing unit generating a focus error signal from a signal output by the photodetector; a focus hold unit holding a focus servo of the optical pickup; a focus servo control unit controlling the focus servo of the optical pickup using the focus error signal; and a driving unit driving the optical pickup using a signal output by the focus servo control unit.

Abstract: A method and apparatus for reading an index mark pattern. The pattern may be formed on an optical disc medium. The optical disc medium may include a set of data arranged in a data field, and an index mark pattern for identifying a relative location of the data field.

Abstract: A method for deriving a tracking error signal based on a first analog detection signal and a second analog detection signal. The method includes summing the first analog detection signal and the second analog detection signal to generate an analog sum signal. An analog delay device is utilized to delay the analog sum signal to be a delay signal. The delay signal is digitalized into a digital delay signal. The first analog detection signal and the second analog detection signal are respectively transformed into a first digital detection signal and a second digital detect signal. The tracking error signal is then generated utilizing a comparing operation among the digital delay signal, the first digital detect signal, and the first digital detect signal.

Abstract: Minimum deflection acceleration point detection, focus pull-in, and layer jump methods, and an optical disc drive capable of performing the methods. The method of detecting a minimum deflection acceleration point in an optical disc drive includes rotating a disc loaded in the optical disc drive, detecting a first minimum deflection acceleration point of the disc during one rotation cycle of the disc, and detecting a second minimum deflection acceleration point of the disc during one rotation cycle of the disc. Thus, a stable focus pull-in and layer jump is available.

Abstract: An optical disc drive and a method of controlling the same, capable of receiving or ejecting an optical disc in either direction thereof to easily insert and exchange the optical disc. The optical disc drive includes a main body provided on opposite sides thereof with first and second openings for receiving or ejecting an optical disc, a spindle motor installed in the main body and having a chuck to mount the optical disc, and a loading unit provided in the main body to move the optical disc inserted through any one of the first and second openings toward the spindle motor, and to eject the optical disc on the spindle motor through any one of the first and second openings.

Abstract: A method and apparatus for realizing a stable focus jump operation even in a case where a waveform of an S-curve of a focus error signal fluctuates due to aberration due to fluctuation of a multilayer optical disk substrate thickness or the level of the S-curve fluctuates due to reflectance fluctuation are provided.

Abstract: An optical recording medium playing apparatus and method thereof to play an optical disc includes a signal processor to process signals read from the optical disc as a reproduced signal. A timer counts a preset time from when the <play> key is entered a first time and transmitting a signal indicative of whether the <play> key is entered a second time within the preset time. A controller executes a backward search of a desired scene when the <play> key is entered the first time, ends the backward search when the <play> key is re-entered or in response to the signal from the timer, and outputs a signal to command normal playing at a point in time when the backward search has ended. A displayer displays the signals read from the optical disc.

Abstract: A method of recording data on a compact disc is provided includes modulating the data of 1 byte to p-channel bits, recording the modulated data when a minimum mark length is greater than 0.5 ?m and smaller than 1.0 ?m, p/q is greater than 4.5 and smaller than 8 when the minimum mark length corresponds to q-channel bits, and a format efficiency is greater than 0.6 and smaller than 1.0. Thus, data can be recorded on an existing compact disc at a higher density.

Abstract: A method of determining a type of a disc for a disc system to record/reproduce a plurality of recordable discs having different track pitches, including detecting a plurality of signals for determination while moving an objective lens up or down and simultaneously making the objective lens vibrate in a radial direction of the disc, and determining the types of the discs having different track pitches by using the detected signals for determination.

Abstract: An apparatus for recording data on and reproducing data from the disk in which a recording area is divided into sectors, includes a reproducing signal generator for generating a reproducing signal including sum signals V1 and V2 of radial pairs, a sum signal RF_sum, and a push-pull signal RF_pp from an optical signal reflected from the disk, a header area detector for generating a header area signal including a header area from the reproducing signal, a first synchronous signal level detector for detecting a magnitude Ivfo1 of a first synchronous signal in the first header by being synchronized with the header area signal, a second synchronous signal level detector for detecting a magnitude Ivfo3 of a second synchronous signal in the second header by being synchronized with the header area signal, and a balance calculator for calculating the balance of the magnitude Ivfo1 and the magnitude Ivfo3.

Abstract: A chromatic aberration correcting method to correct chromatic aberration generated during a conversion from a reproducing mode to a recording mode in an optical recording and reproducing apparatus which uses an optical pickup to form a light spot on an optical information storage medium by focusing light emitted from a light source using an objective lens and to detect light reflected from the optical information storage medium using a photodetector includes applying a focus offset to the objective lens before the conversion from the reproducing mode to the recording mode to reduce defocus caused by chromatic aberration generated according to the change in wavelength generated when an output light power of the light source is changed from a reproducing light power to a recording light power, and correcting the defocus by outputting the recording light power from the light source during the conversion to the recording mode while the focus offset is applied to the objective lens.

Abstract: An off-track state is to be detected accurately. A photodetector 11 converts the light reflected from an optical disc into an electrical signal. A MIRR signal generating circuit 16 generates a bi-level MIRR signal 23, indicating whether the photodetector 11 is in an on-track state or an off-track state with respect to a track of the optical disc, based on an output signal of the photodetector 11. A TEC signal generating circuit 17 generates a bi-level TEC signal 24, indicating whether the photodetector 11 is on an inner side or on an outer side in the radial direction of the optical disc with respect to the track in the optical disc currently closest to the photodetector, based on the output signal of the photodetector 11. An off-track detector 18 outputs an off-track signal 25 if, after the level of the MIRR signal 23 is changed from an on-track state to an off-track state, the level of the TEC signal 24 is changed without the level of the MIRR signal 23 being changed.

Abstract: According to the present invention, even if tracking fails during reproduction of information from an optical disk and a movement is made to an adjoining track, the reliability of data to be transferred is improved and a countermeasure can be taken immediately. An unrecorded area decision unit decides based on the amplitude of a reproduction signal whether a block concerned is a recorded area or an unrecorded area. A track-off detection unit monitors a tracking servo signal, detects occurrence of a tracking failure, and registers a block, which is recognized as an area where the tracking failure has occurred. If the block is an unrecorded area and recognized as an area where a tracking failure has occurred, reproduction is ceased but data signifying that the block is an unrecorded area is not transferred to an upper-level system and retry is performed to achieve reproduction.

Abstract: An optical disc apparatus comprises a control circuit for performing a first calibration process before the initiation of a write operation and performing a second calibration process during the write operation; the first calibration process includes the steps of: performing focus calibration for the objective lens at a plurality of radial positions on the optical disc based on the output of a photodetector; calculating the vertical disc deviation at the radial positions on the optical disc based on the results of the focus calibration; and based on information about the calculated vertical disc deviation, setting radial positions on the optical disc at which to perform focus calibration during the write operation; wherein the second calibration process includes the steps of: calculating the focus drive amounts, or focus movement ranges, at the set radial positions on the optical disc based on the results of the focus calibration in the first calibration process; and performing focus calibration at the set ra

Abstract: A method of improving readability in an optical drive is disclosed. In one aspect, the present disclosure teaches a method of improving readability in an optical drive including monitoring a compact disc (CD) media for tracking errors using a differential push-pull (DPP) method during an input/output (I/O) operation in an optical drive. The method further includes determining whether a tracking error is above a predetermined error threshold or if a read error has occurred. In response to a read error or tracking error, the method further includes switching from the DPP method to a three-beam tracking method based on the determination.

Abstract: A driver IC 1 has a bias terminal 20a via which a bias voltage fed from a microcomputer 2 to drive and control a loading motor 4 is fed in and a bias terminal 20b via which a bias voltage fed from a DSP 3 to drive and control a focus coil 5, a tracking coil 6, a sled motor 7, and a spindle motor 8 is fed in.

Abstract: A method for determining the position of a pick-up head involves retrieving the respective parameter values relating to the linear velocity and angular velocity of the pick-up head at a certain place on the optical disk, and then calculating the ratio of the parameter value of the linear velocity to the parameter value of the angular velocity. Since the ratio is linearly correlated with the distance between the pick-up head and the center of the optical disk, the absolute position of the pick-up head can be determined, as far as its whereabouts is concerned.

Abstract: An optical disk apparatus and method having a pick-up part for emitting a light onto a recording surface of an optical disk and receiving the light reflected from the recording surface of optical disk and a driving part for controlling the pick-up part. The apparatus and method comprise an error detection part for detecting a tracking error based on a distribution of the received and reflected light, when the pick-up part traces vertical movement of the optical-disk according to control of the driving part; a capacity calculation part for calculating capacity of an optical-disk corresponding to the calculated tracking error size; and a tracking control part for resetting a control method of the driving part for the pick-up part to trace a track of the optical-disk based on the calculated capacity. As such, the track of an optical disk may be minutely traced.

Abstract: A finite optical system that a laser beam from a light source is allowed to be directly incident on an objective lens without passing a collimate lens is employed. The reference position of the objective lens is set so that converged light from the objective lens forms a focal point on a recording layer remoter from the light source of two recording layers in an optical disk. The objective lens moves in a direction of the light source side from the reference position to perform a focusing operation and read information recorded on the recording layer nearer to the light source.

Abstract: An optical disc apparatus includes an optical pickup which irradiates a first laser beam for reproducing a first DVD medium, or a second laser beam for reproducing a second DVD medium onto a installed optical disc, and receives the reflected light from the installed optical disc, a controller determines that the installed optical disc is the second DVD medium when a value by normalizing the amplitude of a RF signal generated from the reflected light with a coefficient is larger than first threshold value and smaller than a second threshold value, and the controller determines that the installed optical disc is the first DVD medium when the value is not larger than first threshold value and smaller than a second threshold value.

Abstract: An information processing apparatus includes: a converging section for converging light; a shifting section for shifting the focus of the light by moving the converging section perpendicularly to an information storage layer of a storage medium responsive to a drive signal; a position control section for generating a position control signal to move the converging section at variable velocities; a focus control section for generating a focus control signal based on a light amount signal representing reflected light such that the focus is located in a focus controllable range; a switching section for selectively outputting the position control or focus control signal; and a driving section for outputting a drive signal responsive to the output signal.

Abstract: A method for recognizing at least two types of optical discs, which are associated with multiple different numerical apertures, includes the step of setting the numerical aperture of a focusing mechanism equal to a first one of the multiple different numerical apertures. The focusing mechanism is used to focus a light beam on a data storage layer of a given optical disc. The first numerical aperture is smaller than any of the other numerical apertures. The method further includes the step of recognizing the type of the given optical disc by the first numerical aperture that has been selected in the step of setting the numerical aperture.

Abstract: An optical information processing apparatus includes: an optical head for irradiating an optical information recording medium with light, converting the light reflected by the optical information recording medium into a head signal and outputting the head signal; a signal quality index detector for detecting a signal quality index representing quality of the head signal on the basis of the head signal; and a two-dimensional probe for varying the focal position and the spherical aberration of the light radiated onto the optical information recording medium so as to search for a focal position and a spherical aberration that optimize the signal quality index detected by the signal quality index detector.

Abstract: An optical disk unit of this invention includes a defocus detecting system for detecting a defocus of an objective lens, a thickness unevenness detecting system for detecting a thickness unevenness of a transparent resin layer provided nearest the objective lens of a recording medium, and a thickness unevenness correcting mechanism for changing the focusing characteristic of light impinging upon the objective lens based on a change in the thickness of the transparent resin layer detected by the thickness detecting system.