Abstract: The present invention relates to a method and an apparatus of adjusting a focusing servo in an optical disc device. According to an embodiment of the present invention, a focusing servo is coarsely adjusted using a tracking error signal for a blank disc, data is recorded in a predetermined area of the disc, and then the focusing servo is finely adjusted using the characteristics of a reproduced signal for the recorded data. In this case, the focusing servo is adjusted to adjust a focusing position of an objective lens, and the predetermined area is a region provided on the disc to detect optimum recording power. The characteristics of the reproduced signal include magnitude and/or jitter value of the reproduced RF signal. Therefore, the present invention can optimally adjust a focusing servo even for a blank disc, and can improve data recording quality.

Abstract: A recording device (1T or the like) is provided with (i) recording elements (50, 40) for recording data by irradiating a recording medium with laser beams; (ii) driving members (33T, 33F, 55T, 55F, 54) for performing tracking process or focusing process; (iii) a servo elements (31T, 31F) for automatically controlling the driving members based on an error signal; (iv) specifying elements (21, 22) for specifying an area where a recording medium characteristic (core eccentricity or the like) is not good, based on a high frequency component included in the error signal; and (v) a control unit (10) for (v-i) controlling the servo unit to change the gain in the automatic control, and for (v-ii) controlling the recording elements to change the recording power of the laser beams, in the specified area.

Abstract: An optical disk apparatus is constructed for writing or reading information by irradiating a laser beam onto an optical disk while rotating the optical disk under a focus control of the laser beam relative to the rotated optical disk. In the optical disk apparatus, an irradiating section is operated to irradiate a laser beam onto the optical disk. A determining section determines a process pattern of the focus control by operating the irradiating section to irradiate the laser beam onto a predetermined area of the optical disk and by monitoring the laser beam reflected back from the predetermined area. A focusing section performs the focus control to regulate a spot diameter of the laser beam based on the determined process pattern during either of the writing or reading of information.

Abstract: An optical disk as disclosed herein includes, among other things, a summing module that sums a compensation signal to a predetermined signal in a servo loop. The compensation signal compensates for a periodical disturbance input into a servo system of the optical disk device in units of a rotation angle of the disk rotating module. A phase lead imparting module imparts a predetermined amount of phase lead to an output signal from an optical detector module and outputs the predetermined amount of phase lead as the compensation signal. The predetermined amount of phase lead is determined in accordance with the rotation period information. The optical disk device performs an accurate iterative learning control to provide stable servo performance. The iterative learning control is performed such that the signal having imparted an optimal amount of phase lead in accordance with the rotation period information is added to the servo loop.

Abstract: A recording apparatus includes: a recording device for recording data onto each of a plurality of types of recording media by irradiating a light beam corresponding to each of the types of recording media; a diffracting device disposed on an optical path of the light beam from the recording device to the recording medium, for generating a main beam and a plurality of sub beams by diffracting the optical beam, the main beam recording data and performing a tracking process, the sub beams performing the tracking process, an amplitude of a tracking signal generated by each or one portion of the sub beams and by the main beam being maximum; a controlling device for controlling the diffracting device to adjust a position on which each of the plurality of sub beams is focused, in accordance with the type of the recording medium; and a tracking device.

Abstract: An objective lens is moved with a disc irradiated with laser light. A maximum value FEmax and a minimum value FEmin of the focus error signal, and a maximum value FSmax of the amplitude of a focus sum signal are measured. “(FEmax?FEmin)/FSmax” is compared with a determination value to determine the type of a disc.

Abstract: A method for discriminating an optical storage medium is disclosed. A predetermined range of the optical storage medium is read after the light source is focused on; and thereby a plurality of data transition points and transition regions defined by an interval of two neighboring points are obtained. Thereafter, the time-consumption for reading the longest transition region is used to determine the type of the currently accessed optical storage medium. Another physical characteristics according to data storage formats, such as the PLL clock frequency or the distance between the reflection layer and the surface layer of the optical storage medium, may be used as references to discriminate the currently accessed optical storage medium.

Abstract: There is provided an optical information recording/reproducing apparatus capable of obtaining a high super-resolution effect using an optical information recording medium in which a super-resolution thin film is formed. An optical information recording medium 1 having a super-resolution layer is irradiated with a laser light in a light emission pattern such that a bias light emission portion that does not cause the super-resolution layer to be in the state of super-resolution and a pulse light emission portion that causes the super-resolution layer to be in the state of super-resolution alternatively appear, and reflected light is detected. A reproduction signal based on the pulse light emission portion and a reproduction signal based on the bias light emission portion are acquired.

Abstract: An optical disk apparatus according to the present invention includes: a rotation driving section on which an optical disk is to be mounted and which drives the optical disk so as to be rotated; a light source; an objective lens for converging light from the light source onto an optical disk mounted on the rotation driving section; a photodetector having at least two detection sections for detecting reflected light, from the optical disk, of the light; and an error signal generation section for deriving a difference signal and a sum signal of respective outputs from the two detection sections of the photodetector, adjusting an offset in at least the sum signal among the difference signal and the sum signal, and thereafter dividing the difference signal by the sum signal whose offset has been adjusted to generate a position error signal of the objective lens.

Abstract: A method for demodulating a tracking error signal comprising the steps of (A) demodulating the tracking error signal when starting motion, (B) demodulating the tracking error signal after motion has started, and (C) demodulating the tracking error signal before and after lens motion stops.

Abstract: A second tracking error detector detects the displacement between the track and the light beam and outputs a second displacement detection result based on the comparison of the reproduction signals between first and second pit strings respectively. A second tracking error controller corrects a target position for push-pull control based on the second displacement detection result. A third tracking error controller calculates a correction data of a first displacement detection result based on the correction amount of the target position by the second tracking error controller, and corrects the first displacement detection result based on the calculated correction data.

Abstract: An optical recording medium having a plural number of recording layers includes a n-th recording layer (23) (n?1), made up by a substrate (20) and a semi-reflective layer (21) carried by the substrate (20) and adapted for partially reflecting and partially transmitting the incident light, a (n+1)th recording layer (28), made up by another substrate (25) and a reflecting layer (26) carried by the substrate (25) and adapted for reflecting the incident light, and a light condensing layer (24) for condensing the light incident via the n-th recording layer (23) on the (n+1)th recording layer (28).

Abstract: When a type of an optical disc is discriminated by disc type discriminating processing, search operation by a CD light beam is carried out in CD discriminating processing, and a distance from a position xf where a large signal change of a first time is detected as a fake phenomenon to a position xs where the large signal change of a second time corresponding to a recording layer is detected as a moving distance d3. Based on the moving distance d3, whether the optical disc is a CD medium is determined. In this manner, whether the optical disc is the CD medium or not can be determined correctly with high precision.

Abstract: An optical disk recording/reproduction device and a disk determination method for an optical disk recording/reproduction device. The disk determination method compares with a threshold value a drive value when the arrival of a focus point at a recording surface is detected during a focus search relative to an optical disk (301) or a drive value during an on-focus state. By this, two or more kinds of optical disks having different substrate thicknesses are determined. The threshold value is determined based on a drive value during an on-focus state when one or more kinds of disks out of the two or more kinds of optical disks become reproducible.

Abstract: The method for estimating recording power Pow_tilting of a tilting part of a tilting disk is shown based on a power compensation formula: Pow_comp=A*(A*K). After a focus error (FE) signal of the tilting part of the tilting disk is manipulated as a focus servo output (FOO) signal, the parameter A is derived by low-pass filtering the FOO signal. Thereafter, another parameter K is then derived from a reference lookup table by using curve fitting approach based on parameter A such that the power compensation Pow_comp could be estimated by substituting parameters A and K into the above formula. A recording power Pow_tilting of the tilting part of the tilting disk could be estimated by adding a given recording power Piwrtpwr to the power compensation Pow_comp.

Abstract: After an optical disk drive according to the present invention has been loaded with an optical disk and before the operation of recognizing the type of the given disk is finished, the drive presumes one of multiple types of candidate optical disks, from/on which data is readable and writable using a light beam with the shortest wavelength among the candidate disks, to be the disk being driven by the motor now and gets the beam for the presumed type of disk radiated from a light source (Step (A)). Next, the drive gets the disk spun at a rotational velocity that realizes a linear velocity equal to or higher than a standardized normal velocity when data is read from the presumed type of disk (Step (B)). Thereafter, the drive starts a focus control in a situation where the spot of the beam being formed on the disk is moving on the disk at the linear velocity equal to or higher than the normal velocity (Step (C)).

Abstract: Whether an optical disc is a first optical disc or not is determined with reference to at least one of first and second focus error signal amplitude values. Then, if a sum value of the addition of a first focus balance signal value (CD-FBAL signal value) to a second focus balance signal value (DVD-FBAL signal value) is equal to or more than a predetermined threshold value, the signal surface of the optical disc is determined to be a CD signal surface of a dual disc. On the other hand, if the sum value is smaller than the predetermined threshold value, the signal surface of the optical disc is determined to be a DVD signal surface of a DVD or a DVD signal surface of a dual disc.

Abstract: In a multilayer disc has an increased number of recording layers) spaced by spacing from each other, a generation interval between focus error (FE) signals detected from the respective recording layers becomes small. This causes mutual interference between the FE signals and a resulting undesired offset and the like in the signals, leading to a significantly deteriorated quality of the FE signals. To avoid this, in an optical pickup device according to the present invention, detection surfaces are newly added at positions adjacent to the FE signal detection surfaces, a predetermined detection signal obtained from the newly-added detection surfaces is multiplied by a predetermined coefficient value depending on the spacing between the recording layers, and the multiplied signal is subtracted from the original FE signal. As a result, mutual interference between the FE signals can be remarkably reduced.

Abstract: A focusing controller and the method thereof for an optical disk drive. The focusing controller includes a filter, a coupler and a focus compensator. The filter filters out a high-frequency component of the track error signal and derives an adjusted signal, while the coupler eliminates the adjustment signal from the focusing error signal so as to generate a coupled signal. The focus compensator generates a focus control signal used for controlling a position of the pick up head of the optical disk drive according to the coupled signal during a focusing operation.

Abstract: The present invention is to provide an apparatus and method for calibrating focus balance in an optical disk drive. A focus servo unit controls a pick-up head to focus and read a mark for generating an RF signal. A jitter generator separates a jitter signal from the RF signal to form a jitter frequency. A focus balance unit compares sequential jitter frequencies to check the convergence and the goal, and determines the direction and variable of calibrating focus balance to generate an error signal. A compensator receives the error signal through the focus servo unit to control the pick-up head for calibrating focus balance.

Abstract: An apparatus and method to accurately discriminate an optical disc type in an optical disc system which records and/or reproduces data to and/or from high density optical discs and low density optical discs includes irradiating a laser beam onto a given one of the optical discs, measuring a track error signal generated from light reflected by the given optical disc, comparing a level of the track error signal with a predetermined reference value, and discriminating a type of the given optical disc according to a comparison result.

Abstract: This invention provides an optical disc device that can prevent the occurrence of an error in a starting position of a write operation due to off-tracking, and to avoid an unnecessary stop of the write operation during writing. A tracking error signal generator generates a tracking error signal from a signal which has been detected by an optical pickup, and a system controller detects off-tracking by comparing the tracking error signal with a threshold level, and turns control operation of a tracking servo controller off if the threshold level is exceeded. The off-tracking detection threshold level applied during a time period from completion of seek operation to a start of movement of the optical pickup to the starting position of the write operation is set to be lower than a threshold level applied during a time period of data recording.

Abstract: An optical disc identification apparatus is disclosed. The optical disc identification apparatus includes an optic pickup unit and a control unit. The optic pickup unit has a plurality of laser sources. The optic pickup unit emits any of lasers to the optical disc and detects the reflected laser from the optical disc to transduce the reflected laser to a detection signal. The control unit controls the optic pickup unit to activate any of the laser sources and moves an object lens of the optic pickup unit. When the object lens moves, the control unit obtains a sectional width value of an S-curve of a focus FE signal according to the detection signal. The control unit repeats above steps to obtain the sectional width values of the S-curves of all the laser sources and identifies the optical disc according to all the sectional width values.

Abstract: In an optical recording medium drive apparatus, an optical recording medium is illuminated with a laser beam emitted from a head via an objected leans, and the head detects light reflected from the optical recording medium being illuminated with the laser beam. A signal generator generates a reflected light signal in accordance with the reflected light detected by the head. A controller drives the objective lens via a focusing unit, and detects peaks in the reflected light signal obtained when the objective lens is driven in a focusing direction. The controller determines whether the optical recording medium is of a single layer type or a multiple layer type by determining whether a pattern of the detected peaks is similar to one of patterns which can occur if the optical recording medium is of the single layer type.

Abstract: This optical disk device includes a pickup head, a spindle motor, a signal generation unit, a runout amount calculation unit, and an out of balance disk detection unit. The signal generation unit generates a tracking error signal. The runout amount calculation unit controls the rotational speed of the spindle motor to first and second disk rotational speeds, and obtains, at these rotational speeds, runout amounts TE1 and TE2 of a tracking error signal, and runout amounts FE1 and FE2 of a focus error signal. And an out of balance disk detection unit detects that this optical disk is an out of balance disk, if the absolute value of (TE2×FE2)/(TE1×FE1) is greater than or equal to a threshold value.

Abstract: The invention provides an optical disk device that has a laser unit including a first objective lens and a second objective lens. A numerical aperture of the first objective lens is different from a numerical aperture of the second objective lens. The optical disk device has a first focus driver that detects a first voltage value indicating the value of a driving voltage to drive the first objective lens when light beams are irradiated onto the surface of an optical disk via the first objective lens and a focus is achieved. The optical disk device has a second focus driver that detects a second voltage value indicating the value of a driving voltage to drive the second objective lens when light beams are irradiated onto the recording surface of said optical disk via the second objective lens and a focus is achieved. The optical disk device has a controller that discriminates the type of an optical disk, based on a difference between the first voltage value and the second voltage value.

Abstract: An apparatus and a method for determining the type of an optical disk are provided. Firstly, an RF signal of the optical disk in an optical disk drive is read out. Next, a bandpass signal is extracted from the RF signal by a bandpass filter whose central frequency is a wobble frequency. Then, whether the bandpass signal corresponds to a wobble signal is determined. If so, the optical disk is a recordable optical disk; otherwise, the optical disk is a read-only optical disk.

Abstract: A method for identifying an optical disk according to a radio frequency integration filtering signal includes the steps of: moving an optical head to an initial position; rotating the optical disk and making focus, moving the optical head in a direction toward an inner ring until the optical head is moved to a home position or the focus fails, reading the radio frequency integration filtering signal, and recording a maximum and a minimum thereof when the optical head is being moved; stopping the optical head and determining whether a difference between the maximum and the minimum is greater than a predetermined threshold value; setting the optical disk as a second type of disk if the difference is greater than the predetermined threshold value; and setting the optical disk as a first type of disk if the difference is smaller than or equal to the predetermined threshold value.

Abstract: A system for supplying a driving voltage to move an optical pickup unit to a predetermined position includes a storage unit, an output unit, and a drive module. The storage unit is used for storing instructions. The instructions include a move-outwards instruction, a move-inwards instruction, and a move discriminate-position instruction. The output unit is constructed and arranged for outputting the instructions. The drive module is coupled to the output unit for supplying the driving voltage to move the optical pickup unit toward an outermost position based on the move-outwards instruction, move the optical pickup unit to an innermost position based on the move-inwards instruction, and move the optical pickup unit from the innermost position to the predetermined position based on the move discriminate-position instruction.

Abstract: An optical disc apparatus includes an emitter which emits a laser beam to a optical disc, a divided photodetector including a first divided portion and a second divided portion disposed in a light path of the reflected beam from the optical disc, and producing a first photodetector signal and a second photodetector signal, a phase difference detector which produces a phase difference signal from a phase difference between the first and the second photodetector signals, an integrator which produces a integral signal from a integration of the phase difference signal, a tracking controller configure to perform tracking control based on the integral signal, and a limiter which limits a signal to be supplied from the divided photodetector to the phase difference detector or a signal to be supplied from the phase difference detector to the integrator based on a detection status of a signal detected by the divided photodetector.

Abstract: A tracking error control system includes a tracking error signal generator in communication with an optical pickup head, a DC detector in communication with the tracking error signal generator and a comparator in communication with the DC detector and the tracking error signal generator. The operating optical signals received by the optical pickup head are operated with an offset signal to generate a tracking error signal. A direct current voltage of the tracking error signal is detected and compared with a reference voltage. The offset signal is adjusted according to the comparison result and fed back to the tracking error signal generator to adjust the tracking error signal.

Abstract: A method of determining a size of an optical disc inserted into an optical disc drive is disclosed. The method includes driving a turntable motor of the optical disc drive to rotate the optical disc at a predetermined rotation frequency for reading data stored on the optical disc, measuring a rotation frequency of the turntable motor, applying a kick-pulse voltage to the turntable motor of the optical disc drive for a predetermined period of time, measuring a change in the rotation frequency of the turntable motor after applying the kick-pulse voltage, comparing the change in the rotation frequency of the turntable motor to a threshold value, and determining that the optical disc is an 8 cm disc when the change in the rotation frequency of the turntable motor is above the threshold value.

Abstract: A method for controlling focus loop of an optical storage device includes: moving a lens of an optical pick-up head in a first moving direction; performing a focusing operation when a first S-curve sequence appears in a focus error signal; and when a light beam generated from the optical pick-up head is not focused on an optical disc, performing the focusing operation when a second S-curve sequence appears in the focus error signal; wherein the first S-curve sequence and the second S-curve sequence appear in the focus error signal during one revolution of the optical disc.

Abstract: Disclosed are an apparatus and a method for controlling a tracking servo in a near field optics. Gap error signals are detected in a divided state, and a push pull signal is compensated based on the detected gap error signals. A photo detector detecting the gap error signals is divided into two areas such that movement of an image formed on the photo detector can be detected. The push pull signal is compensated by subtracting a value proportional to a difference value between the two gap error signals detected in the photo detector. The difference value between the two gap error signals is proportional to a dc offset component included in the push pull signal. Accordingly, it is possible to simply remove a dc offset included in a push pull signal without largely modifying the near field optics, so that it is possible to exactly perform a tracking servo operation.

Abstract: An S-curve discriminating portion discriminates that a recording face of an optical disk is opposed to a pickup when a normal S-curve appears in a waveform of a focus error signal Fe that appears when an objective lens fluctuates vertically, while discriminates that a label face is opposed when the waveform of the focus error signal is distorted and two S-curves with large and small magnitudes appear. A signal indicating this discriminated result is supplied to a control portion for controlling respective portions of an optical disk drive.

Abstract: A method and an apparatus for determining types of digital versatile discs (DVDs) are provided. The method includes setting related parameters, acquiring a wobble signal from a DVD, setting a frequency dividing factor, and dividing the frequency of the wobble signal by the frequency dividing factor. Then, the time required for the digital versatile disc to spin one round, which is driven by a spindle motor of a disc player, is set as a unit time to calculate the frequency of the frequency-divided wobble signal. Finally, the type of the digital versatile disc is determined according to the frequency of the wobble signal.

Abstract: A gap pull-in method that minimizes overshoot due to a moving speed of a light focusing element and disturbance of a disk when the light focusing element is converted from an open loop state to a closed loop state during a gap pull-in of a near-field optical disk driver, and an optical disk driving apparatus using the method, the gap pull-in method including: generating an inverse actuator driving signal having a pulse duration and a pulse amplitude according to a moving speed of a light focusing element when an open loop state is changed to a closed loop state in the gap pull-in; and driving an actuator using the inverse actuator driving signal.

Abstract: An off-track duty measurement unit measures off-track detection sensitivity on the basis of an off-track signal, and track cross cycle information that is obtained from a tracking error signal measured by a track cross cycle measurement unit, whereby off-track detection sensitivity can be measured more accurately. Further, an off-track detection sensitivity controller changes the detection sensitivity of an off-track signal detector according to the obtained off-track detection sensitivity, whereby the off-track sensitivity can be kept constant for various kinds of discs, and accordingly, stabilities of off-track detection, track pull-in judgement, and track jumping can be secured.

Abstract: A method for determining a kind of optical recording medium includes: performing focus searching and track searching on an optical recording medium; and determining a kind of optical recording medium according to an optical signal generated by the focus searching and an optical signal generated by the track searching.

Abstract: An optical disc apparatus, as a learning operation before a recording or reproducing operation, rotates an optical disc at a first speed to read PID information, discriminates between lands and grooves of the optical disc, detects switching positions between lands and grooves, sets a rotation angle position of tracking pull-in of an objective lens of a time length that allows the PID information to be stably read, with respect to the switching position, and stores the set position information of tracking pull-in as learning result information. During recording or reproducing, the optical disc apparatus rotates the optical disk at a second speed higher than the first speed, pulls in the objective lens for tracking based on the stored position information of tracking pull-in, reads PID information, and performs the recording or reproducing operation while discriminating between lands and grooves and detecting switching positions between lands and grooves.

Abstract: A method of identifying a type of an optical disc applied in an optical drive is provided. The optical drive at least comprises an optical pickup head. First, move the optical pickup head continually from an initial position. Then, emit a light beam on an optical disc continually and receive a reflected light beam from the optical disc to generate a servo signal. Next, detect a waveform pattern of the servo signal continually to determine whether the waveform pattern of the servo signal changes, if so, the optical disc is identified as a Digital Video Disk-Random Access Memory (DVD-RAM).

Abstract: A discriminating method of ascertaining the format of the loaded optical disc for an optical disc device is disclosed. When the optical disc device operates under a close-loop control, related central error signal is amplified and measured, while the peak-to-peak value of the amplified central error signal is then compared with a threshold. The loaded optical disc will be discriminated as a R-type medium if the peak-to-peak value of the amplified central error signal is larger than the threshold. On the contrary, the loaded optical disc is identified as a ROM-type medium if the peak-to-peak value of the amplified central error signal is smaller than the threshold.

Abstract: Disclosed is an apparatus and method for determining the type of an optical disk so as to implement an optimal servo operation according to the type of a loaded optical disk. In the method, the level of a wobble extraction signal is detected while a focusing servo is turned on, and the type of the loaded optical disk is determined based on the detected signal level, and then a tracking servo adjustment operation is performed according to the determined optical disk type. Accordingly, optical disk reproduction and/or recording characteristics are improved by performing an optimal tracking servo adjustment operation according to the determined optical disk type. Further, if the type of the loaded optical disk is read-only, there is no time loss, thus allowing a swift reproduction operation, since unnecessary operations such as recording mode adjustment and gain adjustment of a digital recording signal processor are omitted.

Abstract: An off-format condition in a digital tracking servo is presented. An off-format condition can be detected by low pass filtering a tracking control signal, detecting a DC level over a threshold level, and indicating the off-format condition if the DC level is above the threshold level for a maximum number of cycles.

Abstract: A method, medium, and device changing a play mode if an error occurs in a process of discriminating the type of optical discs. The method includes the operation of discriminating a type of an optical disc loaded in an optical player, and if the optical disc is discriminated as one of a plurality of optical discs that belong to a first type, setting the play mode of the optical player to a play mode corresponding to the type of the discriminated optical disc, reading and playing data recorded in the loaded optical disc, and if the optical player is unable to reproduce the data recorded in the optical disc, then changing the play mode of the optical player to a play mode for reproducing one of a plurality of optical discs that belong to a second type.

Abstract: Embodiments of a method and apparatus of identifying optical disk types according to the present invention can identify the type of an optical disk (e.g., DVD-RAM, DVD-RAM, or DVD+/?RW) based on comparisons between a plurality of signals. For example, comparisons between the magnitudes of DPD and DPP tracking error signals and their respective reference values can be used. If an optical disk is identified as DVD+RW or DVD?RW, embodiments according to the present invention can further determine whether the optical disk is DVD+RW or DVD?RW. For example, the frequency of a wobble signal resulting from the shape of tracks formed on the optical disk and variables that affect the wobble frequency (e.g., the rotational speed of the optical disk and the current track position) can be used.

Abstract: Calibration of a focus offset in an optical drive. A calibration pattern, comprising a plurality of marked areas, is marked upon a medium. A user input is received, identifying a perceived darkest marked area of the calibration pattern. The focus offset is determined corresponding to the perceived darkest marked area.

Abstract: A method for determining the type of digital versatile discs (DVDs) is provided, for distinguishing among a read only memory (ROM) DVD, a recordable DVD and a re-writable DVD. The method includes reading a tracking error signal from a DVD. If the amplitude of the tracking error signal is greater than a first predetermined value, the DVD is a recordable DVD; otherwise, a recorded area (RECD) signal is read from the DVD. If the RECD signal is zero, the DVD is a blank re-writable DVD; otherwise, a total RF level signal is read from the DVD. If the total RF level signal is greater than a second predetermined value, the DVD is a DVD ROM; otherwise, the DVD is a re-writable DVD with data.

Abstract: A diffractive optical element for dividing a light emitted from a light source into a main beam and at least one sub-beam, an objective lens for focusing the beams on a disk-shaped optical recording medium with spiral tracks, and a photodetector for receiving the beams reflected from the optical recording medium are provided. At least a part of the diffractive optical element includes a diffraction grating divided into four or more plural areas by three or more plural lines in parallel with a direction corresponding to a tangential direction of the optical recording medium, and in two adjacent areas among the plural areas, phases of the lattices are shifted by n to each other.

Abstract: An optical disk apparatus comprises a focusing means for focusing a light beam on a recording medium having first and second information faces; means for moving a focal point of the light beam in a direction substantially perpendicular to the information faces of the recording medium; means for detecting a reflected light from the recording medium; means for detecting a focus condition of the light beam on the basis on an output signal from the reflected light detecting means; a focus control means for driving the focal point moving means on the basis of an output signal from the focus condition detecting means, and controlling the light beam so that the focus condition of the light beam becomes a prescribed focus condition; and a focus jumping means for moving the focal point of the light beam from the first information face to the second information face by driving the focal point moving means.