Abstract: Provided is an optical pickup device that suppresses a fluctuation of a tracking error signal caused by stray light when recording/reproducing information on/from an optical disc including a plurality of recording layers and attains size reduction. It includes a laser diode emitting laser light of about 405 nm in wavelength, an objective lens irradiating the optical disc with an optical beam emitted from the laser diode and having a numerical aperture of about 0.85, and a detector including a detection part receiving the optical beam reflected from the optical disc. An optical magnification from the optical disc to the detector is set within a range from about 10× to 15×.

Abstract: In one embodiment, the optical pickup device includes: a light source that emits a light beam; a diffractive element that diffracts the light beam and generates a zero-order and ±first-order diffracted light beams; an objective lens that converges the diffracted light beams onto the same track on the storage medium; and a photodetector that receives the diffracted light beams reflected from the storage medium. If a distance from a light beam spot left by the zero-order diffracted light beam on the track to light beam spots left by the ±first-order diffracted light beams on that track is d [?m], the scanning linear velocity of the storage medium is v [m/s], and a time it takes for a phase-change material of the storage medium that has once been melted by the zero-order diffracted light beam to solidify is T [?s], vT?d is satisfied.

Abstract: An optical pickup includes an object lens; a moving part including the object lens and coils; rod-shaped support members disposed in a focusing direction, one end of each of the support members being attached to side surfaces of the moving part in a tracking direction; a fixing part for fixing the other end of each of the support members; a yoke including magnets; and gel holding parts, each of the gel holding parts including walls on both sides of the support members in the tracking direction, and the support members being disposed on both sides of the moving part in the tracking direction. Each of the gel holding parts includes an opening at one end on an optical disc side in the focusing direction and includes a cutout in the wall farther from the object lens in the tracking direction, the cutout extending from an edge of the opening.

Abstract: In one embodiment, an optical pickup includes an optical system which forms multiple light beams based on the light emitted from a light source and which converges a write beam and a read beam, thereby forming a main spot and a sub-spot, respectively, on an optical storage medium. This optical system converges the write and read beams onto the optical storage medium so that the main spot moves through the same region on the optical storage medium ahead of the sub-spot. The optical pickup further includes a detector for sensing the write and read beams reflected from the storage medium. The detector includes a first photodiode 10 that receives the reflected light from the main spot 50R on the storage medium and a second photodiode 11 that receives a portion of the reflected light from the sub-spot 51R.

Abstract: The apparatus includes a pickup for reading data from a super-resolution optical disc, the pickup comprising a laser for generating a main beam, a first and a second satellite beam, the two satellite beams each having a radial offset with regard to the main beam, a third satellite beam following the first satellite beam, having the same radial offset as the first satellite beam, and a fourth satellite beam following the second satellite beam, having the same radial offset as the second satellite beam, for providing a crosstalk correction of the HF data signal. The track pitch between adjacent tracks of the optical disc is particularly below the diffraction limit of the pickup, and the light intensity of each of the first and second satellite beams and of the main beam is sufficient to provide a super-resolution effect on the optical disc and the light intensity of each of the third and fourth satellite beams is not sufficient to provide the super-resolution effect.

Abstract: A method for calibrating a tilt of an actuator includes the following steps: focusing a light beam projected from an objective lens onto a data layer of an optical disc; utilizing a digital signal processor to output control voltages through an analog driving circuit for driving the actuator to tilt the objective lens, and accordingly recording corresponding displacement signals of the objective lens; fitting a tilt curve through the recorded control voltages and the displacement signals; utilizing the digital signal processor to output a zero control voltage, not through the analog driving circuit, for tilting the objective lens, and accordingly measuring a standard displacement signal; acquiring a bias voltage from the tilt curve according to the standard displacement signal; and calibrating the tilt of the actuator by offsetting a control voltage outputted from the digital signal processor according to the bias voltage for controlling the analog driving circuit.

Abstract: A servo control device includes: a phase compensator configured to generate a plurality of types of control values for controlling a driver based on a signal output from an optical pickup, and output the control values; and a transfer data generator configured to serially transfer the control values to the driver. The phase compensator sends, to the transfer data generator, a notification that the phase compensator has output a control value which needs to be sent with a reduced delay among the control values. In response to the notification, the transfer data generator determines whether or not the transfer data generator is transferring one of the control values, and if the transfer data generator is not transferring one of the control values, the transfer data generator starts transferring a control value associated with the notification among the control values.

Abstract: Provided is a recording apparatus including a light irradiation and receiving unit configured to irradiate recording light for performing mark recording to a recording layer and an adjacent servo light for an adjacent track servo onto an optical disc recording medium having the recording layer through a common objective lens, and to receive reflected light from the recording layer of the adjacent servo light, a tracking mechanism configured to drive the objective lens in a tracking direction which is the disc radial direction, a tracking servo signal generation unit configured to obtain a corrected servo error signal as a servo error signal based on a light receiving signal for the adjacent servo light, and to generate a tracking servo signal using the corrected servo error signal, and a tracking driving unit configured to drive the tracking mechanism based on the tracking servo signal.

Abstract: An optical pickup device includes a light source for emitting a light beam, an objective lens for collecting the light beam which is emitted and for irradiating an optical disc with the collected light beam, a diffraction element with a plurality of areas for dividing the light beam which is reflected from the optical disc, a detector with a plurality of detection parts for receiving the light beam which is made to diverge by the diffraction element, and a branching mirror for making the light beam branch into an optical path from the light source to the objective lens and an optical path from the objective lens to the detector. The diffraction element gives an aberration to the light beam diffracted at a specified area.

Abstract: An optical disc apparatus includes: a light irradiation/reception section to irradiate an optical disc recording medium with light via an objective lens and receive return light of the light; a tilt adjustment section to tilt the lens; a focus servo control section to exert focus servo control over the lens; a focus bias application section to apply a focus bias to a focus servo loop; a tracking direction error signal generation section to generate a tracking direction error signal representing an error between light-reception signals; and a control section to perform a tilt adjustment value search process for making a search for a tilt adjustment value with which the tracking direction error signal is maximized, a tilt adjustment value revision process for revising the tilt adjustment value found by the tilt adjustment value search process, and an adjustment control process for causing the tilt adjustment section to perform tilt adjustment.

Abstract: An optical information device used with a grooveless multilayer disc including multiple recording layers used to record and reproduce information signals and a guide layer dedicated to detect tracking error signals (TES) can always stably detect the TESs when the distance between the recording layer and guide layer varies due to selection of a target recording layer. For example, a plurality of light spots for detecting the TESs are formed by a holographic grating on the guide layer, but are defocused with respect to each other. The TESs are detected individually from the respective light spots. The TESs are subjected to an addition operation to be a signal for tracking control, thereby extraordinary increasing the defocus dynamic range of the TESs.

Abstract: An optical pickup whose thickness is small and power consumption is low is provided, in which these advantages are achieved by increasing the driving force generated in the tilt coil in an objective lens driving apparatus and by making the thickness of the objective lens driving apparatus to be small. In an optical pickup including: an objective lens for condensing light onto an optical disc; a lens holder to which the objective lens has been attached; a focusing coli, a tracking coil, and a tilt coil, which have been attached to the lens holder; and a reflection mirror for reflecting light toward the optical axis of the objective lens, the tilt coil is made to have a shape in which the tilt coil is not brought into contact with the side of the reflection mirror, the side being near to the objective lens.

Abstract: A reproducing method includes: irradiating a laser spot for servo to which astigmatism making up a generally 45-degree angle in the tangential direction of an information recording track has been applied, and one or more laser spots for reproduction, onto a recording medium where a track group is formed with multiple information recording tracks adjacent with a narrower track pitch than a track pitch equivalent to optical cut-off, and also where a track group pitch is wider than the track pitch equivalent to optical cut-off; and subjecting one or more laser spots for reproduction to on-track control as to one of the information recording tracks by taking a tangential push pull signal obtained from reflected light information of the laser spot for servo as a tracking error signal, and performing tracking servo control using this tracking error signal, and reproducing data from the reflected light information thereof.

Abstract: The present invention provides a unit and method for implementing an optical head and optical drive device whose configuration is simple, and which allows the generation of a track error signal in which no offset is caused to occur. The optical drive device includes a light source for emitting light beams, an objective lens for converging the light beams onto an optical disc, an optical-signal generation element for dividing the light beams into at least four regions by using a division line extending in the radial direction of the optical disc, and a division line extending in the track direction of the optical disc, the light beams being reflected by the optical disc, and an optical detector for receiving the light beams divided by the optical-signal generation element, wherein the up and down or right and left areas of the four regions are made different from each other.

Abstract: Stable performance of additional recording and erasing and rewriting operations is allowed regardless of a change in inclination of a guide layer separable optical disc. An optical pickup device includes an angle variable reflection mirror (an optical axis angle variable element) which changes directions of optical axes of first and second light beams when the first light beam for recording or reproduction and the second light beam for servo signal detection are emitted from laser diodes and incident upon the optical disc through an objective lens. When additional recording is performed on the optical disc, the optical axis angle of the angle variable reflection mirror is adjusted such that a tracking error signal detected from a record layer with the first light beam is reduced to almost zero while tracking control is being performed on a guide layer with the second light beam.

Abstract: Provided is an optical disc device including: an objective lens; a plurality of light-receiving elements each for outputting an output signal corresponding to a light amount of reflected light from the optical disc medium; a plurality of amplifiers each for amplifying the output signal from a corresponding one of the light-receiving elements; and a signal output circuit for outputting a focus error signal based on amplified signals from the amplifiers. The optical disc device executes focus servo control of controlling, based on the focus error signal, a position of the objective lens so as to keep constant a distance between the objective lens and a signal surface; moves the objective lens to a position at which accuracy of reading information from the optical disc medium becomes high; and thereafter adjusts a gain of each amplifier so that levels of the amplified signals become close to each other.

Abstract: To prevent the peak power/current consumption from exceeding a permitted level when more than one active mechanical mechanism of an electronic device (e.g., an optical storage apparatus) is involved in accomplishing a particular task, a method of controlling the electronic device is provided. The electronic device has a plurality of mechanical mechanisms including at least a first mechanical mechanism and a second mechanical mechanism. The method includes following steps: driving the first mechanical mechanism by applying a first control signal to the first mechanical mechanism; driving the second mechanical mechanism by applying a second control signal to the second mechanical mechanism; comparing the first control signal with a first predetermined threshold, and accordingly generating a first comparison result; and selectively adjusting the second control signal according to at least the first comparison result.

Abstract: According to one embodiment, a pickup head includes a plurality of light sources, a first objective lens, second objective lens, a driving unit, a first control unit, a second control unit, light receiving units. The first objective lens focuses a first light beam at a first recording layer. The second objective lens focuses a second light beam at a second recording layer. The driving unit moves the first objective lens and the second objective lens in a first direction and a second direction. The first control unit corrects displacement from target track along the first direction. The second control unit controls a moving direction of a position of the second light spot in the second direction.

Abstract: An optical disc device includes an optical source for emitting an optical beam, an incident intensity control circuit for controlling an intensity of the optical beam emitted from the optical source, an objective lens for focusing the optical beam on an optical disc, an optical detector for receiving the optical beam reflected from the optical disc, and a servo signal generation circuit for generating a focus error signal from the optical detector, by this configuration, the optical beam is varied once to a third optical beam intensity to be present in between a first optical beam intensity and a second optical beam intensity when varying from the first optical beam intensity up to the second optical beam intensity different from the first optical beam intensity, and the incident intensity control circuit is controlled such that the variation of focus error signal is not exceeded over a predetermined range.

Abstract: A disc drive includes an optical pickup that emits laser light to a predetermined layer position via an objective lens and detects reflection light of the laser light, a tracking mechanism that drives the objective lens in a tracking direction, a tracking error signal generation unit that generates a tracking error signal, based on a light detecting signal for the reflection light obtained by the optical pickup, a tracking servo control unit that performs a tracking servo control based on the tracking error signal, and a control unit that makes the tracking servo control unit perform tracking servo pull-in on the basis of a frequency measurement result of the tracking error signal and a recording or non-recording determination result based on the light detecting signal.

Abstract: An optical system capable of obtaining a high-resolution image using interference and thus capable of providing a stable signal is realized. A particular polarization state of response light emitted from an object is selected, and light in the selected particular polarization state is split into two beams. The split two beams are polarized into two different polarization states. After one of the two beams is subjected to an image inversion, the two beams are condensed such that they interfere with each other. The interfering light is split into a plurality of beams, and each of these beams is detected after they are passed through different polarizing filters. Detected signals are combined together and processed to obtain high-stability amplitude information without being influenced by a phase difference between the two beams.

Abstract: The present invention can properly correct spherical aberration. An optical disk device (10) displaces an objective lens (18) so that the objective lens is displaced to a reference lens position as a reference. The optical disk device (10) controls an information light condensing point changing mechanism (55) so as to adjust the focus (FM) of an information light beam (LM) to a recording depth (X) at which the information light beam (LM) is to be applied in a state of the objective lens (18) being placed at a reference lens position (SL). The optical disk device (10) controls a servo light condensing point changing mechanism (35) so as to adjust the focus (FS) of a servo light beam (LS) to a servo layer (104) in the state of the objective lens (18) being placed at the reference lens position (SL).

Abstract: A storage system includes a first buffer configured to store a first repeatable runout profile (RRP) for a sector of a rotating storage medium. A second buffer is configured to store a second RRP for the sector. A controller: controls a servo of the rotating storage medium based on the first RRP during a first revolution of the rotating storage medium; and learns the second RRP (i) while operating in a track-following mode, and (ii) during the first revolution. The controller ceases learning of the second RRP when one of (i) the controller is operating in a seek mode and (ii) the rotating storage medium is in an off-track state. Subsequent to the first revolution of the rotating storage medium and based on whether the learning of the second RRP was stopped during the first revolution, the controller replaces the first RRP with the second RRP in the first buffer.

Abstract: A guide-layer separated optical disk which includes a guide layer having a guide structure whose tracking guide tracks are divided into areas by discontinuous portions, the areas each having concentric guide tracks of arc shape at a regular track pitch, the guide tracks in adjoining two of the areas across one of the discontinuous portions deviating from each other in a radial direction of the disk by ¼ the track pitch. An optical disk drive apparatus and a tracking control method in which a servo optical system switches the tracking center of the irradiation spot of a first laser beam between on the guide tracks and in between the guide tracks alternately each time the irradiation spot passes two of the discontinuous portions.

Abstract: A recording apparatus including: a light-illuminating/receiving-unit illuminating an optical-disc-recording-medium through a common object-lens with recording-light and ATS-light and receiving reflected-ATS-light; a rotation-driving-unit driving rotation of the medium; a tracking-mechanism driving the lens in a tracking-direction parallel to the radial direction; a tracking-error-signal-generation-unit generating a tracking-error-signal; and a tracking-servo-controller performing tracking-servo-control on the lens based on the tracking-error-signal, wherein the tracking-servo-controller includes: a servo-calculation-unit based on the tracking-error-signal in a feedback-loop as a tracking-servo-loop; and a feed-forward-controller calculating an estimated control-target-value of the tracking-servo-control based on an estimated illumination-spot-position value of the ATS-light obtained in a first-filter-process emulating a transfer-characteristic of the tracking-mechanism on an output of the servo-calculation-un

Abstract: Provided are an optical disc recording device and a recording signal generating device which enable to correct displacement between a reproducing position of a reproduction signal from a concave-convex mark preformed in an optical disc, and a recording position of second information to be recorded in synchronism with the reproduction signal, and stably and speedily record the second information. A digital signal processor (202) specifies a reproducing position in the concave-convex mark, using a reproduction signal and a channel clock. A recording signal generator (211) generates a recording signal alternately including a plurality of additionally recordable data, each of which includes second information and has a predetermined length, and a plurality of dummy data.

Abstract: A device and method for reducing power consumption of an optical drive are proposed. The present invention samples a carrier control signal and then compares the samples of the signals with predetermined threshold signals. According to the comparison result, the present invention produces at least one diphase excitation control signal. The diphase excitation control signal comprises at least one impulse signal, and a negative edge of the impulse signal is adjusted to a predetermined level during the period of the diphase excitation control signal. The present invention reduces the time for outputting the control signals and greatly reduces the power consumption of the optical drive thereby.

Abstract: A recording and reproducing apparatus includes: an optical head unit irradiating a laser beam on an optical recording medium and performing writing and readout of information represented by marks and spaces on the medium; a laser-driving-pulse generating unit generating and supplying a laser driving pulse to the head unit, and causing the head unit to execute laser beam irradiation; an evaluation-value measuring unit measuring an evaluation value representing an error of an edge position of the mark; and a control and calculating unit causing the apparatus to separately execute, concerning mark lengths to be adjusted among mark lengths of the laser driving pulse, for each set of mark lengths grouped in advance, trial writing with shift amounts of edge positions of a laser driving pulse concerning the lengths belonging to the set changed, causing the apparatus to execute readout of a signal recorded by the execution of the trial writing, causing the measuring unit to measure an evaluation value under setting o

Abstract: To provide an optical disk device, an optical disk control method and an integrated circuit, which are capable of writing a recordable mark by changing the reflectance ratio of a reflective film formed on concave-convex pits without using an industrial special device or a high-power laser light source. A data reproduction controller (103) sets a first rotation speed in a disk rotation speed switching unit (108) and a first laser power in a laser power switching unit (107) when reproducing the concave-convex pits. When writing the recordable mark, a mark recording controller (104) sets in the disk rotation speed switching unit (108) a second rotation speed that is slower than the first rotation speed and the lowest rotation speed at which the concave-convex pits can be reproduced, and sets a second laser power greater than the first laser power in the laser power switching unit (107) in accordance with the emission timing.

Abstract: In an optical disk having multiple layers for which a correction of spherical aberration is required, a spherical aberration correcting element is set to a predetermined spherical aberration correction amount; a laser light source is turned ON; an objective lens is swept; when it is discriminated that the optical disk has two or more layers, or has more than two information recording planes, the spherical aberration correction amount is changed into a spherical aberration correction amount suitable for information recording planes of three, or more layers; and the objective lens is again swept so as to discriminate a total layer number thereof.

Abstract: A method for inspecting an optical information storage medium includes the steps of: irradiating the storage medium with a laser beam and rotating the medium by a constant linear velocity control technique by reference to the radial location at which the laser beam forms a spot on the medium; changing the rotational velocities according to the radial location on the medium between at least two linear velocities that include a first linear velocity Lv1 and a second linear velocity Lv2 higher than the first linear velocity Lv1; generating a focus error signal and/or a tracking error signal based on the light reflected from the medium; performing a focus control and/or a tracking control on the laser beam that irradiates the medium based on the focus and/or tracking error signal(s); and passing the branched outputs of control loops for the focus and/or tracking error signal(s) through predetermined types of frequency band-elimination filters for the focus and/or tracking error signal(s) to obtain residual errors

Abstract: A tracking signal and a focusing signal are stabilized by eliminating multi-layer crosstalk. The diffraction position, with respect to a semiconductor detector, from a center region of a multi-region diffraction grating disposed along the return path of reflection light from the layer of interest is placed further away from the optical axis than the diffraction position from a peripheral part of the diffraction grating. Stray light from other layers is thus prevented from being incident on a sensing region for a peripheral region of the diffraction grating. Further, the area of the semiconductor detector is reduced by dividing the center region.

Abstract: An integrated circuit includes a focus control section configured to perform focus control to generate a drive signal for the focus direction displacement section based on a focus error signal, a focus control error determination section configured to determine whether there is a focus control error or not, and a memory section configured to store error-time control signals which are used when there is a focus control error and correspond to a plurality of rotation angles. The focus control section stops the focus control and generates the drive signal for the focus direction displacement section, according to a rotation angle, based on the error-time control signals stored in the memory section at a radial position where it is determined by the focus control error determination section that there is a focus control error.

Abstract: The optical disc comprises a substrate layer and a data layer disposed on the substrate layer, the data layer having a mark/space data structure arranged in tracks which are arranged in groups being separated each by a land section. The tracks of the groups are each arranged as a spiral, and the start of a track of a consecutive group begins at a position corresponding with the end of a track of a preceding group. A group comprises advantageously an inner track, a center track and an outer track. The optical disc comprises in a preferred embodiment a nonlinear layer with a super-resolution structure and the track pitch between neighboring tracks within a group is below the diffraction limit of a corresponding pickup for reading of data. Further, a tracking method is described which does not rely on tracking offsets to detect the inner and outer tracks of a group.

Abstract: The optical disc device has a circuit which forms a focus error signal for focus servo control based on reflection light from an optical disc exposed to laser light. Also, the device has a data processing unit which can control by feedback a position to which an objective lens is moved by a focusing actuator based on a focus error signal. In label printing, the data processing unit controls, by feedforward, a position to which the objective lens is moved by the focusing actuator based on control data for label printing. The operation resolution of the focusing actuator in feedforward control is made higher than that in feedback control. Thus, an intended position control accuracy is achieved in feedforward control. For instance, in feedforward control, the gain of the driver circuit for the focusing actuator is switched to a smaller one in comparison to that in feedback control.

Abstract: In servo control of actuators of an optical disc unit, a gain margin is secured by measuring a mean current or mean voltage applied to each of a focus actuator and a tracking actuator, estimating a displacement quantity of each of the actuators from the measurement values, changing the frequency characteristic or overall servo loop characteristic of a focus servo filter and a tracking servo filter respectively by switching ON/OFF a notch filter according to a displacement condition of the corresponding actuator, and switching control operation between stages of servo control characteristic of each of the focus servo filter and tracking servo filter. The optical disc unit can achieve a stable servo control of the actuators thereof without performing disturbance injection or taking measurement of the disturbance. Thus, the optical disc unit can ensure stable operations.

Abstract: A disc apparatus is disclosed that includes a jitter-value detection unit configured to detect a jitter value based on a signal to be read from a medium. A detrack-value setting unit is configured to set a detrack value for focusing an objective lens in the medium based on the jitter value. A detrack-value adjusting unit is configured to detect the jitter value every time the detrack value is changed stepwise within a predetermined range of the detrack value including a reference value of the detrack value, to obtain an optimum detrack value to be set in the detrack-value setting unit, based on a maximum jitter value and a minimum jitter value of the detected jitter values.

Abstract: An optical-pickup apparatus includes: a first-objective lens; a second-objective lens; a lens holder including a first-lens barrel having the first-objective lens mounted on an end face thereof and a second-lens barrel having the second-objective lens mounted on an end face thereof; an actuator unit having the lens holder mounted thereon; and a housing having the actuator unit mounted thereon, the first and second objective lenses each being mounted on the lens holder such that a direction, in which wavefront of coma aberration on each lens face is most advanced in phase, is aligned with a radial direction of an information-recording medium, the actuator unit being mounted on the housing such that an optical axis of the first-objective lens is inclined in the radial direction at an inclination angle of the axis toward a recording surface of the medium required to cancel coma aberration of the first-objective lens to the surface.

Abstract: An apparatus for recording and reproducing an information signal on and from an optical disc includes a memory. The information signal is written into the memory. The information signal is read out from the memory. An optical head generates a laser beam in response to the readout information signal, and applies the laser beam to the optical disc to record the readout information signal on the optical disc. A test signal is recorded on a position of the optical disc near a recording position thereof via the optical head during the writing of the information signal into the memory. The test signal is reproduced from the optical disc. The reproduced test signal is evaluated to generate an evaluation result An intensity of the laser beam is optimized in response to the evaluation result.

Abstract: An apparatus for recording and reproducing an information signal on and from an optical disc includes a memory. The information signal is written into the memory. The information signal is read out from the memory. An optical head generates a laser beam in response to the readout information signal, and applies the laser beam to the optical disc to record the readout information signal on the optical disc. A test signal is recorded on a position of the optical disc near a recording position thereof via the optical head during the writing of the information signal into the memory. The test signal is reproduced from the optical disc. The reproduced test signal is evaluated to generate an evaluation result. An intensity of the laser beam is optimized in response to the evaluation result.

Abstract: An objective lens unit according to the present invention includes a first objective lens 41; and a first lens holder 2 for supporting the first objective lens 41. The first lens holder 2 is formed of a material which transmits ultraviolet. Preferably, the first lens holder 2 includes a through-hole, having first and second openings 2a and 2b, through which light incident on the first objective lens 41 passes, and an opening limiting section 3 provided along a circumferential direction of the through-hole and projecting toward a central axis of the through-hole. The first objective lens 41 is supported so as to block the first opening 2b. The opening limiting section 3 guides light incident thereon from the second opening 2a in a direction away from an optical axis of the first objective lens.

Abstract: An objective lens unit according to the present invention includes a first objective lens 41; and a first lens holder 2 for supporting the first objective lens 41. The first lens holder 2 is formed of a material which transmits ultraviolet. Preferably, the first lens holder 2 includes a through-hole, having first and second openings 2a and 2b, through which light incident on the first objective lens 41 passes, and an opening limiting section 3 provided along a circumferential direction of the through-hole and projecting toward a central axis of the through-hole. The first objective lens 41 is supported so as to block the first opening 2b. The opening limiting section 3 guides light incident thereon from the second opening 2a in a direction away from an optical axis of the first objective lens.

Abstract: A tracking error (TE) signal is formed from a single spot on a photodetector 25 to improve the robustness in optical disc applications having a reduced track-pitch. Reduced track pitches are employed in high data capacity optical disc formats. By using high frequency cross-correlation of a central aperture signal, the differences within the left 21 and right 23 detector halves yield a divergence from the zero crossing that produces a more pronounced tracking signal. The more pronounced tracking signal is insensitive to incoherent cross talk in multi-layer discs.