Abstract: A method for performing a seek control operation for a disk device of the type having a pickup for reading/writing data from and to a disk is provided. The method includes the steps of counting mirror signals generated for every revolution of the disk recording medium, where each mirror signal corresponds to one of the tracks radially arranged on the disk recording medium; moving a pickup until the counted number of mirror signals is equal to a predetermined number of tracks required for the pickup to pass to reach a target track. The method further includes the steps of checking respective intervals of successive mirror signals; determining if there is a difference in length between intervals of two successive mirror signals; and executing a correction mode by adding or subtracting a correction value to the counted number of mirror signals if there is a difference in length between intervals of two successive mirror signals.

Abstract: A recording and/or reproducing apparatus for recording and/or reproducing data on or from an optical disc, in which the tracking error signal format for a recordable optical disc differs from that for a replay-only optical disc. The recording and/or reproducing apparatus includes a read-out processing unit for reading out data from the optical disc, a write processing unit for writing data on the optical disc and a system controller for managing control to verify the recordable optical disc having data recorded by the write processing unit by a reproducing system conforming to the standard for the replay-only optical disc. The recordable optical disc is verified by the reproducing system for the replay-only optical disc.

Abstract: A data recording and/or reproducing apparatus which scans a head over a disc on which a servo pattern for moving the head to a predetermined position is recorded in an arc forming a part of a concentric circle. The apparatus comprises a track No. detector and fine signal detector, for detection of the servo pattern, a circumferential position detector to detect a circumferential position on the disc, an offset calculator to calculate an offset of a current position on the disc from the detected circumferential position, and a positional difference calculator. The calculated offset of the current position is added to the positioning signal to control the head scanning orbit on the disc to be spiral.

Abstract: There is provided an optical storage device that can position a lens carriage and objective lens even when position sensors for the lens carriage and objective lens are excluded in an effort to make an optical disk unit thinner. When a seek of the carriage relative to an optical disk is started, the carriage is accelerated smoothly, decelerated smoothly, and thus positioned on a target track. The vibration of a lens actuator on the carriage occurring during seek can be minimized, and the lens actuator is locked substantially in the center of the carriage. During a seek operation of the carriage, a false lens signal equivalent to a lens signal used to lock the lens actuator in the center of the carriage is produced using the envelope of a tracking error signal obtained from reflected light of the light beam emanating from the optical disk. With the false lens signal, the lens actuator is locked in the center of the carriage.

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

Abstract: An optical disc device includes a laser light source for radiating a laser light beam illuminated via an objective lens on a signal surface of an optical disc, a return light detection unit for detecting the reflected light radiated from the laser light source and reflected from the signal surface of the optical disc, a disc discriminating unit for discriminating the type of the optical disc based on a detection output of the return light detection unit, a unit for detecting tracking error signals of plural different types of different detection systems based on the detection output of the return light detection unit, a tracking unit for displacing the objective lens along the radius of the optical disc responsive to the tracking error signals for tracking-controlling a laser spot of the laser light focussed on the signal surface of the optical disc and a controlling unit for switching the detection system based on a discriminating output by the disc discriminating unit for selecting one of the plural types o

Abstract: An optical disc device includes a laser light source for radiating a laser light beam illuminated via an objective lens on a signal surface of an optical disc, a return light detection unit for detecting the reflected light radiated from the laser light source and reflected from the signal surface of the optical disc, a disc discriminating unit for discriminating the type of the optical disc based on a detection output of the return light detection unit, a unit for detecting tracking error signals of plural different types of different detection systems based on the detection output of the return light detection unit, a tracking unit for displacing the objective lens along the radius of the optical disc responsive to the tracking error signals for tracking-controlling a laser spot of the laser light focussed on the signal surface of the optical disc and a controlling unit for switching the detection system based on a discriminating output by the disc discriminating unit for selecting one of the plural types o

Abstract: An optical pickup including a light source for radiating a light beam, a diffraction element for separating a light beam radiated from the light source into at least three beams, namely a main beam and two side beams, an objective lens for converging the light beams separated by the diffraction element on a signal recording surface of the optical recording medium, a light receiving unit having a four-segment first light receiving portion for receiving the main beam reflected by the recording surface of the optical recording medium and second and third light receiving portions arranged on both sides of the first light receiving portion for receiving the side beams reflected by the recording surface of the optical recording medium, and a calculation unit for generating a first tracking signal based on respective outputs of the first light receiving portion and for generating a second tracking signal based on outputs of the second and third light receiving portions.

Abstract: In a focus control of an optical disk with a fast reproduction velocity and a large face deflection, the present invention can effect a mistakeless and reliable focus pull-in method. The present invention comprises: means for applying a braking signal to a focus actuator before closing a focus control loop; means for detecting a reversal of a relative velocity between an objective lens performing a focus search operation and an optical disk which effects an up-and-down motion due to the face deflection; and means for detecting the relative velocity between the objective lens and the optical disk from a focus error signal which is detected in each layer of a multi-layer disk.

Abstract: A device for finding the focus between an optical pickup head and an optical disk by tapping signals from a radio frequency amplifier comprises a high-pass filter for receiving a focus error signal from the radio frequency amplifier and generating a focus error high-pass signal; and a decision circuit that couples to the high-pass filter for receiving the focus error high-pass signal and using a focus zero cross level as a reference for determining a correct focusing point. The focus between the optical pickup head and the optical disk is found when the focus error high-pass signal reaches the positive focus zero cross level or the focus error high-pass signal reaches the negative focus zero cross level.

Abstract: Address groups are composed of two of address blocks 16, 17, 18, and 19, where the address blocks 16, 17, 18, and 19 are disposed in a sector address region 5 and include identifiable information of address numbers 13 and overlapping sequential numbers 14. The address groups are disposed so that each group is alternately shifted from a track center 2 toward the inner periphery side or the outer periphery side, by a width substantially equal to half the track pitch, along the radius direction.

Abstract: A recording and/or reproducing apparatus for a disc-shaped recording medium which includes an optical head, a motor driven table for rotating the disc-shaped recording medium, a slider for moving the optical head relative to the motor driven table in a radial direction of the disc-shaped recording medium, an error signal generator for generating an error signal exhibiting the amount of the relative shifting of a spot of a light beam irradiated from the optical head on the disc-shaped recording medium with respect to a track on the disc-shaped recording medium, and a controller which detects a peak value and a trough value of the error signal supplied from the error signal generator and compares the difference between the detected peak value and the detected trough value with a reference threshold value to generate a drive signal for the slider on the basis of the comparison, wherein the drive signal from the controller is supplied to the slider to shift the optical head relative to the motor driven table in t

Abstract: The invention concerns an apparatus for reading or writing optical recording carriers, the apparatus using the differential phase detection process for tracking purposes. This process exhibits shortcomings when optical recording carriers of different pit depths are to be used. The object of the invention is to design an apparatus of this type which can also be used with said optical recording carriers. This object is achieved in that delay members are disposed between the photodetector and phase detector. The apparatus according to the invention is used as a playback or recording apparatus for optical recording carriers, such as CDs, CD-ROMs, CD-Is, CD-Rs, DVDs, DVD-ROMs, DVD-Rs, etc.

Abstract: An apparatus for reproducing a multiple layer disk, which comprising a plurality of layers each having an information record surface on which record information is recorded, is provided with: a read device for reading the record information from each of the layers; a reproduction process device for applying a predetermined reproduction process to the record information read by the read device in accordance with a reproduction process parameter, which is set therein and which comprises at least one of a gain value and an equalizer value, to thereby output a reproduction information signal; a drive device for driving the read device to jump from one reading state for reading one of the layers to another reading state for reading another of the layers; a memory for storing a plurality of reproduction process parameters corresponding to the layers in advance of reproduction; and a set device for reading out one of the stored reproduction process parameters, corresponding to another of the layers as a destination

Abstract: In an optical pick-up position detector, an optical pick-up is movable by a motor in radial directions of an optical disk for detecting signals on the optical disk. A driver applies a driving voltage to terminals of the motor for forward or reverse rotation of the motor according to a control signal from a controller. The controller has an input terminal connected to a power supply via a resistor and further has a control terminal for outputting the control signal to the driver according to an electric potential at the input terminal of the controller. A switch is disposed between the input terminal of the controller and one of the terminals of the motor. The switch changes its operating state when the optical pick-up moves to exceed a reference position in a radially inward or outward direction with respect to the optical disk. The switch may be connected to the input terminal of the controller via a diode.

Abstract: A recording/reproducing optical disk of the present invention comprises a first recording section formed on a spiral track in an area in the shape of a land, a second recording section formed on the spiral track in an area in the shape of a groove, the second recording section being adjacent to the first recording section, a first half header section in which first address information of the first recording section is recorded, and a second half header section, in which second address information of the second recording section is recorded, and which is disposed in pair with the first half header section in a zig-zag shifted manner, wherein the first half header section and the second half header section are located ahead of the first recording section to assume a first positional relation relatively to the first recording section and the first half header section and the second half header section are located ahead of the second recording section to assume a second positional relation other than the first po

Abstract: Method and device for controlling an optical recording/reproducing device, for detecting a wobble signal in advance during free running when only a focus servo is turned on, carrying out wobble PLL, detecting the present rotating speed of the optical disk from the wobble signal, and controlling the spindle to reach to a target speed quickly, thereby stabilizing the servo in advance before regular data recording/reproduction, and enhancing performance of the optical recording/reproduction device.

Abstract: An apparatus and method for automatically controlling the focusing of a compact disc player (CDP) performs more reliable automatic control operation upon abnormal conditions of a disc, such as a scratch and dust. The automatic focus controlling apparatus includes a pickup assembly for reading recorded data from a disc; and RF signal converter for converting the output signal read by the pickup assembly into an RF signal; a signal separator for separating a signal corresponding to a 3T component from the RF signal; a phase comparator for comparing the separated 3T signal with a predetermined frequency to provide a phase difference value; and a controller for controlling a focusing operation of an objective lens based on the phase difference value to provide a focus control signal.

Abstract: An optical disc device including a laser light source for radiating a laser light beam illuminated via an objective lens on a signal surface of an optical disc, a laser light volume detection unit for detecting the light volume of the laser light radiated from the laser light source, an automatic power controlling unit for controlling a laser output of the laser light source so that a detection output by the laser light volume detection unit will be constant, a return light detection unit for detecting the return light of the laser light beam radiated by the laser light source and reflected by the signal surface of the optical disc, a focusing control unit for displacing the objective lens along the optical axis responsive to focusing error signals generated on the basis of a detection output of the return light detection unit for controlling the focusing state of a beam spot of the laser light on the signal surface of the optical disc and a controlling unit for controlling the closed-loop gain of the automat

Abstract: The present invention measures first and second detection signals respectively obtained at two focuses during a focus search by means of an optical head 2. Then, a type of a disk-shaped optical record medium is determined by a microcomputer in a system controller 7, from a comparison between characteristics of the first and second measured detection signals. Moreover, the present invention can measure an amplitude and a frequency of the detection signal obtained at the focus during the focus search to thereby determine the type of the disk by using the measured result. After the parameters are set in accordance with the determined result, the focus servo control is turned on.

Abstract: A correction processing unit for correcting a level fluctuation appearing on a tracking error signal when a laser beam passes an ID area on a medium track during an on-track control is provided. That is, in the correction processing unit, a correction value determined by a correction value determining unit at a correction timing detected by a correction timing discriminating unit is subtracted by a correcting unit from a signal value obtained by sampling and converting the tracking error signal into digital data by an A/D converter at a predetermined period and reading, thereby performing the correction.

Abstract: A malfunction during focussing pull-in in an optical disc recording/reproducing apparatus is to be prevented. To this end, the optical disc recording/reproducing apparatus includes an optical pickup 7 having an objective lens 8 and a biaxial actuator, a photodetector for generating tracking error signals from the return light of the laser light illuminated on the optical disc and a position sensor for detecting the position of the objective lens relative to the optical disc. The optical disc recording/reproducing apparatus also includes an actuator driving circuit for controlling the servo operation of a biaxial actuator 9, based on the tracking error signals, so that the converging point of the light beam will be on the signal recording surface of the optical disc, and a pull-in range decision unit for outputting a permission signal according permission for the servo operation when the position of the objective lens 8 is within a preset range.

Abstract: The present invention relates to a servo control apparatus of a disk recording system and particularly to a servo control apparatus and method which are capable of controlling position of a head for recording digital data on a disk as recording media and reading the digital data.

Abstract: A tracking servo control method for preventing a tremble of an object lens installed in a pickup in an optical disk drive. A determination is made whether a distance between a target track and a current track where the pickup is presently placed is longer than a first distance. When the distance between the target track and the current track is longer than the first distance, both ends of a tracking coil through which a driving current for moving the object lens flows, are shorted. In the meantime, when the distance between the target track and the current track is shorter than a second distance as the pickup moves to the target track, both ends of the tracking coil are opened. The first distance is equivalent to a distance of 1000 tracks, and the second distance is equivalent to a distance of 100-200 tracks.

Abstract: An optical drive system includes an optical assembly, a light source, a lens positioned to direct light between the optical assembly and an information storage medium or disc, and an actuator suspending the lens. A photodetector is disposed in a path of returning light to measure light received from the medium. A monitoring circuit is provided to monitor a Quad Sum signal associated with return light. A first servomotor is employed to move the lens in a tracking direction and to move the lens during focus capture while system circuitry searches for a maximum Quad Sum signal. A second servomotor is employed to move the lens in a focusing direction. A first electronic circuit is provided to control the first and second servomotors.

Abstract: An apparatus for reproducing a multiple layer disk, which comprising a plurality of layers each having an information record surface on which record information is recorded, is provided with: a read device for reading the record information from each of the layers; a reproduction process device for applying a predetermined reproduction process to the record information read by the read device in accordance with a reproduction process parameter, which is set therein and which comprises at least one of a gain value and an equalizer value, to thereby output a reproduction information signal; a drive device for driving the read device to jump from one reading state for reading one of the layers to another reading state for reading another of the layers; a memory for storing a plurality of reproduction process parameters corresponding to the layers in advance of reproduction; and a set device for reading out one of the stored reproduction process parameters, corresponding to another of the layers as a destination

Abstract: While discerning whether the laser beam spot is positioned on a land track or a groove track according to the L/G switch signal LGS from the land groove detection unit 34, the focus position rough detection unit 50 and the focus position precise detection unit 60 detect two new focus positions (for the land and the groove) so that the bit error rate BER that is measured in the error rate measurement unit 33 and the envelope of and the jitter in the reproduction signal RF would improve, and output two control signals (FBAL and FOFF) for changing the control target position into the new two focus position to the focus error detection unit 36.1.

Abstract: A tracking servo device for use with an optical disc apparatus includes a photodetector unit having a plurality of photodetectors each of which is split in association with the direction of tracks formed on the optical disc, and a tracking error generating unit for finding the difference in outputs from at least two of the photodetectors of the photodetector unit for generating a tracking error signal. The tracking servo device also includes a first correction unit for removing an offset produced in the tracking error signal when the tracking servo is on, and a second correction unit for removing an offset produced in the tracking error signal when the tracking servo is off.

Abstract: A polarity switching signal generator able to stably generate a suitable polarity switching signal for inverting the polarity of a tracking error signal, wherein a reference value stored in a reference value storage circuit is updated by a rotational angle indicated by a rotational angle signal at a switching position of a land and groove captured by a capture circuit when an address decode signal is normal and wherein, further, a comparator compares the reference value stored in the reference value storage circuit with the rotational angle indicated by the rotational angle signal and generates a polarity switching signal instructing the switching of the polarity when they match.

Abstract: A central servo control system is used in an optical disc drive to control an optical pickup head. The optical at least includes a lens. The central servo control system includes a radio frequency (RF) amplifier, a sled motor, a tracking coil, and a central servo controller. The RF amplifier chip is coupled to the optical pickup head so as to receive the optical signal, which is amplified and processed so as to produce a RF data signal, a tracking error (Te) signal, and a central servo (Tcs) signal. The sled motor is used to hold the optical pickup head and move the optical pickup head to a desired position. The tracking coil located on the optical pickup head is used to move the lens to a designed position so as to allow the optical signal to be easily detected by the optical pickup head. The central servo controller receives the RF data signal, the Te signal, and the Tcs signal from the RF amplifier chip, and accordingly exports a tracking control signal to the tracking coil.

Abstract: The invention provides an apparatus and method which allows playback of both of a first optical disc wherein the opposite side faces of a groove formed thereon are wobbled at a first predetermined frequency and a second optical disc wherein one of the opposite side faces of a groove formed thereon is wobbled at a second frequency shorter than the first predetermined frequency while the other face of the groove is formed as a flat face. In the apparatus and method, it is discriminated whether an object optical disc of playback is the first optical disc or the second optical disc, and various servo systems are switched based on a result of the discrimination.

Abstract: In an optical information recording medium having at least two information layer, guide grooves for tracking or sample pits or information pits corresponding to information signals are formed on a surface of a first substrate. A first information layer formed by a thin line for reflecting a portion of a light beam made incident on the first substrate and permitting penetration of a portion of the light beam is formed on a surface of the first substrate. Guide grooves for tracking or information pits corresponding to information signals are formed on a surface of a second substrate. A second information layer having a reflection higher than that of the first information layer is formed on a surface of the second substrate. Between the first information layer and the second information layer, there is formed a transparent separation layer for positioning the first information layer and the second information layer to be spaced a predetermined distance apart from each other.

Abstract: An optical pickup including a light source for radiating a light beam, a diffraction element for separating a light beam radiated from the light source into at least three beams, namely a main beam and two side beams, an objective lens for converging the light beams separated by the diffraction element on a signal recording surface of the optical recording medium, a light receiving unit having a four-segment first light receiving portion for receiving the main beam reflected by the recording surface of the optical recording medium and second and third light receiving portions arranged on both sides of the first light receiving portion for receiving the side beams reflected by the recording surface of the optical recording medium, and a calculation unit for generating a first tracking signal based on respective outputs of the first light receiving portion and for generating a second tracking signal based on outputs of the second and third light receiving portions.

Abstract: This invention provides an optical head apparatus that is not influenced by the offset component contained in a track deviation signal and the track offset caused by lens shift control. According to an optical head apparatus of this invention, portions of light-receiving regions of a photodetector for detecting a track deviation signal are used as offset component detection light-receiving regions for removing any offset component from a track deviation signal. With this arrangement, the offset component contained in a track deviation signal, i.e., the influence of a lens shift on a tracking error signal, is removed by using light from the region where all the 0th-order diffracted light, 1st-order diffracted light, and −1st-order diffracted light of the light reflected by the optical disk overlap each other.

Abstract: A device for automatically controlling a sled loop gain in an optical disc drive having a sled motor.

Abstract: An optical disc recording and/or reproducing apparatus 1 is provided in which servo having high followup performance can be applied without impairing steady-state stability under suppression of servo errors. The optical disc recording and/or reproducing apparatus 1 includes a shock sensor 7 for detecting an impact applied from outside, and a servo unit 14 which performs servo on the basis of focussing error signals and tracking error signals and in which the servo operation is switched between a first state having a usual servo followup performance and a second state having a servo followup performance higher than said first state. The apparatus 1 also includes a controller 15 having the finction of discriminating the impact strength sensed by the shock sensor 7 and of switching the servo operation of the servo unit 14 to the second state when the impact strength exceeds a pre-set strength.

Abstract: A device for reading from and/or writing to optical recording media, including a beam generator, a focus device, which focuses the beam generated onto the optical recording medium at a focal point, a displacement device, which displaces the position of the focal point on the recording medium in accordance with a first direction of movement in dependence on an actuating signal, and a detector, which detects a beam reflected from the optical recording medium and outputs a regulating signal to a regulator. The regulator generates an actuating signal for the displacement device. The invention allows a higher data transfer rate to be achieved with an acceptable outlay. This is achieved by a beam influencing device arranged in the beam path and, in dependence on a further actuating signal of the regulator, influences the position of the focal point on the recording medium in accordance with the first direction of movement.

Abstract: A high speed optical disc reproducing device includes: a gain amplifier for amplifying data picked-up from an optical disc, with a specific amplification gain and a frequency and boost control unit for outputting a frequency and boost gain control signal under the control of a main control unit in accordance with the kind of pick-up and disc used in the reproducing device. The device also includes a boost filter, which serves the functions of boosting high frequency parts of the output signal of the gain amplifier according to the frequency and boost gain control signal, and a uniform group-delaying section which group-delays all of the frequency areas of the output signal. The device minimizes the signal distortion, caused by the difference in the pick-up and disc characteristics of a high speed optical disc reproducing device.

Abstract: A transfer control system of an information read beam for transferring an information read beam from one recording side to another in an information reader comprising offset error signal generation means for piggybacking a predetermined offset level onto a focus error signal indicating a shift from the focus position of the information read beam to generate an offset error signal in order to shape the beam form of the information read beam for reading record information from an information recording medium having a plurality of laminated recording sides on the recording side. It comprises offset level setting means for setting the predetermined offset level in the offset error signal generation means, transfer signal generation means for generating a transfer signal for forcibly transferring the information read beam, and transfer means for transferring the information read beam from one recording side to another based on the transfer signal.

Abstract: An optical pickup position control device according to the present invention automatically adjusts tracking with precision and in a short time. Two deviation signals, which express deviation of a light beam, projected by a pickup which uses the three-beam method, from a target track of a disk, are digitized by two AD converters. Two high-pass filters extract from the deviation signals AC signals, producing a tracking error signal. Further, two low-pass filters extract from the deviation signals DC signals (offset components). Two other low-pass filters extract from the deviation signals low-band signals containing DC components. Using the various foregoing signals, a control circuit calculates correction values to be applied to two offset correcting circuits and to two gain/balance correcting circuits, and corrections are performed collectively and simultaneously on the basis of these correction values.

Abstract: A gain controlling apparatus is provided with: an adjusting device (6, 7, 8) for adjusting a gain of a generation signal, which is generated on the basis of a light reception signal obtained by receiving a reflection light of a light beam from an information recording medium (1); and a detecting device (21, 14, 16) for detecting whether or not the generation signal is generated and outputting a detection signal when the generation signal is generated. The gain controlling apparatus is also provided with a controlling device (18) for controlling the adjusting device to increase the gain by a predetermined value set in advance when the detection signal is not outputted by the detecting device.

Abstract: An apparatus and method is provided for use on the pickup head of an optical disc drive for the purpose of adjusting the pickup head to the optimal focus point through a featured tree-structured search algorithm. The apparatus and method can perform the adjustment automatically so as to eliminate the need to use laborious work to make the adjustment in manufacture. The apparatus is activated each time the optical disc drive is started so as to offset the unbalanced condition in the focusing error signal, which allows the optical disc drive to perform the access operation more reliably. Moreover, the apparatus is realized in a digital manner that allows easy implementation and a low manufacturing cost.

Abstract: The method and apparatus for testing quality of an optical disk medium reproduce an auxiliary signal from an optical disk wherein the auxiliary signal corresponds to a preformatted structure of the optical disk. The quality of the optical disk is then determined based on the auxiliary signal.

Abstract: A disk drive system includes a servo system for driving mechanical parts, including a read/write head, to a desired track on a disk. The mechanical parts undesirably resonate at a frequency f, where f is a function of a temperature t of those mechanical parts. The servo system includes a notch filter responsive to an indication of temperature t, to attenuate the amplitude of frequency f in a broadband control signal that is applied to move the mechanical parts.

Abstract: A tracking method discriminates whether an optical disc loaded in a recording and/or reproduction system is a shallow groove type optical disc or a deep groove type optical disc, and corrects the phase of the tracking error signal detected from the optical disc according to the discrimination result, to then perform a tracking servo control using the corrected result. A tracking apparatus includes an optical signal detector detecting a tracking error signal from an optical disc loaded in a recording and/or reproduction system. A groove type discriminator analyzes the tracking error signal output from the optical signal detector to discriminate a groove type of the loaded optical disc and generates a corresponding control signal. A phase corrector corrects the phase of the tracking error signal output from the optical signal detector according to the control signal applied from the groove type discriminator.

Abstract: An adaptive, discrete-time sliding mode controller (SMC) is disclosed which detects and adapts to gain variations in the controlled plant. The overall control effort is generated by combining a linear control effort with a discrete-time sliding mode control effort generated by switching between gains in order to drive the system's phase states toward a sliding line trajectory. A sliding mode variable &sgr;k defines the position of the system phase states relative to the sliding line. The SMC controller is designed such that the sliding mode variable &sgr;k crosses the sliding line and changes sign at every sample interval. For the nominal plant gain, the SMC controller is also designed such that the magnitude of the sliding mode variable &sgr;k+1=−&sgr;k will remain constant (&sgr;k+1=−&sgr;k) and substantially constrained to |&sgr;k|=&Dgr;/(1+&lgr;) where &Dgr; and &lgr; are predetermined design constants.

Abstract: A focus servo control system is a system for selectively applying a light beam to a disk on which data is recorded on plurally layered recording surfaces and setting the focus position of the light beam on a selected recording surface of the two-layered recording surfaces based on a signal read from reflected light from the selected recording surface of the plurally layered recording surfaces of the disk and includes a focus error detector for detecting a positional difference between the focus position of the light beam and the selected recording surface of the plurally layered recording surfaces, a sample-hold circuit for sampling and holding an output of the focus error detector, a focus position correcting circuit for correcting the focus position of the light beam based on one of the output of the focus error detector and an output of the sample-hold circuit, a data signal level detector for detecting the signal level relating to data read out from the disk, a comparator for comparing a signal level dete

Abstract: A magneto-optical information recording/reproducing apparatus in which a magneto-optical information recording medium at least including a first magnetic film having perpendicular magnetic anisotropy, and a second magnetic film to which information recorded on the first magnetic film is transferred by irradiation of a laser beam, is used so that a readout laser beam is irradiated onto the second magnetic film to thereby readout the information transferred to the second magnetic film. The apparatus includes a 2-split detection circuit for receiving the readout laser beam reflected from the second magnetic film of the recording medium, and a subtraction circuit in which output signals of the two detection elements of the 2-split detection circuit are subtracted from each other to generate a differential signal.