JP2006196121A - Optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording/reproducing device, of which the error increase of a DPP signal in a multi-layer disk is suppressed and automatic adjustment for every recording/reproducing information surface of the disk is attained. <P>SOLUTION: The optical information recording/reproducing device is constituted in such a manner that a push-pull signal of a main beam by an output from a detector and push-pull signals of 1st, 2nd sub-beams by the output from the above detector are used, and after the push-pull signals of the 1st, 2nd sub-beams are amplified by a 1st predetermined rate, a tracking signal is obtained by taking a differential with the push-pull signal of the main beam, and after the push-pull signals of the 1st, 2nd sub-beams are amplified by a 2nd predetermined rate, a signal regarding the position of an objective lens is obtained by taking the differential with the push-pull signal of the main beam. It is characterized by that adjustment means for respectively adjusting the above 1st and 2nd predetermined rates are prepared for each of a plurality of recording/reproducing information surfaces of the optical recording medium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical information recording / reproducing apparatus that generates a tracking error signal and a position detection signal of an objective lens by a differential push-pull method on an optical disc medium having a plurality of recording / reproducing information surfaces. Is.

  A differential push-pull method (hereinafter referred to as DPP method) is known as one of tracking servo methods in a drive device for optical recording disks such as CD-R and DVD-R.

  In the DPP method, a disk is irradiated with a plurality of beams at a predetermined interval, and a detection signal obtained from each reflected light is calculated, thereby generating a tracking error signal in which an offset due to movement of the objective lens is suppressed.

  Further, the position detection signal of the objective lens is generated by changing the calculation method of the detection signal. Such a technique is disclosed in, for example, Patent Documents 1 and 2.

The DPP method will be described below. A light beam from a light source is divided into a main beam that is zero-order light and two sub-beams that are ± first-order light by a wavefront splitting element disposed between the light source and the objective lens, and the optical disk is used by the objective lens. Then, the reflected light from the optical disk of the main beam and the two sub beams is received by a photodetector as shown in FIG. The main beam photodetector 100 that receives the 0th-order light main beam is divided into four vertically and horizontally, and the sub-beam photodetectors 101 and 102 that receive the ± first-order subbeams are divided into two vertically. When the output from each divided element is indicated by A, B, C, D, E, F, G, and H, a tracking error signal and a lens position detection signal are generated by calculating these signals. Is done. That is, it is generated as follows.

The push-pull signal MPP of the main beam is
MPP = (A + D)-(B + C)
The sub-beam push-pull signal sum SPP is obtained as an output obtained by adding the push-pull signal outputs of the sub-beams.
SPP = (E−F) + (G−H)
Is obtained. And the DPP signal takes the differential of MPP and the signal obtained by multiplying SPP by K0,
DPP = MPP · K0 × SPP
Is obtained.

  Here, K0 is a constant determined so as to correct and calibrate the difference in light intensity between the main beam and the two sub beams. For example, K0 is set so that a DC offset due to the movement of the objective lens does not occur. ing.

On the other hand, the lens position detection signal LSP is
LPS = MPP + K0 × SPP
Is obtained.

  At this time, the arrangement of the spots on the optical disc is such that the main spot 200 by the main beam is on the groove and the sub-spots 201 and 202 by the sub beam are as shown in FIG. 9 by adjusting the rotation around the optical axis of the diffraction grating. The lands are symmetrically located across the main spot (the groove portion of the disk is hatched in FIG. 9). That is, when the groove period is used as a reference, the interval between spots and sub-spots is substantially half of the groove period.

  As a result, by setting K0 to an appropriate value, the DPP signal has an amplitude substantially equal to the expected maximum value, and the occurrence of an offset due to the objective lens position movement is suppressed. At the same time, in the LPS signal, only the offset component generated in each push-pull signal due to the objective lens position movement is extracted, and a signal corresponding to the objective lens position movement is obtained.

  This LPS signal is used to suppress vibration of the objective lens that occurs when the optical head seeks in the radial direction of the disk, or to prevent the objective lens from being displaced by its own weight due to the attitude of the optical head.

  In addition, the adjustment of K0 is performed so that the AC component (tracking modulation component) included in the LPS signal is minimized, or the objective lens is shifted by a predetermined amount as disclosed in, for example, Patent Document 2. In this way, the DC offset component included in the DPP signal is minimized.

JP-A-7-093764 JP 2000-331356 A

  In recent years, multi-layer discs having two or more layers of information have appeared in DVDs and next-generation optical discs such as Blu-ray discs and HD-DVD discs. Such a multi-layer disc is produced by laminating a large number of discs, and the characteristics of each information surface vary in the same manner as discs having different single layers. When the disc has a tilt, the influence of the tilt increases in proportion to the thickness of the medium. Therefore, the influence of the tilt increases as the information surface becomes farther from the disc surface. As described above, the quality of the main beam and the sub beam is deteriorated due to the characteristics of the disc and the tilt, but the deterioration rate may be different. When this occurs, the ratio of the MPP signal obtained from the main and sub beams to the push-pull amplitude of the DC offset due to the movement of the objective lens of the SPP signal may change.

  That is, in the case of a multi-layer disc, the ratio of the DPP signal due to the objective lens position shift and the mixing ratio of the tracking error component of the LPS signal change due to the difference in characteristics and the influence of tilt for each information surface. The occurrence of offset due to the position of the objective lens of the DPP signal results in tracking control errors, writing to the adjacent track during recording, increasing crosstalk from the adjacent track to the reproduction signal, and the like, causing deterioration of the recording / reproduction signal. .

  In addition, the mixing of tracking error components into the LPS signal causes disturbance to the lens position fixing control at the time of seeking, etc., makes the seek unstable, and causes an increase in access time and seek failure.

  An object of the present invention is to provide an optical information recording / reproducing apparatus capable of suppressing an increase in error of a DPP signal in a multi-layer disc and automatically adjusting each recording / reproducing information surface of the disc.

  In order to achieve the above object, according to the first aspect of the present invention, a light beam from a light source is divided into a main beam and first and second sub beams by a wavefront splitting element disposed between the light source and the objective lens, and the objective beam is divided. The light is condensed on an optical recording medium having a plurality of recording / reproducing surfaces by a lens, and the reflected light from the optical recording medium of the main beam and the first and second sub beams is received by a photodetector, and the photodetector A tracking error signal and a lens position detection signal for obtaining a tracking control signal and a lens position detection signal from the output from the main beam, a push-pull signal of the main beam by the output from the detector, and the detector After the first and second sub-beam push-pull signals are amplified by a first predetermined ratio using the first and second sub-beam push-pull signals generated by A tracking signal is obtained by taking a differential from the push-pull signal of the main beam, and after amplifying the push-pull signal of the first and second sub-beams at a second predetermined ratio, the push-pull signal of the main beam In the optical information recording / reproducing apparatus for obtaining a signal relating to the position of the objective lens by taking the difference between the first predetermined ratio and the first for each of a plurality of recording / reproducing information surfaces of the optical recording medium. And adjusting means for adjusting the predetermined ratio of 2.

  According to a second aspect of the present invention, in the first aspect of the present invention, a spherical aberration generating means for generating a spherical aberration in the light flux and the spherical aberration generating means are further adjusted between the light source and the objective lens. The second adjustment means has an adjustment by the adjustment means for adjusting the first predetermined ratio and the second predetermined ratio for each of the plurality of recording / reproduction information surfaces. It is performed before.

  According to the present invention, the adjustment means for adjusting the first predetermined ratio and the second predetermined ratio for each of the plurality of recording / reproducing information surfaces of the optical recording medium has the adjustment means for adjusting each of the information surfaces of the optical recording medium. Even if the influence of the tilt or the like and the characteristics of the disc are different, the optimum tracking error signal and lens position signal can always be obtained for each information surface.

  In addition, optimum DPP and LPS signals can always be obtained regardless of the state of spherical aberration and the adjustment error of the mechanism.

  Further, even when the offset due to the objective lens position shift of the DPP signal or the mixing ratio of the tracking error component of the LPS signal changes depending on the information surface of the disc, the DPP and LPS can be adjusted correctly.

  Further, the adjustment of the second adjusting means is performed before adjustment by the adjusting means for adjusting the first predetermined ratio and the second predetermined ratio for each of the plurality of recording / reproducing information surfaces, so that the optical recording medium Regardless of the state of the spherical aberration generating means, the optimum tracking error signal and lens position signal are always obtained on any information surface.

  Thus, it is possible to provide an adjustment method that suppresses an increase in the error of the DPP signal due to the adjustment of the spherical aberration generating means and enables automatic adjustment for each disk or for each of a plurality of recording / reproduction information surfaces of the disk.

  Further, even when the offset due to the objective lens position shift of the DPP signal or the mixing ratio of the tracking error component of the LPS signal changes depending on the position of the spherical aberration generating means, the DPP and LPS can be adjusted correctly.

  Furthermore, the occurrence of offset due to the position of the objective lens of the DPP signal is suppressed, writing to the adjacent track during recording, and the increase in crosstalk from the adjacent track to the reproduction signal are prevented, and the deterioration factor of the recording / reproduction signal is eliminated. Can do.

  In addition, mixing of tracking error components into the LPS signal is suppressed, lens position fixing control at the time of seek becomes stable, and there is an effect of preventing an increase in access time and seek failure.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
FIG. 1 is a block diagram of an optical disc apparatus that realizes DPP adjustment according to the present invention.

  In FIG. 1, 1 is an optical disc having a two-layer information recording / reproducing surface, 2 is an optical head, 3 is a photodetector in the optical head, A to H are each one of division patterns of the photodetector, 4 to 13 is an arithmetic circuit for adding and subtracting multiplication for generating the DPP signal and the LPS signal, 14 is a tracking control circuit that receives the DPP signal, 15 is a lens position control circuit that receives the LPS signal, 16 is a switch, and 17 is tracking. A driver circuit for driving the actuator, 18 is a controller, and 19 is a spindle.

  The optical disc 1 is composed of two information surfaces: a first information surface 75 μm from the disk surface and a second information surface 100 μm from the disk surface with a 25 μm intermediate layer in between.

  Three beams divided by a diffraction grating (not shown) in the optical head 2 are reflected by the optical disk 1 and returned to the optical head again, and received by the photodetector 3. The zero-order diffracted light is received on the ABCD element among the eight divided elements of the photodetector 3, and the two first-order diffracted lights are received on the EF and HG elements. The outputs of the photodetectors A and D are added by the adder circuit 5 and the outputs of B and C are added by the adder circuit 6 and then subtracted by the subtractor circuit 8 to be the main beam push-pull signal MPP. The outputs of F and F are subtracted by the subtracting circuit 4, and the outputs of G and H are subtracted by the subtracting circuit 7, respectively, to become push-pull signals for the two sub-beams. The sum SPP of the pull signals.

  The SPP signal is multiplied by the gain K1 in the multiplication circuit 10, and then subtracted from the MPP signal in the subtraction circuit 12 to become a DPP signal. The SPP signal is multiplied by the gain K2 in the multiplication circuit 11 and then added to the MPP signal in the addition circuit 13 to become an LPS signal.

  The DPP signal is further input to the switch 16 via the tracking control circuit 14, and the LPS signal is input to the other terminal of the switch 16 via the lens position control circuit 15. The SW 16 is controlled by the controller 18, and is connected to the tracking control circuit 14 side during tracking control and to the lens position control circuit 15 side during lens position control, and connected to a tracking actuator in the optical head via a driver 17. Each of which constitutes a control loop.

  Next, a method for adjusting DPP and LPS for each information plane will be described with reference to the flowchart of FIG.

  When the optical disk apparatus according to the present embodiment is activated, the controller 18 activates the spindle 19, performs laser lighting, pulls in the focus, and the like. The initial focus pull-in is performed so as to pull into the second information surface far from the disk surface.

  The adjustment is performed in a state where focus control is applied to the second information surface of the optical disc 1 (S1).

  The tracking servo is performed in an off state, that is, in a state where the SW 16 is not connected to either the tracking control circuit 14 or the lens position control circuit 15.

Although focus control is not described in detail, a focus error signal is detected by a general astigmatism method from four ABCD outputs of the photodetector, and focus control is applied. First, adjustment is performed from K2. First, K2 is set to an initial value of the smallest value that can be considered in design (S2).

  In this state, the controller 18 observes the tracking error modulation component of the LPS and determines whether it is less than a predetermined amount (S3).

  As a method for observing the modulation component, the peak hold value and the bottom hold value of LPS are observed, and a determination is made based on whether the difference is equal to or less than a predetermined amount. The maximum value and minimum value may be detected and the difference between them may be used.

  If it is not less than the predetermined amount, the value of K2 is increased by a predetermined amount, the tracking error component of LPS is detected again, and the process is repeated until it becomes less than the predetermined amount (S4).

  The value of K2 that has become equal to or less than the predetermined amount is stored as the optimum value on the second information surface (S5).

  At this point, the zero point of the LPS signal is almost the center position during factory adjustment.

  Next, the controller 18 sets the target value for lens position control to 0, connects the SW to the lens position control circuit 15 side, and turns on the lens position control loop. As a result, the objective lens is fixed to a point that becomes LPS0 (S6).

  The control band for lens position control at this time is about 500 Hz, and is a band that can sufficiently withstand disturbances such as gravity and vibration.

  Subsequently, the controller 18 changes the target value of the lens position control with a sine wave having a predetermined amplitude centered on 0 and a predetermined frequency. For example, the predetermined frequency is 10 Hz, and the amplitude is a value by which the objective lens moves about ± 150 μm (S7).

  The controller 18 sets the value of K1 as an initial value that is the optimum design value on the second information surface (S8).

  The initial value of K1 at this time may be the optimum value of K2. If the optical system including the disk transmission layer is ideal and the optical system is correctly adjusted, K1 and K2 are equal, the difference between K1 and K2 is an adjustment error, and if the adjustment error is within a predetermined range, Giving the optimum value of K2 as the initial value of K1 leads to shortening of the convergence time of the subsequent adjustment of K1.

  The controller 18 detects an offset amount that is an intermediate value between the maximum value and the minimum value of the DPP signal, and increases or decreases the magnitude of K1 from the polarity of the lens position target value and the polarity of the offset.

  To detect the offset amount, the DPP signal may be peak-held and bottom-held, and an intermediate value between them may be used as the offset amount.

  The magnitude of K1 increases or decreases, for example, when the DC offset of the main beam (MPP) and sub beam (SPP) changes negatively when the objective lens moves to the inner peripheral side and changes positively on the outer peripheral side. If the position control target value is negative on the inner periphery side and positive when it is on the outer periphery side, the DPP signal is MPP-K1xSPP. Therefore, when the lens position control target value is positive, the offset of DPP is positive. It is not necessary to increase K1. On the other hand, if the DPP offset is negative when the lens position control target value is positive, K1 may be reduced because correction is excessive. If the lens position target value is negative, the opposite is the opposite, and the DPP offset is negative. This means that the correction is not enough, and K1 is large. If the DPP offset is positive, K1 is overcorrected. Just make it smaller.

  This is repeated until the amount of change in the DPP offset falls within a predetermined range during one sine wave cycle (S9, S10).

  If it is within the predetermined range, the value of K1 at that time is stored as the optimum value of the second information surface (S11). By adjusting in this way, it is possible to adjust K1 and K2 of the second information surface to the optimum values of LPS and DPP, respectively.

  From now on, the controller 18 sets K1 and K2 at this time as the optimum values of the second information surface, and sets and uses the values of K1 and K2 when they are on the second information surface.

  Next, a focus jump is performed to the first information surface while the tracking control is off (S12).

  When the focus jump is finished, the adjustment of K1 and K2 on the first information surface is started. First, K2 is adjusted.

  First, K2 is set to an initial value of the smallest value that can be considered in design (S13).

  In this state, the controller 18 observes the tracking error modulation component of the LPS, and determines whether it is less than a predetermined amount (S14).

  If it is not less than the predetermined amount, the value of K2 is increased by a predetermined amount, the tracking error component of LPS is detected again, and the process is repeated until it becomes less than the predetermined amount (S15).

  The value of K2 that has become the predetermined amount or less is stored as the optimum value of the first information surface (S16). At this point, the zero point of the LPS signal is almost the center position during factory adjustment.

  Next, the controller 18 sets the target value for lens position control to 0, connects the SW to the lens position control circuit 15 side, and turns on the lens position control loop. As a result, the objective lens is fixed to a point that becomes LPS0 (S17). The control band for lens position control at this time is about 500 Hz, and is a band that can sufficiently withstand disturbances such as gravity and vibration.

  Subsequently, the controller 18 changes the target value of the lens position control with a sine wave having a predetermined amplitude centered on 0 and a predetermined frequency. The predetermined frequency is, for example, 10 Hz, and the amplitude is a value by which the objective lens moves about ± 150 μm (S18).

  The controller 18 sets the value of K1 as an initial value that is the optimum design value on the first information surface (S19).

  The controller 18 detects an offset amount that is an intermediate value between the maximum value and the minimum value of the DPP signal, and increases or decreases the magnitude of K1 from the polarity of the lens position target value and the polarity of the offset. This is repeated until the amount of change in the DPP offset falls within a predetermined range during one sine wave cycle (S20, S21).

  When it is within the predetermined range, the value of K1 at that time is stored as the optimum value of the first information surface (S22). By adjusting in this way, it is possible to adjust K1 and K2 of the first information surface to optimum values of LPS and DPP, respectively.

  From now on, the controller 18 sets K1 and K2 at this time as the optimum values of the first information surface, and sets and uses the values of K1 and K2 when they are on the first information surface.

  As described above, the adjustment is performed in the order of the second information surface and the first information surface, and all the adjustments are completed.

  In this embodiment, the adjustment is performed from the second information surface far from the disk surface. However, the adjustment may be performed first from the first information surface.

  In the present embodiment, the reason why the second information surface is performed first is that, in the case of a single-layer disc, the case where there is an information surface at the position of the second information surface in the case of two layers is considered. This is because by making this position the first target, the first adjustment is possible without worrying about the number of layers of the disk.

  In the present embodiment, since the adjustment of all the layers is completed in the tracking control off state, it is not necessary to turn on the tracking control with the DPP signal that has not been adjusted.

  In addition, the objective lens must be moved by a predetermined amount during the K1 adjustment, but can be moved by a predetermined amount while applying the lens position control by the previously adjusted LPS signal, so that it is not affected by disturbances such as gravity and vibration. Stable and adjustable within the operating range.

  In addition, although the target value for lens position control at the time of K1 adjustment is a sine wave, any waveform that can move the objective lens position by a predetermined amount, such as a ramp wave, a triangular wave, or a square wave, may be used.

  In this embodiment, it is also possible to turn on the lens position control with the target value set to 0 until the adjustment of K2 is completed. In this case, in order not to respond to a high frequency component of the tracking error modulation component, the control band of the lens position control is preferably set to about 100 Hz so as to suppress the movement of the objective lens due to gravity.

  By doing so, the lens position control can be turned on in any adjustment of DPP and LPS, and the adjustment within the operation range can be stably performed regardless of disturbances such as gravity and vibration. .

  In addition, the MPP signal, DPP signal, and LPS signal calculation circuit in FIG. 1 may be used when the laser power and the disk reflectivity do not change after the adjustment of K1 and K2, as in the case of a read-only disk. When there is a change in laser power due to recording power, recording in the disk, change in reflectance in an unrecorded state, etc., as in a recordable / reproducible disc, the configuration of the arithmetic circuit shown in FIG. 3 is necessary. .

  FIG. 3 will be briefly described.

  The difference from the arithmetic circuit of FIG. 1 is that 21 to 26 addition circuits and division circuits are added. The MPP signal is obtained by dividing (A + D)-(B + C) by the output {(A + D) + (B + C)} of the adder circuit 25 (divider circuit 26), and the SPP signal is obtained by dividing the (EF) signal by The addition circuit 9 adds the result of division by the output (E + F) of the addition circuit 21 (division circuit 23) and the result of division of the (GH) signal by the output (G + H) of the addition circuit 22 (division circuit 24). Will be. Each beam is normalized by dividing the push-pull signal of each of the three beams by the sum signal of the respective beams. With this configuration, the amplitude of the MPP signal can be obtained regardless of the change in the laser power and the change in the reflectance in the disk, and the spherical aberration can be accurately corrected for each disk. The optimum DPP signal and LPS signal can be obtained by adjusting K2.

<Embodiment 2>
FIG. 4 is a block diagram of an optical disc apparatus realizing DPP adjustment according to the present invention.

  In the first embodiment, an example in which an element for correcting spherical aberration is not provided in the optical head has been described. However, in the present embodiment, a case in which an element for correcting spherical aberration is provided in the optical head 2 is described. An example will be described.

  In FIG. 4, 1 is an optical disk, 2 is an optical head, 3 is a photodetector in the optical head, A to H are one of the division patterns of the photodetector, and 4 to 13 are a DPP signal and LPS. An arithmetic circuit such as addition / subtraction / multiplication for signal generation, 14 is a tracking control circuit that receives a DPP signal, 15 is a lens position control circuit that receives an LPS signal, 16 is a switch, and 17 is for driving a tracking actuator. A driver circuit, 18 is a controller, 19 is a spindle, 20 is a driver circuit for operating the spherical aberration generating means, and 21 is an MPP signal amplitude measuring circuit.

  The optical head 2 is configured as shown in FIG.

  In FIG. 5, the beam emitted from the semiconductor laser 101 is divided into three beams by the diffraction grating 102, converted into parallel light by the collimator 103, and enters the polarization beam splitter 104 with beam shaping. A part of the beam is reflected, enters the AP sensor 105, and is used for monitoring the amount of light emitted from the semiconductor laser 101. The transmitted beam is condensed on the recording layer surface via the light transmission layer on the optical disk 1 by the objective lens 112 through the quarter-wave plate 106, the lens 107, and the lens 108, and is used for reproducing and recording information. The The beam reflected by the optical disc 1 is reflected by the polarizing beam splitter 104 with beam shaping, enters the photodetector 3 through the sensor lens 114, and is used for reproducing the information signal.

  Here, the lens 107 and the lens 108 are fixed so that the lens 107 is fixed, and the lens 108 is held by the electromagnetic driving means 110 so that the distance in the optical axis direction from the lens 107 is variable, thereby forming the spherical aberration generating means 111. is doing. The shape of the lens 107 and the lens 108 and the glass material are configured such that only spherical aberration occurs when the lens interval changes. The electromagnetic drive means 110 moves the lens 108 on the micron order with a lead screw using a stepping motor.

  It is designed so that the optimum focus position on the disk changes by about 1 μm per 20 μm movement of the lens 108. This ratio depends on the design of the optical system, and is determined to be an optimal ratio depending on the purpose of use.

  The spherical aberration generating means 111 has a sufficiently wide aberration generating range so as to be compatible with a two-layer disc, and moves the lens 108 on the micron order with a lead screw using a stepping motor.

  DPP signal. The LPS signal calculation method is the same as that of the first embodiment.

  The DPP signal is input to the switch 16 via the tracking control circuit 14, and the LPS signal is input to the other terminal of the switch 16 via the lens position control circuit 15. The SW 16 is controlled by the controller 18, and is connected to the tracking control circuit 14 side during tracking control and to the lens position control circuit 15 side during lens position control, and connected to a tracking actuator in the optical head via a driver 17. Each of which constitutes a control loop.

  Further, the controller 18 controls the spherical aberration generating means 111 shown in FIG. 5 in the optical head 2 to adjust the spherical aberration to an optimum state by controlling the driver circuit 20.

  Next, a method for adjusting spherical aberration, DPP, and LPS for each information surface will be described with reference to the flowchart of FIG.

When the optical disk apparatus according to the present embodiment is activated, the controller 18 activates the spindle 19, performs laser lighting, pulls in the focus, and the like. The first focus pull-in is performed on the second information surface far from the disk surface. The adjustment is performed in a state where focus control is applied to the second information surface of the optical disc 1. Although focus control is not described in detail, the focus error signal is detected by a general astigmatism method from the four ABCD outputs of the photodetector and the focus control is applied.

  When the spherical aberration correction routine starts, first, the spherical aberration generating means 111 is set to a predetermined start position (S1).

  For example, when the medium substrate thickness of the second information surface is standard, the position is deviated by a predetermined amount from the reference position on the design value that gives aberration that eliminates spherical aberration on the second information surface. The amount of spherical aberration generated is −4. For example, the lens 108 is moved by 10 μm per unit. Since the movement amount of the lens 108 is 20 μm and the appropriate focal position of the spherical aberration is moved by 1 μm, the spherical aberration generation amount 1 is 0.5 μm unit at the focal position. -4 is a state in which the 40 μm lens 108 is moved from the reference position in a direction approaching the lens 107. This state is a position where the spherical aberration becomes optimal when the medium substrate thickness up to the second information surface is increased by 2 μm in the design direction.

  Next, the controller 18 inputs the output signal amplitude of the MPP signal, which is a push-pull signal of the main beam, from the MPP signal amplitude measurement circuit 21, and stores it in a memory or the like as an evaluation index in association with the correction amount -4 (S2). .

  Next, the controller 18 confirms whether the spherical aberration spherical aberration generating means is at the end position (S3).

  The end position is a state where the spherical aberration generation amount is set to +4, and the 40 um lens 108 is moved in a method of moving away from the lens 107 from the reference position. This state is a position where the spherical aberration is in an optimum state when the medium substrate thickness of the second information surface is reduced by 2 μm in the direction of design.

  If it is not the end position, the spherical aberration correction amount is incremented by 1 until the end position is reached (S4), and the MPP signal amplitude measurement circuit 21 measures the MPP amplitude and stores it in association with the correction amount (S2). Since the correction amount is increased by one, the lens 108 is moved by 10 μm and the MPP amplitude at that location is measured.

  The MPP signal amplitude measuring circuit 21 may be configured to obtain the amplitude of the MPP signal using a peak hold circuit and a bottom hold circuit. Alternatively, the MPP amplitude may be acquired by an AD converter and the MAX value and the MIN value may be stored.

  When the correction amount is plotted on the horizontal axis and the MPP amplitude value is plotted on the vertical axis, a graph represented by a circle in FIG. 7 is drawn. The MPP amplitude value associated with the stored correction amount is used to determine the optimum spherical aberration correction amount. Two correction amounts where the MPP amplitude value exceeds the reference value are obtained, and the median value of the two correction amounts is set as the optimum spherical aberration correction amount. In order to accurately obtain the optimum spherical aberration correction amount from the discrete correction amount, a correction amount exceeding the reference value is obtained from each correction amount by linear interpolation or the like. In the example of ○ in FIG. 7, the correction amount straddling the reference value on the minus side is 3.3 on the −3.0 plus side, so the optimum spherical aberration correction amount is found to be 0.15.

  The determined correction amount is stored as the correction amount of the second information surface (S5).

  The spherical aberration correction is thus completed. Subsequently, K1 and K2 of the DPP and LPS signals are adjusted. Since this adjustment method is the same as the adjustment method of Embodiment 1, description here is abbreviate | omitted (S6).

  When the values of K1 and K2 are determined, the values are stored as values of the second information surface (S7).

  Next, the tracking control is kept in an off state, and the spherical aberration generating means 111 is made a focus jump to the first information surface as the optimum value for designing the first information surface (S8).

  When the focus jump is finished, the spherical aberration generating means 111 is set to a predetermined first information surface start position (S9).

The start position is, for example, a position that deviates a predetermined amount from a reference position on the design value that gives an aberration that eliminates spherical aberration on the first information surface when the medium substrate thickness of the first information surface is standard. is there. The reference position here is different from the first reference position of the second information surface. Since the second information surface and the first information surface are separated by 25 μm and the first information surface is closer to the disc surface, the first information surface is determined from the reference position on the second information surface. The reference position at is away from the 500 um lens 107. The start position of the first information surface starts from a position deviated by a predetermined amount from this position.

  The amount of spherical aberration generated is −4. Reference numeral -4 denotes a state in which the 40 μm lens 108 is moved from the reference position in a direction approaching the lens 7. This state is a position where the spherical aberration becomes optimal when the medium substrate thickness up to the first information surface is increased by 2 μm in the design direction.

  Next, the controller 18 inputs the output signal amplitude of the MPP signal, which is a push-pull signal of the main beam, from the MPP signal amplitude measurement circuit 21, and stores it in a memory or the like as an evaluation index in association with the correction amount -4 (S10). .

  Next, the controller 18 confirms whether the spherical aberration spherical aberration generating means is at the end position (S11).

  The end position is a state where the spherical aberration generation amount is set to +4, and the 40 um lens 108 is moved in a method of moving away from the lens 107 from the reference position. This state is a position where the spherical aberration is in an optimum state when the first information surface is reduced by 2 μm in the direction in which the thickness of the medium substrate is thin.

  If it is not the end position, the spherical aberration correction amount is increased by 1 until the end position is reached (S12), and the MPP signal amplitude measurement circuit 21 measures the MPP amplitude and stores it in association with the correction amount (S10). Since the correction amount is increased by one, the lens 108 is moved by 10 μm and the MPP amplitude at that location is measured.

  The configuration of the MPP signal amplitude measurement circuit 21 is the same as the method performed on the second information surface. The method for determining the optimum spherical aberration correction amount from the correction amount and the MPP amplitude value is also the same. The determined correction amount is stored as the correction amount of the first information surface (S13).

  The spherical aberration correction is thus completed.

  Subsequently, K1 and K2 of the DPP and LPS signals are adjusted.

  Since this adjustment method is the same as the adjustment method of Embodiment 1, the description about this again is abbreviate | omitted (S14).

  When the values of K1 and K2 are determined, the values are stored as values of the first information surface (S15).

  This completes the adjustment of the spherical aberration correction amount of each information surface and the DPP and LPS coefficients K1 and K2.

  Recording / reproduction on each information surface is performed using an adjustment value for each information surface.

  In this embodiment, since the adjustment of all the information surfaces is completed in the tracking control off state, it is not necessary to turn on the tracking control with a DPP signal for which adjustment has not been completed.

  In addition, by adjusting spherical aberration first for each information surface, and then adjusting DPP and LPS, the spherical aberration, DPP and LPS signals are all optimum values after adjustment. The recording / playback operation can be immediately started.

  In this embodiment, the optical system as shown in FIG. 5 is used as the spherical aberration correcting means. However, any system such as a liquid crystal element that affects the DPP signal due to the occurrence of spherical aberration can be used. Applicable.

  In the present embodiment, a two-layer disc has been described as an example. However, the number of layers is not limited to two, and any number of layers can be dealt with by adjusting each layer.

It is a block diagram of Embodiment 1 of the present invention. This is a configuration of an optical system including spherical aberration generating means. It is a flowchart of Embodiment 1 of the present invention. It is a block diagram which shows another structure of the calculating means of this invention. It is a block diagram of Embodiment 2 of the present invention. It is a flowchart of Embodiment 2 of the present invention. It is a relationship diagram of spherical aberration correction amount and signal amplitude. It is a figure which shows the structure of a photodetector. It is a figure which shows arrangement | positioning of the spot on an optical disk.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Optical pick-up 3 Photo detector 4,7,8,12 Subtractor 5,6,9,13 Adder 10,11 Multiplier 14 Tracking control circuit 15 Lens position control circuit 16 Switch 17 Driver 18 Controller 19 Spindle 20 Spherical aberration element driver 21 MPP amplitude measurement circuit 22 Reproduction signal amplitude measurement circuit

Claims (2)

A light beam from a light source is divided into a main beam and first and second sub beams by a wavefront splitting element disposed between the light source and an objective lens, and is focused on an optical recording medium having a plurality of recording / reproducing surfaces by the objective lens. Then, reflected light from the optical recording medium of the main beam and the first and second sub beams is received by a photodetector, and a tracking control signal and a lens position detection signal are obtained from the output from the photodetector. An apparatus for generating a tracking error signal and a lens position detection signal, wherein a push-pull signal of a main beam by an output from the detector and a push-pull signal of first and second sub beams by an output from the detector The first and second sub-beam push-pull signals are amplified at a first predetermined ratio and then differential with the main beam push-pull signal. The objective lens is obtained by obtaining a tracking signal, amplifying the push-pull signal of the first and second sub-beams at a second predetermined ratio, and taking a difference from the push-pull signal of the main beam. In an optical information recording / reproducing apparatus for obtaining a signal related to the position of
An optical information recording / reproducing apparatus comprising adjusting means for adjusting the first predetermined ratio and the second predetermined ratio for each of a plurality of recording / reproducing information surfaces of the optical recording medium.   Between the light source and the objective lens, there is further provided spherical aberration generating means for generating spherical aberration in the light beam, and second adjusting means for adjusting the spherical aberration generating means, and adjustment of the second adjusting means. 2. The optical system according to claim 1, wherein the optical recording is performed before adjustment by the adjusting means for adjusting the first predetermined ratio and the second predetermined ratio for each of the plurality of recording / reproducing information surfaces. Information recording / reproducing apparatus.

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