JP2007026611A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive that does not make the focus servo unstable when moving the spherical aberration correcting lens for a focus jump, has an optimally compensated spherical aberration after the focus jump, and operates the stabilized focus servo from immediately after the focus jump. <P>SOLUTION: This optical disk drive has a gain control section (14) to control the gain of the focusing errors, a focus jump control section (21) to move the focusing point of the laser beam, a memory (23) to store the data of the focusing error amplitudes with respect to the position of the spherical aberration correcting lens, and a control section (20) to start to move the spherical aberration correcting lens before the focus jump, to control the gain control to provide stable focusing errors based on the data from the memory while moving the correction lens, and to drive the focus jump control for the focus jump after completion of moving and to switch the gain control to the predetermined gain simultaneously. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus, and more particularly to an optical disc apparatus that performs a focus jump in a multilayer disc that requires spherical aberration correction.

  As a cover layer for protecting the information recording surface, an optical disc is formed with a transmission layer having a predetermined thickness so as to cover the recording surface. In the optical disc apparatus, the recording surface is read or irradiated with a recording laser beam through the cover layer, thereby reading and recording information data on the optical disc.

  In order to realize a high density optical disc, in addition to shortening the laser wavelength, a method of increasing the lens numerical aperture has been adopted in order to condense the light beam from the light source into a smaller spot. However, when the numerical aperture of the lens is increased, the spherical aberration is likely to fluctuate due to the influence of uneven thickness of the cover layer.

Such spherical aberration is a phenomenon in which the focal point of the laser beam is not focused on one point on the optical axis, but shifted in the depth direction. As a result, the focal point spreads a little round on the recording surface. There arises a problem of reducing accuracy.
Such spherical aberration can be reduced by providing a spherical aberration correction lens in the optical path of the laser beam and moving the position of the correction lens.

  When such spherical aberration correcting means is used, in the case of an optical disc having a multi-layer recording layer, the focal point of the laser beam is moved from one recording layer to another recording layer (this is called “focus jump”). Therefore, it is necessary to simultaneously switch and control the spherical aberration correction means. This is because moving the recording layer also changes the thickness of the cover layer, so that the value of the spherical aberration changes, so that the correction value also needs to be changed.

  However, in general, the response speed for moving the focal point of the laser beam by the focus jump is fast, but the switching speed of the correction means for correcting the spherical aberration is slow. For this reason, there is a problem that the focus servo after the focus jump becomes unstable because the timing of the end of switching between the two does not coincide.

In order to solve such a problem, in Patent Document 1 below, as a technique for improving the focus jump in a multilayer disc that requires spherical aberration correction, the position of the spherical aberration correction lens is used when performing the focus jump to the recording layer to be focused. A technique is disclosed in which a focus jump is started when an intermediate position between the optimum value of the recording layer currently focused and the optimum value of the target recording layer is reached.
Japanese Patent Laid-Open No. 2003-22545

  However, in the case of Patent Document 1, in addition to the fluctuation in the amplitude of the focus error signal due to the movement of the spherical aberration correction lens before the focus jump, the fluctuation in the amplitude of the focus error signal due to the movement of the spherical aberration correction lens also occurs after the focus jump. There is a problem that a focus servo of a type that controls the focal position of a laser beam using this focus error signal becomes unstable for a long time after a focus jump.

  The present invention has been made in view of such conventional problems, and when performing a focus jump on an optical disk having a multi-layer recording surface, the focus servo becomes unstable during the movement of the spherical aberration correction lens. In addition, an object of the present invention is to provide an optical disk apparatus in which the spherical aberration is corrected to an optimum value after the focus jump is completed, and the focus servo is stably operated immediately after the focus jump.

The present invention has the following configuration as means for solving the above problems. That is,
Focus obtained by condensing a laser beam emitted from a light source onto each recording layer of an optical disc having a plurality of recording layers via an objective lens, and photoelectrically converting return light from each recording layer with a photodetector In an optical disc recording / reproducing apparatus that corrects spherical aberration of the objective lens that focuses the laser beam on each recording layer when performing focus error control based on an error signal,
A first spherical aberration correction lens that is arranged on the optical path of the laser beam between the light source and the objective lens and serves as a fixed reference, and a second spherical aberration that is movable with respect to the first spherical aberration correction lens A spherical aberration correction unit having a correction lens;
A memory storing a relationship between a position of the second spherical aberration correction lens with respect to the first spherical aberration correction lens and an amplitude of the focus error signal in each recording layer;
A focus jump control unit for focusing the laser beam on each recording layer of the plurality of recording layers;
A gain control unit for controlling the amplitude of the focus error signal of each recording layer obtained by photoelectric conversion with the photodetector;
To switch the focus position of the laser beam from one recording layer of the plurality of recording layers to the other recording layer so that the amplitude of the focus error signal is the same based on the relationship stored in the memory The first control signal is output to the gain control unit, the second control signal for focusing the laser beam on the other recording layer is output to the focus jump control unit, and is obtained from the other recording layer. A control unit that outputs to the gain control unit a third control signal that causes the in-focus amplitude of the focus error signal to be the same as that of the one recording layer;
An optical disc recording / reproducing apparatus comprising:

According to the present invention, the first spherical aberration correction lens which is disposed on the optical path of the laser beam between the light source and the objective lens and serves as a fixed reference and moves with respect to the first spherical aberration correction lens. A spherical aberration correction unit having a second spherical aberration correction lens that is possible, and a relationship between the position of the second spherical aberration correction lens with respect to the first spherical aberration correction lens and the amplitude of the focus error signal in each recording layer. Memory, a force jump control unit for focusing the laser beam on each recording layer of the plurality of recording layers, and an amplitude of the focus error signal of each recording layer obtained by photoelectric conversion by the photodetector A gain control unit that controls the laser beam, and when the focus position of the laser beam is switched from one of the plurality of recording layers to the other recording layer, the memory Based on the stored relationship, a second control signal for outputting a first control signal to the gain control unit to make the amplitude of the focus error signal the same and focusing the laser beam on the other recording layer Is output to the focus jump control unit, and a third control signal is output to the gain control unit for causing the focus error signal of the focus error signal obtained from the other recording layer to be the same as that of the one recording layer. The spherical aberration correction lens has been moved to the optimal correction position immediately before the focus jump, and the focus error is constant during the movement of the spherical aberration correction lens. Since it is controlled, the focus servo does not become unstable.
Furthermore, since the gain of the gain control unit is switched to the optimum value of the target recording layer simultaneously with the focus jump operation, the focus servo is quickly stabilized immediately after the focus jump.

Hereinafter, an optical disk device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of an optical disk apparatus according to the present invention, FIG. 2 is a block diagram in which the internal configuration of the optical system in FIG. 1 is added, and FIG. 3 is a focus error signal at the moving position of a spherical aberration correction lens. FIG. 4 is a diagram showing signal waveforms and timings of respective parts during a focus jump operation.

First, the configuration of the optical disc apparatus according to the present invention will be described with reference to FIGS.
In FIG. 1, an optical disc 24 as an information recording medium is provided with a first recording layer (L0) 1, a second recording layer (L1) 2, and a cover layer 3 for protecting the recording layer.
An optical system 26 including the objective lens 4 fitted to the lead screw 28 is provided below the cover layer 3, and the objective lens 4 is transferred in the radial direction of the optical disk 24 by rotating the stepping motor 27. The

Next, the internal configuration of the optical system 26 will be described with reference to FIG.
The laser beam emitted from the laser diode 5 passes through the spherical aberration correction lenses 6 and 7, obtains the beam splitter 11 and the objective lens 4, and is irradiated to the first recording layer 1 or the second recording layer 2, and these recordings are performed. The return light from the layer is converted into an electrical signal by the optical sensor (PD) 12 in the optical system via the objective lens 4 and the beam splitter 11 and output to the error detection unit 13.

  The spherical aberration correction lens 6 is fixed, but the spherical aberration correction lens 7 is attached to a support member 9 fitted to the lead screw 8, and is moved in the direction of the optical axis by the rotation of the stepping motor 10 to move the laser. Correct spherical aberration at the focal point of the beam.

  The error detection unit 13 generates a focus error signal corresponding to the focal point of the laser beam based on the electrical signal converted by the optical sensor (PD) 12, and the focus error signal then passes through the gain control unit 14. Then, it is supplied to one input terminal of the adder 25.

The other input terminal of the adder 25 is supplied with a reference voltage corresponding to a target in-focus position, and a position error voltage that is a difference from the focus error signal is supplied to the next phase compensation circuit 16. .
The output of the phase compensation circuit 16 is applied to the actuator driver 19 through the contact a of the switch 18 and is driven so as to focus on the first recording layer 1 or the second recording layer 2 by driving the focus actuator 15. .

The focus switching to the first recording layer 1 or the second recording layer 2 is performed by driving the focus actuator 15 with the actuator driver 19 through the contact b of the switch 18 with the jump pulse output from the focus jump control unit 21. Is called.
Setting and switching timing of the gain control unit 14, the focus jump control unit 21, the switch 18 and the like are controlled by a control unit 20 configured by a microprocessor.
Further, as shown in FIG. 1, the optical system 26 is also transferred by rotation of the stepping motor 27 according to a control command from the control unit 20.

Next, the procedure for performing the focus jump in this embodiment will be described.
FIG. 3 is a diagram showing the relationship between the position (horizontal axis) of the spherical aberration correction lens 7 and the amplitude (vertical axis) of the focus error signal in the first recording layer (L0) 1 and the second recording layer (L1) 2. It is.
In each recording layer, the amplitude of the focus error signal becomes maximum when the spherical aberration correction is optimally adjusted, but the difference in reflectance between the first recording layer (L0) and the second recording layer (L1). Therefore, the maximum value of the amplitude of the focus error signal is different. Therefore, correction is performed so that the maximum amplitude of the focus error signal of each recording layer becomes equal under the control of the gain control unit 14.

  In FIG. 3, when the currently focused recording layer is the (L1) layer, the spherical aberration correction lens 7 is at the position lp1, and the maximum amplitude of the focus error signal is lower than that of the (L0) layer. Therefore, the gain control unit 14 increases the gain so that it is at the same level as the (L0) layer ((A) point).

  In this state, when performing a focus jump from the (L1) layer to the (L0) layer, first, the stepping motor driver 22 is driven under the control of the control unit 20 to move the position of the spherical aberration correction lens 7 from lp1 to lp0. To do. The characteristic curve of FIG. 4D shows the state of this movement.

During this movement period, the amplitude of the focus error signal gradually decreases, and as a result, the loop gain decreases and the focus servo becomes unstable.
Therefore, simultaneously with the movement, the gain control unit 14 is controlled according to the position of the spherical aberration correction lens 7 so that the amplitude of the focus error signal is always constant as indicated by points (B), (C), and (D) in FIG. Correct the gain. This gain correction is shown in the characteristic curve of FIG. This correction can avoid the phenomenon that the focus servo becomes unstable.

  At this time, since the data (data in FIG. 3) representing the relationship between the position of the spherical aberration correction lens 7 and the amplitude of the focus error signal is necessary for the gain correction, this data is stored in the memory 23 and sequentially stored. Read and use.

  When the movement of the spherical aberration correction lens 7 to the position lp0 is completed, the switch 18 is switched from the contact point a to the contact point b according to a control command from the control unit 20, and at the same time, the focus jump control unit 21 changes to FIG. As shown in FIG. 4C, the objective lens 4 starts to move instantaneously from the (L1) layer toward the (L0) layer.

  At this time, under the control of the control unit 20, the gain that is optimized by the focus servo in the focus target (L0) layer at the timing shown in FIG.

  When the focus position of the objective lens 4 approaches the (L0) layer and a focus error in the (L0) layer is detected as shown in FIG. 4 (b), focus jump control is performed as shown in FIG. 4 (a). A deceleration pulse is output from the unit 21. Thereby, the in-focus position of the objective lens 4 can reach the (L0) layer in a state where the speed is sufficiently suppressed as shown in FIG.

  When the focus position of the objective lens 4 reaches the (L0) layer, the control unit 20 causes the switch 18 to switch the contact b to the contact a, and the focus servo with the optimum loop gain of the (L0) layer being ensured. To loop on again.

  As described above in detail, in the present invention, the movement of the spherical aberration correction lens 7 is started before the focus jump operation, and the gain control unit is set so that the focus error becomes constant based on the data from the memory 23 during the movement period. 14 and after the movement is completed, the focus jump control unit 21 is driven to perform a focus jump, and at the same time, the gain of the gain control unit 14 is switched to a predetermined optimum gain.

Thus, immediately before the focus jump, the spherical aberration correction lens 7 has been moved to the optimum correction position, and the focus error is controlled to be constant during the movement of the spherical aberration correction lens 7. The focus servo does not become unstable.
In addition, since the gain of the gain control unit 14 is switched to the optimum value of the target recording layer simultaneously with the focus jump operation, the focus servo quickly stabilizes immediately after the focus jump.

1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. It is the block diagram which added the internal structure of the optical system in FIG. It is the figure which showed the relationship of the amplitude of the focus error signal in the movement position of the spherical aberration correction lens. It is the figure which showed the signal waveform and timing of each part at the time of focus jump operation.

Explanation of symbols

1 ... Recording layer (L0)
2 Recording layer (L1)
DESCRIPTION OF SYMBOLS 3 ... Cover layer 4 ... Objective lens 5 ... Laser diode 6, 7 ... Spherical aberration correction lens 8, 28 ... Lead screw 9 ... Spherical aberration correction lens support member 10, 27 ... Stepping motor 11 ... Beam splitter 12 ... Optical sensor (PD) )
DESCRIPTION OF SYMBOLS 13 ... Focus error detection part 14 ... Gain control part 15 ... Focus actuator 16 ... Phase compensator 17, 22 ... Stepping motor driver 18 ... Switch 19 ... Actuator driver 20 ... Control part 21 ... Focus jump control part 23 ... Memory 24 ... Optical disk 25 ... Adder 26 ... Optical system

Claims (1)

Focus obtained by condensing a laser beam emitted from a light source onto each recording layer of an optical disc having a plurality of recording layers via an objective lens, and photoelectrically converting return light from each recording layer with a photodetector In an optical disc recording / reproducing apparatus that corrects spherical aberration of the objective lens that focuses the laser beam on each recording layer when performing focus error control based on an error signal,
A first spherical aberration correction lens that is arranged on the optical path of the laser beam between the light source and the objective lens and serves as a fixed reference, and a second spherical aberration that is movable with respect to the first spherical aberration correction lens A spherical aberration correction unit having a correction lens;
A memory storing a relationship between a position of the second spherical aberration correction lens with respect to the first spherical aberration correction lens and an amplitude of the focus error signal in each recording layer;
A focus jump control unit for focusing the laser beam on each recording layer of the plurality of recording layers;
A gain control unit for controlling the amplitude of the focus error signal of each recording layer obtained by photoelectric conversion with the photodetector;
To switch the focus position of the laser beam from one recording layer of the plurality of recording layers to the other recording layer so that the amplitude of the focus error signal is the same based on the relationship stored in the memory The first control signal is output to the gain control unit, the second control signal for focusing the laser beam on the other recording layer is output to the focus jump control unit, and is obtained from the other recording layer. A control unit that outputs to the gain control unit a third control signal that causes the in-focus amplitude of the focus error signal to be the same as that of the one recording layer;
An optical disc recording / reproducing apparatus comprising: