JP2003099970A - Optical disk apparatus and focus control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that the shape of a focus error signal is varied not only by the difference among the reflectance of respective recording layers but also a spherical aberration due to the difference among the distances between each recording layer and the disk surface by an information protection layer positioned between an optical beam and the recording layer, and that it is difficult to pull in the focusing on a desired recording layer because the variation is a variation due to the spherical aberration, in a conventional optical disk. SOLUTION: The optical disk apparatus is characterized in that it is controlled by a spherical aberration providing means giving the spherical aberration to an optical beam and a focusing means so that the spherical aberration is given by the spherical aberration providing means before the focal point of the optical beam is positioned to the information recording layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc apparatus which reproduces information by irradiating a condensed light beam on an optical disc having an information recording layer for recording information, and particularly to the information recording layer. The present invention relates to an optical disk device and a focus control method for facilitating focusing pulling of a focused light beam onto a disk.

[0002]

2. Description of the Related Art An optical disk is known as a medium for recording information. Of the optical discs, the DVD has one information recording layer on which information can be recorded in advance or can be recorded.
Layers and multiple layers (mainly two layers) are known.

Among them, in an optical disc having two recording layers, in order to focus the focus of a light beam condensed for reproducing information on each recording layer, the focus error signal is focused to zero. We are in control. However, since the reflectances of the two recording layers are different, the amplitude of the focus error signal is different in each recording layer, and there is a problem that the signal for focus pull-in must be adjusted for each recording layer.

As a method for solving this problem,
Japanese Patent Laid-Open No. 11-161977 is known.

In this publication, before the focus is pulled in,
By optimizing the gain of the focus servo for the recording layer desired to be pulled in and making the amplitude of the focus error signal constant in any recording layer, focus pulling can be performed without adjusting the focus pull-in signal.

Further, a next-generation optical disc system is being studied as an optical disc capable of recording a larger amount of information than a DVD, and a higher NA is required in the next-generation optical disc system.
We are studying an optical disk device with (numerical aperture) objective lens, and an optical disk in which information can be recorded in advance by fine pits or marks under a thinned information protection layer. In this case, since it is necessary to reproduce finer pits or marks in the next-generation optical disc, a high NA objective lens is used.
Not only the difference in reflectance of each recording layer, but also the influence of spherical aberration due to the difference in the distance between each recording layer and the disc surface due to the information protection layer located between the light beam and the recording layer, the focus error signal The shape changes. Since this change is due to spherical aberration, not only the amplitude but also the inclination and the shape of the signal itself change.

Therefore, there is a problem that the focus error signal cannot be optimized only by adjusting the gain of the focus servo as in the technique disclosed in the above publication.

[0008]

As described above, in the conventional optical disk device, the change in the focus error signal amplitude due to the difference in the reflectance of each recording layer is adjusted only by adjusting the gain of the focus servo. However, in consideration of reproduction by an optical disc device having an objective lens with a high NA, which is being considered as a next-generation optical disc system, and when the optical disc has a structure in which the information protection layer is thinned, an objective lens with a high NA is used. Therefore, the focus error signal is caused not only by the difference in the reflectance of each recording layer but also by the spherical aberration due to the difference in the distance between each recording layer and the disc surface due to the information protection layer located between the light beam and the recording layer. The shape of changes. Since this change is a change due to spherical aberration, not only the amplitude but also the inclination and the shape of the signal itself change, so the focus error signal cannot be optimized simply by adjusting the gain of the focus servo. There is a problem that it becomes difficult to pull the focus to a desired recording layer.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an optical disk device and a focus control method capable of easily focusing the focus of a condensed light beam on a desired information recording layer.

[0010]

In order to achieve the above object, in an optical disc apparatus of the present invention, an optical disc having an information recording layer for recording information is provided with a light beam focused on the information recording layer. An optical disk device which reproduces information by irradiating, focusing means for focusing so that the condensed light beam is positioned on the information recording layer, and spherical aberration is given to the light beam. And a control means for controlling the spherical aberration imparting means to impart the spherical aberration by the spherical aberration imparting means before the focus of the light beam is positioned on the information recording layer by the focusing means. Characterize.

By imparting the spherical aberration before the focusing pull-in, it is possible to reduce the aberration in the information recording layer, thereby making the S-curve of the focus error signal steep and increasing its amplitude. Yes, you can reliably pull in the focus.

Further, focus error amplitude amount detecting means for detecting the amplitude amount of the focus error signal by the focusing means is provided, and the focusing means functions based on the amplitude amount of the focus error signal by the control means. The spherical aberration imparting amount by the spherical aberration imparting means is determined so that the amplitude amount of the focus error signal increases to such an extent.

The amount of spherical aberration imparted is determined by the focus error amplitude amount detecting means for detecting the amplitude amount of the focus error signal and the focusing means for focusing the light beam in the depth direction of the information recording layer. A peak timing detection means for detecting the timing of the peak of the signal based on the reflected light from each layer of the information recording layer obtained by moving the information recording layer, and the amplitude amount of the focus error signal by the focusing means according to the appearance timing. A focus error signal amplitude amount storage means to be stored and a spherical aberration imparting amount optimizing means are provided, and the spherical aberration imparting amount optimizing means controls the spherical aberration imparting means to control the spherical aberration in a predetermined step. And the amount of the spherical aberration applied is stored in the amplitude amount storage means of the focus error signal. By comparing the amplitude of the Kasuera signal, the amplitude of the focus error signal to determine the spherical aberration application amount becomes maximum.

By optimizing the addition amount of spherical aberration based on the S-shaped amplitude amount of the focus error signal,
Aberrations in the information recording layer can be optimized, whereby the S-curve of the focus error signal can be made steep and its amplitude can be increased, so that reliable focus pull-in can be performed.

Further, the present invention is characterized in that a storage means for storing the spherical aberration application amount provided by the spherical aberration application means is provided, and the spherical aberration amount determined by the control means is stored in the storage means.

By storing the optimum spherical aberration imparting amount in the storage means, the spherical aberration amount can be utilized unless the disc is replaced, so that it becomes necessary to re-focus. It is not necessary to optimize the amount of spherical aberration applied again, and the focus can be pulled in quickly and reliably.

An optical disk device for reproducing information by irradiating a light beam focused on the information recording layer to an optical disk having two information recording layers for recording information, comprising: The focus of the emitted light beam is
Focusing means for focusing on the information recording layer based on a focus error signal, spherical aberration imparting means for imparting spherical aberration to the light beam, and focusing means for the information recording layer Peak timing detection means for detecting the timing of the peak of the signal based on the reflected light from each layer of the information recording layer obtained by moving the focus of the light beam in the depth direction, and the focus error signal by the focusing means. Focus error amplitude amount detecting means for detecting the amplitude amount of the in accordance with the appearance timing, comparing means for comparing the amplitude amount of the focus error signal of each detected information recording layer, from the comparison result of the comparing means, The focus in the information recording layer for performing the focusing A control means for controlling the focusing means to focus after the spherical aberration is imparted by the spherical aberration imparting means so that the amplitude amount of the error signal becomes larger than that of the other information recording layer. Is characterized by.

Then, the S-shaped amplitude amount of the focus in each information recording layer is detected, and the spherical aberration imparting amount is determined so that the amplitude of the information recording layer for performing the focus pull-in becomes larger than the other amplitude. It is possible to reliably pull the focus to a desired information recording layer, and it is possible to prevent the focus from being accidentally pulled to another information recording layer.

The appearance interval storage means for storing the appearance interval of the peaks in each of the information recording layers detected by the peak timing detection means, and the appearance interval stored in the appearance interval storage means Spherical aberration imparting amount determining means for determining the spherical aberration imparting amount, and control for performing focusing by the focusing means after imparting the spherical aberration imparting amount determined by the spherical aberration imparting amount determining means And a control means for controlling the operation.

By moving the amount of spherical aberration imparted by a predetermined constant amount, the optimizing operation is not performed, but the amount based on the appearance interval corresponding to the layer interval of the information recording layer is used. By doing so, it is possible to quickly and accurately optimize the spherical aberration imparting amount.

An optical disk device for reproducing information by irradiating a light beam focused on the information recording layer to an optical disk having two information recording layers for recording information, The focus of the emitted light beam is
Focusing means for focusing on the information recording layer based on a focus error signal, spherical aberration giving means for giving spherical aberration to the light beam, and giving spherical aberration by the spherical aberration giving means. And a control means for controlling the timing of the information recording layer, wherein the light beam has a focal point on one of the information recording layers, and when the focal point is moved to the other side of the information recording layer, the control means controls the information recording. Before focusing on the other layer, the spherical aberration imparting means imparts spherical aberration to increase the amplitude amount of the focus error signal on the other side of the information recording layer to such an extent that the focusing means functions. And

Then, when performing an interlayer jump from one of the information recording layers to the other, it is possible to surely perform focus pull-in to the information recording layer of the jump destination.

Further, in the control means, the minimum position of the spherical aberration is within a range of 3/2 of the layer distance between the information recording layers from the midpoint of the two information recording layers including the information recording layer for focusing. The addition amount of the spherical aberration is controlled so as to be positioned at.

Then, if the minimum position of the spherical aberration is located within a range of 3/2 of the layer spacing of the information recording layers from the middle point of the two information recording layers including the information recording layers to be focused, the focusing is performed. Since the focus S-shaped amplitude in the information recording layer for performing the above is sufficiently large with respect to the focus pull-in and further larger than the focus S-shaped amplitude in the other information recording layer, it is possible to reliably pull in the focus.

Further, there is provided a focus control method for focusing on an optical disc having an information recording layer for recording information so that the focus of the condensed light beam is located on the information recording layer. Before focusing so that the focused light beam is located in the layer, spherical aberration is applied to the focused light beam so as to increase the amplitude of a focus error signal generated when the focus of the focused light beam passes through the information recording layer. Characterized by having a step of giving.

By imparting the spherical aberration before the focus is pulled in, the aberration in the information recording layer can be reduced, whereby the S-curve of the focus error signal can be made steep and its amplitude can be increased. Yes, you can reliably pull in the focus.

Further, there is provided a focus control method for focusing on an optical disc having an information recording layer for recording information such that the focus of the condensed light beam is located on the desired information recording layer. A first step of detecting the amplitude of a focus error signal generated when the focus of the focused light beam passes through the information recording layer; a second step of imparting spherical aberration to the focused light beam; Repeating the first step and the second step, the third step of ending the repetition when the amplitude of the focus error signal becomes a desired magnitude or more, and after the third step, the A fourth step of focusing the focus of the condensed light beam so as to be positioned on the information recording layer.

Then, by optimizing the addition amount of the spherical aberration based on the S-shaped amplitude amount of the focus error signal,
Aberrations in the information recording layer can be optimized, whereby the S-curve of the focus error signal can be made steep and its amplitude can be increased, so that reliable focus pull-in can be performed.

After the completion of the third step, a fifth step of storing information representing the amount of spherical aberration given to the condensed light beam and a fourth step for the optical disk are repeated a plurality of times. When performing, it has a sixth step of giving a spherical aberration to the condensed light beam based on the stored information indicating the spherical aberration amount, and a fourth step after the sixth step. It is characterized by performing.

By storing the optimum amount of spherical aberration, the amount of spherical aberration can be used unless the disc is replaced. Therefore, when it becomes necessary to re-focus, the spherical aberration should be restored. It is not necessary to optimize the amount of application of the focus, and the focus can be pulled in quickly and surely.

Further, a focus control method for selectively focusing on an optical disc having two information recording layers for recording information so that the focal point of the focused light beam is located on the desired information recording layer. A first step of detecting an amplitude of a focus error signal generated when the focus of the focused light beam passes through the two information recording layers; and a focus error generated in the two information recording layers. A second step of comparing the amplitudes of the signals,
Based on the result of the comparison, so that the amplitude of the focus error signal of the selected information recording layer is larger than the amplitude of the focus error signal of the other information recording layer,
Third step of imparting spherical aberration to the focused light beam, and fourth step of focusing the focused light beam so as to be positioned on the selected information recording layer after the imparting of the spherical aberration. And having.

Then, the S-shaped amplitude amount of the focus in each information recording layer is detected, and the spherical aberration imparting amount is determined so that the amplitude of the information recording layer for performing the focus pull-in becomes larger than the other amplitude. It is possible to reliably pull the focus to a desired information recording layer, and it is possible to prevent the focus from being accidentally pulled to another information recording layer.

Further, before the third step, there is a fifth step of storing the appearance interval of the focus error signal generated when the information recording layer is passed, and based on the stored appearance interval, In the third step, the amount of spherical aberration given at one time is determined.

Then, the amount of spherical aberration imparted is moved by a predetermined fixed amount, and the optimizing operation is not performed, but the amount based on the appearance interval corresponding to the layer interval of the information recording layer is used. By doing so, it is possible to quickly and accurately optimize the spherical aberration imparting amount.

Further, there is provided a focus control method for focusing on an optical disc having two information recording layers for recording information so that the focus of the focused light beam is located on the information recording layer. From the state where the focus of the light beam is focused on one of the information recording layers,
Before moving the focus to the other side of the information recording layer before focusing on the other side of the information recording layer, a spherical surface is formed so that the amplitude of the focus error signal in the information recording layer becomes large enough to perform the focusing. It is characterized by having a step of giving an aberration.

When an interlayer jump is performed from one of the information recording layers to the other, spherical aberration is imparted to the jumping information recording layer, so that the amplitude of the focus error signal in that layer becomes large. It is possible to reliably pull in the focus.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION First, an outline of an embodiment of the present invention will be described.

As a background of the present embodiment, in an optical disc having a plurality of information recording layers, since the distance between the disc surface and the recording layer is different for each recording layer, the amount of spherical aberration generated is different for each recording layer. . Therefore, even if the spherical aberration is adjusted to be the minimum in a certain recording layer, the spherical aberration is increased in the other layers. Further, when spherical aberration occurs, the focus error signal amplitude and sensitivity decrease. Therefore, when the amount of aberration of the laser beam is constant or not adjusted, the amplitude and sensitivity of the focus error signal are different for each recording layer. Is easy to focus on, and it is difficult to focus on a layer with a large spherical aberration. Furthermore, even if the information recording layer is a single-layer optical disc, the thickness of the information protection layer is incorrect and the amount of spherical aberration of the optical system is large. In some cases, when the focus is pulled in, the amount of spherical aberration in the vicinity of the recording layer to be pulled in becomes large, which makes it difficult to pull in the focus.

In this embodiment, with respect to the optical disc,
A device that records or reproduces information, has a spherical aberration correction mechanism, and optimizes the spherical aberration of the laser beam that is irradiated before focus is drawn to the layer that pulls focus, so that it can be used for any recording layer. The point is that the focus can be reliably pulled in.

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

FIG. 1 is a block diagram of an optical disk device according to the first embodiment of the present invention.

FIG. 2 shows an enlarged view of the objective lens 103, the spherical aberration adding mechanism 104 and the optical disc 100 shown in FIG.

FIG. 3 is a diagram showing the relationship between the sectional view of the optical disc 100, the amount of spherical aberration, and the focus error signal.
Shows a cross-sectional view of an optical disc 100 having two recording layers,
FIG. 3 (b) shows changes in the spherical aberration amount at the focal position when a laser beam having a constant spherical aberration at the time of emission is incident and the focal position is moved in the focus direction (z direction) perpendicular to the optical disc 100. FIG. 3C shows a change in the focus error signal in the same case. Here, the focus error signal is a signal detected based on, for example, the astigmatism method.

FIG. 4 shows a change in spherical aberration amount and a focus error signal at the focal position when a laser beam having a spherical aberration different from that in FIG. 3 is incident and the focal position is moved in a direction perpendicular to the optical disc 100. Is shown.

FIG. 5 is a diagram showing the amount of change in the amplitude of the focus S-shaped signals of layers 0 and 1 and the amplitude difference of the S-shaped curves in each layer when the optimum spherical aberration position is moved in the Z direction. is there. Fig. 5 (a) shows the focus S of layer 0 and layer 1 when the optimum spherical aberration position is moved in the Z direction.
FIG. 5 (b) shows the change in the S-shaped signal, and FIG. 5 (b) shows the difference between the amplitude of the S-shaped curve in Layer 0 and the amplitude of the S-shaped curve in Layer 1.

First, the spherical aberration will be described. The spherical aberration adding mechanism 104 shown in FIG. 2 is the optical pickup 1000 shown in FIG.
It is composed of a beam expander having two lenses incorporated in a part of the laser beam to the objective lens 103 composed of two lenses, the spherical aberration adding mechanism 104
By changing the distance between the two lenses, spherical aberration can be imparted to the laser beam passing therethrough. The optical disc 100 has a protective layer 20 extending in the depth direction from the disc surface on which the laser beam from the objective lens 103 is incident.
3, first recording layer, layer 0 # 210, intermediate layer 202, second
The recording layer is a layer 1 # 220 and a substrate 201. Then, by changing the distance between the lenses, the distance that the laser beam passes through the optical disc 100 is increased because the error in the thickness of the protective layer 203 and the thickness of the recording layers, Layer 0 # 210 and Layer 1 # 220, are different. The spherical aberration that occurs due to the change is canceled out, and the recording layer (layer 0
The laser spot (focus) formed on # 210 and layer 1 # 220) can be reduced. That is, if the desired recording layer changes due to an error in the thickness of the protective layer 203 or movement from layer 0 # 210 to layer 1 # 220, and the distance from the surface of the optical disk to the focal point changes, the spherical surface at the focal point Although the aberration increases, if the spherical aberration opposite to this is given by adjusting the lens distance L between the two lenses of the spherical aberration adding mechanism 104 in response to the change, the increase in spherical aberration can be suppressed. it can. Specifically, when the spacing L of the spherical aberration adding mechanism 104 is L = L0,
It is assumed that the optical system is designed so that the spherical aberration is minimized when the distance from the disk surface to the focal point is l = l0. Here, in the actual optical disc 100, the distance from the disc surface to the recording layer is l = 10 + η, and if it is desired to minimize the spherical aberration at this position, the spherical aberration adding mechanism 10
The distance between the two lenses of 4 should be L = L0 + k · η. Here, k is a constant and is a value determined by the design of the optical system of the spherical aberration adding mechanism 104. In the following description, the distance from the disk surface to the focal point is defined as Z, and the distance between the focal point position and the disk surface where the spherical aberration is minimized is defined as the distance l.

FIG. 3 (b) shows a state where spherical aberration is added so that the spherical aberration at the focal point is minimized when the focal point is focused at the position Z = a, that is, when the distance is l = a. It shows a change in the amount of spherical aberration at the focal point when the position is swept. Focus position Z and distance as the focus moves away from Z = a
Since l = a is far apart, spherical aberration generated at the focal point increases. Here, since the position Z = z0 of the layer 0 # 210 is close to a, the laser spot formed on the layer 0 # 210 can be narrowed down. On the other hand, Layer 1 # 220 position Z = z
Since 1 is far from a and the spherical aberration that occurs is large, the laser spot in Layer 1 # 220 becomes small and cannot be stopped. Therefore, as shown in FIG. 3 (c), in the focus error signal, the S-shaped curve generated in layer 0 # 210 has a larger amplitude and zero-cross point than the S-shaped curve generated in layer 1 # 220. The inclination of becomes large.

Next, the spherical aberration adding mechanism 104 is adjusted as shown in FIG.
The spherical aberration amount at the focus when the spherical aberration is added to (a) so that the distance l = b and the focal position is swept is shown. Spherical aberration increases as the focus moves away from Z = b.
Here, since the position Z = z1 of the layer 1 # 220 is close to b, the laser spot formed on the layer 1 # 220 can be narrowed down. On the other hand, the position Z = z0 of layer 0 is far from b and the spherical aberration generated is large, so layer 0 #
With 210, the laser spot becomes too small to be focused. Therefore, in the focus error signal shown in FIG. 4B, the layer 1 # 220 is different from the S-shaped curve generated in the layer0 # 210.
The S-shaped curve generated in 1 has larger amplitude and slope at the zero cross point.

FIG. 5A is a diagram in which changes in the amplitude of the focus S-shaped curve shown in FIGS. 3 and 4 are continuously plotted. For example, if Z = l = a as shown in Figure 3, layer 0 #
The amplitude of the S curve at 210 is large, and the amplitude at Layer 1 # 220 is small. Further, as shown in FIG. 4, when Z = l = b, the amplitude of the S-shaped curve in layer 1 # 220 is large and the amplitude in layer 0 # 210 is small. Thus, by changing the spherical aberration added to the laser beam by the spherical aberration adding function, the amplitude and sensitivity of the S-shaped curve of focus can be changed. Further, from the amplitude ratio shown in FIG. 5 (b), if the spherical aberration addition amount is given so that the spherical aberration is minimized when the focus is achieved at any position, the desired focus S-curve at the time of focus pull-in can be obtained. I know if I can get. For example, when the focus is pulled in with the added amount of spherical aberration adjusted to be the minimum when the focus is in the position of range A, the focus S of layer 0 # 210 is smaller than that of layer 1 # 220. Since the amplitude of the curve is large, it is easy to pull focus on Layer 0 # 210 and hard to pull on Layer 1 # 220. vice versa,
When the focus is drawn in the position of range B and the focus amount is adjusted so that the spherical aberration is minimized, layer 1 # 220 is compared to layer 0 # 210.
Focus S-curve amplitude is large, so layer 1 # 2
It is easy to pull the focus to 20, and hard to pull to layer 0 # 210. In the range C, layer 0 # 210
It is easy to pull the focus to both and Layer 1 # 220. Here, the range A is centered on the position of layer 0 # 210, and the amplitude difference of the S-shaped curve of layer 0 # 210 and layer 1 # 220 is larger than the allowable minimum difference that can be reliably detected.
The range where the amplitude of the curve is larger than the minimum allowable amplitude required to pull in the focus. Range B is centered on the position of layer 1 # 220, layer 0 # 210 and layer 1 # 22
The amplitude difference of the S-curve of 0 is larger than the minimum allowable difference for sure detection, and the amplitude of the S-curve of layer 1 # 220 is larger than the minimum allowable amplitude for pulling in the focus. Further, the range C is between the range A and the range B.

In the optical disc device of the present embodiment, when the focus is pulled in, before the focus is pulled in the layer 0 # 210, when the focus is in the position of the range A, the spherical aberration amount of the focus is the minimum. Spherical aberration is added so that Further, when the focus is pulled into the layer 1 # 220, when the focus is in the position of the range B, the spherical aberration is added so that the spherical aberration amount of the focus becomes the minimum. Empirically, the range A has two recording layers (layer 0 # 210, layer 1 # 22
Centering the position of layer 0 # 210 with respect to the interval D of (0), -D / 2
To about D. Range B is Layer 1 # 22 as well
It is from about -D to about D / 2 centered on the 0 position.

Here, the direction in which the distance 1 becomes longer is negative. However, in reality, there is an error in the amplitude comparison, so the difference in the amplitude of the focus S-shaped signal is 1/3 of the maximum difference.
Considering that if there is a degree, there will be a difference in advantage at the time of pulling in, the range A is layer 0 # 210 with respect to the distance D between the two recording layers.
Centered around the position of -D / 3 to almost D. Similarly, the range B is about -D to D / 3 around the position of layer 1 # 220. Here, the direction in which the distance l increases becomes negative.

Next, based on the block diagram shown in FIG.
Details of the optical disk device according to the first embodiment of the present invention will be described.

The optical disc 100 has the layer 0 # 21 shown in FIG.
0, layer 1 # 220, and is mounted on the spindle motor 102 by a clamp hole (not shown) and a clamper 101. Spindle motor 102 is a motor driver 1
It is driven to rotate by 11. An optical pickup 1000 is provided facing the optical disc 100, and recording or reproduction is performed on the optical disc 100 by a laser beam emitted from the optical pickup 1000. The optical pickup 1000 has the objective lens 103 and the spherical aberration adding mechanism 104 shown in FIG. Further, a focus actuator 108 and a tracking actuator 109 that move the objective lens 103 in the focus direction (z direction) and the radial direction of the disk are attached. A spherical aberration adding mechanism 110 composed of two lenses is equipped with a spherical aberration adding actuator 110 that drives one lens in the focus direction to adjust the spherical aberration adding amount. In addition to this, the optical pickup 1000 includes a semiconductor laser (LD: Laser Diode) 105 that is a light source, a light-transmitting optical system 1010, a light-receiving optical system 1020, and a split PD (that extracts a reproduction signal and a servo signal from reflected light from the optical disc 100 It has a multi-division detector (PD) consisting of a Photo Detector a106 and a division PD b107. LD1 which is the light source with the power specified by the LD driver 112
The laser beam emitted from 05 is the optical pickup 10
After passing through the light transmission optical system 1010 in 0, the spherical aberration adding mechanism 1
After spherical aberration is added by 04, it is condensed on the optical disc 100 by the objective lens 103. The reflected light of the laser beam focused on the optical disc 100 is again returned to the objective lens 10
3. After passing through the spherical aberration adding mechanism 104, the light receiving optical system 1020
The light is received by the plurality of divided PDa 106 and the divided PDb 107. The electric signal output of each element of the plurality of divided PDs is supplied to the focus error (FE) signal generation circuit 118, the tracking error (TE) signal generation circuit 119, the spherical aberration error (AE) generation circuit 117, and the reproduction signal processing circuit 120, respectively. Is entered. The FE signal generation circuit 118 generates a focus error signal from the supplied electric signal by performing a predetermined calculation based on, for example, the astigmatism method, and supplies the focus error signal to the amplification circuit. The TE signal generation circuit 119 generates a tracking error signal by performing a predetermined calculation based on, for example, the push-pull method, and supplies the tracking error signal to the amplification circuit. Similarly, a spherical aberration correction signal is also generated by the AE signal generation circuit 117 and supplied to the amplification circuit a121. The spherical aberration correction signal is output by the AE signal generation circuit 117.
Is generated by performing a predetermined calculation. Here, the focus error signal is S as shown in FIG.
The signal has a shape called a curve, and the tracking error signal is a sinusoidal signal.

On the other hand, the reproduction signal processing circuit 120 performs reproduction processing of preformat data and user data included in the reproduction signal from the optical disc 100. Further, the reproduction signal processing circuit 120 recognizes the ID address and the like recorded in the preformat section of the optical disc 100 from the reproduction signal and transmits the recognized digital signal to the control section 133. Since the ID address includes the layer number, the track number, the sector number, etc., the control unit 133 can recognize the physical address where the focused beam is currently scanning.

Next, in each amplifier circuit 121, 122, 123, amplification of each error signal and offset voltage adjustment are performed. The focus error signal amplitude is set to an optimum gain in the amplifier circuit c123. Further, an offset voltage is applied for the focusing operation so that the shape of the laser spot is optimized on the desired recording layer of the disc. After that, the focus error signal is sent to the phase compensation circuit c126 and the switch b1.
It is supplied to the focus driver 113 through 28. In addition, a focus jump signal is appropriately applied during this process. The focus jump signal is a signal generated by the focus jump signal generation circuit 136. When the focus jump signal generation circuit 136 receives a focus jump command from the control unit 133, the phase compensation circuit c outputs a jump pulse composed of a kick pulse and a brake pulse.
Applied to the focus error signal from. By supplying the focus error signal to the focus driver 113, a drive current is supplied from the focus driver 113 to the focus actuator 108, and the objective lens 103 is driven in the focus direction perpendicular to the optical disc 100. Further, when the focus is pulled in, the sweep signal generated by the sweep circuit 135 is supplied to the focus driver 113 for the sweep operation in the focus direction. Switching of this signal is performed by the switch b128. Here, the sweep signal is an electric signal that changes in a sawtooth shape, and is a signal in which changes in the increase and decrease in the voltage value correspond to changes in the positive and negative directions of the moving direction of the objective lens 103, respectively. In this embodiment, the positive direction is the direction in which the objective lens 103 approaches the optical disc 100, and the negative direction is the direction in which the objective lens 103 moves away from the optical disc 100.

Similar to the focus error signal, the tracking error signal passes through the amplifier circuit b122 and the phase compensation circuit b125, and is then supplied to the tracking driver 114 via the switch c127. As a result, a drive current is supplied to the tracking actuator 109, and the objective lens 103 is driven in the radial direction parallel to the optical disc 100. After passing through the phase compensation circuit b, the track jump signal generation circuit 137 appropriately applies the track jump signal. Here, the track jump signal is a signal composed of a kick pulse and a brake pulse.

Similar to the focus error signal, the spherical aberration error signal passes through the amplifier circuit a121 and the phase compensation circuit a124, and is then supplied to the spherical aberration adding mechanism driver 115 via the switch a129. As a result, a drive current is supplied to the spherical aberration adding actuator 110, and the spherical aberration adding mechanism 104
One of the lenses is driven in the focus direction perpendicular to the optical disc 100.

Further, the spherical aberration adding mechanism driver 115 is provided with an offset applying circuit 116, and an offset voltage is applied by a control signal from the control unit 133. The operating lens of the spherical surface adding mechanism 104 moves in the direction perpendicular to the optical axis by the voltage (or current) applied by the spherical aberration adding mechanism driver 115, and the amount of spherical aberration generated changes depending on the position. Therefore, if a DC offset voltage is applied, the position of the lens is fixed as desired, and a certain amount of spherical aberration is always generated. That is, even if the spherical aberration error signal is not transmitted, the amount of spherical aberration generated in the spherical aberration adding mechanism 104 can be controlled in a DC manner by this offset voltage.

A memory 134 is connected to the control unit 133. The memory 134 stores the aberration compensation amount initial setting value. The value to be stored is, for example, a digital value indicating the above offset voltage. This is, for example, the optical disc 100
If the nominal value of the film thickness of the protective layer 203 is 0.1 mm, for example, the spherical aberration adding mechanism 104 is controlled so that the spherical aberration is minimized when the distance l = 0.1 mm is focused. It is an initial setting offset voltage value. Therefore, the optical disc 10
When 0 is loaded and the spherical aberration adding mechanism 104 is operated for signal reproduction, the control unit 133 first reads the initial setting offset voltage set in the memory 134,
By controlling the spherical aberration adding mechanism driver 115 to generate this voltage value, the operating lens of the spherical aberration adding mechanism 104 is moved to the initial setting position.

FIG. 6 is a flow chart showing the procedure of focus pull-in by the optical disk device in FIG.

A focus pull-in procedure by the optical disc apparatus of FIG. 1 will be described with reference to FIG.

First, the switches a129, b128, and c127 are all grounded. When the optical disc 100 having two recording layers of layer 0 # 210 and layer 1 # 220 is loaded in the optical disc device, the control unit 133 controls the motor driver 111 to rotate the spindle motor 102 (step 301). Here, the optical disc 100
It is assumed that the protective layer 203 has a nominal value of 0.1 mm and the layer distance D is 0.025 mm. Next, after moving the optical pickup head 1000 to a predetermined position on the inner peripheral side of the optical disc 100 by a carriage (not shown), the control unit 133 controls the LD driver 112 to cause the LD 105 to emit light with reproduction power (ste
p302). Subsequently, the optical disc 100 inserted is discriminated by an optical disc discriminating mechanism (not shown) (step 303). If the inserted optical disc 100 is an optical disc having a plurality of recording layers, the control unit 133 determines the layer to be accessed (step 304). Here, the control unit 133 is always the layer
Suppose you specify 0. If the optical disc inserted in step 303 is an optical disc having one recording layer, the process proceeds to step 305 described later. The control unit 133 reads the layer 0 from the memory 134.
Read the initial value of the aberration correction amount when pulling the focus to # 210, and according to this value, the offset application circuit
116 is controlled to drive the spherical aberration adding mechanism 104 (step 30
Five).

Next, the control unit 133 switches the switch b128 to supply the sweep signal from the sweep circuit 135 to the focus driver 113 (step 306). The focus driver 113 drives the focus actuator 108 in the focus direction according to the sweep signal. At this time, the focus error signal is S at layers 0 # 210 and 1 # 220 respectively.
A curved curve occurs. Here, although not shown in the figure, if the peak does not appear twice before the polarity of the sweep signal is switched, the control unit 133 determines this and returns to the determination of the optical disc 100 again, or offsets to the sweep signal. Then, the objective lens 103 is brought closer to the optical disc 100 and the sweep is performed again.

Here, if the thickness of the protective layer 203 is exactly 0.1 mm and there is no error in the initial value of the spherical aberration addition amount,
The amplitude of the S curve in Layer 0 # 210 is Layer 1 # 220
Should be big enough for. Further, even if Z = z0 slightly deviates from 0.1 mm due to uneven thickness of the protective layer 203, or even if the distance l deviates slightly from 0.1 mm due to an error in the initial setting value, l falls within the range A shown in FIG. 5. If so, it is possible to reliably pull in the focus. Therefore, in this state, the process moves to the next focus step.

In the focus pull-in step (step 307), the control unit 133 functions as a reproduction signal peak detection means and a focus error signal zero-cross detection means. In order to pull the focus to the target layer 0 # 210,
The control unit 133 starts the peak detection of the reproduction signal and the zero-cross detection of the focus error signal from the moment when the polarity of the sweep circuit 135 switches to the plus (increasing) direction. When the zero cross of the focus error is detected during the first peak, the control unit 133 switches the switch b128 to connect the sweep circuit 135 to the output of the phase compensation circuit c126. At this time, the output of the phase compensation circuit c126 is supplied to the focus driver 113, and the focus pull-in is completed (step 307).

Then, the switch c127 is controlled, the output of the phase compensation circuit b125 is supplied to the tracking driver 114, and the tracking pull-in is completed. Similarly, the switch a129 is controlled to pull in the spherical aberration adding mechanism 104 (step 308).

Note that the pull-in by the spherical aberration adding mechanism 104 in step 308 means, for example, that the switch a129 is subsequently controlled and the output of the phase compensation circuit a124 is the aberration adding mechanism driver.
This is equivalent to being supplied to 104 and being pulled in by the spherical aberration adding mechanism 104.

In this state, the ID address and the like recorded in the preformat section of the optical disc 100 are reproduced, and the target layer information and the like are reproduced (step 309). The layer in which the focus is drawn is determined from the playback result (step3
10) If the layer is the target layer 0 # 210, the pulling of the focus is completed (step 311). Further, when the layer in which the focus is pulled is not the target layer 1 # 210 but the layer 1 # 220, the focus is re-pulled to the layer 0 # 210 by the focus jump described later (step 312).

Next, when a focus jump command is input to the control unit 133 from an interface (not shown), or when the control unit 133 determines that the focus jump is necessary, as in step 312 of FIG. The focus jump operation that transfers the beam spot from the layer being played back to the other layer is started.

FIG. 7 is a flowchart of focus jump between layers. Focus jump between layers will be described based on this flowchart. In addition, here, it is assumed that the state where the layer 1 # 220 is being reproduced is changed to the layer 0 # 210.

The control unit 133 first controls the switch c127 to turn off the tracking error signal input to the tracking driver 114 (step 201). Here, since the spherical aberration correction mechanism 104 is driven, the spherical aberration is added so that the spherical aberration becomes the smallest when the layer 1 # 220 is currently in focus. Therefore, in this state, layer 0 #
When the focus moves to 210, the aberration at the focus is large, and sufficient amplitude and sensitivity of the focus S-shaped curve cannot be obtained. Therefore, next, the control unit 133 controls the offset applying circuit 116 to add spherical aberration. At this time, the layer interval D is predetermined depending on the type of optical disc,
When moving from layer 1 # 220 to layer # 2100, distance l
If the spherical aberration addition amount is determined so as to be shorter than the current value by about D, the focus error signal in layer 0 # 210 becomes large enough to perform focus pull-in, and thus pull-in to layer 0 # 210 is performed. It can be done reliably. In the present embodiment, since the applied voltage value for this purpose is set in the memory 134 in advance, the control unit 133
Reads out this value from the memory 134 and controls the offset applying circuit 116 based on this value (step 202). Where D =
Since it is 0.025mm, the distance l is from Layer 1 # 220 playback
If it falls within the range of 0.0125 to 0.025, the focus can be pulled in reliably. At this time, the sensitivity of the S-shaped curve in Layer 0 # 210 actually increases, whereas the sensitivity in Layer 1 # 220 decreases,
Since the focus is stably applied on Layer 1 # 220, the residual amount of focus control is increased even if the sensitivity is slightly lowered, but the possibility of defocusing is low. After the readjustment of the offset voltage applying circuit 116 is completed, the focus jump signal generation circuit 136 adds the focus jump signal to the focus error signal (s
tep203). This jump signal is a signal composed of rectangular waves of two polarities. Layer 1 # by the leading square wave
From the state where 220 is focused, objective lens 1
03 is transported in the direction of layer 0 # 210. Then, the second rectangle brakes the movement of the focus actuator 108, stabilizing the focus and layering.
The pulling in to 0 # 210 is completed (step 204). Then, tracking is pulled in (step 205). In this state,
The ID address and the like recorded in the preformatted part of the optical disc 100 are reproduced, and the layer information and the like of the optical disc are reproduced (step 206). The layer in which the focus is drawn is determined from the reproduction information (step 207), and if the layer in which the focus is drawn is the target layer 1 # 210, the focus drawing is completed (step 208). If the layer that pulled the focus is Layer 0 (step
(No in 207), the focus is re-pulled into the layer 1 # 220 by the focus jump again.

In this embodiment, the spherical aberration adding mechanism 104 is composed of a beam expander composed of two lenses. However, the spherical aberration adding mechanism 104 has a desired spherical aberration for the beam passing through the mechanism. The mechanism is not limited to this as long as the mechanism can add. For example, the spherical aberration adding mechanism can be configured by a liquid crystal element that adds a spherical aberration by changing the refractive index by applying a voltage. Further, when the objective lens is composed of a second group lens like the objective lens 103, spherical aberration can be added by changing the distance between the second group lenses. The additional mechanism may be composed of only two groups of lenses.

Further, although an optical disc having two recording layers has been described as the optical disc to be reproduced in the present embodiment, the effect of the present invention is also exerted on an optical disc having a plurality of recording layers of two or more layers. . In addition, with respect to the content excluding the focus jump, the effect of the present invention is exerted even for an optical disc device having only one recording layer.

FIG. 8 is a block diagram of an optical disk device according to the second embodiment of the present invention. In the optical disk device of FIG. 8 and the optical disk device of FIG. 1, an amplitude comparison circuit 130 and a peak timing detection circuit 13 are included in the optical disk device of FIG.
1, the peak interval detection circuit 132 is newly added. The same elements as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The added circuit includes a peak timing detection circuit 131 for detecting the appearance timing of the peak of the reproduction signal while the voltage value of the sweep circuit 135 is increasing or decreasing, and the interval between the detected peaks. A peak interval detection circuit 132 for detection, and an amplitude comparison circuit 130 for comparing the amplitudes of the S-shaped curves of the focus error signals generated in layers 0 # 210 and 1 # 220. The peak timing detection circuit 131 and the peak interval detection circuit 132 are connected to the division PDb 107 together with the reproduction signal generation circuit 120 in order to receive the output from the division PDb 107 in order to detect from the reproduction signal. Also,
The amplitude comparison circuit 130 is connected to the amplification circuit c123 that amplifies the output from the FE signal generation circuit 118 in order to receive the focus error signal.

Then, the peak timing detection circuit 131
Is specifically composed of a comparator, etc., and normally outputs an L (Low) level signal, but when the input playback signal exceeds a predetermined reference level, H ( This is a circuit that outputs a (High) level signal. The peak interval detection circuit 132 receives the output from the peak timing detection circuit 131 via the control unit 1338, and also receives the sweep signal from the sweep circuit 135 and a signal indicating the polarity of the sweep signal as an input via the control unit 1338. ,
Detection is started after the polarity of the sweep signal is switched, and the voltage value of the sweep signal at the moment when the input signal from the peak timing detection circuit 131 is switched to H level is stored in the memory 1348 via the control unit 1338. Next, the peak timing detection circuit
The voltage value of the sweep signal at the moment when the input signal from 131 switches to the H level again is received, and the difference with the voltage value stored in the memory 1348 is calculated.
It is output to the control unit 1338 as d. In addition, the amplitude comparison circuit 130
Stores the amplitude of the S-curve of the focus error signal in the memory 1348 according to the timing detected by the peak timing detection circuit 131, and determines which of the amplitude of the S-curve corresponding to layer 0 # 210 and the amplitude of layer 1 # 220. Determine how big it is.

Next, FIG. 9 is a flow chart showing a procedure for pulling in the focus by the optical disk device of FIG.

First, the switches a129, b128, and c127 are all grounded. When the optical disc 100 having two recording layers of layer 0 # 210 and layer 1 # 220 is loaded, the control unit 1338 controls the motor driver 111 to rotate the spindle motor 102 (step 101). Here, it is assumed that the optical disc 100 has a nominal value of the protective layer 203 of 0.1 mm, and the layer distance D between the layer 0 # 210 and the layer 1 # 220 is unknown. Next, after moving the optical pickup head 1000 to a predetermined position on the inner peripheral side by a carriage (not shown), the control unit 1338 sets the LD driver.
Control LD 112 to cause LD 105 to emit light at playback power (step 10
2). Then, the inserted optical disc 100 is discriminated by an optical disc discriminating mechanism (not shown) (step 103). Here, since the inserted optical disc 100 is an optical disc having a plurality of recording layers, the control unit 1338 determines the layer to be accessed (step 104). Here, the control unit 1338 always specifies layer 0. Control unit 1338 is memory 1
The aberration correction amount initial setting value when pulling the focus to the layer 0 # 210 from 348 is read, the offset applying circuit 116 is controlled according to the value, and the spherical aberration adding mechanism 104 is driven (step 105). The initial value of the aberration correction amount is the nominal value of the film thickness of the protective layer 203 of the optical disc 100, and in this embodiment, the protective layer thickness is 0.1 mm, that is, the layer 0 # 210 is focused when the distance l = 0.1 mm. It is a value calculated so that spherical aberration is minimized.

If the optical disc inserted in step 103 is an optical disc having one recording layer, the memory 1
The aberration correction amount initial setting value is read from 348, the offset applying circuit 116 is controlled according to the value, and the steer described later
Go to p114. The aberration correction amount initial setting value in this case is, for example, a digital value indicating the above-described offset voltage. For example, if the nominal value of the film thickness of the protective layer 203 of the optical disc 100 is 0.1 mm, for example, the spherical aberration adding mechanism is such that the spherical aberration is minimized when the distance l = 0.1 mm is focused. It is an initial setting offset voltage value that controls 104.

Next, the control unit 1338 switches the switch b128 to supply the sweep signal to the focus driver 113 (step
107). The focus driver 113 drives the focus actuator 108 in the focus direction according to the sweep signal. At this time, the focus error signal is layer 0 # 210
And S-curve occurs at the position corresponding to layer 1 # 220. Also, the playback signal is layer 0 # 210 and layer 1 # 220
Peaks are generated at the corresponding positions. The peak timing detection circuit 131 checks whether or not the polarity of the focus sweep signal has been inverted (step 108), and starts the detection from the moment when it switches to the increasing direction. At this time, the objective lens 103 is moving toward the disk surface of the optical disk 100, and the focus of the laser beam is also moving in the same direction. Therefore, the first detected peak indicates that the focus has moved to the position of layer 0 # 210. Also, the next detected peak indicates that the focus has moved to the position of Layer 1 # 220. At this time, the peak interval detection circuit 132 detects the voltage difference of the sweep signal when these two peaks occur. The coefficient representing the relationship between the voltage difference of the sweep voltage and the moving distance of the focus actuator 108 of the objective lens 103 is predetermined according to the drive sensitivity of the focus actuator 108 and is recorded in the memory 1348. From this coefficient and the detected voltage difference, the distance D between Layer 0 # 210 and Layer 1 # 220
To decide. Further, at the same time as detecting the peak interval, the amplitude comparison circuit 130 that compares the amplitudes of the S-shaped curves is
S-curve amplitude at 10 and S at Layer 1 # 220
Compare the amplitudes of the curved curves and detect the difference in amplitude and the magnitude (s
tep109).

Here, although not shown in the flow chart, if the peak does not appear twice before the polarity of the sweep signal is switched, the control unit 1338 judges this and returns to disc judgment again, or An offset is given to the sweep signal, the objective lens 103 is brought closer to the optical disc 100, and the sweep is performed again.

From the above operation, the thickness of the protective layer is exactly 0.
It is 1 mm, and if there is no error in the initial value of the spherical aberration addition amount, the amplitude of the S-curve in layer 0 # 210 should be sufficiently larger than that in layer 1 # 220. However, it is conceivable that the layer 0 # 210 does not exist at the position of Z = 0.1 mm due to the thickness unevenness of the protective layer 203, or that l = 0.1 mm cannot be set due to an error in the initial setting value.

When the result of comparing the amplitude difference between the two S-shaped curves is less than or equal to the predetermined allowable amplitude difference (ste
p110), that is, when the distance 1 is within the range C shown in FIG. 5B, the control unit 1338 controls the offset applying circuit 116 to adjust the spherical aberration addition amount. Here, the allowable amplitude difference is 1/3 of the maximum amplitude difference as shown in the range C of FIG. 5 (b).
At this time, if the relationship between the amplitude difference and the thickness error of the protective layer 203 is almost linear as shown in FIG. 5, it can be seen that the thickness error with respect to 1/3 of the maximum amplitude difference is D / 3 at the maximum. When focusing on layer 0 # 210, it is desirable that the spherical aberration be the smallest when focused in the vicinity of position a in Fig. 3 (a), so the amount of spherical aberration newly added at this time When converted to an error in the thickness of the protective layer 203, does not exceed the layer interval D, so if D or less, between D / 3 and 2D / 3,
The polarity is such that the distance l becomes shorter. In this way, the spherical aberration distance l is set to be shorter by a predetermined amount, and it is checked again whether the polarity of the sweep signal is inverted (step 112). However, since a difference in amplitude can be obtained even if the value is larger than this, a margin may be taken to set D / 3 to D.

Next, in step 110, when the amplitude difference between the two S-shaped curves exceeds a predetermined allowable amplitude difference, and further, the amplitude of layer 1 # 220 is larger than that of layer 0 # 210. That is, when the distance 1 is considered to be within the range B in FIG. 5 (step 111), the control unit 1338 controls the offset applying circuit 116 to adjust the spherical aberration addition amount. At this time, in order to perform focus pull-in from the range B to the layer 0 # 210, the amount of spherical aberration newly added is converted into an error in the thickness of the protective layer 203, and the polarity is between 2D / 3 and 2D. The distance l is set shorter by a predetermined amount, and it is checked again whether the polarity of the sweep signal is reversed (step 113). As a result, by adding -2 / 3D to -2D to the already added 1 / 3D aberration, the range from -1 / 3D to -D-2 / 3D
It is possible to bring the focus S-shaped amplitude and the peak difference of the focus S-shaped curve to A. For this reason, layer 0 # 21
If you try to focus on 0, layer 0
1 / 2D or less between # 210 and Layer 1 # 220 in the direction toward Layer 0 # 210, and a layer in the direction near Layer 0 # 210 except between Layer 0 # 210 and Layer 1 # 220 Interval D
In the following range, it is possible to pull the focus S-curve amplitude larger than the allowable minimum amplitude and the peak difference of the focus S-curve in the layer 0 # 210 into a range larger than the allowable minimum difference.

When the difference between the amplitudes of the two S-shaped curves exceeds a predetermined allowable amplitude difference and the amplitude of layer 0 # 210 is larger than that of layer 1 # 220, that is, FIG. If the distance l is within the range A, the control unit 1338 does not newly apply the offset and moves to the next focus pull-in step.

In the focus pull-in step (step 114), the control unit 1338 functions as a peak detecting means of the reproduction signal and a zero cross detecting means of the focus error signal. Sweep circuit 135 to bring focus to layer 0 # 210
The control unit 1338 starts the peak detection of the reproduction signal and the zero-cross detection of the focus error signal from the moment the polarity of is switched to the plus (increasing) direction. If the focus error zero cross is detected while the first peak is occurring, the controller 1338 switches the switch b128 to switch the sweep circuit.
Reconnect from 135 to the output of phase compensation circuit c126. At this time, the output of the phase compensation circuit c126 is the focus driver.
It is supplied to 113 and focus pulling is completed (step
114).

The steps after step 114 are the steps in FIG.
Since it is the same as 308-312, it is omitted. Also in FIG. 8, as in FIG. 1, focus jump between layers in FIG. 7 can be performed.

Further, although the peak is detected from the reproduction signal in this embodiment, it is also possible to detect the peak using the focus error signal.

Further, another first procedure for pulling in the focus by the optical disk device in FIG. 8 will be described with reference to the flowchart.

FIG. 10 is a flowchart showing a first procedure of another focus pull-in by the optical disk device in FIG. The characteristic point in FIG. 10 is that the spherical aberration correction is performed before the focus is pulled in, and the spherical aberration correction is optimized again after the focus is located on the target layer.

In this embodiment, the optical disc 100
Although the nominal value of the film thickness of the protective layer 203 is 0.1 mm, it is assumed that the actual thickness deviates from the nominal value due to manufacturing accuracy and the like. After steps 101 and 102, which are the same as those in the flowchart of FIG. 9, the control unit 1338 reads from the memory 1348 the aberration correction amount initial setting value when pulling the focus, controls the offset applying circuit 116 according to the value, and controls the spherical aberration adding mechanism. Drive 104 (step 1003). Next, the spherical aberration addition amount optimization operation is performed to optimize the spherical aberration correction amount and reset (step 1004). The optimum operation of the spherical aberration addition amount will be described later. When the spherical aberration addition amount is reset to the optimum value, the control unit 1338 sets the switch b128 to the phase compensation circuit c126.
The focus pull-in operation is performed by switching to the output signal from (4) and the focus is pulled into the target recording layer, Layer 0 # 210 (step 1005). Next, the control unit 1338 uses the switch c127.
Is switched to the output signal from the phase compensation circuit b125 to perform tracking pull-in (step 1006). Furthermore, the control unit 1338
Switches the switch a129 to the output signal from the phase compensation circuit a124 and operates the spherical aberration adding mechanism 104 based on the spherical aberration error signal from the information of the reproduction signal to perform pull-in (st
ep407). Then, finally, the preformat signal of the optical disc 100 is reproduced, and when the desired reproduction signal is obtained, the focus pull-in is completed (step 1008).

In this embodiment, the initial value of the aberration correction amount is the nominal value of the film thickness of the protective layer 203 of the optical disc 100.
It is desirable that the value be calculated so that the spherical aberration when focusing on the recording layer, Layer 0 # 210, when the thickness is 0.1 mm is minimized. However, if there is a reset step of step 1004, it is not always necessary to set or read the initial value. If there is no reset step in step 1004, it is necessary to accurately correct the spherical aberration with the initial setting value in step 1003.

In the above description, the "optimizing operation" of the spherical aberration addition amount is, for example, the following operation. Figure
The offset voltage of the offset application circuit 116 of 8 is changed in a predetermined step, the focus S-shaped amplitude is detected at the timing detected by the peak timing detection circuit 131, and the result is stored in the memory 1348.
The stored value is updated each time the offset voltage changes by one step, and the previously stored value and the detected amplitude are compared with the amplitude comparison circuit 130.
The offset voltage at which the S-shaped amplitude is maximized is detected by making a comparison with, and this value is set in the offset applying circuit 116 as the optimum offset voltage. When the optical disc 100 has a plurality of recording layers, the S-shaped amplitude of the recording layer (layer) desired to be focused is recorded and compared, and the optimum offset voltage may be detected and set.

Then, according to the present embodiment, spherical aberration is imparted before focus pull-in and after focus pull-in. Therefore, by giving the spherical aberration before the focus pull-in, the focus S-shape has a sufficient amplitude, and the focus pull-in is surely performed. Further, after the focus is pulled in, the spherical aberration addition amount is optimized from the information obtained from the reproduction signal, so that a more accurate reproduction signal can be obtained.

Further, another second procedure for pulling in the focus by the optical disk device in FIG. 8 will be described with reference to the flowchart.

FIG. 11 is a flowchart showing a second procedure for pulling in another focus by the optical disk device in FIG. The characteristic point in FIG. 11 is that the spherical aberration correction addition amount is learned and obtained before focus pull-in, and this is stored in the memory 1348.

In this embodiment, the optical disc 100
Although the nominal value of the film thickness of the protective layer 203 is 0.1 mm, it is assumed that the actual thickness deviates from the nominal value due to manufacturing accuracy and the like. After steps 101 and 102, which are the same as those in the flowchart of FIG. 9, and after steps 1003 and 1004, which are the same as those in FIG. 10, the value set in step 1004 is stored in the memory 1348 as a learning result (step 110).
Five). After that, the same steps 1005 to 1008 as in FIG. 10 are performed.

In FIG. 11, the optimum value of the spherical aberration addition amount recorded in the memory 1348 is held unless the optical disk 100 is removed from the optical disk device. And
When the re-focusing occurs, the value is used as the spherical aberration correction amount initial setting value. Therefore, in this case, the focus pull-in operation can be performed without performing the optimization operation.

According to the present embodiment, the learning operation, that is, the operation of holding the optimized spherical aberration correction amount in the memory 1348 is performed, and this value is used as the spherical aberration correction amount initial setting value unless the optical disc 100 is replaced. Therefore, when it becomes necessary to perform re-focusing or focus jumping, it is possible to always perform stable focusing without performing the optimizing operation again.

[0100]

As described above, according to the optical disk device and the focus control method of the present invention, the focus of the condensed light beam can be easily focused on the desired information recording layer.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical disc device according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of an objective lens 103, a spherical aberration adding mechanism 104, and an optical disc 100.

FIG. 3 is a diagram showing a relationship between a sectional view of the optical disc 100, a spherical aberration amount, and a focus error signal.

FIG. 4 is a diagram showing a relationship between a spherical aberration amount and a focus error signal when a laser beam having a spherical aberration different from that in FIG. 3 is incident on the optical disc 100.

FIG. 5 is a diagram showing the amount of change in the amplitude of the focus S-shaped signals of layers 0 and 1 and the amplitude difference of the S-shaped curves in each layer when the optimum spherical aberration position is moved in the Z direction.

FIG. 6 is a flowchart showing a procedure for pulling in a focus.

FIG. 7 is a flowchart of focus jump between layers.

FIG. 8 is a block diagram of an optical disc device according to a second embodiment of the present invention.

9 is a flowchart showing a procedure of focus pull-in by the optical disc device in FIG.

10 is a flowchart showing a first procedure of another focus pull-in by the optical disk device in FIG.

11 is a flowchart showing a second procedure of another focus pull-in by the optical disk device in FIG.

[Explanation of symbols]

100 ... Optical disc 101 ... Clamper 102 ... Spindle motor 103 ... Objective lens 104… Spherical aberration adding mechanism 105 ... Semiconductor laser (LD) 106… Split detector (PD) a 107… Split detector (PD) b 108 ... Focus actuator 109 ... Tracking actuator 110 ... Spherical aberration addition actuator 111 ... Motor driver 112 ... LD driver 113 ... Focus driver 115 ... Spherical aberration addition mechanism driver 116 ... Offset applied circuit 117… Spherical aberration error (AE) generation circuit 118 ... Focus error (FE) signal generation circuit 119 ... Tracking error (TE) signal generation circuit 120 ... Playback signal processing circuit 121 ... Amplifying circuit a 122 ... Amplifying circuit b 123 ... Amplifying circuit c 124 ... Phase compensation circuit a 125 ... Phase compensation circuit b 126 ... Phase compensation circuit c 127… switch c 128… Switch b 129 ... Switch a 130 ... Amplitude comparison circuit 131… Peak timing detection circuit 132… Peak interval detection circuit 133, 1338 ... Control unit 134, 1348 ... Memory 135 ... Sweep circuit 136 ... Focus jump signal generation circuit 201 ... Substrate 202 ... Middle class 203… Protective layer 210 ... Layer 0 (recording layer) 220 ... Layer 1 (recording layer) 1000 ... Optical pickup 1010 ... Sending optical system 1020 ... Receiving optical system

Continued front page    F-term (reference) 5D118 AA13 BA01 CA11 CB03 CD02                       DA12 DA40                 5D119 AA28 BA01 EA03 EB20 EC01                       JA49                 5D789 AA28 BA01 EA03 EB20 EC01                       JA49

Claims (13)

[Claims] 1. An optical disc apparatus for reproducing information by irradiating an optical disc having an information recording layer for recording information with a light beam focused on the information recording layer, Focusing means for performing focusing so that the light beam is positioned on the information recording layer, spherical aberration giving means for giving spherical aberration to the light beam, and focus of the light beam by the focusing means for the information recording An optical disc device comprising: a control unit that controls the spherical aberration imparting unit to impart the spherical aberration before the layer is positioned on the layer. 2. A focus error amplitude amount detecting means for detecting the amplitude amount of the focus error signal by the focusing means is provided, and the focusing means functions based on the amplitude amount of the focus error signal in the control means. So that the amplitude amount of the focus error signal becomes large to the extent that
2. The optical disk device according to claim 1, wherein the amount of spherical aberration applied by the spherical aberration applying means is determined. 3. The storage means for storing the spherical aberration application amount provided by the spherical aberration application means is provided, and the spherical aberration amount determined by the control means is stored in the storage means. Item 2. The optical disk device according to item 2. 4. An optical disc device for reproducing information by irradiating an optical disc having two information recording layers for recording information with a light beam focused on the information recording layer, Focusing means for focusing based on a focus error signal so that the focus of the emitted light beam is located on the information recording layer; spherical aberration imparting means for imparting spherical aberration to the light beam; and the focusing By means of means, peak timing detection means for detecting the timing of the peak of the signal based on the reflected light from each layer of the information recording layer obtained by moving the focus of the light beam in the depth direction of the information recording layer, A focus for detecting the amplitude amount of the focus error signal by the focusing means at the appearance timing. Focus error signal in the information recording layer for performing the focusing based on the comparison result of the comparison means for comparing the detected error amounts of the focus error signals of the respective information recording layers So that the amplitude amount of is larger than that of the other information recording layer,
After giving spherical aberration by the spherical aberration giving means,
An optical disc device comprising: a control unit that controls to perform focusing by the focusing unit. 5. An appearance interval storing means for storing appearance intervals of peaks in each of the information recording layers detected by the peak timing detecting means, and the appearance intervals based on the appearance intervals stored in the appearance interval storing means. Spherical aberration imparting amount determining means for determining the spherical aberration imparting amount to the spherical aberration imparting means, and control for performing focusing by the focusing means after imparting the spherical aberration imparting amount determined by the spherical aberration imparting amount determining means 5. The optical disc device according to claim 4, further comprising: 6. An optical disc device for reproducing information by irradiating an optical disc having two information recording layers for recording information with a light beam focused on the information recording layer, Focusing means for focusing based on a focus error signal so that the focus of the emitted light beam is located on the information recording layer; spherical aberration imparting means for imparting spherical aberration to the light beam; and the spherical surface. A control means for controlling the timing of giving the spherical aberration by the aberration giving means, wherein one of the information recording layers has a focus of the light beam, and when the focus is moved to the other of the information recording layers, Before focusing on the other side of the information recording layer by the control means, the focus aberration of the other side of the information recording layer is controlled by the spherical aberration imparting means. Optical disc apparatus characterized by performing the application of the spherical aberration to increase the amplitude of the signal to the extent that the focusing means to function. 7. A minimum position of spherical aberration in the control means is within a range of 3/2 of a layer interval between the information recording layers from an intermediate point between the two information recording layers including the information recording layer for focusing. 5. The spherical aberration imparting amount is controlled so that the spherical aberration is located at the position.
The optical disk device described. 8. A focus control method for focusing on an optical disc having an information recording layer for recording information such that the focus of a focused light beam is located on the information recording layer. Before focusing so that the focused light beam is located in the layer, spherical aberration is applied to the focused light beam so as to increase the amplitude of a focus error signal generated when the focus of the focused light beam passes through the information recording layer. A focus control method comprising the step of giving. 9. A focus control method for focusing on an optical disc having an information recording layer for recording information such that the focus of a focused light beam is located on the desired information recording layer, A first step of detecting the amplitude of a focus error signal generated when the focus of the focused light beam passes through the information recording layer; a second step of imparting spherical aberration to the focused light beam; Repeating the first step and the second step, a third step of ending the repetition when the amplitude of the focus error signal becomes equal to or larger than a desired magnitude, and after the third step, A fourth step of focusing the focus of the condensed light beam so as to be positioned on the information recording layer. 10. After the completion of the third step, a fifth step of storing information indicating a spherical aberration amount given to the condensed light beam, and a fourth step for the optical disc are performed a plurality of times. When performing, based on the information indicating the stored spherical aberration amount,
10. The focus control method according to claim 9, further comprising a sixth step of imparting spherical aberration to the condensed light beam, and performing the fourth step after the sixth step. 11. A focus control method for selectively focusing on an optical disc having two information recording layers for recording information so that the focus of a focused light beam is located on the desired information recording layer. A first step of detecting an amplitude of a focus error signal generated when the focus of the focused light beam passes through the two information recording layers; and a focus error generated in the two information recording layers. A second step of comparing the amplitudes of the signals, and based on the result of the comparison, the amplitude of the focus error signal of the selected information recording layer is larger than the amplitude of the focus error signal of the other information recording layer. To
Third step of imparting spherical aberration to the condensed light beam, and fourth step of focusing the focal point of the condensed light beam so as to be positioned on the selected information recording layer after the imparting of the spherical aberration. A focus control method comprising: 12. Before the third step, the method further comprises a fifth step of storing an appearance interval of the focus error signal generated when the information recording layer is passed, and based on the stored appearance interval, The focus control method according to claim 11, wherein the amount of spherical aberration given at one time is determined in the third step. 13. A focus control method for focusing on an optical disc having two information recording layers for recording information such that the focus of a focused light beam is located on the information recording layer, Before focusing on the other side of the information recording layer, when the focus of the light beam is focused on one side of the information recording layer, the focus is moved to the other side of the information recording layer. A focus control method, comprising the step of imparting spherical aberration so that the amplitude of the focus error signal in (3) becomes large enough to perform focusing.