KR20050016276A - Optical recording/reproduction device and focal point control method - Google Patents

Abstract

An optical recording / reproducing apparatus capable of realizing reliable focusing control to a recording layer as a target of a single-layer disc or a multi-layer disc. When the focusing control is performed on the target information recording layer in the recording medium, first, the recording medium is set to a state in accordance with the thickness of the light transmission protective layer (cover layer) in the information recording layer for the purpose of the spherical aberration correction state. Or it is set in the state which matched the average value of the thickness of each light transmission protective layer (cover layer) of a some information recording layer. Then, a focus servo operation for moving the objective lens in the optical axis direction is performed, and focusing is performed by observing the polarity of the focus control error signal and the level of the reflected light intensity signal generated as the reflected light information.

Description

Optical recorder and focus control method {OPTICAL RECORDING / REPRODUCTION DEVICE AND FOCAL POINT CONTROL METHOD}

The present invention relates to an optical recording and reproducing apparatus and a focus control method thereof.

First, the reference document referred in the following description is shown.

Reference (1): S. Kubota, “Aplanatic condition required to reproduce jitter-free signals in optical disk system,” Appl. 0pt. Vo1.26, pp. 3961-3973 (1987)

Reference (2): I. Ichimura, F. Maeda, K. Osato, K. Yamamoto, and Y. Kasami, “Optical disk recording using a GaN blue-violet laser diode,” Jpn. J. App1. Phys.Vol. .39, pp. 937-942 (1999)

Reference (3): M. Itonaga, F. Ito, K. Matsuzaki, S. Chaen, K. 0ishi, T. Ueno, and A. Nishizawa, “NA = 0.85 single objective lens for a high density optical disk system, '' Digest of International Symposium on Optica1 memory, Taipei, pp. 26-27 (2001)

Reference (4): T. Ariyoshi, T. Shimano, and K. Maruyama “0.85-NA sigle-objective lens using aberration-compensation methods," Digest of Internation a1 Symposium on 0ptical memory, Taipei, pp. 268-269 (2001 ).

(5): S. Ohtaki, N. Murao, M. Ogasawara, and M. Iwasaki, “The application of a liquid crystal panel for the 15 Gbyte optical disk systems,” Jpn. J. App1. Phys. 38, pp. 1744-1749 (1999)

(6): M. Iwasaki, M. Ogasawara, and S. Ohtaki, “A new liquid crystal panel for spherical aberration compensation,” Digest of Optical Data Storage Topical Meeting, SPIE 4342, pp. 103-105 (2001).

(7): K. Osato, I. Ichimura, F. Maeda, K. Yamamoto, and Y. Kasami, “Progress in optical disk recording with over 20 GB of capacity,” Tech. Digest of Optical Data Storage Topical meeting, Whistler, pp. 15-17 (2000))

(8): T. Shimano, M. Umeda, and T. Ariyoshi, “Spherical aberration detection in the optical pickups for high-density digital versatile discs," Jpn. J. Appl. Phys. 40, pp. 2292- 2295 (2001)

As a technique for recording and reproducing digital data, for example, an optical disk (including a magneto-optical disk) such as a compact disk (CD), a mini-disk (MD), a digital versatile disk (DVD), or the like as a recording medium. There is a data recording technique used. An optical disc is a general term for the recording medium which irradiates a laser beam to the disk which protected the metal thin film with the plastic, and reads out a signal by the change of the reflected light.

Optical discs may be, for example, CDs, CD-ROMs, DVD-ROMs, or the like dedicated to playback; MD, CD-R, CD-RW, DVD-R, DVD-RW, DVD + RW, DVD There is a type in which user data can be recorded, as is known as RAM.

As the recordable type, a magneto-optical recording method, a phase change recording method, a dye film change recording method and the like are used, and data can be recorded. The dye film change recording method is also referred to as a write once recording method, and since data can be written only once and cannot be rewritten, it is suitable for data storage applications. On the other hand, the magneto-optical recording method and the phase change recording method are capable of rewriting data and are used for various purposes including recording of various content data such as music, video, games, and application programs.

In addition, in recent years, a high density optical disc called DVR (Data & Video Recording) has been developed, and a significant capacity is being increased.

For example, in an optical recording / reproducing apparatus represented by a disk drive apparatus for recording and reproducing these optical disks, the spot size Φ on the recording medium is a wavelength of laser light, and the numerical aperture of the objective lens is NA. In general, it is given by the following formula (1).

Φ = λ / NA Equation (1)

In other words, the shorter the wavelength of the light source and the larger the numerical aperture of the objective lens, the smaller the value of the spot size Φ, and the higher density recording becomes possible.

The objective lens used in the optical recording / reproducing apparatus is generally designed so that the wave front aberration is minimized with respect to a specific light transmission protective layer (cover layer) of a recording medium such as a disk. For example, in a CD drive apparatus, the cover layer thickness of CD is optimized with respect to 1.2 mm, and in a DVD drive apparatus, it is optimized with respect to the cover layer thickness of 0.6 mm of DVD.

In the DVD drive apparatus for a DVD having a two-layer structure as an information recording layer, the numerical aperture of the objective lens is 0.6, and a red semiconductor laser having a wavelength of 650 nm is used as the light source.

Tolerance of the objective lens with respect to the different cover layer thicknesses is given by reference (1) by the following formula (2), with the thickness variation of the cover layer being Δt and the refractive index of n.

Formula (2)

As an example, when the value of the allowable spherical aberration W4O is λ / 4, the allowable variation Δt of the thickness of the cover layer in the DVD drive device is ± 27 μm. In the case of the two-layer disc realized in the DVD drive apparatus, the space between the information recording layers is defined to be about 40 m, and is considered to fall within the allowable value.

On the other hand, as a large-capacity optical disk drive apparatus realized by shortening the wavelength of the light source and high numerical aperture of the objective lens, in Reference Document (2), a DVD-sized optical disk using a group II lens with a numerical aperture of 0.85 and a blue violet semiconductor laser is used. A method for realizing a capacity over 22 Gbytes has been proposed.

Moreover, in recent years, the method of changing to the structure of a 2nd-group lens, the objective lens of 0.85 is realized by a single lens, and the method which ensures the larger working distance (Workfng Distance) compared with a 2nd-group lens is also proposed. (Reference (3), Reference (4)).

In the optical disc drive device described in References (2) to (4), it is necessary to set the accuracy of the cover layer thickness to ± 4 μm or less from the above formula (2).

In the optical disc drive device described in Reference (2) using a high numerical aperture lens, when realizing a two-layer disc similar to the DVD drive device, the interlayer distance is secured about 20 μm in order to prevent interlayer interference of the information signal. It is necessary to do so and does not fall within the allowable range of the cover layer thickness (± 4 μm).

Therefore, as disclosed in, for example, Japanese Patent Laid-Open No. 2000-131603, in order to correspond to different cover layer thicknesses for a plurality of recording layers, a method of correcting spherical aberration by an expander lens has been proposed and a more effective correction method. As a method, a method of using a liquid crystal element has also been reported (references (5) and references (6)).

However, when the setting value of the spherical aberration correction method represented by the expander lens or the liquid crystal element is different from the appropriate value for the cover layer thickness of the target information recording layer, the optical focus control error signal is caused by the generated spherical aberration. There is a fear that it may not generate, and it may cause a problem in the focusing.

In particular, when focus control is performed on an optical recording medium having two or more information recording layers, it is essential to optimize spherical aberration correction for each target information recording layer.

Therefore, in order to perform access to a specific information recording layer in a multilayer optical recording medium using a high numerical aperture objective lens such as NA = 0.85, a suitable method for focusing the focusing spot of laser light is provided. It is required.

In the actual optical recording / reproducing apparatus, it is assumed that the case where the recording medium having a single information recording layer is loaded and the case where the recording mediums of a plurality of information recording layers are loaded are mixed. In this case, it is necessary to determine the number of layers of the information recording layer in advance and to perform the pulling-in operation with respect to the desired information recording layer.

For example, when a recording medium such as a disk is loaded in a cartridge or the like, the number of layers of the information recording layer is determined by reading the presence or absence of a detection hole for determining the type provided in the cartridge by a mechanical or optical method. Although one may also be considered, when a disk or the like that does not require a cartridge is assumed, a discriminating method is required separately.

1 is an explanatory diagram of a layer structure of a disc to be recorded and reproduced in the embodiment of the present invention.

2 is an explanatory diagram of a structure of the objective lens of the embodiment.

3 is an explanatory view of the structure of the optical system of the embodiment.

4 is an explanatory diagram of an electrode pattern of the liquid crystal element of the embodiment.

5 is an explanatory diagram of a wavefront approximately equivalent to the spherical aberration correction amount of the embodiment.

6 is an explanatory diagram of a light receiving pattern of the light receiving element of the embodiment.

7 is a block diagram of the recording and reproducing apparatus of the embodiment.

8A to 8B are explanatory diagrams of a focus control error signal obtained by moving the objective lens of the embodiment.

9 is an explanatory diagram of a light reception state of a focus control error signal in the astigmatism method in the light receiving element of the embodiment.

10 is an explanatory diagram of operation waveforms of a two-layer disk of the first focusing control method of the embodiment.

11 is an explanatory diagram of an operation waveform of a tomographic disk of the first focusing control method of the embodiment.

12 is a flowchart of processing of the first focusing control method of the embodiment.

Fig. 13 is an explanatory diagram of an operation waveform when L1 layer is focused in the second focusing control method of the embodiment;

14 is a flowchart of processing at the time of L1 layer focusing of the second focusing control method of the embodiment.

15 is an explanatory diagram of an operation waveform when L0 layer is focused in the second focusing control method of the embodiment;

Fig. 16 is a flowchart of processing at the time of focusing L0 layer of the second focusing control method of the embodiment.

17 is a flowchart of processing of the third focusing control method of the embodiment.

In view of these circumstances, an object of the present invention is to enable appropriate focusing control of an information recording layer of a single layer or a plurality of recording media, and particularly when a high numerical aperture objective lens is used for a large capacity disk or the like. Etc., a preferred method is provided.

Therefore, the optical recording and reproducing apparatus of the present invention is an optical recording and reproducing apparatus for recording or reproducing information by irradiating a laser beam to a recording medium having a single or a plurality of information recording layers. Objective lens means provided as an output end of light, correction optical means for correcting spherical aberration caused by the thickness of the light transmitting protective layer (cover layer) with respect to the information recording layer of the recording medium, and conveying the objective lens means in the optical axis direction Conveying means for detecting, reflected light detecting means for detecting the reflected light from the recording medium by the laser light irradiation, and outputting the reflected light information, polarity of the focus control error signal (focus error signal) generated as the reflected light information, and the reflected light Discriminating means for discriminating the level of the reflected light intensity signal generated as the information, and the correction optical Focusing control for moving the objective lens means in the optical axis direction by the conveying means and setting focus in accordance with the discrimination information by the discriminating means while the means is set to be optimal for the thickness of the specific light transmissive protective layer. Means.

In this case, the objective lens means has a numerical aperture of 0.8 or more.

Moreover, the said discriminating means outputs the comparison result of each threshold value of a positive predetermined level, a negative predetermined level, and the said focus control error signal as polarity information of the said focus control error signal.

The focusing control means focuses on the target information recording layer according to the moving direction of the objective lens means by the transfer means and the generation order of the polarity information of the focus control error signal obtained by the discriminating means. Is done.

The focusing control means further comprises a target information recording layer in accordance with the movement direction of the objective lens means by the transfer means and the generation order and the number of occurrences of the polarity information of the focus control error signal obtained by the determination means. Perform focus in for.

The focusing control means sets the correction optical means by setting the average value of the thicknesses of the light transmission protective layers to the plurality of information recording layers of the recording medium as the thickness of the specific light transmission protection layer.

Alternatively, the focusing control means comprises the correction optical, wherein the thickness of the light transmission protective layer with respect to the information recording layer which is the target of focal drawing among the plurality of information recording layers of the recording medium is the thickness of the specific light transmission protection layer. The means is set.

Further, in the case where the focus is introduced into a certain information recording layer to a recording medium having a plurality of information recording layers and then the focus is introduced into another information recording layer, the focusing control means is configured to specify the correction optical means for light transmission. In the state set to be optimal with respect to the thickness of the protective layer, the objective lens means is moved in the optical axis direction by the conveying means, and the focus is introduced into the other information recording layer in accordance with the discrimination information by the discriminating means. .

At this time, the focusing control means sets the correction optical means by setting the thickness of the light transmissive protective layer to the other information recording layer as the thickness of the specific light transmissive protective layer.

Alternatively, the focusing control means sets the correction optical means by setting the average value of the thicknesses of the light transmission protective layers with respect to the information recording layer and the other information recording layer as the thickness of the specific light transmission protection layer. Is done.

Further, after focusing on the target information recording layer, an optimization means for optimizing the correction amount by the correction optical means according to the reproduction signal as the reflected light information or the spherical aberration error signal as the reflected light information is added. To be equipped with.

The focus control method of the present invention is an optical recording and reproducing apparatus for recording or reproducing information by irradiating a laser beam to a recording medium having a single or a plurality of information recording layers. A focus control method to be performed, wherein the correction optical portion for correcting spherical aberration caused by the thickness of the light transmissive protective layer with respect to the information recording layer of the recording medium is set to be optimal for the thickness of the specific light transmissive protective layer, and the predetermined opening The polarity of the focus control error signal obtained as the reflected light information from the recording medium by the laser light irradiation and the level of the reflected light intensity signal generated as the reflected light information while moving the objective lens provided with the number as an output end of the laser light in the optical axis direction The discrimination process obtained by the discrimination process It is carried out along the focus lead-in.

In this case, the objective lens has a numerical aperture of 0.8 or more.

In addition, the determination process of the polarity of the focus control error signal compares each of the threshold values of the positive predetermined level and the negative predetermined level with the focus control error signal, and compares the result of the determination of the polarity of the focus control error signal. It is information.

Further, focusing on the target information recording layer is performed in accordance with the moving direction of the objective lens and the generation order of the polarity information of the focus control error signal obtained by the determination processing.

Further, the focal lead-in to the target information recording layer is performed in accordance with the movement direction of the objective lens and the generation order and the number of occurrences of the polarity information of the focus control error signal obtained by the determination processing.

In addition, the correction optical unit is set with an approximately average value of the thicknesses of the light transmissive protective layers for the plurality of information recording layers of the recording medium as the thickness of the specific light transmissive protective layer.

Alternatively, the correction optical unit is set by setting the thickness of the light transmission protective layer with respect to the information recording layer which is the target of focal drawing among the plurality of information recording layers of the recording medium as the thickness of the specific light transmission protection layer.

When focusing in a certain information recording layer to a recording medium having a plurality of information recording layers and then focusing in another information recording layer, the correcting optical part is optimized for a specific light transmission protective layer thickness. In the set state, the objective lens is moved in the optical axis direction, and processing for discriminating the polarity of the focus control error signal obtained as the reflected light information from the recording medium by laser light irradiation and the level of the reflected light intensity signal generated as the reflected light information is performed. Then, focus in is performed on the other information recording layer in accordance with the discrimination information obtained by the discrimination process.

At this time, the correction optical unit is set by setting the thickness of the light transmission protective layer with respect to the other information recording layer as the thickness of the specific light transmission protection layer.

Or the said correction optical part is set by making the approximate average value of the thickness of each light transmission protective layer with respect to the said one information recording layer and the said other information recording layer the thickness of the said specific light transmission protective layer.

In addition, after focusing is performed on the target information recording layer, the amount of correction by the correction optical unit is optimized according to the reproduction signal as the reflected light information or the spherical aberration error signal as the reflected light information.

That is, according to the present invention, when the focusing control is performed on the information recording layer of interest in the recording medium, first, the thickness of the light transmission protective layer (cover layer) in the information recording layer for the purpose of the spherical aberration correction state is Set to the correct state. Or it is set in the state which matched the average value of the thickness of each light transmission protective layer (cover layer) of a some information recording layer.

Then, a so-called focus search operation for moving the objective lens in the optical axis direction is performed, and then the focus is input by observing the polarity of the focus control error signal and the level of the reflected light intensity signal generated as the reflected light information.

As the focus control error signal, an S-shaped curve is obtained when the focus position passes through the information recording layer by the movement in the optical axis direction of the objective lens. Therefore, since the polarity of the focus control error signal is detected, it is possible to detect the number of layers of the information recording layer and the entry timing of the target information recording layer.

In addition, when focus search is performed in a state in which the light transmissive protective layer (cover layer) of the plurality of information recording layers is set to an average value, the S-shape at the same level as the focus control error signal passes through each information recording layer. Since the curve is detected, the insertion timing in the target information recording layer can be detected in accordance with the generation order of the polarity in the moving direction. The number of layers of the information recording layer can also be detected in accordance with the number of occurrences of the S-curve.

If the focus search is performed in a state that is set in accordance with the thickness of the light transmission protective layer (cover layer) in the information recording layer for the purpose of spherical aberration correction state, a large S-shape at the time of passing the target information recording layer Since the curve is detected, the insertion timing in the target information recording layer can be detected accurately by the polarity detection.

Embodiments of the present invention will be described in the following order.

1.Layer structure of disk

2. Configuration of the recording / playback device

3. Spherical Aberration Correction State and S-curve

4. First Focusing Control Method

5. Second Focusing Control Method

6. Third focusing control method

7. Optimization after Focus Control

1.Layer structure of disk

First, a single-layer disc and a two-layer disc will be described as discs recorded and reproduced by the recording / reproducing apparatus of the embodiment.

The disk of this example is of the category as a high-density disk such as a DVR developed in recent years, and has a cover layer (light transmissive protective layer: sub straight) of 0.1 mm in the disk thickness direction.

The phase change mark (phase change mark) is recorded and reproduced under the condition that a combination of a laser having a wavelength of 405 nm (so-called blue laser) and an NA of 0.85 is used, and a track pitch of 0.32 μm and a linear density of 0.12 μm / bit are used. When a 64 KB (kilobyte) data block is used as one recording / reproducing unit, and the format efficiency is about 82%, a capacity of about 23.3 GB (gigabytes) can be recorded and reproduced on a 12 cm disc.

In addition, when the recording layer has a multilayer structure, a new capacity can be realized, for example, when the recording layer has two layers, the capacity can be 46.6 GB, which is twice that of the above.

Of course, an n-layer structure of three or more layers is also possible, and the capacity can be n times as described above.

In Fig.1 (a) and (b), the layer structure of a 1-layer disk and a 2-layer disk is respectively shown typically.

The disk thickness is 1.2 mm, and the thickness of the substrate RL made of polycarbonate is about 1.1 mm.

Although the optical beam from the disk drive apparatus (recording and reproducing apparatus) for recording and reproducing the disk 1 is indicated by a dashed-dotted line, the optical beam is a blue laser having a wavelength of 405 nm, and the NA is represented by an objective lens of 0.85. As described above, light is collected from the cover layer (sub-straight) CVL side.

In the case of the one-layer disk of Fig. 1A, for example, the recording layer L0 of the phase change recording film is formed on the substrate RL having a thickness of 1.1 mm, and a cover layer CVL of 100 mu m is formed thereon. .

At the time of recording and reproduction, the optical beam is focused on the recording layer L0 from the cover layer CVL side.

In the case of the two-layer disk of Fig. 1B, for example, the recording layer L0 of the phase change recording film is formed on the substrate RL having a thickness of 1.1 mm, and the second phase change is sandwiched by sandwiching the intermediate layer ML of 25 mu m. The recording layer L1 of the recording film was formed, and a cover layer CVL of 75 mu m was formed.

At the time of recording reproduction, the optical beams are focused on the recording layers L0 and L1 from the cover layer CVL side.

Here, the first recording layer L0 is formed at a position of 100 µm from the surface CVLs of the cover layer CVL as in the case of the one-layer disk.

Therefore, as for the recording layer L0 of the one-layer disk and the recording layer L0 of the two-layer disk, the thickness of the cover layer CVL is 100 m.

On the other hand, with respect to the recording layer L1 of the two-layer disc, the thickness of the cover layer CVL is 75 µm.

Although not illustrated, when three or more n-layer discs are considered, for example, a recording layer Ln is formed by sandwiching an intermediate layer ML of 25 µm from the recording layer L1 in FIG. 1 (b) to the cover layer surface CVLs side. Is considered.

That is, the nth recording layer L (n-1) is formed on the nth recording layer L (n-2) by sandwiching the intermediate layer ML. As for the nth recording layer L (n-1), the thickness of the cover layer CVL is 100- (n-1) x 25 µm.

2. Configuration of the recording and playback device

As a recording and reproducing apparatus of the embodiment, an apparatus configuration using a two-group objective lens having a numerical aperture of 0.85 and a blue violet semiconductor laser light source having a wavelength of 405 nm will be described.

2 shows the configuration of a two-group objective lens mounted on an optical head (optical pickup) of a recording / reproducing apparatus.

The two-group objective lens serving as the output end of the laser beam to the disk 11 is composed of a first lens (prison lens 12) and a second lens (condensing lens 14).

The jadeite lens 12 and the condenser lens 14 are supported by the lens holder 13 so as to be positioned on the same optical axis, and these two lenses function as a two-group objective lens having a numerical aperture of 0.85.

The lens holder 13 holding the jaundice lens 12 and the condenser lens 14 as the two-group objective lens is mounted on the electromagnetic actuator 15. The electromagnetic actuator 15 is a so-called biaxial mechanism and moves the two-group objective lens in the optical axis direction and the disc radial direction. The optical axis direction is a direction in which the disk 11 is folded, that is, a focusing control direction. The disc radial direction is a direction traversing the track on the disc 11, that is, a tracking control direction.

The light beam from the semiconductor laser light source mentioned later is condensed on the disk 11 by passing these two lenses 12 and 14. Moreover, by realizing a high numerical aperture, compared with the conventional optical pickup, the operating distance of the objective lens in the focusing direction is smaller, and in this example, the value is about 140 µm.

As the numerical aperture of the objective lens becomes larger, the disc tilt tolerance in the optical disc recording / reproducing apparatus generally decreases.

When the inclination angle of the disk with respect to the optical axis is θ, the coma aberration W31 that is generated is given by Reference (1) by the following equation (3), which is generally the third power of the numerical aperture NA and the disk cover layer. Proportional to thickness t.

....... Equation (3)

Therefore, in the optical disc recording / reproducing apparatus in which the numerical value of the numerical aperture is increased to 0.85 when the value of the allowable coma aberration W31 is λ / 4, in order to ensure the disc tilt tolerance equivalent to that of the DVD reproducing apparatus, FIG. As shown in Fig. 2, the thickness of the cover layer CVL of the disk 11 needs to be reduced to about 0.1 mm.

3 shows the configuration of an optical system of the optical pickup having the two-group objective lens.

The semiconductor laser 16 is a blue violet semiconductor laser light source having a wavelength of 405 nm.

The collimator lens 17 uses the emitted light of the semiconductor laser 16 as parallel light. The half wave plate 18 adjusts the amount of incident light to the light receiving element 22.

The diffraction grating 19 produces side spots used to compute the tracking control error signal.

The polarization beam splitter 20 controls the optical path according to the polarization state.

The liquid crystal element 23 performs spherical aberration correction according to the cover layer thickness of the recording layer. The quarter wave plate 24 is circularly polarized by the linearly polarized light of the semiconductor laser in front of the condenser lens 14 and the prison lens 12 (hereinafter also referred to as the two-group objective lens 14, 12). Convert to

The light emitted from the semiconductor laser 16 becomes parallel light by the collimator lens 17, passes through the half wave plate 18 and the diffraction grating 19, and then reaches the polarization beam splitter 20. After passing through the liquid crystal element 23 and the quarter wave plate 24, the light is collected on the disk 11 by the two-group objective lenses 14 and 12.

A part of the emitted light from the semiconductor laser 16 is reflected by the polarization beam splitter 20 and then guided by the condenser lens 21 to the light receiving element 22 for detecting the light emission output, and the laser output is fixed at a constant value. Used for control purposes. The amount of incident light on the light receiving element 22 for light emission output detection can be adjusted by rotating the half wave plate 18.

The actual laser output level from the semiconductor laser 16 is controlled to any light emission output value by an APC (Auto Power Control) circuit not shown. That is, the APC circuit controls the output of the semiconductor laser 16 in accordance with the comparison of the laser output level information obtained from the light emitting element 22 for light emission output detection with the target laser level.

The liquid crystal element 23 is provided as a correction optical means for correcting spherical aberration caused by the thickness of the cover layer with respect to the information recording layers L0 and L1 of the disk 11.

The electrode pattern of the liquid crystal element 23 is shown in FIG. As shown, the liquid crystal element 23 has concentric electrode patterns 23a, 23b, and 23c reported in References (5) and (6), and applied to the voltage applied to the electrodes. Accordingly, as shown in FIG. 5, it is possible to generate a wavefront approximately equivalent to the correction amount of the spherical aberration caused by the thickness error of the cover layer.

In FIG. 3, the reflected light from the disk 11 is reflected by the polarization beam splitter 20 and then guided to the detection light path. In this example, the convergence light passed through the condensing lens 25 and the multi-lens 26 in the detection optical path using the astigmatism method as the focus control error signal and the differential push-pull method as the track control error signal. Is incident on the light receiving element 27 for detecting the servo error signal and the reproducing RF signal, and is photoelectrically converted.

The light receiving element 27 has the same light receiving pattern as shown in FIG. 6. That is, it consists of a 4 split detector which has light receiving parts A, B, C, and D, a 2 split detector which has light receiving parts E and F, and a 2 split detector which has light receiving parts G and H.

Each light receiving unit A, B, C, D, F, F, G, H outputs a current signal according to the amount of received light, and the current signal is converted into a voltage signal and calculated, and the focus control error signal FE and the tracking control error signal TE, a reproduction RF signal is generated.

The focus control error signal FE, the tracking control error signal TE and the reproduction RF signal are generated by the following calculation.

FE = (A + C)-(B + D) ..... (4)

TE = (A + D)-(B + C) -k {(E-F) + (G-H)} ..... Equation (5)

RF = A + B + C + D ..... Equation (6)

7 shows the configuration of the recording / reproducing apparatus. Incidentally, the information recording / reproducing processing system is not shown, and mainly represents a servo system.

The disk 11 is loaded on a turntable (not shown) and is driven to rotate at a constant linear velocity CLV or a constant angular velocity CAV by the spindle motor 43 in the recording / reproducing operation.

Then, the optical pickup (optical head) 10 reads the information on the disk 11, that is, information recorded by emboss pits, wobbling grooves, phase change marks, or the like, or on phase change marks on the disk 11. Information is written.

The optical head 10 includes the optical system of FIG. 3, and the signal (reflected light information) read from the disc 11 by the optical system, that is, the output signal of each of the light receiving units A to H of FIG. 31). The head amplifier 31 amplifies the reflected light information signal from the optical head 10 to a predetermined level necessary for processing at a later stage.

In the equalizer amplifier 32, the amplified reflected light information signal is generated and echoized by a calculation of Equation (6), and supplied to a signal processing system (not shown). The signal processing system is a reproduction signal processing system that decodes data, corrects errors, and the like.

The reproduction RF signal according to Equation (6) corresponds to the sum signal SUM as the reflected light intensity signal (SUM = A + B + C + D), and the equalizer amplifier 32 uses a comparator for the sum signal SUM. And level information of the sum signal SUM is formed and output to the CPU 40.

The output of the head amplifier 31 is also sent to the focus matrix circuit 33 and the tracking matrix circuit 37.

The focus matrix circuit 33 performs an operation based on equation (4) on the input signal to generate a focus control error signal (focus error signal) FE.

In addition, the sum signal SUM (= A + B + C + D) may be generated as the reflected light intensity signal.

The tracking matrix circuit 37 performs an operation based on equation (5) on the input signal to generate a tracking control error signal (tracking error signal) TE.

The focus servo control unit 35 performs phase compensation on the focus control error signal FE from the focus matrix circuit 33, and generates a focus drive signal. The focus drive signal is amplified by the drive amplifier 36, drives the focus coil of the electronic actuator 15 in the optical head 10, and the group 2 objective lens 12 so that the laser spot remains in focus with respect to the recording layer. (14) is moved in the optical axis direction to control the focus servo.

In other words, the focus servo loop is formed by the optical head 10, the focus matrix circuit 33, the focus servo control unit 35, and the electromagnetic actuator 15.

The focus servo control unit 35 performs the focus search operation under the control of the CPU 40. That is, this operation is for pulling in the confocal state with respect to the target recording layer in the disk 11. In this case, a search drive signal is generated while the focus servo loop is turned off to drive the focus coil of the electromagnetic actuator 15. As a result, the two-group objective lenses 12 and 14 are forcibly moved in the optical axis direction in the focus stroke range, thereby performing focus in. This focus search operation will be described later.

The tracking servo controller 38 performs phase compensation on the tracking control error signal TE from the tracking matrix circuit 37 and generates a tracking drive signal. The tracking drive signal is amplified by the drive amplifier 39 to drive the tracking coil of the electronic actuator 15 in the optical head 10, so that the laser spot keeps tracking the tracks of the disk 11, the group 2 objective. The tracking servo control is performed by moving the lenses 12 and 14 in the disc radial direction.

In other words, the tracking servo loop is formed by the optical head 10, the tracking matrix circuit 37, the tracking servo control unit 38, and the electromagnetic actuator 15.

In addition, the tracking servo controller 38 turns off the tracking servo loop and outputs a jump drive signal in response to the track jump command and the access command from the CPU 40 to execute the track jump operation and the access operation.

Although not shown, the entire optical head 10 is movable in the disc radial direction by a thread mechanism.

The tracking servo controller 38 generates a thread drive signal in accordance with a thread error signal obtained as a low pass component of the tracking control error signal TE, an access execution control from the CPU 40, and the like, and drives a thread mechanism to drive an optical head ( 10) the disk radial movement is performed.

The spindle servo control section 42 controls to rotate the spindle motor 43, for example, CLV or CAV.

In the case of performing CLV control, for example, the data reproduction clock (or wobble reproduction system clock) of the PLL system obtained from the reproduction signal processing system is used as the current rotation speed information, and the error information is compared with a frequency corresponding to the reference speed. By controlling the spindle rotation speed.

In the case of performing CAV control, the spindle rotational speed is controlled so that the rotational speed information obtained by the FG or the like of the spindle motor 43 becomes a constant rotational speed.

The spindle servo control unit 42 also generates a spindle drive signal in accordance with the spindle kick / brake control signal from the CPU 40, and also executes operations such as starting, stopping, accelerating and decelerating the spindle motor 43.

The LCD control unit 41 applies voltage to the liquid crystal element 23 of the electrode pattern as shown in FIG. 4 under the control of the set value of the spherical aberration correction from the CPU 40, and executes the spherical aberration correction.

The S-level detection circuit 34 is formed of, for example, a plurality of comparators, and compares the focus control error signal FE (S curve) obtained by the focus matrix circuit 33 to perform the comparison of the focus control error signal FE. Polarity information is output to the CPU 40.

When the sum signal SUM is generated by the focus matrix circuit 33, a comparator for the sum signal SUM is also provided in the S level detection circuit 34, and the level information of the sum signal SUM is formed to form a CPU ( You may output to 40).

Various operations of the servo system and the recording / reproducing signal processing system (not shown) described above are controlled by the CPU 40 functioning as a system controller.

3. Spherical Aberration Correction State and S-curve

Here, the S curve of the spherical aberration correction state and the focus control error signal FE obtained at that time will be described.

Fig. 8A shows a reproduction-only (R0M type) disc having two information recording layers L0 and L1 as shown in Fig. 1B, wherein the liquid crystal element 23 for correcting spherical aberration is set to a second value. The cover layer thickness (75 μm) of the layer (information recording layer Ll) is optimized, and the focus control error signal FE observed when the two-group objective lenses 12 and 14 are moved in one direction along the optical axis direction is shown.

In this case, the objective lens is moved in a direction approaching the disk 11.

In the focus control error signal FE of the astigmatism method of this example, the multi-lens 26 shown in FIG. 3 is circular on the light receiving portions A, B, C, and D of the light receiving element 27, and other than that. Oval intensity distribution.

In Fig. 9, intensity distributions of the light receiving sections A, B, C, and D are shown. Moreover, when it is not in a confocal state, it will become an elliptical intensity distribution as shown as defocus (+) and (-).

Therefore, as the focus control error signal FE obtained by the above formula (4), an output (commonly known as an S-curve) that becomes zero level at the time of combining is generated.

However, when the setting of the spherical aberration correction is greatly deviated from the optimum value for the target recording layer, the generated spherical aberration causes the condensation spot on the recording medium to be extremely degraded, and an S-curve having the original signal amplitude can be obtained. Can not get

Therefore, if the objective lens is moved in an optimized state with the cover layer thickness of the information recording layer L1, as shown in Fig. 8A, when the laser spot focal point passes through the information recording layer L1, a large amplitude S-shaped curve is obtained. Is observed, the S-shaped curve observed when passing through the information recording layer L0 is of small amplitude.

In addition, if the objective lens is moved in a state of adjusting the cover layer thickness of 100 μm corresponding to the information recording layer L0 in advance, the focus control error signal FE becomes as shown in Fig. 8B, that is, the laser spot. When the focal point passes the information recording layer L1, a small amplitude S curve is observed, and when the focal position passes through the information recording layer L0, a large amplitude S curve is observed.

On the other hand, in a state where the set value of the liquid crystal element 23 is optimized to a cover layer thickness of 87 μm as an average value of the respective cover layer thicknesses of the information recording layers L0 and L1, that is, an average value of 100 μm and 75 μm, for example, FIG. In C), the S-curve when the laser spot focal position passes through the information recording layer L1 and when passing through the information recording layer L0 is approximately at the same level. However, the amplitude level is about medium.

4. First Focusing Control Method

In view of the above situation, a first focusing control method for reliably focus servo insertion into a target information recording layer with respect to a multilayer disk such as a single-layer disk or a two-layer disk will be described.

This first focusing control method is a method of ensuring focus control retracting operation for a two-layer disk, wherein the set value of the liquid crystal element 23 for spherical aberration correction is set with respect to the intermediate positions of the information recording layers L0 and L1. I'll adjust it.

That is, it adjusts previously to the optimum state with respect to the cover thickness of 87 micrometers, for example. Then, the focus control error signal FE obtained in that case is as shown in Fig. 8B, and the amplitude of the S-curve is not maximum, but the focus control is approximately equal in both information recording layers L0 and L1. It is possible to obtain the error signal FE. Then, by determining the number of occurrences of the S-curve and the signal polarity, it is possible to perform the focus control pulling-in operation to the target information recording layer.

The specific method is demonstrated.

First, in the S-level detection circuit 34 shown in FIG. 7, the focus control error signal FE is defined as a predetermined level (return), a negative level (Level L), and a zero level (Level) as shown in FIG. A comparator to compare at each threshold of 0) is provided, and the output of the comparison is output to the CPU 40.

Fig. 10A shows the focus control error signal FE observed when the two-group objective lenses 12 and 14 are reciprocated in the optical axis direction with respect to the two-layer disk.

"Route" shows a state in which the two-group objective lenses 12 and 14 are moved in a direction approaching the disk 11, and "return" means a direction away from the disk 11 The moving state is shown.

Fig. 10C is a comparison output in which the focus control error signal FE is compared at a positive level (back).

Fig. 10 (d) is a comparison output in which this focus control error signal FE is compared at a negative level (Level L).

FIG. 10E shows a comparison output in which the focus control error signal FE is compared at a zero level (Level 0).

10B shows the sum signal SUM (reproduced RF signal) observed when the two-group objective lenses 12 and 14 are reciprocated in the optical axis direction with respect to the two-layer disk.

Fig. 10 (f) is a comparison output in which the sum signal SUM is compared with a predetermined threshold shown in Fig. 10 (b).

Each comparison output in Fig. 10 (c) (d) (e) (f) is supplied to the CPU 40.

The CPU 40 sets the comparison output pulse of FIG. 10C as the generation information of the positive level as the polarity in the focus control error signal FE. In addition, the comparison output pulse of FIG. 10 (d) is referred to as occurrence information of the negative level as the polarity in the focus control error signal FE. In addition, the comparison output pulse of FIG. 10 (e) is referred to as zero cross generation information in the focus control error signal FE.

In addition, the CPU 40 uses the comparison output pulse of FIG. 10 (f) as a detection signal of a so-called focus lead-in range (linear region of S-curve).

The CPU 40 adjusts the set value of the liquid crystal element 23 for spherical aberration correction with respect to the intermediate positions of the information recording layers L0 and L1, and reciprocates the two-group objective lenses 12 and 14 in the optical axis direction. When moving, the information recording layer for focus control is selected by detecting the order of appearance of the positive level and the negative level in the polarity of the focus control error signal FE by the comparison outputs in FIG. 10 (c) (d). .

That is, at the time of the movement of the path in FIG. 10, the CPU 40 is supplied to the CPU 40 in the order of pulses P1, P2, P3, and P4 as information on the polarity of the focus control error signal FE.

That is, the polarity of the focus control error signal FE is detected in the order of positive → negative → positive → negative in the backward path.

In the retrace, the CPU 40 is supplied to the CPU 40 in the order of pulses P5, P6, P7, and P8 as information on the polarity of the focus control error signal FE. That is, the polarity of the focus control error signal FE is detected in the order of negative → positive → negative → positive in the return path.

Therefore, for example, when performing the focus in operation to the information recording layer L0, the two-group objective lenses 12 and 14 are moved in the optical direction, and the polarity detection result of the focus control error signal FE is 1. What is necessary is just to start the pulling-in operation in the vicinity of the zero cross point after obtaining the part 2, part 3. and positive, and then, by taking a logical sum with the comparison output of Fig. 10 (f) in which the level of the sum signal SUM is equal to or greater than a predetermined threshold. The focus control is reliably implemented.

Alternatively, the retraction operation may be started near the zero cross point after the first negative polarity is obtained as a result of the polarity detection of the focus control error signal FE in the retrace.

For example, when performing the focus-in operation on the information recording layer L1, the two-group objective lenses 12 and 14 are moved in the optical direction, and the first plus polarity is obtained as the polarity detection result of the focus control error signal FE. It is only necessary to start the pulling-in operation near the zero cross point after this is obtained. At that time, the focus control is reliably shifted by taking a logical sum with the comparison output of Fig. 10 (f) in which the level of the sum signal SUM is equal to or greater than a predetermined threshold. .

Alternatively, the retraction operation may be started in the vicinity of the zero cross point after the polarity detection result of the focus control error signal FE is obtained in the order of 1. part, 2. positive, and 3. part.

On the other hand, in the case of a single-layer disc, as in FIG. 10, the focus control error signal FE, the sum signal SUM, the focus control error signal FE and the output of comparison with the positive level (return), the focus control error signal FE and the sublevel (Level L) 11A to 11F show a comparison output, a comparison control of the focus control error signal FE and a zero level (Level 0), and a comparison output of the sum signal SUM and a predetermined threshold.

As can be seen from Fig. 11, in the case of a tomographic disk, the CPU 40 is supplied to the CPU 40 in the order of pulses P1 and P2 as information on the polarity of the focus control error signal FE during the movement of the backward path. That is, the polarity of the focus control error signal FE is detected in the order of positive to negative in the backward path. In the retrace, as the information on the polarity of the focus control error signal FE, the CPU 40 is supplied in order of pulses P3 and P4. That is, the polarity of the focus control error signal FE is detected in the order of negative 10 tablets in the return path.

In other words, the number of appearances and the signal polarity state are different from those of the two-layer recording medium.

In this case, since the S-curve can be detected according to the comparison result of Fig. 11 (c) (d) in both the path and the return path, the zero cross point is detected in accordance with the detection of the pulse in Fig. 11 (c) (d). The pulling-in operation may be started in the vicinity, and focus control is reliably shifted by taking a logical sum with the comparison output of Fig. 11F in which the level of the sum signal SUM is equal to or higher than a predetermined threshold.

In other words, the CPU 40 can determine the number of information recording layers of the disc 11 by the number of appearance of the polarity information, for example, when the two-group objective lenses 12 and 14 are moved, and in accordance with the polarity information. In this way, the focus retraction can be reliably performed on the target information recording layer.

Since the actual focus control insertion operation is generally performed while the disk 11 is rotating, it cannot be concluded that an ideal detection signal as shown in Figs. 10 and 11 is obtained. That is, since the focus control error signal also appears by the disk up and down with rotation, the error is included in the total number of detections of the signal output obtained when the two-group objective lenses 12 and 14 are moved in the optical axis direction.

However, since a certain rule exists in the order of appearance of polarity, by using this example, it becomes possible to perform a reliable focus control pull-in operation on the multilayer information recording medium.

12 is a flowchart of a processing example of the specific CPU 40.

The CPU 40 instructs the LCD control unit 41 in step F101 to set the spherical aberration correction by the liquid crystal element 23 according to the average value of the cover layer thickness (for example, the cover layer thickness of 87 μm). Set to state.

In step F102, the focus servo control unit 35 is instructed to start the focus search. In other words, the reciprocating operation in the optical axis direction of the two-group objective lenses 12 and 14 is started. In step F103, the comparison result information from the S level detection circuit 34 and the comparison result information of the sum signal SUM are detected. That is, the comparison result information of each (c)-(f) of FIG. 10, FIG. 11 is detected.

By the detection, when the polarity detection of positive → negative → positive → negative is performed in step F104 in the path, the CPU 40 can determine the disk 11 as a two-layer disk. In that case, it progresses to step F105 and branches a process according to the target information recording layer.

If it is aimed at the focusing control to the information recording layer L1, the flow proceeds to step F107, for example, the focus lead-in (focus servo-on) at the timing near the zero cross immediately after the first S-shaped detection (plus polarity detection) in the path, for example. ). If the comparison result information of the sum signal SUM at step F109 is " H " at this time, since focusing control is performed on the information recording layer L1, the focus search off is instructed at step F110, and the processing is finished.

If it is aimed at the focusing control to the information recording layer L0, the flow proceeds to step F106, for example, at a timing near the zero cross immediately after the first second S-shape detection (positive-positive-positive detection) in the path. Focus in (focus servo on) is performed. If the comparison result information of the sum signal SUM is " H " at step F109 at that time, the focusing control is performed correctly on the information recording layer L0. Therefore, the focus servo-off is instructed at step F110, and the processing ends.

In step F104, when the polarity detection of positive → negative → positive → negative in the path is not performed, it can be determined that the disc is a single layer disk. In this case, it progresses to step F108 and focus in (focus servo on) is performed in the timing of zero cross vicinity immediately after S-shaped detection. If the comparison result information of the sum signal SUM at step F109 is " H " at this time, since the focusing control is performed precisely on the information recording layer L0 of the single-layer disc, the focus search off is instructed at step F110, and the processing ends.

If the comparison result information of the sum signal SUM is "L" in step F109, the focusing control can be performed on the target information recording layer, and the process returns to step F103 to repeat the process.

5. Second Focusing Control Method

Next, a second focusing control method will be described.

In the first focusing control method, the setting value of the spherical aberration correction is set to an average cover layer thickness to selectively perform the focus control retracting operation for the plurality of information recording layers.

However, in the case of a two-layer disc having a large interlayer distance of the information recording layer, it is not conceivable that the focus control error signal FE that can achieve the above-described stable pulling-in operation can not be obtained due to spherical aberration generated.

In other words, if the set value of the spherical aberration correction is set to the average cover layer thickness, the S-curve amplitude levels at the time of passing through each of the information recording layers L1 and L0 are equal as described in Fig. 8C, but the residual wavefront aberration The amplitude becomes smaller. The phenomenon that this amplitude becomes small becomes more remarkable when the interlayer distance is large, and it is also assumed that the waveform of the focus control error signal FE largely deviates from the S curve in some cases.

In the second and third focusing control methods described later, the setting value of the spherical aberration correction is optimized for the cover layer thickness of the specific information recording layer in advance, so that a more stable drawing operation can be realized.

Now, when the two-group objective lenses 12 and 14 are reciprocated in the optical axis direction in a state where the setting value of the spherical aberration correction is optimized to the cover layer thickness (75 μm) of the information recording layer L1 in advance with respect to the two-layer disc, As in FIG. 10, the focus control error signal FE, the sum signal SUM, the focus control error signal FE and the output of the comparison between the positive level (return), the focus control error signal FE and the sublevel (Level L), and the focus control error The comparison output of the signal FE and the zero level (Level O), and the comparison output of the sum signal SUM and a predetermined threshold are shown in Figs. 13A to 13F.

As can be seen from the description of Fig. 8A, when the setting value of the spherical aberration correction is optimized to the cover layer thickness of the information recording layer L1, when the laser spot focal position passes through the information recording layer L1, An S-shaped curve is observed, and when passing through the information recording layer L0, a small amplitude S-shaped curve is observed.

In this case, the polarity of the focus control error signal FE is the information of the polarity of the focus control error signal FE at the time of movement of the focus, and is supplied to the CPU 40 in the order of pulses P1, P2, P3, and P4. That is, the polarity of the focus control error signal FE is detected in the order of positive → negative → positive → negative in the backward path.

Compared with the S-curve detected as the first set of pulses P1 and P2, the amplitude of the S-curve detected as the second set of pulses P3 and P4 is very small.

In the retrace, the CPU 40 is supplied to the CPU 40 in the order of pulses P5, P6, P7, and P8 as information on the polarity of the focus control error signal FE. That is, the polarity of the focus control error signal FE is detected in the order of negative → positive → negative → positive in the return path.

Compared to the S curves detected as the second set of pulses P7 and P8, the amplitude of the S curves detected as the first set of pulses P5 and P6 is very small.

In addition, when the two-group objective lenses 12 and 14 are reciprocated in the optical axis direction in a state where the setting value of the spherical aberration correction is optimized to the cover layer thickness (100 µm) of the information recording layer L0 in advance with respect to the two-layer disk. As in FIG. 10, the focus control error signal FE, the sum signal SUM, the focus control error signal FE and the output of comparison between the positive level (LevelH), the focus control error signal FE and the output of the sublevel (Level L), and the focus control error The comparison output of the signal FE and the zero level (Level O), and the comparison output of the sum signal SUM and a predetermined threshold are shown in Figs. 15A to 15F.

As can be seen from the description of Fig. 8, when the setting value of the spherical aberration correction is optimized to the cover layer thickness of the information recording layer L0, when the laser spot focal position passes through the information recording layer L0, a large amplitude S-shaped curve is obtained. Is observed, and a small amplitude S-shaped curve is observed when passing through the information recording layer L1.

Also in this case, the polarity of the focus control error signal FE is the information of the polarity of the focus control error signal FE at the time of movement of the focus, and is supplied to the CPU 40 in the order of pulses P1, P2, P3, and P4. That is, the polarity of the focus control error signal FE is detected in the order of positive → negative → positive → negative in the backward path.

Compared with the S-curve detected as the second set of pulses P3 and P4, the amplitude of the S-curve detected as the first set of pulses P1 and P2 is very small.

In the retrace, the CPU 40 is supplied to the CPU 40 in the order of pulses P5, P6, P7, and P8 as information on the polarity of the focus control error signal FE. That is, the polarity of the focus control error signal FE is detected in the order of negative → positive → negative → positive in the return path.

Compared to the S curves detected as the first set of pulses P5 and P6, the amplitude of the S curves detected as the second set of pulses P7 and P8 is very small.

That is, for example, when performing the focus in / out operation on the information recording layer L1, the voltage applied to each electrode in the liquid crystal element 23 is adjusted in advance, and the spherical aberration correction amount is optimized for the information recording layer L1. Next, the two-group objective lenses 12 and 14 are moved in the optical axis direction, and the detection result of the focus control error signal FE is drawn in the vicinity of the zero cross point after initially reaching the positive level (P1 in FIG. 13) in the path. The operation is started, and at that time, by performing a logical sum with the condition that the sum signal level becomes equal to or greater than a predetermined threshold value, the focus control on the information recording layer L1 is reliably implemented.

In addition, when performing the focus-in operation to the information recording layer L0, the voltage applied to each electrode in the liquid crystal element 23 is adjusted in advance, and the spherical aberration correction amount is optimized for the information recording layer L0. Next, the two-group objective lenses 12 and 14 are moved in the optical axis direction, and the detection result of the focus control error signal FE is drawn in the vicinity of the zero cross point after the initial level becomes the negative level (P5 in FIG. 15) in the return path. The operation starts, and at that time, by taking a logical sum with the condition that the sum signal level becomes equal to or greater than a predetermined threshold value, the focus control on the information recording layer L0 is reliably implemented.

14 shows a process of the CPU 40 in the case of performing the focus in / out operation on the information recording layer L1.

The CPU 40 instructs the LCD control unit 41 in step F201 to set the setting of the spherical aberration correction by the liquid crystal element 23 in a state corresponding to the cover layer thickness (75 μm) of the information recording layer L1.

In step F202, the focus servo control unit 35 is instructed to start the focus search. In other words, the reciprocating operation in the optical axis direction of the two-group objective lenses 12 and 14 is started. In step F203, the comparison result information from the S level detection circuit 34 and the comparison result information of the sum signal SUM are detected. That is, the comparison result information of FIG.13 (c)-(f) is detected.

In step F204, the polarity change of the focus control error signal FE from positive to zero is observed in the path, and the timing at which the comparison result information of the sum signal SUM is "H" is monitored at that time.

Since the timing becomes the focus lead-in timing to the information recording layer L1, if the condition of the polarity change of the focus control error signal FE from positive to zero and the comparison result information "H" of the sum signal SUM can be obtained, the focus lead-in at step F205. Is done. In other words, the focus servo-on is performed on the first S-curve in the path. As a result, since focusing control is performed on the information recording layer L1, the focus servo-off is instructed in step F206 to complete the processing.

FIG. 16 shows a process of the CPU 40 in the case of performing a focus in operation to the information recording layer L0.

The CPU 40 instructs the LCD control unit 41 in step F301 to set the setting of the spherical aberration correction by the liquid crystal element 23 in a state corresponding to the cover layer thickness (10 μm) of the information recording layer L0.

In step F302, the focus servo control unit 35 is instructed to start the focus servo. In other words, the reciprocating operation in the optical axis direction of the two-group objective lenses 12 and 14 is started. In step F303, the comparison result information from the S level detection circuit 34 and the comparison result information of the sum signal SUM are detected. That is, the comparison result information of FIG.15 (c)-(f) is detected.

In step F304, the polarity change from negative to zero of the focus control error signal FE is observed in the return path, and at that time, the timing at which the comparison result information of the sum signal SUM is "H" is monitored.

Since the timing becomes the focus lead-in timing to the information recording layer L0, if the condition of the polarity change of the focus control error signal FE from negative to zero and the comparison result information "H" of the sum signal SUM can be obtained, the focus lead-in at step F305. Is done. In other words, the focus servo-on is performed on the first S curve in the return path. As a result, since focusing control is performed on the information recording layer L0, the focus search off is instructed in step F306, and the processing is finished.

In other words, in the second focusing control method, the spherical aberration correction setting value is optimized for the target information recording layer in advance, so that a certain S-curve for the target information recording layer can be observed, and the polarity thereof. Performs focus entry based on the information.

This makes it possible to reliably focus control on any information recording layer of the multilayer disk.

In particular, it is effective when reproducing or recording / reproducing a multi-layer optical disc having two or more information recording layers by using a high numerical aperture objective lens realized by the two-group objective lenses 12 and 14, and in particular, interlayer. Stable focus control lead-in operation is realized for multilayer optical discs with large distances.

Since the actual focus control pulling-in operation is generally performed while the optical disc medium is rotating, it cannot be concluded that an ideal detection signal is obtained as shown in FIGS. 13 and 15. That is, since the focus control error signal appears due to the disk up and down accompanied by rotation, the error is included in the number of times of detection of the signal output obtained when the two-group objective lenses 12 and 14 are moved in the optical axis direction. In addition, when the spherical aberration correction is not properly performed, the amplitude of the focus control error signal FE becomes small and does not draw an ideal S curve. However, when the spherical aberration correction amount is optimized for the cover layer of the target information recording layer by the retracting operation, a good S-curve can be obtained at least in the information recording layer, and at the same time, the order of appearance of signal polarity is a constant rule. This exists. Therefore, by this example, it becomes possible to perform a reliable focus control insertion operation on any information recording layer of the multilayer disk.

6. Third focusing control method

Next, a third focusing control method will be described.

The third focusing control method is the same as the second focusing control method until the first focusing operation is performed on a certain information recording layer, and when entering into another information recording layer, the information recording layer which performed focusing in is performed. A method of focus jumping from the target information recording layer to the target information recording layer.

First, when the focus is introduced into the information recording layer L1 and the focus is introduced into the information recording layer L0, the CPU 40 is used as an example of focus jump to the information recording layer L0 after the insertion into the information recording layer L1. ) Is shown in FIG. 17.

Steps F401 to F406 in Fig. 17 are the same as steps F201 to F206 in Fig. 14 described above.

Therefore, the focus lead-in is completed with respect to the information recording layer L1 by the process of step F401-F406.

In step F407, the processing branches according to the target information recording layer. If the information recording layer L1 was the target, since the drawing is completed at this point, the process ends from step F407.

On the other hand, when the information recording layer L0 is the target, the process shifts to the focus jump process. The CPU 40 first instructs the LCD control unit 41 in step F408 to set the spherical aberration correction by the liquid crystal element 23 in a state corresponding to the cover layer thickness (100 μm) of the information recording layer L0. Set it.

In step F409, the focus servo control unit 35 is instructed to start the focus jump. That is, the two-group objective lenses 12 and 14 are moved in the direction of the information recording layer L0 (in this case, the backward direction).

In step F410, the comparison result information from the S level detection circuit 34 and the comparison result information of the sum signal SUM are monitored.

Since the setting of the spherical aberration correction is optimized for the cover layer thickness of the information recording layer L0 in step F408, the waveform of the path in Fig. 15 is observed during the focus jump.

As a result of the focus jump, in step F410, a polarity change (i.e., P2-> P3-> zero cross) in the focus control error signal FE in the backward path (i.e., P2-> P3-> zero cross in Fig. 15) is observed. When the comparison result confirms that the information is "H", the jump to the information recording layer L0 is completed correctly (insertion completion) at that point, and thus the process is finished.

Also in this third focusing control method, it becomes possible to reliably perform focus control on any information recording layer of the multilayer disk. In addition, the interlayer movement of the light collecting spot can be easily realized.

At the time of focus jump, the spherical aberration correction setting value is optimized with respect to the cover layer thickness of the information recording layer of the jump destination, so that an S-curve of sufficient intensity can be observed and an accurate jump operation can be performed.

And in step F408 of FIG. 17, you may optimize the setting value of spherical aberration correction with respect to the thickness (87 micrometer) of each cover layer of information recording layers L1 and L2.

In addition, although FIG. 17 described as an example of the process of first entering into the information recording layer L1 and then jumping to the information recording layer L0, the process of initially entering into the information recording layer L0 and then jumping to the information recording layer L1 is described later. Examples are of course considered.

7. Optimization after Focus Control

By the way, in general, the correction setting value of the spherical aberration correction element (liquid crystal element 23) is preset to a value that is optimally assumed for each information recording layer in advance. However, in an actual multilayer optical recording medium, there is a fear that a manufacturing error occurs in the cover layer thickness of each recording layer.

In addition, since the deviation of the correction amount with respect to the applied voltage also exists in the spherical aberration correction element itself, it is preferable to fine-tune the spherical aberration correction amount so as to be optimal after completing the focus control pull-in operation by the method described above. .

That is, after performing the focus in on the target information recording layer, the spherical aberration correction amount is optimized according to the reproduction signal or the spherical aberration error signal as the reflected light information, so that stable recording and reproduction can be performed regardless of the manufacturing error of the recording medium. It becomes possible to do it.

Specifically, the information is recorded using the jitter value, the signal amplitude of the reproduced RF signal, the error rate of the reproduced data, or the like, which is expressed as a fluctuation of the data edge with respect to the reproduced clock (usually a PLL clock synchronized with the reproduced data). Consideration is given to a method of adjusting so that the reproduction signal from the medium is optimal. For example, the method described in Reference (7) can be applied.

In addition, a method of providing an automatic correction mechanism based on the spherical aberration error signal generated by the feedback light intensity from the recording medium, as shown in Reference (8), can also be applied.

As mentioned above, although the Example was described, this invention is not limited to these, A various modified example is considered within the range of a summary.

In addition, although the above-mentioned pulling-in process was demonstrated with the example of a single-layer disk and a two-layer disk, similarly about the optical recording medium which has a recording layer of three or more layers, by determining the frequency | count of appearance of an S-shaped curve, and the signal polarity, Therefore, the focus control retracting operation can be performed on the target information recording layer.

As can be understood from the above description, according to the present invention, when the focusing control is performed on the information recording layer of interest in the recording medium, first, the light transmission protection in the information recording layer for the purpose of correcting the spherical aberration state. The state is set in accordance with the thickness of the layer (cover layer). Or it is set in the state which matched the average value of the thickness of each light transmission protective layer (cover layer) of a some information recording layer. Then, a so-called focus servo operation is performed in which the objective lens is moved in the optical axis direction. At this time, the polarity of the focus control error signal and the level of the reflected light intensity signal generated as the reflected light information are observed to perform the focus in. As a result, in the optical recording / reproducing apparatus for a recording medium having a plurality of information recording layers, such as a multilayer optical disc, there is an effect that it is possible to reliably perform the focus retracting operation on the target information recording layer.

In particular, it becomes effective when the multi-layer recording medium is reproduced or recorded and reproduced by using an objective lens having a high numerical aperture (for example, 0.85) realized by a two-group lens or the like.

In addition, since the polarity of the focus control error signal is detected, the number of S-curve occurrences obtained when the focal position passes through the information recording layer by movement in the optical axis direction of the objective lens is also known, whereby the information on the recording medium is obtained. The number of layers in the recording layer can be detected.

Therefore, even when a type detection hole or the like cannot be detected mechanically or optically as an optical recording medium not loaded in a cartridge such as a bare disk, the number of layers of the information recording layer depends on the reflected light from the optical recording medium. It is possible to determine.

In addition, when focus search is performed in a state in which the light transmission protective layer (cover layer) in the information recording layer for spherical aberration correction state is set, the focus search is performed on an arbitrary information recording layer in the multilayer optical recording medium. With respect to this, the focus control can be performed more reliably. In addition, it is also possible to easily and reliably realize the operation of incorporating the confocal into the other information recording layer after the confocal introduction into one information recording layer, that is, the inter-layer movement of the condensed spot.

In particular, it is effective when a multi-layer optical disc recording medium having two or more information recording layers or recording and reproducing is performed by using a high numerical aperture objective lens realized by a two-group lens or the like. With respect to the multi-layer optical disc recording medium, stable focus control pulling-in operation can be realized.

In addition, after focusing is performed on the target information recording layer, the spherical aberration correction amount is optimized according to the reproduction signal or the spherical aberration error signal as the reflected light information, so that stable recording and reproduction can be performed regardless of the manufacturing error of the recording medium. It becomes possible to do it.

According to the present invention, when the focusing control is performed on the information recording layer of interest in a recording medium, first, the thickness of the light transmission protective layer (cover layer) in the information recording layer for the purpose of the spherical aberration correction state is matched. Set to state. Or it is set in the state which matched the average value of the thickness of each light transmission protective layer (cover layer) of a some information recording layer.

Then, a so-called focus search operation for moving the objective lens in the optical axis direction is performed, and then the focus is input by observing the polarity of the focus control error signal and the level of the reflected light intensity signal generated as the reflected light information.

As the focus control error signal, an S-shaped curve is obtained when the focus position passes through the information recording layer by the movement in the optical axis direction of the objective lens. Therefore, since the polarity of the focus control error signal is detected, it is possible to detect the number of layers of the information recording layer and the entry timing of the target information recording layer.

In addition, when focus search is performed in a state in which the light transmissive protective layer (cover layer) of the plurality of information recording layers is set to an average value, the S-shape at the same level as the focus control error signal passes through each information recording layer. Since the curve is detected, the insertion timing in the target information recording layer can be detected in accordance with the generation order of the polarity in the moving direction. The number of layers of the information recording layer can also be detected in accordance with the number of occurrences of the S-curve.

If the focus search is performed in a state that is set in accordance with the thickness of the light transmission protective layer (cover layer) in the information recording layer for the purpose of spherical aberration correction state, a large S-shape at the time of passing the target information recording layer Since the curve is detected, the insertion timing in the target information recording layer can be detected accurately by the polarity detection.

Claims (22)

An optical recording and reproducing apparatus for recording or reproducing information by irradiating a laser beam to a recording medium having a single or a plurality of information recording layers, An objective lens means having a predetermined numerical aperture and provided as an output stage of a laser beam, Correction means for correcting spherical aberration caused by the thickness of the light transmitting protective layer with respect to the information recording layer of the recording medium; Transfer means for transferring the objective lens means in the optical axis direction; Reflected light detecting means for detecting reflected light from the recording medium by the laser light irradiation and outputting reflected light information; Discriminating means for discriminating the polarity of the focus control error signal generated as the reflected light information and the level of the reflected light intensity signal generated as the reflected light information; The objective lens means is moved in the optical axis direction by the transfer means in a state where the correcting optical means is set to be optimal for the thickness of a specific light transmission protective layer, and focusing is performed in accordance with the discrimination information by the discriminating means. Focusing control means Optical recording and reproducing apparatus comprising a. The method of claim 1, And the objective lens means has a numerical aperture of 0.8 or more. The method of claim 1, The discriminating means outputs the result of comparing each of the threshold values of the positive predetermined level and the negative predetermined level with the focus control error signal as polarity information of the focus control error signal. Recording and playback device. The method of claim 1, The focusing control means performs focusing on the target information recording layer in accordance with the movement direction of the objective lens means by the transfer means and the generation order of the polarity information of the focus control error signal obtained by the discriminating means. An optical recording and reproducing apparatus, characterized in that. The method of claim 1, The focusing control means focuses on the target information recording layer in accordance with the movement direction of the objective lens means by the transfer means and the order and number of occurrences of the polarity information of the focus control error signal obtained by the discriminating means. An optical recording and reproducing apparatus, wherein the drawing is performed. The method of claim 1, The focusing control means sets the correction optical means as a thickness of the specific light transmissive protective layer as a rough average of the thickness of each light transmissive protective layer for a plurality of information recording layers of the recording medium. Playback device. The method of claim 1, The focusing control means sets the correction optical means for the thickness of the light transmission protective layer with respect to the information recording layer aiming at the focal point in of the plurality of information recording layers of the recording medium as the thickness of the specific light transmission protection layer. Optical recording and reproducing apparatus. The method of claim 1, In the case of focusing on another information recording layer after focusing on one information recording layer with respect to the recording medium having the plurality of information recording layers The focusing control means moves the objective lens means in the optical axis direction by the conveying means in a state where the correcting optical means is set to be optimal for the thickness of a particular light transmission protective layer, and the focusing control means And focusing on the other information recording layer accordingly. The method of claim 8, And the focusing control means sets the correction optical means for the thickness of the light transmissive protective layer with respect to the other information recording layer as the thickness of the specific light transmissive protective layer. The method of claim 8, The focusing control means sets the correction optical means as a thickness of the specific light transmissive protective layer as an approximate average of the thicknesses of the respective light transmissive protective layers with respect to the certain information recording layer and the other information recording layer. Optical recording and reproducing apparatus. The method of claim 1, And further comprising optimization means for optimizing the correction amount by the correction optical means according to the reproduction signal as the reflected light information or the spherical aberration error signal as the reflected light information after focusing on the target information recording layer. An optical recording and reproducing apparatus, characterized in that. An optical recording and reproducing apparatus for recording or reproducing information by irradiating a laser beam to a recording medium having a single or a plurality of information recording layers, wherein the focus control method performs focusing on a target information recording layer. A correction optical portion for correcting spherical aberration caused by the thickness of the light transmissive protective layer with respect to the information recording layer of the recording medium is set to be optimal for the thickness of the specific light transmissive protective layer, Polarity of the focus control error signal obtained as the reflected light information from the recording medium by the laser light irradiation while moving the objective lens provided as the output end of the laser light with a predetermined numerical aperture in the optical axis direction and the reflected light intensity signal generated as the reflected light information And discrimination processing is performed according to the discrimination information obtained by the discrimination processing. The method of claim 12, And said objective lens has a numerical aperture of 0.8 or more. The method of claim 12, The determination processing of the polarity of the focus control error signal compares each of the threshold values of the positive predetermined level and the negative predetermined level with the focus control error signal, and sets the comparison result as the discrimination information of the polarity of the focus control error signal. A focus control method characterized by the above-mentioned. The method of claim 12, And focusing the target information recording layer in accordance with the movement direction of the objective lens and the generation order of the polarity information of the focus control error signal obtained by the discrimination process. The method of claim 12, And focusing on the target information recording layer in accordance with the movement direction of the objective lens and the generation order and the number of occurrences of the polarity information of the focus control error signal obtained by the determination processing. The method of claim 12, And an approximate average value of the thickness of each light transmitting protective layer for the plurality of information recording layers of the recording medium is set as the thickness of the specific light transmitting protective layer for the correction optical unit. The method of claim 12, A focus control method characterized in that the correction optical unit is set as a thickness of the specific light transmission protective layer with a thickness of the light transmission protective layer with respect to the information recording layer aiming at the focus in of the plurality of information recording layers of the recording medium. . The method of claim 12, In the case of focusing on another information recording layer after focusing on one information recording layer with respect to the recording medium having the plurality of information recording layers The objective lens is moved in the optical axis direction while the correction optical unit is set to be optimal for the thickness of a specific light transmission protective layer, Discriminating the polarity of the focus control error signal obtained as the reflected light information from the recording medium by the laser light irradiation and the level of the reflected light intensity signal generated as the reflected light information, And focusing on the other information recording layer in accordance with the discrimination information obtained by the discrimination process. The method of claim 19, And the correction optical unit is set as the thickness of the specific light transmissive protective layer with the thickness of the light transmissive protective layer relative to the other information recording layer. The method of claim 19, And an approximate average value of the thickness of each light transmitting protective layer relative to the one information recording layer and the other information recording layer as the thickness of the specific light transmitting protective layer. The method of claim 12, After focusing on the target information recording layer, the amount of correction by the correction optical unit is optimized according to a reproduction signal as the reflected light information or a spherical aberration error signal as the reflected light information. .