JP2000048407A - Optical recording medium, master disk for production of optical recording medium and optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to stably execute tracking servo and track seeking even if a track pitch is narrowed by forming two grooves varying in depth in such a manner that these grooves are adjacent to each other and forming both grooves so as to satisfy respectively prescribed relations. SOLUTION: This optical recording medium is formed with the grooves in such a manner that the first grooves and second grooves varying in depth are adjacent to each other. The first grooves and the second grooves are so formed as to satisfy equation I and equation II or equation III and equation IV. The phase depth X of the first grooves is expressed by xXn/λ and the phase depth Y of the second grooves by y×n/λ when the refractive index of the medium from the light incident surface to the grooves is defined as (n), the depth of the first grooves as (x) and the depth of the second grooves as (y). In the equation I and equation II, N is an arbitrary integer and in the equation III and equation IV, M is an arbitrary integer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording medium on which land-groove recording is performed. The present invention also relates to an optical recording medium manufacturing master used for manufacturing an optical recording medium on which land-groove recording is performed. Further, the present invention relates to an optical recording / reproducing apparatus that performs recording and / or reproduction on an optical recording medium on which land / groove recording is performed.

[0002]

2. Description of the Related Art As an optical recording medium, an optical disk formed in a disk shape and optically recorded and / or reproduced has been put to practical use. Optical disks include read-only optical disks in which embossed pits corresponding to data are formed in advance on disk substrates, magneto-optical disks that record and reproduce data using the magneto-optical effect, and phase changes in the recording film. Phase-change type optical discs for recording and reproducing data.

[0003] Of these optical disks, writable optical disks such as magneto-optical disks and phase-change optical disks usually have grooves along recording tracks formed on the disk substrate. Here, the groove is a so-called guide groove formed along a recording track in order to mainly perform tracking servo and track seek.

Incidentally, the tracking servo is to make a light spot follow a recording track. Track seek refers to moving the light spot to a desired recording track. In order to perform track seek, it is necessary to detect the number of tracks that the light spot has traversed during the movement of the light spot. Such detection of the number of tracks is generally called traverse counting.

By the way, in the conventional optical disk, mainly,
High recording density has been achieved by improving the reproduction resolution of an optical pickup mounted on an optical recording / reproducing apparatus. The improvement in the reproduction resolution of the optical pickup is mainly achieved by shortening the wavelength λ of the laser beam used for data reproduction,
This has been realized by increasing the numerical aperture NA of an objective lens that focuses a laser beam on an optical disc.

Here, as a specific example of an optical disk,
CD, MD, MDData2, DVD + RW, DVD-
Table 1 shows the values of the wavelength λ of the laser beam used for data reproduction, the numerical aperture NA of the objective lens, and the track pitch of the ROM as an example.

[0007]

[Table 1]

As shown in Table 1, in the conventional optical disk, narrowing the track is realized by shortening the wavelength λ of the laser beam or increasing the numerical aperture NA of the objective lens. Higher recording density has been achieved.

However, in the conventional optical disk, even if the track is narrowed, the spatial frequency of the track pitch is set to about 1/2 to 2/3 of the cutoff frequency of the optical pickup of the optical recording / reproducing apparatus. ing. Here, the cut-off frequency is a frequency at which the amplitude of the reproduction signal becomes substantially zero, the wavelength of the laser light used for reproducing the data is λ, and the aperture of the objective lens for condensing the laser light on the optical disk. When the number is NA, it is represented by 2NA / λ.

The reason why the spatial frequency of the track pitch is set to about 1/2 to 2/3 of the cutoff frequency is as follows.
Signals required for tracking servo and track seek are provided at a sufficient level to stably perform tracking servo that causes the light spot to follow the recording track and track seek that moves the light spot to the desired recording track. It is necessary to be able to obtain.

For example, in an optical disk such as MDData2, a push-pull signal is used for tracking servo. To stably perform tracking servo, the amplitude ratio of the push-pull signal needs to be about 0.15 or more. Also, at the time of track seek, a cross track signal is used for traverse counting, but in order to perform track seek stably, the cross track signal amplitude needs to be about 0.06 or more. In the conventional optical disk, in order to set the push-pull signal amplitude ratio to 0.15 or more and the cross-track signal amplitude to 0.06 or more, the spatial frequency of the track pitch is set to 1/2 to 2 of the cutoff frequency. It was necessary to be about / 3.

The push-pull signal detects reflected light from the optical disk by two photodetectors A and B symmetrically arranged with respect to the track center as shown in FIG. The difference between the outputs from detectors A and B (A−
B). The cross track signal is obtained by taking the sum (A + B) of the outputs from the two photodetectors A and B.

That is, when the light reflected from the optical disk during recording and / or reproduction is detected by two photodetectors symmetrically arranged with respect to the track center, the amount of light detected by one of the photodetectors is determined. A, when the light amount detected by the other photodetector is B, a difference signal represented by AB is a push-pull signal, and a sum signal represented by A + B is a cross-track signal. Further, assuming that the amplitude of the push-pull signal is C, the amplitude of the cross-track signal is D, and the value of the cross-track signal at the mirror portion where no groove is formed is Mmax, the amplitude ratio of the push-pull signal is C / Mmax.
, And the cross-track signal amplitude ratio is represented by D / Mmax.

[0014]

By the way, the demand for higher recording density for an optical recording medium such as an optical disk is not known to end, and further higher recording density is desired.
As one of the techniques for realizing a higher recording density of an optical recording medium, a technique of recording an information signal on both a groove portion and a land portion between the grooves has been devised. Recording an information signal on both a groove and a land in this way is generally called land-groove recording. In land-groove recording, the recording density is ideally doubled as compared with groove recording in which an information signal is recorded only in a groove portion or land recording in which an information signal is recorded only in a land portion. Is possible.

In land-groove recording, it is desirable that the groove width and the land width be the same in order to make the recording / reproducing characteristics in the groove portion and the recording / reproducing characteristics in the land portion the same. However, when the groove width and the land width are the same, the difference between the cross-track signal obtained when the light spot is on the groove and the cross-track signal obtained when the light spot is on the land disappears, and the track At the time of seeking, the land and the groove cannot be distinguished. That is, conventionally, in an optical recording medium employing land / groove recording, there has been a problem that a land and a groove cannot be distinguished during track seek.

Further, in the land-groove recording optical recording medium, there is a problem that when the track pitch is reduced, the push-pull signal is significantly reduced. For example, in a conventional land-groove recording optical recording medium,
When the track pitch is 1.00 μm, the amplitude ratio of the push-pull signal is 0.48, which enables stable tracking servo. However,
When the track pitch is set to 0.75 μm, the push-pull signal amplitude ratio is reduced to about 0.09.
In this case, it is difficult to perform tracking servo stably. Therefore, conventionally, it has been difficult to increase the recording density by narrowing the track pitch in the land-groove recording optical recording medium.

The present invention has been proposed in view of the above-described conventional circumstances, and it is possible to stably perform tracking servo and track seek while employing land / groove recording suitable for high recording density. It is an object to provide a possible optical recording medium. Another object of the present invention is to provide an optical recording medium manufacturing master disc capable of manufacturing such an optical recording medium. Another object of the present invention is to provide an optical recording / reproducing apparatus using such an optical recording medium as a recording medium.

[0018]

According to the first optical recording medium of the present invention, a groove is formed along a recording track,
An optical recording medium on which recording and / or reproduction is performed by irradiating light of a predetermined wavelength λ, and information signals are recorded on both a groove portion and a land portion between the grooves. In this optical recording medium, a first groove and a second groove having different depths are formed adjacent to each other, and the first groove and the second groove are formed by the following formula (1). ) And formula (2), or the following formulas (3) and (4). Here, assuming that the refractive index of the medium from the light incident surface to the groove is n, the depth of the first groove is x, and the depth of the second groove is y, the phase depth X of the first groove is x × n / λ, and the phase depth Y of the second groove is represented by y × n / λ. In the following formulas (1) and (2), N is an arbitrary integer, and in the following formulas (3) and (4), M is an arbitrary integer.

Y ≧ 0.5N + 26.83705−266.3275X + 987.8340X ² −1624.4709X ³ + 1000.2368X ⁴ ... (1) Y ≦ 0.5N−1003.7399 + 15110.1053X−94546.0895X ² + 314796.5182X ³ −588227.8600X ⁴ + 584832.1407X ⁵ -241694.0163X ⁶ ... (2) Y ≧ 0.5M−0.612030 + 7.861006X−22.53486X ² + 19.37300X ³ ... (3) Y ≦ 0.5M−5.553633 + 32.00983X−57.62127X ² + 33.37140X ³ (4) In the first optical recording medium according to the present invention as described above, the first groove and the second groove having different depths correspond to the above formulas (1) and (2). ) Alternatively, since signals are formed so as to satisfy Expressions (3) and (4), even if the track pitch is narrowed while land-groove recording is employed, signals necessary for tracking servo and track seek can be sufficiently obtained. Can be obtained at different levels.

In the first optical recording medium, it is preferable that at least one of the first groove and the second groove is a wobbling groove formed so that at least a part thereof meanders. By making the groove meander as described above to form a wobbling groove, it is possible to add address information and the like to the groove itself.

In the first optical recording medium, the numerical aperture of the objective lens used for recording and / or reproduction is NA, and the wavelength of light is λ. It is preferable that the spatial frequency of the track pitch is higher than the off frequency. By making the spatial frequency of the track pitch higher than the cutoff frequency, it is possible to further increase the recording density of the optical recording medium.

Further, a second optical recording medium according to the present invention comprises:
An optical recording medium in which a groove is formed along a recording track and is irradiated with light to perform recording and / or reproduction, and an information signal of an information signal is formed on both a groove portion and a land portion between the grooves. A record is made. And
This optical recording medium has a first groove having a different depth as a groove.
And the second groove are formed adjacent to each other. Here, when the light reflected by the optical recording medium is detected by two photodetectors arranged symmetrically with respect to the track center, the amount of light detected by one of the photodetectors Is A, the light amount detected by the other photodetector is B, the amplitude of the difference signal represented by AB is C,
Let D be the amplitude of the sum signal represented by A + B, and Mmax be the value of the sum signal at the mirror surface where no groove is formed. At this time, the optical recording medium is characterized in that the difference signal amplitude ratio represented by C / Mmax is 0.15 or more and the sum signal amplitude ratio represented by D / Mmax is 0.06 or more. .

In the second optical recording medium according to the present invention as described above, even if land / groove recording is adopted, even if the track pitch is narrowed by changing the depth of adjacent grooves. In addition, signals required for tracking servo and track seek can be obtained at a sufficient level. Specifically, in this optical recording medium, the difference signal amplitude ratio is set to be 0.15 or more.
Tracking servo can be stably performed using the difference signal. Further, since the sum signal amplitude ratio is set to 0.06 or more, the track seek can be stably performed using the sum signal.

In the second optical recording medium, it is preferable that at least one of the first groove and the second groove is a wobbling groove formed so that at least a part thereof meanders. By making the groove meander as described above to form a wobbling groove, it is possible to add address information and the like to the groove itself.

In the second optical recording medium, when the numerical aperture of the objective lens used for recording and / or reproduction is NA, and the wavelength of light is λ, the cutoff represented by 2 × NA / λ. It is preferable that the spatial frequency of the track pitch is higher than the off frequency. By making the spatial frequency of the track pitch higher than the cutoff frequency, it is possible to further increase the recording density of the optical recording medium.

The master for producing an optical recording medium according to the present invention produces an optical recording medium on which recording and / or reproduction is performed by forming a groove along a recording track and irradiating light of a predetermined wavelength λ. This is a master for producing an optical recording medium used at the time. Here, the target optical recording medium is a recording medium on which information signals are recorded on both the groove portion and the land portion between the grooves.

The master for manufacturing an optical recording medium according to the present invention is formed such that a first groove pattern and a second groove pattern are adjacent to each other as a concave / convex pattern corresponding to the groove. Here, the refractive index of the medium from the light incident surface of the optical recording medium to the groove is n,
When the depth of the groove pattern is x ′ and the depth of the second groove pattern is y ′, the phase depth of the first groove pattern represented by x ′ × n / λ is X ′, y '× n / λ
Let Y ′ be the phase depth of the second groove pattern represented by. And, the master for optical recording medium production according to the present invention,
The first groove pattern and the second groove pattern are expressed by the following expressions (5) and (6) or the following expression (7)
And formula (8). In the following formulas (5) and (6), N is an arbitrary integer, and in the following formulas (7) and (8),
M is an arbitrary integer.

[0028] Y '≧ 0.5N + 26.83705-266.3275X' + 987.8340X '2 -1624.4709X' 3 + 1000.2368X '4 ··· (5) Y' ≦ 0.5N-1003.7399 + 15110.1053X'-94546.0895X ' ^{2 + 314796.5182X '3 -588227.8600X' 4} + 584832.1407X '5 -241694.0163X' 6 ··· (6) Y '≧ 0.5M-0.612030 + 7.861006X'-22.53486X' 2 + 19.37300X '3 ·· in · (7) Y '≦ 0.5M -5.553633 + 32.00983X'-57.62127X' 2 + 33.37140X ' optical recording medium manufacturing master according to ³ (8) the present invention as described above,
The first groove pattern and the second groove pattern are expressed by the above formulas (5) and (6) or the above formula (7).
And the formula (8) are satisfied, the use of this master for producing an optical recording medium allows the use of the formulas (1) and (2) or the formulas (3) and (4). An optical recording medium having a first groove and a second groove satisfying the above conditions can be manufactured. Therefore, according to this master for producing an optical recording medium, even if the track pitch is narrowed while using land-groove recording,
An optical recording medium capable of obtaining signals required for tracking servo and track seek at a sufficient level can be manufactured.

In the above-mentioned master for producing an optical recording medium, at least one of the first groove pattern and the second groove pattern is a concavo-convex pattern corresponding to a wobbling groove formed so that at least a part thereof is meandering. It is preferred that According to such a master for manufacturing an optical recording medium, an optical recording medium having a wobbling groove can be manufactured. Then, by making the groove meander and forming a wobbling groove, it is possible to add address information and the like to the groove itself, so that at least one of the first groove pattern and the second groove pattern corresponds to the wobbling groove. According to the optical recording medium manufacturing master having the concave-convex pattern, an optical recording medium in which address information and the like are added to the groove itself can be manufactured.

An optical recording / reproducing apparatus according to the present invention is an optical recording / reproducing apparatus for irradiating light onto an optical recording medium having grooves formed along recording tracks to perform recording and / or reproduction. . As an optical recording medium to be recorded and / or reproduced, information signals are recorded on both the groove portion and the land portion between the grooves, and the grooves have different depths. An optical recording medium in which a first groove and a second groove are formed adjacent to each other is used. The optical recording / reproducing apparatus according to the present invention includes two photodetectors symmetrically arranged with respect to the track center of the optical recording medium. Here, when the light reflected by the optical recording medium is detected by the two photodetectors, the amount of light detected by one of the photodetectors is A, and the amount of light detected by the other photodetector is detected by the other photodetector. Let B be the amount of light to be emitted. In the optical recording / reproducing apparatus according to the present invention, a tracking servo for causing an optical spot to follow a recording track during recording and / or reproduction is A-
The track seek for moving the light spot to a desired recording track by using the difference signal represented by B is performed by A + B
This is performed using the sum signal represented by

In the optical recording / reproducing apparatus according to the present invention as described above, an optical recording medium in which adjacent grooves have different depths is used as an optical recording medium to be recorded and / or reproduced. In such an optical recording medium, signals required for performing track seek and tracking servo can be obtained at a sufficient level even when land-groove recording is employed. That is, in the optical recording / reproducing apparatus according to the present invention, by using an optical recording medium having adjacent grooves having different depths, track seek can be stably performed by using the sum signal while employing land / groove recording. And the tracking servo can be stably performed by using the difference signal.

In the above-mentioned optical recording / reproducing apparatus, the optical recording medium to be recorded and / or reproduced is such that at least one of the first groove and the second groove is at least partially meandering. It is preferable that the optical recording medium is a wobbling groove formed.
By making the groove meander as described above to form a wobbling groove, it is possible to add address information and the like to the groove itself.

Further, the optical recording / reproducing apparatus is capable of recording and / or
Alternatively, an objective lens for condensing light on an optical recording medium at the time of reproduction is provided. When the numerical aperture of the objective lens is NA and the wavelength of the light is λ, the track of the optical recording medium to be recorded and / or reproduced is more than the cutoff frequency represented by 2 × NA / λ. It is preferable that the spatial frequency of the pitch is large. By making the spatial frequency of the track pitch higher than the cutoff frequency, it is possible to further increase the recording density of the optical recording medium.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings, taking the case where the present invention is applied to a magneto-optical disk as an example.

In the following description, a meandering groove is called wobbling, and a groove formed so as to wobble is called a wobbling groove. Also, a groove formed without meandering with respect to the wobbling groove is called a straight groove.

In the following description, when the light reflected by the magneto-optical disk is detected by two photodetectors symmetrically arranged with respect to the track center, the light is detected by one of the photodetectors. When the light amount detected by the other photodetector is A and the light amount detected by the other photodetector is B, the difference signal represented by AB is referred to as a push-pull signal, and the sum signal represented by A + B is referred to as a cross signal. This is called a track signal. When the value of the sum signal at the mirror surface portion where no groove is formed is Mmax, the value represented by C / Mmax is called the push-pull signal amplitude ratio, and the value represented by D / Mmax is the cross-track It is called a signal amplitude ratio.

<Magneto-Optical Disk> FIG. 1 is an enlarged cross-sectional view of a main part of a magneto-optical disk according to the present invention.

The magneto-optical disk 1 is formed in a disk shape, and data is recorded and reproduced using the magneto-optical effect. The magneto-optical disk 1 is made of polymethyl methacrylate (PMMA) or polycarbonate (P
A recording layer 3 for performing magneto-optical recording and a protective layer 4 for protecting the recording layer 3 are formed on a disk substrate 2 made of C) or the like. Here, the recording layer 3 is made of, for example, SiN
, A perpendicular magnetic recording film made of a TeFeCo alloy or the like, a dielectric film made of SiN or the like, and a light reflection film made of Al or the like. In addition, the protective layer 4
For example, the recording layer 3 is spin-coated with an ultraviolet curable resin. In the present invention, the configurations of the recording layer 3 and the protective layer 4 are arbitrary, and are not limited to this example.

As shown in FIG. 2 in which a part of the recording area is enlarged, the magneto-optical disk 1 has two wobbling grooves 6 having different depths and substantially equal widths.
And the straight groove 7 are formed on the disk substrate 2 so as to draw a double spiral (that is, in a double spiral shape). FIG. 2 also shows the correspondence between the cross track signal and the push-pull signal obtained from the magneto-optical disk 1 and the grooves 6 and 7.

In the magneto-optical disk 1 shown in FIGS. 1 and 2, the wobbling groove 6 is a deep groove and the straight groove 7 is a shallow groove. Conversely, the wobbling groove 6 is a shallow groove. The groove or the straight groove 7 may be a deeper groove. When the wobbling groove 6 is a shallow groove and the straight groove 7 is a deep groove, the phases of the cross track signal and the push-pull signal are inverted as compared with the examples shown in FIGS. Become.

In this magneto-optical disk 1, the wobbling groove 6 is formed so as to meander at a constant period with an amplitude of ± 10 nm, for example. That is, in the magneto-optical disk 1, address information is added to the groove by wobbling one of the grooves (that is, the wobbling groove 6).

The magneto-optical disk 1 is a recording medium on which land and groove recording is performed, and includes a wobbling groove 6 and a straight groove 7 and a land between the wobbling groove 6 and the straight groove 7. Data is recorded by magneto-optical recording. That is, as shown in FIG. 2, in the magneto-optical disk 1, the portion of the straight groove 7 becomes a first recording track TrackA on which an information signal is recorded. Further, the portion of the land between the straight groove 7 and the wobbling groove 6 and the portion where the inner circumferential side of the disk is the straight groove 7 is the second portion where the information signal is recorded.
Recording track TrackB. Further, the portion of the wobbling groove 6 becomes a third recording track TrackC on which the information signal is recorded. Wobbling groove 6
And the land between the straight groove 7 and
The portion where the inner circumferential side of the disc is the wobbling groove 6 is the fourth recording track Trac where the information signal is recorded.
kD.

Here, the two grooves formed in a double spiral shape are the wobbling grooves 6.
And an example consisting of a straight groove 7, but in the optical recording medium according to the present invention, these two grooves only need to have different depths, and both may be straight grooves. , Both may be wobbling grooves. However, when the groove is wobbled, there is an advantage that address information and the like can be added to the groove itself. Moreover,
When one groove is used as a wobbling groove and the other groove is used as a straight groove as in this example, it is easier to narrow the track than when both grooves are used as a wobbling groove. Is suitable for

Then, in this magneto-optical disk 1,
The track pitch TPitch is set to 0.50 μm. Here, the track pitch TPitch corresponds to an interval between the center positions of the wobbling groove 6 and the straight groove 7. That is, in the magneto-optical disk 1, the interval between the center positions of the wobbling groove 6 and the straight groove 7 is 0.50 μm.

In the following description, the interval between the center positions of the adjacent straight grooves 7 is referred to as a track period TPeriod. The track period TPeriod is equivalent to twice the track pitch TPitch. In this magneto-optical disk 1, the track period TPeriod is:
1.00 μm.

In the magneto-optical disk 1 to which the present invention is applied, the wobbling groove 6 and the straight groove 7 are formed so as to have different depths. Specifically, the phase depth of the deeper groove of the wobbling groove 6 and the straight groove 7 is set to X.
Assuming that the phase depth of the shallower groove is Y, the wobbling groove 6 and the straight groove 7 are expressed by the following equations (1-1) and (1-2) or the following equation (1-
3) and Formula (1-4).

Y ≧ 0.5N + 26.83705−266.3275X + 987.8340X ² −1624.4709X ³ + 1000.2368X ⁴ ... (1-1) Y ≦ 0.5N−1003.7399 + 15110.1053X−94546.0895X ² + 314796.5182X ³ −588227.8600 X ⁴ + 584832.1407X ⁵ -241694.0163X ⁶ ... (1-2) Y ≧ 0.5M−0.612030 + 7.861006X−22.53486X ² + 1.37300X ³ ... (1-3) Y ≦ 0.5M−5.553633 + 32 .00983X−57.62127X ² + 33.37140X ³ (1-4) Note that the wavelength of the laser beam used for recording / reproducing on the magneto-optical disk 1 is λ, and the light is incident from the light incident surface of the magneto-optical disk 1 to the groove. Medium to reach (ie disk substrate 2)
Is the refractive index of n, the phase depth X of the deeper groove
Is represented by x × n / λ, where x is the depth of the groove. The phase depth Y of the shallower groove is represented by y × n / λ, where y is the depth of the groove.

In the magneto-optical disk 1 as described above, as can be seen from the experimental results described later, the wobbling groove 6 and the straight groove 7 are determined by the above equations (1-1) and (1-2) or the above equations (1-2). 1-3) and the formula (1-
Since it is formed so as to satisfy 4), signals necessary for tracking servo and track seek can be obtained at a sufficient level.

In this magneto-optical disk 1, FIG.
As shown in (2), at least one of the level of the push-pull signal, the polarity of the push-pull signal, the level of the cross-track signal, and the polarity of the cross-track signal differs for each recording track. Therefore, in the magneto-optical disk 1, the first recording track TrackA and the second recording track TrackA are detected by detecting the levels and polarities of the push-pull signal and the cross-track signal during the track seek.
Of the recording track TrackB and the third recording track TrackC
And the fourth recording track TrackD.

<Laser Cutting Apparatus> When the above-described magneto-optical disk 1 is manufactured, a laser cutting apparatus is used for manufacturing an optical recording medium manufacturing master as the master of the magneto-optical disk 1. Hereinafter, an example of a laser cutting device used for manufacturing an optical recording medium manufacturing master will be described in detail with reference to FIG.

The laser cutting device 10 shown in FIG.
Is the photoresist 1 applied on the glass substrate 11
Exposure No. 2 to form a latent image. When a latent image is formed on the photoresist 12 by the laser cutting device 10, the glass substrate 11 coated with the photoresist 12 is attached to a rotary driving device provided on a movable optical table. When exposing the photoresist 12, the glass substrate 11 is driven to rotate by a rotation driving device as shown by an arrow A <b> 1 in the drawing so that exposure with a desired pattern is performed over the entire surface of the photoresist 12. Is translated by the moving optical table.

The laser cutting apparatus 10 is capable of exposing the photoresist 12 with two exposure beams, and forms a latent image corresponding to the wobbling groove 6 and a latent image corresponding to the straight groove 7. It is formed by each exposure beam. That is,
In the laser cutting apparatus 10, a latent image corresponding to the wobbling groove 6 is formed by the first exposure beam, and the straight groove 7 is formed by the second exposure beam.
Is formed.

The laser cutting device 10 includes a light source 13 for emitting laser light and an electro-optic modulator (EO) for adjusting the light intensity of the laser light emitted from the light source 13.
M: Electro Optical Modulator 14, an analyzer 15 arranged on the optical axis of the laser light emitted from the electro-optic modulator 14, and the laser light transmitted through the analyzer 15 into reflected light and transmitted light. First beam splitter 17 for splitting
A second beam splitter 18 that divides the laser light transmitted through the first beam splitter 17 into reflected light and transmitted light, and a photodetector (PD) that detects the laser light transmitted through the second beam splitter 18 : Photo De
tector) 19 and an auto power controller (AP) that applies a signal electric field to the electro-optic modulator 14 to adjust the intensity of laser light emitted from the electro-optic modulator 14.
C: Auto Power Controller) 20.

In the laser cutting device 10, the laser light emitted from the light source 13 is first given a predetermined light intensity by an electro-optic modulator 14 driven by a signal electric field applied from an auto power controller 20. And enters the analyzer 15. Here, analyzer 1
Reference numeral 5 denotes an analyzer that transmits only S-polarized light.
The laser beam transmitted through 5 becomes S-polarized light.

Although any light source can be used as the light source 13, a light source which emits a laser beam having a relatively short wavelength is preferable. Specifically, for example, the wavelength λ is 351 nm.
Kr laser that emits laser light of a wavelength of 442n
A He—Cd laser that emits m laser light is suitable as the light source 13.

The S-polarized laser light transmitted through the analyzer 15 is first split into reflected light and transmitted light by the first beam splitter 17, and further, the laser light transmitted through the first beam splitter 17. The light is split by the second beam splitter 18 into reflected light and transmitted light.
In this laser cutting device 10, the laser beam reflected by the first beam splitter 17
And the laser beam reflected by the second beam splitter 18 becomes a second exposure beam.

The light intensity of the laser beam transmitted through the second beam splitter 18 is detected by the photodetector 19, and a signal corresponding to the light intensity is sent from the photodetector 19 to the auto power controller 20.
Then, in response to the signal sent from the photodetector 19, the auto power controller 20 applies the light to the electro-optic modulator 14 so that the light intensity detected by the photodetector 19 becomes constant at a predetermined level. Adjust the signal electric field. As a result, automatic power control (APC: Auto Power Control) is performed so that the light intensity of the laser light emitted from the electro-optic modulator 14 becomes constant, and a stable laser light with less noise is obtained.

The laser cutting device 10
Is a first modulation optical system 22 for modulating the light intensity of the laser light reflected by the first beam splitter 17.
And a second modulation optical system 23 for modulating the light intensity of the laser beam reflected by the second beam splitter 18.
And an optical system 24 for recombining the respective laser beams subjected to the light intensity modulation by the first and second modulation optical systems 22 and 23 and condensing them on the photoresist 12.

Then, the first exposure beam reflected by the first beam splitter 17 is guided to the first modulation optical system 22, and is subjected to light intensity modulation by the first modulation optical system 22. Similarly, the second beam splitter 1
The second exposure beam reflected by 8 is guided to a second modulation optical system 23, where the light intensity is modulated by the second modulation optical system 23.

That is, the first exposure beam incident on the first modulation optical system 22 is condensed by the condensing lens 29 and then incident on the acousto-optic modulator 30. The light intensity is modulated so as to correspond to a desired exposure pattern. Here, as the acousto-optic element used for the acousto-optic modulator 30, for example, an acousto-optic element made of tellurium oxide (TeO ₂ ) is suitable. The first light intensity modulated by the acousto-optic modulator 30
Is collimated by the collimator lens 31 and then emitted from the first modulation optical system 22.

Here, the acousto-optic modulator 30 has a driver 32 for driving the acousto-optic modulator 30.
Is attached. At the time of exposing the photoresist, a signal S1 corresponding to a desired exposure pattern is input to the driving driver 32, and the acousto-optic modulator 30 is driven by the driving driver 32 according to the signal S1, and the second exposure Light intensity modulation is performed on the beam.

More specifically, for example, when a latent image having a groove pattern corresponding to the wobbling groove 6 having a constant depth is formed on the photoresist 12, a DC signal of a constant level is transmitted to the driving driver 32. The acousto-optic modulator 30 is driven by the driving driver 32 according to the input DC signal. Thus, light intensity modulation is performed on the first exposure beam so as to correspond to a desired groove pattern.

The second exposure beam incident on the second modulation optical system 23 is condensed by a condenser lens 33 and then incident on an acousto-optic modulator 34, which The light intensity is modulated so as to correspond to a desired exposure pattern. Here, as the acousto-optic element used for the acousto-optic modulator 34, for example, tellurium oxide (T
An acousto-optic device made of eO ₂ ) is preferred. And
The second exposure beam, the light intensity of which has been modulated by the acousto-optic modulator 34, is collimated by the collimating lens 35 and transmitted through the λ / 2 wavelength plate 36, so that the polarization direction is rotated by 90 °. Then, the light is emitted from the second modulation optical system 23.

Here, a driving driver 37 for driving the acousto-optic modulator 34 is provided in the acousto-optic modulator 34.
Is attached. Then, when exposing the photoresist 12, a signal S2 corresponding to a desired exposure pattern is input to the driving driver 37, and the acousto-optic modulator 34 is driven by the driving driver 37 according to the signal S2, and the second Light intensity modulation is performed on the exposure beam.

Specifically, for example, when a latent image having a groove pattern corresponding to the straight groove 7 having a constant depth is formed on the photoresist 12, a DC signal of a constant level is supplied to the driving driver 37. Input and the D
The acousto-optic modulator 34 is driven by the driving driver 37 according to the C signal. Thereby, light intensity modulation is performed on the second exposure beam so as to correspond to a desired groove pattern.

As described above, the first exposure beam is subjected to light intensity modulation by the first modulation optical system 22,
Is subjected to light intensity modulation by the second modulation optical system 23. At this time, the first exposure beam emitted from the first modulation optical system 22 remains S-polarized light, but the second exposure beam emitted from the second modulation optical system 23 has a wavelength of λ / 2 wavelength. Since the polarization direction is rotated by 90 ° by passing through the plate 36, the polarization is P-polarized.

Then, the first exposure beam emitted from the first modulation optical system 22 is reflected by the mirror 41, guided horizontally and parallel on the moving optical table, and enters the deflection optical system 46. And the first exposure beam is
After being optically deflected by the deflecting optical system 46, the light is reflected by the mirror 44 and its traveling direction is bent by 90 ° before being incident on the polarization beam splitter 45. On the other hand, the second
The second exposure beam emitted from the modulation optical system 32 of
The light is reflected by the mirror 42 and is guided horizontally and parallel on the moving optical table, and the polarization beam splitter 4
5 is incident.

Here, the deflecting optical system 46 is for optically deflecting the first exposure beam so as to correspond to wobbling of the wobbling groove. That is, the light emitted from the first modulation optical system 22 and the deflection optical system 4
The first exposure beam incident on the wedge prism 4
7 through an acousto-optic deflector (AOD: Acousto Optical
Deflector) 48 and is subjected to optical deflection by the acousto-optic deflector 48 so as to correspond to a desired exposure pattern. Here, as an acousto-optic element used for the acousto-optic deflector 48, for example, tellurium oxide (TeO
_The acousto-optic element consisting of ₂ ) is preferred. The first exposure beam that has been optically deflected by the acousto-optic deflector 48 passes through the wedge prism 49 to the deflection optical system 4.
6 is emitted.

Here, the acousto-optic deflector 48 includes a driving driver 50 for driving the acousto-optic deflector 48.
Is attached, and the driving driver 50 includes:
Voltage Controlled Oscilla (VCO)
tor) 51 is FM-modulated by a control signal S3 including address information and supplied. When the photoresist 12 is exposed, a signal corresponding to a desired exposure pattern is input from the voltage controlled oscillator 51 to the driving driver 50, and the driving driver 5
The acousto-optic deflector 48 is driven by 0, whereby the first exposure beam is optically deflected.

Specifically, for example, a frequency of 84.672
By wobbling the groove at kHz,
In a case where address information is added to a groove, for example, a high frequency signal having a center frequency of 224 MHz
The signal FM-modulated by the control signal of 4.672 kHz is
It is supplied from the voltage controlled oscillator 51 to the driving driver 50. In response to this signal, the driving driver 50 drives the acousto-optic deflector 48 to change the Bragg angle of the acousto-optic element of the acousto-optic deflector 48. Optical deflection is performed on the first exposure beam.

The first exposure beam optically deflected by the deflection optical system 46 so as to correspond to the wobbling of the wobbling groove 6 is reflected by the mirror 44 and travels in the traveling direction as described above. Is 9
After being bent by 0 °, the light enters the polarization beam splitter 45.

Here, the polarization beam splitter 45
It reflects the polarized light and transmits the P-polarized light.
Then, the first exposure beam emitted from the first modulation optical system 22 and subjected to optical deflection by the deflection optical system 46 is:
The second exposure beam emitted from the second modulation optical system 23 is S-polarized light and is P-polarized light. Therefore,
The first exposure beam is reflected by the polarization beam splitter 45, and the second exposure beam passes through the polarization beam splitter 45. Thus, the first exposure beam emitted from the first modulation optical system 22 and optically deflected by the deflection optical system 46 and the second exposure beam emitted from the second modulation optical system 23 Re-combination is performed so that the traveling directions are the same.

The first and second exposure beams recombined so that the traveling directions are the same and emitted from the polarizing beam splitter 45 are adjusted to a predetermined beam diameter by the magnifying lens 52, and are then mirrored. The light is reflected by the objective lens 54 and guided to the objective lens 54, and is focused on the photoresist 12 by the objective lens 54. This allows
The photoresist 12 is exposed, and a latent image is formed on the photoresist 12. At this time, as described above, the glass substrate 11 on which the photoresist 12 is applied is rotated by a rotary driving device as shown by an arrow A1 in the figure so that the entire surface of the photoresist 12 is exposed in a desired pattern. , And is translated by a moving optical table. As a result, a latent image corresponding to the irradiation locus of the first and second exposure beams is formed over the entire surface of the photoresist 12.

The objective lens 54 for condensing the exposure beam on the photoresist 12 has a numerical aperture of N in order to form a finer groove pattern.
It is preferable that A is large, and specifically, an objective lens having a numerical aperture NA of about 0.9 is suitable.

When irradiating the photoresist 12 with the first and second exposure beams, the beam diameters of the first and second exposure beams are changed by the magnifying lens 52 as necessary. The effective numerical aperture for the objective lens 54 is adjusted. Thereby, the spot diameters of the first and second exposure beams focused on the surface of the photoresist 12 can be changed.

The first exposure beam incident on the polarization beam splitter 45 is combined with the second exposure beam on the reflection surface of the polarization beam splitter 45. Here, the polarization beam splitter 45 is disposed such that the reflection surface of the polarization beam splitter forms an appropriate reflection angle with respect to the traveling direction of light that is synthesized and emitted by the reflection surface.

More specifically, the reflection angle of the reflection surface of the polarizing beam splitter 54 is determined by the difference between the spot corresponding to the first exposure beam and the spot corresponding to the second exposure beam in the radial direction of the glass substrate 11. The interval is the track pitch
Set to correspond to TPitch. This makes it possible to expose the portion corresponding to the wobbling groove 6 with the first exposure beam, and at the same time, to expose the portion corresponding to the straight groove 7 with the second exposure beam.

The laser cutting apparatus 10 as described above
Then, an optical system corresponding to a first exposure beam for forming a latent image corresponding to the wobbling groove 6 and an optical system corresponding to a second exposure beam for forming a latent image corresponding to the straight groove 7 Therefore, the latent image corresponding to the wobbling groove 6 and the latent image corresponding to the straight groove 7 can be collectively formed only by the laser cutting device 10. Moreover,
In the laser cutting apparatus 10, the irradiation position of the first exposure beam and the second exposure beam are adjusted by adjusting the direction of the polarizing beam splitter 45 for synthesizing the first exposure beam and the second exposure beam. Can be easily adjusted.

<Method of Manufacturing Magneto-Optical Disk> Next, a method of manufacturing the magneto-optical disk 1 shown in FIGS. 1 and 2 will be described in detail with a specific example.

When manufacturing the magneto-optical disk 1, first,
As a mastering step, an optical recording medium manufacturing master having an uneven pattern corresponding to the wobbling groove 6 and the straight groove 7 is manufactured.

In this mastering step, first, a disk-shaped glass substrate 11 whose surface has been polished is washed and dried, and then a photoresist 12 as a photosensitive material is applied on the glass substrate 11. Next, the photoresist 12 is exposed by the laser cutting device 10 to form a latent image corresponding to the wobbling groove 6 and the straight groove 7 on the photoresist 12.

When manufacturing a magneto-optical disk for evaluation described later, a Kr laser emitting a laser beam having a wavelength λ of 351 nm is used as the light source 13 of the laser cutting device 10, and the first and second exposures are performed. The objective lens 54 for condensing the beam on the photoresist 12 has a numerical aperture NA of 0.9. The magnifying lens 52
Used had a focal length of 80 mm.

When exposing the photoresist 12 by the laser cutting device 10, the first and second
The latent image corresponding to the wobbling groove 6 and the straight groove 7 is formed on the photoresist 12 by exposing the photoresist 12 with the exposure beam.

Here, when forming a latent image corresponding to the wobbling groove 6 on the photoresist 12 by exposing the photoresist 12 with the first exposure beam, the first exposure beam is applied to the first exposure beam. Modulation optical system 2
The light intensity modulation is performed by 2 and the optical deflection is performed by the deflection optical system 46.

More specifically, first, a DC signal of a certain level is input to the driving driver 32, and the acousto-optic modulator 30 is driven by the driving driver 32 based on the DC signal. The light intensity modulation is performed on the first exposure beam so as to correspond to the pattern (1). Here, since the wobbling groove 6 is a continuous groove having a constant depth, while the latent image corresponding to the wobbling groove 6 is being formed, light is emitted so that the light intensity of the first exposure beam is constant. Apply intensity modulation.

Next, the first exposure beam subjected to the light intensity modulation by the first modulation optical system 22 is optically deflected by the deflection optical system. Specifically, a high frequency signal is FM-modulated from the voltage controlled oscillator 51 by a control signal and supplied to the driving driver 50, and the driving driver 50 drives the acousto-optical deflector 48 based on this signal, and The Bragg angle of the acousto-optic element of the acousto-optic deflector 48 is changed, and thereby the first exposure beam is optically deflected.

When a magneto-optical disk for evaluation described later is manufactured, a high-frequency signal having a center frequency of 224 MHz is FM-modulated by a control signal having a frequency of 84.672 kHz.
The voltage-controlled oscillator 51 supplied the driving driver 50. Then, based on this signal, the driving driver 50
Drives the acousto-optic deflector 48 to change the Bragg angle of the acousto-optic element of the acousto-optic deflector 48, whereby the position of the light spot of the first exposure beam focused on the photoresist 12 is changed. , Frequency 84.672 kHz
Optical deflection was performed so as to vibrate in the radial direction of the glass substrate 11 at z and amplitude ± 10 nm.

The first exposure beam subjected to the light intensity modulation and the optical deflection is condensed on the photoresist 12 by the objective lens 54, thereby exposing the photoresist 12 to the wobbling groove 6. A corresponding latent image is formed on the photoresist 12.

A latent image corresponding to the straight groove 7 is formed on the photoresist 12 by simultaneously exposing the photoresist 12 with the first exposure beam and exposing the photoresist 12 with the second exposure beam. I do.

When a latent image corresponding to the straight groove 7 is formed on the photoresist 12 by exposing the photoresist 12 with the second exposure beam, the second
Is subjected to light intensity modulation by the second modulation optical system 23.

Specifically, a DC signal of a certain level is input to the driving driver 37, and the acousto-optic modulator 34 is driven by the driving driver 37 based on the DC signal.
As a result, light intensity modulation is performed on the second exposure beam so as to correspond to the pattern of the straight groove 7. Here, since the straight groove 7 is a continuous groove having a constant depth, while the latent image corresponding to the straight groove 7 is being formed, light is emitted so that the light intensity of the second exposure beam is constant. Apply intensity modulation.

Then, the second exposure beam subjected to the light intensity modulation as described above is condensed on the photoresist 12 by the objective lens 54, so that the photoresist 12
Is exposed to form a latent image corresponding to the straight groove 7 on the photoresist 12.

When the photoresist 12 is exposed to form latent images corresponding to the wobbling groove 6 and the straight groove 7, the photoresist 1 is exposed.
The glass substrate 11 coated with 2 is rotationally driven at a predetermined rotation speed and is translated at a predetermined speed.

More specifically, when producing a magneto-optical disk for evaluation, which will be described later, the rotation speed of the glass substrate 11 depends on the relative moving speed of the light spot by the first and second exposure beams and the photoresist 12. Was set to a linear velocity of 1.0 m / sec. Then, the glass substrate 11 was translated in the radial direction of the glass substrate 11 by 1.00 μm (that is, the track period TPeriod) for each rotation by a moving optical table.

By exposing the photoresist 12 with the first and second exposure beams as described above, the latent image corresponding to the wobbling groove 6 and the latent image corresponding to the straight groove 7 are formed into a double spiral. Formed on photoresist 12.

When the photoresist 12 is exposed by the first and second exposure beams as described above, the level of the DC signal input to the driving drivers 32 and 37 is adjusted to adjust the level of the second exposure beam. The power is set to be different from the power of the third exposure beam. As a result, the depth of the latent image corresponding to the wobbling groove 6 is different from the depth of the latent image corresponding to the straight groove 7.

In the laser cutting apparatus 10, the distance between the light spot of the first exposure beam and the light spot of the second exposure beam in the radial direction of the glass substrate 11 corresponds to the track pitch TPitch. The reflection angle of the reflection surface of the polarization beam splitter 45 is set in advance.

By setting the reflection angle of the reflection surface of the polarizing beam splitter 45 in this way, a latent image corresponding to the wobbling groove 6 is formed by the first exposure boom, and the latent image adjacent to the wobbling groove 6 is formed. A latent image corresponding to the straight groove 7 thus formed is formed by the second exposure beam. This means
In other words, the relative positioning of the wobbling groove 6 and the straight groove 7 can be realized by adjusting the direction of the polarization beam splitter 45.

After the latent image is formed on the photoresist 12 as described above, the glass substrate 11 is placed on a turntable of a developing machine such that the surface on which the photoresist 12 is coated is the upper surface. I do. Then, while rotating the glass substrate 11 by rotating the turntable, a developing solution was dropped on the photoresist 12 to perform a developing process, and the wobbling groove 6 and the straight groove 7 were formed on the glass substrate 11. An uneven pattern is formed.

Next, a conductive film made of Ni or the like is formed on the concave / convex pattern by an electroless plating method. Thereafter, the glass substrate 11 on which the conductive film is formed is attached to an electroforming apparatus, and the electroplating method is used. A plating layer made of Ni or the like is formed on the conductive film so as to have a thickness of about 300 ± 5 μm. Thereafter, the plating layer is peeled off, and the peeled plating is washed with acetone or the like to remove the photoresist 12 remaining on the surface to which the uneven pattern has been transferred.

By the steps described above, an original master for manufacturing an optical recording medium made of plating to which the uneven pattern formed on the glass substrate 11 is transferred, that is, an uneven pattern corresponding to the wobbling groove 6 and the straight groove 7 is formed. The master for manufacturing an optical recording medium is completed.

The master for producing an optical recording medium is a master for producing an optical recording medium to which the present invention is applied. In other words, the master for producing an optical recording medium includes a wobbling groove 6 and a straight groove 7 along a recording track.
Is a master for manufacturing an optical recording medium used when manufacturing the magneto-optical disk 1 on which is formed the first groove pattern which is a concavo-convex pattern corresponding to the wobbling groove 6 and the straight groove 7. The second groove pattern, which is an uneven pattern, is formed in a double spiral shape. The first groove pattern and the second groove pattern are formed so that their depths are different from each other.

Next, as a transfer step, a disk substrate on which the surface shape of the master for producing an optical recording medium is transferred is manufactured by using a photopolymer method (so-called 2P method).

More specifically, first, a photopolymer is applied smoothly on the surface of the master for producing an optical recording medium on which the concave / convex pattern is formed to form a photopolymer layer. And garbage,
The base plate is brought into close contact with the photopolymer layer. Here, as the base plate, for example, a base plate made of polymethyl methacrylate (refractive index: 1.49) having a thickness of 1.2 mm is used.

Thereafter, the photopolymer is cured by irradiating ultraviolet rays, and then, the master disc for producing an optical recording medium is peeled off, thereby producing a disk substrate 2 on which the surface shape of the master disc for producing an optical recording medium is transferred. .

Here, an example has been described in which the disk substrate 2 is manufactured by using the 2P method so that the concave / convex pattern formed on the master for manufacturing an optical recording medium is more accurately transferred to the disk substrate 2. Needless to say, when the disk substrate 2 is mass-produced, the disk substrate 2 may be manufactured by injection molding using a transparent resin such as polymethyl methacrylate or polycarbonate.

Next, as a film forming step, the recording layer 3 and the protective layer 4 are formed on the disk substrate 2 on which the surface shape of the optical recording medium manufacturing master has been transferred. Specifically, for example,
First, a first dielectric film made of SiN or the like and a TeFeCo
A perpendicular magnetic recording film made of an alloy or the like and a second dielectric film made of SiN or the like are sequentially formed by sputtering,
Further, by forming a light reflecting film made of Al or the like on the second dielectric film by vapor deposition, the light reflecting film comprises a first dielectric film, a perpendicular magnetic recording film, a second dielectric film, and a light reflecting film. The recording layer 3 is formed. Thereafter, an ultraviolet curable resin is applied on the recording layer 3 by a spin coating method, and the ultraviolet curable resin is irradiated with ultraviolet light to be cured, thereby forming the protective layer 4.

Through the above steps, the magneto-optical disk 1 is completed.

<Evaluation of Magneto-Optical Disk> Next, a plurality of evaluation magneto-optical disks having different depths of the wobbling groove 6 and the straight groove 7 were manufactured by the above-described manufacturing method, and their evaluation was performed. The result of the above will be described.

Here, the depth of the wobbling groove 6 and the straight groove 7 can be controlled by changing the power of the first exposure beam and the second exposure beam when the master for manufacturing the optical recording medium is manufactured. Alternatively, it was performed by changing the thickness of a photoresist formed on a glass substrate.

That is, in evaluating the evaluation magneto-optical disk, the power of the first exposure beam for forming the latent image corresponding to the wobbling groove 6 and the latent image corresponding to the straight groove 7 are formed. The power of the second exposure beam for changing the thickness of the photoresist formed on the glass substrate or the thickness of the photoresist formed on the glass substrate is changed to form a plurality of masters for manufacturing optical recording media having different depths of the concavo-convex pattern. After that, a magneto-optical disk for evaluation was manufactured by the above-described 2P method using the master disks for manufacturing optical recording media. In addition, polymethyl methacrylate having a refractive index of 1.49 was used as a material of the disk substrate of these evaluation magneto-optical disks.

In each evaluation magneto-optical disk,
In the cross-sectional shape of the groove, parameters other than the depth were made substantially constant. Specifically, in each of the evaluation magneto-optical disks, as shown in FIG. 4, grooves G1 and G2 formed so as to be adjacent to each other and have different depths.
Among them, the upper width t1 of the shallower groove G1 is about 300 n
m, the bottom width t2 is about 200 nm, the top width t3 of the deeper groove G2 is about 280 nm, and the bottom width t4 is about 220 n.
m, and the width t5 of the land between the groove G1 and the groove G2 is set to about 210 nm.

The tracking servo characteristics and the track seek characteristics of the plurality of evaluation magneto-optical disks having different groove depths manufactured as described above are evaluated, and the push-pull signals obtained from the evaluation magneto-optical disks are evaluated. The amplitude ratio and the cross-track signal amplitude ratio were measured. For evaluation of tracking servo characteristics and track seek characteristics, and measurement of push-pull signal amplitude ratio and cross-track signal amplitude ratio, an optical pickup having a laser beam wavelength λ of 650 nm and a numerical aperture NA of an objective lens of 0.52 is used. Was used.

Tables 2 and 3 show the results of the above measurements together with the depths of the grooves formed on each evaluation magneto-optical disk.
Shown in Since the wobbling amplitude of the evaluation magneto-optical disk is very small, the push-pull signal amplitude ratio and the cross-track signal amplitude ratio are hardly affected by the presence or absence of wobbling. Therefore, here, the grooves formed on the evaluation magneto-optical disk are not distinguished by the wobbling groove 6 and the straight groove 7 but by the deeper groove and the shallower groove. In Tables 2 and 3, a negative cross-track signal amplitude ratio indicates that the phase of the cross-track signal has been inverted.

[0115]

[Table 2]

[0116]

[Table 3]

In Tables 2 and 3, the depth of the groove formed on the magneto-optical disk for evaluation is shown, but the depth of the groove is actually measured on the magneto-optical disk for evaluation. Instead of using an atomic force microscope (AFM: Atomic
Force Microscope). That is, here, assuming that the concavo-convex pattern formed on the optical recording medium manufacturing master is accurately transferred to the disk substrate, the results of measuring the shape of the concavo-convex pattern formed on the optical recording medium manufacturing master are described below. The value was used as a value indicating the cross-sectional shape of the groove of the magneto-optical disk for evaluation.

For each evaluation magneto-optical disk, tracking servo characteristics and track seek characteristics,
The relationship between the push-pull signal amplitude ratio and the cross-track signal amplitude ratio was examined. As a result, when the push-pull signal amplitude ratio was 0.15 or more, tracking servo could be stably performed using the push-pull signal. When the amplitude ratio of the push-pull signal is 0.15 or more and the amplitude ratio of the cross-track signal is 0.06 or more, the levels and polarities of the push-pull signal and the cross-track signal are detected to detect the first to fourth signals. Recording Track Track
A, TrackB, TrackC, and TrackD were discriminated, and track seek could be performed stably. From this, it was found that tracking servo and track seek can be stably performed on a magneto-optical disk having a push-pull signal amplitude ratio of 0.15 or more and a cross-track signal amplitude ratio of 0.06 or more.

Therefore, the push-pull signal amplitude ratio is 0.1
The depth of the wobbling groove 6 and the straight groove 7 when the cross-track signal amplitude ratio was 5 or more and the cross-track signal amplitude ratio was 0.06 or more were examined. As a result, the point a in FIG.
1, a2, a3, a4, a5, a6, a7, a8, a
In the area surrounded by 9, a10, a11, a12, and a13, or points b1, b2, b3, b4, and b in FIG.
It was found that the push-pull signal amplitude ratio was 0.15 or more and the cross-track signal amplitude ratio was 0.06 or more in the region surrounded by 5 and b6.

In FIG. 5, the vertical axis indicates the phase depth Y of the shallower groove of the wobbling groove 6 and the straight groove 7. The horizontal axis shows the phase depth X of the deeper groove of the wobbling groove 6 and the straight groove 7.

Here, the points a1, a2, a3, a4, a
The approximate straight line L1 connecting the points a5, a6 is represented by the following equation (2-1), and the points a6, a7, a8, a9, a10, a11, a1
The approximate line L2 connecting 2, a13 and a1 is expressed by the following equation (2-
2).

Y = + 26.83705−266.3275X + 987.8340X ² −1624.4709X ³ + 1000.2368X ⁴ ... (2-1) Y = −1003.7399 + 15110.1053X−94546.0895X ² + 314796.5182X ³ −588227.8600X ⁴ +584832 .1407X ⁵ -241694.0163X ⁶ (2-2) Therefore, the area surrounded by the points a1 to a13 is approximately an area satisfying the following equations (2-3) and (2-4). Can be represented.

Y ≧ + 26.83705−266.3275X + 987.8340X ² −1624.4709X ³ + 1000.2368X ⁴ ... (2-3) Y ≦ −1003.7399 + 15110.1053X−94546.0895X ² + 314796.5182X ³ −588227.8600X ⁴ +584832 .1407X ⁵ -241694.0163X ⁶ (2-4) That is, of the wobbling groove 6 and the straight groove 7, the phase depth of the deeper groove is X,
Assuming that the phase depth of the shallower groove is Y, if those grooves are formed so as to satisfy the above equations (2-3) and (2-4), the push-pull signal amplitude ratio becomes 0. .15 or more and the cross-track signal amplitude ratio is 0.0
6 or more, which enables stable tracking servo and track seek.

By the way, according to the principle of light diffraction, the same diffraction effect can be obtained for every integral multiple of the wavelength within the coherent length. Therefore, the same diffraction effect is exhibited even if the reciprocating optical path of the light incident on and reflected by the groove is increased or decreased by an integral multiple of the wavelength. That is, the same diffraction effect can be obtained even if the phase depths X and Y of the groove are increased or decreased in units of an integral multiple of half a wavelength. Therefore, the above formulas (2-3) and (2-4) can be generalized as shown in the following formulas (2-5) and (2-6) using an arbitrary integer N.

Y ≧ 0.5N + 26.83705−266.3275X + 987.8340X ² −1624.4709X ³ + 1000.2368X ⁴ ... (2-5) Y ≦ 0.5N−1003.7399 + 15110.1053X−94546.0895X ² + 314796.5182X ³ −588227.8600 X ⁴ + 584832.1407X ⁵ −241694.0163X ⁶ (2-6) That is, of the wobbling groove 6 and the straight groove 7, the phase depth of the deeper groove is X,
Assuming that the phase depth of the shallower groove is Y, if those grooves are formed so as to satisfy the above equations (2-5) and (2-6), the amplitude ratio of the push-pull signal becomes 0. .15 or more and the cross-track signal amplitude ratio is 0.0
6 or more, which enables stable tracking servo and track seek.

On the other hand, an approximate straight line L3 connecting the points b1, b2, b3 and b4 is expressed by the following equation (3-1).
The approximate straight line L4 connecting 5, 5, b6 and b1 is expressed by the following equation (3-2).
It was represented by

Y = −0.612030 + 7.861006X−22.53486X ² + 19.37300X ³ (3-1) Y = −5.553633 + 32.00983X−57.62127X ² + 33.37140X ³ (3-2) The area surrounded by the points b1 to b6 can be approximately represented as an area satisfying the following equations (3-3) and (3-4).

Y ≧ −0.612030 + 7.861006X−22.53486X ² + 19.37300X ³ (3-3) Y ≦ −5.553633 + 32.00983X−57.62127X ² + 33.37140X ³ (3-4) , The phase depth of the deeper groove of the wobbling groove 6 and the straight groove 7 is X,
Assuming that the phase depth of the shallower groove is Y, if those grooves are formed so as to satisfy the above equations (3-3) and (3-4), the push-pull signal amplitude ratio becomes zero. .15 or more and the cross-track signal amplitude ratio is 0.0
6 or more, which enables stable tracking servo and track seek.

Then, the above formulas (3-3) and (3-
4) can also be generalized using an arbitrary integer M as in the following formulas (3-5) and (3-6).

Y ≧ 0.5M−0.612030 + 7.861006X−22.53486X ² + 19.37300X ³・ ・ ・ (3-5) Y ≦ 0.5M−5.553633 + 32.00983X−57.62127X ² + 33.37140X ³・ ・ ・ (3 -6) That is, the phase depth of the deeper groove of the wobbling groove 6 and the straight groove 7 is X,
Assuming that the phase depth of the shallower groove is Y, if those grooves are formed so as to satisfy the above equations (3-5) and (3-6), the push-pull signal amplitude ratio becomes 0. .15 or more and the cross-track signal amplitude ratio is 0.0
6 or more, which enables stable tracking servo and track seek.

Incidentally, in the optical pickup used in this example, the wavelength λ of the laser beam is 650 nm, and the numerical aperture NA of the objective lens is 0.52. Therefore, the cut-off frequency 2NA / λ of the optical pickup is 1600
mm ^-1 . On the other hand, since the track pitch TPitch of the evaluation magneto-optical disk is 0.50 μm, its spatial frequency is 2000 mm ⁻¹ . As described above, in the magneto-optical disk for evaluation, the spatial frequency of the track pitch TPitch is higher than the cutoff frequency 2NA / λ of the optical pickup.

Conventionally, the track pitch TPitch
If the spatial frequency is higher than the cut-off frequency 2NA / λ of the optical pickup, a sufficient level of push-pull signal or cross-track signal cannot be obtained, and stable tracking servo and track seek cannot be performed. Was.

However, in the magneto-optical disk 1 to which the present invention is applied, as can be seen from the above-described experimental results, the wobbling groove 6 and the straight groove 7 are replaced by the above equations (2-5) and (2-6) or The above equation (3-
5) and formula (3-6), the spatial frequency of the track pitch TPitch is reduced to the cut-off frequency 2NA / λ of the optical pickup while securing a sufficient level of push-pull signal and cross-track signal. It is possible to make it larger. That is, by applying the present invention, it is possible to secure a sufficient level of a push-pull signal or a cross-track signal while maintaining the track pitch.
By narrowing the TPitch, it is possible to greatly improve the recording density.

The present invention can be widely applied to an optical recording medium having grooves formed along recording tracks, and an optical recording medium manufacturing master used for manufacturing the same. The optical recording medium to be used may be, for example, any one of a read-only optical recording medium, an optical recording medium in which data can be repeatedly written, and an optical recording medium in which data can be additionally written but cannot be erased.

The method of recording data is not particularly limited, and examples of the optical recording medium to which the present invention is applied include a read-only optical recording medium in which data is written in advance by emboss pits or the like, Either a magneto-optical recording medium for recording and reproducing data using an optical effect or a phase-change optical recording medium for recording and reproducing data using a phase change of a recording layer may be used.

The present invention can be widely applied to an optical recording medium in which a groove is formed in at least a part of a recording area, and an optical recording medium manufacturing master used for manufacturing the optical recording medium. That is, for example, a groove may be formed in the entire recording area, or an area in which data is recorded by embossed pits without forming a groove may exist in the recording area. .

The optical recording / reproducing apparatus according to the present invention uses an optical recording medium to which the present invention is applied as a recording medium, performs tracking servo using a push-pull signal, and performs track seek using a cross-track signal. This is characterized in that the configuration is the same as that of the existing optical recording / reproducing apparatus.

[0138]

As described above in detail, according to the present invention, it is possible to stably perform tracking servo and track seek on an optical recording medium of land-groove recording even if the track pitch is extremely narrow. be able to. Therefore, according to the present invention, while adopting land-groove recording, the track can be further narrowed, and the recording density of the optical recording medium can be further increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an enlarged main part of an example of a magneto-optical disk to which the present invention is applied.

FIG. 2 is an enlarged view showing a part of a recording area of an example of a magneto-optical disk to which the present invention is applied.

FIG. 3 is a diagram showing an outline of an optical system of an example of a laser cutting device used when producing an optical recording medium and a master for producing an optical recording medium according to the present invention.

FIG. 4 is a diagram showing a cross-sectional shape of a groove formed on a magneto-optical disk for evaluation.

FIG. 5 is a diagram showing the results of examining the depth of a wobbling groove and a straight groove when the push-pull signal amplitude ratio is 0.15 or more and the cross-track signal amplitude ratio is 0.06 or more.

FIG. 6 is a diagram for explaining a method of detecting a push-pull signal and a cross-track signal.

[Explanation of symbols]

Reference Signs List 1 magneto-optical disk, 2 disk substrate, 3 recording layer, 4 protective layer, 6 wobbling groove, 7
Straight groove

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/26 501 G11B 7/26 501

Claims (11)

[Claims] 1. An optical recording medium in which a groove is formed along a recording track and irradiated with light of a predetermined wavelength λ to perform recording and / or reproduction, wherein a groove portion and a portion between the grooves are provided. The information signal is recorded on both the land portion and the first groove, and the first groove and the second groove having different depths are formed adjacent to each other, and the groove extends from the light incident surface to the groove. When the refractive index of the medium is n, the depth of the first groove is x, and the depth of the second groove is y, the phase depth of the first groove represented by x × n / λ is X , Y × n / λ, when the phase depth of the second groove is Y and N and M are arbitrary integers, the first groove and the second groove are expressed by the following formulas (1) and (2). Equation (2), or satisfying the following equations (3) and (4) Optical recording medium, characterized by being made. Y ≧ 0.5N + 26.83705−266.3275X + 987.8340X ² −1624.4709X ³ ＋ 1000.2368X ⁴・ ・ ・ (1) Y ≦ 0.5N−1003.7399 + 15110.1053X−94546.0895X ² + 314796.5182X ³ −588227.8600X ⁴ + 584832.1407X ⁵ −241694.0163X ⁶・ ・ ・ (2) Y ≧ 0.5M−0.612030 + 7.861006X−22.53486X ² + 19.37300X ³・ ・ ・ (3) Y ≦ 0.5M−5.553633 + 32.00983X−57.62127X ² + 33.37140X ³ ... (4) 2. An optical recording apparatus according to claim 1, wherein at least one of said first groove and said second groove is a wobbling groove formed so that at least a part thereof meanders. Medium. 3. A cut expressed by 2 × NA / λ, where NA is the numerical aperture of an objective lens used for recording and / or reproduction, and λ is the wavelength of light irradiated during recording and / or reproduction. 2. The optical recording medium according to claim 1, wherein the spatial frequency of the track pitch is higher than the off frequency. 4. An optical recording medium in which a groove is formed along a recording track and recorded and / or reproduced by irradiating light, wherein a groove portion and a land portion between the grooves are formed. An information signal is recorded on both, and a first groove and a second groove having different depths are formed adjacent to each other, and the light is reflected by the optical recording medium. When the reflected light is detected by two photodetectors symmetrically arranged with respect to the track center, the light amount detected by one of the photodetectors is A, and the light amount detected by the other photodetector is B. , AB represents the amplitude of the difference signal represented by AB, D represents the amplitude of the sum signal represented by A + B, and M represents the value of the sum signal at the mirror surface where no groove is formed.
An optical recording medium wherein the difference signal amplitude ratio represented by C / Mmax is 0.15 or more, and the sum signal amplitude ratio represented by D / Mmax is 0.06 or more. 5. The optical recording according to claim 4, wherein at least one of the first groove and the second groove is a wobbling groove formed so that at least a part thereof meanders. Medium. 6. A cut expressed by 2 × NA / λ, where NA is the numerical aperture of an objective lens used for recording and / or reproduction, and λ is the wavelength of light irradiated during recording and / or reproduction. 5. The optical recording medium according to claim 4, wherein the spatial frequency of the track pitch is higher than the off frequency. 7. An optical recording medium manufacturing master used for manufacturing an optical recording medium on which a groove is formed along a recording track and irradiated with light having a predetermined wavelength λ to perform recording and / or reproduction. A first groove pattern and a second groove pattern are formed adjacent to each other as an uneven pattern corresponding to the groove, and the refractive index of a medium from the light incident surface of the optical recording medium to the groove is formed. N, the depth of the first groove pattern x ', the second
When the depth of the groove pattern is y ′, x ′ × n
X ′ is the phase depth of the first groove pattern represented by / λ, Y ′ is the phase depth of the second groove pattern represented by y ′ × n / λ, and N and M are arbitrary integers. When the first groove pattern and the second groove pattern are obtained, the following expressions (5) and (6) or the following expression (7)
And the optical recording medium is formed so as to satisfy Expression (8). The optical recording medium is a recording medium in which an information signal is recorded in both a groove portion and a land portion between the grooves. A master for producing optical recording media. Y '≧ 0.5N + 26.83705-266.3275X' + 987.8340X '2 -1624.4709X' 3 + 1000.2368X '4 ··· (5) Y' ≦ 0.5N-1003.7399 + 15110.1053X'-94546.0895X '2 +314796. ^{5182X '3 -588227.8600X' 4 + 584832.1407X} '5 -241694.0163X' 6 ··· (6) Y '≧ 0.5M-0.612030 + 7.861006X'-22.53486X' 2 + 19.37300X '3 ··· (7 ) Y '≦ 0.5M-5.553633 + 32.00983X'-57.62127X' 2 + 33.37140X '3 ··· (8) 8. The first groove pattern and the second groove pattern.
8. The master for producing an optical recording medium according to claim 7, wherein at least one of the groove patterns is an uneven pattern corresponding to a wobbling groove formed so that at least a part of the groove pattern is meandering. 9. An optical recording / reproducing apparatus for performing recording and / or reproduction by irradiating light to an optical recording medium having grooves formed along recording tracks, wherein the recording and / or reproduction target is As an optical recording medium, information signals are recorded on both a groove portion and a land portion between the grooves, and the first groove and the second groove having different depths are formed as the grooves. Using an optical recording medium formed so as to be adjacent to each other, and comprising two photodetectors arranged symmetrically with respect to the track center of the optical recording medium, and at the time of recording and / or reproduction, the optical recording medium When the two light detectors detect reflected light resulting from the reflection of the light, the light amount detected by one of the light detectors is A, and the light amount detected by the other light detector is B. A tracking servo for causing the light spot to follow the recording track is performed using a difference signal represented by AB, and a track seek for moving the light spot to a desired recording track is performed by a sum signal represented by A + B. An optical recording / reproducing apparatus characterized in that the optical recording / reproducing apparatus is used. 10. A wobbling groove in which at least one of the first groove and the second groove is formed so as to meander at least partially as an optical recording medium to be recorded and / or reproduced. The optical recording / reproducing apparatus according to claim 9, wherein an optical recording medium is used. 11. An objective lens for condensing the light on an optical recording medium, wherein a numerical aperture of the objective lens is NA, and a wavelength of the light is λ, a cut represented by 2 × NA / λ. 10. The optical recording / reproducing apparatus according to claim 9, wherein the spatial frequency of the track pitch of the optical recording medium to be recorded and / or reproduced is higher than the off-frequency.