JP2004087034A - Optical information recording medium, magneto-optical recording medium, and method of manufacturing magneto-optical recording medium - Google Patents

Abstract

An optical information recording medium capable of recording / reproducing information at a higher density is provided.
At least two rows of information tracks for recording or reproducing information are formed in one land (L) or groove (G). In addition, by performing an annealing process in advance so that the lands L or the grooves G having at least two rows of information tracks are almost equally divided in the direction perpendicular to the track direction, the magnetism is changed and the information tracks are magnetically separated. An anneal region is formed.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical information recording medium, and more particularly to an optical information recording medium having at least two rows of information tracks in one groove or between grooves, a magneto-optical recording medium, and a method of manufacturing the same.
[0002]
[Prior art]
Generally, reproduction of information recorded on an optical information recording medium is performed by forming a minute spot on a signal surface by a condenser lens and receiving reflected light by a photoelectric conversion element. The demand for higher density of this optical information recording medium is only increasing year by year.
[0003]
As a method of realizing this high density, for example, it is known to realize high density in the track direction beyond the limit of optical resolution by using means such as domain wall motion detection (DWDD). I have. In order to further increase the density, it is necessary to narrow the track pitch to achieve a higher density in the radial direction. However, when the period of the guide groove approaches the resolution of the optical system, a sufficient tracking signal cannot be obtained. As is well known, the resolution d of the optical system is given by the wavelength λ of the convergent light and the numerical aperture NA of the objective lens.
d = λ / (2 · NA)
Determined by
[0004]
For example, in an optical system used in a DVD-RW, the wavelength d of the light source is 635 nm and the numerical aperture NA of the objective lens is 0.60, so that the resolution d is 0.53 μm. If the track pitch of the medium approaches 0.53 μm, it becomes impossible to obtain a sufficient tracking signal. Therefore, in the DVD-RW, the track pitch is obtained at 0.74 μm.
[0005]
In order to alleviate such a limitation due to the resolution of the optical system, for example, as described in JP-A-2000-331383, an optical recording medium in which grooves are formed so that adjacent grooves have different widths has been proposed. . FIG. 14 shows a recording medium of the publication. According to the publication, a two-track apparently has a periodic structure of one period, so that a tracking signal can be obtained even if the track pitch is reduced to a track pitch exceeding the resolution limit.
[0006]
[Problems to be solved by the invention]
However, in the recording medium described in the publication, it is necessary to form grooves having different widths on both sides of each track, and in order for the tracking signal to have sufficient modulation, the difference in groove width must be increased. However, this has been a cause of limiting further densification.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an optical information recording medium, a magneto-optical recording medium, and a method for manufacturing the same, which can record information at a higher density.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the optical information recording medium of the present invention has lands and grooves, and has at least two rows of information tracks for recording or reproducing information in the lands or grooves. An annealing region is formed in a land or groove having information tracks in a row so that the magnetic properties are changed by performing an annealing process in advance so as to be substantially equally divided in a direction perpendicular to the track direction, and the information tracks are magnetically separated. It is characterized by having been done.
[0009]
Further, in the magneto-optical recording medium of the present invention, in a domain wall displacement type magneto-optical recording medium having at least a domain wall displacement layer, a switching layer and a recording holding layer, at least two information tracks for recording or reproducing information in a land or a groove are provided. The lands or grooves having rows and the at least two rows of information tracks are preliminarily subjected to an annealing treatment so as to be substantially equally divided in a direction perpendicular to the track direction, so that the information tracks are deteriorated in magnetic properties. An annealing region which is magnetically separated is formed.
[0010]
Further, the method of manufacturing a magneto-optical recording medium according to the present invention further comprises: means for irradiating the two sub-beams onto the magneto-optical recording medium with a main beam for annealing between the two sub-beams; A detection element for detecting, first tracking control means for performing tracking control based on an output difference between the two detection elements corresponding to the two sub-beams, and at least a groove of the medium for detecting the reflected light of the main beam by the medium Detecting element divided into two in a direction parallel to the direction, second tracking control means for performing tracking control based on the output of the dividing detecting element, and a groove direction of the medium for detecting reflected light of the two sub-beams, respectively. And a third tracking device that performs tracking control based on the output of the two-divided detection element. Controlling means for switching between the first to third tracking control means, and switching between the first to third tracking control means in accordance with the annealing position of the recording medium, whereby the groove or land is switched. Is characterized by annealing a desired position.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
(1st Embodiment)
FIG. 1 is a sectional view showing a first embodiment of the optical information recording medium of the present invention. FIG. 1 shows a magneto-optical disk as an optical information recording medium. FIG. 1A is a sectional view of a substrate of a magneto-optical disk, and FIG. 1B is a sectional view of a magneto-optical disk. The substrate 32 is formed by injection molding of a resin material such as polycarbonate, and lands L and grooves G are formed on the surface thereof. The magneto-optical disk 8 is a domain wall moving type magneto-optical medium for reproducing recorded information by moving a domain wall of a recording mark.
[0013]
The domain wall displacement type magneto-optical medium is described in detail in, for example, Japanese Patent Application Laid-Open No. 6-290496, and thus detailed description is omitted. On the substrate 32, a moving layer, a switching layer, and a recording layer are laminated. Magnetic film M is formed. The layer configuration of the magneto-optical disk 8 is not limited to this, and it goes without saying that there are various layer configurations as described in the above publications.
[0014]
In addition, as shown in FIG. 1B, two rows of tracks T1 and T2 are provided in the groove G at equal widths as shown in FIG. At the center of the groove G, there is provided a region A in which the magnetic properties are changed by the annealing process. Similarly, in the center of the land L, there is provided a region B in which the magnetic properties are changed by the annealing process. The tracks T1 and T2 are magnetically separated by the region A and the region B.
[0015]
More specifically, the land width _{W L} is 0.2 [mu] m, the groove width _{W G} is 0.8 [mu] m, the land pitch _{P L} is 1.0 .mu.m, the depth D of the groove G is 0.03 .mu.m. Annealed region A of the groove center 0.2μm about, annealed region B on the land occupies a whole substantially land width W _L. Incidentally, the land width _{W L} 0.8 [mu] m, may become a groove width _{W G} to 0.2μm opposite, in which case performing recording by providing a track T1, T2 on the land L.
[0016]
Next, a method of altering the magnetism of the center of the groove G and the center of the land L by annealing will be described. FIG. 2 shows an optical system of the annealing apparatus according to the present embodiment. First, a light beam from the semiconductor laser 1 having a wavelength of 410 nm is divided into three light beams by the diffraction grating 2, and each light beam is converted into a parallel light beam by the coupling lens 3. The parallel light beam passes through the polarizing beam splitter 4 and further passes through the quarter-wave plate 5, and is then condensed by an objective lens 7 having an NA of 0.85 whose position is controlled by an actuator 6. Light enters from the surface side.
[0017]
The reflected light from the information recording surface of the magneto-optical disk 8 passes through the objective lens 7 again, further passes through the quarter-wave plate 5, is reflected by the polarization beam splitter 4, passes through the sensor lens 9, and passes through the sensor lens 9. It is incident on 10. The focus error signal is obtained by an astigmatism method using a main beam. The annealing process is performed using the main beam converged by the objective lens 7.
[0018]
FIG. 3 shows a light receiving surface on the light receiving element 10. The reflected light of the main beam is received by the four divided light receiving surfaces 10a, 10b, 10c, and 10d on the light receiving element 10, and when the respective outputs are A, B, C, and D, an operation of (A + C)-(B + D) is performed. Is used as a focus error signal.
[0019]
Next, a tracking method during the annealing process will be described. FIG. 4 shows a tracking error signal with respect to the beam spot on the medium surface when the area A at the center of the groove G is annealed, and the spot position of the main beam 13 on the information recording surface. The spot size is indicated by a half value. Disk radial spacing of the sub-beams 11 and 12, and to the extent below the groove width W _G 1/4 or more of the land pitch P _L on the information recording surface, the main beam 13 is located in the middle of the two sub-beams 11 and 12 To do. The reflected lights of the sub-beams 11 and 12 are received by light-receiving surfaces 10e and 10f on the light-receiving element 10, respectively, and when their outputs are TE1 and TE2,
TE3 = TE1-TE2
The tracking control is performed using the signal TE3 obtained in step (1). FIG. 4 shows TE1, TE2, and TE3. As described above, while performing the focus control and the tracking control, the main beam 13 is scanned to the center of the groove G to perform the annealing process on the region A.
[0020]
When tracking control is performed, push-pull signals of the sub beams 11 and 12 may be used. In this case, the disk radial spacing of the sub-beams 11 and 12, to be equal to the land pitch P _L on the recording surface.
[0021]
FIG. 5 shows a tracking error signal TE3 with respect to the beam spot on the medium surface and the spot position of the main beam 13 when the area B on the land L is annealed. When the main beam 13 is tracked at the center of the land L as shown in FIG. 5, the reflected light of the main beam 13 is received by the four-divided light receiving surfaces 10a, 10b, 10c, and 10d on the light receiving element 10. When the outputs are A, B, C, and D, tracking control is performed using a so-called push-pull signal obtained by a calculation of (A + D)-(B + C) as a tracking error signal.
[0022]
The focus control is the same as the case of annealing the groove. The annealing process of the region B is performed by scanning the main beam 13 at the center of the land L while performing the focus control and the tracking control using the push-pull signal as described above. I do.
[0023]
By switching the tracking between the case where the land is annealed and the case where the groove is annealed, the annealing process is performed on the region A at the center of the groove and the region B on the land. By annealing the center of the groove G and the center of the land L in this manner, the magnetic properties are altered and a domain wall displacement type magneto-optical medium can be realized.
[0024]
Next, a method of recording information and reproducing recorded information using the above-described magneto-optical disk 8 will be described. FIG. 6 shows an example of an optical system for recording / reproducing information using the magneto-optical disk 8 according to the present embodiment. First, a light beam emitted from the semiconductor laser device 14 having a wavelength of 650 nm is divided by the diffraction grating 15 into three light beams. Each light beam is converted into a parallel light beam by the coupling lens 16 and passes through the polarization beam splitter 17. Further, this light beam is condensed by an objective lens 19 having an NA of 0.6 whose position is controlled by an actuator 18, and is irradiated on the magneto-optical disk 8 as a minute spot. A magnetic head 20 for applying a modulation magnetic field is provided on the upper surface of the magneto-optical disk 8 so as to face the objective lens 19.
[0025]
The reflected light from the information recording surface of the magneto-optical disk 8 passes through the objective lens 19 again, is reflected by the polarization beam splitter 17, and enters the light receiving element 23 through the sensor lens 21 and the Wollaston prism 22. At the time of reproducing information, magnetic domain wall movement is caused by irradiation of convergent light, and information is read. Since domain wall motion reproduction is well known, detailed description is omitted. On the other hand, when recording information, information is recorded by applying a modulation magnetic field from the magnetic head 20 together with irradiation of convergent light. Recording and reproduction of information are performed by the main beam converged by the objective lens 19, and the focus error signal is generated by an astigmatism method using reflected light of the main beam.
[0026]
FIG. 7 shows a light receiving surface of the light receiving element 23. The reflected light of the main beam is received by the four divided light receiving surfaces 23a, 23b, 23c and 23d on the light receiving element 23, and when the respective outputs are A, B, C and D, an operation of (A + C)-(B + D) is performed. Is used as a focus error signal. This is a focus error signal obtained by the astigmatism method described above. When a reproduced signal is generated, light beams polarized and separated into components orthogonal to each other by the Wollaston prism 22 are received by the light receiving surfaces 23i and 23j, and when the respective outputs are I and J, IJ It is obtained by performing the following calculation.
[0027]
Next, a tracking method when recording and reproducing information using the magneto-optical disk 8 having the above-described configuration will be described. FIG. 8 shows a beam spot and a tracking signal on the medium surface during recording and reproduction. The spot size is indicated by a half value.
[0028]
The sub-beams 24 and 25 as spacing disc radial direction is equal to 1/2 of the land pitch P _L on the information recording surface of the medium, the main beam 26 to be positioned at the center of the sub-beams 24 and 25. The reflected light of the sub beams 24 and 25 is received by light receiving surfaces 23e, 23f and 23g and 23h, which are divided into two in a direction parallel to the groove direction of the magneto-optical disk 8. When each output is E, F and G, H,
TE4 = EF
TE5 = GH
By performing the following calculation, so-called push-pull signals TE4 and TE5 are obtained as shown in FIG.
[0029]
At this time, the push-pull signal TE4 and TE5 is the periodic signal having a period of land pitch _{P L.} Thus, if one half of the distance the land pitch _{P L} between the sub-beams 24 and 25, the phase between the push-pull signal TE4 and TE5 sub-beams 24 and 25 are shifted a half cycle, further, performs an operation comprising TE4-TE5 As a result, a tracking error signal TE6 (see FIG. 8) by the well-known differential push-pull method is obtained.
[0030]
Based on the tracking error signal TE6, tracking control is performed so that the main beam 26 traces the tracks T1 and T2. At this time, by switching the polarity of the tracking error signal, it is possible to switch the track pull-in from the track T1 to the track T2 or from the track T2 to the track T1. As described above, by using the tracking error signal TE6, information can be recorded / reproduced satisfactorily on an optical information recording medium having two information tracks in one groove (or land).
[0031]
(Second embodiment)
FIG. 9 is a sectional view showing the second embodiment of the present invention. FIG. 9A is a sectional view of the substrate of the magneto-optical disk, and FIG. 9B is a sectional view of the magneto-optical disk. The magneto-optical disk is a domain wall moving type magneto-optical medium. In this embodiment, an example is shown in which one groove has four information tracks. On the substrate 32, a magnetic film M in which a moving layer, a switching layer, and a recording layer are stacked is formed. The layer configuration of the magneto-optical disk 8 is not limited to this.
[0032]
Also, as shown in FIG. 9B, four rows of tracks T1, T2, T3 and T4 are provided in the groove G at equal widths as shown in FIG. On both sides separated by a quarter of the land pitch P _L from the center of the center and the groove G of the groove G, is provided with regions A and C is made to alter the magnetic by annealing. Similarly, in the center of the land L, there is provided a region B in which the magnetic properties are changed by the annealing process. The information tracks T1, T2, T3, and T4 are magnetically separated by the areas A, B, and C.
[0033]
Land width _{W L} is 0.2 [mu] m, the groove width _{W G} is 2.0 .mu.m, the land pitch _{P L} is 2.20, the depth D of the groove G is 0.03 .mu.m. Anneal region A and the region C in the groove 0.2μm about, annealed region B on the land occupies the entire approximately land width W _L. Incidentally, the land width _{W L} 2.0 .mu.m, may become a groove width _{W G} to 0.2μm opposite, in which case performing recording by providing a track T1, T2, T3, T4 to the land L.
[0034]
Then, on both sides away from the center of the center and the groove G of the groove G 1/4 of the land pitch P _L, and a method of changing quality magnetic by annealing the center of the land L is described. The annealing is performed using the optical system shown in FIG. 2, but the diffraction grating 2 and the light receiving element 10 are different. FIG. 10 shows a diffraction grating used in the present embodiment, and FIG. 11 shows a light receiving surface of a light receiving element.
[0035]
Subsequently, a method of the annealing treatment will be described. First, the method of annealing the region A at the center of the groove and the region B on the land is the same as in the first embodiment. FIG. 12 shows a beam arrangement and a tracking error signal when the annealing beam is tracked in a region C which is separated from the center of the groove by 1/4 of the land pitch. The sub-beams 26, 27 as spacing disc radial direction is equal to 1/2 of the land pitch P _L on the information recording surface of the medium, the main beam 28 to be positioned at the center of the sub-beams 26, 27.
[0036]
Moreover, the grating of the grating section 15a is to that of the incident beam diameter D _M is smaller than a circular shape as shown in FIG. 10, the magneto-optical disc 8 the beam diameter D _S of the diffracted light is made smaller than D _M dropped the NA of the condenser at the time of to, the spot of the sub-beams 26, 27 on the information recording surface is increased to about land pitch P _L. The reflected light of the sub-beams 26 and 27 is received by the light receiving surfaces 10e, 10f and 10g and 10h divided into two in a direction parallel to the groove direction of the magneto-optical disk 8 as shown in FIG. When the output of 10h is E, F and G, H,
TE8 = EF
TE9 = GH
Is performed, so-called push-pull signals are obtained.
[0037]
Further, by performing the operation of TE8-TE9, a tracking error signal TE10 by the well-known differential push-pull method is obtained, and the region C is annealed using this TE10. In this way, the regions A and C in the groove G and the region B on the land are annealed.
[0038]
Next, a method for recording / reproducing information using the magneto-optical disk 8 of the second embodiment will be described. The apparatus used for recording / reproduction is the same as that of the first embodiment, but the diffraction grating 15 shown in FIG. FIG. 13 shows a beam arrangement on a medium and a tracking error signal during recording / reproduction. The sub-beams 29 and 30 as spacing disc radial direction is equal to 1/2 of the land pitch P _L on the information recording surface of the medium, the main beam 31 to be positioned at the center of the sub-beams 29 and 30.
[0039]
Moreover, the grating of the grating section 15a is to that of the incident beam diameter D _M is smaller than a circular shape as shown in FIG. 10, the magneto-optical disc 8 the beam diameter D _S of the diffracted light is made smaller than D _M dropped the NA of the condenser at the time of to, the spot of the sub-beams 29 and 30 on the information recording surface is increased to about land pitch P _L.
[0040]
When tracking the main beam to the tracks T1 to T4 in the groove G, a differential push-pull signal is used as in the case of annealing (TE10). First, when tracking the tracks T1 and T4, a servo control circuit (not shown) adds a track offset to the tracking error signal and shifts the tracking position by P _L / 8 as shown in FIG.
[0041]
Further, when tracking is performed on the tracks T2 and T3, tracking control is performed by adding a track offset having a polarity opposite to that for tracking on the tracks T1 and T4. In this manner, information is recorded / reproduced on four tracks in one groove.
[0042]
In the above embodiment, an example is shown in which two or four information tracks are formed in one groove or land. However, the present invention is not limited to this, and three or five or more information tracks are formed. It is also possible to form In this case, recording / reproduction of information can be performed on a desired track by switching between the track offset and the polarity according to the tracking position.
[0043]
In the case where three or five or more information tracks are formed in one groove or land, when the annealing process is performed, similarly, by switching between the track offset and the polarity according to the tracking position, a desired value can be obtained. It is possible to perform an annealing process at the position.
[0044]
【The invention's effect】
As described above, according to the present invention, the track density can be increased beyond the optical resolution, and good recording / reproducing performance can be obtained even if the track density is increased. Therefore, a higher-density memory system can be realized as compared with the related art.
[Brief description of the drawings]
FIG. 1 is a sectional view showing one embodiment of an optical information recording medium of the present invention.
FIG. 2 is a diagram illustrating an example of an optical system of an annealing apparatus that anneals a recording medium according to the embodiment of FIG. 1;
FIG. 3 is a diagram showing a light receiving surface of a light receiving element used in the annealing apparatus of FIG. 2;
4 is a diagram showing a beam spot on a recording surface of a recording medium and a tracking error signal when the center of a groove of the magneto-optical disk of FIG. 1 is annealed by using the annealing apparatus of FIG. 2;
FIG. 5 is a diagram showing a beam spot on a recording surface of a recording medium and a tracking error signal when annealing is performed on a land of the magneto-optical disk of FIG. 1 using the annealing apparatus of FIG. 2;
FIG. 6 is a diagram showing an example of an optical system of a recording / reproducing apparatus for recording / reproducing information on / from the optical information recording medium of the embodiment of FIG.
7 is a diagram showing a light receiving surface of a light receiving element used in the recording / reproducing apparatus of FIG.
8 is a diagram showing a beam spot on a recording surface and a tracking error signal when information is recorded / reproduced using the recording / reproducing apparatus of FIG.
FIG. 9 is a sectional view showing a second embodiment of the present invention.
FIG. 10 is a diagram illustrating a diffraction grating of an optical system used for an annealing process according to a second embodiment.
FIG. 11 is a diagram illustrating a light receiving element of an optical system used for an annealing process according to a second embodiment.
FIG. 12 is a diagram illustrating a beam spot on a medium and a tracking error signal when an annealing process according to a second embodiment is performed.
FIG. 13 is a diagram showing a beam spot on a medium and a tracking error signal when recording / reproducing is performed using the medium of the second embodiment.
FIG. 14 is a diagram showing a conventional medium structure.
[Explanation of symbols]
1, 14 Semiconductor laser 2, 15, 33 Diffraction grating 3, 16 Coupling lens 4, 17 Polarization beam splitter 5 Quarter-wave plate 6, 18 Actuator 7, 19 Objective lens 8 Magneto-optical disk 9, 21 Sensor lens 22 Wallace Ton prism 10, 23 Light receiving elements 11, 12, 26, 27 Sub-beams 13, 28 during annealing Main beam 20 during annealing Magnetic heads 24, 25, 29, 30 Sub-beams 26, 31 during recording / reproducing Recording / reproducing Main beam 32 Substrate T1, T2, T3, T4 Information track G Groove L Land M Magnetic film

Claims (5)

A land or groove having at least two rows of information tracks for recording or reproducing information in the land or groove, and a land or groove having at least two rows of information tracks is perpendicular to the track direction. An optical information recording medium, characterized in that an annealing region is formed in such a manner that the magnetic property is changed by performing an annealing process in advance so as to be substantially equally divided in the direction, and an information track is magnetically divided. At least, a domain wall displacement type magneto-optical recording medium having a domain wall displacement layer, a switching layer, and a recording holding layer, has at least two rows of information tracks for recording or reproducing information in a land or a groove, and In a land or a groove having an information track, an annealing region is formed by performing an annealing process in advance so as to be substantially equally divided in a direction perpendicular to the track direction, thereby changing the magnetism and magnetically separating the information track. A magneto-optical recording medium. 3. The method of manufacturing a magneto-optical recording medium according to claim 2, further comprising: means for irradiating the recording medium with two sub-beams and a main beam for annealing between the two sub-beams; A detection element for detecting, first tracking control means for performing tracking control based on an output difference between the two detection elements corresponding to the two sub-beams, and at least a groove of the medium for detecting the reflected light of the main beam by the medium Detecting element divided into two in a direction parallel to the direction, second tracking control means for performing tracking control based on the output of the dividing detecting element, and a groove direction of the medium for detecting reflected light of the two sub-beams, respectively. A third detector for performing tracking control based on the output of the two-divided detection element; King control means, and means for switching between the first to third tracking control means, and switching between the first to third tracking control means in accordance with the annealing position of the recording medium, whereby the groove or A method for manufacturing a magneto-optical recording medium, comprising annealing a desired position of a land. The first and second tracking control means, and a means for switching between the first and second tracking control means, wherein the first and second tracking control means are controlled in accordance with the annealing position of the recording medium. 4. The method according to claim 3, wherein a desired position of the groove or the land is annealed by switching. A second tracking control unit, a detection element divided into two in a direction parallel to a groove direction of a medium for detecting at least one reflected light of the two sub-beams, and tracking based on an output of the two-division detection element A fourth tracking control unit for performing control; and a unit for switching between the second and fourth tracking control units, wherein the second and fourth tracking control units are switched according to the annealing position of the recording medium. 4. The method according to claim 3, wherein a desired position of the groove or the land is annealed.

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