JP3550408B2 - Information recording method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an apparatus for optically recording and reproducing information. More particularly, the present invention relates to an apparatus and a method for rotating a disk-shaped medium, relatively moving a recording / reproducing means in a rotating circumferential direction, and recording / reproducing using a magneto-optical effect.
[0002]
[Prior art]
As a device as described above, information is recorded in an optically identifiable information form, and a micro disk having a two-dimensional substantially isotropic intensity distribution on a rotating disk-shaped record carrier for rotating a light beam emitted from a light source. 2. Description of the Related Art There is an optical disk device that irradiates as a light spot and records and reproduces information. Conventionally, in such an apparatus, the recording form of information is recorded as tracks, which are information strings one-dimensionally arranged on the circumference of a disk, and there is no overlap of information strings. In this case, even when the recording wavelength is 680 nm, the numerical aperture is about 0.55, the spot diameter is 1.23 μm, and the smallest mark that can be recorded is about 0.6. The track spacing also extends to 1.2 microns in consideration of thermal interference during recording and crosstalk during reproduction. In recording density is limit ² about 1.2 Gbit / inch.
[0003]
[Problems to be solved by the invention]
In the related art, when the track interval or the mark interval is further reduced for higher density, interference at the time of recording from an adjacent track or mark increases, and a problem occurs that information cannot be stably recorded. An object of the present invention is to provide a recording / reproducing method capable of stably recording / reproducing information even when a track interval and an information mark interval are narrowed and achieving high density, and an apparatus using the same.
[0004]
[Means for Solving the Problems]
A pre-recorded mark array is provided, information is superimposed and recorded thereon, and information is recorded and reproduced by a difference in physical configuration of the mark array and a change in light emission intensity. The range of the influence of the mark created in advance on the recording condition is made smaller than the area where the recording form of the information recording medium is originally changed.
[0005]
That is, in an information recording method of applying a converged light spot and a magnetic field to a magnetic film and magnetically forming a mark on the magnetic film to record information, instead of using an external magnetic field as in the related art, a magnetic field is used. Is applied to only a local region of the magnetic film, and a mark is formed only in the range of this local region. Further, in order to apply such a local magnetic field, a first magnetic film on which information is magnetically recorded by applying a converged light spot and a magnetic field, and a first magnetic film below the first magnetic film. An information recording medium having a second magnetic film disposed thereon and having a magnetic embedded mark for applying a local magnetic field to the second magnetic film is used.
[0006]
The basic idea of the present invention is to form a light spot on a recording medium, modulate the light intensity of the light spot to record information, and form an embedded mark on the recording medium in advance. And irradiating the buried mark with the above light spot to record a recording mark. The recording medium typically a magnetic layer, the buried mark is formed by magnetically resistant quality stations plants alter the magnetic film. Preferably, a buried mark is formed on a first magnetic film such as a base film using a multilayer magnetic film, and a recording mark is recorded on a second magnetic film. For example, a buried mark can be formed by using a perpendicular magnetization film as the first magnetic film and magnetizing the magnetization direction of the perpendicular magnetization film in a direction different from the initial magnetization direction. At this time, it is preferable that the Curie temperature of the first magnetic film be higher than the Curie temperature of the second magnetic film. When a disc-shaped recording medium is used as the recording medium, the embedding marks can be arranged in a track shape in the circumferential direction. Further, by embedding the mark constitutes a sequence to appear in every other track on the recording medium and a half radial, it can be realized higher density recording.
[0007]
[Action]
The range of physical interference given to the conditions for recording additional recording information due to the difference in the physical configuration of the pre-recorded mark arrangement is larger than the area where the information recording medium is optically changed for information recording by light spot irradiation. By making the shape narrower, the shape of the information mark changes under the influence of physical interference and becomes narrower than the optically changing region.
[0008]
【Example】
The solid line in FIG. 1 shows the intensity distribution of the light spot used in the present invention. The wavelength used is 680 nm, and the numerical aperture of the objective lens is 0.55. The dotted line also shows the recording spot of the cutting device currently used for preparing the original optical disk. The minimum mark diameter is determined in an area where the spot intensity is about half from the current recording film characteristics. With a cutting device, marks having a width as small as about 0.2 microns can be recorded. However, in the recording / reproducing apparatus, the mark diameter is about three times as large as that of the numerical aperture and the shape of the light source, and is about 0.6 μm.
[0009]
Taking the case where a magneto-optical film is used as a recording film, for example, when the temperature exceeds the Curie temperature, the magnetization characteristics of the magnetic film are lost. It is recorded by a recording mechanism in which the magnetization of the changed area changes. Although the temperature distribution on the recording film changes depending on the irradiation time, the linear velocity, and the like, the shape of the temperature distribution does not become steeper than the spot distribution even if these measures are devised. The position of the end of the recording mark is determined by the intersection of the recording temperature determined by the magnetic characteristics of the recording film and the temperature distribution of the recording film. When the recording temperature changes due to the fluctuation of the recording film, the position of the recording mark changes slightly. Appears as noise in the reproduced signal. In order to reduce this noise, it is desirable to record at a place where the gradient of the temperature distribution is steep. That is, in the temperature distribution as shown in FIG. 1, a half value of the intensity is optimal. Therefore, the minimum recording mark diameter is the half value width of the spot distribution.
[0010]
As described above, the recording mark shape up to now has been determined by the temperature distribution. Therefore, the mark diameter cannot be reduced unless the spot diameter is significantly reduced. However, considering the recording mechanism, if the shape of the external magnetic field is made minute and a recording mark can be formed in accordance with this, the mark diameter can be further reduced. Therefore, instead of applying a magnetic field from the outside of the conventional disk, a physical structure for generating a magnetic field is provided in a recording medium in advance, and information is recorded thereon.
[0011]
2 and 3 show the recording mechanism of the present invention. The direction perpendicular to the paper surface is the direction of the track, and the inside of the paper surface represents a cross section perpendicular to the track. As in the prior art, the recording film is provided with a reflection layer and the like with the recording film sandwiched between interference layers in consideration of thermal characteristics and optical characteristics. Here, the recording film and the film structure according to the present invention are shown. A buffer layer 101 and a buried layer 102 are provided below the recording film 100. In this buried layer 102, magnetization regions 103 and 104 having magnetization directions indicated by arrows in a direction perpendicular to the tracks are alternately arranged. The temperature distribution on the recording film is shown above the film structure.
[0012]
As the light intensity increases, the temperature on the film surface increases as shown in FIGS. 2 (a), 2 (b) and 2 (c). In the recording area 110 exceeding the recording temperature Tc1 of the film, the magnetization is lost as shown by the oblique lines in FIG. When the temperature is lowered from this point, the temperature distribution changes as shown in FIGS. 3A, 3B, and 3C, and the magnetization of the recording film changes following the magnetization of the buried layer.
[0013]
As the magnetization direction, the magnetization direction of the magnetization region 103 is made to correspond to the magnetization direction of the recording mark, and the initialization direction of the recording film is made to correspond to the magnetization direction of the magnetization region 104. Then, even if the recording area 110 is large, the recording mark 111 is smaller than the recording area.
[0014]
There are various methods for forming the buried layer 102. When the same magneto-optical film as the recording film 100 is used, it is preferable that the buried layer 102 has a recording characteristic as shown in FIG.
[0015]
That is, the Curie temperature Tc2 of the buried layer 102 is set higher than the Curie temperature Tc1 of the recording film 100, and the temperature characteristic of the coercive force is set to be larger for the recording film at room temperature. In order to form the buried layer with a magneto-optical film, recording is performed in advance by a normal magneto-optical recording method using a short-wavelength recording device in order to make the magnetized area minute. As such a device, the optical system of the cutting device shown in FIG. 1 may be used. At this time, the magnetized region can be formed to have a width of about 0.2 μm. Alternatively, a green or blue laser light source currently used in research and development may be used. In this case, the size of the device can be made about the same as that of the information recording / reproducing device. However, since the numerical aperture of the objective lens cannot be made large, the recording mark width becomes about 0.4 μm.
[0016]
FIG. 5 shows the shape of the magnetized region recorded in advance. A stripe shape having a constant width in a straight line parallel to the traveling direction of the track and the light spot can be considered. In FIG. 5, the magnetized region corresponding to the recorded magnetization is represented by a diagonal stripe when viewed from the upper surface of the medium. When a spot having a two-dimensionally isotropic recording area 110 is scanned thereon and the information is recorded by modulating the light intensity in the traveling direction of the track, marks 120 to 140 representing the recorded information are formed. The width of this mark is almost equal to the width of the stripe-shaped magnetized region that has been prepared in advance.
[0017]
In FIG. 5, the recording film and the buried layer are viewed from above, and the magnetization region and the recording mark are overlapped. As a modulation method in the track traveling direction, an information mark can be recorded by a conventional recording method, a mark position recording method, or a mark length recording method. According to the present invention, the width can be reduced as compared with the information mark recorded by the conventional method. Further, since the recording width is determined by the magnetization width of the buried layer, the distance between adjacent tracks can be reduced. That is, as can be seen from FIG. 3C, the interval between the adjacent magnetization regions can be reduced to the width of the recording region. In the recording spot of FIG. 1, the track interval can be reduced to about 0.4 microns.
[0018]
FIG. 5 shows an example in which recording marks 130 to 140 are recorded on the magnetization stripes 103-2 and 103-5 having a magnetization region width of 0.2 μm by a mark position recording method. Further, an example is shown in which recording marks 120 to 129 are recorded on the magnetic stripes 103-1, 103-4, and 103-6 having a magnetization region width of 0.4 μm by a mark length recording method. In each case, the track interval was 0.6 microns.
[0019]
Although the above embodiment is an example in which the track interval is narrowed, the mark interval can also be narrowed by using the present invention in the linear density direction. FIG. 6 shows the magnetization region viewed from above. The magnetized area has, for example, a square shape, and the magnetized areas 1000A and 1000B having different magnetization directions are arranged so as to form a mosaic pattern in both the spot traveling direction and the direction perpendicular to the track. That is, in the track rows 103-7 to 103-9 in which the magnetization regions are alternately arranged in the spot traveling direction, the positional relationship of the alternate arrangement of the magnetization regions is inverted, and the magnetization polarities of the adjacent magnetization regions are different. Are arranged. In this way, crosstalk from adjacent tracks can be reduced when recording marks are read, and the track can be further narrowed by a synergistic effect with the removal of thermal interference in the recording according to the present invention.
[0020]
In FIG. 6, the size of the magnetization region from 103-7 to 103-9 is about 0.4 μm square, and the track interval is 0.6 μm. By increasing the light intensity of the recording light spot 1001 on the magnetization region 1000A corresponding to the recording mark and raising the temperature to the recording temperature or higher, it is possible to form an information mark following the magnetization region. Further, in the reproduction, information can be reproduced based on the rotation of the polarization plane of the reflected light, for example, by irradiating the reproduction spot 1002, for example, as in the reproduction of the conventional magneto-optical disk.
[0021]
Further, FIG. 7 shows an example of a magnetized region array 103-10 to 103-14 in which the magnetized region is narrowed, the size of the magnetized region is reduced to about 0.25 μm, and the track interval is reduced to about 0.45 μm. By increasing the light intensity of the spot 151 located on the recording film above the magnetization sequence 103-11 according to the light pulse 150 shown in the lower part of FIG. 7, a recording mark sequence as shown above the magnetization sequence 103-13 152 are formed. The magnetization arrangement of the magnetization arrays 103 to 13 is not shown, and only the magnetization arrangement of the recording mark array 152 is shown by hatched regions.
[0022]
In order to make the magnetization arrangement mosaic, some timing information is required when the buried layer is formed of a magneto-optical film. As a method of producing this, a method of arranging pits discretely on a medium and creating a clock for recording tracking information and data from the pits can be used. The magnetization arrangement is recorded by using a clock to be created from now on, and when recording an information mark, a recording pulse train corresponding to the recording information is also created by using this clock.
[0023]
In the above description, a buried mark 103 magnetized in a direction opposite to the initial magnetization direction of the magnetic film 102 as the buried layer was formed, and a local magnetic field was applied to the recording layer 100. However, the present invention is not limited to this.For example, a magnetic film magnetized in a predetermined direction is used as a buried layer, and a portion other than the buried mark is made non-magnetic by applying a technique such as ion implantation. It can be configured by changing to a film. It is also possible to apply a local magnetic field by providing irregularities in the embedded magnetic layer by using a technique such as a replica.
[0024]
【The invention's effect】
According to the invention described above, the track pitch can be increased by half or more and the linear density can be increased by 1.5 times or more as compared with the conventional optical disk recording method. For example, when a laser having a wavelength of 680 nm is used as a light source, a recording density of 3.6 Gbit / inch ² or more can be achieved.
[Brief description of the drawings]
FIG. 1 is a graph showing the intensity distribution of a recording spot according to the present invention.
FIG. 2 is a conceptual diagram illustrating the recording principle of the present invention.
FIG. 3 is an explanatory conceptual diagram of a recording principle of the present invention.
FIG. 4 is a graph showing the magnetization characteristics of the recording medium of the present invention.
FIG. 5 is a plan view showing the arrangement of recording marks and magnetized regions according to the present invention.
FIG. 6 is a plan view showing the arrangement of recording marks and magnetized regions according to the present invention.
FIG. 7 is a plan view showing the arrangement of recording marks and magnetized regions according to the present invention.
[Explanation of symbols]
1000A: magnetized area corresponding to recording mark; 103-7 to 103-9: track row; 1001: recording light spot; 1002: reproduction spot.

Claims (2)

Forming a light spot on a recording medium, an optical information recording and reproducing method for recording information by modulating the light intensity of the light spot,
As the recording medium, a multilayer magnetic film having a first magnetic film in which an embedded mark is formed by locally changing a magnetization direction in advance is used,
The embedded mark is smaller in width and / or length than a region where the medium is optically changed in order to record information during recording,
The light spot is irradiated onto the second magnetic layer overlapping the buried mark, to record a recording mark superimposed so as to follow the magnetization direction and shape of the buried mark in the second magnetic layer Characteristic information recording / reproducing method. 2. The information recording / reproducing method according to claim 1, wherein a disc-shaped recording medium is used as the recording medium, and the embedding marks are arranged in a circumferential direction.

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