JPH087386A - Multivalue recording/reproducing method of optical disc - Google Patents

Abstract

PURPOSE:To obtain a method and an apparatus for recording/reproducing information stably by a method wherein a magneto-optical recording medium which facilitates quaternary recording of signals with layer-built two recording layers laminated. CONSTITUTION:A first recording layer 4 in which recording states exist in two different magnetic field regions corresponding to an applied external magnetic field and a second recording layer 6 in which one recording state exists in a magnetic field region different from those of the first recording layer 4 are provided in a recording medium. By starting the recording from marks which are exclusively for generating clock signals and provided on a disc as a pit row, the influence of the level fluctuation is hardly given and a modulation magnetic field intensity and a light intensity in a data region can be varied without giving the influence upon servo signals. As a result, a narrow allowance of the fluctuation of the recording conditions of a conventional multivalue recording medium can be widened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium and a recording / reproducing method for the recording medium, and more particularly to recording / reproducing by applying a medium capable of multilevel recording to a sample servo format type optical disc. Regarding the method.

[0002]

2. Description of the Related Art Regarding the technology for increasing the density of magneto-optical recording media, Proceedings of the 13th Annual Meeting of the Japan Society of Applied Physics (198)
A multi-valued recording system has been proposed as described on page 63 of (9th year).

In the known method, a plurality of recording layers having different coercive forces are laminated and the strength of the magnetic field applied to the recording layers is modulated in multiple steps to selectively reverse the magnetization of a specific recording layer. It is to let.

However, according to the multi-valued recording method of the above-mentioned known example, when the magneto-optical recording medium is irradiated with a laser beam at the time of recording a signal and each recording layer is heated to near the Curie temperature, each recording layer is protected. Since there is almost no difference in magnetic force, it is practically difficult to selectively reverse the magnetization of each recording layer. Considering the actual usage conditions, it is important to allow a certain amount of allowance for variations in magnetic field strength and light strength.

On the other hand, in an optical disc using a multilevel recording medium, a mark is accurately recorded and formed at a desired position at the time of recording / reproducing, and at the time of reproducing, the mark position is acquired by a reproduction clock to accurately recognize the multilevel level. This is very important.
Particularly, in the case of a multi-valued recording system, it is important that both the position of the mark in the clock pull-in area and the signal level obtained from the mark are stable in the case of the so-called self-clock system in which the clock is generated from itself. is there.

A sample servo format is known as a method for processing a servo system and a data system from mark rows provided in different areas. In the multi-valued recording medium shown in the present invention, when used in combination with the sample servo format, a clock signal can be obtained regardless of the signal level, so that stable recording / reproducing of information can be performed.

[0007]

SUMMARY OF THE INVENTION In the present invention, in order to expand the narrowness of the allowable value for fluctuations in recording conditions, which is a problem in the conventional multi-valued recording medium, a small external magnetic field and a small output laser beam are used. By providing a medium capable of recording and erasing signals and having a high SN ratio and high recording density, and by applying a sample servo format, stable information recording / reproduction is realized. .
A clock generation reference for reproduction is not obtained from a data area where a multi-valued signal level is obtained, and a mark for exclusive use of clock generation provided in advance as a pit string on the disc is used to reduce the influence of level fluctuations. By changing the modulation magnetic field intensity and the light intensity in the data area without affecting the servo signal, the recording condition can be expanded.

In the field of magneto-optical recording media, increasing the recording density has become one of the most important technical problems. Conventionally, as a means for increasing the density of a magneto-optical recording medium, multilevel recording of signals is performed, as described on page 63 of the 13th Japan Applied Magnetics Society Academic Lecture Summary (published in 1989). A scheme has been proposed.

In the known multilevel recording method, a plurality of recording layers having different coercive forces are laminated and the magnetic field strength applied to the recording layers is modulated in multiple steps to selectively magnetize a specific recording layer. It is to reverse the magnetization. According to this method, four-value recording is possible by providing three recording layers having different coercive forces.

However, according to the known multilevel recording method,
When the recording layer is heated to near the Curie temperature by irradiating the magneto-optical recording medium with a laser beam during signal recording,
Since there is almost no difference in coercive force between the recording layers, it is practically difficult to selectively reverse the magnetization of each recording layer.
Suppose that the magnetic characteristics of each recording layer are strictly adjusted and the laser intensity and external magnetic field intensity during recording are strictly controlled, so that the magnetization of each recording layer can be selectively reversed at the laboratory level. Even if it becomes, mass production of such a magneto-optical recording medium and a recording / reproducing device is impossible in terms of cost. In addition, since the margin for fluctuations in laser intensity and external magnetic field intensity during recording is extremely small, it is impossible to maintain a stable recording / reproducing state for a long period of time, which is extremely impractical. Incidentally, if the signal is recorded in a state where the difference in coercive force between the recording layers is sufficiently large without raising the temperature of each recording layer to the vicinity of the Curie temperature, such an inconvenience does not occur, but on the other hand, Since a large magnetic field is required for recording and erasing signals, the magnetic field generating device such as a magnetic head becomes large, the recording and reproducing device becomes large, and another serious inconvenience such as an increase in power consumption occurs. Is virtually impossible.

This magneto-optical recording medium has two recording layers.
The efficiency of improving the recording density with respect to the number of laminated recording layers is such that only three-valued recording can be performed even if the recording layers are laminated, and three recording layers must be laminated to realize four-valued recording. There is also the problem that is bad. That is, for example, as shown in FIG. 19, when two recording layers (A layer and B layer) having different temperature characteristics of coercive force are laminated, and when an external magnetic field having the magnitude of H2 shown in FIG. 19 is applied, As shown in FIG. 20B, only the B layer can be magnetization-reversed, but H shown in FIG.
Fig. 20 (c) when an external magnetic field of magnitude 1 is applied
As shown in (2), both the A layer and the B layer undergo magnetic reversal, so that only the three values shown in (a), (b), and (c) can be recorded.

Furthermore, when a signal is recorded on this magneto-optical recording medium by, for example, a magnetic field modulation method, when a signal is recorded on a magnetic film having a larger coercive force by applying a larger external magnetic field, the external magnetic field has a predetermined value. Since the coercive force always passes the value of the recording magnetic field for the magnetic film having a smaller coercive force until reaching the value, a recording portion with a smaller external magnetic field is always formed around the recording portion with a larger external magnetic field. Therefore, not only a reproduced signal with a high S / N cannot be obtained, but also if the signal is recorded at a high density, it is a recording portion by a larger external magnetic field or a recording portion by an originally smaller external magnetic field. There is also a problem that the recording density cannot be increased because it becomes difficult to determine. Such inconvenience also occurs when a signal is recorded by the light modulation method.

[0013]

The medium used in the present invention is capable of recording and erasing signals with a laser having a small external magnetic field and a small output, and is capable of recording signals with a high S / N and a high recording density. It is a realizable magneto-optical recording medium. That is, at least two recording layers stacked on each other are carried on a substrate, and at least one recording layer among these recording layers is recorded in two or more different magnetic field regions with respect to an applied external magnetic field. Is formed, and the other recording layer is formed of a magneto-optical recording film having at least one recording state in a magnetic field region different from that of the first recording layer.

Of the first recording layer and the other recording layers, the recording layer in which the recording state exists in two or more different magnetic field regions with respect to the applied external magnetic field is the perpendicular magnetic film and the perpendicular magnetic film. It is composed of an auxiliary magnetic film which is magnetically coupled and is made of a magnetic material whose magnetization is more likely to rotate in the direction of the external magnetic field when irradiated with a laser beam for recording or erasing than this perpendicularly magnetized film. In this case, the perpendicular magnetization film is an amorphous alloy of a rare earth and a transition metal, and the sublattice magnetic moment of the rare earth atom is more dominant than the sublattice magnetic moment of the transition metal atom from room temperature to the Curie temperature. The auxiliary magnetic film may be composed of a body, a transition metal, an alloy of a transition metal and a noble metal, an alloy of a rare earth containing at least one of oxygen and nitrogen and a transition metal, and the perpendicular magnetization film. It can be composed of any magnetic material selected from alloys of rare earths and transition metals having a small perpendicular magnetic anisotropy energy.

The transition metal is [Co, Fe, Ni].
At least one kind of transition metal element selected from the above is preferable, and the noble metal includes [Pt, Al,
At least one kind of noble metal element selected from Au, Rh, Pd] is suitable. More specifically, as the auxiliary magnetic film, a Co film, a PtCo alloy film, an oxidized TbFeCo alloy film, a GdFeCo alloy film, GdTbF
eCo alloy film, NdFeCo alloy film, GdDyFeCo
Any magnetic film selected from alloy films can be used.

On the other hand, regarding the signal recording method, the optical head and the magnetic head are driven relative to the magneto-optical recording medium of the present embodiment, and the optical head moves along the recording track of the magneto-optical recording medium. While irradiating a laser beam, an external magnetic field whose applied magnetic field intensity is signal-modulated in multiple steps according to a recording signal is applied to the laser beam irradiating section by applying a magnetic field to the two recording layers. It was made possible to perform multilevel recording of four or more levels. in this case,
The laser beam can be continuously irradiated with a laser beam having a constant intensity, or can be irradiated periodically or in a pulsed manner.

Further, the optical head and the magnetic head are driven relative to the magneto-optical recording medium, and an external magnetic field is applied to the magneto-optical recording medium from the magnetic head, while recording tracks are recorded on the magneto-optical recording medium. Along with this, the multi-valued recording of four or more values can be performed on the two recording layers also by irradiating the laser beam whose laser intensity is signal-modulated in multiple steps according to the recording signal from the optical head. it can. In this case, it is preferable to change the external magnetic field strength at a constant frequency. As a signal recording method, either mark position recording or mark edge recording can be applied.

[0018]

According to the present invention, a first recording layer having a recording state in two different magnetic field regions with respect to an applied external magnetic field, and one recording in a magnetic field region different from the first recording layer. When a magneto-optical recording medium in which a second recording layer in which a state exists is laminated is used, by applying different external magnetic fields of four stages corresponding to each recording state of each recording layer
Value recording becomes possible. In addition, a first recording layer having a recording state in two different magnetic field regions with respect to an applied external magnetic field, and a second recording layer having two recording states in a magnetic field region different from the first recording layer. Even in the case of using a magneto-optical recording medium in which recording layers are stacked, four-level signal recording can be performed by applying four different external magnetic fields corresponding to each recording state of each recording layer.

That is, in the first recording layer formed by laminating the perpendicular magnetization film and the predetermined auxiliary magnetic film, for example, as shown in FIG. 21, the carrier-to-noise ratio of the optical modulation recording signal to the external magnetic field is 2 It has two peaks (recording status). On the other hand, in the second recording layer having no auxiliary magnetic layer, the carrier-to-noise ratio of the optical modulation recording signal with respect to the external magnetic field has one peak, as shown in FIG. 22, for example. In addition, Japanese Patent Application No. 3-210
430 and Japanese Patent Application No. 4-153882 (Japanese Patent Application Laid-Open No. 5-1
As disclosed in Japanese Patent No. 82264),
In the first recording layer formed by stacking the perpendicular magnetic film and the predetermined auxiliary magnetic film, the sublattice magnetic moment of the transition metal in the perpendicular magnetic film is easily inverted in the exchange coupling magnetic field direction by the action of the auxiliary magnetic layer. Therefore, the magnetization of the entire recording layer can be oriented in the direction of the external magnetic field or in the opposite direction. On the other hand, the second recording layer having no auxiliary magnetic layer and having one recording state in the magnetic field region different from that of the first recording layer is:
In the temperature rising state, the magnetization direction of the entire recording layer is easily reversed to the direction of the external magnetic field.

Therefore, as shown in FIG. 23A, for example, the first recording layer made of a ferrimagnetic material in which the sublattice magnetic moment of the rare earth atom is more dominant than the sublattice magnetic moment of the transition metal atom from room temperature to the Curie temperature. A and
The second recording layer B made of a ferrimagnetic material in which the sublattice magnetic moment of the transition metal atom is more dominant than the sublattice magnetic moment of the rare earth atom from room temperature to the Curie temperature is laminated, and a downward external magnetic field is applied to the external magnetic field in the recording direction. When a signal is recorded by using the upward external magnetic field as the external magnetic field in the erasing direction, (i) the external magnetic field H0 of a magnitude capable of directing the magnetization of the entire first recording layer A in the erasing direction (shown in FIG. 21). (External magnetic field in the region (1)) is applied in the erasing direction to cause the sublattice magnetic moment of the transition metal atoms of the first recording layer A to the recording direction and the sublattice magnetic moment of the transition metal atoms of the second recording layer B to be recorded. The moment can be directed in the erasing direction.

(Ii) Application of an external magnetic field H1 (the external magnetic field in the area (2) shown in FIG. 21) having a magnitude capable of orienting the entire magnetization of the first recording layer A in the recording direction. Thereby, both the sublattice magnetic moments of the transition metal atoms of the first recording layer A and the second recording layer B can be directed in the erasing direction.

(Iii) Applying an external magnetic field H2 (the external magnetic field in the region (3) shown in FIG. 21) having a magnitude capable of orienting the entire magnetization of the first recording layer A in the erasing direction. Thereby, both the sublattice magnetic moments of the transition metal atoms of the first recording layer A and the second recording layer B can be directed in the recording direction.

(Iv) Applying an external magnetic field H3 (the external magnetic field in the area (4) shown in FIG. 21) having a magnitude capable of orienting the entire magnetization of the first recording layer A to the recording direction. This makes it possible to direct the sublattice magnetic moment of the transition metal atoms of the first recording layer A in the erasing direction and the sublattice magnetic moment of the transition metal atoms of the second recording layer B in the recording direction.

The magnitude of the change in the Kerr rotation angle detected as a signal from the magneto-optical recording medium is proportional to the sum of the sublattice magnetic moments of the respective transition metal atoms in the first recording layer A and the second recording layer B. , H0, H1, H2, and H3, the relative signal output shown in FIG. 23B is obtained from the recording tracks to which the external magnetic fields are sequentially applied. Therefore, for example, as shown in the figure, the recording state by the external magnetic field H1 is "0", the recording state by the external magnetic field H0 is "1", the recording state by the external magnetic field H3 is "2", and the recording state by the external magnetic field H2 is "3"
The four-valued recording of the signal can be made by locating each of them.

A first recording layer having a recording state in two different magnetic field regions with respect to an applied external magnetic field,
When a magneto-optical recording medium in which a second recording layer having two recording states in a magnetic field region different from that of the first recording layer is laminated is used, four-value recording of signals is performed by the same principle. It can be carried out. For example, in the case where the first recording layer having the characteristic indicated by the alternate long and short dash line in FIG. 24B and the second recording layer having the characteristic indicated by the broken line in FIG.
By applying the external magnetic fields of H0, H1, H2, and H3 shown in (a), the four recording states "0", "1", "2", and "3" shown in FIG. Can be revealed. Therefore, for example, as shown in these figures, the recording state by the external magnetic field H0 is "0", the external magnetic field H0
By positioning the recording state by 1 as "1", the recording state by the external magnetic field H2 as "2", and the recording state by the external magnetic field H3 as "3", the four values of the signal can be obtained with an external magnetic field of about ± 100 (Oe). You can record. In this case, as shown in FIG. 25, if a DC bias magnetic field is applied to the external magnetic field to shift the central magnetic field of the external magnetic field to the minus side by about −50 (Oe), it is as small as ± 50 (Oe). It also enables ternary recording of signals in an external magnetic field.

As described above, the magneto-optical recording medium of the present invention has 2
Since four-level signal recording can be performed with two recording layers, a higher-density signal recording can be achieved with a simpler structure than a conventional magneto-optical recording medium in which only two signal recording levels can be three-valued. it can. Further, as is clear from FIGS. 21, 24, and 25, each recording state is extremely stable against fluctuations in the external magnetic field, and the magnetic characteristics of each recording layer, the laser beam intensity during recording and reproduction, and the external magnetic field intensity. Since it is not necessary to make a delicate matching, it is possible to construct a magneto-optical recording / reproducing system with excellent mass productivity and reliability.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the overall structure of a magneto-optical recording medium according to the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of essential parts of a magneto-optical recording medium according to the present invention.

As shown in FIG. 1A, the magneto-optical recording medium according to the present invention has a transparent substrate 1 having a desired preformat pattern 2 formed on one side thereof, and a first substrate formed on the preformat pattern 2. A first enhancement film 3, a first recording layer 4 formed on the first enhancement film 3, and a second enhancement film 5 formed on the first recording layer 4 as necessary.
The second recording layer 6 formed on the second enhancement film 5 or the first recording layer 4, the third enhancement film 7 formed on the second recording layer 6 as needed, and the third enhancement film 7 The reflective film 8 formed on the reflective film 8 and the protective film 9 formed on the reflective film 8.

The transparent substrate 1 is formed by molding a transparent resin material such as polycarbonate, polymethylmethacrylate, polymethylpentene, or epoxy into a desired shape, or a desired shape formed on one side of a glass plate. It is possible to use any known transparent substrate such as one in which a transparent resin layer onto which the preformat pattern 2 is transferred is adhered. Note that the configuration, arrangement, forming method, and the like of the preformat pattern 2 are matters that are publicly known and are not the gist of the present invention, so description thereof will be omitted.

The first to third enhancement films 3, 5 and 7 are
It is provided in order to increase the apparent Kerr rotation angle by causing multiple interference of reproducing light beams in the film, and is formed of an inorganic dielectric material having a refractive index larger than that of the transparent substrate 1. As the enhancement film material, oxides or nitrides of silicon, aluminum, zirconium, titanium, tantalum are particularly suitable. The first enhancement film 3 is 600Å
It is formed to a film thickness of ~ 1200Å. Also, the second and third
The enhancement films 5 and 7 are formed as needed, and are formed to have a film thickness of 0Å to 500Å.

The reflective film 8 is provided to increase the effective Kerr rotation angle of the medium by increasing the reflectance and to adjust the recording sensitivity of the medium by adjusting the thermal conductivity. It is formed of a material having a high reflectance for the light beam. Specifically, (Al, Ag, Au,
One or more metal elements selected from the group of Cu, Be) and (Cr, Ti, Ta, Sn, Si, Rb, P)
e, Nb, Mo, Li, Mg, W, Zr), alloys composed of one or more kinds of metal elements selected from the group of (e, Nb, Mo, Li, Mg, W, Zr) are particularly preferable.
It is formed to a film thickness of 00Å.

The protective film 9 is for protecting the film bodies 3 to 8 from mechanical impact and chemical adverse effects, and is applied to cover the entire film body. The protective film material may be a resin material. In particular, an ultraviolet curable resin is suitable because it is easy to form a film.

The first recording layer 4 is an amorphous rare earth-transition metal system in which the rare earth sublattice magnetization moment is predominant in the temperature range from room temperature to the Curie temperature, or in the temperature range from room temperature to the maximum reached temperature during recording or erasing. 100-
The amorphous perpendicular magnetization film 4a having a thickness of 500 Å and the auxiliary magnetic film 4b having a film thickness of 5 to 100 Å provided in contact therewith.

As the rare earth-transition metal-based amorphous perpendicular magnetization film, those represented by the following general formula are particularly preferable.

General formula; (Tb100-AQA) XFe100-XY-ZCoYMZ, where 20 atomic% ≤ X ≤ 35 atomic% 5 atomic% ≤ Y ≤ 15 atomic% 0 atomic% ≤ Z ≤ 10 atomic% 0 atomic% ≤ A ≦ 20 atomic% M is at least one element selected from Nb, Cr, Pt, Ti and Al.

Q is at least one element selected from Gd, Nd and Dy.

The auxiliary magnetic film 4b is composed of a magnetic material containing a transition metal element and having a small perpendicular magnetic anisotropy. As a specific example, (1) [Pt, Al, Ag, A
alloy thin film of at least one element selected from the group of noble metal elements such as u, Cu, Rh] and at least one element selected from the group of transition metal elements such as [Fe, Co, Ni], ( 2) For example, GdFeCo alloy, GdT
bFeCo alloy, GdDyFeCo alloy, NdFeCo
Alloys such as Gd and Nd, thereby reducing the perpendicular magnetic anisotropy, and rare earth-transition metal alloys, (3) By containing oxygen and nitrogen in a larger amount than usual (for example, 5 atomic% or more). , Rare earths with reduced perpendicular magnetic anisotropy
A transition metal-based alloy, (4) a simple transition metal such as [Fe, Co, Ni], or an alloy containing a large amount of these metals is used
Examples include a film having a thickness of -30 Å and several atomic layers.

Depending on the composition, the auxiliary magnetic film 4b has a perpendicular magnetic anisotropy energy equal to or lower than the shape anisotropy, and the magnetization is in-plane (auxiliary) before an external magnetic field is applied. It can be oriented in a direction parallel to the film surface of the magnetic film 4b). The auxiliary magnetic film 4b thus adjusted is heated to a temperature near the Curie temperature, and when an external magnetic field is applied, the magnetization direction rises from the in-plane direction to generate a magnetic moment component in the external magnetic field direction. An exchange coupling force is exerted on the transition metal magnetic moment of the amorphous perpendicularly magnetized films 4a stacked in contact with each other. Therefore, in the first recording layer formed by stacking the amorphous perpendicular magnetization film 4a and the auxiliary magnetic film 4b, changes in the carrier wave and noise level of the optical modulation recording signal with respect to the external magnetic field are as shown in FIG. To
It has two peaks.

The second recording layer 6 is composed of a magneto-optical recording film having at least one recording state in a magnetic field region different from that of the first recording layer 4. Therefore, it is also possible to use an amorphous perpendicular magnetization film and an auxiliary magnetic film of the same kind as the first recording layer 4 and having two recording states in magnetic field regions different from those of the first recording layer 4. , The first
It is also possible to use a recording layer having a configuration different from that of the recording layer 4 and having one recording state in a magnetic field region different from that of the first recording layer 4, as shown in FIG. The second recording layer 6 belonging to the latter includes (1) an amorphous perpendicular magnetization film of a rare earth-transition metal system in which the transition metal sublattice magnetization is predominant in the temperature range from room temperature to the maximum reached temperature during recording and erasing. (2) An amorphous perpendicular magnetization film of a rare earth-transition metal system in which the rare earth sublattice magnetization is dominant in the same temperature range as above, (3) a compensation temperature between room temperature and the Curie temperature There is a rare earth-transition metal-based amorphous perpendicular magnetization film in which In particular,
Those represented by the following general formula are particularly preferable. The thickness of the second recording layer 6 is preferably formed in the range of 100 to 500Å.

General formula; TbXFe100-XY-ZCoYMZ where 15 atom% ≤X≤30 atom% 5 atom% ≤Y≤15 atom% 0 atom% ≤Z≤10 atom% M is selected from Nb, Cr and Pt. At least one element.

The respective film bodies 3 to 8 are formed on the transparent substrate 1 by a vacuum film forming method such as sputtering or vacuum deposition.
Are sequentially laminated on the pre-format pattern forming surface.
Each of these film bodies 3 to 8 has a difference in reproduction output level (size of Kerr rotation angle) depending on each recording level as much as possible when signals are read from the optical information recording medium in which multi-value recording is performed. The film thickness and the optical constant are selected so as to be uniform. Depending on the selection at that time, the second and third enhancement films and / or the reflection film may be omitted. Further, the first recording layer 4 and the second recording layer 6 may have their stacking positions interchanged with each other. When the stacking position of each recording layer is changed, the Kerr rotation angle in each recording state corresponding to the magnitude of the external magnetic field at the time of recording and the magnitude of the laser power applied changes, but It is possible, and there is no change in the characteristics and effects of the magneto-optical recording medium. Further, by stacking the recording layers in three or more layers, it is possible to perform higher-order multilevel recording,
The composition of each film can be changed accordingly.

Examples of the magneto-optical recording medium according to the present invention will be illustrated below.

<First Embodiment> As shown in FIG. 2, in the magneto-optical recording medium of the present embodiment, a SiN film having a film thickness of 100 nm and a film thickness of 15 nm are formed on a preformat pattern forming surface 2 of a transparent substrate 1. Tb19Fe62Co10Cr9 (subscripts indicate atomic%; the same applies below), SiN film with a thickness of 10 nm, Tb32Fe56Co12 film with a thickness of 20 nm, Pt80Co20 film with a thickness of 5 nm, and SiN with a thickness of 10 nm. A film and an Al film having a film thickness of 70 nm are sequentially laminated, and each of these films is covered with an ultraviolet curable resin film.

The SiN film having a film thickness of 100 nm constitutes the first enhance film 3, and the two SiN films having a film thickness of 10 nm constitute the second and third enhance films 5 and 7, respectively.
The Tb19Fe62Co10 film constitutes the first recording layer 4 with a single layer, and one recording state exists in a specific magnetic field region.
Tb32Fe56Co12 film and Pt80C laminated directly on each other
The o20 film constitutes the second recording layer 6, and the first recording layer 4
There are two recording states in different magnetic field regions. Further, the Al film constitutes the reflective film 8 and the ultraviolet curable resin film constitutes the protective film 9.

<Second Embodiment> As shown in FIG. 3, in the magneto-optical recording medium of the present embodiment, a SiN film having a film thickness of 100 nm and a film thickness of 15 nm are formed on the preformat pattern forming surface 2 of the transparent substrate 1. Tb32Fe56Co12 film, a GdFeCo film with a thickness of 2 nm, a SiN film with a thickness of 10 nm, a Tb19Fe62Co10Cr9 film with a thickness of 20 nm, and a thickness of 1
A 0 nm SiN film and an Al film having a film thickness of 70 nm are sequentially laminated, and each of these films is covered with an ultraviolet curable resin film.

Tb32Fe56Co12 laminated directly to each other
The film and the GdFeCo film constitute the first recording layer 4,
There are two recording states in different magnetic field regions. Tb19F
The e62Co10 film constitutes the second recording layer 6 with a single layer,
One recording state exists in a magnetic field region different from that of the first recording layer 4. The magneto-optical recording medium of the present example is different from the magneto-optical recording medium according to the first embodiment in that the first recording layer 4 is provided on the side close to the substrate, that is, on the incident side of the recording / reproducing laser beam.
Is composed of a laminated body of two magnetic films. Therefore, for the purpose of not reducing the incident amount of the laser beam on the second recording layer 6, GdFe having a low absorptance of the laser beam is used as an auxiliary magnetic film forming the first recording layer 4.
A Co film was used and its thickness was made extremely thin to 2 nm.

Since the other parts are the same as those in the first embodiment, the same reference numerals are given to the corresponding parts and the description thereof will be omitted.

<Third Embodiment> As shown in FIG. 4, the magneto-optical recording medium of this embodiment has a SiN film having a film thickness of 100 nm and a film thickness of 15 nm on the preformat pattern forming surface 2 of the transparent substrate 1. Tb32Fe56Co12 film, 7 nm thick (Tb32Fe56Co12) 92O8 film, 10 nm thick SiN film, and 20 nm thick Tb19Fe62Co10Cr film.
9 films, SiN film with a thickness of 10 nm, and a film thickness of 70 nm
Al films are sequentially laminated, and each of these films is covered with an ultraviolet curable resin film.

Tb32Fe56Co12 laminated directly to each other
The film and the (Tb32Fe56Co12) 92O8 film are the first recording layer 4
And two recording states exist in different magnetic field regions. The Tb19Fe62Co10 film is a single layer of the second recording layer 6
In a magnetic field region different from that of the first recording layer 4.
There are two record states. The magneto-optical recording medium of this example has a low absorption rate of the laser beam as an auxiliary magnetic film forming the first recording layer 4 (Tb32Fe56Co12) for the purpose of not reducing the incident amount of the laser beam on the second recording layer 6. )
A 92O8 film was used and its thickness was adjusted to 7 nm.

Since the other parts are the same as those in the first embodiment, the same reference numerals are given to the corresponding parts and the description thereof will be omitted.

<Fourth Embodiment> As shown in FIG. 5, in the magneto-optical recording medium of the present embodiment, a SiN film having a film thickness of 100 nm and a film thickness of 15 nm are formed on the preformat pattern forming surface 2 of the transparent substrate 1. Tb32Fe56Co12 film, a GdFeCo film having a film thickness of 2 nm, a SiN film having a film thickness of 10 nm, a Tb34Fe52Co14 film having a film thickness of 20 nm, a PtCo film having a film thickness of 5 nm, and a SiN film having a film thickness of 10 nm, Film thickness 7
A 0 nm Al film is sequentially laminated, and each of these films is covered with an ultraviolet curable resin film.

Tb32Fe56Co12 directly laminated to each other
The film and the GdFeCo film constitute the first recording layer 4,
There are two recording states in different magnetic field regions. Further, the Tb34Fe52Co14 film and the PtCo film which are directly laminated on each other form the second recording layer 6, and two recording states exist in the magnetic field region different from that of the first recording layer 4. In the magneto-optical recording medium of the present example, for the purpose of not reducing the incident amount of the laser beam on the second recording layer 6, a GdF having a low absorption rate of the laser beam is used as an auxiliary magnetic film forming the first recording layer 4.
An eCo film was used and its thickness was adjusted to 2 nm.

Since the other parts are the same as those in the first embodiment, the same reference numerals are given to the corresponding parts and the description thereof will be omitted.

Next, a multilevel signal recording method using the magneto-optical recording medium according to the present invention will be described.

The multilevel recording method of this example is characterized in that the external magnetic field is modulated in four steps according to the recording signal, and the recording laser beam is modulated in a pulse shape. The magneto-optical recording medium according to the first embodiment (FIG. 2) is used as the magneto-optical recording medium.

First, the magneto-optical recording medium is mounted on a medium driving unit such as a turntable, the optical head is arranged on the transparent substrate side, and the magnetic head is arranged on the protective film side. The medium drive unit is activated to drive the magneto-optical recording medium, the optical head and the magnetic head relatively at a predetermined linear velocity, and position the optical head and the magnetic head on a predetermined track.

Thereafter, as shown in FIG. 6A, the magnetic field strength applied from the magnetic head is from H0 to H in accordance with the recording signal.
An external magnetic field that is signal-modulated into four values of 3 and synchronized with a recording clock is applied to the optical information recording medium. Then, after the external magnetic field is switched to a predetermined value, the optical head is moved to the position shown in FIG.
By irradiating the optical pulse shown in (b), each recording layer of the optical pulse irradiation part is heated to a temperature at which the magnetization can be reversed by an external magnetic field. As a result, the magnetization domain of FIG. 6C corresponding to the magnitude of the external magnetic field is formed in the irradiation portion of each light pulse.

Signal modulation of the magnetic field strength can be performed by the system of FIG. 7 and the signal modulation circuit of FIG. 8 or 9.
That is, in the circuit of FIG. 8, the recording signal is separated into even-numbered bits and odd-numbered bits, and after waveform processing such as timing adjustment and pulse length adjustment is performed, the amplifier G having different gains is used.
Amplify by 1 and G2 respectively, and add them. Then
The added signal is subjected to voltage-current conversion by the magnetic head drive circuit to apply the external magnetic field shown in FIG. 1A from the magnetic head. Also, in the circuit of FIG.
The recording signal is separated into even-numbered bits and odd-numbered bits, and after waveform processing such as timing adjustment and pulse length adjustment is performed, the gains are respectively amplified by the same amplifier G. Next, each amplified signal is subjected to voltage-current conversion by a separate magnetic head drive circuit, and the external magnetic field shown in FIG. 6A is applied from a magnetic head having two windings with different numbers of turns. Instead of the magnetic head, it is of course possible to use another magnetic field generator such as an electromagnetic coil.

The recording state of the magnetization domain according to the magnitude of each external magnetic field is as shown in FIG. Therefore, the reproduction signal read from the magnetization domain sequence is
It becomes like FIG.6 (d). When this reproduced signal is sliced at three slice levels set to predetermined values according to the reproduced signal output from each recording state, as shown in the timing chart of FIG. 6E, three binarized signals sig
1, sig2, sig3 are obtained. Next, from the signals (1) to (4) of the timing chart, (5) to
By performing the logical operation of (8), the even bit and the odd bit are separated, and the even bit and the odd bit are combined by the procedure reverse to that when the magnetic head drive signal is generated. Can be played. Figure 10
A block diagram of the signal reproducing circuit is shown in FIG.

As a discrimination circuit for a multi-valued amplitude signal, Japanese Patent Laid-Open No.
In No. 94416, a configuration example for a multilevel modulation signal used in a general communication channel is given. The discrimination circuit described above has the effect of always keeping the threshold value of the discrimination circuit optimal by controlling the DC offset of the input signal of the A / D converter. However, it is difficult to apply it to a reproduced signal detected from an optical disk or the like. That is, it is necessary to devise an identification method considering the recording / reproducing characteristics of the optical disk.

When the signal from the mark recorded on the optical disk is detected by the photodetector and amplified by the AC amplifier, the average value level changes due to the density of the recorded data. If the modulation method is used so that the average value level is almost maintained, the fluctuation of the average value is small. However, the above-mentioned modulation method cannot be applied to a digital optical disk in which an unrecorded area and a recorded area are mixed. Further, in the magneto-optical disk, the level of the reproduction signal fluctuates due to the birefringence localized in a minute area existing on the substrate. At present, the optical disk takes only two levels of signals, and no detection is made at the midpoint. Therefore, there is no problem in signal detection even if the average value of the signal changes a little. However, in the multi-valued recording medium described later, the level of the signal is determined by using a plurality of levels, so that it becomes difficult to detect information unless some correction means or an accurate reference level is obtained. Therefore, at the same time as recording information is recorded, a mark group indicating a reference level at the time of reproduction is provided, and a plurality of threshold values are set by using the reproduction level of this signal as a reference. This mark group must have an interval at which the influence of the above-mentioned fluctuation factors can be ignored. Since it can be considered that it is constant in a small area, for example, in one sector from the characteristics of the medium, it may be provided in the header area of each sector.

When the logical unit sector recorded by the user is different between the inner circumference and the outer circumference of the disk as in the zone CAV method, it is necessary to provide each logical sector. Of course, the mark groups may be arranged at uniform intervals in the data area. If this reference level is used as a threshold setting reference value for data identification, a plurality of values correspond to information bits as long as the signal-to-noise ratio of the reproduced signal allows, without using special correction means in the detection circuit. Can be made. That is, it is possible to realize multi-value recording, which is one means of high-density recording. Also,
If the reference marks are provided at regular intervals in the data area, they can be used as the phase reference of the clock at the time of modulation / demodulation, whereby the clock for data modulation / demodulation can be obtained stably and accurately.

An embodiment of the present invention will be described below. FIG.
Reference numeral 1 (a) is an optical disc 11, which has a concentric or spiral track guide groove and a structure in which the track is divided into a plurality of areas (sectors) by a header area 202 containing address information and the like. . Figure 11
(B) A diagram showing an example of a format for a certain sector including the header area.

In the format shown in FIG. 11B, the area where the reproduction signal amplitude is minimum and the area where the reproduction signal amplitude is maximum are set as the area of the level detection signal 15 in the header area 202 of each sector. Provided, the detection signal 2
This is a configuration example in which each level of No. 05 is sample-held and used as a reference of the quantization threshold of the multi-valued recording data recorded in the user data area 207 that follows. An identification mark 203 indicating the start of a sector is placed at the beginning of each header area, and next, a synchronization signal 204, a level detection signal 205, and an address signal 206 indicating clock generation and demodulation start are provided as a header area 202. , Recorded.

In FIG. 11B, the level detection signal 205
Is placed immediately after the synchronizing signal 204, but it does not matter if it is immediately after the identification mark 203 or immediately after the address signal 206 as long as the area of the detection signal 5 is detected and confirmed.

FIG. 11C shows an example of mark arrangement of the level detection signal 205. The level detection mark 208 is formed so that the mark shape is the same as the subsequent information data and the multilevel information is reflected in the reproduction signal level. This forming method will be described later.

The maximum reproduction signal level from the level detection mark 208 is sampled and held, and the hold value is used as a slice level. Level detection mark 208
Following this, a region 209 is provided. Similarly, the area 209
By sampling and holding the playback signal level of
Used as the minimum playback level.

FIG. 12 shows a circuit configuration example for sampling and holding each level. FIG. 13 shows the time chart of the circuit operation. In FIG. 12, a sync signal detection circuit
The reproduction pulse 11 which has already been binarized is input to 10. The reproduction pulse 11 may be generated by a conventionally used generation circuit. Further, the detection of the synchronization signal 204 may also be performed by a conventionally used configuration. For example, a method is conceivable in which a shift register is used to determine a pattern match for every several marks of a data pattern, a majority decision is taken for the decision logic level, and a detection pulse is output. The detection pulse 12 detected by the detection circuit 10 is input to the delay circuit 13. The delay circuit 13 can be easily configured using a normal delay element or a shift register. The role of the delay circuit 13 is to position the reproduction signal level of the level detection mark 208 by delaying by the time difference because the lepel detection mark 208 is after the time when the sync signal detection pulse 12 is output. This is to generate a sample pulse for The delay pulse 14 is used as the sample pulse, and the delay pulse 16 obtained by delaying the delay pulse 14 by the mono-multi-vibrator (MM) 15 is used as the hold pulse. Using these control pulses, the sample-hold circuit (S / H) 17 holds the level of the reproduction signal 19 which is inverted and amplified by the amplifier 18. Here, it is desirable that the amplifier 18 be a DC amplifier with a small drift.

Similarly, regarding the level of the area 209 placed immediately after the level detection mark 208, the delay circuit 20, the mono-multi-vibrato (MM) 22, the sample hold circuit are provided.
It is held by a circuit composed of 24. These elements are easily available as off-the-shelf elements.

Next, the operation of the above circuit including the following signal processing will be described in detail with reference to the time chart of FIG. In FIG. 13A, a detection pulse 12 is output from the pulse train of the reproduction pulse 11 by the sync signal detection circuit. A delay circuit 14 produces a delay pulse 14 from the detection pulse 12. With this delay pulse 14, the level of the level detection mark 208 of the reproduction signal 19 is sampled by the sample hold circuit 17. Next, the reproduction level of the level detection mark 208 is held by the delay pulse 16 generated by the mono-multi-bi-plech 15 from the trailing edge of the delay pulse 14. The sampled and held level is input as the maximum level signal 25 to the inverting input of the comparator 27 via the resistor 29.

On the other hand, the delay pulse 14 is generated by the delay circuit 20. The delayed pulse 21 has a region 9
The playback signal level of the sample is sampled. The hold pulse is
A delay pulse 23 obtained by delaying the delay pulse 21 by the mono-multipiperator 22 is used to obtain a minimum level signal 26. The level signal 26 is input to the inverting input of the comparator 28 via the resistor 30. The resistors 29, 30, and 31 are for dividing the maximum level 25 and the minimum level 26 to create two threshold values. Although FIG. 13 shows the case where there are two threshold values, the same applies to the case where there are three or more threshold values. The logic level of "H" level is output by the comparator 27 only when the repelling level of the reproduction signal 19 to the non-inverting input of the comparator 27 is higher than the input level to the inverting input of the comparator 27. The same applies to the comparator 28.

Next, a method of quantizing multi-valued data will be described with reference to FIG. In FIG. 13B, the information signal is recorded with marks indicating three-valued amplitudes of 0, 1, and 2, and is assumed to be user data as shown by the reproduction signal 19. By the thresholds 34 and 35 set by the resistors 29 to 31,
The outputs 32 and 33 of the comparators 27 and 28 are as shown in the figure. Here, the output 41 of the AND gate 36 becomes the H level only when both the outputs 32 and 33 become “H.” The output 42 of the AND gate 37 is output by the inverter 39.
The output 43 of the AND gate 3208 is the output of the AND gate 3208 only when the logic level of the comparator output 32 inverted and the logic output of the comparator output 33 both become “H”.
Since the inverted levels of the comparator outputs 32 and 33 are input by the circuits 9 and 40, the comparator outputs 32 and 33 become the "H" level only when both the inverted logic levels are the "H". Here, when the data level is "0", the AND output 43 becomes H, but rather, both the AND outputs 41 and 42 are at the "L" level or the data level "0". It is more convenient to judge that. In this case, it is possible to make a decision by using a NOR gate with the AND outputs 41 and 42 as inputs. When the present invention is combined with the sample servo described below, the effect can be further enhanced.

FIG. 14 shows an example of the sample servo format. The sample servo method has a feature that the area for automatic focus adjustment and tracking and the data area can be separated in the format, and further, the detection of the pre-pit in which a clock for recording and reproducing data is provided in advance is detected. Since it can be generated based on the signal, there is little interference between data and servo. In FIG. 14, the track on the disc is divided into a plurality of sectors. In the figure, N
It is composed of +1 sector. A mark called a servo mark is provided at the beginning of each sector,
An access mark indicating the beginning of a sector, a tracking mark displaced left and right from the track center line, and a clock mark for extracting a clock are provided between them. In the area from the latter half of the servo mark to the sector mark, marks are arranged with a unique distance which does not exist in the data, to ensure sector recognition. Following the header existing at the beginning of each sector, the data area continues. Servo marks are also placed at the beginning of each data area.

The above-mentioned sector and the servo mark area in the sector are provided at a constant interval for each information track. These can be applied to both the formatting method in which the entire disc is equidistant at a physical distance and the formatting method in which it is equidistant in time. In the case of all persons, there can be considered a format system in which a zone in which the servo marks are provided at equal intervals is defined for each of a plurality of tracks, and the number of sectors and the number of servo marks per track are constant in the zone.

In the sample servo system, since the data area and the servo area can be physically separated as described above, mutual influence is small, and the clock signal for recording / reproducing / erasing is independent of the data signal. Since it can be generated from a clock mark, there are few restrictions on the data recording / reproducing system, and the synchronization area for clock pull-in, which is found in the normal self-clock system format, is not required. It is possible to design to increase the data capacity, that is, the data efficiency of the format.

In the case of the multilevel recording medium targeted by the present invention,
When the reproduction clock is generated based on the reproduction signal obtained from the recorded data, it may be difficult to set the slice level because the reproduction level has multiple values. According to the sample servo method, the reproduction clock can be extracted without depending on the data format and the presence or absence of data, which is convenient.

No consideration is given to the non-linearity of the recording characteristics and the point that the recording characteristics change due to laser power, magnetic field, etc. When an erasable recording material is used, it is stable against an input multilevel signal. It is difficult to obtain the reproduction signal level. Another object of the present invention is to perform multi-level recording on an optical disc capable of stabilizing the level of a reproduction signal regardless of the non-linearity of recording characteristics and the change of recording characteristics even when an erasable recording material is used. Provide a playback method. Therefore, a signal having a preset pattern is recorded on the optical disc surface, a reproduction signal corresponding to this pattern is accurately detected, the detection result is compared with the set pattern, and the recording condition is determined according to the comparison result. This is achieved by adopting a method of controlling. A preset pattern signal,
By comparing it with the detected reproduction signal level, it is possible to know the non-linearity and change of the recording characteristics. Therefore, by adopting a control method that changes the recording condition according to the comparison result, the multilevel level of the reproduction signal is changed. Can be stabilized.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 15 is a block diagram of the embodiment. On the optical disc, a guide groove for guiding the laser beam spot to record information and reading the recorded information is formed in an information recording area. There is. As this guide groove, the pre-groove disclosed in JP-A-491 / ll360l,
There is a guide groove formed of a pre-pit row disclosed in Japanese Patent No. 1189843, and a guide groove formed of a pre-pit row disclosed in Japanese Patent Laid-Open No. 58-185046. On these guide grooves, the information is divided into block units (generally called sectors), which are the divisions of the information shown in FIG. 14, and the address information indicating the position of each sector is recorded and reproduced.
Is recorded in the form of an optically distinguishable multi-valued level in the data area indicated by.

Next, the generation and recording of test patterns in this embodiment will be described. The alarm signal read from the guide groove is input to the reproducing circuit 307, where known analog signal processing is performed to obtain an optimum amplitude level and band for data processing. Using this processed signal, the preformatted ID part is detected, and the clock required for data processing is obtained from the timing generation circuit 308. Using the obtained timing information, the test pattern generation circuit, at the timing corresponding to the part of the preamble located immediately before the ID part and immediately before the data part in the sector,
A preset test pattern is generated and input to the modulation circuit 304 for modulation, and this signal is input to the recording circuit 3 to modulate the magnetic field intensity in the recording optical system 302 and at the same time drive control of the laser light source. To do.

The recording of the data is performed as shown in FIG. 14, and the reproduction signal takes a multi-valued repell between the pits. Regeneration is performed as follows. Recording optical system 30
The mark recorded by 2 is read by the reproduction optical system l0, analog processing is performed by the reproduction circuit 311, the clock is detected from the detection of the ID portion by the timing generation circuit 312, and this timing information is used. , The test pattern recorded in the preamble is fetched from the reproducing circuit 31l to the data processing circuit 313, and the signal is processed there to reproduce the test pattern. The reproduction test pattern output from the data processing circuit 3l3 and the set test pattern generated from the test pattern generation circuit 309 are compared and judged by the judgment circuit 314, and the modulation circuit 304 is controlled according to the comparison result. Output from the determination circuit 314, that is, the modulation circuit 304 is controlled by the control signal from the determination circuit 314 so that the set test pattern and the reproduction test pattern match exactly, and thus the erasable For an optical disc as a recording medium, it is possible to always perform multi-level recording at a stable level even when the recording characteristic is non-linear or the recording characteristic changes due to the magnetic characteristic of the medium, laser power, etc. Become.

The timing chart of the signals of the respective parts shown in FIG. 16 will be described. In the sector structure as shown in FIG. 16 (a), the SM part is detected as shown in FIG. 16 (b), the signal (d) from the prepit is detected, and the signal (e) phase-synchronized with the prepit by the PLL circuit is detected. Create a clock as. A test pattern is generated using this clock so that the waveform after the modulation circuit output becomes a staircase waveform as shown in (f), and the recording circuit 303 is used by the recording optical system 30.
The magnetic field intensity in 2 is modulated, and a test pattern is recorded on the optical disc 301. The reproduced signal of the recorded test pattern is as shown in (g), and PreAmb1e appears immediately after the SM and ID sections.
Is arranged. This reproduction signal is obtained from the reproduction optical system 10 via the reproduction circuit 11. The details of the multi-valued recording signal and the pre-pit signal of the test pattern are as shown in Fig. (I), and the reproduction signal from the pre-pit is as shown in Fig. (J). From this, a clock is created using the PLL circuit. The clock signal and the reproduction signal are input to the data processing circuit 313, and the multilevel level of the test pattern is sampled as shown in FIG. 9 (k) using the clock signal to remove the prepit portion. A sample of the reproduced signal of the test pattern,
The test pattern generated from the test pattern generation circuit 309 is input to the determination circuit 314, where both test patterns are compared and determined, and a signal for controlling the modulation circuit 304 is output according to the comparison result.

The operation of each part will be described in more detail with reference to FIGS. 17 to 18 and FIG.

First, the test pattern generation circuit 309 operates as follows. The signal from the recording optical system 302 is input to the timing generation circuit 308 via the reproduction circuit 307. The timing generation circuit 308 detects the SM mark at the head of the data section as shown in FIG. The ID data is recognized and the sector to record is avoided.
This method is detailed in, for example, JP-A-58-169337 and JP-A-58-16934l. Further, a clock is generated from the prepit mark. Regarding this method, Patent No. 1189
Since I am familiar with No. 843, I will omit it here.

The logic circuit 320 of the detailed configuration diagram shown in FIG.
Input the SM mark timing and clock to, where Pr
Generates a pulse that causes recording of the test pattern recorded in eAmb1e. This is up power unta 32
Input to l and the counter output is used as the address input of ROM322. In the ROM 322, data RD having a value proportional to the increase of the address RA as shown in FIG. 18A is recorded as the relationship between the address and the data. The data RD read from the ROM 322 is D / A via the switching circuit 323 which selects the test pattern or the encoded data.
Input to converter 324, and recording circuit 3 as an analog signal
Sent to 03.

By doing so, a recording signal as shown in FIG. 16 (f) is generated. Next, the operation of controlling the modulation circuit 304 using the test pattern recorded as described above will be described. The reproduction signal [FIG. 16 (i)] obtained from the reproduction circuit 311 is input to the sample hold circuit 325, and only the test pattern portion is extracted. As the sample hold timing, a pulse indicating the test pattern recording timing described when the test pattern is generated is used. The timing signal is generated by inputting the SM mark and the clock generated from the timing generation circuit 312 to the reproduction signal of the reproduction optical system to the logic circuit 320. Therefore, the logic circuit 320 has a function of switching between the signal from the recording optical system and the signal from the reproducing optical system. Output of sample hold circuit 325 [Fig.
It is sent to the A / D converter 326 and converted into a digital signal.
This value is, for example, Y (i) (i corresponds to the order of the test patterns recorded at the sample points).

On the other hand, a signal desired as the reflected light from the pit recorded according to the data of the test pattern (the reflected light amount has a linear relationship corresponding to the modulation input) is X ^
As (i), X ^ (i) is stored in the ROM 327 and is read out according to the address generated from the up counter 321 as shown by the dotted line in FIG. 18 (b). Also, ROM3
The pattern generation signal stored in 22 is X (i). From these signals X ^ (i), X (i), and Y (i), a signal Z (i) that determines the characteristics of the modulation circuit 304 is produced as follows. One way is by hardware to make Z (i)
There is a way to make. Here, the recording characteristic of the disc is Y
(I) / X (i), and the characteristics of the modulation circuit are Z (i) / X
(I) and X ^ (i) for the recorded data of X (i)
X ^ (i) = Y (i) / X (i) (Z (i) / X (i)) X
The relationship of (i) needs to be established.

From this, assuming that ε (i) = X ^ (i) -Y (i) and ε (i) is smaller than X (i), Z (i) = (X ^ (i) .multidot. X (i) / Y (i)) = (X ^ (i) ・
X (i) / (X ^ (i) −ε (i))) = X (i) / (1−ε
(I) / X ^ (i)) ≈ {1 + ε (i) / X ^ (i)} · X (i) =
X (i) + ε (i) ・ {X (i) / X (i) ^} ＝ 2X (i) −Y (i) ・
It becomes {X (i) / X (i) ^}. If the above formula is realized by hardware, ROM22
The data X (i) read from is doubled by the multiplication circuit 28, and this is input to the addition terminal of the addition / subtraction circuit 29, while
Input Y (i) to one of the multiplication circuits 336, and R for the other.
By inputting the value of X (i) / X ^ (i) read from the OM327 and inputting the value of this multiplication result to the subtraction terminal of the addition / subtraction circuit 329, Z ( i) is waited. This Z (i) is a characteristic that samples the input repel of data at equal intervals and generates levels corresponding to the discrete values in order. In order to take this into the modulation circuit 4, Z is stored in the RAM 330 according to the address controlled by the up counter 321 (corresponding to i above).
Record (i).

In the modulation circuit 4, as shown in FIG. 18C, the data 316 which takes the values of the multi-valued lapels Ll to L4 is stored in the RAM 330.
, And the Z (i) level corresponding to the levels Ll to L4 is input to the D / A converter 324 via the switching circuit 323. The output analog signal of the D / A converter 324 becomes the output of the modulation circuit 4 and is sent to the recording circuit 3 to drive the laser light source in the recording optical system 302. The above is the signal Z
The case where (i) is manufactured by hardware is shown.
As shown in FIG. 6, it can also be produced by software using a microcomputer (hereinafter referred to as CPU) 331. In this case, the test pattern generation circuit 309
In accordance with the timing from, the reflected light signal X (j) from the data processing circuit 313 is taken into the CPU 331, Z (i) is produced using this signal, and the modulation level corresponding to the multilevel rapel is set in the modulation circuit 4. Are set in the registers 332 to 334 corresponding to the respective multi-valued levels. As the characteristic of the modulation circuit, the inverse characteristic of the recording characteristic is required, and this can be calculated in the CPU 33l to obtain Z (i).

There is a possibility that multi-valued magnetic characteristics will change from medium to medium and from manufacturer to manufacturer. Therefore, for compatibility, the magnetic field strength and the reproduction signal characteristic are measured in advance, Y (i) is obtained, and the inverse characteristic can be calculated to obtain Z (i) corresponding to the multilevel. . It is also possible to write the above-mentioned recording characteristics in a predetermined area and read the same when the medium is mounted for use. In this case, the change in the recording characteristics is almost the change in the recording state due to the temperature characteristics, and fine correction is sufficient.

As the modulation circuit, registers 332 to 334 indicating the level of Z (i) corresponding to each multi-valued level are connected to the selector 335, and the data 316 having the multi-valued repel is input to the selector 335. Selected register value. As described above, after the modulation circuit 4 is optimally adjusted according to the recording characteristics of the recording medium, the data is sent from the data generation unit 5 and input to the modulation circuit 4 via the encoding circuit 306 so that the data is It is recorded in the data part of the sector.

Although the test pattern is used in the above-described embodiment, the data to be recorded in one sector is used instead of the test pattern, and the modulation circuit 4 is set during the data duplication period of one sector. A control signal may be generated. Alternatively, one round of the track may be used for this purpose.

Although the recording optical system and the reproducing optical system are separately shown in the embodiment, if the test pattern or the recording data is read after waiting for one rotation and the modulation circuit 4 is controlled, the recording The reproduction optical system may be the same.

[0093]

As described above, according to the present invention,
Since four-level signal recording can be performed by stacking two recording layers, higher-density signal recording can be realized with a simpler film stack structure. Further, in the magneto-optical recording medium of the present invention, each recording state is extremely stable against the fluctuation of the external magnetic field, and the magnetic characteristics of each recording layer, the laser beam intensity at the time of recording / reproducing, and the external magnetic field intensity are subtly matched. Since it is not necessary, a magneto-optical recording / reproducing system excellent in stability, mass productivity and practicality can be constructed.

Further, according to the present invention, since a plurality of threshold values can be generated with reference to the value of the level detection mark at which the reproduction signal recorded in advance is maximum and the value of the minimum reproduction signal area, it is possible to stably generate. It makes it possible to handle multi-valued recorded data and is effective in improving the bit density of data.

Further, according to the present invention, it is possible to stabilize the recording / reproducing level of multilevel recording in an optical disc using an erasable recording material in which the level of the reproducing signal becomes non-linear with respect to the recording condition. Higher density than the binary recording of.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a magneto-optical recording medium according to the present invention.

FIG. 2 is a main-portion cross-sectional view schematically showing a magneto-optical recording medium according to the first embodiment.

FIG. 3 is a main-portion cross-sectional view schematically showing a magneto-optical recording medium according to a second example.

FIG. 4 is a cross-sectional view of a main part schematically showing a magneto-optical recording medium according to a third example.

FIG. 5 is a cross-sectional view of a main part schematically showing a magneto-optical recording medium according to a fourth example.

FIG. 6 is an explanatory diagram showing a first example of a four-value recording / reproducing system.

FIG. 7 is an explanatory diagram showing a signal modulation method of an external magnetic field strength.

FIG. 8 is a block diagram showing a first example of an external magnetic field intensity signal modulation circuit.

FIG. 9 is a block diagram showing a second example of the external magnetic field strength signal modulation circuit.

FIG. 10 is a block diagram of a signal reproduction circuit.

FIG. 11 is a structural diagram of an optical disk for implementing the present invention.

FIG. 12 is a circuit diagram for reproducing a multi-valued information pit signal with a plurality of threshold values.

FIG. 13 is a time chart showing the circuit operation shown in FIG.

FIG. 14 is an explanatory diagram of an embodiment applied to a sample servo.

FIG. 15 is a block diagram of an embodiment of the present invention.

16 is a time chart showing waveforms of signals of respective parts in FIG.

FIG. 17 is a block configuration diagram for explaining the detailed operation of the modulation circuit.

FIG. 18 is an explanatory diagram for producing a signal Z (i) for controlling the modulation circuit by hardware.

FIG. 19 is a graph showing a temperature-coercive force characteristic of a recording layer laminated on a conventional magneto-optical recording medium.

FIG. 20 is an explanatory diagram showing a multilevel recording principle of a magneto-optical recording medium according to a conventional example.

FIG. 21 is a graph illustrating an external magnetic field characteristic of a recording layer having two recording states with respect to an external magnetic field.

FIG. 22 is a graph showing an external magnetic field characteristic of a recording layer having one recording state with respect to an external magnetic field.

FIG. 23 is an explanatory diagram showing a first example of the multi-value recording principle of the magneto-optical recording medium according to the present invention.

FIG. 24 is an explanatory diagram showing a second example of the multi-valued recording principle of the magneto-optical recording medium according to the present invention.

FIG. 25 is an explanatory diagram showing a third example of the multilevel recording principle of the magneto-optical recording medium according to the present invention.

FIG. 26 is an explanatory diagram of a case where the control of the modulation circuit is performed by software.

[Explanation of symbols]

1 ... Transparent substrate, 2 ... Preformat pattern, 3 ... First enhance film, 4 ... First recording layer, 4a ... Amorphous perpendicular magnetization film, 4b ... Auxiliary magnetic film, 5 ... Second enhance film, 6 ...
Second recording layer, 7 ... Third enhance film, 8 ... Reflective film, 9 ...
Protective film.

Claims (7)

[Claims] 1. An information recording medium having at least two recording layers laminated on each other, and at least one recording layer among these recording layers is 2 or more with respect to an applied external magnetic field. Of the magneto-optical recording film in which the recording state exists in the different magnetic field regions, and the other recording layer includes the magneto-optical film in which at least one recording state exists in the magnetic field region different from the one recording layer. By using a disc-shaped recording medium, irradiating a laser beam to a small light spot on the recording medium disc surface, and modulating the intensity and polarity of the externally applied magnetic field according to the information to be recorded,
A multilevel recording / reproducing method for an optical disc, which comprises forming a binary state or more. 2. A recording / reproducing method according to claim 1, wherein automatic focus control for keeping a distance between a light spot and a disc recording surface constant, and the light spot scanning an information track on the disc. Tracking control,
And a multilevel recording / reproducing method for an optical disc, wherein a mark serving as a reference for generating a clock signal for recording / reproducing information is provided on the disc in advance. 3. The recording / reproducing method according to claim 2, wherein automatic focus control, tracking control, and recording / reproducing clock generation reference marks are provided on the track at regular intervals, and the user data includes the control mark sequence. A multilevel recording / reproducing method for an optical disc, wherein recording is performed in an area different from the area. 4. A recording / reproducing method according to claim 3, wherein a pair of marks displaced left and right with respect to an information track are used as marks for generating a signal used for tracking control. Value recording / playback method. 5. The recording / reproducing method according to claim 1, wherein a recording state exists in two or more different magnetic field regions in the one recording layer and the other recording layer with respect to an applied external magnetic field. The recording layer is made of a perpendicular magnetic film and a magnetic material that is magnetically coupled to the perpendicular magnetic film and whose magnetization is more likely to rotate in the direction of an external magnetic field when irradiated with a laser beam for recording or erasing than the perpendicular magnetic film. A multilevel recording / reproducing method for an optical disc, comprising: an auxiliary magnetic film. 6. The recording / reproducing method according to claim 1, wherein an automatic focus control, a tracking control, and a clock generation mark are present as a reference signal for generating a threshold value for detecting a multilevel signal. A multilevel recording / reproducing method for an optical disc, characterized in that the reproduction signal level of an unrecorded area in the area to be used is used. 7. The recording / reproducing method according to claim 1, wherein an automatic focus control, a tracking control, and a clock generation mark are present as a reference signal for generating a threshold value for detecting a multilevel signal. A multilevel recording / reproducing method for an optical disc, characterized in that a mark serving as a level reference is provided in the area to be recorded.