JPH08287468A - Optical information reproducing method, device and optical information recording medium - Google Patents

Abstract

PURPOSE: To make it possible to record and reproduce multi-valved information of with good accuracy. CONSTITUTION: The information marks to be recorded are formed to a specified shape without changing their shapes and the recording positions thereof are deviated, from the grid points of information recording according to the information to be recorded. Further, the optical nature of the information marks to be recorded is changed according to the information to be recorded and the information is so recorded that the reproduced signals attain levels of the many values. An optical recording medium capable of recording the signal of the many valued levels by magnetic field modulation recording is used. The zero cross point 810 of the signal obtd. by difference or differentiation of the reproduced signal obtd. with respect to any of the information marks as the peak position of the signal, for example, 854', is detected and the mispositioning between the recording position and the grid point of the information recording is detected by using the information mark as the recording position. Further, the peak value of the reproduced signal 854' is quantized by plural quantization levels. The set of the mispositioning and the result of the quantization is decoded and the signal indicating the recorded information is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing method for recording / reproducing information on / from an optical recording medium using a laser beam, an apparatus for carrying out this method, and a medium used therefor.

[0002]

2. Description of the Related Art In order to increase the density of optical discs, there has been proposed a method of minutely changing an information mark to be recorded depending on multivalued information. For example, JP-A-6-7630
The specification of No. 3 proposes a method of independently changing the leading edge and the trailing edge of a long mark according to multi-valued information to be recorded. This method is applied to a read-only optical disc in which an information mark is formed as an uneven relief pattern. Further, the track pitch is separated by about the size of the light spot diameter as in the conventional optical disc, so that the crosstalk from the adjacent tracks is reduced.

Further, as a multi-value recording medium, Japanese Patent Laid-Open No. 64-64-
The medium disclosed in Japanese Patent No. 32442 or Japanese Patent Laid-Open No. 3-5932 is known. In this, the magneto-optical recording films are laminated in multiple layers, each layer is magnetically independent of each other, and the multi-valued level is the sum of signal levels determined by each layer. Therefore, for example, in order to represent four values, four recording films are laminated.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the prior art described in Japanese Patent Publication No. 03, it is necessary to record an information mark that slightly changes according to multi-valued information, and it is difficult to accurately record or reproduce such an information mark that slightly changes. Have.

That is, as described in the above-mentioned prior art, in the conventional method, the optical disk has given information to the mark shape and its position. For example, taking an oval shape as an example, the parameters that determine this shape are the curvature of the leading edge,
The width, the curvature and width of the trailing edge, the positions of the leading edge and the trailing edge, and the distance from the leading edge to the trailing edge, etc. On the contrary, control becomes difficult.

In particular, the uneven relief pattern is difficult to accurately control the shape and position because the above-mentioned parameters delicately change in the course of a plurality of processes including master cutting, stamping, and injection.
In order to detect slight fluctuations in the edge position, a light spot having a two-dimensional distribution scans the mark having the shape parameter to process a waveform converted into a one-dimensional electric signal. Therefore, even if the above parameters other than the edge position variation fluctuate, they are erroneously regarded as position variation. Therefore, it is difficult to stably detect information by the conventional method of slightly moving the edge of the long mark.

Further, in an optical disk device for recording and reproducing information, fluctuations (power fluctuations, peculiar to the device) during the recording process.
Defocus, track shift, uneven recording sensitivity of the medium, etc. occur and the recording conditions change, so that the shape of the recording mark is further affected and fluctuates. Therefore, the method of slightly moving the edge of the long mark cannot be applied to the optical disc device for recording / reproducing information.

Further, the multilevel recording medium proposed in the above-mentioned JP-A-64-32442 or JP-A-3-5932 is provided with a number of recording layers independently corresponding to each multilevel value. It was intended to obtain a multi-valued level by controlling the recording state of. However, this is a structure in which four layers are stacked to realize four values, which is difficult to realize.

For example, an object of the present invention is to provide an optical information reproducing method, an apparatus and a recording medium therefor capable of accurately reproducing information marks representing multi-valued information which can be recorded with high accuracy.

Still another object of the present invention is to provide an optical information recording / reproducing method capable of recording / reproducing multi-valued information by using a recording medium having a small number of recording layers, and an apparatus and a recording medium therefor. That is.

[0011]

In order to reproduce information marks representing multi-valued information with high accuracy, the present invention records circular information marks capable of minimizing the mark shape parameter of an optical disc. As a result, one type of information mark shape is recorded. The center position of this mark is slightly changed depending on the information to be recorded. When the information mark recorded in this way is reproduced, the peak position of the reproduction signal is detected, the detected information is decoded, and the information recorded in the information mark is reproduced.

More preferably, a recording medium having a plurality of optical characteristics such that the reproduction signal level becomes multi-valued is used, and the recording position of the information mark written therein is changed according to the information to be recorded, The optical characteristics of the information mark are changed according to the information to be recorded. When reproducing the information mark recorded in this way, the level of this reproduction signal and the peak position of this reproduction signal are detected, the detected information is decoded, and the information recorded in the information mark is detected. To play.

Further, in order to record multi-valued information using a recording medium having a smaller number of recording layers, magnetically coupled multi-layered recording films are used, and depending on the multi-valued information to be recorded, By changing the magnetic field applied from the outside, the irradiation light power, and the irradiation timing, the magnetic coupling relationship and the recording position according to the multivalued information to be recorded are realized.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The optical information recording / reproducing method and apparatus according to the present invention and the optical information recording medium used for the same will be described below in more detail with reference to some embodiments shown in the drawings. To do. In the following, the same reference numbers represent the same or similar items. Further, in the second and subsequent embodiments, differences from the first embodiment will be mainly described.

<First Embodiment of the Invention> In the conventional recording method, information is represented by whether or not an information mark is recorded at an information recording grid point. In the present embodiment, in order to increase the information recording density, information marks of a constant shape are recorded at each information recording grid point, and the position where the information mark is recorded is shifted from the information recording grid point according to the information to be recorded. . That is, the recording phase of the information mark is changed to a multivalue according to the information to be recorded. Therefore, the present embodiment realizes multi-valued phase recording as one form of multi-valued recording.

(1) Recording of Information Marks A specific mark arrangement is shown in FIG. Also in this embodiment, the information recording grid points form a face-centered rectangular grid as in Reference Example 1 described later. The relationship between the value of the information to be recorded and the recording position of the information mark is defined as shown in FIG. 14 with the spot scanning direction being positive. FIG. 15A illustrates a plurality of information marks recorded in one sector of the i-th track. Although a plurality of information marks are superposed on the same grid point in the figure, only one information mark is actually recorded at one grid point. In the figure, the wobble mark shown in FIG. 2 which is worthy of the head of each sector is not shown for simplification. The learning mark shown in FIG. 2 is not used in this embodiment. As an optical recording medium,
Similar to Reference Example 1 described later, a magneto-optical medium is used and laser light having a constant intensity is irradiated to record an information mark. Therefore, the shape of the recorded information mark is circular. In this circle, the only parameter that determines the shape is the radius, so
It is easy to make a constant shape, and it is easy to control the center position. 654, 655, 657, 658
Are −2Δ and − for the p + 5th grid point on the i-th track (this is assumed to be an information recording grid point).
The marks are recorded at positions shifted by Δ, + Δ, and + 2Δ. Reference numeral 600 is a publicly known reference recording mark for determining the read timing of the recorded information mark.

Specifically, in this embodiment, the recording circuit shown in FIG. 16 is used. The pre-pit detection circuit 716 is provided in the optical head (not shown) when the optical head scans a plurality of pre-pits (not shown) known per se which are created in advance at a constant repetition period at the head of each track on the disk surface. The total light amount signal representing the total light amount detected by the total light amount detector (not shown) is used to generate a reference clock signal having a cycle and a phase determined by those prepits. The reference clock signal is a clock signal synchronized with the scanning timing of each grid point (each of the information recording grid point and the grid point where information is not recorded). The recording timing generation circuit 717 produces a recording timing clock that coincides with the scanning timing of the information recording grid point from this reference clock signal. The phase of this recording timing clock differs depending on whether the scanning track is an even-numbered track or an odd-numbered track, as in Reference Example 1 described later. Encoding circuit 70
Reference numeral 9 divides the user data into 2 bits, converts each 2 bits into positional deviation information according to FIG. 14, and supplies each information to the phase shift circuit 711. The phase shift circuit 711 modulates the phase of the recording timing clock output from the recording timing generation circuit 717 according to this positional deviation information. The optical pulse generation circuit 714 intensity-modulates the laser light in synchronization with this phase-modulated clock. FIG.
6, the circuit for writing the reference recording mark 600 shown in FIG. 15 is omitted for simplification.

(2) Reproduction of Information Marks FIG. 15B shows information marks 654 and 6 of FIG. 15A.
Signal outputs when 55, 657, and 658 are reproduced are overlapped and shown. The reproduced waveforms corresponding to these information marks have a timing 60 when the center of the spot passes through the grid point 608.
The peaks are unimodal waveforms 654 ′, 655 ′, 657 ′, and 658 ′ that are deviated by Δ or 2Δ from 9 respectively. There are various methods for detecting the amount of deviation from this waveform, but considering that the peak position of each unimodal reproduced waveform matches the center position of the corresponding information mark, these reproduced waveforms 654 The method of utilizing the difference (or differential) signal from'to 658 'is simple. The difference output of these reproduction signals has a waveform as shown in FIG. The zero cross points 610 to 614 of the respective waveforms represent the time when the center position of the corresponding information mark is detected. Therefore, by measuring the time difference between these zero-cross points and the grid point passage timing 609, the deviation amount of the recording position of the corresponding information mark from the information recording grid point can be obtained.

Specifically, the reproducing circuit shown in FIG. 17 is used. Like the pre-pit detection circuit 716 of FIG. 16, the pre-pit detection circuit 708 utilizes the total light amount signal from the optical head (not shown) when the optical head scans a plurality of pre-pits (not shown). A reference clock signal indicating the scanning timing of each grid point (however, each of the information recording grid point and the grid point where no information is recorded) is output in synchronization with the prepits. Reference numeral 600 in FIG. 15 is a reference recording mark known per se for determining the read timing of the recorded information mark. The reference recording mark detection circuit 706 of FIG. 17 is a circuit for detecting this mark 600 of each sector. The detection timing generation circuit 717 is
From the reference clock output from the pre-pit detection circuit 708, a detection timing clock indicating the scanning timing of the information recording grid point is generated. At this time, the phase of this detection timing clock is made to coincide with the detection timing of the reference recording mark by the reference recording mark detection circuit 706. That is, the deviation between the reference clock signal corresponding to each lattice point generated by the pre-pit detection circuit 708 and the detection timing of the center of the reference recording mark 600 is detected, and the phase of the detection timing clock is shifted by the deviation. .

Also in this embodiment in which information is recorded at the recording position of the information mark, the reproduction output fluctuates due to various fluctuation factors. In the above method of obtaining the zero cross point, it is necessary to accurately grasp the timing when the light spot passes through the information recording grid point, but this slightly changes depending on the shape of the spot, the deformation of the substrate and the like. Therefore, the reference recording mark 600 is recorded in advance at the information recording grid points in the data recording area, then the information mark is recorded, and the reference clock and the reference recording mark 600 generated from a plurality of prepits at the time of reproducing the information mark are detected. The deviation from the timing is detected to correct the phase of the detection timing clock. Therefore,
When recording, the recording marks are linear velocity, recording power, magnetic field strength,
Even if the shift occurs due to the medium sensitivity or the like, the corrected detection timing signal can be used to create the timing indicating the scanning of the information recording grid point. Therefore, the center position of the information mark can be accurately detected. Incidentally, such correction of the detection timing is described in detail in Japanese Patent Application Laid-Open No. 64-1167 or corresponding US Patent Application No. 07 / 169,595 and Japanese Patent Application Laid-Open No. 1-155535. The techniques described therein are incorporated herein by reference.

The difference circuit 705 is an optical head (not shown).
The differential signal (see FIG. 15C) of the information reproduction signal (magneto-optical signal) output by the reproduction photodetector (not shown) is generated. This difference signal becomes a signal that becomes zero at the center of the information mark being scanned. The zero-cross detection circuit 704 detects a zero-cross point of the difference signal and generates a signal indicating its timing. The time measuring circuit 703 measures the time difference between this timing signal generated by the zero cross detection circuit 704 and the detection timing signal generated by the detection timing generation circuit 707. This time difference represents the deviation of the recording position of the scanned information mark. In the decoding circuit 702,
The position of the information mark scanned according to FIG. 14 is decoded based on this position shift.

In FIG. 14, four positional displacement amounts are associated with 2-bit information, but this association can be variously modified. Examine and examine specific numerical values. The relationship between the mark pitch Mp and the remaining equalization is already shown in FIG. If the adjacent marks cause the maximum displacement with respect to each other and the distance between the information marks when the marks are closest to each other is about 60% or more of the spot diameter Ws, the influence of the crosstalk from the adjacent tracks is substantially eliminated in this embodiment as well. It can be reduced to the extent that there is no problem. That is, the mark pitch Mp ′ in the present embodiment is calculated using FIG.
The following conditions may be satisfied using p.

Mp ′> Mp + 2nΔ For example, from the wavelength of FIG. 4 and the numerical aperture of the objective lens, the spot diameter is about 1.4 μm and the mark pitch Mp is 0.88 μm.
Therefore, if Δ is set to 0.1 μm, Mp ′ is set to 1.08 μm or more, the equalization residual of −20 dB or less can be left, and high-density recording / reproducing can be realized. If n displacements satisfying this condition are used, lo
When g is used, log (2n) -bit information can be given per one grid point. Here, log is a base 2 logarithm. However, as can be seen from the circuit of FIG. 17, the present embodiment does not use the learning mark, the equalization coefficient learning circuit, and the two-dimensional equalization circuit used in Reference Example 1 described later. Due to crosstalk from adjacent tracks,
The track interval and the mark pitch are made large enough to ignore the detection error of the peak position of the reproduction signal of the information mark.

<Modification of Embodiment 1 of the Invention> (1) As another detection method of the recording position of the information mark,
There is also a method of detecting the deviation of the center position of the corresponding information mark from the information recording grid point by sample-holding the difference or differential value of the reproduction signal at the timing of passing the information recording grid point and using the absolute value and the sign. is there.

(2) In the method for detecting the positional deviation of the information mark by using the difference or differential value of the reproduction signal obtained at the timing when the light spot passes through the information recording grid point, the reference recording mark is used. 600 can also be used. That is, if the size of the recorded information mark fluctuates during recording, the absolute value of the difference or differential output value of the reproduction signal fluctuates. In order to standardize this value, first, the difference between the reproduction signals at the reference recording mark 600 or the positive and negative peak values of the differential output are sample-held, and the gain of the reproduction circuit is controlled so that these values become constant values. To do. This can be realized by a normal auto gain control circuit. By doing so, even if the size of the information mark varies, the difference between the reproduction signals at the timing of passing the information recording grid point or the value that can be obtained by the differential output does not depend on the size of the information mark The value depends only on. Therefore, the position shift of the information mark can be detected by determining the level of the information mark at the timing of passing the information recording grid point.

<Second Embodiment of the Invention> In the second embodiment, in order to further improve the density, the first embodiment is to shift the recording position of the information mark from the information recording grid point according to the information to be recorded. In addition to performing the multi-valued phase recording used, the optical property of the information mark to be recorded is changed according to the information to be recorded, and the multi-valued level signal is generated so that the reproduction signal has a multi-valued level. Record. For this reason, a multi-level recordable medium is used as the optical recording medium, and the optical modulation recording that has been described so far is not used as the recording method.
Magnetic field modulation recording is used.

As a result of using this recording method, the recorded information mark becomes an arrow blade type as shown in FIG. 18 (a). In the present embodiment, the recorded information mark has four multi-valued levels, and each level is "0", "1", "2", "3" in order from the smallest reproduction signal level.
And Information marks 854, 855, 856, 857,
Reference numeral 858 denotes five information marks, each of which has a level "3" and which can be recorded with different positional deviations with respect to the same grid point. The information mark group 881 has a level “1” and shows five information marks that can be recorded with different positional deviations with respect to the same lattice point. The information mark group 882 has a level “2” and the same. 5 shows five information marks that can be recorded with different displacements with respect to the grid points. Reference numeral 880 indicates four information marks which have different levels and can be recorded at positions where there is no positional deviation with respect to the same grid point. Although only one mark can be recorded at the same grid point, recordable marks are shown superimposed on the same grid point for simplification. FIG. 19 shows the correspondence between the information to be recorded and the information mark to be recorded. That is, the user data is divided into a plurality of 4-bit parts,
For the combination of the front 2 bits and the rear 2 bits of each 4-bit portion, the positional deviation between the position where the information mark is recorded and the information recording grid point, and the level of the signal recorded at the information mark to be recorded are determined. The eye pattern showing the change of the information signal recorded by this recording method depending on the position of the reproduction signal is as shown in FIG. 20, and 16 black dots represent the peak value of the reproduction signal that can be taken by the 4-bit user data. Show.

(1) Magneto-Optical Recording Medium Next, the characteristics of the magneto-optical recording medium capable of recording multilevel signals will be described. FIG. 21A illustrates a schematic structure of such a recording medium. At least two recording layers 14 and 1 laminated on the transparent substrate 10
8, the first recording layer 14 is in a recording state in at least one or more magnetic field regions of the applied external magnetic field, and the second recording layer 18 is two or more different magnetic field regions different from the magnetic field regions. The magneto-optical recording film of the second recording film is different from that of the first recording layer, and the magneto-optical recording film of the second recording film is different from that of the first recording layer. As such a medium, Japanese Patent Application No. 6-96690 and Japanese Patent Application No. 6-1436 previously filed by one of the present applicants.
There is one described in No. 34.

Light enters from the substrate 10 side, passes through the films 16 and 20 and the recording layers 14 and 18 from the first enhance film 12, is reflected by the reflective film 22, and returns to the substrate 10 again. During this time, the first and second recording layers undergo a change in magnetic characteristics. These first enhancing film 12, second enhancing film 16, and third enhancing film 20 are provided between the substrate 10 and the first recording layer 14, the first and second recording layers 14, respectively.
18 and between the second recording layer 18 and the reflective film 22 to prevent chemical interference between the layers. For example, components from each layer are prevented from diffusing and unnecessary components from other layers are not mixed. Therefore, a chemically stable material is used. Furthermore, these enhance films are used for the substrate 1.
It is necessary to have an optical transmission characteristic that allows light from 0 to pass therethrough and also allows light returning from the reflective layer 22 to pass therethrough. further,
By controlling the film thickness of these enhance films, the amount of light reflected from the medium having the multilayer structure is increased (enhanced). As such an enhancement layer, for example, Si
O2, SiN, etc. are used.

The second recording layer 18 is magnetically coupled to the perpendicularly magnetized film and the perpendicularly magnetized film is magnetized in the direction of the external magnetic field when irradiated with a laser beam for recording or erasing than the perpendicularly magnetized film. It is composed of an auxiliary magnetic film made of a magnetic material that easily rotates. In this case, this 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. This auxiliary magnetic film may be composed of 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. When such a magneto-optical recording medium is used, it corresponds to each recording state of each recording layer.
By applying different steps of the external magnetic field, four-value recording of signals becomes possible.

In a specific example, the substrate 10 is a transparent substrate made of glass or polycarbonate. The first enhancement film 12 is made of a SiN film having a thickness of 100 nm.
The recording layer is 15 nm thick Tb19Fe62Co10Cr.
It consists of 9 films. The second enhancement film 16 is a 10 nm thick SiN film. The second recording layer 18 is a 20 nm-thick Tb32Fe56 layered on the second enhancement film 16.
It is composed of a perpendicular magnetization film made of Co12 and an auxiliary magnetic film made of Pt80Co20 having a thickness of 5 nm, which is further stacked thereon. The third enhancement film 20 is a 10 nm thick SiN film.
The reflection film 22 is made of an Al film having a thickness of 70 nm. The protective film 24 is made of UV resin.

In order to write multi-valued information on such a magneto-optical recording medium, an optical head (not shown) and a magnetic head (not shown) are relatively moved with respect to the magneto-optical recording medium. While driving and irradiating the laser beam from the optical head along the recording track of the magneto-optical recording medium, the magnetic field intensity was modulated in multiple steps according to the information to be recorded in the portion irradiated with the laser beam. An external magnetic field is applied from the magnetic head. As a result, it is possible to record an information mark having a multi-valued level of four or more values on the first and second recording layers 14 and 18. In this case, the laser beam may be continuously irradiated with a laser beam having a constant intensity, or may be irradiated periodically or in a pulsed manner.

The optical head and the magnetic head are driven relative to the magneto-optical recording medium, and an external magnetic field is applied from the magnetic head to the magneto-optical recording medium, while recording tracks 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.

The principle of multilevel recording on such a recording medium will be described in detail below. A second recording layer 18 formed by laminating a perpendicular magnetization film 18A and a predetermined auxiliary magnetic film 18B.
Is due to the action of the auxiliary magnetic layer 18B.
Since the sublattice magnetic moment of the transition metal therein is easily reversed in the exchange coupling magnetic field direction, the magnetization direction of the entire recording layer 18 can be oriented in the external magnetic field direction or the opposite direction. On the other hand, the first recording layer 1 without the auxiliary magnetic layer
1 recording state exists in a magnetic field region different from 8
In the recording layer 14, the magnetization direction of the entire recording layer 14 easily reverses to the direction of the external magnetic field when the temperature is raised.

Therefore, for example, as shown in FIG. 21A, 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. 14
And a second recording layer 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, and a downward external magnetic field is applied outside the recording direction. A signal is recorded by using the magnetic field and the upward external magnetic field as the external magnetic field in the erasing direction.

The overall magnetic moment of each recording layer is determined by the composition of the magnetic moment of the rare earth element and the magnetic moment of the transition metal atom that compose the recording layer. In FIG. 21B, the magnetic moment of each atom with respect to each external magnetic field of the second recording layer 18 is shown by the white arrow and the black arrow in the upper part. In the lower part, the magnetic moment of each atom with respect to each external magnetic field of the first recording layer 14 is shown using the same arrow.

FIG. 22 shows the result of recording / reproducing on the second recording layer. The laser is irradiated at a constant cycle in accordance with the clock, and the recording magnetic field is changed between 0 and in synchronization with this.
A reproduced signal component corresponding to the repetition frequency of the recording magnetic field was detected and shown together with noise. Therefore, even in one recording layer, a recording state can be created in two different magnetic field regions of the external magnetic field by combining the magnetic moment of the rare earth element and the magnetic moment of the transition metal. Furthermore, when the first recording layer 14 is combined with such a second recording layer, these combinations operate as follows.

(I) By applying in the erasing direction an external magnetic field H0 (the external magnetic field of the region (1) shown in FIG. 22) having such a magnitude that the entire magnetization direction of the first recording layer 14 is oriented in the erasing direction. The sublattice magnetic moment of the transition metal atoms of the first recording layer 14 can be directed in the recording direction, and the sublattice magnetic moment of the transition metal atoms of the second recording layer 18 can be directed in the erasing direction.

(Ii) by applying in the erasing direction an external magnetic field H1 (the external magnetic field of the area (2) shown in FIG. 22) having such a magnitude that the entire magnetization direction of the first recording layer 14 is oriented in the recording direction. , The sublattice magnetic moments of the transition metal atoms of the first recording layer 14 and the second recording layer 18 can both be directed in the erasing direction.

(Iii) The external magnetic field H2 (FIG. 22) having such a magnitude that the entire magnetization direction of the first recording layer 14 is oriented in the erasing direction.
By applying the external magnetic field of the region (3) shown in (3) in the recording direction, both the sublattice magnetic moments of the transition metal atoms of the first recording layer 14 and the second recording layer 18 can be directed in the recording direction.

(Iv) By applying in the recording direction an external magnetic field H3 (the external magnetic field of the region (4) shown in FIG. 22) having a magnitude such that the entire magnetization direction of the first recording layer 14 is oriented in the recording direction. The sublattice magnetic moment of the transition metal atoms of the first recording layer 14 can be directed in the erasing direction, and the sublattice magnetic moment of the transition metal atoms of the second recording layer 18 can be directed 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 determined by the first recording layer 14 and the second recording layer 14.
Since it is proportional to the sum of the sublattice magnetic moments of the respective transition metal atoms of the recording layer 18, as shown in FIG.
From the recording track to which the external magnetic fields of 1, H2, and H3 are sequentially applied, outputs having four different values depending on the magnitude of the external magnetic field are obtained. FIG. 21C schematically shows the relationship between the magnitude of the external magnetic field and the relative signal output. 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",
By arranging the recording state by the external magnetic field H3 at "2" and the recording state by the external magnetic field H2 at "3", a four-valued signal can be recorded.

(2) Recording of Multi-Valued Information Next, a method of multi-valued recording of signals using the magneto-optical recording medium in the present embodiment will be described. In the present embodiment, in order to record a multi-level signal using the above-mentioned magneto-optical recording medium, an external magnetic field of 4 is applied depending on the information to be recorded.
As in the first embodiment, the multi-level phase recording is performed by modulating the signal in stages and recording the multi-level signal and changing the laser beam irradiation timing according to the information to be recorded.

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 (not shown). 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.

In this embodiment, the reference recording mark 600 used in the first embodiment (FIG. 15) is used on this recording medium.
Similarly, the reference recording mark 800 for indicating the position of the information recording grid point is recorded in advance. See FIG. Although not shown in FIG. 18, a plurality of pre-pits (not shown) having a constant interval are pre-recorded on the head portion of each track on this recording medium, as in the first embodiment. At the beginning of each sector of the track,
It is assumed that wobbling marks 151 to 153 shown in FIG. 2 used in Reference Example 1 described later are recorded in advance. Furthermore, in the present embodiment, unlike the first embodiment, the learning mark 15 used in Reference Example 1 described later.
4, 155 are also recorded in advance in the equalization coefficient learning area of each sector. Also in this embodiment, the information recording grid points form a face-centered rectangular grid as in Reference Example 1 described later or Embodiment 1 described above.

In the following, the user data recording operation will be described in detail with reference to circuit diagrams 24 and 25 and time charts 26 and 27. The pre-pit detection circuit 716 is provided at the head of the track on which information on the disc surface is to be recorded, using the total light amount signal provided from the total light amount detector (not shown) of the optical head (not shown). A plurality of pre-pits (not shown) having a constant interval are detected, and a reference clock 900 having a period and a phase synchronized with these is generated.
The recording timing generation circuit 717 uses the reference clock 900
A clock 934 which is obtained by dividing the frequency by two, and a clock 910 that indicates the scanning timing of each of the plurality of information recording grid points, and an information that is not recorded between two adjacent information recording grid points. A clock 932 indicating the scanning timing of each grid point is generated.

The multi-level encoding circuit 709 uses the reference clock 90.
It operates in synchronization with 0, and divides the time-series user data signal 901 to be recorded into a plurality of 4-bit parts, and each 4-bit part is divided into data consisting of two bits before and two bits after. Separated from them, magnetic field control 2-bit data 930 and position control 2-bit data 920 for controlling the value of the magnetic field and the amount of positional deviation are generated in accordance with the relationship shown in FIG. 710 and the phase shift circuit 711. In this embodiment, the preceding 2 bits "00" of each 4-bit portion of the user data,
“10” and “11” are multi-levels “1”,
It corresponds to "3" and "2", respectively. When the previous 2 bits have these values, the 2 bits after each 4-bit portion of the user data "00", "01", "10",
“11” is the position deviation “−2Δ”, “−Δ”,
They correspond to “+ Δ” and “+ 2Δ”, respectively. However, the preceding 2 bits "01" correspond to the positional deviation "0", and in this case, the 2 bits after each 4 bit part of the user data "00", "01", "10", "11". Respectively correspond to multi-valued levels “1”, “0”, “3”, “2”. Therefore, the multi-level encoding circuit 709 depends on the value of the previous 2 bits when the previous 2 bits of each 4-bit portion of the user data are not "01", and FIG.
Output 2-bit data for magnetic field control representing a multi-valued level, depending on 2 bits after the 4-bit portion, and
According to FIG. 19, position control 2-bit data 920 representing the amount of positional deviation is output. However, the previous 2 bits are "0"
In the case of 1 ", the magnetic field control 2-bit data 930 representing the multilevel is generated according to FIG. 19 depending on the value of the 2-bit after the 4-bit portion, and the position shift representing" 0 "is used for the position control. The 2-bit data 920 is output.

In the multi-level generation circuit 710, as shown in FIG.
Magnetic field control 2-bit data 93 for each 4-bit portion of user data, which is given from the multi-level encoding circuit 709.
The first bit of 0 (hereinafter referred to as an even bit) 903 and the next bit of magnetic field control 2-bit data 930 (hereinafter referred to as an odd bit) 902
Divided into Specifically, this circuit 950 uses the clock 9
34 inverted signal and magnetic field control 2-bit data signal 930
It has a circuit for taking the logical product of the above and creating the odd-numbered bit signal 902. Further, it has a circuit for taking the logical product of the clock 934 and the magnetic field control 2-bit data 930 to generate the even-bit signal 903. Timing shift circuit 951
Generates a signal 904 obtained by shifting the even-bit signal 903 so as to be delayed by one cycle of the clock 934.
The pulse length doubling circuits 952 and 954 extend the pulse lengths of the shifted signal 904 and the odd-numbered bit signal 902 by one cycle of the signal 934 to generate signals 905 and 906, respectively. Inverter circuit 9
56 produces an inverted signal 931 of the signal 906.

Then, the amplifiers 953 and 957 generate signals having amplitudes obtained by multiplying the signals 905 and 931 by G ′ and G, respectively. Here, the relationship between G'and G is G '=
-2 × G. The two signals generated by these amplifiers are added by an adder 958 to generate a multilevel voltage. After that, this voltage is converted into a voltage / current by a magnetic head drive circuit 713, so that a magnetic head (not shown)
The external magnetic field shown in FIG. 27 is generated and applied to the recording medium. In this embodiment, a magnetized area for the level “0” is always generated at an intermediate grid point located between a pair of information recording grid points. To this end, the adder 958 shifts the output 916 of the adder 958 so as to produce the above-mentioned magnetic field H1 corresponding to the reproduction level "0" at the intermediate grid point where no information mark is recorded. The offset amount V0 is further added. Output 9 of this adder 958
16 is four levels corresponding to 2-bit data for magnetic field control generated from each 4-bit portion of user data.
It will have one of 0 "," 1 "," 2 "or" 3 ".

In FIG. 24, the switching circuit 712 is
The signal 916 and the offset V0 are selected so that the signal 916 is selected when the clock 934 is low and the offset V0 is selected when the clock 934 is high.
Select in synchronism with. The output 917 of the switching circuit 712 is input to the magnetic head drive circuit 713, and the output of this circuit causes the magnetic head (not shown) to generate an external magnetic field. As a result, the adder 9 is added to the information recording grid point.
The magnetic field H for generating the magnetization state corresponding to the level "0", "1", "2" or "3" of the output 916 of 58.
1, H0, H3, or H4 is generated, and a magnetic field H1 for generating a magnetization state corresponding to the reproduction level "0" is generated at a grid point where an information mark is not recorded.

On the other hand, in FIG. 24, the phase shift circuit 7
Reference numeral 11 indicates the phase of the clock 910 indicating the scanning timing of the information recording grid point according to the position control 2-bit data 920 generated from each 4-bit portion in the user data 901 generated by the multi-level encoding circuit 709. shift. The optical pulse generation circuit 714 receives the shifted clock signal via the logical sum circuit 730, and controls the irradiation timing of the laser light in synchronization with the shifted clock. In this way, after the external magnetic field is switched to the predetermined value, the optical head irradiates the optical pulse with the timing shown by the signal 933 in FIG. 27, and the portion of each recording layer of the recording medium irradiated with the optical pulse is magnetized by the external magnetic field. It is heated to a temperature at which it can be reversed. As a result, the magnetization domain shown in FIG. 27 is formed in the portion of each recording layer irradiated with the optical pulse, depending on the magnitude of the external magnetic field. In this way, the multi-value level generation circuit 710 and the magnetic head drive circuit 7
According to the multi-valued magnetic field generated by the action of 13 and the multi-valued phase generated by the phase shift generating circuit 711, the magnetization state depending on each 4-bit part of the user data is formed at the information recording lattice point. With respect to the grid point that does not record information, the optical pulse generation circuit 714 generates an optical pulse at the timing of scanning this grid point in response to the clock 932 provided from the recording timing generation circuit 717 via the logical sum circuit 730. To do. Therefore, the switching circuit 7
12 and the constant magnetic field H1 generated by the operation of the magnetic head drive circuit 713 and this optical pulse generate a constant magnetization state at the lattice point where information is not recorded.

(3) Reproduction of Information Mark To reproduce the information mark thus recorded, for example,
The reproducing circuit of FIG. 28 is used. Pre-pit detection circuit 70
8 detects a plurality of pre-pits formed in advance at the head portion of the track being reproduced by using a total light amount signal from a total light amount detector (not shown) in an optical head (not shown), A reference clock having a cycle and a phase synchronized with these is generated. The reference recording mark detection circuit 706 performs reference recording from a reproduction signal (magneto-optical signal) output from a reproduction photodetector (not shown) in the optical head while the optical head is scanning each sector. Mark 800 (Fig. 18)
Is detected and a signal indicating the timing at which the center point of this information mark is scanned is output.

The detection timing generation circuit 707 uses the reference clock generated by the pre-pit detection circuit 708 to detect the reference recording mark 80 detected by the reference recording mark detection circuit.
A phase is shifted according to the scanning timing of 0, and a signal 707A indicating the timing of scanning each information recording grid point in the data recording area from the shifted reference clock and a pair of adjacent information recordings in the data recording area. A clock 707B indicating the scanning timing of a grid point that does not record information located in the middle of the grid point is generated.

The difference circuit 705 generates a difference signal of the magneto-optical signal detected by the optical head, the zero cross detection circuit 704 detects the timing of the zero cross of this difference signal, and outputs the zero cross timing signal 704A. . The timing time measuring circuit 703 detects and detects a time difference between the zero cross timing indicated by the zero cross timing signal 704A and the scanning timing of the information recording grid point given from the detection timing generating circuit 707. The digital data representing the positional deviation corresponding to the temporal deviation is output.

In FIG. 18B, 854 ',
855 ', 856', 857 ', 858' indicate the waveforms of the magneto-optical signals detected for the information marks 854, 855, 856, 857, 858. In FIG. 18C, 810, 811, 813, and 814 are reproduction signals 85.
4 ', 855', 857 ', 858' show the zero crossing points of the differential signal. FIG. 27 also shows a reproduced waveform for a magnetic domain shape generated for specific user data. The operation of the circuit described above is the same as that of the first embodiment.
It is basically the same as the circuit of the same name in.

The slice level generation circuit 720 receives the reference recording mark 800 from the reference recording mark detection circuit 706.
27 is shown as a slice level for taking in the peak value of the magneto-optical signal with respect to the reference recording mark 800 in response to the timing signal indicating the detection of The slice levels L1, L2 and L3 are determined. In order to determine these slice levels, a reference recording mark for giving a maximum reproduction signal is recorded as the reference recording mark 800, and another reference recording mark for giving a minimum reproduction signal is provided after the mark. And the slice level generation circuit 720 causes the reference recording mark detection circuit 7
06, in response to the timing signal indicating that the reference recording mark 800 has been detected, the peaks of the reproduction signal for the two reference recording marks are fetched, and the slice level 1, 2,
Determine 3. The other reference recording marks described here are not shown in FIG. 18 for simplification.

The sample hold circuit 700 has an intermediate grid point between the zero cross timing signal 704A given from the zero cross detection circuit 704 via the OR circuit 734 and the information recording grid point given from the detection timing generation circuit 707. Signal 70 indicating the scanning timing of
In response to each of 7B, the magneto-optical signal is sampled and held at the timing indicated by each timing signal.
The two-dimensional equalization circuit 732 is substantially the same as the circuit of the same name used in Reference Example 1 described later, and is for the reproduction signal (magneto-optical signal) for each information recording grid point of the track being scanned. Crosstalk components from two adjacent tracks are removed by using a pair of reproduction signals for a pair of intermediate grid points located immediately before and immediately after the information recording grid point, and after removing crosstalk. The inter-symbol interference component remaining in the reproduction signal of the reproduction signal for at least one information recording grid point located before the information recording grid point and at least one information recording grid point located after the information recording grid point And the reproduction signal for

The equalization coefficient learning circuit 731 is a circuit having substantially the same function as the circuit of the same name used in Reference Example 1 described later, and is used to calculate the equalization coefficient used in the two-dimensional equalization circuit 732. , Is calculated using a reproduction signal for a learning mark (not shown) recorded in the sector being scanned by the optical head. In the present embodiment, the learning mark for learning the equalization coefficient is also recorded by magnetic field modulation and has an arrow blade shape. However, even if the learning mark having such a shape is used, the learning of the equalization coefficient can be performed in exactly the same manner as in Reference Example 1 described later. However, it is desirable to match the level of information recorded as the learning mark at this time with one of the four levels of the information mark recorded in the data area. In particular, it is desirable that this one level be the maximum level. In the present embodiment, unlike Reference Example 1 described later, the learning mark is recorded at a position slightly displaced from the information recording grid point. This shift amount is made to coincide with one of the four possible positional shifts of the information marks recorded in the data recording area, which are given in FIG. For example, this shift amount is matched with + Δ or −Δ.

The timing for reading the learning mark having such a positional deviation is the zero cross detection circuit 704.
The equalization coefficient learning circuit 731 is instructed by the zero-cross timing signal 704A given by The equalization coefficient learning circuit 731 needs to use the reproduction signals at the intermediate points located before and after the learning mark. The timing of reading the reproduced signal at this intermediate point is the clock signal 707 given by the detection timing generation circuit 707.
Instructed by B. The deviation amount of the information mark recorded in the data recording area from the nearest information recording grid point is shown in FIG.
As shown in FIG. 3, it is one of + 2Δ, + Δ, −Δ, and −2Δ, and the positional deviation between the position where the learning mark is recorded and the nearest information recording grid point is different. But
Since the reference deviation amount Δ itself is sufficiently smaller than the grid point interval and the track interval, the equalization coefficient learned as described above is recorded in the data area in the information marks having various positional deviations. On the other hand, if you use it as it is,
The crosstalk component can be removed as in Reference Example 1 described later.

Such equalization coefficient learning circuits 731, 2
Due to the function of the dimensional equalization circuit 732, the two-dimensional equalization circuit 732 outputs a peak value obtained by removing the crosstalk component from a pair of adjacent tracks with respect to the peak value of the reproduction signal for each information recording grid point. Then, the quantization circuit 701 outputs the output peak value as
Quantization is performed by the slice levels L1, L2, and L3 generated by the slice level generation circuit 720, and a digital signal representing the level for the information mark recorded at the information recording grid point is output. Although the slice level generation circuit 720 determines the slice level from the reproduction signal for the reference recording mark 800, it is assumed that there is no mark near this mark that causes crosstalk with respect to this mark. Therefore, the two-dimensional equalization circuit described above is not used for the reproduction signal supplied to the slice level generation circuit 720. The same applies to the reproduction signal for the learning mark used by the equalization coefficient learning circuit 731.

The multi-level decoding circuit 702 outputs digital data representing the positional deviation data output by the time measuring circuit 703 for each information recording grid point and multi-value output by the quantizing circuit for the information recording grid point. According to FIG. 19, from the digital data representing the value level, the preceding 2 bits of the 4-bit data represented by the information mark recorded at the information recording grid point are shown.
Decode the bit and the last two bits.

As described above, in this embodiment, since the information marks representing the multi-valued level can be recorded at each information recording grid point with different positional deviations, the amount of information that can be recorded at one information recording grid point. Will increase.

<Modified Example of Embodiment 2 of the Invention> (1) As the magneto-optical recording medium, another medium can be used to record multilevel levels. For example, when an external magnetic field belonging to two different magnetic field regions is applied, two different recording states (magnetization states) are obtained.
Recording layer and two recording states different from each other for two magnetic field regions different from these two magnetic field regions.
It is also possible to use a magneto-optical recording medium in which the first recording layer and a material having different magneto-optical characteristics are laminated. In this case, the second recording layer does not have to be composed of the perpendicular magnetization film and the auxiliary magnetic film described in the second embodiment, and may be a single magnetic film. However, the second recording layer is It is necessary that the first recording layer has two different recording states in two magnetic field regions different from the two magnetic field regions having the recording state. Specific examples of such a medium are described in Japanese Patent Application No. 6-96690 and Japanese Patent Application No. 6-143634 previously filed by one of the applicants. The techniques described therein are incorporated herein by reference.

With respect to such a medium as well, FIG. 21 (b) and FIG.
The description of (c), FIG. 22 and FIG. 23 is applicable. For example,
When the first recording layer having the characteristics shown by the one-dot chain line in FIG. 23 and the second recording layer having the characteristics shown by the broken line in FIG. 23 are stacked, H0, H1, H2, and H3 shown in FIG. By applying each external magnetic field, the four recording states "0", "1", "2", shown in FIG.
"3" can appear. Therefore, for example, as shown in these figures, the recording state by the external magnetic field H0 is "0", the recording state by the external magnetic field H1 is "1", the recording state by the external magnetic field H2 is "2", the recording state by the external magnetic field H3. By positioning each at “3”,
Four-value recording of signals can be performed with an external magnetic field of about 100 (Oe).

(2) As shown in FIG. 29, a DC bias magnetic field is applied to the external magnetic field to change the central magnetic field of the external magnetic field to the material described in the second embodiment and the material described in the first modification. By shifting to the minus side by about -50 (Oe), it becomes possible to record a ternary signal with an external magnetic field as small as ± 50 (Oe).

(3) The recording circuit shown in FIG. 24 can be modified as follows, for example. The multilevel level generation circuit 710 is configured so that the outputs of the amplifiers 953 and 957 are output separately without using the adder 958 shown in FIG. 25, and the magnetic head is provided in the recording circuit shown in FIG. A second magnetic head drive circuit is provided in addition to the drive circuit 713, and the output signals of the two amplifiers are separately voltage-current converted by these two magnetic head drive circuits. One magnetic head having two windings with different numbers of turns is driven by these magnetic head drive circuits.

(4) Instead of the magnetic head, it is of course possible to use another magnetic field generator such as an electromagnetic coil.

(5) As described in Embodiment 2, instead of providing two reference recording marks in the same sector, one reference recording mark is recorded in each sector and two adjacent sectors are recorded. It is also possible to determine the above three slice levels using the two recorded reference recording marks.

<Reference Example 1> This reference example is for explaining a technique for reducing the crosstalk component and the intersymbol interference component used in the second and third embodiments. Therefore, here, the optical information recording / reproducing apparatus which does not use the multi-phase recording or the multi-value recording used in the first to third embodiments is used as an example.

(Related Prior Art) Generally, an optical information recording is performed in which an information mark is recorded on an information track by using a laser beam and an optical change according to the presence or absence of the information mark is detected to reproduce the information. In order to improve the recording density of the medium, the interval between information tracks (track pitch) is narrowed,
In addition, it is necessary to narrow the arrangement interval (mark pitch) of the information marks in the light spot scanning direction. However, when the track pitch and the mark pitch become smaller, the light spot becomes 1
When one information mark is irradiated, part of other surrounding information marks is also irradiated at the same time, which causes a problem that signals of surrounding information marks two-dimensionally leak into signals of information marks to be reproduced. This leakage interferes as a noise component and reduces the reproduction accuracy. Therefore, the usable track pitch and mark pitch are limited by the diameter of the light spot.

A technique for reducing the track pitch and the mark pitch by performing a two-dimensional equalization process and canceling the leak component generated by such a two-dimensional information leak is disclosed in Japanese Patent Laid-Open No. 2-257474. It is disclosed in the publication. In this conventional technique, information is recorded on a predetermined lattice point on a recording medium. The optical spot tracking method is a discrete block servo format (hereinafter, referred to as DBF).
Abbreviated) is used. Conventionally, the DBF is characterized by its easiness of detecting the tracking signal and stability of the clock detection of the recording / reproducing data. Since all the timings can be detected by using the clock pits written on the disc, the DBF is two-dimensional. Marks can be accurately recorded on the grid points. When playing back information, track i-1,
Signal processing is performed based on the reproduction signals from the lattice points on three adjacent tracks of the track i and the track i + 1, and information leakage from adjacent tracks to the reproduction signal of the target track i (crosstalk) And leakage (intersymbol interference) from the target track i is reduced.

In the signal processing in this prior art, first, the track i-1 and the track i are sequentially reproduced by one light beam, the reproduced signals are stored in the corresponding three memories, and then the track is tracked by the light beam. While reproducing i + 1, the intersymbol interference on the tracks i-1, i, i + 1 is reduced by the three transversal filters corresponding to the respective tracks, and then the reproduced signals of the tracks i-1, i, i + 1 are reproduced. The addition by the adder reduces the two-dimensional leakage from the reproduction signal of the track i.

In the technique disclosed in Japanese Patent Laid-Open No. 5-205280, a plurality of crosstalk detection areas are provided on the recording medium so that the crosstalk detection pits do not interfere with each other on each track in the crosstalk detection area. Before the information reproduction, the crosstalk detection pits on the track to be information-reproduced and the crosstalk detection pits on the adjacent tracks are simultaneously reproduced by using three light spots, and the obtained reproduction is performed. The amount of crosstalk from adjacent tracks is learned based on the signal. Also when reading a mark for information reproduction, the track for information reproduction and a pair of tracks adjacent thereto are irradiated with the above three light spots so as to be adjacent to each other included in the reproduction signal for the track for information reproduction. Crosstalk from a pair of tracks,
It is removed using the reproduced signal for a pair of adjacent tracks and the learned crosstalk amount.

Other techniques for achieving high recording density have been proposed in ANSI documents. There, the information recording position is changed for every two tracks so that the information recording position on the track having an even track number is located exactly in the middle of the information recording position on the track having an odd track number. .

(Problems to be Solved by the Reference Example) The conventional technique for reducing crosstalk from adjacent tracks by signal processing has a problem that the device becomes complicated. For example, the above-mentioned JP-A-2-2574.
In the prior art described in Japanese Patent Publication No. 74, the optical system is simple because a one-beam optical system may be used, but in order to remove crosstalk, the intensity of reproduced signals of three tracks is maintained. Memory and three transversal filters are required, which increases the cost of the device. Further, according to the conventional technique described in Japanese Patent Laid-Open No. 205205/1993, it is necessary to use three light spots in order to reduce crosstalk from adjacent tracks, and the optical system is extremely difficult. It gets complicated. Further, since there is no clock synchronized with the crosstalk detection pit, it is not possible to grasp the reproduction signal detection points before and after the crosstalk detection pit, and therefore it is possible to detect the intersymbol interference amount on the target track. Can not.

The details of this reference example will be described below. (1) Overview of Device FIG. 1 shows an optical information recording / reproducing device (hereinafter,
FIG. 3 is a schematic configuration diagram of an optical disc device).

This optical disc apparatus is equipped with an optical information recording medium (hereinafter referred to as an optical recording medium) 100 mounted on a driving device (not shown) and one for recording information or reproducing the recorded information. Based on an optical head 102 that irradiates the optical recording medium 100 with one optical spot 101, a synchronization signal generator 105 that generates a signal synchronized with the rotation of the optical recording medium 100, and a synchronization signal that the synchronization signal generator 105 generates. A positioning circuit 110 that executes tracking of the light spot 100, and a data control circuit 116 that modulates user data to be recorded at the time of information recording, binarizes the reproduction signal 104 at the time of information reproduction, and demodulates and outputs the recorded data. And the intensity of the light spot is modulated based on the modulation signal output from the data control circuit 116, and the optical recording medium 10 A laser driving circuit 119 for recording the above-modulated data and a reproduction signal obtained by scanning the track with the light spot 101 are included in the reproduction signal after analog / digital conversion (hereinafter referred to as A / D conversion). A pre-processing circuit 112 for reducing the offset component generated,
A two-dimensional equalization circuit 114 that reduces two-dimensional leakage based on the output signal of the pre-processing circuit 112, and an optimum equalization coefficient used by the two-dimensional equalization circuit 114 with an optical recording medium mounted in the optical disc device. And an equalization coefficient learning circuit 121 for obtaining

The two-dimensional equalizing circuit 114 is used for the optical recording medium 10.
When information is being reproduced from one track of 0,
For one light spot 101 on that track,
The crosstalk from the adjacent track included in the reproduction light from the position where the information mark is to be recorded is used by using the reproduction light for the position where the information mark is not recorded in the vicinity of the reproduction position for this light spot. It is characterized by removing it. Further, the two-dimensional equalization circuit 114 is
Intersymbol interference from different information marks in this track, which remains in the signal after removing this crosstalk, is also removed. In order to realize this, information marks are recorded on the optical recording medium 100 as shown in FIG.

FIG. 2 shows various areas included in each of the plurality of sectors included in the optical recording medium 100. An information mark 157 is recorded in each data recording area 14 when the user data is 1. The position where the information mark 157 can be recorded is one of a plurality of lattice points scanned at the same time interval when the optical recording medium 100 is rotated. In the present reference example, information marks 157 can be recorded on every other grid point (referred to as type 1 grid point or information recording grid point in this reference example) on the same track. The information mark 157 is not recorded at other grid points (called type 2 grid points or intermediate points in this reference example) on that track. Moreover, the track-direction position of the first-type lattice points capable of storing information marks on even-numbered tracks is relative to the track-direction position of the first-type lattice points capable of recording information marks on odd-numbered tracks. , So that it is shifted by one grid point,
First-type lattice points are defined. In FIG. 2, a plurality of short vertical lines attached to the uppermost track indicate information recording grid points and intermediate points. On the other hand, a plurality of short vertical lines attached to tracks other than the uppermost track indicate information recording grid points, and no midpoint, for example, 156, has such vertical lines.

As shown in FIG. 2, shifting the information recording grid points for each track is known per se for high density recording, but this reference example uses this arrangement with one light beam. It is used to effectively remove crosstalk from the reproduced signal.

In FIG. 2, the equalization coefficient learning circuit 121 includes the equalization coefficient learning circuit 121 in the two-dimensional equalization circuit 1 in the equalization coefficient learning area 13.
Learning marks 154 and 155 for calculating the equalization coefficient used in the equalization processing performed by the controller 14 are recorded. The learning marks 154 and 155 are learning marks recorded on even-numbered tracks and odd-numbered tracks, respectively, and are separated so as not to cause interference with each other. The servo area 11
Is used for highly accurate tracking with the one light spot 101, and the clock mark 15
3 and wobble marks 151 and 152 are recorded.
The offset amount detection area 12 is used to eliminate the adverse effect of tracking deviation on the calculation of the equalization coefficient.

(2) Principle of Equalization Processing in the Reference Example Before the detailed description of the reference example, the principle of the equalization processing in the reference example will be described.

In FIG. 3, assuming that the j-th grid point on the i-th track is (i, j), (i-1, j-1), ( i-1, j),
(I-1, j + 1), (i, j-1), (i, j +)
1), (i + 1, j-1), (i + 1, j), (i +
There are eight adjacent grid points (1, j + 1). When the light spot 101 irradiates a grid point of (i, j), if there are information marks on these adjacent grid points, part of the information mark is also irradiated. Crosstalk, which is a leak of information, occurs. For example, if there is an isolated mark on the grid point (i, j), the signal S (i, j) is obtained. On the other hand, the grid point (i-1, j
-1) If there is a mark in the isolated state, the signal aS (i-1, j-1) leaks from this mark to the lattice point (i, j). Similarly, if there is an isolated mark on the grid point (i−1, j), the signal b · S
(I-1, j) leaks into (i, j). Lattice points (i-
If there is an isolated mark on (1, j + 1), the signal cS (i-1, j) leaks from this mark to the lattice point (i, j). If there is an isolated mark on the grid point (i, j-1), the signal dS (i, j-1) leaks from this mark to the grid point (i, j). If there is an isolated mark on the grid point (i, j + 1), the signal eS
(I, j + 1) leaks into the grid point (i, j). If there is an isolated mark on the grid point (i + 1, j−1), the signal f · S (i + 1, j−1) leaks from this mark to the grid point (i, j). If there is an isolated mark on the lattice point (i + 1, j), the signal g · S (i +
1, j) leaks into the grid point (i, j). Lattice points (i +
If there is an isolated mark on (1, j + 1), the signal h · S (i + 1, j + 1) from this mark is the grid point (i, j).
Leak into. Here, as shown in FIG. 3, a to h represent the leakage amount of information from the adjacent grid points, and the value is smaller than 1. It should be noted that the arrows in a to h only indicate where information leaks in and do not indicate the size. At this time, the grid point (i, j) as shown in FIG.
Considering the reproduction signal S ′ (i, j) that has been interfered with by the adjacent information mark obtained in step 1, it can be expressed as follows using the information leakage amount shown in FIG.

S ′ (i, j) = S (i, j) + a · S (i−1, j−1) + b · S (i−1, j) + c · S (i−1, j + 1) + d S (i, j-1) (1) + eS (i, j + 1) + fS (i + 1, j-1) + gS (i + 1, j) + hS (i + 1, j + 1) where S (I, j) is a reproduction signal level when an information mark exists independently at a grid point (i, j) and no adjacent information mark exists (hereinafter, referred to as an isolated signal). For the sake of simplicity, if an information mark exists at the grid point (i, j), S (i, j) will be 1, for example, and the grid point (i, j) will be
If there is no information mark in j), then S (i, j)
Is 0, for example. In the equation (1), aS (i-
1, j-1) + b.S (i-1, j) + c.S (i-
1, j + 1) + f · S (i + 1, j−1) + g · S (i
+ 1, j) + h · S (i + 1, j + 1) represents crosstalk from adjacent lattice points.

On the other hand, the reproduced signal S'received interference from the adjacent information mark obtained at the lattice point position (i, j-1).
Reproduced signal S ′ that has received interference from adjacent information marks obtained at the lattice point positions of (i, j−1) and (i, j + 1)
Considering (i, j + 1), it can be expressed as follows.

S ′ (i, j−1) = S (i, j−1) + a · S (i−1, j-2) + b · S (i−1, j−1) + c · S (i -1, j) + d * S (i, j-2) (2) + e * S (i, j) + f * S (i + 1, j-2) + g * S (i + 1, j-1) + h * S ( i + 1, j) S '(i, j + 1) = S (i, j + 1) + a * S (i-1, j) + b * S (i-1, j + 1) + c * S (i-1, j + 2) + d * S (i, j) (3) + eS (i, j + 2) + fS (i + 1, j) + gS (i + 1, j + 1) + hS (i + 1, j + 2) If S (i-1, j) -2) = S (i-1, j) = S
(I-1, j + 2) = S (i, j-1) = S (i, j +
1) = S (i + 1, j-2) = S (i + 1, j) = S
If (i + 1, j + 2) = 0 always holds, (2)
The crosstalk from the adjacent tracks included in the equation (1) can be deleted by using the equation and the equation (3). That is, if the lattice points where the marks can be recorded are arranged in a face-centered rectangular lattice shape as shown in FIG. 2, this condition is satisfied, so that crosstalk from the adjacent tracks can be achieved without using the reproduction signal of the adjacent tracks. Can be reduced. This will be described in detail below.

If the lattice points on which the marks can be recorded are arranged in a face-centered rectangular lattice shape, the above equations (1) to (3) are respectively represented by equations (1-1) to (3-1). Represented by. S '(i, j) = S (i, j) + a * S (i-1, j-1) + c * S (i-1, j + 1) + f * S (i + 1, j-1) (1-1 ) + H * S (i + 1, j + 1) S '(i, j-1) = b * S (i-1, j-1) + d * S (i, j-2) + e * S (i, j) ( 2-1) + g · S (i + 1, j + 1) S ′ (i, j + 1) = b · S (i−1, j + 1) + d · S (i, j) + e · S (i, j + 2) (3-1 ) + G · S (i + 1, j + 1) a · S (i−1, j−1) + c · S in the equation (1-1)
(I-1, j + 1) + f * S (i + 1, j-1) + h *
S (i + 1, j + 1) represents crosstalk from adjacent lattice points when the lattice points where marks can be recorded are arranged in a face-centered rectangular lattice shape. Further, a = b · d, c = b · e, f = for the information leakage amounts a, b, c, and h.
Since the relationship of g · d and h = g · e is almost true, (2
-1) and (3-1) are respectively (2-2) and (3).
-2) It is represented as in the equation. S '(i, j-1) = d * S (i, j-2) + e * S (i, j) + (a * S (i-1, j-1) + f * S (i + 1, j-) 1)) / d (2-2) S '(i, j + 1) = d * S (i, j) + e * S (i, j + 2) + (c * S (i-1, j + 1) + h * S ( i + 1, j + 1)) / e (3-2) If the equation (2-2) is multiplied by d, and if the equation (3-2) is multiplied by e, the crosstalk component which is a problem in the equation (1-1), a
-S (i-1, j-1), c-S (i-1, j + 1),
f · S (i + 1, j−1), h · S (i + 1, j + 1)
Turns out. Therefore, as shown below, crosstalk from adjacent tracks can be reduced by performing the calculation of (1-1) formula-d. (2-2) formula-e. (3-2) formula. it can.

S ″ (i, j) = A0 · S ′ (i, j) + A1 · S (i, j−1) + A2 · S (i, j + 1) (4) where A0 = 1 / ( 1-2d · e) A1 = −d / (1-2d · e) A2 = −e / (1-2d · e).

The result of the calculation of this equation (4) can be expressed as follows.

S ″ (i, j) = S (i, j) −A0 · (square (d) · S (i, j−2) (5) + square (e) · S (i, j + 2)) Here, square (d) and the like represent the square of d.

As shown in the equation (5), this equation is an equation in which only the target track i is involved. You can see that the crosstalk can be completely removed. However, as it is, the target grid point (i,
j), the grid point (i, j-2) and the grid point (i, j +)
Intersymbol interference from 2) becomes a problem. For example, when the lattice spacing T and the track pitch Tp are about 50% of the spot diameter, b = d = e = g = 0.2 and a = c = f = h = 0.
The maximum intersymbol interference is about 0.09.

Therefore, in order to reduce intersymbol interference, for example, when a 5-tap transversal filter is used, the following calculation is performed.

S ′ ″ (i, j) = C0 · S ″ (i, j) + C1 · S ″ (i, j−2) + C2 · S ″ (i, j + 2) (6) + C3 · S ″ (i, j-4) + C4 · S ″ (i, j + 4)) where B = 1 / (1-3 square (d · e / (1-2d · e))) C0 = B · (1-square (d * e / (1-2d * e))) C1 = -B * square (d) / (1-2d * e) C2 = -B * square (e) / (1-2d *) e) C3 = B · square (squire (d) / (1-2d · e)) C4 = B · square (squire (e) / (1-2d · e)).

The result of this calculation can be expressed as follows.

S ″ ′ (i, j) = S (i, j) + D1 · S (i, j−6) (7) + D2 · S (i, j + 6) where D1 = B · cube (C1 ), D2 = B · cu
be (C2). cube (C1) etc. is C1 3
Represents the square. For example, when the lattice spacing T and the track pitch Tp are about 50% of the spot diameter, b = d = e = g = 0.2
Then, a = c = f = h = 0.04, and the maximum intersymbol interference is about 0.0002.

When using a transversal filter having a different number of taps, the same calculation may be performed according to the number of taps. For example, the equation corresponding to the equation (6) is the equation (6a) for the 3-tap transversal filter,
In the case of a tap transversal filter, the formula (6b) is used.

S ′ ″ (i, j) = S ″ (i, j) + G1 · S ″ (i, j−2) (6a) + G2 · S ″ (i, j + 2) where F = 1 / (1-2 square (d · e / (1-2d · e))), G1 = −F · (square (d) / (1-2d · e)), G2 = −F · (square ( e) / (1-2d · e)).

S ′ ″ (i, j) = Z0 · S ″ (i, j) + Z1 · S ″ (i, j−2) + Z2 · S ″ (i, j + 2) + Z3 · S ″ (I, j-4) + Z4 * S '' (i, j + 4) + Z5 * S '' (i, j-6) + Z6 * S '' (i, j + 6) (6b) where Y = 1 / ( 1-4 C1 ・ C2 + 2 square
(C1) · square (C2)), Z0 = Y · (1-2C1 · C2), Z1 = −Y · (C1 · (1-C1 · C2)), Z2 = −Y · (C2 · (1- C1 * C2)), Z3 = Y * square (C1), Z4 = Y * square (C2), Z5 = -Y * cube (C1), Z6 = -Y * cube (C2).

The leak amounts a to h shown in FIG. 3 are the light spots at the time of recording, the shape and position of the recording mark fluctuating due to fluctuations of the spot shape at the time of recording, recording power, recording clock timing, focus and tracking. shape,
Changes due to fluctuations in tracking, focus, and sampling clock timing. Therefore, in this reference example, this leakage amount is measured with the optical information recording medium mounted in the actual optical information recording / reproducing apparatus. However, if the variation is small or negligible, for example, an equalization coefficient that is experimentally obtained in advance before shipment of the optical information recording device may be used.

In order to carry out the measurement with the optical information recording medium mounted in the actual optical information recording / reproducing apparatus, a predetermined mark group, that is, a mark row pattern is recorded in advance at a predetermined position on the optical recording medium. Keep it. Before reproducing information, this mark row pattern is reproduced with a light spot, and the leak amount is learned based on the reproduced signal. As described above, a = b · d, c
= B · e, f = g · d, and h = g · e are substantially established,
The two-dimensional leakage can be reduced by performing the calculation of the equations (4) and (6). At this time, as is clear from the equations (4) and (6), The equalization coefficient applied to the signal is a function of only d and e. Therefore, it is sufficient to learn d and e as the leak amount, and the equalization coefficient may be calculated based on this learned value. It should be noted that the equalization coefficients in the equations (6a) and (6b) are also the leak amounts d and e.
Of course, since it is a function of, the same thing can be done.

A method for learning the leak amounts d and e will be described below.

First, a recording method of a learning mark will be described using an example of the equalization coefficient learning area shown in FIG. The learning marks for learning the equalization coefficient are arranged at a distance that does not interfere with each other in the light spot scanning direction. When the track i is specifically described as an even track, as shown in FIG. 2, for example, the learning mark 155 is recorded at the grid point (i, p + 5) on the even track i, and the learning mark 155 is learned on the odd tracks i-1 and i + 1. The mark 154 is assigned to a grid point (i-1, p +
2) and (i + 1, p + 2), respectively. Here, p is a value indicating the start position of the learning area.

Next, a method of learning the leak amounts d and e will be described with reference to FIG. Since the equalization coefficient learning mark 155 is recorded at the grid point (i, p + 5) on the even track i, the leak amount d is determined by the grid point (i, p).
+6) and the reproduced signal S '(i, p + 6) obtained at +6) and the reproduced signal S' (i, p + 5) obtained at the lattice point (i, p + 5).
5) ratio, that is, S '(i, p + 6) / S' (i,
p + 5). Also, odd track i-1
Then, the equalization coefficient learning mark 154 indicates that the grid point (i-1, p +
Since it is recorded in 2), the grid point (i-1, p + 3)
And the reproduction signal S '(i-1, p + 2) obtained at the grid point (i-1, p + 2).
ratio of p + 2), that is, S '(i-1, p + 3) /
It is calculated as S '(i-1, p + 2).

On the other hand, since the equalization coefficient learning mark 155 is recorded at the grid point (i, p + 5) on the even track i, the leak amount e is the reproduction signal S ′ obtained at the grid point (i, p + 4). (I, p + 4) and the grid point (i, p + 5)
The ratio of the reproduced signal S ′ (i, p + 5) obtained in step S, that is, S ′ (i, p + 4) / S ′ (i, p + 5). Further, since the equalization coefficient learning mark 154 is recorded at the grid point (i-1, p + 2) in the odd track, the reproduction signal S'obtained at the grid point (i-1, p + 1) is obtained.
The ratio of (i-1, p + 1) to the reproduction signal S '(i-1, p + 2) obtained at the lattice point (i-1, p + 2), that is, S' (i-1, p + 1) / S '( i-1, p + 2)
Is required. The equalization coefficient can be obtained from the leak amounts d and e obtained as a result of this learning.

Then, the reproduced signal is two-dimensionally equalized by using the obtained equalization coefficient to cancel the signal leakage from the adjacent marks and detect the information depending on the presence or absence of the marks. In the optical information recording / reproducing method according to the present invention, the positions of the grid points for recording the information marks are changed for each track so that the adjacent tracks are shifted from each other by a half cycle, and the adjacent tracks which become a problem during reproduction are The amount of crosstalk can be reduced, and further, crosstalk from adjacent tracks can be completely eliminated by the two-dimensional equalization signal processing, and intersymbol interference can be reduced.

(3) Recording and Reproduction of Information on Optical Recording Medium In this reference example, the optical recording medium 100 is a magneto-optical disk, and at the time of recording information, the laser drive circuit 119 sets the value of the information to be recorded. The intensity of the laser beam is modulated according to 1 or 0. The optical recording medium 100 is driven by a spindle motor (not shown). The optical head 102 narrows this modulated laser beam onto the optical recording medium 100, irradiates the magneto-optical disk 100 with a light spot 101, and the light spot is irradiated onto a portion of the magneto-optical disk 100 where the light spot is irradiated. This causes a change in the direction of magnetization depending on the intensity of 101. At the time of reproducing information, the laser drive circuit 119 and the optical head 102 set the light spot 1 of a constant intensity.
The optical recording medium 100 is irradiated with 01. Optical recording medium 100
The polarization angle of the reflected light with respect to the light spot 101 irradiated on the surface changes depending on the direction of the magnetization. Optical head 102
Is a detector (not shown) that generates a reproduction signal (hereinafter also referred to as a magneto-optical signal) 104 whose magnitude changes depending on whether or not the polarization of the reproduction light is in a specific direction, and the reproduction light. Signal 10 that represents the total amount of reproduction light, regardless of the polarization of
3 has a detector (not shown) that produces 3.

(4) Track Pitch Tp, Spot Size Ws, Mark Pitch Mp In the present reference example, when the i-th track in FIG. 2 is reproduced, the i-1 immediately adjacent to the track by the method described in detail later. Crosstalk from the (th) track and the (i + 1) th track can be removed. In order for the method to be effective, there must be virtually no crosstalk from tracks farther from them. For this reason, in the present reference example, the track pitch Tp is set to an interval such that the light spot 101 does not reproduce the information on the i−2nd track and the i + 2nd track.

The spot diameter Ws becomes a value of about λ / NA or more depending on the wavelength λ and the numerical aperture NA of the aperture lens, and the diameter Wm of the information mark is the minimum necessary to obtain a signal of sufficient S / N. It must be larger than the mark diameter.

When the light spot 101 reproduces the i-th track, the minimum value of the track pitch Tp is such that the light spot 101 does not reproduce the information of the i−2nd track and the i + 2nd track. Is i-2
The track spacing when contacting the information mark on the 2nd track and the i + 2nd track is (Ws + W
m) / 4. For example, when the light source wavelength is λ = 780 nm, the numerical aperture NA of the focusing lens is 0.55, the spot diameter is 1.42 μm, and the information mark diameter Wm = 0.5 μm, the minimum track pitch is 0.48 μm. Actually, considering that a positional deviation occurs during tracking, it is necessary to make the minimum track pitch larger than this. In this reference example, the track pitch is 0.5 μm.

Next, the mark pitch will be described. The mark pitch is the interval between grid points that can record adjacent information marks on the same track. In this reference example, in order to remove the crosstalk from the adjacent tracks, as shown in FIG.
As shown in, information marks can be recorded at alternate grid points on the same track, and on even-numbered tracks and odd-numbered tracks, information marks can be recorded at grid points in the track direction. It is offset by one grid point distance along. Therefore, the mark pitch Mp is twice the distance between the lattice points.

As described above, the track pitch Tp is set to (W
s + Wm) / 4 or more, and when using a five-tap transversal filter described later in the two-dimensional equalization circuit 114, as a result of calculating equations (4) and (6), the residual leakage in the signal The maximum value of the inclusion component can be expressed as in equation (8) from equation (7).

E = B · cube (C1) + B · cube (C2) (8) FIG. 4 shows, for example, the light source wavelength λ = 780 nm, the numerical aperture NA = 0.55 of the focusing lens, and the mark diameter W = 0.5 μ.
This is a graph obtained by simulating the value of the equation (8) when the mark pitch Mp is changed at m and the track pitch Tp = 0.5 μm. In this simulation, considering the light diffraction and the numerical aperture of the focusing lens,
Journal of Optical Society of America Vol. 69, No. 1, January 1979, pages 4 to 24
The Hopkins diffraction calculation described on page was used. From the graph of FIG. 4, it can be seen that the equalization residual is about −20 dB with respect to the signal component when the mark pitch Mp = 0.88 μm. That is, in this reference example, the mark pitch Mp needs to be about 60% or more of the spot diameter Ws.

(5) Tracking In the present reference example, when the i-th track is reproduced, the i-th track is removed in order to remove crosstalk from the i−1-th track and the i + 1-th track immediately adjacent to the track. It is not necessary to use a laser beam other than the laser beam used to reproduce the track. Therefore, as a result, the structure of the optical head 102 is simplified. To take advantage of this advantage, it is desirable not to use another laser beam for tracking. Therefore, in this reference example,
Japanese Patent Application No. 5-255354 (see Japanese Patent Application Laid-Open No. 7-
(Published as 110958) or the corresponding technology described in US application Ser. No. 08/321619. The techniques described therein are incorporated herein by reference. In the following, this technique will be briefly described.

As shown in FIG. 2, in the servo area 11 of each sector, ANSI Doc. No. : X3B11 / 9
According to the DBF method described in 0-003-R1, clock marks 153 linearly arranged at intervals P in the radial direction are pre-recorded at the 0 position of each track. Furthermore, in this reference example, according to the technique described in the patent application referred to above,
The wobble marks 151 and 152 are replaced with clock marks 153.
The phase difference is ± P / 4 in the radial direction as compared with the above. In this reference example, this P is equal to twice the track pitch Tp. Incidentally, instead of these marks, a preliminary pit may be formed on the optical recording medium 100.

When the light spot 101 passes the clock mark 153 of any sector at the time of recording or reproducing information, the total light amount signal 103 changes. A PLL (Phase Locked Loop) (not shown) in the synchronization signal generator 105 responds to the change in this signal by detecting a clock signal 106 for detecting a servo signal which is synchronized with the time when the light spot passes through the clock mark 153. Sample hold signal 1
07 is generated. The period of the clock signal 106 is the time required for the light spot to move in the track direction at the distance between the lattice points on the optical recording medium 100.

The sample hold signal 107 is a signal that maintains the level H from the time when the light spot passes the clock mark 153 to the end of the sector to which it belongs, and otherwise maintains the level L. Similarly, the light spot 101 changes the wobble marks 151 and 152.
Sample hold signal 10 in synchronization with the time when
8 and 109 are generated. Light spot positioning circuit 110
Is the total light amount signal 1 based on the clock signal 106 for servo signal detection and the sample and hold signals 107 to 109.
A plurality of tracking error signals and a position signal indicating the position of the light spot are generated from 03, an actuator control signal 111 is further generated based on these signals, and a tracking operation of an actuator (not shown) of the optical head 102 is performed. According to this technique, even when the information tracks are arranged at intervals smaller than the interval P in the radial direction, for example, P / 8, it becomes possible to reproduce or record / reproduce information. In this reference example, the clock mark 153
With a radial period P of 1.0 μm and a track pitch T
It is assumed that p is P / 2 and the positioning of the light spot is also performed within this track pitch Tp.

(6) Recording of Learning Mark As shown in FIG. 7, the equalization coefficient learning circuit 121 includes an odd-even track discriminating circuit 201, a learning mark recording signal generating circuit 203, a counter 364, and a learning mark gate generator 36.
5, equalization coefficient calculation circuit 206. The odd-even track identification circuit 201 includes a comparator 210, an address area recognition circuit 367 and a track address identification circuit 212.

At the time of recording information, first, the optical head 10
2 detects an address pit (not shown) in the address area provided at the head of each sector. The address area recognition circuit 367 recognizes whether or not the light spot is in the address area based on the total light amount signal 103 including the detection signal of the address pit, and if the light spot is in the address area, it becomes level H, and otherwise. An address gate signal 368 holding the level L is output. When the address gate signal 368 is at level H, the track address identification circuit 212 recognizes the track address based on the total light quantity signal 211 binarized by the comparator 210, and whether the light spot 101 scans an even numbered track. , It is discriminated whether or not the odd-numbered tracks are being scanned, and the resultant track discrimination result signal 202 is output. Specifically, it is determined whether the least significant bit of the track address is 0 or 1, and the least significant bit 0 or 1 is output. This identification circuit holds the track identification result signal 202 until the next track identification is performed. In the following, when the least significant bit is 0, it is an even track, and when the least significant bit is 1, it is an odd track.

The counter 364 is reset to 0 when the sample and hold signal 107 becomes the level L, and becomes 0, and at the same time the clock signal 106 starts counting. The learning mark gate generator 365 outputs the output signals Q0 to Q0 of the counter 364.
Based on Qn, the learning mark recording trigger 366 is generated when the value of the counter 364 is p representing the first type lattice point at the head of the equalization coefficient learning area 13. The learning mark recording signal generation circuit 203 outputs the learning marks 154, 1 based on the track identification result signal 202 and the learning mark recording trigger 366.
The learning mark recording signal 122 for recording 55 is output.

Specifically, for odd-numbered tracks,
When indicating the number of the first type lattice point next to the first type lattice point p at the head of the equalization coefficient learning area 13, that is, p + 2, this counter is further set for even-numbered tracks.
The first-type lattice point p + at the beginning of the equalization coefficient learning area 13
When the number of the first type of lattice point next to 1 is indicated, that is, p + 5, a pulse is output. As a result, the learning mark recording signal 122 becomes a pulse signal output at different timing depending on whether the track being scanned is an even-numbered track or an odd-numbered track.

The laser drive circuit 119 outputs the recording pulse 120 in synchronization with the learning mark recording signal 122 to the optical head 10.
2, and the optical head 101 modulates the intensity of the light spot 101 according to the recording pulse 120. As a result, as shown in FIG. 2, in the equalization coefficient learning area 13 on the optical recording medium 100, the first-type lattice point p + 2 or the first-type lattice point p + 1 depending on whether or not the track number is an even number. Grid point p
The learning mark 154 or the learning mark 155 is recorded at +5.

The learning marks 154 and 155 are arranged at a distance that does not interfere with each other in the light spot scanning direction. That is, the reproduction signal from each learning mark 154 or 155 is placed at a distance such that crosstalk does not occur from the learning mark on the track adjacent to the track to which the learning mark belongs. In this reference example, the distance between three grid points is set. For example, the spot diameter Ws is 1.42 μm, the track pitch Tp is 0.5 μm, the mark pitch Mp is 0.88 μm,
When the mark diameter W is set to 0.5 μm, the lattice spacing T = Mp / 2 in FIG. 2 is satisfied. Therefore, in FIG. A mark having the same shape as that of 157 is recorded as the equalization coefficient learning mark 155.
At u-1, if a mark having the same shape as the information recording mark 157 is recorded as the equalization coefficient learning mark 154 on the first type lattice point (2u-1, p + 2), the learning marks 154 and 155 will be obtained.
Interference does not occur between them.

(7) Recording of user data The user data is recorded after the recording of the learning mark described above is completed. In FIG. 5A, the counter 361
Resets to 0 when the sample and hold signal 107 goes to level L, and starts counting the clock signal 106 at the same time as the sample and hold signal 107 goes to level H. The recording area gate generator 362 becomes the level H at the counter value q based on the output signals Q0 to Qn of the counter 361, and becomes the level L at the end of the data recording area.
A recording area gate signal 363 is generated.

The multiplication circuit 354 outputs an even clock signal 355 and an odd clock signal 356 which are obtained by doubling the cycle of the clock signal 106. As shown in FIG. 5B, the rising edges of the even-numbered clock signals 355 are synchronized at the time corresponding to the positions of the first-type lattice points q + 2, q + 4 ... In the data recording area 14, and the first-type lattice points q + 1, q + 3, q + 5 ...
The rising edges of the odd-numbered clock signal 356 are synchronized at the time corresponding to the position. The selector 357 outputs the track identification result signal 202 output from the odd-even track identification circuit 201.
Is 0, the even track signal 355 is output as the recording / reproducing clock 358, and the track identification result signal 202
If is 1, the odd-numbered track signal 356 is output as the recording / reproducing clock 358. The modulation circuit 204 operates when the recording area gate signal is at level H, modulates the user data 117 to be recorded according to an appropriate encoding rule, and depends on the recording / reproducing clock signal 358 which is the output of the selector 357. Modulation data 118 at different timing
Is output. As shown in FIG. 2, in the case of an even-numbered track, for example, 2u, the modulated data 118 has a time corresponding to the positions of the first type grid points q + 2, q + 4 ... Next, odd track 2u
In the case of -1, the lattice point of the first kind q + in the data recording area
It becomes significant at the time corresponding to the positions of 1, q + 3, q + 5 ....

The laser drive circuit 119 uses the modulation data 118.
In accordance with the above, the intensity of the laser beam is modulated so that the optical head 102 records or does not record the information recording mark 157 at every other grid point where information in the data recording area 14 on the optical recording medium should be written. To Thus, the information recording mark 157 has the first type lattice points q, q + 2, q in the data recording area in the case of an even numbered track.
+4 ... recorded on any or all of them, and in the case of an odd numbered track, the grid point q of the first kind in the data recording area
It is recorded at any or all of the positions of +, q + 3, q + 5 ....

(8) Pre-processing at the time of reproducing information The pre-processing circuit 112 reduces the extra offset component contained in the magneto-optical signal 104 given from the optical head 102 and not related to the presence or absence of the information mark. Specifically, the reflected light level from the offset detection area 12 in which the information mark of the optical recording medium 100 is not recorded is detected,
This reflected light level is subtracted from the subsequently detected magneto-optical signal 104. Referring to FIG. 6, the preprocessing circuit 112
Is composed of a sample hold circuit (S / H circuit) 221, an offset amount difference circuit 223, an analog-digital conversion circuit (A / D circuit) 225, a counter 226, and a sample pulse generator 227. The counter 226 is reset to 0 when the sample-hold signal 107 goes to level L, and starts counting the clock signal 106 at the same time when the sample-hold signal 107 goes to level H. The sample pulse generator 227 has a counter 226.
A sample pulse 228 is generated when the counter value is n based on the output signals Q0 to Qn. The S / H circuit 221 receives the sample pulse 228 and at the same time receives the magneto-optical signal 10
4 levels are sampled and the sample level 222 is held until the next sample pulse 228 is input.
The sampled level is the reflected light level from the offset detection area 12 in which the information mark is not recorded. The offset amount difference circuit 223 uses the magneto-optical signal 10
4 and the sampled level 222 offset difference signal 224
Is output. The A / D circuit 225 converts the offset difference signal 224 into a digital signal based on the clock signal 106 and outputs it as a digital difference signal 113.

(9) Measurement of equalization coefficient The equalization coefficient calculation circuit 206 in the equalization coefficient learning circuit 121
Is used to find the optimum equalization coefficient that reduces the two-dimensional leakage. Referring to FIG. 8, this circuit includes a circuit 241 for detecting a leak amount d and a leak amount e.
Circuit 242, and arithmetic circuits 245 to 250 and 254 to 258 for calculating the equalization coefficient from the leak amounts d and e detected by these detection circuits.

A schematic structure of the leak amount detection circuit 241 is shown in FIG. The counter 268 is reset to 0 when the sample-hold signal 107 goes to level L, and starts counting the clock signal 106 at the same time when the sample-hold signal 107 goes to level H. The sample pulse generator 260 uses the output signal Q of the counter 268.
Sample pulses 261 and 262 are generated based on 0 to Qn. When the light spot 101 scans an even-numbered track, for example, a 2u-th track, the track identification result signal 202 generated by the odd-even track identification circuit 201 is "
0 ". At this time, as shown in FIG.
55 is recorded at the position of the first type grid point (2u, p + 5), and the sample pulse generator 260 generates the sample pulse 261 at the first type grid point (2u, p + 6) and at the same time, the first type grid point A sample pulse 262 is generated at (2u, p + 5) (see FIG. 9B). The sample and hold circuits 263 and 264 are respectively provided with the sample pulse 261.
The digital difference signal 113 is sampled at pulse positions 262 and 262 to obtain a grid point signal S ′ (2u, p + 6) and a grid point signal S ′ (2u, p + 5). The divider 267 receives the signals S ′ (2u, p + 5) and the signals S ′ (2u, p + 5).
6) ratio (S '(2u, p + 6) / S' (2u, p +
5)) is output as the leak amount d. On the other hand, when the light spot 101 is scanning an odd-numbered track, for example, 2u−1, the track identification result signal 202
Becomes "1". At this time, as shown in FIG. 2, the learning mark 155 is recorded at the position of the first-type lattice point (2u-1, p + 2), and the sample pulse generator 260 has the first-type lattice point (2u-1, p + 3). ), The sample pulse 261 is generated, and the sample pulse 262 is generated at the first type lattice point (2u−, p + 2) (see FIG. 9B). The sample hold circuits 263 and 264 sample the digital difference signal 113 at the pulse positions of the sample pulses 261 and 262, respectively, and calculate the grid point signal S ′ (2u-1,
p + 3) and the lattice point signal S '(2u-, p + 2) are obtained.
The divider 267 receives these signals S '(2u-1, p + 3).
To the signal S '(2u-1, p + 2) (S' (2u-
1, p + 3) / S '(2u-1, p + 2)) is output as the leak amount d.

The schematic structure of the leak amount detection circuit 242 is also shown in FIG. 9A similarly to the leak amount detection circuit 241. The schematic configuration and operation of the leak amount detection circuit 242 will be described below with reference to FIG. The difference between the leak amount detection circuits 242 and 241 is that the sample pulse generator 2
The timing of sample pulses 261 and 262 generated by 60 is different. When the light spot 101 is scanning an even-numbered track, for example, a 2u-th track, the track identification result signal 202 is "0". At this time, as shown in FIG. 2, the learning mark 155 has the first type grid point (2
u, p + 5), the sample pulse generator 260 generates the sample pulse 261 at the first-type lattice point (2u, p + 4), and also the first-type lattice point (2
u, p + 5) generates a sample pulse 262 (FIG. 9).
(B)). Sample and hold circuits 263 and 264
Sample the digital difference signal 113 at the pulse positions of the sample pulses 261 and 262, respectively, and calculate the grid point signal S ′ (2u, p + 4) and the grid point signal S ′ (2u, p +
5) is obtained. The divider 267 receives these signals S ′ (2u,
p (5+) to signal S '(2u, p + 4) (S' (2
u, p + 4) / S '(2u, p + 5)) is output as the leak amount e. On the other hand, when the light spot 101 is scanning an odd-numbered track, for example, 2u−1, the track identification result signal 202 is “1”.
At this time, as shown in FIG. 2, the learning mark 155 is recorded at the position of the type 1 lattice point (2u-1, p + 2),
The sample pulse generator 260 has a first-type lattice point (2u−
1, p + 1) generates the sample pulse 261 and also generates the sample pulse 262 at the first-type lattice point (2u-1, p + 2) (see FIG. 9B). The sample and hold circuits 263 and 264 respectively operate on the sample pulse 26
At the pulse positions of 1 and 262, the digital difference signal 113
Are sampled to obtain a grid point signal S ′ (2u−1, p + 1) and a grid point signal S ′ (2u−1, p + 2). Divider 2
67 is a ratio (S '(2u-1, p + 2) of these signals S' (2u-1, p + 1) and signal S '(2u-1, p + 2).
1) / S '(2u-1, p + 2)) is output as the leak amount e.

The arithmetic circuits 245-250 and 254-258 shown in FIG. 8 are circuits for calculating an equalization coefficient used at the time of equalization based on the leak amounts d and e obtained by the detection circuits 241, 242. . Among these, the arithmetic circuits 245 to 247 set the equalization coefficients A0, A1 and A2 for removing the crosstalk from the track adjacent to the track being scanned by the light spot 101 from the reproduction signal (4).
Calculate each according to the formula. The arithmetic circuits 248 to 250 and the arithmetic circuits 254 to 258 have the coefficient A calculated above.
Equalization coefficients C0 to C4 used to remove components due to intersymbol interference on the track are calculated from the reproduced signal after removing the crosstalk using 0, A1, and A2, respectively, according to the equation (6). To do.

That is, the arithmetic circuit 245 calculates the equalization coefficient A0 shown in the equation (4) based on the leak amount d and the leak amount e. The arithmetic circuit 246 calculates the equalization coefficient A1 shown in the equation (4) based on the leak amount d and the leak amount e. Further, the arithmetic circuit 247 calculates the equalization coefficient A2 shown in the equation (4) based on the leak amount d and the leak amount e. The arithmetic circuit 248 calculates the equalization coefficient C0 shown in the equation (6) based on the leak amount d and the leak amount e. The arithmetic circuit 249 calculates and outputs the equalization coefficient C1 shown in the equation (6) based on the leak amount d and the leak amount e. The arithmetic circuit 250 uses the leak amount d and the leak amount e.
Based on the above, the equalization coefficient C2 shown in the equation (6) is calculated.
The arithmetic circuit 251 calculates the equalization coefficient C3 shown in the equation (6) based on the leak amount d and the leak amount e. The arithmetic circuit 252 calculates the equalization coefficient C4 shown in the equation (6) based on the leak amount d and the leak amount e.

(10) Reproduction of Information At the time of information reproduction, the two-dimensional equalization circuit 114 is a two-dimensional element for reducing the two-dimensional leakage of the digital difference signal 113 output from the preprocessing circuit 112. Executes equalization processing. In this reference example, the two-dimensional leakage is reduced by performing the calculations of the expressions (4) and (6) already described. In FIG. 10, the two-dimensional equalization circuit 114 is
Comprising equalization circuits 331 and 332, equalization circuit 331
Is the equalization coefficient A output from the equalization coefficient learning circuit 121.
Based on 0 to A2, the preprocessing circuit 112 according to the equation (4)
The crosstalk reduction signal 321 is output by reducing the crosstalk included in the digital differential signal 113 supplied from The equalization circuit 332 reduces the intersymbol interference component included in the crosstalk reduction signal 321 according to the equation (6) based on the equalization coefficients C0 to C4 output from the equalization coefficient learning circuit 121, and outputs the equalized signal. 115 is output.

The equalizing circuit 331 includes delay circuits 270 and 27.
1, gain adjusting circuits 280 to 282, adder 290,
It is a 3-tap transversal filter configured with 291 and.

The delay circuits 270 and 271 are controlled by the clock signal 106 and delay the digital difference signal 113 by the time D required for the optical spot to scan the grating interval T to generate the delay signals 300 and 301. The gain adjustment circuit 280 is configured to adjust the digital difference signal 113 and the equalization coefficient A2.
A gain adjustment signal 310 obtained by multiplying by is output. The gain adjustment circuit 281 outputs a gain adjustment signal 311 obtained by multiplying the delay signal 300 and the equalization coefficient A0, and the gain adjustment circuit 281.
2 outputs a gain adjustment signal 312 obtained by multiplying the delay signal 301 and the equalization coefficient A1. Gain adjustment signals 310 to 31
2 is added by adders 290 and 291 and then output as a crosstalk reduction signal 321. Thus, the crosstalk reduction signal 321 becomes the signal S ″ (i, j) shown in the equation (4), and the crosstalk from the adjacent track is reduced.

However, if this signal 321 is left as it is, the grid point (i, j) is changed with respect to the target grid point (i, j).
-2) and intersymbol interference from the lattice point (i, j + 2). The equalizing circuit 332 calculates the equation (6) in order to reduce the intersymbol interference. That is, in the equalization circuit 332, the delay circuits 272 to 275 of four stages are connected to the clock signal 10.
Controlled by 6, the crosstalk reduction signal is delayed by 2D in time to generate delayed signals 302 to 305. The gain adjustment circuit 283 uses the crosstalk reduction signal 321 and the equalization coefficient C4.
A gain adjustment signal 313 obtained by multiplying by is output. Similarly, the gain adjustment circuits 284 to 287 are configured to delay the delay signals 302 to
Gain adjustment signals 314 to 317 obtained by multiplying 305 by the equalization coefficients C2, C0, C1 and C3 are output. The gain adjustment signals 313 to 317 are added by the adders 292 to 295 and then output as the equalized signal 115. The equalized signal 115 is the signal S ″ ′ (i,
j), which is a signal with reduced crosstalk from adjacent tracks and intersymbol interference from the track being scanned.

The data control circuit 116 outputs the signal 1 after the equalization.
15 is demodulated and the recorded data is reproduced. That is, referring to FIG. 5A, in the data control circuit 116, the equalized signal 11 supplied from the two-dimensional equalization circuit 114 is used.
5 is binarized by the comparator 350 based on the threshold signal 351.

The multiplication circuit 354 multiplies the clock signal 106 and outputs the even track signal 355 whose rising edge is synchronized with the lattice points q + 2, q + 4 ... And the lattice points q + 1, q.
An odd-numbered track signal 356 whose signal rising edge is synchronized with +3 ... Is generated (see FIG. 5B). Light spot 1
When 01 scans an even-numbered track, information is recorded at the positions of grid points q + 2, q + 4 ... In the data recording area 14. At this time, the track identification result signal 202 becomes "0", and the selector 357 selects the even clock signal 355 and outputs it as the recording / reproducing clock signal 358. Since the latch circuit 353 latches the input 352 at the same time when the recording / reproducing clock signal 358 rises, the lattice points q + 2, q + 4 ... Included in the comparison result 352.
... The position data can be collected and the result is latched.
Output as 9.

On the other hand, when the light spot 101 scans an odd numbered track, information is recorded at the positions of the grid points q + 1, q + 3 ... In the data recording area 14. At this time, the track identification result signal 202 becomes "1", and the selector 357 selects the odd track signal 356 and outputs it as the recording / reproducing clock signal 358. Since the latch circuit 353 latches the input 352 at the same time when the recording / reproducing clock signal 358 rises, the comparison result 35
The data of the grid points q + 1, q + 3 ... Positions included in 2 can be sampled, and the result is output as the latch result 359. The latch result 359 obtained as described above is used as the demodulation circuit 36 for demodulating data based on the coding rule at the time of recording.
It is demodulated at 0, and data 117 is obtained. Demodulation circuit 36
0 operates when the recording area gate signal 363 is at level H.

As described above, in this reference example, crosstalk and intersymbol interference can be eliminated by using one laser beam. Moreover, the two-dimensional equalization circuit 114 is an equalization circuit having a simple configuration in which two transversal filters are arranged in series, and further, the equalization coefficient calculation circuit 20 shown in FIG.
As described with reference to 6, since the equalization coefficient can be calculated by a simple arithmetic circuit, it takes a shorter time than the case where the equalization coefficient is obtained by using the conventional least square error method, and the random access can be performed at high speed. It becomes possible to do.

According to the prior art disclosed in the above-mentioned Japanese Patent Laid-Open No. 2-257474, there are the following problems.

(1) One light spot is enough, but at least 2
Since it is necessary to temporarily store the information of one track in the memory, in order to reduce crosstalk and intersymbol interference from adjacent tracks, the playback signal can be obtained only after at least two revolutions of the disk. .

(2) Since the least-squares error method, which is generally widely used, is applied as an adaptive algorithm for adaptively obtaining the equalization coefficient when a variation factor occurs, the optimum equalization coefficient is determined. It takes hundreds of milliseconds to discover, high-speed random access cannot be realized, and if there is asymmetrical aberration (coma aberration) of the lens system or warp of the disk, the effect cannot be eliminated.

Further, the conventional technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 5-205280 has the following problems.

(3) Although the amount of crosstalk from adjacent tracks can be detected using the learning mark, intersymbol interference on the target track cannot be detected.

However, the method of this reference example does not have such a problem.

Reference Example 2 In this reference example, the equalization coefficient is not detected by using the equalization coefficient learning area in each sector of each track as in Reference Example 1, but is shared by a plurality of tracks. Detect equalization coefficients using multiple equalization coefficient learning tracks for use.

That is, as shown in FIG. 11A, a data storage track area 502 is formed on the optical recording medium 100.
a, 502b, 502c and equalization coefficient learning track areas 501a, 501b, 501 for learning the equalization coefficient.
c is provided. Equalization coefficient learning tracks 501a, 501
b and 501c are data recording track areas 502, respectively.
a, 502b, 502c and provided outside the track areas thereof, and used when recording data in and reproducing data from the data recording track areas 502a, 502b, 502c, respectively. . As a result, each sector of the recording medium 100 includes an area 15 used for equalization coefficient learning or data recording as shown in FIG. 11B, and the equalization coefficient shown in FIG. The learning area 14 does not exist.

A track area for equalization coefficient learning, for example,
501b is composed of a fixed number of tracks, and from the first type lattice point p + 2 next to the first type lattice point p at the tip of the area 15 for learning the equalization coefficient of each sector of the center track or for data recording. Learning mark 1 before the end of the sector
58 are recorded at regular intervals. This interval is selected so that interference between adjacent learning marks can be ignored. In this reference example, this interval is a distance between 6 lattice points. These learning marks are not recorded on other tracks in the equalization coefficient learning track area. These other tracks are dummy tracks for the learning mark 158 so that crosstalk from the data recording track in the vicinity to the center track can be ignored. In this reference example, each equalization coefficient learning track area has a total of four dummy tracks.

These learning marks are recorded on all the equalization coefficient learning track areas before the information marks are recorded. For this purpose, the light spot positioning circuit 110 shown in FIG. It is configured to position on one central track of 501c. Further, the learning mark generation circuit 203 in the equalization coefficient learning circuit 121 shown in FIG. 7 is configured to record a series of learning marks 158 on its track, as shown in FIG. 11B. . In this reference example, the lattice points for recording the learning marks are the same for all equalization coefficient learning track areas. Therefore, this learning mark generation circuit 203
It does not respond to the identification result of the odd-even track identification circuit 201 of FIG. Such recording of learning marks is repeated for all other equalization coefficient learning track areas.

When the recording of the equalization coefficient learning mark 158 is completed, the equalization coefficient learning mark 158 is reproduced on the spot 101 to learn the equalization coefficient.

The writing of the equalization coefficient learning mark 158 for each data track area is carried out together with the initialization work when an unrecorded disc is inserted. The learning of the equalization coefficient is performed before reading the data when the disc is inserted.

Unlike the first reference example, a plurality of learning marks are recorded in each sector of the center track of one of the equalization coefficient learning track areas in the present reference example.
The leak amount detection circuits 241 and 242 shown in FIG. 2 are configured to detect the leak amounts d and e as follows. That is, the learning mark 158 is recorded on each of the sectors on the same track.
Seed grid points (i, p + 2), (i, p + 8), (i, p +
14) ,, The digital difference signals 113 for, are averaged to calculate an averaged grid point signal M ′ (i, p + 2). Furthermore, the second kind lattice points (i, p + 3), (i, p + 9), (i, p + 1) immediately after those first kind lattice points.
5) ,, The digital difference signals 113 for are averaged to calculate an averaged grid point signal M ′ (i, p + 3).
The leak amount detection circuit 241 detects the signal M ′ (i, p + 2).
And the signal M '(i, s + 3) ratio M' ((i, p + 3) /
M ′ (i, p + 2)) is calculated, and the leak amount for the sector is obtained. This calculation is performed for all sectors, and the average of the leak amounts obtained for each sector is obtained as the leak amount d of the equalization coefficient learning track area.

Similarly, the second-type lattice points (i, p + 1) and (i, p +) immediately preceding those first-type lattice points of each sector.
7), (i, p + 13) ,, and the averaged digital difference signal 113 for the averaged grid point signal M ′ (i, p
Calculate +1). The leak amount detection circuit 242 calculates the ratio M ′ of the signal M ′ (i, p + 1) and the signal M ′ (i, p + 2).
((I, p + 1) / M '(i, p + 2)) is obtained as the leak amount of the sector. After that, the average of the leak amounts obtained for all the sectors is obtained as the leak amount e of the equalization coefficient learning track area.

Leakage amounts d and e thus obtained
Therefore, the equalization coefficient can be calculated by the same method as in Reference Example 1. The learning of the equalization coefficient is performed by learning each equalization coefficient learning track 501a.
~ 501c, and stores the obtained equalization coefficient corresponding to each equalization coefficient learning track area. Information recording / reproduction is performed after the above-described learning of the equalization coefficient is completed. When accessing a track in any of the data track areas for data reproduction, the equalization coefficient calculated for the equalization coefficient learning track area corresponding to the data track area is used. In the method of Reference Example 2, since the learning mark is not recorded on each track, the equalization coefficient learning area can be reduced, and the data recording density can be improved accordingly.

<Modifications of Reference Examples 1 and 2> (1) Instead of the formula (6) used in Reference Example 1, (6
When the equation (a) or the equation (6b) is used, the arithmetic circuits 248 to 250 and 254 to 258 in FIG. 8 are respectively calculated from the output signals of the leak amount detection circuits 241 and 242, and the equation (6a) or the equation (6b) is used. ) Equalization coefficients G1 to G shown in the equation
2 and the equalization coefficient Y and Z0 to Z6 may be obtained. At this time, the equalization circuit 332 of FIG. 10 may be configured by a 3-tap transversal filter or a 7-tap transversal filter, respectively. This technique can also be used in Reference Example 2.

(2) In Reference Examples 1 and 2, the light spot 10
When 1 detects the offset amount, the intensity of the reflected light at one grid point in the offset amount detection area 12 is detected and used as an offset. It is also possible to detect the light intensity and use the average value of the detection values at those grid points as the offset amount. With this method, the detection accuracy of the offset amount can be improved.

(3) In Reference Examples 1 and 2, a magneto-optical disk was used as the optical recording medium, but the optical information reproducing method according to the present invention may be any recording medium. For example, a write-once medium,
It may be a phase change medium or a ROM medium. Since the reproduction signal of the information mark is given by the total light amount signal in these media, the magneto-optical signal may be replaced with the total light amount signal in the optical information recording / reproducing apparatus described in Reference Example 1 or 2. The mark diameter of the ROM medium is slightly different from the values described in Reference Examples 1 and 2, and is defined as follows. FIG. 12 is a result of simulating the relationship between the standard modulation index 0-p and the mark diameter W of the ROM medium. From this graph, the mark diameter W is the light spot diameter Ws (≈
It can be seen that the maximum modulation degree is obtained for 55% for λ / NA). However, when the ROM medium is reproduced by the optical information recording / reproducing method according to the present invention, about 40% of the modulation degree of 0 to 100% is used for the crosstalk from the adjacent track, so that it is isolated. The modulation of the signal should be about 60%. Further, in order to secure the S / N of the isolated signal, it is necessary to set the modulation degree to about 40% or more. From this, the modulation factor of the isolated signal is 40%.
The mark diameter W is 25% to 40% of the light spot diameter Ws.

(4) In Reference Examples 1 and 2, the intermediate point used for detecting the leak amount and removing the crosstalk is located exactly at the center of two information recording grid points on the same track. This is desirable from the perspective of effective removal of crosstalk, but intermediate points slightly off center can also be used if desired. This also applies to some of the embodiments of the invention described above and other reference examples described later.

Reference Example 3 In Reference Examples 1 and 2, an optical modulation system for modulating the intensity of laser light to record information on an optical recording medium was adopted, but in this Reference Example, information by a magnetic field modulation system was used. Use records.

In the magnetic field modulation method, the information mark is recorded on the optical recording medium by modulating the magnetic field instead of modulating the intensity of the light beam. Therefore, in the present reference example, a circuit for driving a magnetic field and a coil for generating a magnetic field are added to the optical disk device of the reference example 1. FIG. 18 shows information recorded on the optical recording medium by the magnetic field modulation method in the device of Reference Example 1. The information mark recorded by the light modulation method is shown in FIG.
The information mark recorded by using the magnetic field modulation method has an arrow vane shape, although it has a substantially circular shape as shown in FIG.

Note that the present reference example is similarly applied to the case where the equalization coefficient learning track is provided and the equalization coefficient is obtained in advance before recording / reproducing as described in the second reference example. it can.

Instead of the magnetic field modulation method of this reference example, information recording by the optical magnetic field modulation method can be used. The optical magnetic field modulation method records an information mark on an optical recording medium by modulating the intensity of a light beam and the magnetic field in synchronization.

Reference Example 4 In the first embodiment, multi-value phase recording is performed in which the positional deviation between the position where the information mark is recorded and the information recording grid point is changed according to the information to be recorded. It was In the second embodiment, the multilevel recording is performed so that each information recording grid point has an information mark having a level depending on the information to be recorded and representing a signal capable of having a multilevel level. The same multi-valued phase recording as in the form 1 was performed. In this reference example, the multi-valued level recording of the second embodiment is performed, but when the multi-valued phase recording is not performed, the two-dimensional equalization circuit and the equalization coefficient learning circuit described in the reference example 1 are used in the second embodiment. It is used similarly to.

That is, the information mark recorded on each information recording grid point is changed according to the information to be recorded, but the recording position of the information mark is not displaced from the information recording grid point. To this end, unlike the second embodiment, the user data is divided into a plurality of 2-bit portions, and the strength of the applied magnetic field is changed according to the value of the 2-bit portions. That is, in FIG. 19, the relationship between the previous 2 bits and the multi-valued level when the latter 2 bits are “01” or “11” is used. Also in this reference example, the same two-dimensional equalization circuit and equalization coefficient learning circuit as described in the second embodiment are used to remove the crosstalk component from one adjacent track to the information mark. To do.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various design changes can be made without departing from the spirit of the present invention. Of course.

[0166]

According to the present invention, it is possible to accurately reproduce an information mark which represents multi-valued information and is recorded in a multi-valued phase.

Furthermore, according to the preferred embodiment of the present invention, it is possible to accurately reproduce the information mark that represents multi-valued information and is recorded with multi-valued phases and multi-valued levels.

According to another preferred embodiment of the present application,
By using a recording medium having a small number of recording layers, it is possible to accurately reproduce information marks recorded with multi-valued phases and multi-valued levels.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical information recording / reproducing apparatus as a reference example for explaining a technique used in some embodiments of the present invention.

2 is a diagram showing recorded information on an optical information recording medium used in the apparatus of FIG.

FIG. 3 is a diagram for explaining a leak amount in the device of FIG.

4 is a diagram showing a simulation result of a relationship between a mark pitch and an equalization residual in the apparatus of FIG.

5A is a diagram showing a schematic configuration of a data control circuit (116) used in the device of FIG. FIG. 5B is shown in FIG.
6 is a time chart of a plurality of clock signals used in the circuit of (a).

6 is a pretreatment circuit (112) used in the apparatus of FIG.
FIG.

FIG. 7 is an equalization coefficient learning circuit (1
21) is a schematic configuration diagram.

8 is an equalization coefficient calculation circuit (2
06) schematic configuration diagram.

9A is a schematic configuration diagram of a leak amount detection circuit (241) used in the circuit of FIG. 8B shows a leak amount detection circuit (24) included in the circuit of FIG. 8 and the circuit of FIG.
The time chart of the multiple signals used in 2).

FIG. 10 is a two-dimensional equivalent circuit (1
14) Schematic configuration diagram of FIG.

FIG. 11A is a diagram showing tracks of different types recorded on an optical information recording medium used in an optical information recording / reproducing apparatus as another reference example of the invention. (B) is shown in FIG.
The figure which shows the information recorded on the optical information recording medium of 1 (a).

FIG. 12 shows an RO as an optical information recording medium in the apparatus of FIG.
The figure which shows the simulation result of the relationship between a mark diameter and a modulation degree when M medium is used.

FIG. 13 is a diagram illustrating recording positions of a plurality of information marks recorded in a data storage area used in the optical information recording / reproducing device according to the present invention.

14 is a diagram showing a relationship between information to be recorded and a recording position of the information mark with respect to the information, in relation to the information mark shown in FIG.

FIG. 15A is a diagram showing a plurality of recordable information marks superimposed on various information recording grid points. (B)
FIG. 16 is a diagram showing waveforms of reproduction signals for a plurality of information marks recordable on one information recording grid point of FIG.
FIG. 16C is a diagram showing a signal obtained by differentiating the plurality of reproduction signals shown in FIG. 15B.

16 is a schematic block diagram of a circuit for recording a plurality of information marks shown in FIG.

17 is a schematic block diagram of a circuit for reproducing a plurality of information marks shown in FIG.

FIG. 18A is a diagram for explaining a plurality of information marks recorded by another optical information recording / reproducing device according to the present invention. FIG. 19B is a diagram showing waveforms of reproduction signals for a plurality of information marks recordable on one information recording grid point in FIG. 18A. 18C is a diagram showing a signal obtained by differentiating the plurality of reproduction signals shown in FIG. 18B.

19 is a diagram showing the relationship between the information to be recorded, the multi-valued level of the signal to be recorded on the information mark, and the recording position of the information mark in relation to the information mark shown in FIG. 18;

20 is a diagram showing an eye pattern for an information mark recorded in the relationship shown in FIG.

21A is a diagram showing a schematic structure of a multilevel recording medium used for recording the information mark shown in FIG. FIG. 21B is a diagram showing the relationship between the magnetic moment and the magnetic field of the magnetized regions formed in the two recording layers in the multilevel recording medium shown in FIG. 21C is a diagram showing the level of a reproduction signal for the external magnetic field applied to the multilevel recording medium shown in FIG. 21A and the recorded information.

FIG. 22 is a level of a signal reproduced from the first and second recording layers in the multilevel recording medium shown in FIG. 21A when an external magnetic field having no DC bias is applied to the multilevel recording medium. The figure which shows the relationship between a magnetic field and an external magnetic field.

FIG. 23 is a diagram showing the relationship between the external magnetic field applied to the multi-valued recording medium shown in FIG. 21A and the reproduction signals from the first and second recording layers in this recording medium.

FIG. 24 is a schematic block diagram of an information recording circuit for the multilevel recording medium shown in FIG.

FIG. 25 is a circuit diagram of the multi-level level generation circuit (71 in FIG.
0) is a schematic block diagram.

FIG. 26 is a timing chart of some signals used in the circuit of FIG. 24.

FIG. 27 is a timing chart of some other signals used in the circuit of FIG. 24.

FIG. 28 is a schematic block diagram of an information reproducing circuit for the multilevel recording medium shown in FIG.

FIG. 29 shows the levels of signals reproduced from the first and second recording layers in the multilevel recording medium shown in FIG. 21A when an external magnetic field having a DC bias is applied to the multilevel recording medium. The figure which shows the relationship with an external magnetic field.

[Explanation of symbols]

103 ... Total light amount signal, 104 ... Magneto-optical signal, 106 ... Clock signal, 107 ... Clock mark sample hold signal, 108, 109 ... Wobble mark sample hold signal, 111 ... Actuator control signal, 113
... Digital difference signal, 115 ... Equalized signal, 117 ...
User data, 118 ... Modulation data, 120 ... Recording pulse, 122 ... Learning mark recording signal, 150 ... Information recording grid point, 151, 152 ... Wobble mark, 153 ... Clock mark, 154, 155 ... Equalization coefficient learning mark 156 ... track, 157 ... information mark, 202 ...
Track identification result signal, 222 ... Sample level, 32
1 ... Crosstalk reduction signal, 501a-501c ... Equalization coefficient learning track, 502a-502c ... Data storage area, 550 ... Learning execution signal, 600 ... Reference recording mark,
610-614, 810-814 ... Zero cross points.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G11B 11/10 586 9296-5D G11B 11/10 586E (72) Inventor Hisaki Sugiyama Higashi Koikeku, Kokubunji, Tokyo 1-280, Central Research Laboratory, Hitachi, Ltd.

Claims (7)

[Claims] 1. A plurality of tracks, a predetermined information recording area on each of a plurality of tracks of at least a part of the plurality of tracks, and a plurality of information recording grid points provided in the information recording area. And a plurality of information marks recorded respectively corresponding to one of the plurality of information recording grid points, and each information mark is, with respect to the information recording grid point to which the information mark corresponds, Information recorded on an optical information recording medium having a predetermined shape which does not depend on the information to be recorded and which is recorded at a position having a positional deviation in the track direction depending on the information to be recorded. Is a method for optically reproducing data on a track by scanning an information recording area on any one track from which information is to be read out with one light spot, and performing the scanning on the one track. In the step of detecting the reproduction light supplied to the one optical spot by the optical information recording medium when the optical spot is scanning the information recording area, generating a reproduction signal, and detecting and generating the reproduction signal. The recording position of the information mark recorded corresponding to each of the plurality of information recording grid points in the information recording area is detected from the generated reproduction signal, and the position of each information recording grid point and its position are detected. An optical information reproducing method for decoding a positional deviation between the detected recording positions to generate a signal representing information recorded at each information recording grid point. 2. Each information mark is recorded at one corresponding information recording grid point among a plurality of information recording grid points on the plurality of tracks among a plurality of predetermined optical characteristics. Which has one optical characteristic selected depending on the information to be recorded, and the step of reproducing the recorded information is performed by detecting the recorded signal detected for each information recording grid point from the generated reproduction signal. The reproduction signal for the position is extracted as a reproduction signal for each information recording grid point, and the amplitude of the reproduction signal extracted for each information recording grid point is quantized using a plurality of quantization levels, Decoding a combination of the positional deviation detected for each of the information recording grid points and a signal obtained by quantizing the reproduction signal extracted for each of the information recording grid points by the quantization. And each information The optical information reproducing method according to claim 1, further comprising the step of generating a signal indicating the information recorded for recording lattice points. 3. A plurality of tracks, a predetermined information recording area on each of a plurality of tracks of at least a part of the plurality of tracks, and a plurality of information recording grid points provided in the information recording area. And a plurality of information marks recorded corresponding to at least some of the plurality of information recording grid points among the plurality of information recording grid points, and each information mark has a plurality of information marks. It is recorded at a position having a positional deviation in the track extending direction depending on the information to be recorded with respect to the corresponding information recording grid point, and further has a predetermined shape that does not depend on the information to be recorded. A device for optically reproducing information recorded on an optical information recording medium, which is irradiating one optical spot to an information recording area on any one track from which the information is to be read out. The optical information recording medium detects the reproduction light supplied to the one optical spot and outputs a reproduction signal, and the optical spot scans the information recording area,
An apparatus for driving the optical head relative to the optical information recording medium, and information recording from the reproduction signal output by the optical head when the optical spot is scanning the information recording area. A position detection circuit that detects the recording position of the information mark recorded corresponding to each of the plurality of information recording grid points in the area, and the position of each information recording grid point and each information recording grid point An optical information reproducing device having a circuit for decoding a positional deviation between the detected recording position and the detected recording position and generating a signal representing the information recorded at each information recording lattice point. 4. Each of the information marks has one optical characteristic selected among a plurality of predetermined optical characteristics depending on information to be recorded at an information recording grid point corresponding to the information mark. The circuit for reproducing the above-mentioned information has a characteristic and reproduces a reproduction signal corresponding to a recording position detected for each information recording grid point from the above-mentioned reproduction signal generated by the optical head. A circuit for extracting the reproduced signal for each point as the reproduction signal, a circuit for quantizing the amplitude of the reproduced signal extracted for each point using a plurality of quantization levels, and each information recording grid Each of the information recording grids is decoded by decoding the combination of the positional deviation detected for the point and the reproduction signal extracted for each information recording grid point and quantized by the quantization circuit. Recorded against points 4. The optical information reproducing apparatus according to claim 3, further comprising a decoding circuit that generates a signal representing the stored information. 5. A plurality of tracks, a plurality of predetermined information recording grid points in an information recording area in each of the plurality of tracks, and each corresponding to one of the plurality of information recording grid points. And a plurality of information marks that are recorded by each information mark, and each information mark has a positional deviation in the track direction depending on the information to be recorded at the corresponding information recording grid point with respect to the corresponding information recording grid point. An optical information recording medium having a predetermined shape which is recorded at a position where the information is recorded and which does not depend on the recorded information. 6. Each of the information marks has one optical characteristic selected among a plurality of predetermined optical characteristics depending on the information to be recorded at the information recording lattice point corresponding to each information mark. The optical information recording medium according to claim 5, which further has characteristics. 7. The plurality of tracks are formed on a magneto-optical recording medium, and the magneto-optical recording medium has a substrate and a plurality of recording layers laminated on the substrate. At least a first recording layer therein is formed of a magneto-optical recording film that changes to one of a plurality of mutually different magnetization states when an external magnetic field belonging to one of a plurality of different magnetic field ranges is applied, The other second recording layer of the recording layers changes to a specific magnetization state when an external magnetic field belonging to at least one other magnetic field range that does not overlap the plurality of magnetic field ranges is applied, and the first recording layer 7. The optical information recording medium according to claim 6, which is formed of a magneto-optical recording film having a magneto-optical characteristic different from that of the recording layer.