JPH1186375A - Magneto-optical recording and reproducing method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an amplitude margin at the time of a binary detection from being lowered by respectively detecting the leading edge and the trailing edge of a magneto-optical reproduced signal to be generated while detecting the change of the plane of deflection of the reflected light of a reproduced light beam individually and binalizing them. SOLUTION: An envelope detecting circuit 19 determines a leading Ref. level and a trailing Ref. level for binalizing respective leading edge and trailing edge of a magneto-optical reproduced signal being the output of a differential amplifier by comparators 21, 23 so that the amplitude margin becomes maximum by detecting the maximum voltage of the pulsively rising part and the minimum voltager of the falling part of the magneto-optical reproduced signal. Thus, the leading edge and the trailing edge of the magneto-optical reproduced signal can be both subjected to a binary processing with the best amplitude margin and a correct reproduced signal is obtained with high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating a magneto-optical recording medium having a multilayer structure with a light beam, utilizing a temperature gradient of a temperature distribution, and without changing recording data on a recording layer. The present invention relates to a magneto-optical recording / reproducing method for reproducing a recording mark by detecting a change in a deflecting surface of reflected light of the light beam by moving a domain wall of the light beam, and a device therefor.

[0002]

2. Description of the Related Art As a rewritable high-density recording method,
There is a magneto-optical recording medium on which information is recorded by writing magnetic domains on a magnetic thin film using the heat energy of a semiconductor laser and reading this information using a magneto-optical effect. In recent years, there has been an increasing demand for a higher-capacity recording medium by further increasing the recording density of the magneto-optical recording medium. The linear recording density of an optical disk such as a magneto-optical recording medium greatly depends on the laser wavelength of a reproducing optical system and the numerical aperture of an objective lens. That is,
When the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the diameter of the beam waist is determined, so that the spatial frequency at the time of reproducing the recording mark is about 2NA / λ, which is a detectable limit. Therefore, in order to realize a higher density in a conventional optical disk, it is necessary to shorten the laser wavelength of the reproducing optical system and increase the NA of the objective lens. However, there is a limit to the improvement of the laser wavelength and the numerical aperture of the objective lens. For this reason, techniques for improving the recording density by devising the configuration of the recording medium and the reading method have been developed.

For example, Japanese Patent Application Laid-Open No. H06-290496 discloses a multi-layer recording medium having a reproducing layer and a recording holding layer which are magnetically coupled to each other. Using the temperature gradient caused by the irradiation of the beam, the magnetic domain wall of the recording mark of the reproducing layer is moved without changing the recording data of the recording holding layer, and the reproducing layer is adjusted so that a partial area of the light beam spot has the same magnetization. A signal reproducing method for magnetizing, detecting a change in the deflection surface of the reflected light of the light beam, and reproducing a recording mark below the optical diffraction limit;
And devices have been proposed. According to this method, as shown in FIG. 7, the reproduction signal becomes rectangular, and the recording mark having a period equal to or less than the optical diffraction limit is formed without reducing the reproduction signal amplitude depending on the optical resolution. Playable,
It is possible to provide a magneto-optical recording medium capable of greatly improving the recording density and the transfer speed, and a reproducing method thereof. According to FIG.
FIG. 7A shows the relationship of light beam irradiation at the time of reproduction, in which the state of the recording track of the recording medium, the irradiation range of the light beam, and the moving direction of the light beam are indicated by hatching. 3 shows a Ts isotherm indicating a Curie temperature region of the intermediate layer formed on the track, and a moving state of the domain wall of the domain wall moving layer which is a reproducing layer within the Ts isotherm. FIG. 7B is a cross-sectional view of the internal structure of the recording medium. The recording medium has a lowermost recording holding layer on the light beam irradiation surface, and the recording holding layer and the domain wall moving layer. An intermediate layer having a low Curie temperature for controlling the coupling and a domain wall displacement layer used during reproduction. In this record holding layer,
Recordable information is recorded in units of magnetic domains,
By raising the temperature of the intermediate layer and breaking the magnetic coupling between the recording holding layer and the domain wall motion layer, it is possible to reproduce the recorded information by moving the domain wall of the domain wall motion layer. FIG.
(C) shows the temperature state of the recording medium by the light beam, and the point of the highest temperature rises higher than the Curie temperature Ts of the intermediate layer. Further, the reproduction signal is a reproduction signal waveform when information recorded in the recording holding layer is read.

FIG. 5 shows the configuration of a magneto-optical recording / reproducing apparatus according to a conventional embodiment. In the drawing, reference numeral 1 designates a reproducing spot on a substrate 2 made of glass or plastic by using a temperature gradient caused by irradiation of a light beam to move a domain wall of a recording mark of a reproducing layer without changing recording data of the recording layer. A magneto-optical recording medium 3 capable of detecting a change in the deflection surface of the reflected light of the light beam, reproducing a recording mark below the optical diffraction limit, and further protecting the protective film. 4 is a magneto-optical disk on which No. 4 is formed. The magneto-optical disk 1 is supported by a spindle motor by magnet chucking or the like, and has a structure rotatable with respect to a rotating shaft. 5 to 13 irradiate the magneto-optical disk 1 with laser light,
FIG. 3 is a schematic view of individual components constituting an optical head for obtaining information from reflected light, 6 is a condenser lens, 5 is an actuator for driving the condenser lens 6, 7 is a semiconductor laser, 8 is a collimator lens, and 9 is The beam splitter 10 is λ /
Two plates, 11 are polarization beam splitters, 13 is a photo sensor, 12 is a condensing lens for the photo sensor 13, 14 is detected by the photo sensor 13, and differentially amplifies the signals condensed and detected depending on the deflection direction. It is a differential amplifier circuit.

In this configuration, the laser light emitted from the semiconductor laser 7 is applied to the magneto-optical disk 1 via a collimator lens 8, a beam splitter 9, and a condenser lens 6. At this time, the condenser lens 6 is moved in the focusing direction and the tracking direction by the control of the actuator 5 so that the laser light is controlled so as to sequentially focus on the magneto-optical recording medium 3. It is configured to track along the guide groove engraved on the surface. The optical path of the laser beam reflected by the magneto-optical disk 1 is changed by the beam splitter 9 in the direction of the polarization beam splitter 11, and the magnetization of the magneto-optical recording medium 3 is changed via the λ / 2 plate 10 and the polarization beam splitter 11. Depending on the polarity, the light is collected on the photosensor 13 by the condenser lens 12. The output of each photosensor 13 is differentially amplified by a differential amplifier 14 and outputs a magneto-optical signal.

An envelope detection circuit 19 detects the envelope of the magneto-optical reproduction signal and outputs a center value of the envelope. The low-pass filter 20 is a filter for filtering the output of the center value of the envelope to limit excessive following. This output value becomes a reference level for performing binarization. The reference level and the magneto-optical signal of the source signal are compared by the comparator 21 and binarized.

A controller 16 outputs a recording power, a recording signal, and the like using the rotation speed of the magneto-optical disk 1, recording radius, recording sector information, and the like as input information, and controls the LD driver 15, the magnetic head driver 18, and the like. Things. The LD driver 15 drives the semiconductor laser 7, and controls the desired recording power and reproducing power in the conventional example.

Reference numeral 17 denotes a magnetic head for applying a modulating magnetic field to a laser-irradiated portion of the magneto-optical disk during a recording operation. When recording, the semiconductor laser 7 is
The recording laser power is irradiated with DC light by the driver 15, and at the same time, the magnetic head 17 generates a magnetic field having a different polarity corresponding to the recording signal by the magnetic field modulation driver 18. The magnetic head 17 moves in the radial direction of the magneto-optical disk 1 in conjunction with the optical head, and at the time of recording, information is recorded by sequentially applying a magnetic field to the laser-irradiated portion of the magneto-optical recording medium 3. Has become.

The guide groove portion sandwiching the land portion of the recording area of the magneto-optical recording medium 3 is irradiated with high-power laser light, the recording medium in the guide groove portion is annealed at a high temperature, and the recording medium in the guide groove portion is irradiated. A process is performed in advance in which the layer is altered so that the domain wall forming the recording mark is not a closed loop, that is, a closed magnetic domain. As a result, the domain wall can be moved at a higher speed, and a stable reproduction signal can be obtained.

The recording / reproducing operation will be described with reference to FIG. In the figure, (a) is a recording signal, (b) is a recording power,
(C) is a modulation magnetic field, (d) is a recording mark sequence, (e) is a reproduced signal, and (f) is a reproduced binary signal. FIG.
When recording a recording signal as shown in (a), the laser power is set to a predetermined recording power as shown in (b) at the start of the recording operation, and a modulation magnetic field (c) based on the recording signal (a) is changed to a magnetic field. It is applied by the head 17. By these operations, a recording mark row (d) is formed in the process of cooling the recording medium. In FIG. 6D, hatched portions represent magnetic domains having a magnetization direction corresponding to the recording mark of this track, and shaded portions represent magnetic domains having the opposite magnetization direction.

The reproduction operation is the same as that described above.
This will be described with reference to FIG. (A) is a schematic diagram showing a magnetic domain reproduction state, (b) is a state diagram of a recording film, (c) is a temperature state diagram of a medium, and (d) is a reproduction signal. At the time of reproduction, as shown in (a), the light is irradiated to a Ts temperature condition at which the domain wall of the reproduction layer of the domain wall moving medium moves. (B)
In the temperature range lower than Ts, the intermediate layer shown in FIG. 3 is in a state of being coupled to the recording holding layer and the domain wall displacement layer by exchange coupling. When the medium is heated to a temperature equal to or higher than the Ts temperature by the irradiation of the light beam, the intermediate layer reaches the Curie point, and the coupling between the domain wall motion layer and the recording holding layer is broken. Therefore, at the same time when the domain wall of the recording mark reaches the Ts temperature region,
The domain wall of the domain wall displacement layer crosses the land at the position where the domain wall is stably present energetically with respect to the temperature gradient of the domain wall displacement layer, that is, the highest temperature point in the linear density direction of the temperature rise due to light beam irradiation. Moves instantaneously. As a result, since the magnetization state of most of the area covered by the reproduction light beam becomes the same, in the ordinary light beam reproduction principle,
Even with a small recording mark that cannot be reproduced, a reproduction signal in a state close to a rectangle as shown in the figure can be obtained.

Therefore, a reproduced signal (e) is obtained by reproducing a recording mark train as shown in FIG. 6 (d) with a light beam. By comparing the reproduced signal (e) obtained here with a predetermined reference level and binarizing it, a binary signal (f) can be obtained. The binarized signal (f) faithfully realizes the recording signal (a), and enables information reproduction. According to this method, most of the magnetized state covered by the light beam is the same, so that the reproduced signal is almost rectangular as shown in (e) in the figure, and the reproduced signal amplitude is hardly reduced. In addition, it is possible to reproduce a recording mark having a period equal to or less than the optical diffraction limit, and it is possible to provide a magneto-optical recording medium and a reproducing method capable of greatly improving a recording density and a transfer speed.

[0013]

However, in the above-mentioned conventional example, the reproduced signal waveform has a waveform as described below.
It has two features.

The first point will be described with reference to FIG. In the figure,
a) is a schematic diagram showing a magnetic domain reproduction state, b) is an intensity distribution of a light beam, c) is a state diagram of a recording film, d) is a temperature state diagram of a medium, and 1) to 3) are magneto-optics described below. Represents a signal. At the time of reproduction, as shown in FIG. 4, for the spot diameter of 1 / e ² , which is usually treated as a light spot diameter, the Ts isotherm generated by the temperature rise of the laser beam irradiation by the domain wall displacement layer is the spot diameter position. And the Ts isotherm is formed at a position closer to the center of the light beam spot according to the moving speed and the light beam intensity of the light beam and the optical disk.

Thus, the light beam intensity distribution b) in FIG.
In the space from the tip of the beam spot to the position where the domain wall of the domain wall motion layer starts to move, as indicated by the hatched portion, irrespective of the sudden change in deflection characteristics caused by the movement of the domain wall of the domain wall motion layer, The change in the deflection characteristic caused by the cross section of the light beam crossing the recording mark is superimposed. Therefore, in the reproduction signal, a sudden change in the deflection characteristic caused by the domain wall movement phenomenon and a normal change in the deflection characteristic caused by crossing the magnetic domain at the hatched portion of the light beam intensity distribution are generated. Therefore, as shown in the figure, a magneto-optical signal in which a rectangular magneto-optical signal (1) due to domain wall movement and a magneto-optical signal (2) due to a Gaussian beam end are superimposed on the reproduced signal (3) as shown in the figure. Becomes

The second point is a transmission / reproduction phenomenon of the recording holding layer. This phenomenon will be described with reference to FIG. This phenomenon is a phenomenon in which the reproduction light is transmitted through the domain wall motion layer and the intermediate layer in the drawing, and the reproduction signal due to the change in the deflection characteristic due to the magnetization of the recording holding layer is superimposed on the reproduction signal from the domain wall motion layer. . FIG. 9 shows an observed waveform in an actual apparatus.
In the figures describing the magnetization state of each magnetic layer in the figure,
The magnetization state of the domain wall displacement layer and the intermediate layer is only a state when the light beam after recording is not irradiated because the operation during the reproducing operation is complicated. Here, the deflection characteristic of the transmission / reproduction of the recording / retaining layer is opposite to the deflection characteristic of the domain wall displacement layer, and the signal superimposed by the transmission / reproduction of the recording / retention layer reduces the amplitude of the signal due to the domain wall displacement of the domain wall displacement layer. Is shown. However, the polarity of the deflection characteristic read from the recording holding layer largely depends on the film thickness and the optical characteristics of the domain wall motion layer and the intermediate layer, and is not limited to this.
In addition, in the transmission / reproduction phenomenon of the recording holding layer, the presence of a plurality of recording marks in the light beam causes intersymbol interference and lowers the amplitude of the superimposed signal as in the case of normal light beam reproduction. That is, the amplitude of the superimposed signal depends on the recording mark length.

In consideration of the two characteristics of the reproduced signal described above, the domain wall of the domain wall motion layer is moved by using the temperature gradient of the reproduced light beam, so that the deflection surface of the reflected light of the light beam can be moved. The reproduced signal by the magneto-optical recording / reproducing method capable of detecting the change and reproducing the recording mark below the optical diffraction limit is not only a reproduced signal due to the movement of the domain wall of the domain wall moving layer but also a domain wall from the light beam tip. A reproduction signal in a form in which a reproduction signal in the light beam space up to the movement start position and a reproduction signal in the transmission reproduction of the recording holding layer are superimposed.

FIG. 8 shows a reproduced signal when a recording mark sequence (2) is recorded based on the recording signal (1) and the recording mark sequence is reproduced. As described above,
The magneto-optical signal (3) due to the domain wall movement, the magneto-optical signal (4) due to the beam tip, the magneto-optical signal (5) due to transmission / reproduction through the recording holding layer, and the reproduction signal (6) in which these are superimposed are shown. It is. As a result, the reproduced signal (6) has a rectangular shape with a distortion. As shown in the enlarged view in the figure, when the reproduced signal (6) is binarized by comparing it with a predetermined reference level, a leading signal is generated by the superimposed signal for the reason described above.
g) At the edge, the reference level reduces the amplitude margin at the low level part from the high level part.On the other hand, at the trailing edge, the amplitude margin at the high level part is higher than the low level part. Decrease. Therefore, there is a problem that the amplitude margin at the time of binarization detection is reduced as a result.

[0019]

The problem of causing a decrease in the amplitude margin at the time of binarization detection is solved by the following method and apparatus.

According to the present invention, a reproducing light beam is irradiated to a magneto-optical recording medium having a multilayer structure such as a recording holding layer and a domain wall moving layer.
Using the temperature gradient of the temperature distribution due to the temperature characteristic of the medium with respect to the magnetic domain of the medium, the domain wall of the recording mark of the domain wall moving layer is moved without changing the recording data of the recording holding layer, and the reflected light of the reproduction light beam is deflected. In a magneto-optical recording / reproducing method for detecting a change in surface and reproducing the recording mark, a leading edge and a trailing edge of a magneto-optical reproduction signal generated by detecting a change in a deflection surface of the reflected light are individually set. A magneto-optical recording / reproducing method and apparatus characterized in that an edge is detected and binarized, and the binarization of a leading edge and a trailing edge of the magneto-optical reproducing signal is performed by using a leading edge of the magneto-optical reproducing signal. ,
Each trailing edge is binarized by comparing it with an individual reference level. Further, each reference level has a leading edge of the magneto-optical reproducing signal and an amplitude margin for detecting an edge of the trailing edge. A magneto-optical recording / reproducing method and apparatus for increasing the level.

Thus, the binarizing operation can be performed with the best amplitude margin at both the leading edge and the trailing edge of the magneto-optical reproduction signal, the error rate can be improved, and the recording density can be reduced. Can lead to improvement.

[0022]

FIG. 1 shows a configuration of a magneto-optical recording / reproducing apparatus according to a first embodiment of the present invention. In the figure, reference numeral 1 denotes a magneto-optical disk, which is formed on a substrate 2 made of glass or plastic by using a temperature gradient caused by light beam irradiation without changing the recording data of the recording layer. To detect the change in the deflection plane of the reflected light of the light beam,
This is a magneto-optical disk on which a magneto-optical recording medium 3 capable of reproducing a recording mark below the optical diffraction limit is adhered and a protective film 4 is further formed. The magneto-optical disk 1 is supported by a spindle motor by magnet chucking or the like, and has a structure rotatable with respect to a rotating shaft. 5 to 13 irradiate the magneto-optical disk 1 with laser light,
Further, individual parts constituting an optical head for obtaining information from the reflected light, 6 is a condenser lens which is an objective lens for forming a spot on the magneto-optical disk, 5 is an actuator for driving the condenser lens 6, and 7 is a laser A semiconductor laser 8 for generating light, 8 a collimator lens for converting divergent light from the semiconductor laser 7 into parallel light, 9 a beam splitter for splitting light by a phase difference of light, 10 a λ / 2 wavelength for delaying the phase of light The plate, 11 is a polarization beam splitter for splitting light according to the phase difference of light, 13 is a photo sensor, and 12 is a condenser lens for condensing light to the photo sensor. Reference numeral 14 denotes a differential amplifier circuit that differentially amplifies signals collected and detected by the photosensor 13 in accordance with the direction of deflection.

The laser light emitted from the semiconductor laser 7 is applied as spot light to the magneto-optical disk 1 via a collimator lens 8, a beam splitter 9, and a condenser lens 6. At this time, the condenser lens 6 is moved in the focusing direction and the tracking direction by the control of the actuator 5, so that the laser beam is controlled so as to sequentially focus on a predetermined track on the magneto-optical recording medium 3, and
The tracking is performed along a guide groove formed on the magneto-optical disk 1. The optical path of the laser beam reflected by the magneto-optical disk 1 is changed by the beam splitter 9 in the direction of the polarization beam splitter 11, and the magnetization of the magneto-optical recording medium 3 passes through the λ / 2 wavelength plate 10 and the polarization beam splitter 11. Depending on the polarity of the photo sensor 1
3 is collected by the condenser lens 12. The output of each photosensor 13 is differentially amplified by a differential amplifier 14 and outputs a magneto-optical signal.

The envelope detection circuit 19 detects the envelope of the magneto-optical reproduction signal, and outputs a desired reference level for a leading edge and a reference level for a desired trailing edge based on the detected signal. The reference level for the leading edge is
The envelope of the maximum voltage at the pulse-like rising portion of the magneto-optical reproduction signal is detected, and for example, a simple diode detection method or a detection circuit using a sample and hold circuit is used. The trailing edge reference level detects the envelope of the lowest voltage at the pulse-like falling portion of the magneto-optical reproduction signal, and a detection circuit using a diode detection method or a sample-and-hold circuit is similarly used.

The low-pass filters 20 and 22 are low-pass filters (LP.L. and L.P.) that cut high-frequency components for limiting excessive amplitude tracking at the respective reference levels for the leading edge and the trailing edge.
F). Each output value after filtering is a leading edge and a trailing edge, respectively.
It becomes a reference level (reference potential) for performing value conversion. The comparators 21 and 23 compare the leading edge reference level and the magneto-optical signal output from the differential amplifier 14 with the trailing edge reference level and the magneto-optical signal, respectively, and binarize according to the difference. This is a comparison circuit. Note that the signal after the binarization of the trailing edge has a polarity of the binary signal such that the trailing edge corresponds to the rising edge of the binarized signal due to a binarized signal combining circuit described later. . The binarized signal synthesizing circuit 24 is a logic circuit including a flip-flop for synthesizing a leading edge, a trailing edge, and each detected edge individually detected. The leading edge corresponds to the rising edge of the binarized signal, and the trailing edge corresponds to the falling edge of the binarized signal.

The controller 16 outputs a recording power, a recording signal, and the like by using the number of rotations of the magneto-optical disk 1, recording radius, recording sector information, and the like as input information, and controls the LD driver 15, the magnetic head driver 18, and the like. Things. The LD driver 15 drives the semiconductor laser 7, and in this embodiment, controls desired recording power and reproducing power.

Reference numeral 17 denotes a magnetic head for applying a modulating magnetic field to a laser-irradiated portion of the magneto-optical disk 1 during a recording operation. During recording, the semiconductor laser 7 is set to L
The D driver 15 irradiates the recording laser power with DC light, and at the same time, the magnetic head 17 generates magnetic fields having different polarities corresponding to the recording signals by the magnetic field modulation driver 18. The magnetic head 17 moves in the radial direction of the magneto-optical disk 1 in conjunction with the optical head, and records information by sequentially applying a magnetic field to a laser-irradiated portion of the magneto-optical recording medium 3 during recording. ing.

The guide groove portion sandwiching the land portion of the recording area of the magneto-optical recording medium 3 is irradiated with high-power laser light, the recording medium in the guide groove portion is annealed at a high temperature, and the recording medium layer in the guide groove portion is irradiated. Are preliminarily processed so that the domain wall forming the recording mark is not a closed loop, that is, a closed magnetic domain. As a result, the domain wall can be moved at a higher speed, and a stable reproduction signal can be obtained. In this embodiment, the recording method is described as a magnetic field modulation recording method. However, the present invention is not limited to this, and there is no particular problem in light modulation recording and pulse assist magnetic field modulation recording.

The principle of operation of the present invention will be described with reference to FIGS. In FIG. 3, when recording a recording signal as shown in (1), the laser power is set to a predetermined recording power at the start of the recording operation, and a modulation magnetic field based on the recording signal is applied by the magnetic head 17. By these operations, a recording mark array (2) is formed in the process of cooling the recording medium from the high temperature to the atmospheric temperature by the light beam irradiation. The hatched portion of the recording mark row (2) indicates a magnetic domain having a magnetization direction corresponding to the main recording mark, and the hatched portion indicates a magnetic domain having a magnetization direction opposite to this.

The principle of the reproducing operation for reproducing the recorded marks will be described with reference to FIG. In the figure, (a) is a schematic diagram showing a magnetic domain reproduction state of a reproduction layer magnetic domain pattern, (b) is an intensity distribution of a light beam by a condenser lens 6, and (c) is a recording holding layer recording a record mark sequence. , A state diagram of a recording film comprising an intermediate layer and a domain wall displacement layer, FIG. 4D shows a temperature diagram of a magneto-optical recording medium, and FIGS. 3A to 3C show magneto-optical signals described below.

At the time of reproduction, as shown in (a), the medium is heated to the Ts temperature condition at which the domain wall of the reproduction layer of the domain wall moving medium moves by the light beam irradiation. In the temperature range lower than Ts, the intermediate layer shown in (b) is in a state of being coupled to the recording holding layer and the domain wall displacement layer by exchange coupling. When the medium is heated to a temperature equal to or higher than the Ts temperature by the irradiation of the light beam, the intermediate layer reaches the Curie point, and the coupling between the domain wall motion layer and the recording holding layer is broken. Therefore, at the same time when the domain wall of the recording mark reaches the Ts temperature region, the domain wall of the domain wall displacement layer is stably positioned in terms of energy with respect to the temperature gradient of the domain wall displacement layer, that is, by the light beam irradiation. The domain wall instantaneously moves across the land at the highest temperature point in the linear density direction of the temperature rise. As a result, the magnetization state of most of the area covered by the reproduction light beam becomes the same. Therefore, according to the normal light beam reproduction principle, even a small recording mark that cannot be reproduced is rectangular as shown in the figure. A reproduced signal in a state close to the above can be obtained. Due to this phenomenon, a change in the magneto-optical signal as shown in (1) in FIG. 4 or (3) in FIG. 3 appears.

Further, as shown in FIG. 4A, for a spot diameter of 1 / e ^{2 which} is usually treated as a light spot diameter, a Ts isotherm generated by the temperature rise of the laser beam irradiation when the domain wall motion layer is raised. Does not coincide with the spot diameter position, and the Ts isotherm is formed at a position closer to the center of the light beam spot according to the moving speed and light beam intensity of the light beam and the optical disk. For this reason, in the space from the beam spot tip to the position where the domain wall of the domain wall motion layer starts to move, which is indicated by the hatched portion of the light intensity distribution (b) in FIG. Irrespective of the change in the deflection characteristic, there is a change in the deflection characteristic due to the oblique line portion of the light beam crossing the recording mark. As a result, a change in the magneto-optical signal as shown in (2) in FIG. 4 or (4) in FIG. 3 appears.

Further, as a change in the magneto-optical signal, there is a transmission / reproduction phenomenon of the recording / retaining layer. This phenomenon will be described with reference to FIG. This phenomenon occurs because the recording mark train (1) passes through the domain wall displacement layer and the intermediate layer (2) in the figure,
This is because the reproduction light reaches the recording holding layer, and a magneto-optical signal changes due to a change in magnetization of the recording holding layer. Here, the deflection characteristic of the transmission / reproduction of the recording / retaining layer is opposite to the deflection characteristic of the domain wall displacement layer, and the signal (3) superimposed by the transmission / reproduction of the recording / retention layer changes the amplitude of the signal due to the domain wall displacement of the domain displacement layer. The case where it acts so as to reduce it is shown.
As a result, the detection waveform of the reproduced signal read as the magneto-optical signal shown in (4) can be detected. However, the polarity of the deflection characteristic read from the recording holding layer largely depends on the film thickness and the optical characteristics of the domain wall motion layer and the intermediate layer, and is not limited to this. Further, in the transmission / reproduction phenomenon of the recording holding layer, the presence of a plurality of recording marks in the light beam causes intersymbol interference and lowers the amplitude as in the normal light beam reproduction. That is, the amplitude of the magneto-optical signal depends on the recording mark length. As a result, a change in the magneto-optical signal as shown in (5) in FIG. 3 appears.

As described above, by moving the domain wall of the domain wall displacement layer using the temperature gradient of the reproduction light beam, a change in the deflection plane of the reflected light of the light beam is detected, and the change is less than the light diffraction limit. As shown in FIG. 3, a reproduction signal by the magneto-optical recording / reproducing method capable of reproducing even the recording mark of FIG.
In addition to (3), a magneto-optical signal (4) at the front end of the light beam from the front end of the light beam to the domain wall movement start position and a magneto-optical signal (5) obtained by transmission / reproduction through the recording holding layer are superimposed ( A magneto-optical signal as shown in 6) is a reproduced signal obtained from the detection system.

In the present invention, when binarizing a reproduction signal having the above-mentioned characteristics, the leading edge of the reproduction signal by reproducing the leading end of the recording mark (2) in FIG. It is characterized in that the trailing edge of the reproduced signal by reproducing the trailing edge of the mark is individually detected. As shown in the enlarged view of the reproduced signal read as the magneto-optical signal in FIG. 3 (6), in the leading edge portion which is a read signal at the leading end of the recording mark, an amplitude margin is generated when binarizing the leading edge portion. The binarized reference level is determined so as to be the maximum, and the reference level is determined to be a value that maximizes the amplitude margin. In this case, the magnitude relationship between the reference level and the reproduced signal is compared by the comparator 21 and binarized.

Similarly, at the trailing edge portion which is a reproduction / read signal at the rear end of the recording mark,
At the time of binarization at the trailing edge portion, a binarization reference level is determined so that the amplitude margin is maximized, and the magnitude relationship between the reference level and the reproduction signal is compared by the comparator 23, and 0 or 1 is determined. The binarization of the judgment is performed.

The reference levels for detection of the leading edge and the trailing edge are set at a ratio to the peak value and the bottom value of the envelope detection circuit shown in FIG. 1 to reduce the low-frequency fluctuation that can be detected by the envelope detection circuit. The reference level can be made to follow.

The recording / reproducing operation will be further described with reference to FIG. In the figure, (a) is a recording signal, (b) is recording power, (c) is a modulation magnetic field, (d) is a recording mark,
(E) is a reproduction signal. (F) is a binarized signal binarized by the leading edge detection reference level, (g) is a binarized signal binarized by the trailing edge detection reference level, and (h).
Is a binarized signal obtained by extracting and combining a leading edge and a trailing edge.

When a recording signal as shown in FIG. 2A is recorded, the laser power is set to a predetermined recording power as shown in FIG. 2B when the recording operation is started, and at the same time, a modulation magnetic field based on the recording signal (a) is used. (C) is applied. By these operations, a recording mark row (d) is formed in the process of cooling the recording medium. The hatched portions represent magnetic domains having the direction of magnetization corresponding to the main recording mark row, and the hatched portions represent magnetic domains having the opposite direction of magnetization.

In FIG. 2, a reproduced signal (e) is obtained by reproducing a recording mark train as shown in FIG. 2D with a light beam. The reproduced signal (e) is an output signal of the differential amplifier 14 in FIG. 1 and, as described above, a magneto-optical signal due to the movement of the domain wall of the domain wall moving layer, and a light beam space from the front end of the light beam to the domain wall movement start position. , And a magneto-optical signal superimposed by a magneto-optical signal generated by transmission / reproduction through the recording and holding layer.

Here, as described above, the leading edge of the reproduced signal corresponding to the leading end of the recording mark and the trailing edge of the reproduced signal corresponding to the trailing end of the recording mark are individually amplitude-controlled by utilizing the characteristics of the reproduced signal. The reference level is selected by the envelope detector 19 so as to maximize the margin, and each reference level is compared with the magneto-optical signal to be binarized. FIG. 2 (f) shows a signal binarized by the leading edge and its reference level, and FIG. 2 (g) shows a signal binarized by the trailing edge and its reference level. In addition,
The binarized signal (g) has a polarity such that the binarized signal rises at the trailing edge for the sake of the subsequent processing. Here, the edges necessary for the binarized signals (f) and (g) are rising portions as shown by the solid lines in the figure, and thus are input to the binarized signal synthesizing circuit 24 to select them. . The binarized signal synthesizing circuit 24 resynthesizes the binarized signal with the leading edge corresponding to the rising edge and the trailing edge corresponding to the falling edge. This binarized signal (h) is then converted to a PLL signal, data separation processing,
Decoding processing and the like are performed. The binarized signal (h) faithfully reproduces the recording signal (a), and enables accurate information reproduction. Since the binarized signal (h) reproduces a waveform corresponding to the length of the recording mark in the track direction,
By detecting the recording mark length as well as recording / reproducing a digital signal, not only recording of analog data but also a reproduced signal thereof can be utilized as an analog reproduced signal.

According to this method, the amplitude margin at the time of binarization can be increased for the reproduction signal characteristic of the domain wall displacement type magneto-optical reproduction method, and the recording density and the transfer speed can be improved. A recording medium and a recording / reproducing method can be used.

According to the magneto-optical recording / reproducing method according to the above embodiment, the reference level (reference voltage) for converting the rising waveform of the leading edge of the reproduction signal waveform and the falling waveform of the trailing edge into a binary signal. ) To maximize the amplitude margin for each decision, so that there is a characteristic margin and degree of freedom for controlling the optical output level of the semiconductor laser and controlling the actuator that controls the condenser lens. And a margin can be given to the control system of the entire magneto-optical recording / reproducing apparatus.

[0044]

According to the present invention, a magneto-optical recording medium having a multilayer structure, such as a recording holding layer and a domain wall displacement layer, is irradiated with a reproducing light beam, and a temperature gradient of a temperature distribution due to a temperature characteristic of the medium with respect to magnetic domains of the medium. And reproducing the recording mark by moving the domain wall of the recording mark of the domain wall moving layer without changing the recording data of the recording holding layer, detecting a change in the deflection surface of the reflected light of the reproduction light beam. In the magneto-optical recording / reproducing method, both the leading edge and the trailing edge of the magneto-optical reproducing signal have the best amplitude margin.
It is possible to carry out a value conversion process, and it is possible to improve the reliability of an accurate reproduced signal and to improve the error rate. Further, it is possible to further improve the recording density of the magneto-optical recording medium.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the embodiment of the present invention.

FIG. 3 is a timing chart showing the operation of the embodiment of the present invention.

FIG. 4 is a diagram illustrating an operation principle according to a recording mark reproducing method of the present invention.

FIG. 5 is a configuration diagram of a conventional example.

FIG. 6 is a timing chart showing the operation of the conventional example.

FIG. 7 is an operation principle diagram on which the present invention is based.

FIG. 8 is a timing chart showing the operation of the conventional example.

FIG. 9 is an operation principle diagram on which the present invention is based.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magneto-optical disk 2 Substrate 3 Magneto-optical recording medium 4 Protective layer 5 Actuator 6 Condensing lens 7 Semiconductor laser 8 Collimator lens 9 Optical beam splitter 10 λ / 2 wavelength plate 11 Deflection beam splitter 16 Controller 17 Magnetic head 19 Envelope detection circuit 20 , 22 Low-pass filter 21, 23 Comparator 24 Binary signal synthesizing unit

Claims (6)

[Claims] 1. A reproducing light beam is irradiated to a magneto-optical recording medium having a multilayer structure such as a recording holding layer and a domain wall moving layer, and a temperature gradient of a temperature distribution of a magnetic domain of the recording medium due to a temperature characteristic of the recording medium is used. Then, the domain wall of the recording mark of the domain wall displacement layer is moved without changing the recording data of the recording protection layer, and the change of the deflection surface of the reflected light of the reproduction light beam is detected to reproduce the recording mark. In the magneto-optical recording / reproducing method, a leading edge and a trailing edge of a magneto-optical reproducing signal generated by detecting a change in a deflection surface of the reflected light are detected by using respective edge detecting means. Magneto-optical recording and reproducing method. 2. The apparatus according to claim 1, wherein said edge detecting means performs binarization by comparing each of a leading edge and a trailing edge of the magneto-optical reproduction signal with an individual reference level. The magneto-optical recording / reproducing method according to the above. 3. The reference level according to claim 2, wherein each of the reference levels is determined such that an amplitude margin of edge detection of a leading edge and a trailing edge of the magneto-optical reproduction signal is maximized. Magneto-optical recording and reproducing method. 4. A magneto-optical recording medium having a multilayer structure such as a recording holding layer and a domain wall moving layer is irradiated with a reproducing light beam, and a temperature gradient of a temperature distribution of a magnetic domain of the recording medium with respect to a magnetic domain is used. Magneto-optical recording for reproducing the recording mark by moving the domain wall of the recording mark of the domain wall moving layer without changing the recording data of the recording holding layer and detecting a change in the deflection surface of the reflected light of the reproduction light beam. A magneto-optical recording / reproducing apparatus comprising: a reproducing apparatus comprising: an edge detecting unit configured to detect a leading edge and a trailing edge of a magneto-optical reproducing signal generated by detecting a change in a deflection surface of the reflected light; apparatus. 5. An edge detecting means for detecting a leading edge and a trailing edge of the magneto-optical reproduction signal, by comparing each of the leading edge and the trailing edge of the magneto-optical reproduction signal with a predetermined reference level. 5. The magneto-optical recording / reproducing apparatus according to claim 4, wherein said magneto-optical recording / reproducing apparatus is a binarizing means for binarizing. 6. The reference level of a binarizing means for comparing each of a leading edge and a trailing edge of the magneto-optical reproduction signal with the reference level and binarizing the reference level is an amplitude of each edge detection. 6. The magneto-optical recording / reproducing apparatus according to claim 5, wherein the level is set such that a margin is maximized.