JP2000315340A - Signal recording/reproducing device and signal recording /reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To desirably reproduce a signal recorded in high density by making the diameter vertical to a recording track of a optical spot at the time of reproducing smaller than that at the time of recording. SOLUTION: A laser beam for reproducing or a laser beam for recording emitted from a semiconductor laser 2 is made incident to a collimetor lens 3, is made to be parallel luminous flux by the collimeter lens 3 and is made incident to a LCD panel 4. The LCD panel 4 is a spot shape changing-over means which changes over the size of the diameter vertical to the recording track of the optical spot on a magneto-optical disk 100 through the beam shaping of the laser beam. At the time of reproducing, the drive of the LCD panel 4 is controlled, the size of the diameter of the optical spot is changed over and, thereby, the reading of information signals, that is, the detection of movement of domain walls is performed by the optical spot having a diameter in a track transverse direction which is made to be smaller than that in the track transverse direction of the optical spot at the time of recording.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic domain wall type magneto-optical information recording medium which is irradiated with a laser beam to expand a magnetic domain by domain wall motion to reproduce a signal. The present invention relates to a signal recording / reproducing apparatus and a signal recording / reproducing method for recording a signal by irradiating a recording laser beam thereto and applying a magnetic field.

[0002]

2. Description of the Related Art In recent years, a magneto-optical disk has attracted attention as a high-density recording medium on which information signals can be rewritten. For example, Japanese Patent Application Laid-Open No. 6-290496 (hereinafter referred to as Document 1) discloses that a magneto-optical disk having at least three layers of a moving layer, a switching layer, and a memory layer is used as a magnetic layer. A magneto-optical reproducing system utilizing the fact that the size of a recorded magnetic domain is substantially expanded in a moving layer is disclosed. The magneto-optical reproducing method disclosed in Document 1 is based on a DWDD (Domain Wall Displacement Dete
When the information signal is reproduced, the reproduction layer is irradiated with a laser beam for reproduction, and the magnetic coupling between the memory layer and the moving layer corresponding to the region where the Curie temperature or higher in the switching layer is reached is obtained. By being cut, the magnetic domain wall that moves in the region of the moving layer corresponding to the region where the magnetic coupling has been cut is detected, whereby the size of the magnetic domain recorded in the memory layer is substantially reduced. In the moving layer, the reproduction carrier signal is enlarged.

[0003] The above-described magneto-optical reproducing method based on DWDD (hereinafter, referred to as DWDD reproducing method) will be described in detail. The above-described magneto-optical disk formed by adopting the DWDD reproducing method is composed of three magnetic layers of a moving layer 101, a switching layer 102 and a memory layer 103, as shown in FIG. I have. Then, the memory layer 103, a positive reverse spin with different magnetization directions (in FIG. 8 (a) an arrow M ₁ direction during) a, the data of the data length and the length of the magnetic domain is recorded.
Then, the magnetic domain 104 and the magnetic domain 10 whose magnetization directions are different from each other.
The boundary with 4 is the domain wall 105. The direction of arrow R in FIG. 8A indicates the medium rotation direction.

When the reproducing laser beam BM is irradiated, the magneto-optical disk 100 is locally heated, so that a temperature distribution is generated as shown in FIG. Here, the temperature T
s is the Curie temperature of the switching layer 102, and the magnetism disappears in a region in the switching layer 102 where the temperature is higher than the temperature Ts. Thus, the switching layer 10
By extinguishing the magnetism in 2, the exchange coupling force between the memory layer 101 and the region A where the magnetism has disappeared is cut off. Accordingly, the moving layer 10 having a small domain wall coercive force
1 (the region of the moving layer 101 corresponding to the region A) moves alone to the high temperature side (moves in the direction of arrow B in FIG. 8A). Such movement of the domain wall is caused by the memory layer 1
The domain wall of the moving layer 101 existing as an interval corresponding to the recording mark of 03 is generated each time the domain wall reaches the isothermal line of the temperature Ts as the magneto-optical disk 100 scans. By detecting the movement of the domain wall, the magneto-optical disk 100 reproduces the recorded data recorded in the memory layer 103 in a substantially enlarged manner. The movement of the domain wall to the high temperature side as described above reaches the vicinity of the highest temperature portion, but the highest temperature portion occurs, for example, at a rear position in the light spot.

In the DWDD reproducing method, a very large signal can be reproduced even from a minute recording magnetic domain having a period equal to or less than the optical limit resolution of the reproducing laser beam. One of the most effective reproduction methods that can achieve high density without changing the numerical aperture (NA) of the
One. That is, according to the DWDD reproduction method, it is possible to greatly improve the recording density in the light spot scanning direction.

On the other hand, there are mainly two types of recording methods, optical modulation and magnetic field modulation. The recording method of magnetic field modulation allows recording with a small recording mark and increases the data capacity. it can.

In the magnetic field modulation recording method, a recording laser beam having an output level larger than that at the time of reproduction is applied to the magneto-optical disk 10.
Then, the recording mark is recorded on a desired recording track by applying a modulation magnetic field corresponding to the recording signal. FIG. 9 shows the shape of a light spot SP formed by a recording laser beam formed on a recording track 100a and the shape of a magneto-optical disk 10.
The relationship with the shape of the recording mark 110 recorded in the memory layer 103 of No. 0 is shown.

As shown in FIG. 9, by irradiating a recording laser beam, a high-temperature portion 1 is generated at a substantially central position of the light spot SP in correspondence with the shape of the light spot SP.
11, the recording mark 110a is recorded as a result of the sequential recording by the modulation magnetic field. Since the generation region of the high-temperature portion 111 depends on the shape of the light spot SP,
As shown in FIG. 9, when the light spot SP has a substantially circular shape, the shape of the recording mark 110 is a shape along the rear end of the high-temperature portion 111, and is substantially an arrow shape. That is,
The shape of the edge portion 110a forming the outer shape of the recording mark 111 depends on the curvature of the rear end of the light spot SP. The temperature of the high-temperature portion 111 is higher than the Curie temperature of the memory layer 103, and is different from the temperature of the high-temperature portion generated by irradiating a reproduction laser beam during reproduction.

With respect to the recording mark 110 recorded by the recording method of the magnetic field modulation as described above, in the DWDD reproduction method, the movement of the edge portion 110a caused by irradiating the laser beam for reproduction and heating is detected. Is used to reproduce the signal.

[0010]

By the way, in order to increase the recording capacity of the entire magneto-optical disk, when increasing the track density in the direction perpendicular to the recording tracks (hereinafter referred to as the track crossing direction), In some cases, a narrow track pitch is required.
However, on the other hand, it is also required to prevent crosstalk, that is, to prevent a reproduced signal from being affected by a signal of an adjacent recording track.

For example, when the light spot shape is over an adjacent recording track, it is affected by the signal of the adjacent recording track. Here, FIGS. 10A to 10C show examples of light spot shapes used for reproduction. The light spot SP ₁ shown in FIG.
Has a substantially circular shape, and the diameter _dr is substantially the same as the track width of the recording track 100a. Further, the light spot SP ₂ shown in FIG. 10 (b), the long axis is placed in a direction parallel to the recording track 100a, the diameter d _r of the short axis is substantially oval shape having substantially the same diameter as the track width Have been. Further, the light spot SP ₃ shown in FIG.
In (b) of which is between the light spot SP ₂ and likewise substantially elliptical shape, the major axis is placed in a direction perpendicular to the recording track 100a, greater than the diameter d _r is the track width of the major axis Has become. That is, the light spot SP ₃ in FIG. 10 (c), has a shape such as according to the adjacent recording tracks.

[0012] When such a light spot shape, figure 10 (a) and 10 in the recording track diameter d _r of the light spot in the track crossing direction as shown in (b) 1
By making it fit within the track width of 00a, the signal of the adjacent recording track is not reproduced,
As shown in FIG. 10 (c), the when the diameter d _r in the cross-track direction would be greater than the track width, which may result in reproducing a signal of the adjacent recording tracks.
Therefore, for the purpose of eliminating the influence of the signal of the adjacent recording track, a light spot shape that fits within the recording track as shown in FIG. 10A and FIG. 10B is suitable. A light spot shape as in (c) of 10 is not suitable.

Next, FIG. 10A to FIG.
Consider a case in which the recording mark 110 is recorded by a light spot shaped as shown in FIG. As described above, the recording mark 1 to be detected during reproduction
The ten edge portions 110a depend on the light spot shape. That is, since the shape of the high-temperature portion generated by irradiating the recording laser beam for recording the recording mark 110 depends on the light spot shape, the edge portion 110a of the recording mark 110 also depends on the light spot shape. become. That is, for example, when the light spot SP _1, as shown in FIG. 10 (a), the high temperature portion 111 ₁ is generated as a substantially circular area, and when the light spot SP _2, as shown in FIG. as shown in 10 (b), the high temperature portion 111 ₂ is generated as a region substantially elliptical long axis is parallel to the recording track 110a, also in the case of the light spot SP _3, as shown in FIG. 10 ( As shown in c), the high-temperature portion 111 ₃ is generated as a substantially elliptical region in which the major axis is in the track transverse direction.

Therefore, the edge portion 1 of the recording mark 110
10a, the curvature, the curvature of the edge portion 110a ₂ by the light spot SP ₂ shown in FIG. 10 (b), the edge portion 110 by the light spot SP ₁ shown in FIG. 10 (a)
the curvature of a _1, decreases in the order of the curvature of the edge portion 110b ₂ by the light spot SP ₃ shown in FIG. 10 (c). That is, it is possible to the use of the light spot SP ₃ in FIG. 10 (c), formed to be substantially parallel to an edge portion 110a in the cross-track direction.

In the DWDD reproducing method, the domain wall is moved by irradiating and heating a reproducing laser beam, and a reproduced signal is obtained by detecting the movement of the domain wall. Therefore, the edge portion 110a of the recording mark 110 with respect to the isotherm of the high-temperature portion according to the shape of the light spot for reproduction.
The greater the overlap, the better the reproduction characteristics. Therefore, in the DWDD reproducing method, who recorded mark 110 by the light spot SP ₃ is formed, by increasing the overlap of the edge portions 110a ₃ of the recording mark 110 for isotherms of the high-temperature portion, taking the highest signal level I can do it. However, as described above, when a light spot SP ₃ results in a reproduction of a light spot, since thereby reproducing the signal of the adjacent tracks as noise, the purpose of such particularly to improve the capacity of the entire magneto-optical disk When the track pitch is small, the reproduced signal is deteriorated.

Accordingly, the present invention has been made in view of the above-mentioned circumstances, and enables high-density recording on a domain wall displacement type magneto-optical information recording medium and improves the density of recorded signals. It is an object of the present invention to provide a signal recording / reproducing apparatus and a signal recording / reproducing method which can reproduce the signal.

[0017]

In order to solve the above-mentioned problems, a signal recording / reproducing apparatus according to the present invention performs beam shaping of a laser beam so that a light spot on a magneto-optical information recording medium is perpendicular to a recording track. A spot shape switching means for switching the size of the diameter in the direction is provided, and the spot shape switching means makes the diameter of the light spot in the direction perpendicular to the recording track smaller during recording than during recording.

In the signal recording / reproducing apparatus having such a configuration, the laser beam is shaped by a beam and the spot shape switching means for switching the size of the light spot on the magneto-optical information recording medium in the direction perpendicular to the recording track is used. The signal recorded on the magneto-optical information recording medium is reproduced by making the diameter of the light spot in the direction perpendicular to the recording track smaller than at the time of recording.

The signal recording / reproducing method according to the present invention comprises:
In order to solve the above-mentioned problem, a laser beam emitted from a light source is beam-shaped, and the diameter of a light spot on a magneto-optical information recording medium in a direction perpendicular to a recording track is switched to record the magneto-optical information. The signal is recorded and reproduced on the medium, and the diameter of the light spot in the direction perpendicular to the recording track is made smaller during reproduction than during recording.

In such a signal recording / reproducing method, a laser beam emitted from a light source is beam-shaped, and the diameter of a light spot on a magneto-optical information recording medium in a direction perpendicular to a recording track is switched to perform recording. Make the diameter of the light spot in the vertical direction to the recording track smaller than when
The signal recorded on the magneto-optical information recording medium is reproduced.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. This embodiment is a magneto-optical disk device for recording and / or reproducing information signals on a domain wall displacement type magneto-optical information recording medium.

Here, the domain wall displacement type magneto-optical information recording medium is a so-called DWDD (Domain Wall Displacement Detachment).
Section), a magneto-optical disk is formed by adopting the magneto-optical reproducing method. That is, as shown in FIG. 8, the magneto-optical disk is a magneto-optical information recording medium having at least three magnetic layers of a moving layer 101, a switching layer 102, and a memory layer 103. The magneto-optical disk device irradiates a reproducing laser beam to the magneto-optical disk at the time of reproduction and
02, the magnetic coupling between the memory layer 103 and the moving layer 101 corresponding to the region having the Curie temperature or higher is broken, and the moving layer region corresponding to the region where the magnetic coupling is broken is moved. It is configured to detect a domain wall that changes.

As shown in FIG. 1, the magneto-optical disk device includes a semiconductor laser 2, a collimator lens 3, a liquid crystal panel 4, a beam splitter 5, an objective lens 6, and an analyzer unit 7. The analyzer unit 7 includes a half-wave plate 11, a polarizing beam splitter 12, and a condenser lens 1.
3, a first photodetector 14, a condenser lens 15, and a second photodetector 16.

The semiconductor laser 2 is a laser light source,
The laser beam for reproduction and the laser beam for recording are emitted. The recording laser light output from the semiconductor laser 2 has an output power larger than the output power of the reproduction laser light. The reproduction laser light or the recording laser light emitted from the semiconductor laser 2 is incident on the collimator lens 3,
The collimator lens 3 converts the light into a parallel light beam, which is incident on the liquid crystal panel 4. In the following description, when there is no difference between the case where the reproduction laser light is used and the case where the recording laser light is used, the case where the reproduction laser light is used is simply referred to as the laser light.

The liquid crystal panel 4 is a spot shape switching means for shaping the laser beam and switching the size of the light spot on the magneto-optical disk 100 in the direction perpendicular to the recording track. The liquid crystal panel 4 is driven by application of a voltage to switch the light spot shape.

Specifically, as shown in FIG. 2, the liquid crystal panel 4 includes an emission-side transparent substrate 21, an emission-side transparent electrode 22, an emission-side alignment film 23, a liquid crystal 24, an incidence-side alignment film 25, and an incidence-side transparent film. It has a structure in which the electrode 26 and the incident side transparent substrate 27 are laminated in order. For example, the liquid crystal panel 4 has the emission-side transparent electrode 22 and the emission-side alignment film 23 formed on the emission-side transparent substrate 21, and similarly, the incidence-side transparent electrode 26 and the incidence-side alignment film are formed on the incidence-side transparent substrate 27. A film 25 is formed, and the light emitting side alignment film 23 and the light incident side alignment film 25 are opposed to each other, and the liquid crystal 24 is sealed therebetween. Here, the liquid crystal 2
Reference numeral 4 denotes, for example, a parallel alignment type nematic liquid crystal.

As shown in FIG. 3, the emission side transparent electrode 22 is composed of one side electrode 22 ₁ , center electrode 22 ₂ and other side electrode 22.
₃ is divided into three electrodes are divided Similarly, the incident-side transparent electrode 26 at one side electrode 26 _1, the three electrodes of the central electrode 26 ₂ and the other side electrode 26 _3. For example, the dividing direction of the transparent electrodes 22 and 26 (each electrode 22 ₁ , 22 ₂ , 22 ₃
The direction in which are arranged or the direction in which the electrodes 26 ₁ , 26 ₂ , 26 ₃ are arranged) correspond to the track crossing direction of the magneto-optical disk 100. Then, for example, as shown in FIG. 4, the division direction matches the polarization direction of the laser beam incident on the liquid crystal panel 4 (the incident direct polarization direction).

As shown in FIG. 4, the molecular orientation direction of the liquid crystal 24 is set at an arbitrary angle which does not coincide with the direction of the incident direct polarization. As the voltage applied to the transparent electrodes 22 and 26 increases, the birefringence caused by the liquid crystal 24 decreases. Therefore, in the liquid crystal panel 4, as the voltage applied to the transparent electrodes 22 and 26 increases, the transmission amount of the polarization component of the incident direct polarization direction of the laser beam increases.

Further, at the exit side transparent electrode 22, the center electrode 22 ₂ is a side electrode 22 ₁ is at least another electrode
And are configured to be driven by a different drive voltages other side electrode 22 _3. Similarly, the incident-side transparent electrode 26, central electrode 26 ₂ is adapted to be driven by at least one other side electrode 26 ₁ is the electrode and the different driving voltages other side electrode 26 _3.

The laser light transmitted through the liquid crystal panel 4 as described above is incident on the beam splitter 5. As shown in FIG. 4, the transmission polarization direction of the beam splitter 5 matches the polarization direction of the laser beam (the incident direct polarization direction). That is, the beam splitter 5 and the above-described liquid crystal panel 4 constitute a so-called transmittance variable element that controls the transmittance of laser light.

FIG. 5 shows the relationship between the voltage applied to the liquid crystal panel 4 and the relative light amount of the laser beam transmitted through the beam splitter 5. Here, the relative light amount is represented by a ratio R ₁ / R ₀ between the light amount R ₀ of the laser light before being incident on the liquid crystal panel 4 and the light amount R _{1 of the} laser light emitted from the beam splitter 5. As shown in FIG. 5, the relative light amount increases as the voltage applied to the liquid crystal panel 4 increases.

The laser beam transmitted through the liquid crystal panel 4 and the beam splitter 5 constituting such a variable transmission element is
The light is irradiated onto the magneto-optical disk 100 by the objective lens 2. For example, the objective lens 6 is driven by a two-axis actuator (not shown) that is a driving unit.

At the time of reproduction, the reproduction laser beam transmitted through each of the optical means as described above is applied to the magneto-optical disk 20.
The light is reflected on the reference numeral 0 and is incident on the beam splitter 5 via the objective lens 6 as reflected light. On the other hand, at the time of recording, a recording laser beam transmitted through each optical component is irradiated on the magneto-optical disk 100, and information is written into the memory layer 103 by a modulation magnetic field by a magnetic head (not shown). The magneto-optical disk device 1 has different light spot shapes at the time of recording and at the time of reproduction, which will be described in detail later.

At the time of reproduction, reflected light incident on the beam splitter 5 is reflected toward the analyzer unit 7 by the reflection surface 5a of the beam splitter 5.

The analyzer unit 7, as described above,
It includes a two-wavelength plate 11, a polarizing beam splitter 12, a condenser lens 13, a first photodetector 14, a condenser lens 15, and a second photodetector 16. The reflected light incident on the analyzer unit 7 is first incident on the half-wave plate 11.

The half-wave plate 11 converts the azimuth of the reflected light. The reflected light transmitted through the half-wave plate 11 is
The light enters the polarization beam splitter 12.

The polarization beam splitter 12 splits the incident reflected light into a light beam going to the first photodetector 14 and a light beam going to the second photodetector 16.

A condenser lens 13 is arranged between the polarization beam splitter 12 and the first photodetector 14,
The light beam split by the polarization beam splitter 12 toward the first photodetector 14 is condensed by the condensing lens 13 and received by the first photodetector 14. A condensing lens 15 is disposed between the polarization beam splitter 12 and the second photodetector 16, and the light beam split by the polarization beam splitter 12 toward the second photodetector 16 is: The light is condensed by the condenser lens 15 and received by the second photodetector 16. Then, the first photodetector 1
4 and the second photodetector 15 by differential detection,
A magneto-optical signal as a reproduction signal is obtained.

With the above-described configuration, the magneto-optical disk drive 1 is provided with a magneto-optical disk 10 of a domain wall displacement type.
Recording and reproduction of information signals with respect to 0 can be performed.

The magneto-optical disk device 1 controls the driving of the liquid crystal panel 4 so that the shape of the light spot is different between recording and reproduction, and records and reproduces information signals. Specifically, the magneto-optical disk device 1
During reproduction, by controlling the driving of the liquid crystal panel 4, by switching the size of the diameter in the vertical direction with respect to the recording track of the optical spot, as shown in FIG. 6, the diameter of the cross-track direction of the light spot SP _w during recording reading of information signal by the light spot SP _r having a diameter d _rr cross-track direction is smaller than d _rw, that is, to thereby detect movement of the magnetic wall.

More specifically, by operating the liquid crystal panel 4 as follows, the light spot shape can be switched as described above.

Outgoing side transparent electrode 22 and incoming side transparent electrode 26
Between the output side transparent electrode 22 and the
Side electrode 22₁And one side electrode 26 of the incident side transparent electrode 26₁With
The voltage applied between₁And the transparent
Central electrode 22 of pole 22_TwoAnd the central electrode of the incident side transparent electrode 26.
Pole 26_TwoIs applied to the voltage VE_TwoAnd out
Other side electrode 22 of emission side transparent electrode 22_ThreeAnd incident side transparent electrode 2
6 other electrode 26_ThreeAnd the applied voltage between
E_ThreeWhen playing, VE₁= VE_ThreeAnd VE_Two
<VE₁Of the emission side transparent electrode 22 so as to satisfy the relationship
By applying a voltage between the emitting side transparent electrode 26 and
Central electrode 22 of each transparent electrode 22, 26_TwoAnd central electrode 26_Two
The amount of light transmitted through the liquid crystal portion between
Less than the amount of light. This allows the transparency of the central part
As shown in FIG. 6, since the over-light amount is relatively small,
In addition, the light spot SP which has been made into a substantially circular shape_WIs during playback
Has a smaller diameter in the cross-track direction,
Light spot SP made circular _RChanges to Sand
Light spot SP during recording_wTrack cross direction
Diameter d_rwAnd the diameter d in the direction parallel to the recording track_tAnd the ratio
Rate d_rw/ D_tAt the time of reproduction, the light spot SP_rTiger
Diameter d in the cross direction_rrAnd parallel direction to recording track
Diameter d_tAnd the ratio to d_rr/ D_tAnd (d_rw/ D
_t)> (D_rr/ D_tLight spot shape so that
Is switched.

[0043] By allowing switching of the light spot shape, as described above, the magneto-optical disk device 1, the light spot SP _w, by reducing the curvature of the edge portion,
A recording mark can be recorded in a minute section of the recording track 110a. Therefore, the overlap of the edge portion with the isotherm of the high-temperature portion according to the shape of the light spot for reproduction can be increased, and the reproduction characteristics are improved.

[0044] Further, the magneto-optical disk device 1, the light spot SP _r having a small diameter of the track crossing direction than the light spot SP _w, reproduces only the recording marks recorded on a desired track, adjacent to There is no need to reproduce the signal of the recording track. Therefore, the magneto-optical disk device 1 can effectively prevent reproduction of a signal of an adjacent track even on a magneto-optical disk having a narrow track pitch, and can reproduce a signal from a desired track without including noise. The signal can be reproduced.

As described above, the magneto-optical disk drive 1 independently optimizes the light spot shape at the time of recording and at the time of reproduction, thereby improving the track density by narrowing the track pitch and forming the recording mark in a minute section. Good recording and reproduction can be performed while enabling the data capacity to be improved by enabling recording.

In the description of the embodiment of the present invention, an example is shown in which the liquid crystal panel 4 is used as a means for switching the light spot shape. For example, an optical member for shielding a part of parallel light in a magneto-optical pickup is used. Can be moved on the optical path of the laser light to switch the light spot shape.

The shape of the light spot formed by switching between recording and reproduction is not limited to the shape shown in FIG. For example, as shown in FIG. 7, as the recording time of the optical spot SP _w of generally elliptical shape as it puts the long axis diameter d _rw across the tracks, on the other hand, from the time of recording a diameter in the cross-track direction at the time of reproduction The diameter d _rr (<d _rw ) may be small, and the ratio d _rr / d _t of the diameter d _{t in the} direction parallel to the recording track may also be a light spot SP _r smaller than that at the time of recording.

[0048]

The signal recording / reproducing apparatus according to the present invention comprises a spot shape switching means for shaping a laser beam and switching the size of a diameter of a light spot on a magneto-optical information recording medium in a direction perpendicular to a recording track. The spot shape switching means makes it possible to perform high-density recording on a domain wall displacement type magneto-optical information recording medium by making the diameter of the light spot in the direction perpendicular to the recording track smaller during reproduction than during recording. Thus, a signal recorded at high density can be satisfactorily reproduced.

The signal recording / reproducing method according to the present invention comprises:
The laser beam emitted from the light source is beam-shaped, and the size of the diameter of the light spot on the magneto-optical information recording medium in the direction perpendicular to the recording track is switched to record and reproduce the signal on the magneto-optical information recording medium. By making the diameter of the light spot in the direction perpendicular to the recording track smaller during recording than during recording, high-density recording can be performed on a domain wall displacement type magneto-optical information recording medium, and a signal recorded with high density is recorded. Can be reproduced favorably.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a magneto-optical disk device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a liquid crystal panel of the above-described magneto-optical disk device.

FIG. 3 is a plan view showing a configuration of an electrode of the liquid crystal panel described above.

FIG. 4 is a diagram showing a direction of electrode division, a direction across a disk, a direction of incident linear polarization, a direction of transmission polarization of a beam splitter, and a direction of molecular arrangement of liquid crystal.

FIG. 5 is a characteristic diagram showing a relationship between the voltage applied to the liquid crystal panel and the amount of transmitted light.

FIG. 6 is a plan view showing the shape of a light spot at the time of recording and the shape of a light spot at the time of reproduction formed by the above-described magneto-optical disk device.

FIG. 7 is a plan view showing another example of a light spot shape formed by the above-described magneto-optical disk device, showing a light spot shape at the time of recording and a light spot shape at the time of reproduction.

FIG. 8 is a cross-sectional view showing a magneto-optical disk formed by adopting the DWDD reproduction method.

FIG. 9 is a plan view showing a recording light spot formed on a recording track of a magneto-optical disk and recording marks recorded by the recording light spot.

FIG. 10 is a plan view showing a light spot shape.

[Explanation of symbols]

 1 magneto-optical disk drive, 4 liquid crystal panel

Claims (5)

[Claims] 1. A domain wall moving type magneto-optical information recording medium is irradiated with a reproducing laser beam to expand a magnetic domain by domain wall movement to reproduce a signal, and a recording laser beam is applied to the magneto-optical information recording medium. A signal recording / reproducing apparatus for recording a signal by applying a magnetic field, comprising: a light source for emitting laser light; and a beam shaping of the laser light to form a light spot on the magneto-optical information recording medium. Spot shape switching means for switching the size of the diameter in the vertical direction with respect to the recording track, wherein the spot shape switching means makes the diameter of the light spot in the direction perpendicular to the recording track smaller during reproduction than during recording. Signal recording and reproducing device. Wherein said spot shape switching means, to reduce the ratio d _r / d _t for parallel direction of diameter d _t with respect to the recording track in the radial d _r in the vertical direction with respect to the recording track than the recording at the time of reproduction Claim 1 characterized by the following:
The signal recording / reproducing device according to claim 1. 3. The spot shape switching means is a liquid crystal device which is driven by applying a voltage, wherein the light spot shape is switched by switching the driving of the spot shape switching means. Item 2. The signal recording and reproducing device according to Item 1. 4. A magnetic domain wall moving type magneto-optical information recording medium is irradiated with a reproducing laser beam to expand a magnetic domain by domain wall movement to reproduce a signal. And recording a signal by applying a magnetic field, wherein the laser beam emitted from the light source is beam-shaped so that a light spot on the magneto-optical information recording medium is perpendicular to a recording track. The signal is recorded and reproduced on the magneto-optical information recording medium by switching the size of the diameter in the direction, and the diameter of the light spot in the direction perpendicular to the recording track of the light spot is made smaller during recording than during recording. Recording and playback method. 5. A method according to claim, characterized in that to reduce the ratio d _r / d _t to the diameter d _t of the parallel direction with respect to the recording track in the vertical direction of the diameter d _r with respect to the recording track than the recording during reproduction 4 The signal recording / reproducing method described in the above.