JP3334146B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for reading a signal while irradiating an optical recording medium with a light beam, and more particularly to an optical head device capable of reproducing high-density information.

[0002]

BACKGROUND OF THE INVENTION Optical recording media can be broadly classified into read-only media such as so-called compact discs and media capable of recording signals such as magneto-optical discs.
In any of these optical recording media, it is desired to further increase the recording density. This is because when a digital video signal is considered as a signal to be recorded, the data amount is several times to ten and several times that of a digital audio signal. This is because there is a demand to further reduce the size of the medium to further reduce the size of products such as players. Also, a larger recording capacity is desired for general data disks.

[0003] The recording density of information on an optical recording medium is determined by the S / N of a reproduced signal. In conventional general optical recording / reproducing, as shown in FIG. 18, the entire area of a beam spot SP which is a light irradiation area of a reading light beam such as a laser beam on an optical recording medium is set as a reproduction signal area. . Therefore, reproducible recording density is determined by the diameter D _SP of the beam spot of the reading light.

For example, as shown in FIG. 18A, if the diameter D _SP of the beam spot SP of the read laser beam is smaller than the pitch q of the recording pit RP, two recording pits are included in the spot SP. However, the reproduced output waveform is as shown in FIG. 18B, and the reproduced signal is readable. However, as shown in FIG. 18C, recording pits SP are formed at a high density, and beam spots SP are formed.
When the inner diameter D _SP becomes larger than the pitch q of the recording pit RP, two or more pits enter the spot SP at the same time, and the reproduction output waveform becomes substantially constant as shown in FIG. The two recording pits cannot be reproduced separately and cannot be reproduced.

[0005] The spot diameter _DSP is determined by the wavelength λ of the laser beam and
The pit density (so-called linear density) along the scanning direction (recording track direction) of the read light beam is determined by the spot diameter D _SP depending on the numerical aperture NA of the objective lens.
Also, the track density is determined according to the adjacent track interval (so-called track pitch) in the direction orthogonal to the scanning direction of the read light beam. That is, the physical and optical limits of the linear density and the track density are determined by the wavelength λ of the light source of the reading light and the numerical aperture NA of the objective lens. For example, the spatial frequency at the time of signal reproduction is generally 2NA / λ. The reading limit is set. From this, in order to realize high density in the optical recording medium,
First, the wavelength λ of the light source (for example, a semiconductor laser) of the reproducing optical system
And the numerical aperture NA of the objective lens needs to be increased.

The applicant of the present application has previously proposed an optical recording medium capable of increasing the readable linear recording density and the track density without changing the spot diameter of the reading light beam, and a reproducing method thereof. ing. Optical recording media capable of reproducing such high-density information include magneto-optical recording media capable of recording signals and optical recording media of variable reflectivity capable of at least reproducing.

The magneto-optical recording medium has a magnetic layer having an easy axis of magnetization perpendicular to the film surface and having an excellent magneto-optical effect on one main surface of a transparent substrate made of, for example, polycarbonate or the like. For example, a rare earth-transition metal alloy thin film is laminated with a dielectric layer, a surface protection layer, and the like, and a signal is recorded and reproduced by irradiating a laser beam or the like from the transparent substrate side. In signal recording on the magneto-optical recording medium, the magnetic layer is locally heated to a temperature near the Curie point, for example, by irradiating a laser beam or the like, and the coercive force in this portion is eliminated to reduce the recording magnetic field applied from the outside. This is a so-called thermomagnetic recording performed by magnetizing in the direction. Reproduction of a signal from the magneto-optical recording medium is performed by using a magneto-optical effect (a so-called magnetic Kerr effect or Faraday effect) in which a plane of polarization of linearly polarized light such as laser light is rotated depending on the direction of magnetization of the magnetic layer.

The above-mentioned optical recording medium of variable reflectivity comprises a transparent substrate on which phase pits are formed and a material whose reflectivity changes with temperature is formed. When reproducing a signal, the recording medium is irradiated with read light. Then, the phase pits are read while the reflectance is partially changed within the scanning spot of the reading light.

Hereinafter, high-density reproduction or so-called ultra-high-resolution reproduction on the recordable magneto-optical recording medium will be further described. The present applicant previously disclosed in Japanese Patent Application Laid-Open Nos. 1-143041 and 1-143042, for example, that information bits (magnetic domains) were enlarged during reproduction.
A signal reproducing method for a magneto-optical recording medium has been proposed in which the reproducing resolution is improved by reducing or eliminating the signal. In this technique, the recording magnetic layer is an exchange-coupled multilayer film including a reproducing layer, an intermediate layer, and a recording layer, and a magnetic domain of the reproducing layer heated by a reproducing light beam is enlarged, reduced, or erased at a high temperature portion during reproduction. Thus, interference between information bits at the time of reproduction is reduced, and a signal having a period equal to or less than the diffraction limit of light can be reproduced. Also, Japanese Patent Application No. 1-22
In the specification and drawings of No. 9395, the recording layer of the magneto-optical recording medium is constituted by a multilayer film including a reproducing layer and a recording holding layer which are magnetically coupled, and the magnetization direction of the reproducing layer is previously aligned to erase. At the time of reproduction, the reproducing layer is heated to a predetermined temperature or higher by laser beam irradiation during reproduction, and only when the temperature is raised, the magnetic signal written in the recording holding layer is read while being transferred to the reproducing layer. Thus, a technique for eliminating crosstalk and improving linear recording density and track density has been proposed. These high-density reproduction technologies can be broadly classified into erasure type and emboss type.
The outline of each is shown in FIGS.

First, an erasing-type high-density reproducing technique will be described with reference to FIGS. In the case of this erasing type, as shown in FIG. 19B, the laser beam LB is applied to the recording medium in which the information recording pits RP appear at room temperature.
Is irradiated and heated to form a recording / erasing area ER in the beam spot SP of the irradiation laser beam LB, and a recording pit RP in the remaining area RD in the beam spot SP.
By reading the data, reproduction with an increased linear density is performed. This is the recording pit RP in the beam spot SP
When reading is performed, the width d of the reading area (reproduction area) RD is reduced by using the recording / erasing area ER as a mask, and the density (so-called linear recording density) along the scanning direction (track direction) of the laser beam is increased. That is, it enables reproduction.

The recording medium for the erasure-type high-density reproduction is an amorphous rare earth element (Gd, Tb) for magneto-optical recording.
It has an exchange-coupled magnetic multilayer structure composed of an iron group (Fe, Co) ferrimagnetic film. In the example shown in FIG. 19A, a first surface (a lower surface in the figure) of a transparent substrate 60 made of polycarbonate or the like is provided with a first surface. The magnetic recording layer 61 has a structure in which a reproducing layer 61 as a magnetic film, a cutting layer (intermediate layer) 62 as a second magnetic film, and a recording holding layer 63 as a third magnetic film are sequentially laminated. The first magnetic film (reproducing layer) 61 is made of, for example, GdFeCo and has a Curie temperature T _C1 > 400 ° C. The second magnetic film (cutting layer, intermediate layer) 62 is made of, for example, TbFeCoAl and has a Curie temperature T _C1 . _A third magnetic film (for example, TbFeCo and a Curie temperature T _C3 = 300 ° C.) is used as the third magnetic film. Arrows in the films 61, 62, and 63 indicate the directions of magnetization of the respective magnetic domains, and H _read indicates the direction of the reproducing magnetic field.

[0012] Briefly explaining the operation in reproduction, the recording medium at normal temperature below the predetermined temperature T _OP layers 63,62,6
1 is magnetically coupled in a state of magnetostatic coupling or exchange coupling, and the recording magnetic domain of the recording holding layer 63 is transferred to the reproducing layer 61 via the cutting layer 62. When the recording medium is irradiated with the laser beam LB to increase the medium temperature, a change in the temperature of the medium is delayed with the scanning of the laser beam, and appears in an area where the temperature becomes _{equal to} or higher than the predetermined temperature _TOP (recording / erasing area ER). ) Appear slightly behind the beam spot SP in the laser scanning direction. This is at a predetermined temperature T _OP or magnetic coupling disappears between recording holding layer 63 and the reproducing layer 61, the reproducing layer 61
Are aligned in the direction of the reproducing magnetic field H _read , so that the recording pits are erased on the medium surface. Then, in the region of the scanning spot SP, the region R excluding the region overlapping with the region ER having the predetermined temperature _TOP or higher.
D is a substantial reproduction area. That is, the beam spot SP of the laser beam is partially masked by the region ER where the temperature is _{equal to} or higher than the predetermined temperature _TOP, and a small unmasked region becomes a reproduction region (reading region) RD, thereby realizing high-density reproduction. I have.

In this way, the pits are reproduced by detecting, for example, the Kerr rotation angle of the reflected light from the small reproduction area (reading area RD) where the scanning spot SP of the laser beam is not masked by the mask area (recording / erasing area ER). This is equivalent to reducing the diameter of the beam spot SP, and the linear recording density and the track density can be increased.

Next, in the raised high-density reproducing technique shown in FIG. 20B, a recording medium in which the information recording pits RP have disappeared (initialized state) at normal temperature is irradiated with a laser beam and heated. As a result, a signal detection area DT, which is a recording embossed area, is formed in the beam spot SP of the irradiation laser light, and only the recording pits RP in the signal detection area DT are read to increase the reproduction linear density. .

This recording medium for high-density reproduction has a magnetic multilayer structure of magnetostatic coupling or magnetic exchange coupling. In the example of FIG. The first surface (the lower surface in the figure)
In this structure, a reproducing layer 71 as a magnetic film, a reproducing auxiliary layer 72 as a second magnetic film, an intermediate layer 73 as a third magnetic film, and a recording holding layer 74 as a fourth magnetic film are sequentially laminated. are doing. The first magnetic film (the reproducing layer 71 is made of, for example, GdFeCo
In those Curie temperature T _C1> 300 ° C, the second magnetic layer (reproduction auxiliary layer) 72 is, for example those of the Curie temperature T _C2 ≒ 120 ° C at TbFeCoAl, third magnetic layer (intermediate layer) 73 For example, the Curie temperature T _C3 Ｇ of GdFeCo
250 ° C., fourth magnetic film (recording holding layer) 74
Is a Curie temperature T _C4 Ｔ250 ° for example with TbFeCo.
C is used. Here in the initialization magnetic field H _in
Is larger than the magnetic field H _cp for reversing the magnetization of the reproducing layer (H _in > H _cp ) and sufficiently smaller than the magnetic field H _cr for reversing the magnetization of the recording holding layer (H _in ≪H _cp ). ing. Each magnetic film 71, 72, 7 in C of FIG.
Arrows in 3,74 indicates the magnetization orientation of the magnetic domains, H _in the orientation of the initializing magnetic field, also H _read is respectively the direction of the reproducing magnetic field.

The recording holding layer 74, the initializing magnetic field H _in, a layer holding recording pits reproducing magnetic field H _read, also without being affected by the regeneration temperature and the like, at room temperature, sufficient coercivity regeneration temperature There is.

The vertical anisotropy of the intermediate layer 73 is
2. Smaller than the record holding layer 74. Therefore, the reproduction layer 7
When a magnetic domain wall is formed between the magnetic layer 1 and the recording layer 74, the magnetic domain wall is stably present in the intermediate layer 73. Therefore, the reproduction layer 71 and the reproduction auxiliary layer 72 stably maintain the erased state (initialized state).

The auxiliary reproduction layer 72 functions to increase the coercive force of the reproduction layer 71 at room temperature. Therefore, the magnetizations of the reproduction layer 71 and the auxiliary reproduction layer 72 aligned by the initialization magnetic field are controlled by the domain wall. Exists stably even if exists. In addition, during reproduction, the coercive force of the auxiliary reproduction layer 72 rapidly decreases near the reproduction temperature T _S , so that the domain wall confined in the intermediate layer 73 spreads to the auxiliary reproduction layer 72, and finally the auxiliary reproduction layer 72 is reproduced. The layer 71 is inverted, and the domain wall disappears. Through this process, pits appear on the reproducing layer 71.

The reproducing layer 71 has a small magnetization reversal magnetic field _Hcp even at room temperature, and its magnetization is easily reversed. Therefore, the reproduction layer 71, the initialization magnetic field H _in, the magnetization of the entire surface is aligned in the same direction. The uniform magnetization is supported by the reproduction auxiliary layer 72 and a stable state is maintained even when there is a domain wall with the recording holding layer 74. Then, as described above, at the time of reproduction, a recording pit appears due to disappearance of the domain wall with the recording holding layer 74.

[0020] Briefly explaining the operation in reproduction, first align the direction of magnetization of the reproducing layer 71 and the auxiliary reproducing layer 72 by an initialization magnetic field H _in before playback in one direction (in FIG. 20 upward). At this time, a domain wall (indicated by a horizontal arrow in FIG. 20) is stably present in the intermediate layer 73, and the reproduction layer 71 and the reproduction auxiliary layer 72 stably maintain the initialized state.

Next, a laser beam LB is irradiated while applying a reproducing magnetic field H _read in the reverse direction. As the reproducing magnetic field H _read , the reproducing layer 71 and the auxiliary reproducing layer 72 are inverted at the reproducing temperature T _RP after the temperature rise by the laser beam irradiation, and the intermediate layer 7
A magnetic field more than the magnetic field that eliminates the domain wall 3 is required. In addition, the reproducing layer 71 and the auxiliary reproducing layer 72 have such a size that the magnetic field direction is not reversed.

Since the temperature change of the medium is delayed with the scanning of the laser beam LB, the area (recording embossed area) above the predetermined reproducing temperature T _RP is equal to the beam spot SP.
Appears slightly rearward in the scanning direction. At a temperature _{equal to} or higher than the predetermined reproduction temperature T _RP , the coercive force of the reproduction auxiliary layer 72 decreases, and the magnetic field H _read is applied, thereby eliminating the magnetic domain wall, and the information in the recording and holding layer 74 is transferred to the reproduction layer 71. Thereby, the beam spot S of the laser beam LB
The area within P before the reproduction temperature T _RP is reached is masked, and the remainder in the spot SP becomes a signal detection area (reproduction area) DT which is a recording emboss area. By detecting, for example, the Kerr rotation angle of the deflection surface of the light reflected from the signal detection area DT, high-density reproduction can be performed.

That is, in the inner area of the beam spot SP of the laser beam LB, the area before reaching the reproduction temperature T _RP is a mask area where no recording pits appear,
Since the remaining signal detection area (reproduction area) DT is smaller than the spot diameter, the linear recording density and the track density can be increased as described above.

Further, as a technique combining these erasing type and raised type, a high-density reproducing technique as shown in FIG. 21 has also been considered. In FIG. 21, the recording medium in a state where the information recording pits RP have disappeared at room temperature (initialized state) is irradiated with laser light and heated, so that the laser beam is applied to the beam spot SP of the irradiated laser light. A recording relief area FL is formed at a position slightly shifted to the rear side in the scanning direction, and a higher-temperature recording / erasing area ER is formed in the recording relief area FL. And the beam
In the spot SP, a part (signal detection area) D other than the part masked by the recording erasure area ER in the recording emboss area FL
Only the recording pit RP in T is read. Since the width d of the signal detection region DT along the scanning direction of the laser beam is reduced, the signal can be reproduced at a high linear density. This is, for example, due to the medium temperature distribution caused by laser irradiation,
A portion where the initialization state is maintained in the beam spot SP, a recording relief region FL where the magnetization of the recording holding layer is transferred to the reproducing layer on the surface, and a recording where the magnetization is aligned in the direction of the externally applied magnetic field and erased. This can be realized by generating the erasing area ER.

The applicant of the present application has filed Japanese Patent Application No. Hei 3-4181.
In the specification and the drawings of No. 10, at least a reproducing layer,
Using a magneto-optical recording medium having an intermediate layer and a recording holding layer, irradiating the reproducing layer with laser light and applying a reproducing magnetic field, and utilizing the temperature distribution generated by the laser irradiation to maintain an initialized state; By creating a part in the lens field of view where information is transferred to the recording holding layer and a part where the direction of magnetization is aligned with the direction of the reproducing magnetic field, a state equivalent to optically masking the lens field is obtained, and line recording is performed. A magneto-optical recording medium having an increased density and track density, and a reduced or enlarged area of the recording holding layer to which information is transferred even when the reproducing power fluctuates, and having good frequency characteristics during reproduction. Has proposed a signal reproduction method.

As another type of optical recording medium capable of high-density reproduction, a material whose reflectance changes with temperature is formed on a transparent substrate on which phase pits are formed. There is also known a reflectance changing type optical recording medium which reads a phase pit while partially changing the reflectance in a spot. As a technique relating to the optical recording medium of the reflectance change type, the present applicant has previously proposed a signal reproducing method for an optical disk in the specification and drawings of Japanese Patent Application No. 2-94452. -2
An optical disk is proposed in the specification and drawings of 91773. That is, in the former, readout light is applied to an optical disc in which phase pits are formed in accordance with a signal and reflectivity changes according to temperature, and the reflectivity is partially changed within a scan spot of the readout light. We have proposed a signal reproduction method for optical disks characterized by reading phase pits. In the latter method, a material layer whose reflectivity changes due to a phase change is formed on a transparent substrate on which phase pits are formed. A so-called phase-change type optical disc, characterized in that when irradiated with readout light, the material layer partially changes phase within a scan spot of the readout light and returns to an initial state after reading. is suggesting.

[0027]

By the way, in these high-density reproducing techniques, it is apparent that the density along the track direction, that is, the laser beam scanning direction, that is, the so-called linear recording density can be increased. For the density in the orthogonal direction, the so-called track density,
Further improvements are desired.

For example, FIG. 21 shows an example of a magneto-optical recording medium in which the above-mentioned raised type and erase type are mixed.
In the case of, the size of the signal detection area DT (so-called window portion) tends to expand in the track width direction, and the recording pits RPa of the adjacent track are also detected, so that crosstalk occurs, and this crosstalk is suppressed. Has a limitation on the track pitch p. That is,
Due to the limitation due to crosstalk, it is necessary to increase the track pitch p to some extent to lower the track density. This applies to not only the above-described various types of magneto-optical recording media but also the above-mentioned reflectance-change type optical recording media.

The present invention has been made in view of such circumstances, and the crosstalk can be reduced with a simple structure, and the so-called track density (recording density in a direction perpendicular to the laser beam scanning direction) is further increased. It is an object of the present invention to provide such an optical head device.

[0030]

According to the optical head device of the present invention, the recording layer comprises a multilayer film having at least a magnetically coupled reproducing layer and a recording holding layer. A signal is magnetically recorded on the layer, and the reproducing layer is heated by irradiating the reproducing layer with a light beam to the magneto-optical medium in which the magnetization direction of the reproducing layer is aligned. In the optical head device, a signal recorded magnetically is transferred to the reproduction layer and converted into an optical signal by a magneto-optical effect to read the signal. A portion having a phase difference of an odd multiple of a half wavelength between the portion and the peripheral portion, and a sharper temperature distribution in a direction orthogonal to the scanning direction of the read light beam on a recording medium irradiated with the read light beam. By formed by arranging the optical element to have, to solve the problems described above.

Further, according to the optical head device of the present invention, a readout light beam is applied to a recording medium in which phase pits are formed in response to a signal and the reflectance of which changes with temperature, and the readout light beam In an optical head device that reads a phase pit while partially changing a reflectance in a scanning spot, a passing laser beam is halved at a central portion and a peripheral portion in an emission optical path of the readout light beam. An optical element formed so as to have a phase difference of an odd multiple of the wavelength and having a sharper temperature distribution in a direction perpendicular to the scanning direction of the read light beam on the recording medium irradiated with the read light beam is disposed. By becoming
The above-mentioned problem is solved.

[0032]

With the above-mentioned optical element, a sharper temperature distribution is obtained in a direction orthogonal to the scanning direction of the laser beam on the medium irradiated with the laser beam and heated, so that the width of the high-temperature region in this direction is narrowed, Crosstalk from adjacent tracks can be reduced.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to description of an optical head device according to an embodiment of the present invention, FIG. 1 shows a schematic configuration of an optical head device used for describing the present invention. In the optical head device shown in FIG. 1, a laser beam emitted from a light source of a readout light beam, for example, a semiconductor laser 11 is collimated by a collimator lens 1.
The beam is converted into a parallel beam by the beam splitter 2 and sent to the objective lens 14 via the beam splitter 13. In the position immediately before the objective lens 14, a light-shielding strip 21 as shown in FIG. 2 is provided as an optical element for giving a sharper temperature distribution in a direction (so-called radial direction of the disc) perpendicular to the laser beam scanning direction during reproduction. Is arranged. In the embodiment of the present invention, a phase plate 26 having a step as shown in FIG. 5 which will be described later is used as the optical element, but here, the light shielding shown in FIG. An example in which the band plate 21 is used will be described. The light-shielding band plate 21 has a light-shielding band 22 extending along the laser scanning direction formed on a transparent plate 23 such as a glass plate or a transparent resin plate. The light is radiated from the objective lens 14 to the optical recording medium, for example, a magneto-optical disk 15 via a light-shielding strip 21. The laser beam applied to the magneto-optical disk 15 is reflected by the above-described magnetic multilayer film for magneto-optical recording, is incident on the beam splitter 13 via the light-shielding strip 21 and the objective lens 14, is reflected, and is condensed. The light is condensed by a lens 16 and is incident on a photodetector 17 such as a photodiode. When the magneto-optical disk 15 is used as an optical recording medium, a magnetic head 1 for applying a reproducing magnetic field H _read is provided on the back surface (upper surface in the drawing) of the magneto-optical disk 15 at the laser beam irradiation position.
8 are provided.

FIG. 3 shows the distance (nm) from the center of the laser light spot SP on the magneto-optical disk 15 as shown in FIG. 4 in the direction (disk radial direction) orthogonal to the laser light scanning direction. ) Is plotted on the abscissa and the light intensity normalized with the highest intensity is plotted on the ordinate. The width w of the light-shielding band 22 of the light-shielding band plate 21 is normalized by the diameter of the pupil of the objective lens 14. The obtained value w ^{* is set} to 0, 0.1, 0.
15 shows light intensity distribution characteristic curves when the values are set to 15 and 0.18. At this time, the laser wavelength λ is 780 nm, the numerical aperture NA of the objective lens 14 is 0.53, and the obtained light intensity distribution is equal to the temperature distribution due to the heating of the medium. As is clear from FIG. 3, the light intensity distribution or the temperature distribution in the direction (disc radial direction) orthogonal to the laser light scanning direction is such that the width w (standardized width w ^* ) of the light shielding band 22 is large (wide). ) It is sharp. This is a tendency of the 0th-order spot on the spot center side, and the light intensity of the 1st-order spot outside the 0th-order spot increases.

As described above, a sharp light intensity distribution in the disk radial direction (a direction orthogonal to the scanning direction of the laser beam), that is, the temperature distribution of the medium is obtained. In this way, the width of the high-temperature region (width in the direction orthogonal to the scanning direction of the laser beam) formed slightly behind the beam spot SP of the irradiation laser beam in the scanning direction can be reduced, and the recording pit R of the adjacent track can be reduced.
Crosstalk from P can be greatly reduced. However, if the intensity of the primary spot is excessively increased, a high-temperature region is also formed at the position of the primary spot, and the crosstalk is rather increased. Therefore, it is necessary to select the width w (normalized width w ^* ) in a range where a high-temperature region is not formed in the primary spot.

The high-density reproducing technique shown in FIG. 4 is the same as the technique described with reference to FIG. 21. Laser light is applied to a recording medium in which the information recording pits RP have disappeared (initialized state) at room temperature. By irradiating and heating, an elliptical recording embossed area FL is formed at a position slightly deviated from the beam spot SP of the irradiated laser light in the backward direction in the laser beam scanning direction. Forming the recording / erasing area ER of the beam spot SP
Among them, only the recording pits RP in the portion (signal detection region) DT other than the portion masked by the recording erasure region ER in the recording emboss region FL are read.

At this time, the high-temperature recording floating area F
L has a sharper (sharp) temperature distribution in the radial direction of the disk as described above, so that the width in the radial direction of the disk is narrower than in the case of FIG. Can be improved. As a result, the pitch between adjacent tracks (so-called track pitch) p can be made narrower (higher density) to increase the track density, and the recording density can be improved.

The high-density reproducing technique shown in FIG. 4 is a mixed type of the erasing type and the embossing type described above. For example, a low temperature for maintaining an initialized state in the beam spot SP by a medium temperature distribution generated by laser irradiation. And a high-temperature recording floating region FL where the magnetization of the recording holding layer is transferred to the reproducing layer on the surface, and a recording / erasing region ER where the temperature is further increased and the magnetization is aligned in the direction of the externally applied magnetic field to erase. It can be realized by using a medium as formed.

In FIG. 4, the width of the recording pit RP in the radial direction of the disk is h, and the shortest recording cycle (reciprocal of the maximum linear density) along the track direction is q, and the recording is performed at the shortest recording cycle q. Although an example is shown, it goes without saying that the pit recording cycle changes according to the contents of the recording data.

Next, an optical head device according to an embodiment of the present invention will be described. In the present embodiment, the above-mentioned light-shielding band plate 21 is used as an optical element for giving a sharper temperature distribution on the disk in a direction orthogonal to the laser beam scanning direction during reproduction (so-called disk radial direction). Without using, for example, a phase plate 2 having a step as shown in FIG.
6 is used.

The phase plate 26 having the step shown in FIG.
The thickness of a band-like portion 27 formed in the center portion along the laser beam scanning direction and the thickness of the other portion 28 are different, and the laser beam passing through these portions 27 and 28 is, for example, 1 mm. An optical element having a phase difference of / 2 wavelength (λ / 2). The phase difference at this time is preferably λ / 2 (or an odd multiple of λ / 2), but may be set to any value. However, since nλ (n is an integer) substantially eliminates the phase difference, this is excluded.

FIG. 6 shows a laser beam spot irradiated on a medium (magneto-optical disk 15) via a phase plate 26 having a step having a phase difference of λ / 2 in a direction perpendicular to the laser beam scanning direction ( The value indicates the light intensity (value standardized by the maximum intensity) with respect to the distance (nm) from the spot center along the disk radial direction, and is the value standardized by the diameter of the pupil of the objective lens 14 having the width w of the band-shaped portion 27. w ^* is 0,
The light intensity distribution characteristic curves at 0.1, 0.15, and 0.18 are shown. The laser wavelength λ is 780 nm,
The numerical aperture NA of the objective lens 14 is 0.53, and the obtained light intensity distribution is equal to the temperature distribution due to the heating of the medium.

As is clear from FIG. 6, the light intensity distribution or the temperature distribution in the direction (disc radial direction) orthogonal to the laser beam scanning direction is such that the width W (standardized width w ^* ) of the strip 27 is equal to the width. As the width increases, the zero-order spot width on the center side of the spot becomes narrower and the distribution curve becomes sharper, and the light intensity of the outer primary spot increases.

Also in this case, as described with reference to FIG. 4, the embossed area FL formed slightly behind the beam spot SP of the irradiation laser beam in the scanning direction is perpendicular to the laser beam scanning direction. The width can be reduced, and crosstalk from adjacent tracks can be significantly reduced. However,
Particularly, when the phase difference is set to λ / 2 by the phase plate 26 having the step, when the width w is widened, the intensity of the primary spot increases, and the raised area FL is formed at the position of the primary spot, On the contrary, since the crosstalk increases, it is necessary to select the width w (normalized width w ^* ) in a range in which no raised area is formed in the primary spot.

As the phase plate in which the phase of the passing laser light is partially different, for example, those shown in FIGS. 7 and 8 can be used.

The phase plate 31 shown in FIG. 7 has a band-shaped portion 32 formed along the laser scanning direction and another portion 33.
The band portion 32 is formed of a transparent piezoelectric material (transparent electrostrictive element) such as so-called PLZT, and transparent electrodes 34 and 35 are formed on both surfaces. These transparent electrodes 3
By applying the driving voltage from the voltage source 36 to the portions 4 and 35, the thickness and the phase difference of the belt-shaped portion 32 change, and
, The phase difference of the passing laser light changes. As a result, the sharpness of the light intensity distribution (temperature distribution) characteristic curve in the direction orthogonal to the laser scanning direction can be variably controlled, and the amount of improvement in crosstalk from an adjacent track can be variably controlled.

The phase plate 41 shown in FIG.
At the center of a transparent piezoelectric plate (electrostrictive element) 43 such as T, a band-shaped transparent electrode 44, 4
5 is formed by attaching these transparent electrodes 4.
By applying a driving voltage from the voltage source 36 to the electrodes 4 and 45, the thickness and the phase difference of the portion 42 between the electrodes 44 and 45 are variably controlled.

In each of the specific examples described above, a band-like portion is formed along the laser beam scanning direction. However, as shown in FIG. 9, a substantially circular portion corresponding to the center position of the pupil of the objective lens 14 is formed. The portion 51 may be provided with the above-described light shielding portion, step portion, or piezoelectric element portion.
In this case, the light intensity distribution (temperature distribution) not only in the direction perpendicular to the laser scanning direction (disc diameter direction) but also in the laser scanning direction becomes sharper, so that not only crosstalk can be reduced but also the linear density can be further improved. Can be achieved.

In the embodiment of the present invention described above, the magneto-optical disk 15 is used as the optical recording medium. However, an optical recording medium such as the above-mentioned reflectance-change type optical disk can also be used. The configuration of the optical head in this case is different from the magneto-optical disk 15 shown in FIG.
The other configuration is the same as that of FIG. 1 described above, except that a phase-change-type or other reflectance-change optical disk is used, and the specific configuration and operation are as described with reference to FIGS. . Thus, the optical recording medium of the reflectance change type will be described in detail below.

As a technique relating to the optical recording medium of the reflectance change type, the present applicant has previously proposed a signal reproducing method of an optical disc in the specification and drawings of Japanese Patent Application No. 2-94452. An optical disk is proposed in the specification and drawings of Japanese Patent Application No. 2-291773. That is, in the former, readout light is applied to an optical disc in which phase pits are formed in accordance with a signal and reflectivity changes according to temperature, and the reflectivity is partially changed within a scan spot of the readout light. We have proposed a signal reproduction method for optical disks characterized by reading phase pits. In the latter method, a material layer whose reflectivity changes due to a phase change is formed on a transparent substrate on which phase pits are formed. A so-called phase-change type optical disc, characterized in that when irradiated with readout light, the material layer partially changes phase within a scan spot of the readout light and returns to an initial state after reading. is suggesting.

Here, a phase change material layer which can be crystallized after melting is used as the material layer, and when the reading light is irradiated, this phase change material layer partially melts in the scanning spot of the reading light. It is preferable that the liquid phase be converted into a liquid phase in the oxidized region to change the reflectance and return to a crystalline state after reading.

The optical recording medium of the reflectance change type, in particular, the phase change type optical disk will be described. As shown in FIG. 10, a schematic sectional view of a main part of this phase-change type
A phase change material layer 104 is formed on a transparent substrate 102 on which the phase pits 101 are formed (the lower surface side in the drawing) via a first dielectric layer 103, and the phase change material layer 104 is formed on the material layer 104 (the lower surface in the drawing). Side, the same applies hereinafter), a second dielectric layer 105 is formed, and a reflective film 106 is formed thereon. The first dielectric layer 103 and the second dielectric layer 105 set optical characteristics such as reflectance. Further, a protective film (not shown) is often formed on the reflective film 106 as needed.

In addition, as a structure of this phase change type optical disk, for example, as shown in FIG. 11, a phase change material layer 1 is directly formed on a transparent substrate 102 on which pits 101 are formed.
12, a first dielectric layer 103, a phase change material layer 104, and a first dielectric layer 103 may be formed on a transparent substrate 102 on which phase pits 101 are formed, as shown in FIG. A structure in which the second dielectric layer 105 is sequentially formed may be used.

Here, as the transparent substrate 102, a glass substrate, a synthetic resin substrate such as polycarbonate or methacrylate, or the like can be used. A photopolymer is formed on the substrate, and the phase pits 10 are formed by a stamper.
Various configurations such as forming 1 can be adopted.

As a material that can be used for the phase change material layer 104, a material in which the phase changes partially within the scanning spot of the reading light, returns to the initial state after reading, and the reflectance changes due to the phase change. Can be Specifically, Sb
Chalcogenite, such as ₂ Se ₃ and Sb ₂ Te ₃ , that is, a chalcogen compound is used. As another chalcogenite or a single chalcogen, each of Se and Te alone, and these chalcogenites, that is, BiT
e, BiSe, In-Se, In-Sb-Te, In-
SbSe, In-Se-Tl, Ge-Te-Sb, Ge
A chalcogenite-based material such as -Te is used. When the phase change material phase 104 is composed of such chalcogen and chalcogenite, its properties such as thermal conductivity and specific heat should be set as desirable properties for forming a good temperature distribution by reading light with a semiconductor laser beam. As a result, it is possible to favorably form a molten state in a melt crystallization region as described later, and to perform ultra-high-resolution reproduction with high S / N or C / N.

The first dielectric layer 103 and the second dielectric layer 105 are made of, for example, Si ₃ N ₄ , SiO,
SiO ₂ , AlN, Al ₂ O ₃ , ZnS, MgF ₂ or the like can be used. Further, Al, Cu, Ag, Au, or the like can be used as the reflection film 106, and a material obtained by adding a small amount of an additive to these elements may be used.

Hereinafter, as a specific example of a phase-change type optical disk, a phase-change material layer which can be crystallized after melting is formed on a transparent substrate on which phase pits are formed. The phase change material layer is partially liquid-phased in the melt-crystallized region in the scanning spot of the readout light, changes the reflectance, and returns to the crystalline state after the readout. An optical disk having the above configuration will be described.

As a transparent substrate 102 in FIG. 10, a so-called glass 2P substrate is used, and phase pits 101 formed on one main surface of the substrate 102 have a track pitch of 1.6.
The pit was formed under the following conditions: pit, pit depth: about 1200 °, pit width: 0.5 μm. Then, a first dielectric layer 103 made of AlN is formed on one main surface of the transparent substrate 102 having the pits 101, and a phase change material layer 104 is formed on the first dielectric layer 103 (on the lower side in the figure, the same applies hereinafter). Sb ₂ Se ₃ was deposited. Further, a second dielectric layer 105 of AlN was formed thereon, and an Al reflective film 106 was formed thereon.

The following operation was first performed on the optical disk having such a configuration, using a portion where no signal was recorded, that is, a mirror portion where the phase pit 101 did not exist.

That is, first, a laser beam of, for example, 780 nm is irradiated so as to focus on one point of the optical disk, and the optical disk is gradually cooled and initialized (crystallized). Next, the same point was irradiated with laser pulse light while fixing the laser power P in the range of 0 <P ≦ 10 mW. In this case, the pulse width t
Was set to 260 nsec ≦ t ≦ 2.6 μsec. As a result, before irradiation with pulsed light and after cooling (normal temperature) after irradiation,
If the reflectance in both solid state changes, it means that the material layer has changed from crystalline to amorphous. In this operation, even if the reflectance does not change at the beginning and end, if the amount of return light changes once during the irradiation of the pulsed light, it means that the film in the crystalline state is once liquidized and crystallized again. Means that A region in a molten state in which a liquid state can be once brought into a crystallized state after a temperature drop as described above is referred to as a molten crystallization region.

FIG. 13 shows the phase change material layer 10 as described above.
In the case where Sb ₂ Se ₃ is used as 4, the horizontal axis represents the irradiation laser beam pulse width and the vertical axis represents the laser beam power, and these values and the phase state of the phase change material layer 104 are shown. is there. In the figure, a region R ₁ shown by hatching below the curve a, the phase change material layer 104 is a region where it remains holding the initial state in which no melting of.
Becomes a liquid phase i.e. melted by the laser beam spot irradiation in above the curve a in the figure, in particular a region R ₂ between the curves a and b, the laser beam spot is eliminated (to about room temperature) A melt crystallization region which returns to a crystallized state when cooled to a solid phase by being cooled, whereas a region R ₃ shown by a cross-hatched line above the curve b excludes laser light spots and cools. This is a molten amorphous region which becomes amorphous when it is solidified.

In the above specific example of this embodiment, FIG.
So that the liquid state in the melt crystallized region R ₂ may occur at the time of reproduction in, in the course of cooling from a heated state by the irradiation of the reproduction of the reading light to a normal temperature, the melting point MP
The reproduction light power, the configuration of the optical disc, the material, the thickness of each film, and the like are selected such that the time Δt required to perform the solidification from the time Δt is longer than the time t ₁ required for crystallization.

In the above example, the thickness of each layer is set so that the reflectance in the molten state is higher than the reflectance in the initialized state, that is, the reflectance in the crystallized state. Next, as another specific example of the above-described phase-change optical disk, when Sb ₂ Te ₃ is used for the phase-change material layer 104, the results of measuring the phase-change state in the same manner as in FIG. 13 are shown. 14. In FIG. 14, FIG.
The same reference numerals are given to portions corresponding to and the description will be omitted.
Also in this case, the thickness and the like of each layer are selected so that the reflectance in the molten state is higher than the reflectance in the crystallized state, that is, the initialized state.

In the case of chalcogenite or chalcogen such as Sb ₂ Se ₃ and Sb ₂ Te ₃ , the reflectance in the amorphous state and the reflectance in the molten state show almost the same value. Then, the optical disk used in the embodiment of the present invention reproduces at an ultra-high resolution by utilizing a temperature distribution in a scanning spot on the optical disk upon reproduction.

FIG. 1 shows a case where the above-mentioned phase-change optical disk according to the embodiment of the present invention is irradiated with a laser beam.
This will be described with reference to FIG.

In FIG. 15, the abscissa indicates the position related to the spot scanning method X. The light intensity distribution of the beam spot SP formed by irradiating the laser beam on the optical disk is indicated by a broken line a in FIG. Become like On the other hand, the temperature distribution in the phase-change material layer 104 appears slightly behind on the rear side in the beam scanning direction X corresponding to the scanning speed of the beam spot SP, as shown by a solid line b in FIG.

Here, when the laser light beam is being scanned in the direction of arrow X in the figure, the temperature of the optical disk of the medium gradually rises from the leading end in the scanning direction with respect to the beam spot SP, and finally, Melting point MP of phase change material layer 104
The above temperature is reached. At this stage, the phase change material layer 104
Changes from the initial crystalline state to the molten state, and the transition to the molten state increases, for example, the reflectance. in this case,
Reflectivity region P _X which are denoted by the hatched beam spot in the SP becomes higher. That is, in the beam spot SP, the area P where the phase pit 101 can be read out
And _X, read and retain the crystalline state exists and almost impossible region P _Z. Accordingly, in the case where the phase pit 101 for example, two in the same spot within the SP as shown is also present, it is read out miso for one phase pit 101 present in the region P _X where reflectivity is larger can, for other phase pit, which is not done this read in the very low region P _Z reflectance. As described above, even if a plurality of phase pits 101 exist in the same spot SP, it is possible to read out only a single phase pit 101.

Accordingly, when the wavelength of the reading light beam is λ and the numerical aperture of the objective lens is NA, the shortest phase pit interval (so-called track pitch) of the recording signal in the direction orthogonal to the scanning direction of the reading light beam. It is clear that good reading can be performed even if the spot diameter is 以下 or less of the spot diameter, the signal can be read with ultra-high resolution, the recording density, especially the track density can be improved, and the medium recording capacity can be increased. Can be done.

Further, as in the present invention, the optical element as shown in FIG. 5, FIG. 7, FIG. 8 or FIG. 9 is arranged in the optical path of the light beam from the laser light source to scan the laser light beam. By providing a sharper temperature distribution in the direction orthogonal to the direction _X , the width of the area PX in which the reflectivity is increased as shown in FIG. 15A in the same direction can be further reduced, and the crosstalk from the adjacent track is greatly reduced. This can be reduced.

In the above-described example, various conditions such as a high reflectivity when the phase change material layer 104 is in a molten state and a low film thickness in a crystalline state are set. By selecting various conditions such as the configuration and thickness of the phase change material, the reflectance in the molten state can be reduced and the reflectance in the crystalline state can be increased. In this case, the laser light shown in FIG. One phase pit 101 exists in the high temperature region P _X in the spot SP,
It may be configured to read out miso from one phase pits 101 in the region P _X. Also, the temperature rises by a laser beam irradiation, for example, such as by reaching the fused amorphous region R _3, such as in a state of being cooled to room temperature does not return to the initial state such as the crystalline state reversible Even when a significant phase change occurs, an operation of initializing may be performed by any means, and does not depart from the gist of the present invention. For example, heating a laser spot of elliptical system irradiated after spot, or heat the phase change material layer 104 to above melt crystallization region R _2, the crystallization temperature or higher at a temperature lower than the melting point MP for the reproduction If you do
The phase change material layer 104 returns from an amorphous state to a crystalline state, and is initialized.

In the above embodiment, the reflectivity is changed by the phase change of the medium. However, the change in the reflectivity may use any phenomenon.
As in still another embodiment of the present invention shown in FIG. 16, the reflectance may be changed depending on the temperature by using the change in the spectral characteristic due to the adsorption of moisture in the interference filter.

That is, in FIG. 16, on the transparent substrate 132 on which the phase pits 131 are formed, materials having greatly different refractive indices are placed on the transparent substrate 132, each having a thickness of one wavelength λ of the reproduction light.
The interference filter is formed by repeatedly forming a film so that the ratio becomes / 4. In this example, as a material having a significantly different refractive index, the MgF layer 133 (refractive index 1.
38) and a ZnS layer 134 (refractive index: 2.35). Of course, the present invention is not limited to this, and any combination of materials having a large difference in refractive index may be used.
SiO having a small refractive index (refractive index 1.5) and the like,
TiO ₂ (refractive index 2.
73) and CeO ₂ (refractive index: 2.35).

The above-mentioned MgF layer 133 and ZnS layer 134 are formed by vapor deposition. When these layers are formed by vapor deposition, if the ultimate vacuum is set lower than usual, for example, about 10 ⁻⁴ Torr, the film structure becomes so-called porous. And moisture remains there. Then, in the interference filter made of the film in which the moisture remains, the reflectance spectral characteristics are greatly different between room temperature and when the temperature is raised to near the boiling point of water, as shown in FIG. 17, for example. That is, at room temperature, the characteristic that the wavelength λ _R is an inflection point as shown by the curve i in the figure, whereas when the temperature is raised to near the boiling point, the wavelength λ _H is increased as shown by the curve ii in the figure. A sharp wavelength shift is observed such that the characteristic becomes an inflection point, and returns to the characteristic shown by the curve i when the temperature decreases. This phenomenon is considered to be due to the fact that the refractive index changes significantly due to the vaporization of water, and the spectral characteristics change due to this effect.

Therefore, if the wavelength of the light source of the reproduction light is selected to be the intermediate wavelength λ ₀ between the inflection points λ _R and λ _H , the reflectance changes dynamically between room temperature and heating.

In this specific example, high-density reproduction is performed utilizing this change in reflectance. The principle that enables high-density reproduction is as described with reference to FIG. 15 described above. In this case, a region in which water has vaporized and a wavelength shift has occurred corresponds to a high reflectance region, and the temperature has not risen. The part has a masked shape. In this example, since the reflectance characteristic returns to the original state when the temperature decreases, no special erasing operation is required.

The present invention is not limited to only the above-described embodiment. For example, the position of the optical element such as the phase plate may be any position between the laser light source and a medium such as a magneto-optical disk. For example, it may be arranged immediately before the objective lens (on the side of the laser light source). Also, for example,
The present invention can be applied to not only a disk-shaped medium but also a card-shaped or sheet-shaped medium as the optical recording medium.

[0077]

As is apparent from the above description, according to the optical head device of the present invention, the temperature distribution generated on the magneto-optical recording medium or the reflectance-change type optical recording medium by the irradiation of the laser beam is utilized. When reading a signal only from the signal detection area in the spot of the laser light, the laser light passing therethrough in the emission optical path of the laser light, The optical system is formed so as to have a phase difference of an odd multiple of で wavelength and has a sharper temperature distribution in a direction perpendicular to the scanning direction of the read light beam on the recording medium irradiated with the read light beam. Since the elements are arranged, the width of the signal detection area in the laser beam spot in the direction orthogonal to the laser beam scanning direction can be reduced to reduce crosstalk from an adjacent track and increase the track density. Door can be.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an optical head device used for describing the present invention.

FIG. 2 is a schematic front view of a light-shielding strip.

FIG. 3 is a diagram showing a light intensity distribution of a spot of a laser beam on a medium along a direction orthogonal to a laser beam scanning direction.

FIG. 4 is a plan view schematically showing a spot of a laser beam on a magneto-optical recording medium.

5A and 5B show a phase plate having a step used in the optical head device according to the embodiment of the present invention, wherein A is a front view and B is a side view.

FIG. 6 is a diagram showing a light intensity distribution of a spot of a laser beam on a medium along a direction orthogonal to a laser beam scanning direction.

FIG. 7 shows a phase plate using a transparent piezoelectric material used in an optical head device according to an embodiment of the present invention, where A is a front view,
B is a side view.

FIG. 8 shows another example of a phase plate using a transparent piezoelectric material used in an optical head device according to an embodiment of the present invention, wherein A is a front view and B is a side view.

FIG. 9 is a front view showing another example of an optical element for obtaining a sharp temperature distribution during laser beam irradiation.

FIG. 10 is a schematic cross-sectional view showing a main part of an example of a phase-change optical disc as another example of an optical recording medium usable for the optical head according to the present invention.

FIG. 11 is a schematic cross-sectional view showing a main part of another example of the phase change optical disk.

FIG. 12 is a schematic cross-sectional view showing a main part of still another example of the phase change optical disc.

FIG. 13 is a diagram showing a phase change state for explaining the phase change type optical disc.

FIG. 14 is a diagram showing another phase change state for explaining the phase change type optical disc.

FIG. 15 is a diagram showing a relationship between a read light spot and a temperature distribution for explaining the phase change optical disk.

FIG. 16 is a schematic cross-sectional view showing a main part of a reflectivity change type optical disk using an interference filter.

FIG. 17 is a characteristic diagram showing how the spectral reflectance characteristics of the interference filter change with temperature.

FIG. 18 is a diagram showing the relationship between the spot diameter of a laser beam and the recording density of reproducible recording pits.

FIG. 19 is a diagram for explaining an erasing type magneto-optical recording medium, a reproducing method thereof, and a substantial reproducing area of the medium.

FIG. 20 is a diagram for explaining a floating type magneto-optical recording medium, a reproducing method thereof, and a substantial reproducing area of the medium.

FIG. 21 is a plan view schematically showing a spot of a laser beam on a magneto-optical recording medium.

[Explanation of symbols]

11 laser light source, 12 collimator lens, 13
Beam splitter, 14 objective lens, 15 magneto-optical disk, 16 condenser lens, 17 photodetector,
18 magnetic head, 21 light-shielding band, 22 light-shielding band, phase plate having 26 steps

──────────────────────────────────────────────────続 き Continuing from the front page Examiner Nobuyuki Umeoka (56) References Hikaru 2-132325 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 11/105 G11B 7 / 12-7/22

Claims (4)

(57) [Claims] 1. A recording medium comprising: a multilayer film having at least a reproducing layer and a recording holding layer which are magnetically coupled to each other; a signal is magnetically recorded in the recording holding layer; The reproducing layer is heated by irradiating the reproducing layer with a light beam to the magneto-optical medium in which the signals are aligned, and the signal magnetically recorded on the recording holding layer is transferred to the reproducing layer. In the optical head device, the laser beam is converted into an optical signal by the magneto-optical effect and read, and the laser beam passing through the output optical path of the read light beam is an odd multiple of 1/2 wavelength at the central portion and the peripheral portion. The readout light beam is formed so as to have a phase difference.
An optical head device provided with an optical element having a sharper temperature distribution in a direction perpendicular to the scanning direction of the read light beam on a recording medium to be read. 2. The optical head device according to claim 1, wherein the optical element has a step portion whose central portion has a thickness different from that of a peripheral portion. 3. A recording medium in which a phase pit is formed in accordance with a signal and the reflectance of which changes with temperature is irradiated with a reading light beam, and the reflectance changes partially within a scanning spot of the reading light beam. In an optical head device that reads a phase pit while causing the laser beam to pass through, the laser beam passing through the optical path of the read light beam has a phase difference of an odd multiple of 波長 wavelength between the central portion and the peripheral portion. Formed and irradiated with the read light beam
An optical head device provided with an optical element having a sharper temperature distribution in a direction perpendicular to the scanning direction of the read light beam on a recording medium to be read. 4. The optical head device according to claim 3, wherein the optical element has a step portion whose center portion has a thickness different from that of a peripheral portion.