JPH076409A - Optical disk and its tracking method - Google Patents

Abstract

PURPOSE:To enable sure tracking by extending perpendicularly magnetized layers exhibiting polarization angles according to magnetization directions along one side edge of respective tracks and magnetizing these perpendicularly magnetized layers in the predetermined direction between the adjacent tracks. CONSTITUTION:Information for tracking is recorded on magnet-optical films 5. A laser beam for recording is so controlled that the centers of the magneto- optical films 5 are irradiated with the center of the spot light obtd. by condensing the laser beam for recording at the time of recording the tracking information on the magneto-optical films 5. The directions of the magnetization of the magneto-optical films 5 are unified by heating the magneto-optical films 5 up to a magnetization inversion temp. by this laser beam and impressing a weak magnetic field from the outside when coercive force weakens. Then, the information for tracking is displayed by the difference of the magnetization direction. The optical disk of the high density is thus produced. Tracking by detecting the magnetization direction of the perpendicularly magnetized layers as polarized light from the spot light is possible at the time of reproduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc and its tracking method.

[0002]

2. Description of the Related Art Generally, a conventional optical disc uses a phase change film or a magneto-optical film as a recording layer for recording information. When information is recorded on an optical disc having these as recording layers, the recording layer is irradiated with spot light obtained by condensing a laser beam, and the portion irradiated by the spot light is heated, The recording is performed by changing the crystal structure and the magnetization direction of the.

Further, in the case of tracking an optical disc on which information is recorded by the above-mentioned method, light interference (land) caused by a guide groove (groove) and a flat portion (land) provided when a substrate is formed. Tracking is performed by using the interference of the reflected light from the and the reflected light from the groove).

[0004]

However, in the above-mentioned conventional optical disc, the spot light used for recording information is obtained by converging the laser light with the objective lens, but it is obtained from the diffraction limit. Since the spot diameter depends on the wavelength of the laser light, in other words, unless the wavelength of the laser light becomes shorter, the spot diameter cannot be made smaller, so that it is impossible to record information at a higher density. There was a problem.

Further, even when the conventional optical disc is tracked, a plurality of optical discs having an extremely narrow track pitch (for example, about half the spot diameter) compared with the spot diameter of the laser beam generated from the diffraction limit are used. Since the spot light is irradiated on the track No. 2, the change in the amount of reflected light becomes small, and there is a problem that tracking cannot be performed.

Further, as a method of forming a pit smaller than the spot diameter of the laser beam, there is a so-called writing point recording method in which recording is performed using only the central portion of the spot of the laser beam, but in an optical disc recorded in this way However, there is a problem that tracking cannot be performed as described above.

Further, there is also a method of reading information at a high density by utilizing a difference between a portion irradiated with laser light and a portion heated by forming two or more magneto-optical layers. Even in such cases, there is no specific method for tracking, and it is actually difficult to reproduce.

It is an object of the present invention to solve the above problems and provide an optical disc capable of recording information at high density and a tracking method therefor.

[0009]

In order to solve the above-mentioned problems, an optical disk according to a first aspect of the present invention is a track comprising a recording layer on a substrate, the recording layer showing different reflectances depending on the difference in crystal structure or phase structure. In the optical disc formed adjacent to each other, a perpendicular magnetic layer having different polarization angles depending on the magnetization direction extends along one side edge of each track, and the perpendicular magnetic layer is predetermined between adjacent tracks. It is characterized by being magnetized in the opposite direction.

The optical disc according to the invention of claim 2 is the optical disc of claim 1, wherein the perpendicularly magnetized layers are magnetized in mutually opposite directions between adjacent tracks. It is a thing.

According to a third aspect of the present invention, in the optical disc of the second aspect, the pitch dimension of the track formed by the recording layer and the perpendicular magnetization layer is the laser beam irradiated. It is characterized in that it is formed in the range from 1: 1 to 2/5 times the spot diameter.

According to a fourth aspect of the present invention, in the optical disc according to the first aspect, the perpendicular magnetization layer includes a plurality of pairs of two adjacent tracks magnetized in the same direction. It is characterized in that the magnetization directions of the perpendicular magnetization layers are formed in mutually opposite directions between each adjacent pair.

Further, in the optical disc of the fifth aspect of the present invention, in the optical disc of the fourth aspect, the pitch dimension of the track formed by the recording layer and the perpendicular magnetization layer is the laser beam irradiated. It is characterized in that it is formed in the range from 1: 1 to 2/7 times the spot diameter.

Further, in the optical disc according to the invention described in claim 6, in the optical disc described in claim 1, the partial thermal diffusion layer corresponding to information to be recorded along the track direction is the recording layer. It is characterized by being formed so as to overlap.

Further, in the tracking method according to the invention described in claim 7, the perpendicular magnetization exhibiting different polarization angles according to a predetermined magnetization direction in the recording layer exhibiting different reflectance depending on the difference in crystal structure or phase structure. For an optical disc in which tracks formed by juxtaposing layers are formed adjacent to each other on a substrate,
A tracking method for irradiating a spot light onto a track by converging laser light and performing tracking based on information obtained from the spot light, which is due to a difference in magnetization direction of the perpendicular magnetic layer between adjacent tracks. The tracking information of the optical disk is obtained by detecting the deviation of the polarization plane of light.

Further, in the tracking method according to the invention described in claim 8, in the tracking method according to claim 7, a plurality of spot lights are respectively focused on different tracks by focusing the laser light on the optical disk. It is characterized in that the tracking information of the optical disc is obtained by irradiating the optical disc to the optical disc and performing arithmetic processing on the plural detection signals obtained from the plural spot lights.

[0017]

In the optical disk according to the invention described in claim 1,
The recording layer of the track on the substrate is a recording layer that exhibits different reflectances depending on the difference in crystal structure or phase structure, and therefore is used as an information recording track of a rewritable optical disc, for example. A perpendicular magnetic layer showing a polarization angle different depending on the magnetization direction is extended along each side edge on each track, and the perpendicular magnetic layer is magnetized in a predetermined direction between adjacent tracks. . When a track is illuminated with a light spot, for example, the reflected light contains a polarization component having a polarization angle according to the magnetization direction of the perpendicularly magnetized layer of the track being illuminated. This polarization component is used for detecting the tracking signal by the light receiving element. For example, when the track pitch is equal to the light spot diameter, the perpendicular magnetization layers of the adjacent tracks are located in the light spot in the same area ratio in the tracking state. In this case, the polarization component of the perpendicular magnetic layer of one track and the polarization component of the perpendicular magnetic layer of the other track have different polarization angles, and both are balanced. When the tracking shifts to one side, either polarization component increases and the other decreases. Such changes in the polarization component are used as tracking information.

According to a second aspect of the present invention, in the optical disc of the first aspect, the perpendicular magnetization layers are magnetized in mutually opposite directions between adjacent tracks. This optical disc can detect the tracking state of the light spot to be irradiated by taking the difference between the P-polarized component and the S-polarized component contained in the reflected light when the track is illuminated by the light spot.

In the optical disk according to the present invention, the track pitch dimension can be made equal to or smaller than the light spot diameter to achieve high density. Particularly, in the optical disk according to the third aspect of the present invention,
In the optical disc according to claim 2, the pitch dimension of the track formed by the recording layer and the perpendicularly magnetized layer is formed in the range of 1 to 2/5 times the spot diameter of the irradiated laser beam. .

According to a fourth aspect of the invention, in the optical disc according to the first aspect, a plurality of pairs of adjacent tracks whose perpendicular magnetization layers are magnetized in the same direction are formed adjacent to each other. The magnetization directions of the perpendicular magnetic layers are formed in mutually opposite directions between the adjacent pairs.
Thus, for example, by obtaining the sum or difference of the differentials of the polarization components included in the reflected light when the track is illuminated with the light spot, it is possible to more accurately detect the tracking state of the light spot.

According to the optical disk of the fifth aspect of the present invention, in the optical disk of the fourth aspect, the pitch dimension of the track formed by the recording layer and the perpendicularly magnetized layer is relative to the spot diameter of the laser beam irradiated. 1x to almost 2
It is formed in a range of / 7 times.

According to a sixth aspect of the present invention, in the optical disc of the first aspect, a partial heat diffusion layer corresponding to information to be recorded is superposed on the recording layer along the track direction. Is formed. The recording layer in which such a partial heat diffusion layer is selectively formed is
For example, it is used as an information recording track of a read-only optical disc.

According to a seventh aspect of the present invention, there is provided a tracking method in which a laser beam is focused on the optical disc according to the first aspect to irradiate a spot light onto a track and to obtain information obtained from the spot light. This is a method of tracking based on the above. Here, the tracking information of the optical disc is obtained by detecting the deviation of the polarization plane of light due to the difference in the magnetization direction of the perpendicular magnetization layer between adjacent tracks.

In the tracking method according to the invention described in claim 8, in the method described in claim 7, a plurality of spot lights obtained by focusing the laser light on the optical disk are irradiated to different tracks. The tracking information is obtained by arithmetically processing a plurality of detection signals obtained from the plurality of spot lights. In this case, polarization components having different polarization angles are obtained from the respective spot lights, the polarization components are deviated for each polarization angle, and tracking is performed based on the sum or difference thereof.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing the structure of an optical disk showing a first embodiment of the present invention, and is an enlarged partial sectional view perpendicular to the track direction. As shown in FIG. 1, an optical disc 1 according to this embodiment includes a substrate 2, a first protective film 3, a recording layer (hereinafter, a phase change film) 4, a perpendicular magnetization layer (hereinafter, a magneto-optical film).
5 and the second protective film 6. The substrate 2
Is a circular substrate made of glass or the like and having a diameter of 130 mm. The first protective film 3 is made of ZnS; SiO ₂ and is formed on the substrate 2 with a thickness of about 100 nm by a sputtering method (RF magnetron sputtering). The target used for sputtering was a mixed target of ZnS; SiO ₂ , and the gas pressure in the chamber of the sputtering apparatus was once evacuated to 2 × 10 ⁻⁶ Torr or less, and then Ar gas was introduced into the chamber. Was sputtered at a gas pressure of 5.times.10.sup. ^-3 Torr.

The phase change film 4 is made of Ge ₂ Sb ₂ T.
consist e _5, in order to form a phase change layer 4 on the first protective layer 3, by the same sputtering method as that forming the first protective layer 3 on the substrate 2 the first The phase change film 4 having a thickness of about 50 nm was formed on the protective film 3. The target used for sputtering when forming the phase change film 4 is a Ge ₂ Sb ₂ Te ₅ target.
In FIG. 1, the phase change film 4 constitutes a recording layer for each track, and a magneto-optical film 5 described later is provided along each track, and the phase-change film 4 and the magneto-optical film 5 are alternately arranged when viewed as a whole. It is formed on the first protective film 3 by first forming the phase change film 4 on the entire surface of the first protective film 3 and forming a magneto-optical film forming region for each track by a lithography method. Etching is performed, and the magneto-optical film 5 is formed on the etched portion by a sputtering method.

The magneto-optical film 5 is made of TbFeCo or the like, and is formed on the first protective film 3 in a concentric shape with a thickness of about 50 nm. That is, as described above, first, a resist (not shown) is first applied on the phase change film 4 formed on the entire surface of the first protective film 3, and a concentric circle having a pitch of 1 μm and a width of 0.5 μm. The pattern was patterned by an exposure device such as a stepper. Since the pattern shape is simple, the exposure in this case could be performed relatively easily by exposing while rotating.

After patterning, the resist was developed and the phase change film 4 was etched into the concentric pattern by reactive ion etching (RIE) (or ion beam etching may be used). As a result, the phase change film 4 selectively remained on the first protective film 3 according to the pattern, and the first protective film 3 was exposed in the concentric recesses. The magneto-optical film 5 was formed in this concave portion by sputtering so that the phase change film 4 and the magneto-optical film 5 appeared alternately and concentrically as shown in FIG. The material of the phase change film 4 (Ge ₂ Sb ₂ Te ₅ ) and the material of the magneto-optical film 5 (TbF).
eCo) is set so that the magnetization reversal temperature of the material of the magneto-optical film 5 is equal to or higher than the melting point temperature of the material of the phase change film 4 in consideration of the influence of the temperature of the spot light irradiated during the tracking described later. The materials were selected.

After forming the magneto-optical film 5, Zn is formed on the entire surface.
A second protective film 6 made of S; SiO ₂ was formed. still,
This second protective film 6 is also formed by the same sputtering method as described above.

A similar optical disk can be formed even if the order of forming the phase change film 4 and the magneto-optical film 5 is reversed.
In this case, by forming the magneto-optical film 5 first on a part of the width pitch of each track and then forming the phase change film 4, it is possible to obtain an optical disk having a sectional structure as shown in FIG.

In the optical disc 1 thus formed, each track has a phase change film 4 and a magneto-optical film 5 each having a width of 0.5 μm.
And the track pitch is 1 μm. Therefore,
It can be used as a rewritable optical disc that can record information at a higher density than conventional ones.
The principle of the information recording method will be described.

First, the case of recording tracking information will be described. Information for tracking is recorded on the magneto-optical film 5. When recording the tracking information on the magneto-optical film 5, the recording laser light is focused so that the center of the spot light obtained by condensing the recording laser light is irradiated to the center of the magneto-optical film 5. Adjust. The laser beam heats the magneto-optical film 5 to the magnetization reversal temperature,
When the coercive force becomes weak, a weak magnetic field (in this embodiment, an external magnetic field, about 300 Oe) is applied from the outside to align the magnetization directions of the magneto-optical film 5. Then, the tracking information is represented by the difference in the magnetization direction. still,
In this embodiment, the recording magnetic field is reversed for each track so that the magnetization direction is reversed for each track of the adjacent magneto-optical film 5. Further, since the portion of the portion irradiated by the spot light and heated to the magnetization reversal temperature is smaller than the spot diameter, only the portion having a width smaller than the spot diameter can be magnetized.

Next, the case of recording signal information on the optical disc 1 will be described. When signal information is recorded on the phase change film 4 of the optical disc 1, the recording laser is adjusted so that the center of the spot light obtained by condensing the recording laser light is irradiated to the center of the phase change film 4. Adjust the light tracking. Then, the phase change film 4 is heated above the melting point temperature of the phase change material to change the crystal structure of the phase change material (crystal → amorphous). The optical disk 1 is composed of the part where the crystal structure is changed and the part where it is not changed.
The recorded information of is represented. Here, when the spot light is applied to the phase change film 4, not all of the spot light has a high temperature (because the laser light amount has a Gaussian distribution), and the center portion of the spot light has a particularly high temperature. Becomes
Therefore, at the time of recording, it is possible to perform recording with a width narrower than the spot diameter in the track pitch direction. Since the magnetization reversal temperature of the magneto-optical film 5 is higher than the temperature of the spot light irradiated for recording information on the phase change film 4, when recording on the phase change film 4, It does not affect the magnetization direction of the magneto-optical film 5.

Next, the case of reproducing the information recorded on the optical disc 1 will be described. As described above, the phase change film 4
, There are a part where the crystal structure is changed and a part where the crystal structure is not changed. When these parts are irradiated with spot light obtained by condensing the laser light for reproduction, the reflected light is The reflectance changes between the changed portion and the unchanged portion. When the optical disc 1 is reproduced, this difference in reflectance is detected and information is extracted. Since the diameter of the spot light obtained by condensing the reproducing laser light is larger than the width of the phase change film 3, the reproducing laser is also recorded on the magneto-optical film 5 of the track adjacent to the phase change film 4. Although a spot light of light is emitted, the amount of reflected light from the magneto-optical film 5 is small, and the magneto-optical film 5 does not show different reflectance depending on the presence or absence of information (magneto-optical film). 5
Since the material (1) is not a material whose reflectance changes due to a change in crystal structure or the like), only the information recorded in the phase change film 4 can be reproduced.

Next, the case where the tracking of the optical disc 1 on which the tracking information is recorded as described above is performed will be described. As described above, in the magneto-optical film 5, tracking information having different magnetization directions is recorded for each track (one track) of the adjacent magneto-optical films 5. When the surface of the magneto-optical film 4 is irradiated with spot light obtained by focusing laser light, the reflected light exhibits different polarization angles depending on the direction of magnetization (optical Kerr effect). When the optical disk 1 is tracked, this polarization angle is detected. Since the diameter of the spot light obtained by focusing the laser light is larger than the width of the magneto-optical film 4, the spot light of the laser light is also applied to the phase change film 4 adjacent to the magneto-optical film 5. However, since the reflected light from the phase change film 4 is not reflected light that influences the polarization angle (not magnetized), when tracking is performed, the polarization angle of the polarization angle obtained from the magneto-optical film 5 is changed. Tracking can be performed by detecting only the difference.

FIG. 3 is an explanatory diagram showing a schematic structure of a main part of the reproducing apparatus when the optical disc 1 in the first embodiment is used. As shown in FIG. 3, the reproducing apparatus in the present embodiment is roughly divided into a rotating system, a reproducing laser light source system, and a detecting system, and the rotating system rotates the optical disk 1 at a constant rotation speed. The reproducing laser light source system has λ = 780n
m, the numerical aperture (NA) = 0.55, the semiconductor laser light source 7 and the lens 8, and the filters 9 and 10 are mainly included. Further, the reproducing system includes detectors 11 and 12 such as photodiodes and polarization beam splitters 13 and 1 for transmitting light to the detectors 11 and 12 separately.
4, a summing amplifier 15 for outputting the sum or difference of the output signals from the detectors 11 and 12, and a differential amplifier 1
It is mainly composed of 6.

The optical disk 1 described above is rotated by a rotating system, and laser light is emitted from the semiconductor laser light source 7. This laser light is focused on the optical disc 1 by passing through an optical system, and the spot diameter is determined by the diffraction limit. The spot diameter at this time is about 1.4.
.mu.m, and FIG. 4 (a), (b), (c), (d)
As shown in, the spot light is irradiated on about 1.5 tracks. Then, the tracking information and the signal information described above are read by the spot light. That is, the reflected light of the spot light, after passing through the lens 8, the polarization beam splitter 13, the filter 10 and the like shown in FIG. 3, is divided into two by the polarization beam splitter 14, and is received by the detectors 11 and 12, respectively, and is electrically converted. After being converted into signals, the sum of them is taken by the adding amplifier 15 to reproduce the signal information, and the differential amplifier 16
The tracking signal is extracted by taking the difference between them.

The tracking signal will be described. When the center of the spot light of the reproducing laser beam is on the center of the phase change film 4 of the regular track (FIG. 4C).
The tracking signal from the differential amplifier 16 becomes zero. Further, if the center of the spot light is deviated and is located right above the magneto-optical film 5, the tracking signal has a positive or negative maximum value (see FIGS. 4A and 4B). In the intermediate state, for example, when the spot center of the laser beam is deviated from the center of the phase change film 4 of the regular track as shown in FIG. Since the amount of light of each polarization component from the different magneto-optical film 5 is different, the tracking signal output from the differential amplifier does not become 0 but has a positive or negative certain value.

Therefore, tracking can be performed by controlling the spot position of the reproducing laser light so that the tracking signal from the differential amplifier 16 is always zero. In this case, needless to say, the variation in the amount of reflected light from the phase change film 3 entering the spot does not affect the differential output due to the polarization. In addition, the magneto-optical film 5 does not affect the reproduction output in the tracking enabled state.

5A and 5B, the track pitch is made finer so that the width of the track pitch formed by the phase change film 4 and the magneto-optical film 5 of the optical disk 1 is the laser light irradiated. 2 shows a case where the density is increased to be approximately 2/5 of the spot diameter of 1. In this case also, tracking can be performed by using the reproducing apparatus shown in FIG.
It should be noted that FIG. 5A shows the case where the spot light irradiated on the optical disc 1 is tracked, and FIG. 5B shows the case where the tracking is off.

FIG. 6 is an explanatory diagram showing a schematic structure of a main part of another reproducing apparatus when the optical disc 1 in the first embodiment is used. As shown in FIG. 6, the reproducing apparatus in this embodiment is roughly classified into a rotating system, a reproducing laser light source system, and a detecting system, and the rotating system rotates the optical disk 1 at a constant rotation speed. The reproducing laser light source system has λ = 78
A semiconductor laser light source 7A having 0 nm and a numerical aperture (NA) = 0.55, a grating 18 for flattening the output distribution of laser light, filters 9A, 10A, a hologram 17 and a lens 8A for making three laser lights. More mainly composed. The reproducing system includes detectors 11A and 12A such as photodiodes and the detector 1
A polarization beam splitter 13A for splitting and transmitting light to 1A and 12A, a summing amplifier 15A for outputting the sum and difference of signals output from the detectors 11A and 12A,
The differential amplifier 16A, 16B, 16C and a rectifier circuit 19 for rectifying the output from the differential amplifier 16A, 16B are mainly included.

The difference between the reproducing apparatus shown in FIG. 6 and the reproducing apparatus shown in FIG. 3 is that three spot lights whose center positions are shifted by half tracks from the laser light emitted from the semiconductor laser light source 7A are provided on the optical disc 1. Then, the signal information is reproduced from one spot light in the center (hereinafter referred to as reproduction spot light), and the tracking signal is obtained from the two spot lights at both ends (referred to as tracking spot light). It is in the point that I made it. In this case, the relationship between the spot light irradiated on the optical disc 1 and each track is as shown in FIG.

In FIG. 6, the optical disk 1 is rotated by a rotating system and irradiated with laser light from a semiconductor laser light source 7A. By passing through this optical system, the laser light focuses three spot lights (a reproducing spot light and a tracking spot light) on the optical disc 1, and the spot diameter is determined by the diffraction limit. The spot diameters at this time are about 1.4 μm,
As shown in FIG. 7, spot light is irradiated on about 1.5 tracks. Then, the tracking information and the signal information described above are read by the three spot lights.

That is, the reflected lights of the three spot lights are
Lens 8, hologram 17, filter 10A shown in FIG.
And the like, and then divided into two by the polarization beam splitter 13A, and then received by the detectors 11A and 12A, respectively, and converted into electric signals. After that, the addition amplifier 15A obtains the respective sums to reproduce the signal information, and the differential amplifier 16A
After the difference between A and 16B is obtained and passed through the rectifier circuit 19, the difference is further obtained from the differential amplifier 16C to obtain the tracking signal. The electric signal output to the adding amplifier 15A is the optical signal
The electric signal obtained by converting the reproduction spot light irradiated on the upper side and output by the differential amplifiers 16A and 16B is the electric signal obtained by converting the two tracking spot lights irradiated on the optical disc 1. It is a signal.

The tracking signal of the reproducing apparatus shown in FIG. 6 will now be described. The centers of the two tracking spot lights are the magneto-optical film 5 of the regular track.
In the case of being on the center of (i.e., the case shown in FIG. 7), one of the tracking signals output from the differential amplifiers 16A and 16B has a positive or negative maximum value and the other has a negative or positive maximum value. It becomes a value. This is because the magnetization directions of the magneto-optical film 5 in the spots are different from each other, so that the light amounts of the respective polarization components are different. And
After the tracking signals output from the differential amplifiers 16A and 16B are passed through the rectifier circuit 19, the differential amplifier 1
Taking each difference through 6C, this differential amplifier 1
The tracking signal output from 6C is the sum of the signals output from the differential amplifiers 16A and 16B (maximum negative value).
Becomes

Incidentally, when the centers of the respective spot lights are deviated and located right above the phase change film 4 (cases (a) and (b) shown in FIG. 4), or a 1/4 track deviation occurs. In the case ((d) shown in FIG. 4), one of the tracking signals output from the differential amplifiers 16A and 16B does not have a positive or negative maximum value, and the other also has a negative or positive maximum value. Is not the maximum value of. Therefore, the tracking signal output from the differential amplifier 16C also does not have the maximum value.

Therefore, tracking can be performed by controlling the spot position of the reproducing laser light so that the tracking signal output from the differential amplifier 16C always has a negative maximum value. In this case, needless to say, the variation in the amount of reflected light from the phase change film 4 entering the spot does not affect the differential output due to the polarization. In addition, the magneto-optical film 5 does not affect the reproduction output in the tracking enabled state.

The magneto-optical film 5 of the optical disc 1 is also used.
When the tracking information is recorded in, the magnetization direction of the magneto-optical film 5 may be made different for every two adjacent tracks as shown in FIG. In this case, the width of the track pitch formed by the phase change film 4 and the magneto-optical film 5 of the optical disc 1 can be increased from the same size as the spot diameter of the irradiated laser light to about 2/7 times. . An example of the reproducing apparatus in this case will be described with reference to FIG.

FIG. 8 is an explanatory diagram showing a schematic structure of a main part of still another reproducing apparatus using the optical disk 1.
As shown in FIG. 8, the reproducing apparatus according to the present embodiment is roughly classified into a rotating system, a reproducing laser light source system, and a detecting system.
The rotation system rotates the optical disc 1 at a constant rotation speed. The reproducing laser light source system is a semiconductor laser light source 7 having λ = 780 nm and a numerical aperture (NA) = 0.55.
B, a grating 18A for flattening the output distribution of laser light, filters 9B, 10B, a hologram 17A for making three laser lights, and a lens 8B. The reproducing system includes detectors 11B and 12B such as photodiodes and the detector 11B and
A polarization beam splitter 13B for dividing and sending light to 12B, a summing amplifier 15B for outputting the sum and difference of signals output from the detectors 11B, 12B, differential amplifiers 16D, 16E, 16F, 16G, 16H, 16I.
And a rectifying circuit 19A for arithmetically processing the outputs from the differential amplifiers 16D, 16E, 16F.

The difference between the reproducing apparatus shown in FIG. 8 and the reproducing apparatus shown in FIGS. 3 and 6 is that the semiconductor laser light source 7 is used.
The optical disk 1 is irradiated with three spot lights whose center positions are shifted by about one track from the laser light output from A, and signal information is obtained from one spot light in the center (hereinafter referred to as the center spot light). The point is that reproduction is performed and a tracking signal is obtained from the central spot light and the two spot lights at both ends. That is, there is a difference in that the tracking signal can be obtained from the reproducing spot light shown in FIG. In this case, the relationship between the spot light irradiated on the optical disc 1 and each track is as shown in FIG.

In FIG. 8, the optical disk 1 is rotated by a rotating system, and laser light is emitted from the semiconductor laser light source 7B. This laser light passes through an optical system to focus the three spot lights on the optical disc 1, and the spot diameter is determined by the diffraction limit. The spot diameters at this time are about 1.4 μm,
As shown in FIG. 9, spot light is irradiated on almost three tracks. Then, the tracking information and the signal information described above are read by the three spot lights.

That is, the reflected lights of the three spot lights are
Lens 8B, hologram 17A, and filter 1 shown in FIG.
After passing through 0B etc., it is divided into two by the polarization beam splitter 13B, and then received by the detectors 11B and 12B, respectively, and converted into electric signals. After that, the addition amplifier 15B calculates the sum of the respective signals to reproduce the signal information, and the differential amplifiers 16D, 16E, and 16F calculate the respective differences, and after passing through the rectifier circuit 19A, the differential amplifier 16G, 16
Differences from H are taken, and differential amplifier 16I
The tracking signal is extracted by taking the respective differences. The electric signal output to the addition amplifier 15B is an electric signal obtained by converting the central spot light emitted on the optical disc 1, and the differential amplifiers 16D and 16D are provided.
The electric signals output to E and 16F are the same as the optical disc 1 described above.
It is an electric signal obtained by converting the three spot lights irradiated on the.

Here, the tracking signal of the reproducing apparatus shown in FIG. 8 will be described. When the center of the center spot light is on the center of the phase change film 4 of the regular track (that is, in the case of FIG. 9A). Is, for example, the differential amplifier 16D, 1
Regarding the tracking signals output from 6E and 16F, one of the differential amplifiers 16D and 16F has a positive or negative maximum value, and the other has a negative or positive maximum value. The differential amplifier 16E has the minimum value (0).

This is because the magnetization directions of the magneto-optical film 5 in the spots are different from each other as described above, so that the light amounts of the respective polarization components are different. Then, after passing the tracking signals output from the differential amplifiers 16D, 16E, and 16F through the rectifier circuit 19A,
Further, if the difference is taken through the differential amplifiers 16G and 16H, the tracking signal output from the differential amplifier 16G has a maximum value, and the tracking signal output from the differential amplifier 16H also has a maximum value. After that, when the difference between the tracking signals is further obtained through the differential amplifier 16I, the output becomes 0.

When the center of each spot light is deviated and the center spot light is located right above the magneto-optical film 5 (in the case of FIG. 9B), it is output from the differential amplifier 16E. Tracking signal (difference of tracking signals obtained from the central spot light) does not become 0, and
The tracking signal output from the differential amplifier 16I is also 0.
It does not become.

Therefore, tracking can be performed by controlling the spot position of the reproducing laser light so that the tracking signal from the differential amplifier 16I is always zero. In this case, the phase change film 4 entering the spot
It goes without saying that the fluctuation of the light amount of the reflected light from does not affect the differential output due to the polarization. In addition, the magneto-optical film 5 does not affect the reproduction output in the tracking enabled state.

FIG. 10 and FIG. 11 are enlarged partial sectional views showing the structure of the optical disc according to the second embodiment of the present invention.
10 is a sectional view orthogonal to the track direction, and FIG. 11 is
It is sectional drawing parallel to a track direction. As shown in FIG. 10 and FIG. 11, the optical disc 21 according to this embodiment includes the substrate 2
2, first protective film 23, recording layer (hereinafter referred to as phase change film) 2
4, a perpendicular magnetization layer (hereinafter, magneto-optical film) 25, a second protective film 26, and a heat diffusion film 27, and the substrate 22.
Is a circular substrate made of glass or the like and having a diameter of 130 mm. The first protective film 23 is made of ZnS; SiO ₂ and is formed on the substrate 22 by a sputtering method (RF magnetron sputtering) to a thickness of about 100 nm. still,
The target used for this sputtering is ZnS;
This is a mixed target of SiO ₂ and the gas pressure in the chamber of the sputtering apparatus was once evacuated to 2 × 10 ⁻⁶ Torr or less, then Ar gas was introduced to make the gas pressure in the chamber 5 × 1.
And sputtering was carried out as 0 ^{over 3} Torr.

The magneto-optical film 25 is made of TbFeCo or the like. To form the magneto-optical film 25 on the first protective film 23, the first protective film 23 is formed on the substrate 22. First, the magneto-optical film 25 is formed on the entire surface of the first protective film 23 by a sputtering method similar to
Formed with a thickness of. The target used for sputtering when forming the magneto-optical film 24 was TbFeC.
o Target.

Then, a resist (not shown) is once coated on the magneto-optical film 25, and the pitch is 1 μm and the width is 0.5 μm.
A concentric circular pattern of m was patterned by an exposure device such as a stepper. Regarding the exposure in this case,
Since the pattern shape is simple, it can be performed relatively easily by exposing while rotating.

After patterning, the resist was developed, and the magneto-optical film 25 was etched into the concentric circular pattern by reactive ion etching (RIE) (may be ion beam etching). As a result, the magneto-optical film 25 selectively remains on the first protective film 23 according to the pattern, and the protective film 23 is exposed in the concentric recesses. The phase change film 24 having a thickness of about 50 nm was formed in the recess by the same sputtering method. The target used for sputtering when forming the phase change film 24 is
It is a Ge ₂ Sb ₂ Te ₅ target. The phase change film 24 and the magneto-optical film 25 of the optical disk substrate formed up to this point.
Each has a concentric pattern with a width of 0.5 μm and a pitch of 1 μm on the first protective film 23.

The thermal diffusion film 27 is made of Al or the like. To form the thermal diffusion film 27 on the phase change film 24,
A thermal diffusion film 27 having a thickness of about 50 nm was first formed on the entire surface of the phase change film 24 by using the same sputtering method as that for forming the first protective film 23 on the substrate 22.
The target used for sputtering when forming the thermal diffusion film 27 is an Al target.

The heat diffusion film 2 formed on the entire surface
7 is coated with a resist (not shown) again, a pattern corresponding to "1, 0" of digital information to be recorded is exposed by an exposure device such as a stepper, and then the resist is developed and ion beam etching (RIE) is performed. However, the thermal diffusion film 27 is etched to remove only the portion corresponding to "1" of the information to be recorded. Note that the portion to be removed by etching is only the portion located on the phase change film 24.

After the phase change film 24 and the thermal diffusion film 27 are formed in this way, a second layer of ZnS; SiO ₂ is formed.
The protective film 26 of was formed. When forming the second protective film 26, the same sputtering method as described above was used.

The optical disk 21 formed in this way can be used as a read-only optical disk, and when reproducing the same, when the reproducing laser spot light is irradiated onto the rotating optical disk 21, it becomes a spot on which the spot light hits. A positional shift occurs due to the time delay of the temperature rise between the heating region and the heating region (see FIGS. 12 and 13). Depending on whether the thermal diffusion film 27 such as Al is formed adjacent to the phase change film 24 in the heated region, the phase change film 24 once brought to a high temperature by the reproduction spot light remains in the liquid phase. There is a difference between the presence and the return to the solid phase, and the reflectance in each case is different. Therefore, it is possible to read only the information in the spot light that remains at a high temperature. The method for tracking the optical disk 21 formed in this way is the same as in the case of each of the first embodiments, for example, when the apparatus shown in FIGS. 3, 6, and 8 is used. It is possible.

[0065]

As described above, according to the present invention, it is possible to manufacture a high density optical disk, and even when reproducing an optical disk manufactured with such a high density, the magnetization direction of the perpendicular magnetization layer is set. By detecting the polarized light from the spot light, there is an effect that the optical disc can be reliably tracked.

[Brief description of drawings]

FIG. 1 is an enlarged partial cross-sectional view orthogonal to a track direction showing a configuration of an optical disc according to a first embodiment of the present invention.

FIG. 2 is an enlarged partial cross-sectional view orthogonal to the track direction showing the configuration of the optical disc according to the modification of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a schematic configuration of a reproducing apparatus applied to the tracking method of the present invention.

4 is an explanatory diagram showing a positional relationship between spot light and each track in the reproducing apparatus shown in FIG.

5 is an explanatory diagram showing a positional relationship between spot light and high density tracks in the reproducing apparatus shown in FIG.

FIG. 6 is an explanatory diagram showing a schematic configuration of another reproducing apparatus used in the tracking method of the present invention.

7 is an explanatory diagram showing a positional relationship between spot light and each track in the reproducing apparatus shown in FIG.

FIG. 8 is an explanatory diagram showing a schematic configuration of still another reproducing apparatus used in the tracking method of the present invention.

9 is an explanatory diagram showing a locus of spot light emitted from the output detection device shown in FIG.

FIG. 10 is an enlarged partial cross-sectional view orthogonal to the track direction showing the configuration of the optical disc according to the second embodiment of the present invention.

FIG. 11 is an enlarged partial sectional view parallel to the track direction showing the configuration of the optical disc according to the second embodiment of the present invention.

FIG. 12 is an explanatory diagram showing a state (with a signal) of a phase change film during reproduction of an optical disc according to a second example of the present invention.

FIG. 13 is an explanatory diagram showing a state (no signal) of the phase change film during reproduction of the optical disc according to the second example of the present invention.

[Explanation of symbols]

1, 21: Optical disc 2, 22: Substrate 3, 23: First protective film 4, 24: Recording layer (phase change film) 5, 25: Perpendicular magnetization layer (magneto-optical film) 6, 26: Second protection Films 7, 7A, 7B: Semiconductor laser light sources 8, 8A, 8B: Lenses 9, 9A, 9B: Filters 10, 10A, 10B: Filters 11, 11A, 11B: Detectors 12, 12A, 12B: Detectors 13, 13A, 13B : Polarizing beam splitter 14: Polarizing beam splitter 15, 15A, 15B: Summing amplifier 16, 16A, 16B, 16C, 16D, 16E, 16
F, 16G, 16H, 16I: Differential amplifier 17, 17A, 17B: Hologram 18, 18A, 18B: Rating 19, 19A: Rectifier circuit 27: Thermal diffusion film

Claims (8)

[Claims] 1. An optical disc having adjacent tracks formed of recording layers having different reflectivities depending on the difference in crystal structure or phase structure on a substrate. An optical disk, wherein perpendicular magnetic layers exhibiting different polarization angles extend, and the perpendicular magnetic layers are magnetized in a predetermined direction between adjacent tracks. 2. The optical disk according to claim 1, wherein the perpendicular magnetic layers are magnetized in mutually opposite directions between adjacent tracks. 3. The pitch dimension of the track formed by the recording layer and the perpendicular magnetization layer is formed in the range of 1 to 2/5 times the spot diameter of the irradiated laser beam. The optical disk according to claim 2, characterized in that: 4. The perpendicular magnetic layer comprises a plurality of pairs of two adjacent tracks magnetized in the same direction, and the magnetization directions of the perpendicular magnetic layers are formed in mutually opposite directions between the adjacent pairs. The optical disc according to claim 1, characterized in that: 5. The pitch dimension of the track formed by the recording layer and the perpendicular magnetization layer is formed in the range of 1 to 2/7 times the spot diameter of the irradiated laser beam. The optical disc according to claim 4, wherein: 6. The optical disc according to claim 1, wherein a partial heat diffusion layer corresponding to information to be recorded is formed so as to overlap the recording layer along the track direction. 7. A track formed by juxtaposing a perpendicular magnetic layer showing a different polarization angle according to a predetermined magnetization direction on a recording layer showing a different reflectance depending on a difference in crystal structure or phase structure is adjacent to a substrate. For the optical disc formed by
A tracking method for irradiating a spot light onto a track by converging laser light and performing tracking based on information obtained from the spot light, which is due to a difference in magnetization direction of the perpendicular magnetic layer between adjacent tracks. A tracking method, wherein tracking information of the optical disc is obtained by detecting a deviation of a polarization plane of light. 8. A laser beam is focused on the optical disc to irradiate a plurality of spot lights on different tracks, and a plurality of detection signals obtained from the plurality of spot lights are arithmetically processed. The tracking method according to claim 7, wherein tracking information of the optical disc is obtained.