JP2003308629A - Optical disk recording and/or reproducing device, and optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device and/or reproducing device which enables recording and/or reproducing to a higher density and is made greater in capacity, and an optical disk. <P>SOLUTION: The numerical aperture (NA) of an objective lens 2 for converging a laser beam for recording and/or reproducing to a recording layer 43 through a translucent cover 41 of the optical disk 40 is specified to 0.55 to 0.70. The thickness of the translucent cover 41 of the optical disk 40 is specified to 0.6 to 0.1 mm. In spite of the high NA and large thickness of the objective lens 2, the objective lens 2 does not come into contact with the optical disk 40 and the comatic aberration of the objective lens 2 is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk recording and / or reproducing apparatus and an optical disk for recording and / or reproducing on an optical disk or a magneto-optical disk.

[0002]

2. Description of the Related Art FIG. 5 shows a magneto-optical disk recording and / or reproducing apparatus as an example of an optical disk recording and / or reproducing apparatus for recording and / or reproducing on an optical recording medium such as an optical disk or a magneto-optical disk.

The conventional magneto-optical disk recording and / or reproducing apparatus shown in FIG. 5 is a disk-shaped single-sided magneto-optical recording medium 5.
When 0 is mounted, an optical system including a laser device 58 and an objective lens 59 is provided on the upper surface side of the single-sided magneto-optical recording medium 50, and a magnetic field that is a magnetic system is generated on the lower surface side of the single-sided magneto-optical recording medium 50. A device 60 is provided and configured. The numerical aperture (hereinafter referred to as “NA”) of the objective lens 59 is 0.5.
It is set to 0 to 0.53.

A drive system (not shown) is provided for driving the optical system in the focus direction and the tracking direction with respect to the magneto-optical recording medium 50. Also for the magnetic system, another drive system (not shown) is provided for driving in the arrow direction of FIG. 5 and in the tracking direction.

In this magneto-optical disk recording and / or reproducing apparatus, a magnetic field modulation method is adopted for the recording. In this magnetic field modulation method, it is necessary to control the reversal of the magnetic field at high speed, so a sufficient exciting current cannot be obtained.
Since the generated magnetic field strength is limited, the magnetic field generator 60
Is a recording magnetic layer 53 described later in the single-sided magneto-optical recording medium 50.
Is located near the. According to the magnetic field modulation method, overwriting is possible.

On the other hand, the single-sided magneto-optical recording medium 50 has a dielectric layer 52, for example, a magneto-optical element such as a rare earth-transition metal alloy amorphous thin film, on one side surface of a transparent substrate 51 having a light transmitting property such as polycarbonate. Recording magnetic layer 53 having a large effect,
The dielectric layer 54, the reflective layer 55, and the protective cover 56 are sequentially laminated. In this case, the thickness t ₁ of the base body 51 is constant and has been set to 1.2 mm until now.

Next, a simple operation will be described. First, the one-sided magneto-optical recording medium 50 is placed on a rotating disk (not shown) and driven to rotate, and a magnetic field from the magnetic field generator 60 is applied to the recording magnetic layer 53 in the one-sided magneto-optical recording medium 50. The applied magnetic field is subjected to high-speed inversion control, and the laser beam emitted from the laser device 58 is focused on the recording magnetic layer 53 to which the magnetic field is applied via the objective lens 59, whereby the laser beam is emitted. The recording magnetic layer 53 in the focused region can be magnetized, and the information signal can be overwritten in real time.

By the way, in order to further reduce the size of a magneto-optical pickup including the above-mentioned optical system, the above-mentioned magnetic system, and these drive systems, the above-mentioned optical system and the above-mentioned magnetic system are integrated into a magneto-optical recording medium. It is conceivable to arrange them on the same plane side. That is, this is a case where the magnetic field generator 60 in FIG. 5 is arranged on the objective lens 59 side (translucent base body 51 side) to integrate them, and in this case, the magnetic field generator 60 and the recording magnetic layer 53. Therefore, the magnetic field cannot be applied to the recording magnetic layer 53 with sufficient strength.

Further, with the increase in the amount of information in recent years, double-sided magneto-optical recording in which information signals can be recorded on both sides by providing the recording magnetic layers as described above on both sides of one magneto-optical recording medium. Media are being developed. However, in order to perform recording and / or reproduction in such a double-sided magneto-optical recording medium, a magnetic field is applied to both recording magnetic layers from a magneto-optical pickup including an optical system and a magnetic system as shown in FIG. Is very difficult to apply with sufficient strength.

In the magnetic field modulation type magnetic field generator,
A high-frequency current corresponding to a high-frequency data signal must be passed through the electromagnetic coil. However, the higher the frequency, the more difficult it is for the current to flow through the coil. Because the distance to is quite large. Therefore, it is extremely difficult to perform double-sided magneto-optical recording by the magnetic field modulation method with the current technology.

[0011]

In order to cope with the increase in the amount of information as described above, it is necessary to record more information signals in the recording portion such as the above-mentioned recording magnetic layer of the optical disc. . An object of the invention of the present application is to provide a large-capacity optical disk recording and / or reproducing apparatus and an optical disk capable of higher density recording and / or reproducing.

[0012]

When the laser beam is focused by the objective lens, the minimum diameter (2ω ₀ ) of the focused beam is expressed by the following equation (1). 2ω ₀ = 0.82 × λ / NA (1) (λ: wavelength of laser beam) Therefore, the NA of the objective lens is 0.55 to 0.70, which is the conventional NA (0.50 to 0.53). Larger, the minimum diameter of the focused beam will be smaller and the recording density will be higher. Then, reproduction corresponding to the recording density can be performed.

Further, as the NA increases, the thickness of the objective lens also increases, but the thickness of the translucent cover of the optical disk is 0.6.
Since the thickness is ˜0.1 mm, which is smaller than the conventional thickness (1.2 mm), the thickened objective lens does not come into contact with the optical disc.

When the NA of the objective lens and the thickness t of the transparent cover of the optical disk change, the aberration value of the objective lens changes as follows.

(A) Spherical aberration W ₄₀ W ₄₀ = {t (N ² -1) sin ⁴ α} / (8N ³ ) (2) (sin α = NA) (N: of the transparent cover of the optical disk Refractive index)

(B) Coma aberration W ₃₁ W ₃₁ = {t · (N ² −1) N ² sin θ cos θ · sin ³ α} / {2 (N ² −s in ² θ) ^5/2 } (3) ( θ: skew)

The spherical aberration of (A) can be corrected by the objective lens, so that there is basically no problem. However, variations in the thickness t of the translucent cover pose a problem, so it is desirable to keep this t within the tolerance. Since the coma aberration of (B) cannot be corrected by the objective lens, the smaller the absolute value is, the more preferable. Here, even if NA is increased to 0.55 to 0.70, the thickness t of the translucent cover is decreased to 0.6 to 0.1 mm, so that the absolute value of W ₃₁ is not increased. Therefore, the aberration of the objective lens causes almost no problem even if the NA is increased to 0.55 to 0.70, and the conventional recording and / or reproducing can be performed with higher density.

[0018]

DETAILED DESCRIPTION OF THE INVENTION First to third embodiments of the present invention will be described below with reference to FIGS. Figure 1
FIG. 1 is a sectional view showing a first embodiment in which the invention of the present application is applied to a magneto-optical disc recording and / or reproducing apparatus, showing a basic configuration of the magneto-optical disc recording and / or reproducing apparatus. As shown in FIG. 1, this magneto-optical disk recording and / or reproducing apparatus is composed of an optical glass 8 having a light transmittance and having an objective lens 2 having an NA of 0.55 to 0.70 and a coil pattern 7. And a configured magnetic field generator 9.

Then, the dielectric layer 42 and the recording magnetic layer 4 are formed on the transparent substrate 41 having the thickness t ₂ of 0.1 to 0.6 mm.
3, a disk-shaped single-sided magneto-optical recording medium 40 having a thin transparent substrate part, which is formed by sequentially laminating a dielectric layer 44, a reflective film 45, and a protective cover 46, emits a laser beam from a laser beam device (not shown). It is configured so that irradiation can be performed for recording and reproduction. The magnetic field generator 9 is based on a magnetic field modulation method, which will be described later in detail with reference to FIG.

The thickness of the dielectric layer 42 is t
Since ₂ considerably smaller than, it may not be considered as a thickness for the t _2. The objective lens 2 which is an optical system and the optical glass 8 which is a magnetic system are bonded so as to be integrated, and the coil pattern 7 has a magneto-optical recording medium 40.
Is located close to.

As described above, the thickness t ₂ of the transparent base 41 is considerably smaller than that of the conventional one, and the coil pattern 7 is close to the transparent base 41. Therefore, the coil pattern 7 and the recording magnetic layer 43 are The distance is short, which is preferable. Further, since the optical system and the magnetic system can be integrated, the magneto-optical pickup including them can be downsized and the cost can be reduced, and the double-sided magneto-optical recording can be performed as shown in the second and third embodiments described later. It is possible to record and reproduce on the medium.

In the magneto-optical recording medium used in the magneto-optical disk recording and / or reproducing apparatus, it is preferable to use, for example, a 3.5-inch magneto-optical disk fixedly or housed in a cartridge holder.

The NA of the objective lens 2 is 0.55 to 0.70.
By increasing the depth of focus (= λ / N
(A ² , λ: wavelength of laser beam) becomes shallower, but since the magneto-optical disk is small as described above, the actuator (not shown) constituting the drive system for the magneto-optical pickup is downsized and its frequency is reduced. Since the characteristics are improved and the actuator sufficiently follows, the shallow depth of focus is not a problem.

Further, the above-mentioned spherical aberration W ₄₀ is caused by the objective lens 2
Has been corrected in. Further, as to the coma aberration W ₃₁ , there is no problem even if the NA of the objective lens becomes larger as described above, since the thickness t ₂ of the transparent base is smaller.
Here, the coma aberration W ₃₁ is N of the conventional objective lens.
A = 0.50 and the thickness t of the translucent substrate (translucent cover)
= 1.2 mm, NA and t which are equivalent to the value of the coma aberration W ₃₁ obtained in the case of 1.2 mm are obtained for four cases, and the results are shown in Table 1 below.

[0025]

[Table 1]

As shown in Table 1, NA is 0.5
Even if it is 5 to 0.70, if t is set to 0.6 to 0.1 mm, the coma aberration can be made equal to or smaller than that in the conventional case, and it is understood that there is no problem.

Although the thickness of the objective lens 2 is increased by increasing the NA of the objective lens 2, the thickness t _{2 of the} light-transmitting substrate is small as described above. Therefore, as shown in FIG. The distance d (so-called working distance) between 2 and the magneto-optical recording medium 40 becomes a predetermined value or more, so that the objective lens 2 and the magneto-optical recording medium 40 do not come into contact with each other. In this case, there is no problem with respect to dust, which is a problem in the optical disc recording and / or reproducing apparatus, because the cartridge holder type or the fixed type is adopted in the magneto-optical recording medium.

Although the particle size and distribution of the above-mentioned dust pose a problem, the radius r of the projected circle generated by the laser beam on the translucent substrate 41 (see FIG. 1).
Is r = t · tan (arc sin (NA / N)) (4). As can be seen from the equation (4), when the thickness t of the translucent cover is reduced, the above r is also reduced, but since the NA is larger, the above r is not significantly reduced. There is no particular problem of dust.

As described above, in the magneto-optical disk recording and / or reproducing apparatus of this embodiment, the NA of the objective lens is set to 0.55 to 0.70 and the light-transmitting substrate (light-transmitting cover) is used. Since the thickness t ₂ is set to 0.6 to 0.1 mm, it can be understood from the above formula (1) as compared with the case of the recording and / or reproducing apparatus using the objective lens having the conventional NA of 0.50. The recording density (0.55 /
It is possible to increase 0.50) ² to (0.70 / 0.50) ² ≈1.2 to ² times, and it can be understood that all of the above-mentioned various problems caused by increasing the NA can be solved. .
Therefore, it is possible to increase the capacity of the magneto-optical disk recording and / or reproducing apparatus without any problem.

Next, a more detailed structure of the magneto-optical disk recording and / or reproducing apparatus of the above-described first embodiment will be described with reference to the second and third embodiments. FIG. 2 is a sectional view of a second embodiment of a magneto-optical disc recording and / or reproducing apparatus according to the present invention.

In the second embodiment, first and second magneto-optical pickup devices having an optical system and a magnetic system are opposed to each other via a magneto-optical recording medium 10 as shown in FIG. It is configured by arranging in. The first magneto-optical pickup device arranged on the upper surface side of the medium 10 and the second magneto-optical pickup device arranged on the lower surface side thereof have the same structure as described below,
The constituent parts 1 to 9 and 1'to 9'correspond to each other.

The first and second magneto-optical pickup devices in FIG. 2 are the laser devices 1 and 1'and the objective lens 2 having an NA of 0.55 to 0.70 as described above.
2'and a coil bobbin 4 around which the focus coils 3a, 3a 'and the tracking coils 3b, 3b' are wound,
4'and pickups 6, 6'which are optical systems consisting of magnets 5, 5'disposed around the coil bobbins 4, 4 ', and the above-mentioned magnetic field generators 9, 9'which are magnetic systems. Has been done.

The coil bobbins 4, 4'of the pickups 6, 6'are cylindrical, for example, and the focus coils 3a, 3a for driving the pickups 6, 6'in the F direction shown in FIG. ′ And pickup 6,
Tracking coils 3b and 3b 'are provided so as to drive 6'in the T direction shown in FIG. Further, lens support members 2a and 2a 'are provided at positions close to the ends 4a and 4a' of the coil bobbins 4 and 4 ', whereby the laser beams emitted from the laser devices 1 and 1'are focused. It supports the objective lenses 2 and 2 '.

As shown in FIG. 3, the magnetic field generators 9 and 9'apply a high-frequency signal current to the surfaces 8a and 8a 'of the optical glasses 8 and 8'having a light-transmitting property such as quartz. Conductors 7a, 7a 'for flowing to generate a magnetic field,
It is configured by being formed as a spiral coil pattern 7, 7 '.

On the back surfaces 8b and 8b 'of the optical glasses 8 and 8'on which the coil patterns 7 and 7'are not formed, the end portions 4a and 4a' of the coil bobbins 4 and 4'are provided with the coil patterns 7 and 7 '. The center of 7'is aligned with the centers of the objective lenses 2 and 2'and fixed by adhesion. As a result, the laser beam can be focused on the center of the generated magnetic field, which eliminates the need for adjustment of centering when assembling the pickup.

The use of quartz for the optical glasses 8 and 8'is an example, and any material that is transparent to light may be used. Further, in the coil patterns 7 and 7 ', for example, a print coil or a thin film is used. A coil or the like can be used. Further, the optical glass 8, 8'may be provided with a hole through which a laser beam passes in order to prevent reflection.

On the other hand, the first double-sided magneto-optical recording medium 10 shown in FIG. 2 has been proposed by the applicant of the present application in the specification and drawings of Japanese Patent Application No. 1-142563, and the common base 11 is used. The recording unit 16, the photo-curable resin layer 17, and the transparent protective plate 18 are provided on both surfaces of the above. Both the transparent protective plate 18 and the photocurable resin layer 17 have a light-transmitting property, and the sum of their thicknesses can be 0.6 mm or less.

In each of the recording sections 16, the reflection layer 15 is laminated so as to be disposed closer to the base 11 than the recording magnetic layer 12, and the reflection layer 15 and the second dielectric are arranged from the base 11 side, respectively. The layer 14, the recording magnetic layer 12, and the first dielectric layer 13 are laminated in this order. Since the double-sided magneto-optical recording medium 10 has the common base 11, the thickness of the double-sided magneto-optical recording medium 10 can be reduced to about half that of the conventional double-sided magneto-optical recording medium by pasting the bases together. is there.

Next, the operation will be described. In the first magneto-optical pickup device configured as described above, by supplying the focus drive current to the focus coil 3a, the coil bobbin 4 and the magnetic field generating device 9 provided in the coil bobbin 4 are indicated by arrows in FIG. The objective lens 2 is driven and displaced in the focus direction, which is the optical axis direction of the objective lens 2 indicated by F.

Further, by supplying a tracking drive current to the tracking coil 3b, the coil bobbin 4 and the magnetic field generator 9 are in a tracking direction which is a direction orthogonal to the optical axis of the objective lens 2 shown by an arrow T in FIG. Is driven and displaced. Similarly, the second magneto-optical pickup device is also driven and displaced in the F direction and the T direction in synchronization with the driving of the first magneto-optical pickup device.

At the same time, the conductor 7 of the magnetic field generator 9, 9 '
A magnetic field is generated by supplying a high frequency current signal obtained by amplifying a signal to be recorded to the coil patterns 7 and 7'formed by a and 7a '. This magnetic field is subjected to high-speed inversion control according to the recording signal, and is applied to the recording magnetic layers 12, 12 of the double-sided magneto-optical recording medium 10. And
In the regions of the recording magnetic layers 12, 12 to which the magnetic field is applied,
The laser beams emitted from the laser devices 1 and 1 ′ are objective lenses 2 and 2 ′ and the optical glass 8 having optical transparency,
Information signals can be recorded by focusing through 8'and raising the temperature of the recording magnetic layers 12, 12 to the Curie point or higher.

As is clear from the above description, the magneto-optical disk recording and / or reproducing apparatus in this embodiment is
An optical system which is a pickup 6, 6'comprising laser devices 1, 1 ', objective lenses 2, 2', and an optical glass 8,
A double-sided magneto-optical recording medium 10 including a magnetic system which is a magnetic field generator 9 or 9'formed by forming coil patterns 7 and 7'on 8 '
By providing them on the same plane side, the distance between the coil pattern and the magneto-optical recording medium 10 can be shortened.

Further, the transparent protective plate 18 and the photocurable resin layer 17 are provided.
Since the thickness of the light-transmitting cover made of is small, the distance between the coil patterns 7 and 7 ′ and the recording magnetic layers 12 and 12 of the double-sided magneto-optical recording medium 10 can be extremely shortened. It is possible to perform recording and reproduction on the double-sided magneto-optical recording medium by the magneto-optical modulation method which is said to be.

Further, the coil bobbins 4 and 4'of the pickups 6 and 6'and the magnetic field generators 9 and 9'are fixed to each other by, for example, adhesion or the like, whereby the objective lenses 2 and 2 '
It becomes easy to align the center of the magnetic field generator 9 and the center of the magnetic field of the magnetic field generators 9 and 9 ', and since the pickups 6 and 6'and the magnetic field generators 9 and 9'are linked by the focus servo, double-sided light is generated. The strength of the magnetic field applied to the magnetic recording medium 10 can be kept constant. Further, the drive system for the magnetic system, which has been necessary until now, can be omitted. Further, since a space for disposing the magneto-optical pickup device can be provided, the degree of freedom in design can be increased.

According to the second embodiment described above, it is possible to perform various recording and reproducing operations on the double-sided magneto-optical recording medium. For example, the laser devices 1, 1'and the magnetic generator 9,
By simultaneously using 9 ', simultaneous recording can be performed on the upper surface side and the lower surface side of the double-sided magneto-optical recording medium 10, and simultaneous reproduction is possible by using the laser devices 1 and 1'at the same time. As a result, the capacity can be increased and the information signal can be recorded and reproduced at higher speed.

Further, it is possible to record or reproduce on one surface of the double-sided magneto-optical recording medium 10 first, and then record or reproduce on the other surface. As a result, recording and reproducing can be performed with a capacity twice as large as that of the single-sided magneto-optical recording medium.

In the above case, when recording on one surface, the two magnetic field generators 9 or 9'also generate magnetic fields from the magnetic field generators 9 or 9'disposed on the other surface.
And 9'can be used simultaneously. Therefore, magnetic fields can be applied to the recording magnetic layer 12 from both sides thereof, and recording can be performed with a larger magnetic field. In addition, when recording on one surface, it is possible to perform recording by using only the magnetic field generator arranged on the other surface side.

Next, a third embodiment will be described.
As shown in FIG. 4, the present embodiment uses the same magneto-optical disk recording and / or reproducing apparatus as that shown in FIG. 2, and uses the second double-sided magneto-optical recording medium 30 shown in FIG. It is configured so that reproduction can be performed.

In the second double-sided magneto-optical recording medium 30 described above, one of the inventors of the present application first worked with another inventor in Japanese Patent Application No. 1-2.
No. 74734 specification and drawings, and a high magnetic permeability layer 32, a photocurable resin layer 33, a magneto-optical recording layer 34, an adhesive layer 35, and a transparent protective plate are provided on both surfaces of a common substrate 31, respectively. 36 are sequentially laminated. Both the transparent protective plate 36 and the adhesive layer 35 have a light-transmitting property, and the sum of their thicknesses can be 0.6 mm or less.

The high magnetic permeability layer 32 is made of, for example, Fe, Co, N.
i and other transition metals, and alloys thereof such as permalloy, sendust, or amorphous magnetic alloys having a high magnetic permeability, and the perpendicular magnetic field efficiency of the double-sided magneto-optical recording medium 30 in the vertical direction. It becomes possible to raise.

In the third embodiment, since the second double-sided magneto-optical recording medium 30 has the high magnetic permeability layer 32,
Since the magnetic flux from the magnetic field generators 9 and 9'forms a magnetic closed loop as shown by the broken line in FIG. 4, for example, the magnetic flux applied to the double-sided magneto-optical recording medium 30 during recording is effectively focused. This is preferable because the vertical magnetic field efficiency can be increased.

Also in the third embodiment, it is possible to simultaneously record or reproduce on both sides of the double-sided magneto-optical recording medium 30, and after recording or reproducing on one side, then on the other side. It is possible to record or reproduce.

As described above, in the second and third embodiments, the NA of the objective lenses 2 and 2'is the same as in the first embodiment.
Since it is made larger, recording and reproducing can be performed at higher density, and since a double-sided magneto-optical recording medium can be used, recording and reproducing can be performed with larger capacity and at higher speed. Therefore, it is possible to provide a magneto-optical disk recording and / or reproducing apparatus having a large capacity.

In the first to third embodiments,
Although the magnetic field generators 9 and 9'are based on the magnetic field modulation method, they can be applied to other methods such as an optical modulation method. The first to third embodiments are the magneto-optical disk recording and / or reproducing apparatus, but the invention of the present application is not limited to this, and for example, the optical recording configured by providing pits in the recording layer. Of course, an optical disk recording and / or reproducing device for recording and / or reproducing a medium (including a write-once type optical recording medium etc.) may be used.

[0055]

EFFECT OF THE INVENTION Optical disk recording and / or recording according to the present invention
Alternatively, according to the reproducing apparatus, the NA of the objective lens that focuses the laser beam is set to 0.55 to 0.70, and the thickness of the translucent cover is set to 0.6 to 0.1 mm. Is 0.50 and the thickness of the translucent cover is 1.2 m
While the coma aberration is the same as or less than when m,
Higher density recording and / or reproduction can be achieved to increase the capacity, and even if the objective lens has a large NA and a large thickness, the objective lens does not come into contact with the optical disc, which causes a problem due to dust. It can also be prevented from occurring.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of a magneto-optical disk recording and / or reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the configuration of a magneto-optical disk recording and / or reproducing apparatus according to a second embodiment of the present invention.

FIG. 3 is a magneto-optical disk recording and / or recording medium shown in FIGS.
Or, it is a front view of an optical glass having a coil pattern that can be used in a reproducing apparatus.

FIG. 4 is a cross-sectional view showing a configuration of a magneto-optical disk recording and / or reproducing apparatus according to a third embodiment of the present invention.

FIG. 5 is a sectional view showing a configuration of a conventional magneto-optical disk recording and / or reproducing apparatus.

[Explanation of symbols]

2, 2 '... Objective lens, 10, 30, 40 ... Magneto-optical recording medium (optical disk), 16 ... Recording part (recording layer), 17,
18 ... Photocurable resin layer and transparent protective plate (translucent cover),
34 ... Magneto-optical recording layer (recording layer), 35, 36 ... Adhesive layer and transparent protective plate (translucent cover), 41 ... Translucent substrate (translucent cover), 43 ... Recording magnetic layer (recording layer) ),
t ₁ , t ₂ ... Thickness of translucent cover

Claims (12)

[Claims] 1. An optical disc in which a laser beam emitted from a light source for recording and / or reproducing is focused on a recording material layer using an objective lens having a numerical aperture of 0.55 to 0.70, The optical disc includes at least a reflective layer provided on one surface side of the recording material layer and a translucent cover provided on the other surface side of the recording material layer. An optical disc in which the reflective layer and the translucent cover are laminated, and the total thickness of the recording material layer, the reflective layer and the translucent cover is 0.6 mm or less. 2. The optical disc further comprises first and second protective layers provided so as to sandwich the recording material layer, and the reflective layer is provided on the first protective layer side. And the translucent cover is provided on the surface of the second protective layer opposite to the surface in contact with the recording material layer,
The sum including the first and second protective layers is 0.6 mm.
The optical disc according to claim 1, which is as follows. 3. The optical disc according to claim 2, wherein the optical disc further comprises a substrate, and the reflective layer is provided between the substrate and the first protective layer. 4. A recording material layer, a reflective layer provided on one surface side of the recording material layer, and a translucent cover provided on the other surface side of the recording material layer. The recording material layer, the reflective layer, and the translucent cover are laminated, and the total thickness of the recording material layer, the reflective layer, and the translucent cover is 0.6 mm.
Recording and / or reproduction of an optical disc having an objective lens with a numerical aperture of 0.55 to 0.70 for focusing a laser beam emitted from a light source on the recording material layer through the translucent cover of the following optical disc: apparatus. 5. The optical disk further comprises first and second protective layers provided so as to sandwich the recording material layer, and the reflective layer is provided on the first protective layer side. And the translucent cover is provided on the surface of the second protective layer opposite to the surface in contact with the recording material layer,
The sum including the first and second protective layers is 0.6 mm.
The optical disc recording and / or reproducing apparatus according to claim 4, which is as follows. 6. A first and second protective layer provided so as to sandwich the recording material layer, a reflective layer provided between the first protective layer and a substrate, and the second protective layer. An optical disc in which at least a translucent cover having a thickness of 0.6 to 0.1 mm, which is provided on the surface of the protective layer opposite to the surface in contact with the recording material layer, is laminated. 7. The optical disc according to claim 6, wherein the optical disc further comprises a resin layer having a light-transmitting property between the second protective layer and the light-transmitting cover. 8. A first and second protective layer provided so as to sandwich the recording material layer, a reflective layer provided between the first protective layer and a substrate, and the second protective layer. The light-transmitting cover of an optical disc in which at least a light-transmitting cover having a thickness of 0.6 to 0.1 mm provided on the surface of the protective layer opposite to the surface in contact with the recording material layer is laminated. An objective lens which is disposed so as to face the recording material layer through the translucent cover and focuses the laser beam on the recording material layer; a driving unit which drives the objective lens in the focus direction and the tracking direction; An optical disk recording and / or reproducing apparatus provided with a light source for outputting. 9. The numerical aperture of the objective lens is NA, and the transparent
The thickness of the light-transmitting cover is t, and the refractive index of the light-transmitting cover is N.
And the coma aberration W of the objective lens ₃₁But, W₃₁= {T · (N²-1) N²sin θ cos θ · sin
³α} / {2 (N²-Sin²θ)^5/2} 9. The condition (θ: skew, sin α = NA) is satisfied.
The optical disk recording and / or reproducing apparatus described. 10. The numerical aperture of the objective lens is 0.55 to 0.55.
The optical disk recording and / or reproducing apparatus according to claim 9, which is 0.70. 11. A first and second protective layer provided so as to sandwich the recording material layer, a reflective layer provided between the first protective layer and a substrate, and the second protective layer. The protective layer is arranged so as to face the transparent cover of the optical disc on which at least the transparent cover provided on the side opposite to the surface in contact with the recording material layer is laminated, and the transparent cover is provided. An objective lens having a numerical aperture of 0.55 to 0.70 for focusing the laser beam on the recording material layer through a transparent cover, a driving unit for driving the objective lens in the focusing direction and the tracking direction, and the laser beam. When the numerical aperture of the objective lens is NA, the thickness of the transparent cover is t, and the refractive index of the transparent cover is N,
The coma aberration W _{31 of the} objective lens is W ₃₁ = {t · (N ² −1) N ² sin θ cos θ · sin
An optical disc recording and / or reproducing apparatus satisfying ³ α} / {2 (N ² −sin ² θ) ^5/2 } (θ: skew, sin α = NA). 12. The thickness of the translucent cover is from 0.6 to 10.
The optical disk recording and / or reproducing apparatus according to claim 11, having a size of 0.1 mm.