KR100233420B1 - Optical disk system and optical disk - Google Patents

Abstract

The magneto-optical disk 40 having a translucent cover 41, the objective lens 2 and the optical glass for focusing the laser beam on the recording magnetic layer 43 of the magneto-optical disk 40 for recording and / or reproduction. Disclosed is a magneto-optical disk system including a magnetic field generator (9) formed by forming a coil pattern (7) at (8). According to this magneto-optical disk system, recording density and / or higher density are achieved by setting the thickness t ₂ of the transparent cover 41 to 0.6 to 0.1 mm and the numerical aperture NA of the objective lens 2 to 0.55 to 0.70. You can play.

Description

Optical Disk System and Optical Disk

The present invention relates to an optical disc system and a magneto-optical disc system in which information signals are recorded and / or reproduced, and an optical disc and a magneto-optical disc that can be used in these systems.

FIG. 1 shows an magneto-optical disc system using magneto-optical effects as an example of an optical disc system for recording and / or reproduction in an optical recording medium such as an optical disc or a magneto-optical disc.

The conventional magneto-optical disc system shown in FIG. 1 has a laser beam generator 58 on the upper surface side of the one-sided magneto-optical recording medium 50 when the disc-shaped one-sided magneto-optical recording medium 50 is mounted. And an optical system composed of an objective lens 59 and the like, and a magnetic field generating device 60, which is a magnetic field, is disposed on the lower surface side of the single-sided magneto-optical recording medium 50. The numerical aperture (hereinafter referred to as "NA") of the objective lens 59 is set to 0.50 to 0.53.

A drive system not shown is arranged for driving the optical system in the focusing direction and the tracking direction with respect to the magneto-optical recording medium 50. Also for the magnetic system, other drive systems, not shown, are arranged for driving in the arrow direction and the tracking direction in FIG.

In such a magneto-optical disk system, a magnetic field modulation method is employed for the recording. In such a field modulation method, since it is necessary to invert and control the magnetic field at high speed according to the information signal to be recorded, sufficient excitation current cannot be obtained and there is a limit to the generated magnetic field strength that can be generated in the magnetic field generating device. The device 60 is disposed near the recording magnetic layer 53 described later in the single-sided magneto-optical recording medium 50. According to the magnetic field modulation method, overwriting is possible.

The single-sided magneto-optical recording medium 50 has a dielectric layer 52, for example, rare earth-transition, on one side of a translucent transparent substrate 51 such as polycarbonate. A recording magnetic layer 53 having a large magneto-optical effect such as a metal alloy amorphous thin film, a dielectric layer 54, a reflective layer 55, and a protective cover 56 are sequentially stacked. The thickness t ₁ of the transparent substrate 51 is constant, and is conventionally set to 1.2 mm.

Next, the operation will be briefly described.

First, the single-sided magneto-optical recording medium 50 is disposed on the rotating disk (not shown) to be rotated, and the magnetic field from the magnetic field generating device 60 is applied to the recording magnetic layer 53 in the single-sided magneto-optical recording medium 50. do. The applied magnetic field is controlled by the fast inversion based on the information signal to be recorded, and the laser beam irradiated from the laser beam generator 58 onto the recording magnetic layer 53 to which the magnetic field is applied is collected through the objective lens 59. Belong. As a result, the direction of magnetization can be changed in accordance with the direction of the magnetic field applied from the magnetic field generating device 60 in the recording magnetic layer 53 in the region where the laser beam is focused, thereby realizing the information signal in real time. Can be overwritten.

In order to further reduce the size of the magneto-optical pickup provided with the optical system, the magnetic system and their driving system, it may be considered to arrange the optical system and the magnetic system integrally on the same side of the magneto-optical recording medium. In other words, the magnetic field generating device 60 in FIG. 1 is disposed on the objective lens 59 side (the translucent substrate 51 side) to integrate them. However, in this case, since the distance between the magnetic field generating device 60 and the recording magnetic layer 53 becomes larger, the magnetic field cannot be applied to the recording magnetic layer 53 with sufficient strength.

Background Art In recent years, with the increase in the amount of information, a double-sided magneto-optical recording medium capable of recording information signals on both sides with recording magnetic layers or the like described above on both sides of a single magneto-optical recording medium has been developed. By the way, in order to perform recording and / or reproducing in such a double-sided magneto-optical recording medium, for example, a sufficient intensity of the magnetic field for both recording magnetic layers from the magneto-optical pickup composed of the optical system and the magnetic system as shown in FIG. It is very difficult to apply. For this reason, in the magnetic field generation apparatus of the magnetic field modulation method, a high frequency current corresponding to a high frequency data signal as an information signal to be recorded must flow through the electromagnetic coil, but as the current becomes high frequency, the coil does not flow well. This is because there is a limit to the magnetic field generated. This is because the distance from the magnetic field generating device to the recording magnetic layer is considerably large. Therefore, in the current technology, double-sided magneto-optical recording by the magnetic field modulation method is very difficult.

In order to cope with the increase in the information amount as described above, it is required to record more information signals in the recording layer of the optical disk, for example, the recording magnetic layer or the like described above.

Accordingly, it is an object of the present invention to provide an optical disk system having a large capacity that enables higher density recording and / or reproduction, and an optical disk that can be used for the optical disk system.

1 is a cross-sectional view showing the basic configuration of a conventional magneto-optical disk system.

2 is a cross-sectional view showing the configuration of the magneto-optical disk system of the first embodiment according to the present invention.

3 is a cross-sectional view showing the configuration of the magneto-optical disk system of the second embodiment according to the present invention.

4 is a front view of an optical glass having a coil pattern formed in the magneto-optical disk system shown in FIGS. 2, 3, and 5;

5 is a cross-sectional view showing the configuration of a magneto-optical disk system of a third embodiment according to the present invention.

According to one aspect of the present invention, the present invention provides an information signal to an optical disk having a recording layer to which a laser beam is irradiated for recording or reproduction, and a transmissive cover disposed to cover the recording layer and transmitting the laser beam. A system for recording and / or reproducing an information signal from an optical disc, comprising: a laser beam generating means for generating the laser beam and an objective lens for focusing the laser beam on the recording layer through the transparent cover; In the optical disk system, the thickness of the transparent cover of the optical disk is in the range of 0.6 to 0.1 mm, and the numerical aperture of the objective lens is in the range of 0.55 to 0.70.

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 the laser beam)

Therefore, since the NA of the objective lens is larger than the conventional NA (0.50 to 0.53), the minimum diameter of the focusing beam becomes smaller and the recording density becomes larger. Then, reproduction corresponding to the recording density can be performed.

As NA increases, the thickness of the objective lens also increases. However, since the thickness of the transparent cover of the optical disc is smaller than the conventional thickness (1.2 mm), the objective lens with increased thickness does not contact the optical disc.

When the NA of the objective lens and the thickness t of the translucent cover of the optical disk are changed, the following aberration values of the objective lens change.

(A) Spherical aberration W ₄₀

......... (2)

(sinα = NA; N: refractive index of the transparent cover of the optical disc)

(B) coma aberration W ₃₁

........ (3)

(θ: skew)

Since the spherical aberration of (A) can be corrected in the objective lens, there is basically no problem. However, it becomes a problem if the thickness t of a translucent cover becomes uneven, and it is preferable to suppress this t within a tolerance.

Since the coma aberration of (B) cannot be corrected in the objective lens, the smaller the absolute value is, the better. Here, even if NA is large, the thickness t of the translucent cover is small, so that the absolute value of W ₃₁ is not large.

Therefore, since each aberration of the objective lens becomes little problem even if the NA is made larger, the optical disk system can perform recording and / or reproducing as conventionally at a higher density.

According to another feature of the invention, another invention is provided with a substrate, an optical magnetic recording layer disposed on the substrate and irradiated with a laser beam for recording or reproduction, and disposed to cover the optical magnetic recording layer so that the laser beam A system for recording an information signal on a magneto-optical disk having a transmissive cover and / or reproducing the information signal from the magneto-optical disk, comprising: laser beam generating means for generating the laser beam, and transmitting the laser beam An objective lens focusing on the magneto-optical recording layer through a cover, and magnetic field supply means for applying a magnetic field to the magneto-optical recording layer, wherein the thickness of the translucent cover of the magneto-optical disk is in the range of 0.6 to 0.1 mm. And a magneto-optical disk system in which the numerical aperture of the objective lens is in the range of 0.55 to 0.70.

The optical disc and the magneto-optical disc of the present invention are disposed so as to cover the recording layer in response to the NA of the objective lens becoming larger in the range of 0.55 to 0.70 for high-density recording or reproduction in a system using them. The thickness of the translucent cover disposed so as to transmit to the recording layer is in the range of 0.6 to 0.1 mm.

Thereby, an optical recording medium and a magneto-optical recording medium capable of higher density recording or reproduction can be obtained.

In the magneto-optical disk, when a high permeability layer is disposed between the substrate and the magneto-optical layer, the vertical magnetic field efficiency is increased, which is preferable.

The magneto-optical disk may have recording layers on both sides of the substrate. Such a magneto-optical disk having a recording layer on both sides faces an optical pickup device including a laser beam generating means and an objective lens and a magnetic field supply means in the aforementioned magneto-optical system with a pair of magneto-optical disks interposed therebetween. It can be used in the magneto-optical disk system of the present invention arranged to be in position.

According to the magneto-optical disk having a recording layer on both sides and the magneto-optical disk system which can use the magneto-optical disk, recording and reproduction of a larger capacity can be achieved.

Next, Examples according to the present invention will be described with reference to FIGS. 2 to 5.

2 is a cross-sectional view showing a first embodiment in which the present invention is applied to a magneto-optical disk system, and shows a basic configuration of the magneto-optical disk system.

As shown in Fig. 2, this magneto-optical disk system is composed of a magnetic field generating device comprising an objective lens 2 having a NA of 0.55 to 0.70 and an optical glass 8 having a light transmission with a coil pattern 7 formed thereon. (9) is provided.

This magneto-optical disk system has a dielectric layer 42, a recording magnetic layer 43, a dielectric layer 44, a reflecting film 45 and a protective cover on a light transmissive substrate 41 having a thickness t ₂ of 0.1 to 0.6 mm. The disk-shaped single-sided magneto-optical recording medium 40 formed by stacking 46 in sequence is configured to irradiate a laser beam from a laser beam device, not shown, to record and reproduce. The magnetic field generating device 9 is of a magnetic field modulation method, and supplies the magnetic field to the recording magnetic layer 43 as described in detail with reference to FIG.

The thickness of the dielectric layer 42 is extremely thin, so compared to the t _2, need not be considered as the thickness for the t _2.

The objective lens 2, which is an optical system, and the optical glass 8 constituting the magnetic system are fixed by being bonded to a bobbin, not shown, and the coil pattern 7 approaches the magneto-optical recording medium 40. It is arranged to.

As described above, since the thickness t ₂ of the light transmissive substrate 41 is considerably thinner than before, and the coil pattern 7 approaches the light transmissive substrate 41, the distance between the coil pattern 7 and the recording magnetic layer 43 is shortened. Is preferred. Since the optical system and the magnetic system can be integrated, the magneto-optical pickup device made of these can be miniaturized and the cost can be reduced. Then, as shown in the second and third embodiments described later, recording and reproduction on the double-sided magneto-optical recording medium are enabled.

In the magneto-optical recording medium used for this magneto-optical disk system, for example, it is preferable to use a 3.5-inch magneto-optical disk fixedly or in a cartridge holder.

The NA of the objective lens 2 increases from 0.55 to 0.70 so that its depth of focus (= λ / NA ² , λ: wavelength of the laser beam) becomes shallow, but the magneto-optical disk is small as described above, so that the magneto-optical pickup Since the actuator which does not show the figure which constitutes the drive system for this is reduced in size, the frequency characteristic is improved, and this actuator fully follows, there is no problem that the depth of focus becomes shallow.

The spherical aberration W ₄₀ described above is corrected in the objective lens 2.

As for the coma aberration W ₃₁ , as described above, even if the NA of the objective lens becomes larger, there is no problem because the thickness t ₂ of the light transmissive substrate is smaller.

Here, the coma aberration W ₃₁ is equivalent to a NA that is (等價) to the value of the coma aberration W ₃₁ is obtained in the case of NA = 0.50, and the transparent substrate (the transparent cover) the thickness t = 1.2mm of the objective lens as in the prior art and t The results obtained for four cases are shown in the first table below.

Table 1

NA 0.50 0.55 0.6 0.65 0.70 t (mm) 1.2 0.9 0.69 0.55 0.44

As shown in this first table, even if NA is 0.55 to 0.70, when t is 0.6 to 0.1 mm, the coma aberration can be equal to or less than that of the conventional art, and thus there is no problem.

By increasing the NA of the objective lens 2, the thickness of the objective lens 2 is increased. However, as described above, since the thickness t ₂ of the light transmissive substrate is small, the objective lens 2 and the magneto-optical magnet as shown in FIG. The distance d (working distance) from the recording medium 40 is greater than or equal to a predetermined value, and the objective lens 2 and the magneto-optical recording medium 40 are not in contact with each other, and the optical glass 8 can be interposed therebetween. have.

Dust which is a problem in the optical disk system is not a problem if a cartridge holder type or a fixed type is adopted in the magneto-optical recording medium.

The particle size and distribution of the dust mentioned above are problematic, but the radius r of the projected circle generated by the laser beam on the translucent substrate 41 (see FIG. 1) is

r = ttan (arc sin (NA / N)) ......... (4)

to be. As can be seen from Equation (4), when the thickness t of the light-transmissive cover is smaller, the r is smaller, but since the NA is larger, the r is not significantly reduced. Is not particularly.

As described above, in the magneto-optical disk system of the present embodiment, the NA of the objective lens is 0.55 to 0.70 and the thickness t ₂ of the transparent substrate (translucent cover) is 0.6 to 0.1 mm, so that the NA is 0.50. As can be seen from the above formula (1), the recording density can be increased from (0.55 / 0.50) ² to (0.70 / 0.50) ² ≒ 1.2 to 2 times as compared with the case of the conventional system. In addition, it can be seen that all these problems can be solved by increasing this NA. Therefore, it is possible to increase the capacity of the magneto-optical disk system without any problem.

Next, a more detailed configuration of the magneto-optical disk system of the above-described first embodiment will be described according to the second and third embodiments.

3 is a cross-sectional view of a second embodiment of a magneto-optical disk system according to the present invention.

This second embodiment is constructed by arranging the first and second magneto-optical pickup devices including the optical system and the magnetic field to face each other via the magneto-optical recording medium 10 as shown in FIG. .

The first magneto-optic pickup device disposed on the upper surface side of the magneto-optical recording medium 10 and the second magneto-optical pickup device disposed on the lower surface side thereof have the same configuration as will be described later, and their constituent parts 1 ) To (9) and (1 ') to (9') correspond.

The first and second magneto-optical pickup devices in FIG. 3 include laser beam generators 1 and 1 ', and objective lenses 2 and 2 having NAs of 0.55 to 0.70 as described above. '), Coil bobbins 4 and 4' wound around focus coils 3a, 3a 'and tracking coils 3b and 3b', and coil bobbins 4 and 4 '. Is composed of pickups 6 and 6 ', which are optical systems composed of magnets 5 and 5', which are disposed around the magnetic field, and the above-described magnetic field generating devices 9 and 9 'which are magnetic fields.

The coil bobbins 4 and 4 'of the pickups 6 and 6' are cylindrical, for example, and F around the pickups 6 and 6 'is shown in FIG. Tracking coils 3a, 3a 'for driving in the direction and tracking coils 3b, 3b' wound for driving the pickups 6, 6 'in the T direction shown in FIG. This is arranged. The lens support members 2a and 2a 'are disposed at positions close to the end portions 4a and 4a' of the coil bobbins 4 and 4 '. The lens supporting members 2a and 2a 'support the objective lenses 2 and 2' for focusing the laser beam irradiated from the laser beam generators 1 and 1 '. have.

As shown in FIG. 4, the magnetic field generating devices 9 and 9 'are provided with optically transparent optical glass 8, 8', 8a 'such as quartz, for example. Is formed by forming the coil patterns 7 and 7 'of spiral windings for generating a magnetic field by flowing a current of a high frequency signal. On the other side 8b, 8b 'side in which the coil patterns 7, 7' of the optical glass 8, 8 'are not formed, the objective lens 2, 2' is coiled. The centers of the patterns 7 and 7 'and the centers of the objective lenses 2 and 2' are positioned and disposed so as to coincide with each other. The objective lenses 2 and 2 'are fixed in the vicinity of the ends 4a and 4a' of the coil bobbins 4 and 4 'via the lens supporting members 2a and 2a'. The optical glasses 8 and 8 'are adhesively fixed to the end portions 4a and 4a' of the coil bobbins 4 and 4 '. As a result, the laser beam can be focused at the center of the magnetic field generated, so that the adjustment of the centering at the time of assembling the pickup is unnecessary.

The use of quartz for the optical glasses 8 and 8 'is one example, and any one may be used as long as it is light transmissive. In the coil patterns 7 and 7 ', for example, a print coil, a thin film coil, or the like may be used. Laser beams from the laser beam generators 1 and 1 'on the optical glasses 8 and 8' to prevent reflection from the surfaces of the optical glasses 8 and 8 '. You may provide this hole part which passes.

The first double-sided magneto-optical recording medium 10 shown in FIG. 3 has been previously proposed by the present applicant in the specification and drawings of Japanese Patent Application Laid-Open No. 1 (1989) -142563, respectively, on both sides of the common substrate 11. The recording layer 16, the photocurable resin layer 17, and the transparent protective plate 18 are arrange | positioned. Both the transparent protective plate 18 and the photocurable resin layer 17 have light transmittance, and the sum of these thicknesses can be 0.6 mm or less.

In each of the recording layers 16, the reflective layer 15 is laminated so as to be disposed on the substrate 11 side rather than the recording magnetic layer 12, and the reflective layer 15 and the second dielectric layer (from the substrate 11 side, respectively) 14), the recording magnetic layer 12, and the first dielectric layer 13 are stacked in this order.

Since the double-sided magneto-optical recording medium 10 has a common substrate 11, the thickness of the double-sided magneto-optical recording medium 10 can be suppressed to about half the thickness of the conventional double-sided magneto-optical recording medium.

Next, the operation will be described.

In the first magneto-optical pickup device configured as described above, the coil bobbin 4 and the magnetic field generating device 9 disposed on the coil bobbin 4 are supplied by supplying a focus drive current to the focus coil 3a. The driving displacement is shifted in the focus direction in the optical axis direction of the objective lens 2 indicated by the arrow F in the third diagram.

Similarly, the second magneto-optic pickup device is also displaced in synchronization with the drive of the first magneto-optical pickup device in the F direction and the T direction.

The tracking drive current is supplied to the tracking coil 3b so that the coil bobbin 4 and the magnetic field generating device 9 are in a tracking direction which is a direction perpendicular to the optical axis of the objective lens 2 indicated by the arrow T in the third direction. Drive is displaced.

At the same time, a high frequency current signal amplified by a signal to be recorded is supplied to the coil patterns 7 and 7 'formed of the conductors 7a and 7a' of the magnetic field generators 9 and 9 '. As a result, a magnetic field is generated. This magnetic field is controlled to be fast inverted in accordance with the recording signal, and applied to the recording magnetic layers 12 and 12 'of the double-sided magneto-optical recording medium 10. The laser beams irradiated from the laser beam generators 1 and 1 'on the region to which the magnetic fields of the recording magnetic layers 12 and 12' are applied are subjected to the objective lenses 2 and 2 'and the light transmittance. The information signal can be recorded by focusing through the optical glasses 8 and 8 'which are excited, and raising the temperature of the recording magnetic layers 12 and 12' above the Curie point.

As is apparent from the above description, the magneto-optical disk system according to the present embodiment includes pickups 6, and (made up of laser beam generators 1, 1 ', objective lenses 2, 2', and the like. 6 ') and the magnetic fields of the magnetic field generators 9 and 9' formed by forming the coil patterns 7 and 7 'on the optical glass 8 and 8'. By disposing on the same side of the recording medium 10, the distance between the coil patterns 7 and 7 'and the magneto-optical recording medium 10 can be shortened.

Since the translucent cover made of the transparent protective plate 18 and the photocurable resin layer 17 is thin, the coil patterns 7 and 7 'and the magneto-optical recording layer 12 of the magneto-optical recording medium 10 Since the distance can be made very short, recording on the double-sided magneto-optical recording medium by the magneto-optic modulation method, which has been known to be very difficult until now, becomes possible.

The coil bobbins 4, 4 'of the pickups 6, 6' and the magnetic field generating devices 9, 9 'are integrally coupled and fixed, for example, by bonding or the like, so that the objective lens 2 ), It is easy to center the centers of the magnetic fields of the magnetic field generating devices 9 and 9 '. The pickups 6, 6 'and the magnetic field generating devices 9, 9' are linked to each other by the focus servo, so that the intensity of the magnetic field applied to the double-sided magneto-optical recording medium 10 can be made constant at all times. have. It is possible to omit the driving system for the magnetic field, which has been necessary conventionally. And since the clearance space of the said magneto-optical pick-up apparatus arises, the degree of freedom in design can be increased.

According to the second embodiment, it is possible to variously record and reproduce the double-sided magneto-optical recording medium 10. For example, by simultaneously using the laser beam generators 1, 1 'and the magnetic generators 9, 9', the simultaneous recording on the upper surface side and the lower surface side of the double-sided magneto-optical recording medium 10 is performed. This becomes possible. Simultaneous reproduction is possible when the laser beam generators 1 and 1 'are used simultaneously. As a result, a larger capacity can be achieved, and at the same time, it is possible to record and reproduce information signals at a higher speed.

It is possible to first record or reproduce on one side of the double-sided magneto-optical recording medium 10, and then to record or reproduce on the other side. This allows recording and reproduction of twice the capacity as compared with the single-sided magneto-optical recording medium.

In the case described above, the two magnetic field generating devices 9 and 9 'are generated while generating a magnetic field from the magnetic field generating device 9 or 9' arranged on the other surface side when recording on one surface. Can be used at the same time. Therefore, the magnetic field can be applied to the magnetic recording layer 12 from both sides thereof, and recording can be performed with a larger magnetic field.

When recording on one surface, recording can also be performed by using only the magnetic field generating device arranged on the other surface side.

Next, a third embodiment will be described. As shown in FIG. 5, the present embodiment uses the magneto-optical disk system as shown in FIG. 3 and simultaneously records and reproduces using the second double-sided magneto-optical recording medium 30 shown in FIG. It is configured to be.

The second double-sided magneto-optical recording medium 30 has been proposed by one of the inventors of the present application in the specification and drawings of Japanese Patent Application Laid-Open No. 1 (1989) -274734, together with the other inventors. The high permeability layer 32, the photocurable resin layer 33, the magneto-optical recording layer 34, the adhesive layer 35, and the transparent protective plate 36 are sequentially stacked on both surfaces, respectively. Both the transparent protective plate 36 and the adhesive bond layer 35 have light transmittance, and the sum of these thicknesses can be 0.6 mm or less.

The high permeability layer 32 is made of a material having a high permeability such as transition metals such as Fe, Co, Ni, and these alloys such as permalloy, senddust, or amorphous magnetic alloys. This makes it possible to increase the vertical magnetic field efficiency in the vertical direction of the double-sided magneto-optical recording medium 30.

In the third embodiment, since the second double-sided magneto-optical recording medium 30 includes the high permeability layer 34, the magnetic flux from the magnetic field generating devices 9 and 9 'is, for example, the fifth. Since the magnetic closed loop is constituted as indicated by the broken line in the figure, it is preferable because the magnetic flux applied to the double-sided magneto-optical recording medium 30 can be effectively converged at the time of recording to increase its vertical magnetic field efficiency.

Also in the third embodiment, recording or reproduction can be performed simultaneously on both surfaces of the double-sided magneto-optical recording medium 30. It is possible to record or reproduce on one side and then record or reproduce on the other side.

As described above, in the second and third embodiments, the NA of the objective lenses 2 and 2 'is increased in the same manner as in the first embodiment, so that higher density recording and reproduction are possible, Since a magnetic recording medium can be used, higher capacity and faster recording and reproducing are possible. Therefore, a large capacity magneto-optical disk system can be provided.

In the first to third embodiments, the magnetic field generating devices 9 and 9 'are based on the magnetic field modulation method. However, the magnetic field generating devices 9 and 9' can be applied to other methods, for example, the optical modulation method.

Embodiments 1 to 3 are magneto-optical disk systems, but the present invention is not limited thereto. For example, an optical recording medium (for example, a recordable optical recording medium, etc.) formed by disposing pits in a recording layer. It goes without saying that it may be an optical disc system for recording and / or reproducing an optical disc.

According to the optical disk system of the present invention, since the NA of the objective lens for focusing the laser beam is made larger and the light-transmissive cover of the optical disk is made thinner, higher density recording and / or reproduction can be achieved and the capacity can be increased.

In the optical disc system and the optical disc of the present invention, higher density recording and / or reproduction and large capacity are possible.

Claims (4)

At least one light source for generating a light beam and at least one objective lens for focusing the light beam on an optical axis, wherein the numerical aperture of the objective lens is in the range of 0.55 to 0.70. In the optical recording medium for use, a) a first recording layer 16; b) a first translucent cover layer provided on one surface of the first recording layer to cover the first recording layer and having a first light incident surface irradiated by a light beam passing through the objective lens 2 ( 18); c) a second recording layer 16 'provided parallel to the first recording layer; And d) a second translucent cover layer 18 'provided on one surface of said second recording layer to cover said second recording layer and having a second light incident surface irradiated by a light beam passing through said objective lens; Including, The thicknesses of the first and second translucent cover layers are each in a range of 0.6 to 0.1 mm. Optical recording media. The method of claim 1, And a substrate (11), wherein said recording medium is provided between said first and second recording layers. Optical recording using an optical recording medium having a transparent cover layer 17, 18 capable of transmitting a light beam and a recording layer 16 provided below the light incident surface of the transparent cover layer 17, 18 and / or Or in a playback system, a) a light source 1 for generating a light beam; And b) an objective lens 2 focusing the light beam irradiated from the light source onto the recording layer 16 through the transparent cover layer Including, When the light beam is focused by an objective lens, the ratio of the minimum diameter (2ω ₀ ) of the focused light beam and the wavelength of the light beam generated from the light source is 2ω ₀ / λ = 0.82 / NA Where NA is the numerical aperture of the objective lens in the range of 0.55 to 0.70. Optical recording and / or reproducing system. An optical disc system for recording and / or reproducing an information signal, a) a transparent cover layer 17, 18 capable of transmitting a light beam, wherein the thickness of the transparent cover layer 17, 18 is selected in the range of 0.6 to 0.1 mm; and the light of the transparent cover layer 17, 18. An optical recording medium having a recording layer provided below the incident surface; b) a light source 1 for generating a light beam; And c) an objective lens 2 focusing the light beam irradiated from the light source onto the recording layer through the transparent cover layer Including, When the light beam is focused by the objective lens 2, the ratio of the minimum diameter (2ω ₀ ) of the focused light beam and the wavelength of the light beam generated from the light source 1 is expressed by the following expression, 2ω ₀ / λ = 0.82 / NA Where NA is the numerical aperture of the objective lens in the range of 0.55 to 0.70. Optical disc system.