JP2007018707A - Optical recording medium and optical disk system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium wherein recording and/or reproduction of higher density can be performed and capacity is enlarged and to provide an optical disk system. <P>SOLUTION: In the optical disk system, an optical disk 40 having a light transmission layer 41 composed of a light transmissive base body having 0.44 to 0.6 mm thickness and formed so that a laser beam is made incident thereon, a recording layer 43 on which the laser beam is condensed by passing through the light transmissive base body, a reflection layer 45 and a protective cover layer 46 is irradiated with the laser beam by using an objective lens 2 having a numerical aperture NA of 0.55 to 0.70 so that the laser beam is condensed toward the recording layer 43 from the surface side of the light transmission layer 41 of the optical disk 40. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical recording medium such as an optical disc or a magneto-optical disc, and an optical disc system for recording and / or reproducing the same.

  As an example of an optical disk system for recording and / or reproducing on an optical recording medium such as an optical disk or a magneto-optical disk, a magneto-optical disk recording and / or reproducing apparatus is shown in FIG.

  The conventional magneto-optical disk recording and / or reproducing apparatus shown in FIG. 5 has a laser device 58, an objective lens 59, etc. on the upper surface side of the single-side magneto-optical recording medium 50 when the disk-like single-side magneto-optical recording medium 50 is mounted. And a magnetic field generator 60 that is a magnetic system is provided 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.

  In addition, 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 the tracking direction.

  In this magneto-optical disk recording and / or reproducing apparatus, a magnetic field modulation system is adopted for the recording. In this magnetic field modulation method, since the magnetic field needs to be reversed at high speed, a sufficient excitation current cannot be obtained, and the generated magnetic field intensity is limited. Is disposed near a recording magnetic layer 53 described later. According to the magnetic field modulation method, overwrite (overwriting) is possible.

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

  Next, a simple operation will be described. First, the single-sided magneto-optical recording medium 50 is placed on a rotating disk (not shown) and rotated, and a magnetic field from the magnetic field generator 60 is applied to the recording magnetic layer 53 in the single-sided magneto-optical recording medium 50. The applied magnetic field is subjected to high-speed reversal control, and the laser beam irradiated 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, so that the laser beam is focused. The recording magnetic layer 53 in the focused area 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 comprising the optical system, the magnetic system and the drive system, the same surface of the magneto-optical recording medium is integrated with the optical system and the magnetic system. It can be considered to be arranged on the side. That is, the magnetic field generating device 60 in FIG. 5 is arranged on the objective lens 59 side (translucent substrate 51 side) and integrated with them, but in this case, the magnetic field generating device 60, the recording magnetic layer 53, and the like. Therefore, the magnetic field cannot be applied to the recording magnetic layer 53 with sufficient strength.

  In addition, with the recent increase in the amount of information, a double-sided magneto-optical recording medium has been developed in which a recording magnetic layer as described above is provided on both sides of a single magneto-optical recording medium and information signals can be recorded on both sides. Has been. However, in order to perform recording and / or reproduction on such a double-sided magneto-optical recording medium, a magnetic field is applied to both recording magnetic layers from a magneto-optical pickup comprising, for example, an optical system and a magnetic system as shown in FIG. Is extremely difficult to apply with sufficient strength.

  In a magnetic field modulation type magnetic field generator, a high-frequency current corresponding to a high-frequency data signal must flow through the electromagnetic coil. However, since the higher the current is, the more difficult it is to flow through the coil, the generated magnetic field is limited. In addition, the distance from the magnetic field generator to the recording magnetic layer is considerably large. Therefore, double-sided magneto-optical recording by the magnetic field modulation method is extremely difficult with the current technology.

  In order to cope with the increase in the information amount as described above, it is necessary to record more information signals in a recording unit such as the above-described recording magnetic layer of the optical disc. An object of the present invention is to provide a large-capacity optical recording medium and an optical disc system that can perform recording and / or reproduction with higher density.

  The optical recording medium according to claim 1 is an optical recording medium irradiated with a laser beam emitted from a light source for recording and / or reproduction through an objective lens having a numerical aperture of 0.55 to 0.70. A light-transmitting substrate having a thickness of 0.44 to 0.6 mm, and provided with a light transmission layer provided so that a laser beam emitted from the light source is incident thereon, and the objective lens The irradiated laser beam is focused through the light transmissive substrate and is provided in order from the light transmissive substrate side, and the light transmissive layer with respect to the reflection layer. And a protective cover layer provided on the opposite surface side.

  The optical disk system according to claim 2 is a laser beam emitted from the light source, which is formed of a light-transmitting substrate having a thickness of 0.44 to 0.6 mm, which is irradiated with a laser beam for recording and reproduction from the light source. The laser beam irradiated through the objective lens and the laser beam irradiated through the objective lens is focused through the light-transmitting substrate, and is sequentially provided from the light-transmitting substrate side. The numerical aperture NA is 0.55 to the optical disc having the recording layer and the reflective layer, and the protective cover layer provided on the surface opposite to the light transmissive layer with respect to the reflective layer. A 0.70 objective lens was used to irradiate the laser beam emitted from the light source so as to be condensed toward the recording layer from the light transmitting layer side of the optical disc.

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: Laser beam wavelength)
Therefore, since the NA of the objective lens is 0.55 to 0.70 and larger than the conventional NA (0.50 to 0.53), the minimum diameter of the focused beam becomes smaller and the recording density increases. Then, reproduction corresponding to the recording density can be performed.

  Also, as the NA increases, the thickness of the objective lens also increases, but the thickness of the cover layer of the optical recording medium is 0.1 to 0.6 mm, which is smaller than the conventional thickness (1.2 mm). The increased objective lens does not come into contact with the optical recording medium.

  Further, when the NA of the objective lens and the thickness t of the cover layer of the optical recording medium change, the following aberration values of the objective lens change.

(A) Spherical aberration W ₄₀
W ₄₀ = {t · (N ² −1) · sin ⁴ α} / (8N ³ ) (2)
(Sin α = NA)
(N: refractive index of the cover layer of the optical recording medium)

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

Since the spherical aberration of (A) can be corrected in the objective lens, there is basically no problem. However, since it becomes a problem if the thickness t of the cover layer varies, it is desirable to keep this t within a tolerance. Since the coma aberration of (B) cannot be corrected by the objective lens, the smaller the absolute value, the better. Here, even if NA increases to 0.55 to 0.70, the thickness t of the cover layer decreases to 0.6 mm or less, so the absolute value of W ₃₁ does not increase. Therefore, since the aberration of the objective lens hardly causes a problem even when the NA is increased to 0.55 to 0.70, conventional recording and / or reproduction can be performed at a higher density.

  According to the optical recording medium and the optical disk system of the present invention, the NA of the objective lens for focusing the laser beam is set to 0.55 to 0.70 and the thickness of the light transmission layer is set to 0.44 to 0.6 mm. The recording and / or reproduction can be performed at a higher density while maintaining the coma aberration equal to or less than that when the NA of the objective lens is 0.50 and the thickness of the light transmission layer is 1.2 mm. The capacity can be increased, and even if the NA of the objective lens is large and the thickness thereof is large, the objective lens does not come into contact with the optical recording medium, and the problem due to dust can be prevented.

  Hereinafter, first to third embodiments according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing a first embodiment in which the present invention is applied to a magneto-optical disk recording and / or reproducing apparatus, and shows a basic configuration of the magneto-optical disk recording and / or reproducing apparatus. As shown in FIG. 1, this magneto-optical disk recording and / or reproducing apparatus is made up of an optical glass 8 having light transmittance on which an objective lens 2 having an NA of 0.55 to 0.70 and a coil pattern 7 are formed. The magnetic field generator 9 is configured.

Then, the light-transmitting substrate 41 is a thickness t ₂ is 0.1 to 0.6 mm, the dielectric layer 42, the recording magnetic layer 43, dielectric layer 44, the reflective film 45 and the protective cover 46 are laminated in this order The disc-shaped single-sided magneto-optical recording medium 40 having a thin translucent substrate portion can be recorded and reproduced by irradiating a laser beam from a laser beam device (not shown). The magnetic field generator 9 is based on a magnetic field modulation method, which will be described in detail later with reference to FIG.

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

As described above, since the thickness t ₂ of the translucent substrate 41 is considerably smaller than the conventional one and the coil pattern 7 is close to the translucent substrate 41, the distance between the coil pattern 7 and the recording magnetic layer 43 is as follows. Shortening is preferable. In addition, since the optical system and the magnetic system can be integrated, the magneto-optical pickup composed of these can be reduced in size and cost, and double-sided magneto-optical recording can be performed as shown in the second and third embodiments described later. Recording and reproduction on a medium are possible.

  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.

When the NA of the objective lens 2 is increased to 0.55 to 0.70, the depth of focus (= λ / NA ² , λ: wavelength of the laser beam) becomes shallow, but the magneto-optical disk is small as described above. Therefore, the actuator (not shown) constituting the drive system for the magneto-optical pickup is miniaturized, its frequency characteristics are improved, and the actuator follows sufficiently, so 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. Further, regarding the coma aberration W ₃₁ , there is no problem because the thickness t ₂ of the translucent substrate is smaller even if the NA of the objective lens is larger as described above. Here, the coma aberration W ₃₁ is the value of the coma aberration W ₃₁ obtained when the NA of the objective lens is 0.50 and the thickness t of the translucent substrate (cover layer) is 1.2 mm as in the prior art. Table 1 below shows the results of obtaining equivalent NA and t for four cases.

  As shown in Table 1, even if the NA is 0.55 to 0.70, if the t is 0.6 to 0.1 mm, the coma aberration can be the same as or lower than that of the prior art, so there is no problem. Recognize.

The thickness of the objective lens 2 is increased by having an increased NA of the objective lens 2, but since the thickness t ₂ of the light-transparent substrate as described above is small, and the objective lens 2 as shown in FIG. 1 light Since the distance d (so-called working distance) from the magnetic recording medium 40 is a predetermined value or more, the objective lens 2 and the magneto-optical recording medium 40 are not in contact with each other. Further, in this case, there is no problem with dust which is a problem in the optical recording and / or optical reproducing apparatus because the magneto-optical recording medium employs a cartridge holder type or a fixed type.

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

As described above, in the magneto-optical disk recording and / or reproducing apparatus of the present embodiment, the NA of the objective lens is set to 0.55 to 0.70, and the thickness t _{2 of the} translucent substrate (cover layer). The recording density is 0.6 to 0.1 mm, as can be seen from the above formula (1), as compared with the case of a recording and / or reproducing apparatus using a conventional objective lens having an NA of 0.50. Can be set to (0.55 / 0.50) ² to (0.70 / 0.50) ² ≈1.2 to ² times. It turns out that it can be eliminated. 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 configuration of the magneto-optical disk recording and / or reproducing apparatus according to the first embodiment will be described with reference to the second and third embodiments. FIG. 2 is a sectional view of a second embodiment of the magneto-optical disk recording and / or reproducing apparatus according to the present invention.

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

  The first and second magneto-optical pickup devices in FIG. 2 include laser devices 1 and 1 ', objective lenses 2 and 2' having NA of 0.55 to 0.70 as described above, and focus coil 3a. 3a 'and tracking coils 3b, 3b' are wound around the coil bobbins 4, 4 'and magnets 5, 5' arranged around the coil bobbins 4, 4 '. 'And the above-described magnetic field generators 9 and 9' which are magnetic systems.

  The coil bobbins 4 and 4 'of the pickups 6 and 6' have, for example, a cylindrical shape, and focus coils 3a and 3a 'for driving the pickups 6 and 6' in the F direction shown in FIG. Tracking coils 3b and 3b 'wound to drive 6, 6' in the T direction shown in FIG. 1 are provided. Further, lens support members 2a and 2a 'are provided at positions close to the end portions 4a and 4a' of the coil bobbins 4 and 4 ', thereby focusing the laser beam emitted from the laser devices 1 and 1'. The objective lenses 2 and 2 'are supported.

  As shown in FIG. 3, the magnetic field generators 9 and 9 ′ pass a high-frequency signal current through the surfaces 8 a and 8 a ′ of optical glasses 8 and 8 ′ having optical transparency such as quartz. The conductors 7a and 7a 'for generating the are formed as spiral coil patterns 7 and 7'.

  On the back surfaces 8b and 8b 'where the optical glass 8 and 8' are not formed with the coil patterns 7 and 7 ', the end portions 4a and 4a' of the coil bobbins 4 and 4 'are connected to the coil patterns 7 and 7'. The center and the centers of the objective lenses 2 and 2 'are aligned and bonded and fixed. As a result, the laser beam can be focused on the center of the generated magnetic field, so that adjustment of centering at the time of assembling the pickup becomes unnecessary.

  Note that quartz is used as the optical glass 8 and 8 'as an example, and any optically transparent material may be used. In the coil patterns 7 and 7', for example, a printed coil, a thin film coil, or the like may be used. Can be used. 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 was previously proposed by the applicant in the specification and drawings of Japanese Patent Application No. 1-142563. The recording unit 16, the photocurable resin layer 17, and the transparent protective plate 18 are provided, respectively. Both the transparent protective plate 18 and the photocurable resin layer 17 are translucent, and the sum of their thicknesses can be 0.6 mm or less.

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

  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 generator 9 provided on the coil bobbin 4 are supplied with an arrow in FIG. 2 by supplying a focus drive current to the focus coil 3a. The objective lens 2 indicated by F is displaced in the focus direction which is the optical axis direction of the objective lens 2.

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

  At the same time, 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 the conductors 7a and 7a' of the magnetic field generators 9 and 9 '. This magnetic field is subjected to high-speed inversion control according to the recording signal, and is applied to the recording magnetic layers 12 and 12 of the double-sided magneto-optical recording medium 10. Then, a laser beam irradiated from the laser device 1, 1 ′ is applied to the region of the recording magnetic layer 12, 12 where the magnetic field is applied, and the objective lens 2, 2 ′ and optical glass 8, 8 ′ having optical transparency are provided. Information signal can be recorded by raising the temperature of the recording magnetic layers 12 and 12 to the Curie point or higher.

  As is apparent from the above description, the magneto-optical disk recording and / or reproducing apparatus in the present embodiment is an optical system that is a pickup 6, 6 'composed of a laser device 1, 1', objective lens 2, 2 ', etc. By providing a magnetic system, which is a magnetic field generator 9 and 9 'formed by forming the coil patterns 7 and 7' on the optical glass 8 and 8 ', on the same surface side of the double-sided magneto-optical recording medium 10, The distance from the magneto-optical recording medium 10 can be shortened.

  Furthermore, since the thickness of the cover layer comprising the transparent protective plate 18 and the photo-curing resin layer 17 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 is extremely small. Since it can be shortened, recording and reproduction on a double-sided magneto-optical recording medium by the magneto-optical modulation method, which has been considered extremely difficult until now, become possible.

  Further, the coil bobbins 4 and 4 'of the pickups 6 and 6' and the magnetic field generators 9 and 9 'are coupled and fixed by, for example, adhesion, so that the center of the objective lenses 2 and 2' and the magnetic field generators 9 and 9 are fixed. 'And it becomes easy to match the center of the magnetic field, and since the pickups 6, 6' and the magnetic field generators 9, 9 'are interlocked by the focus servo, the intensity of the magnetic field applied to the double-sided magneto-optical recording medium 10 is increased. Can always be constant. In addition, the drive system for the magnetic system that has been necessary until now can be omitted. Further, since the space for arranging the magneto-optical pickup device can be afforded, the degree of freedom in design can be increased.

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

  In addition, it is possible to perform recording or reproduction on the one surface of the double-sided magneto-optical recording medium 10 first, and then perform recording or reproduction on the other surface. This makes it possible to record and reproduce twice the capacity of a single-sided magneto-optical recording medium.

  In the case described above, when recording on one surface, the two magnetic field generators 9 and 9 'are simultaneously used while generating a magnetic field from the magnetic field generator 9 or 9' arranged on the other surface side. Can do. Therefore, a magnetic field can be applied to both sides of the recording magnetic layer 12, and recording can be performed with a larger magnetic field. Further, when recording on one surface, it is also 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, this embodiment uses the same magneto-optical disk recording and / or reproducing apparatus as shown in FIG. 2, and uses the second double-sided magneto-optical recording medium 30 shown in FIG. It is configured so that playback can be performed.

  The second double-sided magneto-optical recording medium 30 was previously proposed by one of the inventors of the present application together with the other inventors in the specification and drawings of Japanese Patent Application No. 1-274734. 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 36 are sequentially laminated on the both surfaces. Both the transparent protective plate 36 and the adhesive layer 35 are translucent, and the sum of their thicknesses can be 0.6 mm or less.

  The high magnetic permeability layer 32 is made of a material having a high magnetic permeability, such as transition metals such as Fe, Co, and Ni, and alloys thereof such as permalloy, sendust, or amorphous magnetic alloy. The perpendicular magnetic field efficiency in the perpendicular direction of the magneto-optical recording medium 30 can be increased.

  In the third embodiment, since the second double-sided magneto-optical recording medium 30 includes the high permeability layer 32, the magnetic flux from the magnetic field generators 9 and 9 'is, for example, as shown by the broken line in FIG. Since the magnetic closed loop is configured, it is preferable that the magnetic flux applied to the double-sided magneto-optical recording medium 30 during the recording can be effectively focused to increase the perpendicular magnetic field efficiency.

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

  As described above, in the second and third embodiments, similarly to the first embodiment, the NA of the objective lenses 2 and 2 ′ is increased, so that higher-density recording and reproduction can be performed, and both surfaces can be used. Since a magneto-optical recording medium can be used, larger capacity and faster recording and reproduction are possible. Accordingly, it is possible to provide a magneto-optical disk recording and / or reproducing apparatus having a large capacity.

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

1 is a cross-sectional view showing a configuration of a magneto-optical disk recording and / or reproducing apparatus according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the magneto-optical disc recording and / or reproducing | regenerating apparatus which is the 2nd Embodiment of this invention. FIG. 5 is a front view of an optical glass having a coil pattern that can be used in the magneto-optical disk recording and / or reproducing apparatus shown in FIGS. It is sectional drawing which shows the structure of the magneto-optical disc recording and / or reproducing | regenerating apparatus which is the 3rd Embodiment of this invention. It is sectional drawing which shows the structure of the conventional magneto-optical disc recording and / or reproducing | regenerating apparatus.

Explanation of symbols

2 Objective lens 2 'Objective lens 10 Magneto-optical recording medium (optical recording medium)
16 Recording part (recording layer)
17, 18 Photo-curing resin layer and transparent protective plate (light transmission layer, translucent cover)
30 Magneto-optical recording medium (optical recording medium)
34 Magneto-optical recording layer (recording layer)
35, 36 Adhesive layer and transparent protective plate (light-transmitting layer, light-transmitting cover)
40 Magneto-optical recording medium (optical recording medium)
41 Translucent substrate (light transmissive layer, translucent cover)
43 Recording magnetic layer (recording layer)
t ₁ cover layer thickness t ₂ cover layer thickness

Claims (2)

An optical recording medium irradiated with a laser beam emitted from a light source for recording and / or reproduction through an objective lens having a numerical aperture of 0.55 to 0.70,
A light transmissive layer comprising a light transmissive substrate having a thickness of 0.44 to 0.6 mm, and provided so that a laser beam emitted from the light source is incident thereon;
A laser beam irradiated through the objective lens is focused through the light transmissive substrate, and a recording layer and a reflective layer sequentially provided from the light transmissive substrate side;
An optical recording medium comprising: a protective cover layer provided on a surface opposite to the light transmission layer with respect to the reflection layer. A laser beam for recording and reproduction is irradiated from a light source, and is formed of a light-transmitting substrate having a thickness of 0.44 to 0.6 mm so that the laser beam emitted from the light source is incident thereon. A light transmissive layer;
A laser beam irradiated through the objective lens is focused through the light transmissive substrate, and a recording layer and a reflective layer sequentially provided from the light transmissive substrate side;
For an optical disc having a protective cover layer provided on the side opposite to the light transmitting layer with respect to the reflective layer,
Using an objective lens having a numerical aperture NA of 0.55 to 0.70, the laser beam emitted from the light source is irradiated so as to be condensed toward the recording layer from the light transmission layer side of the optical disc. An optical disc system characterized by the above.

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