JP2000251324A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high recording density by making a disk substrate thin and to make the disk substrate compatible with the substrate which is not made thin by sticking a couple of disk substrates together and making the couple of disk substrates thicker for a part where inner-peripheral side recording layers are not formed than a part where the recording layers are formed. SOLUTION: The optical disk 1 is constituted by sticking disk bodies 1a and 1b, having recording layers and protection layers formed on the main surfaces of their substrates via an adhesive layer 65 with the recording layers inside. Here, the disk bodies 1a and 1b in symmetrical structure are so constituted that a hold part 7 which has no inner-peripheral side recording layer formed and which is held on an optical recording. The reproducing device is made thicker than the thickness T2 of a recording part 8 which has a recording layer and severs as a signal recording are. Consequently, high recording density is obtained by reducing the thickness T2 of the recording part 8 and compatibility is obtained by equalizing the thickness T1 of the hold part 7 to the thickness of an existent optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium such as an optical disk having a recording layer such as a phase change recording film, and more particularly to an optical recording medium having a pair of laminated disk substrates.

[0002]

2. Description of the Related Art In the field of information recording, studies on an optical information recording method have been conventionally conducted in various places.
This optical information recording system is capable of non-contact recording and reproduction, achieving a recording density that is at least an order of magnitude higher than that of the magnetic recording system, and can be used in read-only, write-once, and rewritable memory formats. It has a number of advantages such as being able to respond. For this reason, the optical information recording method is considered to be a method capable of realizing an inexpensive large-capacity file for a wide range of uses from industrial use to consumer use.

[0003] Among these, as a read-only recording medium, a digital audio disc on which music information is recorded, an optical video disc on which image information is recorded, and the like are widespread. For example, optical magnetic disks and phase-change optical disks have become widespread. On the other hand, a digital video disk (hereinafter, referred to as D) for recording various information signals such as images, music, and computer data.
It is called VD. ) Is also on the market.

[0004] Depending on the usage, such an optical disc is a ROM (Read Only Memory) disc that performs only reproduction, and a RAM (Random Access Memory) disc that can perform reproduction, additional writing, and rewriting as necessary. There is.

[0005] In a ROM disk, uneven pits are formed on a transparent substrate at a depth of about 1/4 wavelength of the reproduction light, and a reflective film is formed so as to cover the pits. The reproduction is performed by detecting a change in the reflectance due to the interference of the light.

On the other hand, in the case of a RAM type disk, for example, in the case of a phase change type disk provided with a recording layer made of a phase change material, an information signal is recorded and erased by causing a phase change in the recording layer according to recorded information. Reproduction is performed by detecting a change in reflectivity accompanying a phase change.

Incidentally, the above-mentioned DVD has the same diameter as a compact disk (hereinafter, referred to as a CD) 120.
mm, but the recording capacity is increased to 6 to 8 times that of the CD, and the wavelength of the current laser beam is 780 nm.
A shorter laser beam having a wavelength of about 635 nm to 650 nm is used for recording and reproduction. In the case of DVD, the numerical aperture NA of an objective lens used for recording and reproduction is
Is 0.6, and the recording capacity is 4.7 GB.

As shown in FIGS. 13 and 14, a DVD has two disk substrates 100 having a thickness of 0.6 mm.
a and 100b are bonded so that the recording layers 101a and 101b formed on the pair of disk substrates 100 are inside. Thus, in the DVD, the rigidity of the disk substrate 100 is ensured and the warpage of the disk substrate 100 is canceled.

[0009]

On the other hand, in the above-mentioned optical disk, by reducing the wavelength of a laser beam to be irradiated or by increasing the numerical aperture of an objective lens used for recording / reproducing, a narrow track is formed. Is realized,
Thereby, high recording density is achieved.

However, with an increase in the numerical aperture of the objective lens, an allowable amount of aberration caused by an angle (tilt angle) at which the disk surface deviates from the optical axis of the optical pickup, that is, a so-called skew margin, is insufficient. I will.
This is because the aberration generated due to the tilt angle increases as the thickness of the portion through which the reproduction light is transmitted increases.

For this reason, for example, in a DVD, a thickness of 1.
The skew margin is secured by reducing the thickness of the disk substrate to 0.6 mm for a CD of 2 mm.

However, in order to achieve a higher recording density, it is necessary to further reduce the thickness of the disk substrate to secure a skew margin in accordance with an increase in the numerical aperture of the objective lens.

However, when the thickness of the disk substrate is reduced, the thickness differs from that of the conventional optical disk, so that recording and reproduction can be performed using the optical recording and reproducing apparatus used for the conventional optical disk. Therefore, there arises a problem that compatibility with a conventional optical disc cannot be obtained.

Accordingly, the present invention has been proposed in view of such conventional circumstances, and provides an optical recording medium which enables high recording density and has compatibility with the conventional optical recording medium. The purpose is to do.

[0015]

An optical recording medium according to the present invention that achieves this object has a recording layer formed on at least one principal surface of at least one of a pair of disk substrates. When the thickness of the portion on which the recording layer is not formed on the inner peripheral side is defined as t ₁ and the thickness of the portion on which the recording layer is formed is defined as t ₂ , , T ₁ > t ₂ .

In the optical recording medium according to the present invention configured as described above, the thickness t _{1 of the} portion where the recording layer is not formed on the inner peripheral side is larger than the thickness t _{2 of the} portion where the recording layer is formed. It is set thick. Therefore, for example, if the thickness t _{1 of the} portion on the inner peripheral side where the recording layer is not formed is the same thickness as the conventional optical recording medium, compatibility with the conventional optical recording medium can be obtained.
On the other hand, by making the thickness t _{2 of the} portion where the recording layer is formed thinner than before, the horizontal plane of the optical recording medium deviates from the vertical with respect to the optical axis of the optical pickup with the increase in the numerical aperture. The influence of the generated aberration is suppressed.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

An optical recording medium to which the present invention is applied is an optical disk 1 formed in a disk shape and having a center hole 2 in the center, as shown in FIGS. As shown schematically in FIG. 3, this optical disc 1 has a disc body 1 in which a recording layer 4a and a protective layer 5a are formed on one main surface of a substrate 3a.
a and a disk 1b having a recording layer 4b and a protective layer 5b formed on one main surface of a substrate 3b, respectively.
The adhesive layers 6 are attached to each other so that a and 4b are inside.

In such an optical disc 1, when it is held in the optical recording / reproducing apparatus, the optical pickup irradiates a laser beam to record and / or reproduce the information signal.

Here, the allowable amount of aberration caused by the angle (tilt angle) of the disk surface deviating from the perpendicular to the optical axis of the optical pickup, that is, the so-called skew margin, is represented by M, the skew margin, the laser beam to be irradiated. The wavelength is λ and the numerical aperture of the objective lens for condensing the laser light is N
A, where the thickness of the optical disk is T, the relationship of M NA ³ / T is established.

For this reason, for example, when the thickness T of the optical disk is set to 0.3 mm, which is half the conventional value, with respect to the DVD, the skew margin M can be doubled.

Then, the thickness T of the optical disc is set to 0.3 mm.
In order to secure a skew of 0.4 ° equivalent to that of a conventional DVD, it is possible to increase the numerical aperture NA of the objective lens to 0.76.

Therefore, when the thickness T of the optical disk is set to 0.3 mm, which is smaller than the conventional one, the numerical aperture NA of the objective lens can be increased to 0.76. Is 650 nm,
The track pitch, the recording linear density, and the shortest pit length are: track pitch: 0.74 × (0.6 / 0.76) =
0.58 μm Assuming that the signal modulation method is EFM, recording linear density: 0.27 × (0.6 / 0.76) = 0.2
1 μm / bit Minimum pit length: 0.40 × (0.6 / 0.76) = 0.
31 μm.

The recording capacity in the case of the same size as the conventional DVD is as follows: Recording capacity: 4.7 × (0.6 / 0.76) ² = 7.5 G
B, and high recording density can be achieved.

Further, when the wavelength λ of the irradiated laser light is 400 nm, the above-mentioned wavelength λ is 650 n
m, the track pitch, the recording linear density,
The shortest pit length is: track pitch: 0.58 × (400/650) = 0.
Recording linear density: 0.21 × (400/650) = 0.13, where EFM is a signal modulation method of 36 μm.
μm / bit Minimum pit length: 0.31 × (400/650) = 0.1
9 μm.

The recording capacity in the case of the same size as that of a conventional DVD is as follows: recording capacity: 7.5 × (400/650) ² = 20 GB, and it is possible to further increase the recording density.

However, for example, if the optical disc is
In the case of D, if the thickness T of the optical disc is reduced, the recording and / or reproduction of information signals cannot be performed using the optical recording / reproducing apparatus used for the conventional DVD, and the conventional DVD cannot be used. I can't get compatibility.

Therefore, in the optical disk 1, FIGS.
As shown in the figure, the disk bodies 1a and 1b having a symmetrical structure
The thickness t ₁ of the holding portion 7 held in the optical recording / reproducing apparatus in which the inner recording layers 4a and 4b are not formed is the thickness of the recording portion 8 which becomes the signal recording area where the recording layers 4a and 4b are formed. configured to be thicker than the t _2.

In the optical disk 1, the disk bodies 1a, 1b
, For example, the thickness t ₁ of the holding portion 7 is set to 0.1.
6 mm, and the thickness t ₂ of the recording section 8 is 0.3 mm each.
And In the optical disk 1, the diameter of the disk is 1
20 mm or less, and the diameter of the holding portion 7 is 33 mm or less. In this case, in the optical disk 1, the disk 1
The thickness of the holding portion 7 after a and 1b are laminated is 1.2
mm, and the thickness of the recording unit 8 is 0.6 mm.

Therefore, in the optical disc 1, the recording unit 8
Is thinner than that of a conventional DVD, the influence of aberrations generated when the horizontal plane of the optical disc 1 deviates from the vertical with respect to the optical axis of the optical pickup with a higher numerical aperture can be suppressed. High recording density can be achieved. Then, in the optical disc 1, since the thickness of the holding section 7 is the same as that of the conventional DVD, the recording and / or reproduction of the information signal is performed using the optical recording / reproducing apparatus used for the conventional DVD. Therefore, compatibility with the conventional DVD can be obtained.

In the optical disc 1, when the thickness error of the recording portion is ΔT, the wavelength of the laser beam to be irradiated is λ, and the numerical aperture of the objective lens used at the time of recording and / or reproduction is NA, ΔT ≦ | It is preferable that the following relationship be satisfied: 5.96λ / (NA) ⁴ |

Thus, it is possible to suppress the influence of aberration caused by an angle (tilt angle) at which the disk surface deviates from the optical axis of the optical pickup due to an increase in numerical aperture.

In the optical disc 1, the recording layers 4a, 4a
b is a concave / convex pit formed on the substrates 3a and 3b, each having a depth of about 1/4 wavelength of the reproduction light, and a reflective film made of aluminum, gold, silver, or the like formed so as to cover the pit. With this configuration, a high-density ROM disk having a double-sided structure in which only reproduction is performed can be obtained.

In the optical disc 1, the recording layers 4a, 4a
b is a recording film such as a phase change recording film, an organic dye film, a magneto-optical recording film, etc.
A high-density RAM type disk having a double-sided structure can be rewritten as needed.

Further, in the optical disk 1, the disk 1
A high-density optical disc having a two-layer structure capable of irradiating laser light from one side by making one of the recording layers a and 1b translucent to the irradiated laser light. Can be.

Further, in the optical disk 1, by forming a recording layer on only one of the disk bodies 1a and 1b, a high-density optical disk having a one-sided dummy structure can be obtained.

Furthermore, the optical disk 1 may be a high-density optical disk in which one disk 1a is the ROM disk and the other disk 1b is the RAM disk.

In the optical recording medium to which the present invention is applied, like the optical disk 1 described above, the recording layers 4a, 4b are provided on the adhesive layer 6 side of the pair of disk bodies 1a, 1b, respectively.
However, the present invention is not limited to the configuration having

For example, as shown in FIG. 4A, the pair of discs 20a and 20b may have recording layers 22a and 22b on the opposite sides of the adhesive layer 21, respectively. As shown in FIG.
May have a recording layer 22a on the side of the adhesive layer 21 and a recording layer 22b on the side of the other disk body 20b opposite to the adhesive layer 21.

As shown in FIG. 4C, the recording layer 22a may be formed only on one disk body 20a, and the recording layer may be formed only on one disk substrate. As shown in d), the disk bodies 20a, 20
The recording layers 22a and 22b may be formed on both main surfaces of the disk substrate b, respectively, and the recording layers may be provided on both main surfaces of at least one disk substrate.

Next, an optical disk 30 shown in FIG. 5 will be described as an embodiment of the present invention. The optical disk 30 includes a first disk body 31 and a second disk body 32
Are bonded together with an adhesive layer 33 interposed therebetween.

As shown in FIG. 6, the first disk body 31 is made of a first light-transmitting material such as polycarbonate.
And a first recording layer 35 formed by forming uneven pits on the first substrate 34 and forming a semi-transparent film such as a dielectric film on the surface on which the uneven pits are formed. When,
A first protective layer 36 formed on the first recording layer 35 and made of an ultraviolet curable resin or the like.

The first disk body 31 is irradiated with laser light having a wavelength λ of 400 mm, so-called blue laser light, corresponding to the increase in recording density. In the first disk body 31, the track pitch is 0.36 μm, and the numerical aperture of the objective lens used for recording and reproduction is 0.80.

The first disk body 31 is made semi-transparent to laser light having a wavelength λ of 650 mm.
It is configured to be able to transmit this laser light.

The second disk body 32 has a light-transmitting second substrate 37 made of polycarbonate or the like, and a surface on which the uneven pits are formed on the second substrate 37 and on which the uneven pits are formed. A second recording layer 38 on which a high reflection film made of Al or the like is formed, and a second protective layer 39 formed on the second recording layer 38 and made of an ultraviolet curable resin or the like. Is done.

The second disk body 32 has a wavelength λ of 65
A laser beam used for a conventional DVD having a thickness of 0 mm is irradiated. In the second disk body 32, the track pitch is 0.58 μm, and the numerical aperture of the objective lens used for recording and reproduction is 0.60.

In the optical disc 30, the first recording layer 35 of the first disc body 31 is formed on the adhesive layer 33 side, and the second recording layer 38 of the second disc body 32 is opposite to the adhesive layer 33. It has a two-layer structure formed on the side. In the optical disc 30, the first disc body 31 is a so-called HD-DVD in which an information signal corresponding to high recording density is reproduced, and the second disc body 32 is an information signal similar to the conventional one. Playback is done,
It is a so-called conventional DVD.

In the optical disc 30, the first disc body 31 and the second disc body 32 have a symmetrical structure, and the first recording layer 35 and the second recording layer 38 on the inner peripheral side are formed. Holding unit 40 held in an optical recording / reproducing device that is not
Of the first recording layer 35 are set to 0.6 mm, respectively.
The thickness of each of the recording portions 41 serving as signal recording regions where the second recording layer 38 and the second recording layer 38 are formed is 0.3 mm. Therefore, in the optical disc 30, when the first disc body 31 and the second disc body 32 are bonded to each other, the holding portion 4
0 is 1.2 mm, and the thickness of the recording unit 41 is 0.2 mm.
6 mm.

In the optical disk 30 configured as described above, the first recording layer 35 and the second disk body 32 of the first disk body 31 are arranged from the first substrate 34 side of the first disk body 31. The second recording layer 38 is irradiated with a laser beam.

For the first disk body 31, the wavelength λ
Is irradiated with blue laser light having a diameter of 400 mm, and an information signal corresponding to high recording density is reproduced. Specifically, the information signal is reproduced by irradiating the first recording layer 35 with blue laser light from the optical pickup while rotating the optical disc 30, and detecting a change in the intensity of the reflected light.

Here, in the first disk body 31, the thickness from the surface of the first substrate 34 on which the blue laser light is incident to the first recording layer 35 is half that of the conventional DVD, ie, 0%. 0.3 mm. For this reason, in the first disk body 31, even when the information signal corresponding to the higher recording density is reproduced, the horizontal plane of the optical disk 30 with respect to the optical axis of the optical pickup accompanying the higher numerical aperture. Can be suppressed from being affected by aberrations caused by deviation from the vertical. In other words, in the optical disc 30, a skew margin corresponding to a higher numerical aperture can be secured.

On the other hand, for the second disk body 32,
A laser beam having a wavelength λ of 650 mm is irradiated, and an information signal corresponding to a conventional DVD is reproduced. Specifically, by irradiating the second recording layer 38 with laser light from an optical pickup while rotating the optical disc 30, and detecting a change in the intensity of the reflected light,
Reproduce the information signal. At this time, on the optical disc 30,
A laser beam having a wavelength λ of 650 mm is transmitted through the first disk body 31 and is irradiated on the second recording layer 38.

Here, in the second disk body 32, the second substrate 32 is moved from the surface on which the laser light is
Is the same as the conventional DVD, ie, 0.6
mm. For this reason, the second disk body 32 can reproduce the information signal corresponding to the conventional DVD.

In the optical disk 30, the holding section 4
0 is 1.2 mm, which is the same thickness as a conventional DVD. Therefore, the information signal can be reproduced using the optical recording / reproducing apparatus used for the conventional DVD.

As described above, in the optical disk 30, the thickness of the holding section 40 is set to be larger than the thickness of the recording section 41. In the optical disc 30, by setting the thickness of the holding section 40 to 1.2 mm, which is the same as that of the conventional DVD, the information signal can be reproduced using the optical recording / reproducing apparatus used for the conventional DVD. . On the other hand, in the optical disc 30, the thickness of the recording unit 41 is set to 0.3
By setting m, it is possible to suppress the influence of aberration generated when the horizontal plane of the optical disc 30 is shifted from the vertical with respect to the optical axis of the optical pickup due to the increase in the numerical aperture. Therefore, it is possible to obtain an optical disk with a high recording density compatible with the conventional DVD.

Next, a method for manufacturing the optical disk 30 will be described.

First, an injection molding apparatus 60 as shown in FIG.
1st substrate 3 which constitutes 1st disk body 31 using
4 is produced.

This injection molding device 60 is used to
And the other main surface side of the first substrate 34 which is disposed so as to face the fixed die 61 and which can be freely moved toward and away from the fixed die 61. And a peripheral mold 63 that is incorporated into the fixed mold 61 and forms the outer peripheral surface of the first substrate 34.

As shown in FIG. 8, the fixed mold 61, the movable mold 62, and the outer mold 63 form a cavity 64 for molding the first substrate 34 in the clamped state.

A stamper 65 is attached to the fixed mold 61. The stamper 65 has a track pitch of 0.36 μm and a recording linear density of 0.1 by a mastering process.
An uneven pattern having a thickness of 3 μm / bit is formed, and an uneven pit is formed on the first substrate 34 to be injection-molded.

The stamper 65 has a track pitch of 0.36 by a mastering step when a RAM type disc for recording and / or reproducing information signals is manufactured.
An uneven pattern corresponding to the groove and the land is formed so as to be μm.

The fixed substrate 61 has the first substrate 34
A sprue bush 67 having a nozzle 66 for injecting and filling a resin material such as polycarbonate supplied from an injection molding machine into the cavity 65 is provided at the center of the cavity 65 for molding the resin.

The movable mold 62 has a concave portion 62a corresponding to the holding portion 40 of the first disk body 31 at a substantially central portion, and the holding portion 40 of the first disk body 31 is formed by injection molding.
And the recording section 41 are formed to have a desired thickness.

The injection molding apparatus 60 constructed as described above
In this case, when the movable mold 62 moves closer to the fixed mold 61 to be in the mold clamping state, a cavity 64 whose periphery is closed is formed. Then, in this cavity, the nozzle 66 of the sprue bush 67 is
Is injected and filled at a high pressure. Then, in the injection molding device 60, the resin material to be molded is cooled and solidified.

In the injection molding apparatus 60, after the resin material in the cavity 64 is cooled and solidified, the movable mold 62 is separated from the fixed mold 61 by a hydraulic mechanism, thereby performing a mold opening operation. Molded first substrate 34
Is released.

As shown in FIG. 9, the first substrate 34 manufactured as described above has uneven pits formed on the main surface on the side to be bonded to the second disk body 32. Further, a convex portion corresponding to the holding portion 40 and the recording portion 41 is formed on the main surface opposite to the side bonded to the second disk body 32, and the thickness of the holding portion 40 of the first disk body 31 is changed. Is formed thicker than the thickness of the recording section 41.

Next, as shown in FIG.
A semi-transparent film such as a dielectric film is formed on the concave and convex pits formed on the main surface of the substrate 34 by sputtering or the like.
Is formed.

Next, a first protective layer 36 made of an ultraviolet curable resin or the like is formed on the first recording layer 35, whereby the first disk 31 is manufactured.

Next, an injection molding apparatus 7 as shown in FIG.
The second substrate 37 constituting the second disk body 32 is manufactured by using 0.

The injection molding apparatus 70 is provided with a second substrate 37
And the other main surface side of the second substrate 37 which is arranged to face the fixed metal mold 71 and is freely movable toward and away from the fixed metal mold 71. And a peripheral mold 73 forming the outer peripheral surface of the second substrate 37 incorporated in the fixed mold.

As shown in FIG. 11, the fixed mold 71, the movable mold 72 and the outer peripheral mold 73 constitute a cavity 74 for molding the second substrate 37 in the clamped state.

A stamper 75 is attached to the fixed mold 71. The stamper 75 has a track pitch of 0.58 μm and a recording linear density of 0.2 by a mastering process.
An uneven pattern of 1 μm / bit is formed, and an uneven pit is formed on the second substrate 37 by injection molding.

The stamper 75 has a track pitch of 0.58 due to the mastering step when a RAM type disc for recording and / or reproducing information signals is manufactured.
An uneven pattern corresponding to the groove and the land is formed so as to be μm.

The fixed die 71 is provided with the second substrate 37.
A sprue bush 77 having a nozzle 76 for injecting and filling the cavity 74 with a resin material such as polycarbonate supplied from an injection molding machine is provided at the center of the cavity 74 for molding the resin.

The fixed mold 71 has a concave portion 71a at a substantially central portion corresponding to the holding portion 40 of the second disk body 32. The holding portion 40 and the recording section of the second disk body 32 are formed by injection molding. 41 is formed to have a desired thickness.

The injection molding apparatus 70 constructed as described above
Then, since the second substrate 37 is injection-molded in the same manner as in the above-described injection molding apparatus 60, the description of the method of manufacturing the second substrate 37 will be omitted below.

As shown in FIG. 12, concave and convex pits are formed on the second substrate 37 manufactured as described above on the main surface opposite to the side where the first disk body 31 is bonded. . Further, a convex portion corresponding to the holding portion 40 and the recording portion 41 is formed on the main surface opposite to the side bonded to the first disk body 31, and the thickness of the holding portion 40 of the second disk body 32 is increased. Is formed thicker than the thickness of the recording section 41.

Next, as shown in FIG.
A high-reflection film made of Al or the like is formed on the concave and convex pits formed on the main surface of the substrate 37 by sputtering or the like to form a second recording layer 38.

Next, a second protective layer 39 made of an ultraviolet curable resin or the like is formed on the second recording layer 38, whereby the second disk 32 is manufactured.

Next, the first protective layer 36 of the first disk 31 and the second protective layer 39 of the second disk 32 are bonded together with an adhesive. Thereby, FIGS. 5 and 6
As shown in (1), an optical disc 30 in which a first disc body 31 and a second disc body 32 are bonded via an adhesive layer 33 is produced.

The first substrate 34 and the second substrate 37
When manufacturing a, a method other than injection molding may be used, for example, by using a so-called thermal transfer method of transferring a concave and convex pattern by pressing a master for recording medium production onto a resin material or the like softened by heating. Is also good. Also, after applying a photopolymer or the like on a master for recording medium production,
Irradiate ultraviolet light to cure the photopolymer, and then
A so-called 2P method may be used in which a substrate for a recording medium on which a concavo-convex pattern is transferred is formed by peeling off the photopolymer.

The present invention relates to the optical disk 30 described above.
However, the present invention is not limited to such an optical recording medium having compatibility with a DVD, but can be applied to an optical recording medium in which the thickness of a disk is reduced with an increase in numerical aperture. In this case, as in the present invention, the thickness of the portion on the inner peripheral side where the recording layer is not formed is set to be larger than the thickness of the portion where the recording layer is formed. Then, for example, if the thickness of the portion on the inner peripheral side where the recording layer is not formed is the same thickness as the conventional optical recording medium,
Compatibility with conventional optical recording media can be obtained. On the other hand, by making the thickness t _{2 of the} portion where the recording layer is formed thinner than before, the horizontal plane of the optical recording medium deviates from the vertical with respect to the optical axis of the optical pickup with the increase in the numerical aperture. The effect of the generated aberration can be suppressed.

[0083]

As described above in detail, according to the optical recording medium of the present invention, the thickness of the portion on the inner peripheral side where the recording layer is not formed is larger than the thickness of the portion where the recording layer is formed. It is set thick. Therefore, for example, if the thickness of the portion on the inner peripheral side where the recording layer is not formed is the same as that of the conventional optical recording medium, compatibility with the conventional optical recording medium can be obtained. On the other hand, by reducing the thickness of the portion where the recording layer is formed, the effect of aberrations caused by the deviation of the horizontal plane of the optical recording medium from the perpendicular to the optical axis of the optical pickup due to the increase in numerical aperture And an optical recording medium with a high recording density can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one configuration example of an optical recording medium to which the present invention is applied.

FIG. 2 is a schematic sectional view showing a configuration example of the optical recording medium.

FIG. 3 is a cross-sectional view of a principal part schematically showing the configuration of the optical recording medium.

FIG. 4 is a schematic sectional view showing another configuration example of the optical recording medium.

FIG. 5 is a schematic sectional view of an optical disc shown as an embodiment of the present invention.

FIG. 6 is a cross-sectional view of a principal part schematically showing a configuration of the optical disc.

FIG. 7 is a view for explaining a method for manufacturing the optical disc, and is a view for explaining a method for manufacturing the first substrate.

FIG. 8 is a view for explaining a method of manufacturing the optical disc, and is a view showing a state in which a cavity for molding the first substrate is formed by clamping.

FIG. 9 is a diagram for explaining the method of manufacturing the optical disc, and is a schematic cross-sectional view illustrating the manufactured first substrate.

FIG. 10 is a diagram for explaining a method for manufacturing the optical disc, and is a diagram for explaining a method for manufacturing a second substrate.

FIG. 11 is a view for explaining the method of manufacturing the optical disc, and is a view showing a state in which a cavity for molding the second substrate is formed by clamping the mold.

FIG. 12 is a diagram for explaining a method of manufacturing the optical disc, and is a schematic cross-sectional view illustrating a manufactured second substrate.

FIG. 13 is a perspective view showing a configuration of a conventional DVD.

FIG. 14 is a schematic sectional view showing the configuration of the DVD.

[Explanation of symbols]

1 optical disk, 1a, 1b disk body, 3a, 3b
Substrate, 4a, 4b recording layer, 30 optical disk, 31
1st disk body, 32 2nd disk body, 34 first substrate, 35 first recording layer, 37 second substrate, 3
8 Second recording layer

Claims (9)

[Claims] 1. A recording layer is formed on at least one principal surface of at least one disk substrate of a pair of disk substrates, and the pair of disk substrates is adhered to each other. the thickness of the recording layer is not formed part of the peripheral side is t _1, when the thickness of the portion where the recording layer is formed and t _2, the optical recording, which is a t _1> t ₂ Medium. 2. The pair of disk substrates are respectively t
_2. The optical recording medium according to claim 1, wherein ₁ = 0.6 mm. 3. The pair of disk substrates are respectively t
_2. The optical recording medium according to claim 1, wherein ₁ = 0.6 mm and t2 = 0.3 mm. 4. The track pitch is not less than 0.36 μm,
2. The optical recording medium according to claim 1, wherein the thickness is 0.58 [mu] m or less. 5. The laser beam to be irradiated has a wavelength of 400
2. The optical recording medium according to claim 1, wherein the optical recording medium has a thickness of not less than nm and not more than 650 nm. 6. The optical recording medium according to claim 1, wherein the numerical aperture of the objective lens used for recording and / or reproduction is 0.60 or more and 0.80 or less. 6. The pair of disk substrates, wherein ΔT is a thickness error of a portion where the recording layer is formed, λ is a wavelength of an irradiated laser beam, and a numerical aperture of an objective lens used in recording and / or reproducing. 2. The optical recording medium according to claim 1, wherein the relationship of ΔT ≦ | 5.96λ / (NA) ⁴ | 7. The optical recording medium according to claim 1, wherein a recording layer is formed on one main surface of each of the pair of disk substrates. 8. The optical recording medium according to claim 1, wherein a recording layer is formed on each of the pair of disk substrates on both main surfaces of at least one disk substrate. 9. The optical recording medium according to claim 1, wherein each of the pair of disk substrates is injection-molded.