JP2005327328A - Three-dimensional optical information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a realistic information recording method for a 3D optical medium by which smooth data transfer and enhancement of random access properties can be performed by establishing an addressing method of the 3D optical information medium and to provide an information medium and a recording and reproducing device. <P>SOLUTION: In the 3D optical information recording medium in which information can be recorded in plane and thickness directions into one information layer in the medium, the device performing recording and/or reproduction with respect to the information medium has two fluxes of laser beams and has a step for measuring the thickness d of the information layer and the distance between a laser and a reference surface of the medium before performing recording and/or reproduction, and one of the two fluxes of laser beams focuses on the reference surface having address information and the other laser beam accesses the reference surface and a part where a recording or reproduction part is standardized, thereby an information recording method is provided in which accurate addressing onto a three dimensional space is made possible. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an information information medium, an optical information recording method, and an information recording medium device, and more particularly to a high density optical information recording method capable of volume recording in a three-dimensional direction of a recording layer.

  In recent years, not only computer information but also information such as voice, still images, and moving images has been digitized, and the amount of information handled has become extremely large. Along with this, it is necessary to increase the capacity of optical information media for storing such information. With respect to such an optical information medium, CD-R and CD-RW that perform recording / reproduction with a laser beam having a wavelength of about 780 nm have spread worldwide, and recently, recording / reproduction is performed with a laser beam having a wavelength of about 650 nm. Signs of widespread use of recordable DVDs such as DVD-R and DVD-RAM have appeared. More recently, the wavelength of the laser light source has been shortened to near 400 nm, and the numerical aperture (NA) of the objective lens is made 0.6 or more, thereby reducing the diameter of the spot focused on the optical disk surface. A new standard was developed to increase the density, and in March 2003, it was put into practical use as a Blu-ray recorder and released.

By the way, as a method of dramatically increasing the capacity of the optical information medium so far, the laser light wavelength (λ) is shortened, the numerical aperture (NA) of the objective lens is increased, and the laser light of the medium is transmitted. Techniques such as reducing the recording / reproducing laser spot diameter (laser wavelength / NA) by reducing the thickness of the light transmission layer have been performed. However, the shortening of the wavelength of recording / reproducing lasers is approaching the limit, and it is actually the case that the recording material is becoming difficult to form the minimum pits by the technology based on the conventional heat mode recording.
For this reason, attempts have been made to increase the capacity of optical information media by methods other than conventional approaches in various fields. For example, multi-value recording, volume recording using a hologram instead of a flat surface of a disk, and a multilayer information medium having a plurality of information layers on one optical information medium. One of them is, for example, reported in Non-Patent Document 1 at the academic society level.

International Symposium on Optical Memory 2003 Technical Digest PP56-57

Many proposals for 3D recording media have been made so far, and even in the conventional optical disc technology, higher laser power, higher accuracy of pickup actuators, advancement of aberration correction technology, tilt angle of media (tilt). ) Development of a correction mechanism that absorbs margins, practical application of a two-wavelength pickup, and the like, and the practical application of 3D recording that does not have address information in space has become practical. However, there have been no inventions that go beyond the scope of fundamental experiments in proposals related to a large number of 3D recording media, and even in the above-described known examples, the drive stage places the medium on the XYZ stage, and records on the recording material. We have only confirmed playback, discussed realistic margins with respect to actual addressing, and did not consider their solutions.
The present invention has been made to solve such a technical problem, and the object of the present invention is to establish a 3D optical information medium addressing method, which enables smooth data transfer and improved random accessibility. It is an object of the present invention to provide a realistic information recording method, information medium, and recording / reproducing apparatus related to a 3D optical medium.

  For this purpose, in a three-dimensional optical information recording medium that can be recorded in a plane and in the thickness direction on one information layer in the medium, an apparatus for recording and / or reproducing the information medium has two bundles of laser beams. And measuring the thickness d of the recording layer 10 and the distance between the laser and the reference surface of the medium before recording and / or reproduction, and one of the two bundles of laser beams is addressed. An information recording method that enables accurate addressing in a three-dimensional space by focusing on a reference surface having information and accessing the standardized portion of the recording surface or recording or reproducing portion with the other laser beam Can be provided.

In a three-dimensional optical information recording and information recording method capable of recording in one plane on the information layer in the medium to which the present invention is applied, and an information recording method, there are two apparatuses for recording and / or reproducing the information medium. A step of measuring the thickness d of the recording layer 10 and the distance between the laser and the reference plane of the medium before carrying out recording and / or reproduction with a bundle of laser beams, One side focuses on a reference surface having address information, and the other laser beam accesses a standardized portion of the reference surface and a recording or reproducing portion, thereby enabling accurate addressing in a three-dimensional space. An information recording method is provided.

The above apparatus and medium will be described with reference to FIGS. As for the method for producing a 3D recordable information medium, for example, an alumina crystal doped with transition metal molecules such as International Symposium on Optical Memory 2003 Technical Digest PP56-57, a glass matrix by JP2961126, or JP2810542 Recording and reproduction by two-photon molecules as proposed may be used, and taking a publicly known general method does not contradict the gist of the present invention. In FIG. 1, the laser incident surface and the return light from the medium are in the same direction. However, setting the detector on the side opposite to the laser incident as shown in FIG. 7, for example, does not hinder the gist of the present invention. Absent.

FIG. 1 is a schematic diagram of a medium, and FIG. 2 is a diagram illustrating a focal position of a recording pit when the medium is viewed from a cross-sectional direction. As a method of measuring the average thickness d of the recording layer 10 and the distance between the laser and the reference plane of the medium before recording and / or reproduction, the interface between the recording layer 10 and the adjacent layer is optically refractive index. It is desirable to show changes. The apparatus for recording and / or reproducing the information medium has a mechanism for measuring the thickness d of the recording layer 10 and the distance between the laser and the reference plane of the medium by measuring the refractive index change of the interface. Is essential.
Further, the distance obtained by dividing the obtained thickness of the recording layer 10 by (n + m) is calculated (n is the number of divisions in the thickness direction, m is an integer of 0, 1 or 2 less than n), and the address in the thickness direction is calculated. It is desirable to arrange the pits so that (Formula 1) or (Formula 2). As shown in FIG. 2, the film thickness of the recording layer 10 is not always uniform over the entire surface of the medium. Here, the film thickness d of the recording layer 10 is the average value of the recording layer 10, but can be adjusted by increasing or decreasing the numerical value of m as long as it is between the minimum value of the film thickness and the maximum value of the film thickness. Therefore, d is not necessarily an average value of the film thickness of the recording layer 10.
[Reference plane + d / (n + m) × p + e] (Formula 1)
[Reference plane + d × (n + m + p−1) / (n + m) + e] (Formula 2)
(P represents the number of layers from the reference surface at the mark position and is an integer of 1 ≦ p <n. E represents the distance between the reference surface and the pit (center) position of the first layer, and 0 ≦ e ≦ d. / (N + m).)
However, (Expression 1) and (Expression 2) are expressions when the recording position of the medium structure is closer to the laser incident surface than the reference surface, and the recording position of the medium structure is the reference with respect to the laser incident surface. If it is farther than the surface, it is desirable to arrange the pits in the depth direction so that the address in the thickness direction becomes (Expression 3) or (Expression 4).
[Reference plane−d / (n + m) × p + e] (Formula 3)
[Reference plane-d (n + m + p-1) / (n + m) + e] (Formula 4)
In FIG. 2, the arrangement of the marks is drawn on a spiral plane, but in a three-dimensional recording medium, for example, it may be arranged in a spiral shape as disclosed in JP-A-00-228014. The mark arrangement at that time will be described with reference to FIGS. FIG. 3 is a schematic diagram of the medium, and FIG. 4 is a diagram illustrating the focal position of the recording pit when the medium is viewed from the cross-sectional direction. Similar to the above description, the apparatus for recording and / or reproducing the information medium measures the thickness d of the recording layer 10 and the distance between the laser and the reference plane of the medium by measuring the change in the refractive index of the interface. Then, the distance obtained by dividing the obtained thickness of the recording layer 10 by (n + m) is calculated (n is the number of divisions in the thickness direction, and m is an integer of 0, 1 or 2).
Then, the pit position in the depth direction changes by d / (n + m) × (ω / 2π) every time the angle ω advances from the reference position so that the address in the thickness direction becomes (Expression 3) or (Expression 4). It is desirable to arrange the pits in a spiral shape.
[Reference plane + d / (n + m) × {q−1 + (ω / 2π)} + e] (Formula 5)
[Reference plane + d / (n + m) × {n−q− (ω / 2π)} + e] (Formula 6)
However, (Expression 5) and (Expression 6) are expressions when the recording position of the medium structure is closer to the laser incident surface than the reference surface, and the recording position of the medium structure is the reference with respect to the laser incident surface. When it is farther than the surface, it is desirable to arrange the pits in the depth direction so that the address in the thickness direction becomes (Expression 7) or (Expression 8).
[Reference plane−d / (n + m) × {q−1 + (ω / 2π)} + e] (Expression 7)
[Reference plane−d / (n + m) × {n−q− (ω / 2π)} + e] (Expression 8)
(Ω is an angle formed by a recording position, a reference position, and a rotation axis of the medium in a circular medium, and 0 ≦ ω ≦ 2π. The reference position is a position or an angle determined by an arbitrary position and / or format. q represents the number of turns of the spiral at the mark position, and is an integer of 1 ≦ q <n−1, e represents the distance between the reference plane and the pit (center) position of the layer closest to the reference plane, and 0 ≦ e ≦ d / (n + m))
Now, in the description based on the expressions (Expression 1) to (Expression 8) described above, the calculation expression is established after the division number n in the three-dimensional direction is determined in advance. However, in the recording layer 10 in the bulk state, The thickness d of the recording layer 10 is unknown or is expected to be flexible. In this case, what is important is not the division number n but the track pitch l in the thickness direction, and the division number n must be calculated based on l. In this case, the track pitch in the thickness direction including the margin of the recording apparatus is determined. As described above, the apparatus has a step of measuring the thickness d of the recording layer 10, and n can be calculated from d and l according to (Equation 9).
[N = d / l−m] (Equation 9)
(N is the number of divisions in the thickness direction, m is an integer greater than or equal to 0, and l is the track pitch in the thickness direction calculated from the margin in the thickness direction of the recording mark)
By performing recording and reproduction under the conditions in which (Equation 9) is substituted into (Equation 1) to (Equation 8), recording and reproduction are performed at a track pitch in the thickness direction that matches the capability and margin of the recording apparatus. Will be. Further, the calculated values of l, m, and n are stored as recording conditions in the recording area of the medium, and are used as one of the formatting conditions of the medium when played back by the same recording / reproducing apparatus or another reproducing apparatus. It is desirable to make it readable.
Further, in the case of an address having a spiral mark arrangement as shown in (Equation 5) to (Equation 8), the reference plane having the address information is in the zone CLV format, which is a disadvantage of the 3D recording medium. Significant improvement in accessibility can be expected. In addition, a data transfer rate with little interruption is possible.
Next, FIG. 5 shows a method for measuring the thickness d of the recording layer 10 and the distance between the laser and the reference plane of the medium by measuring the change in the refractive index of the interface before performing the above-described recording and / or reproduction. It explains using.
The optical information recording / reproducing apparatus according to the present invention has two bundles of lasers of the optical head 21 and the optical head 22, and one of the two bundles of lasers, the optical head 21, always focuses on the reference plane. The remaining optical head 22 detects a change in refractive index at the interface between the recording layer 10 and the adjacent layer before recording and / or reproduction, and focuses on the interface far from the laser and the interface close to the laser. Thus, the thickness d of the recording layer 10 of the recording layer 10 and the distance between the laser and the reference plane of the medium are measured. Then, the difference from the reference pick 1 is controlled, and the address in the thickness direction of (Expression 1) to (Expression 9) is focused as described above.
At this time, it is desirable that the focus of the optical head 21 and the optical head 22 is the same track with respect to the address information on the reference surface or tracks adjacent to it. This is because accurate tracking of the optical head 22 becomes more difficult as the focus positions of the optical head 21 and the optical head 22 increase.
Further, a method for focusing two optical heads at the same position with respect to the planar direction is proposed in Japanese Patent Laid-Open No. 2001-134961. Based on the contents proposed in the present invention, it will be described in detail with reference to FIG.

The laser 61 focused on the reference plane and the laser 62 focused on the recording / reproducing part have different wavelengths on one information layer 10 in the medium, and the recording / reproducing part has a laser wavelength λ 1. The laser wavelength focused on is λ2. At this time, in order to perform high-density recording, it is desirable that the wavelength of λ1 is short, and the focused laser λ2 on the other reference surface is less dependent on the wavelength, so it is not always necessary to have a short wavelength. Therefore, when λ1 = λ3 and λ2 = λ4, it is desirable that λ1 <λ2.
However, in the case of recording / reproduction using a two-photon molecule as proposed in the above-mentioned known example JP2810542, the laser wavelength λ1 applied to the medium is different from the return light λ3 emitted from the medium. Not. Therefore, it is desirable to tune the filter or dichroic mirror to return light λ3. Furthermore, in the case of a two-photon absorption material, the recording light wavelength and the reproduction light wavelength are different, and therefore it is not always necessary that λ1 <λ2.
Further, as shown in FIG. 7, FIG. 8, or FIG. 9, it is possible to set the detection system on the opposite side of the information medium. In particular, since the return light λ3 generated from the two-photon absorption molecule is emitted in all directions, it is condensed by the dedicated lens 25 as shown in FIG. Those who can collect the signal are the most desirable form.
In addition, as shown in FIG. 8 or FIG. 9, the detection system for the transmitted light λ4 focused on the reference plane can be set on the opposite side of the information medium. FIG. 9 shows a schematic diagram of an example when the reference surface is a surface far from the laser incident surface. However, the laser and the detection system may be in either medium.

So far, an embodiment in which addressing and focusing are performed using two lasers based on a known example has been described. However, one laser is used to branch into two bundles of laser beams by a beam splitter. There is a method of performing focus on the reference plane and 3D recording on the recording layer. This will be described in detail with reference to FIG.
The laser beam emitted from the laser 62 is branched into a main beam and a sub beam by the beam splitter 91, and the main beam is transmitted to the polarizing beam splitter 92 after passing through the half-wave plate, and the sub beam is diffracted by the grating plate. It is sent to the polarization beam splitter 92. Each beam has a mechanism in which a focal position is changed by a lens 26 and a lens 27.
The two bundles of main and sub beams sent to the polarization beam splitter 92 pass through the same objective lens 20, and the sub beam is focused on the reference plane of the recording layer and the main beam is focused on the recording / reproducing mark position. The reflected light is sent to the detector 62, and both the servo signal and the RF signal can be detected. In addition,
When the laser beam focused on the reference surface is L1, and the laser beam focused on the recording or reproducing portion is L2, the laser intensity must be L1 <L2.
Well, what are the proposals that have been made so far? There are many descriptions that indicate that the storage capacity increases as the thickness of the recording layer increases with 100 layers, but it is actually impossible to manufacture such a medium. This is because the production of the medium requires mechanical accuracy, but it is extremely difficult to stably produce a resin substrate having a substrate plane tilt angle of less than 0.1 °, for example. Moreover, when glass with good flatness is used, it is impossible to produce at low cost.
As shown in FIG. 11, when the tilt angle is 0.5 °, the mark recorded at the position farthest from the reference plane is shifted from the original position because the beam is refracted by the change in the refractive index of the recording layer. Will be recorded. As a result, since the recording or reproduction is performed at a position different from the mark to be recorded or reproduced, the limit of the thickness d of the recording layer greatly depends on the track pitch f in the plane direction. The thickness d of the recording layer of an information medium capable of 3D recording that is produced with consideration of mechanical accuracy is limited to a range that satisfies (Equation 12).

f ≦ d × sin (0.1 °) ≈0.02 × d (Equation 12)
If the device tracks only the land portion of the medium or only the groove portion, f in (Equation 12) is (f1 + f2), and if the device tracks only the land portion of the medium or only the groove portion. For example, f in (Equation 12) is (f1 + f2) in FIG. 10. If the apparatus tracks both the land portion and the groove portion of the medium, that is, L & G, f in (Equation 12) is (f1 + f2). / 2.
Therefore, in view of manufacturing technology at present, the thickness d of the recording layer used in the 3D recording medium is limited to 0.3 mm, and the number n of 3D recording is 10 layers, and the DVD size is about 200 GB. Therefore, the most desirable mode of the present invention is a method in which the thickness of the information layer is 0.3 mm or less, and this is used as a unit to stack at least two layers in the medium in multiple layers to achieve both correct addressing and capacity. is there.

It is the schematic of the medium in this invention FIG. 4 is a diagram showing a focal position of a recording pit when the medium in the present invention is viewed from a cross-sectional direction. It is the schematic of the other medium in this invention. It is the figure which showed about the focal position of the recording pit which looked at the other medium in this invention from the cross-sectional direction. FIG. 4 is a diagram for explaining a method of measuring the thickness of a recording layer of a medium and the distance between a laser and a reference surface of the medium in the present invention. It is a figure for demonstrating the method to which two optical heads focus the medium in this invention to the same position with respect to a plane direction. It is a schematic diagram of the recording / reproducing apparatus in this invention. FIG. 6 is a schematic diagram of another recording / reproducing apparatus according to the present invention. FIG. 6 is a schematic diagram of another recording / reproducing apparatus according to the present invention. It is a figure for demonstrating the method of performing the three-dimensional recording in this invention It is a figure for demonstrating the method of performing the three-dimensional recording in this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Recording layer 11 Reference plane 20 of recording layer Objective lens 21 Objective lens for recording / reproduction 22 Address objective lens 23 Lens for λ1 24 Lens for λ2 25 Lens for λ3 30 Reference position in the medium plane 40 Recording mark 60 Semiconductor laser 61 Recording Reproducing laser (λ1)
62 Address laser (λ2)
70 Beam splitter 71 Beam splitter for λ 1 72 Beam splitter for λ 2 80 Detector 81 Detector for λ 3 82 Detector for λ 4 90 Polarizing beam splitter

Claims (9)

In a three-dimensional optical information recording medium capable of recording on one information layer in the medium in the plane and in the thickness direction, the interface between the recording layer and its adjacent layer optically changes the refractive index, and the information medium is recorded. And / or an apparatus for reproducing measures the thickness d of the recording layer and the distance between the laser and the reference plane of the medium before recording and / or reproduction by measuring the change in the refractive index of the interface. The distance obtained by dividing the obtained thickness of the recording layer by (n + m) is calculated as a standard value (n is the number of divisions in the thickness direction, m is an integer of 0 or more), and is calculated based on the obtained standard value. A three-dimensional optical information recording medium characterized in that an obtained numerical value is used as an address in the thickness direction of the medium. In a three-dimensional optical information recording medium capable of recording on one information layer in the medium in a plane and in a thickness direction, the interface between the recording layer and its adjacent layer optically exhibits a refractive index change, and the information medium is A step in which the recording and / or reproducing apparatus measures the thickness d of the recording layer and the distance between the laser and the reference plane of the medium before recording and / or reproducing by measuring a change in refractive index of the interface; The number n of recording marks in the thickness direction of the medium is calculated from the obtained thickness of the recording layer as n = d / lm (n is the number of divisions in the thickness direction, m is 0 or more) , L is the track pitch in the thickness direction calculated from the margin in the thickness direction of the recording mark), and the recording is performed by focusing the numerical value calculated based on the obtained standard value as the address in the thickness direction of the medium. , Calculate as above Numeric information, three-dimensional optical information recording medium, wherein the shim causes store n or l or m on the medium in the recording area. In a three-dimensional optical information recording medium capable of recording on one information layer in the medium in a plane and in a thickness direction, the interface between the recording layer and its adjacent layer optically exhibits a refractive index change, and the information medium is The recording and / or reproducing apparatus measures the thickness d of the recording layer and the distance between the laser and the reference plane of the medium by measuring the change in the refractive index of the interface, and determines the thickness of the obtained recording layer by (n + m ) Calculate the divided distance (n is the number of divisions in the thickness direction, m is an integer of 0 or less of n or less), the address in the thickness direction,
[Reference plane + d / (n + m) × p + e],
Or [reference plane + d × (n + m + p−1) / (n + m) + e],
Or [reference plane−d / (n + m) × p + e],
Or [reference plane-d (n + m + p-1) / (n + m) + e]
(P indicates the number of layers from the reference surface at the mark position, and 0 ≦ p <n. E indicates the distance between the reference surface and the pit (center) position of the first layer, and 0 ≦ e ≦ d / ( n + m))). In a rotating circular three-dimensional optical information recording medium capable of recording in a plane and a thickness direction on one information layer in the medium, the interface between the recording layer and its adjacent layer optically shows a refractive index change, The apparatus for recording and / or reproducing the information medium measures the thickness d of the recording layer and the distance between the laser and the reference plane of the medium by measuring the change in the refractive index of the interface, and determines the obtained recording layer. The distance obtained by dividing the thickness by (n + m) is calculated (n is the number of divisions in the thickness direction, m is an integer of 0, 1, and 2), and the address in the thickness direction is
[Reference plane + d / (n + m) × (q−1 + (ω / 2π)) + e],
Or [reference plane + d / (n + m) × (n−q− (ω / 2π)) + e],
Or [reference plane−d / (n + m) × (q−1 + (ω / 2π)) + e],
Or [reference plane−d / (n + m) × (n−q− (ω / 2π)) + e]
(Ω is an angle formed by a recording position, a reference position, and a rotation axis of the medium in a circular medium, and 0 ≦ ω ≦ 2π. The reference position is a position or an angle determined by an arbitrary position and / or format. q represents the number of turns of the spiral at the mark position, and is an integer of 1 ≦ q <n−1, e represents the distance between the reference plane and the pit (center) position of the layer closest to the reference plane, and 0 ≦ e ≦ d / (n + m).) A three-dimensional optical information recording medium characterized by a spiral shape. In a circular three-dimensional optical information recording medium capable of recording on one information layer in the medium in a plane and a thickness direction, an interface between the recording layer and an adjacent layer optically shows a change in refractive index, and the reference Addressing information is formed on the surface, and the apparatus for recording and / or reproducing the information medium has two bundles of lasers, and measures the refractive index change at the interface before recording and / or reproducing. As a result, the thickness d of the recording layer and the distance between the laser and the reference surface of the medium are measured, and one of the two bundles of laser beams is focused on the reference surface so that the address information formed on the reference surface can be read. The other laser beam is focused on the address to the determined three-dimensional position by calculating the relative position in the depth direction with the focus position of the focused laser beam on the reference surface. Three-dimensional optical information recording medium. In a three-dimensional optical information recording medium capable of recording on one information layer in the medium in the plane and in the thickness direction, the thickness of the recording layer is measured by measuring the refractive index change at the interface before recording and / or reproduction. And an apparatus for recording and / or reproducing the information medium has two bundles of lasers, and focuses on the reference plane of the two bundles of lasers. And the laser focused on the recording or reproducing part has a different wavelength, the laser wavelength focused on the reference surface is λ1, the laser wavelength focused on the recording or reproducing part is λ2, and the light focused on the reference surface is Where λ3 is the wavelength of the returning light, and λ4 is the wavelength of the returning light focused on the recording or reproducing portion, λ1 and λ2 are different wavelengths, and λ3 and λ4. A three-dimensional optical information recording medium having a mechanism for detecting return signals λ3 and λ4 from the medium by dichroic mirrors or filters, and detecting individual signals by filtering. In a three-dimensional optical information recording medium capable of recording in a plane and thickness direction on one information layer in the medium, an apparatus for recording and / or reproducing the information medium includes two bundles of lasers, and the two bundles Among these lasers, one is a laser that focuses on the reference surface and the other is a laser that is focused on the recording or reproducing portion, and these two bundles of laser beams are laser beams output from the same laser, When the laser beam focused on the reference surface is L1, and the laser beam focused on the recording or reproducing part is L2, the laser intensity is branched such that L1 <L2, and the branched laser beam is each optical system. Then, the focus position is mechanically addressed through a three-dimensional optical information recording medium. In a three-dimensional optical information recording medium capable of recording on one information layer in the medium in a plane and in a thickness direction, a laser focused on a reference surface having address information is addressed to both a land and a groove, and the reference surface of the medium The track pitch f of the address information formed in the above satisfies the formula f / 2 ≦ 0.02 × d with respect to the thickness d of the recording layer, and the reference plane having the address information is in the zone CLV format. A characteristic three-dimensional optical information recording medium. In a three-dimensional optical information recording medium capable of recording in the thickness direction, the thickness of at least one information layer in the medium is 0.3 mm or less, and this is used as one unit, and is stacked in multiple layers. A three-dimensional optical information recording medium, wherein n layers are recorded in the depth direction.

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