JP2005044513A - Information recording medium, information reproducing method, and information recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium, an information reproducing method, and an information recording method thereof, for the purpose of attaining high recording density. <P>SOLUTION: The information recording medium has: a first multilayer medium comprising a first substrate and a plurality of recording layers stacked on the first substrate for recording information; and a second multilayer medium comprising a second substrate and a plurality of recording layers stacked on the second substrate for recording information. The first multilayer medium and the second multilayer medium are laminated with the faces of the recording layer sides inside. The first and the second substrates are made of glass or plastic. The information in the information recording medium is reproduced and the information is recorded in the information recording medium by irradiating the medium with light from each of the faces on which the first and the second substrates are prepared. Recording or reproducing information on or from each of both faces of the substrates of disk becomes possible. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical information recording apparatus and an information reproducing apparatus such as an optical disc, an optical tape, and an optical card, and more particularly to an information recording apparatus and an information reproducing apparatus aiming at high recording density.

  A method for increasing the recording density of an optical information recording / reproducing apparatus has heretofore been to improve the recording surface density on a two-dimensional recording medium plane. However, the size of an information recording medium such as a disk is limited due to the miniaturization of the apparatus, and there is a limit in increasing the density on a plane.

JP 59-127237

JP 60-202545 A JP 60-202554 A JP 63-231738 A Japanese Patent Laid-Open No. 1-19535

  Therefore, a three-dimensional recording / reproducing method including the depth direction is essential as a method for achieving higher density. In the three-dimensional recording / reproduction, there is a means for recording / reproducing data by providing a disk having a multilayer film structure and narrowing a light spot in each layer as shown in a publicly known example "Japanese Patent Laid-Open No. 59-127237". However, in this known example, there is no description of a specific disk structure, definition of optical constants, and a method for setting recording conditions, and it is difficult to perform reliable recording. Further, regarding the data reading method, the configuration of the light receiving optical system is unclear, and it is difficult to perform reliable reproduction.

  On the other hand, known examples "Japanese Patent Laid-Open No. 60-202545" and "Japanese Patent Laid-Open No. 60-202554" describe a disc film thickness and a focusing method for forming a diffraction-limited light spot in each layer. However, there is no clear provision for the former. The latter describes the principle of focusing, but does not describe an access method for actually focusing on the target layer. Further, as a method for producing a disk, a known guide groove for tracking is not possible in the known example, and a method of laser exposure for each layer is shown, but this method has no productivity.

  An object of the present invention is to study a light spot narrowing optical system, a disk structure, and a light detection optical system that can be stably recorded and reproduced in a recording process and a reproducing process, and further, encoding that suppresses crosstalk between adjacent layers, which is a problem in particular. This is to examine a method, a crosstalk cancellation method, a three-dimensional data format, a disk creation method associated therewith, and a three-dimensional access method.

To solve the above problem,
Recording film layer whose optical properties change locally due to local light irradiation, antireflection, multiple reflection, light absorption, transfer of optical local change of recording film layer, heat insulation , Heat absorption, heat generation, or a layer for the purpose of reinforcement, or an intermediate layer film, which is a superposition of layers, has a disk in which multiple layers are stacked on an optically transparent substrate. Recording corresponding to the modulated data “1” and “0” is performed by changing the local optical properties of each layer two-dimensionally (independently). Further, in the three-dimensional recording / reproducing apparatus for detecting the change in the local optical property as a change in the reflected light amount (or transmitted light amount) by light spot irradiation on each layer and reproducing the data,
1. In the disk structure, the refractive index of an optically transparent substrate is NB, and the thickness is d0. Further, the intermediate layer and the recording film layer are divided as one layer, and 1 to N layers are assigned in order from the upper layer. The distance between each layer is indicated by the distance dk between the adjacent recording film layers k-th and (k−1) -th film thickness. The film thicknesses of an arbitrary kth recording layer and intermediate layer are dFk and dMk, and the real part of the refractive index is NFk and NMk, respectively. Further, the period b [μm] of local optical property change on the plane of each layer is used. The aperture optical system uses, for example, a semiconductor laser having a wavelength of λ [μm] as a light source, is converted into parallel light by a collimator lens, and is incident on the aperture lens via a deflection beam splitter. Here, the numerical aperture of the aperture lens is NAF, the effective radius is a [mm], and the focal length is fF (≈a / NAF). The reflected light from the disk passes through the aperture lens and is guided to the light receiving image lens by the beam splitter. A change in the amount of reflected light is converted into an electrical signal by a photodetector located near the focal point of the image lens. The numerical aperture of the image lens is NAI, and the focal length is fI (≈a / NAI). When the diameter of the light receiving surface of the photodetector is D, the reflected light from the target layer when the kth layer is the target layer and focused is imaged at the focal position of the image lens. The spot diameter Uk ′ of
Uk ′ = λ / NAI = λ × (fI / a)
m: Lateral magnification of light receiving optical system Next, the spot diameter U (k ± 1) ′ on the focal plane from the adjacent layer (k ± 1) th layer separated from the kth target layer by the interlayer distance d is
U (k ± 1) ′ ≈a × m ² d / fI
= NAI · m ² d
From the above formula, the diameter D of the photodetector is
D = Uk ′ = λ / NAI,
The amount of reflected light from the other layers detected is the transmittance δjk between the target k layer and the other j layer, and the reflectance ratio αjk, and the amount of reflected light received from the n layer at the photodetector is In. Then

(Equation 17) ≈I (k−1) / Ik
= Δ ² (k−1), k × α (k−1), k × (D / U (k−1) ′) ² (Equation 17.5)
The disc structure and optical system are set so that the above equation holds.
2. Further, the minimum value bmin of the two-dimensional period b is set to (λ / NAF), and the maximum value bmax of the two-dimensional period b is made smaller than (d × NAF).

    Further, in the light receiving optical system shown in FIG. 1, the respective optical characteristic functions (OTF) H0 (S), H1 (S) in the target layer surface where recording / reproduction is performed and in the adjacent layer surface separated by the optical distance d [μm]. ) Are shown in FIG. 4 by a straight line 13 and a straight line 14, respectively.

Where S: normalized spatial frequency Here, the optical characteristic function H1 (S) when defocus occurs at the value of the interlayer distance d, the maximum of the period b from S where H1 (S) = 0. Define the repetition bmax. In this way, by defining the relationship between the local optical property change period b on the layer surface, the disc structure, and the light receiving optical system, the interlayer crosstalk component can be determined from the local optical property change period b. Also make it longer.
3. Further, a code is used in which the total area of the local optical change (mark) region included in the spot diameter (2d × NAF) region in the adjacent layer is always a constant value.
4). further,
dk = dF (k−1) + dMk + dFk
≒ dMk (Equation 1)
In addition, the effective refractive index NMk of the intermediate layer is assumed to be the same refractive index NB as that of the substrate. The thickness d up to the Nth layer of the multi-layer disc is

For the spherical aberration amount W40, W40 = | (1 / (8 × NB)) × ((1 / NB ² ) −1) × NAF ⁴ × Δd | (Equation 3)

The intermediate layer thickness dk and the total number N are combined so that W40 ≦ λ / 4. The absolute value on the right side of W40 is normally negative (when NB ≧ 1).
5. Further, the optical constants of the kth recording film layer 1 are a transmittance Tk, a reflectance Rk, and an absorptance Ak. Here, the relationship Tk + Rk + Ak = 1 holds. The optical constant when the local optical property is changed by recording is represented by a dash symbol “′” hereinafter. Generally, an energy threshold value Eth [nJ] always exists in order to cause a thermal structure change in thermal recording. A light spot narrowed down to the diffraction limit on the recording target layer is scanned over the disk at a linear velocity V [m / s].

In order to locally generate a thermal structure change corresponding to the binarized signal after modulation, the light intensity P (recording power) [mW] incident on the disk, where the linear velocity V and the irradiation time t are given In this case, the light intensity density threshold Ith [mW / μm ² ] for the recording film of each layer is set.

Because the spot diameter is λ / NAF for the light intensity density Ik in the k layer when the k layer is focused,
Sk: 1 / e ² spot area when focused on the k layer Sk = π (0.5 × λ / NAF) ²
The light intensity Pk [mW] in the k layer is

δk is the transmittance between the light incident surface on the disk and the kth recording layer.

However, Tn; transmittance of n layer (when n = 0, transmittance of one layer)
From Equation (6), the minimum recording power Pmin necessary for recording with the k layer is:
Pmin ≧ Ikth × Sk / δk (Expression 7)
In addition, since recording is performed on the k layer, the light intensity density Ijk [mW] at the j layer when focusing on the k layer is

It is.

    When recording is performed on the k layer, the upper limit Pmax of the recording power is given by the following equation in order not to destroy the recording of the j layer.

Pmax = Ijth × Sjk / δj (Equation 10)
Sjk is the light spot area in the j layer when focusing on the k layer,

dn: n-th layer thickness TANφ = a / fF≈NAF
The aperture optical system, the disk structure, and the recording conditions are set so that the equations (7, 7) and (9, 10, 11) are simultaneously satisfied.
6). As the role of each layer, a ROM (Read Only Memory) layer or a WOM (Write Once Memory) is provided together with a layer for recording / reproducing user data.
7. As the layer data management layer, the data state of each layer, for example, the presence / absence of data, error management, effective data area, and number of rewrites (overwrite) are recorded as needed.
8). In item 1, information is entered as a replacement layer instead of the layer in which the recording error is detected.
9. In item 1, sectors and tracks are provided as the management format in each layer surface of the disk, and recording is performed in order from the 1 → k → N layer and the upper layer. However, in each layer, information is recorded in all user sectors and tracks and then recorded in the next layer.
10. Recording is performed in order from N → k → 1 layer and lower layers. However, in each layer, information is recorded in all user sectors and tracks and then recorded in the next layer.
11. In each layer, information is recorded in all user sectors and tracks and then recorded in the next layer. The order of the layers to be recorded is random access.
12 The order of the layers to be recorded is random access, but after all data is recorded in the sector in one layer, the sector in the next layer is filled, the sector in all layers is filled, Record the next sector data.
13. In this track, random access is performed in the layer direction. In this case, variable length blocks are used instead of fixed block management by sector.
14 In item 1, as a light spot positioning mechanism, a two-dimensional actuator that drives the aperture lens in the layer direction and the disk radial direction, or a one-dimensional actuator that drives the aperture lens only in the layer direction and a light beam incident on the aperture lens on the disk radius. In the combination of galvanometer mirrors that deflect in the direction, the layer number detection circuit recognizes the number of the current layer by reading the layer address in the preformat part, and from the jth layer that is currently focused Recognize how many (| k−j |) layers should be spot-moved in the upper or lower (sign (k−j)) direction to the k-th target layer, which is a command from the host controller. The jump jump signal is generated in the layer jump signal generation circuit, and the AF actuator To be input to the server.
15. In item 14, the jump signal is composed of a pair of + -polarity pulses for movement between one layer, and the + -pulse is switched depending on the vertical movement direction. The first pulse is used to drive the spot in the moving direction by the moving distance, and the next polarity inversion pulse is used to stabilize the spot so that the spot does not go too far. Also, a pair of pulses of the number of moving layers is input to the driver circuit. Next, the layer number is detected and it is confirmed that j = k.
16. In item 14, there is provided a cross layer signal detection circuit that detects the in-focus detection for each recording layer using the zero cross pulse of the AF error signal and the total light amount pulse as gates.
17. In item 16, by generating and counting up pulses and down pulses from the zero cross pulse, the total light amount pulse, and the two kinds of pulses, it is always recognized which layer the lens is positioned on, and the lens is positioned relative to the disc. Recognize the direction of movement.
18. In item 14, when the saw wave is generated from the AF actuator movement signal generation circuit so that the focal position moves at least from the uppermost layer of the disk to the lowermost layer, and the AF actuator is driven, the cross layer signal detection circuit From the upper limit of the up pulse when the focal point of the N layers is counted and the lens is moved upward, from the lower limit of the down pulse when the uppermost layer (n = 1) or the lens is moved downward The lowermost layer (n = N) is recognized, and the focal position in the disk layer direction is always recognized.
19. In item 5, when recording is stably performed on the k layer which is the recording target, the recording power P (light intensity) in consideration of the transmittance (ΣTn (n = 0, 1, 2,... K−1)) up to the k layer. ) Is set.
20. In item 5, the transmittance up to the k layer is set for layer address recognition.
21. By address recognition, the transmittance ΣTn (n = 0, 1, 2,..., K−1) up to the k layer at the time of disk shipment (or design value) and the transmittance ΣT′n (n = 0, 1, 2,... K−1), that is, the recording power is set in consideration of the change G in transmittance.
22. In Items 6 and 21, the management layer of the layer data is provided, which layer is recorded is recorded, the management layer is reproduced before recording the target layer, and the transmittance ΣT ′ ( k-1) is recognized, and the change G in transmittance is recognized.
23. In item 21, before recording on the target layer, the area to be recorded is reproduced in advance to determine the change G in transmittance.
24. In item 23, as a method of reproducing the area to be recorded in advance, the reproduction check is performed at the first rotation of the disk in the recording mode, the recording is performed at the next rotation, and the recording error is checked at the next rotation.
25. In item 23, the reproduction check is performed at a preceding spot using a plurality of spots.
26. In item 25, in the reproduction check, the reproduction signal C′k (t−τ) received for the preceding spot is used. Here, τ is a time-converted distance between spots of the preceding spot and the recording spot. Here, the change in transmittance G is obtained as the square root of the ratio between the reproduction signal Ck ′ focused on the recording target layer k layer and the designed reproduction signal Ck at the time of shipment of the disc.
27. In item 25, in the reproduction check, the value of the reproduction signal Ck is set as a check area in advance as a disk format, and an area not recorded in the layer direction is provided in the disk surface.
28. In item 23, the photodetector for obtaining the reproduction signal has the shape of claim 1.
29. In item 1, as a reproduction control circuit, in addition to detecting the reflected light component from the target layer, in particular, the reflected light component from the adjacent layer occupying most of the interlayer crosstalk is also detected, and the components included in each other are calculated. Get rid of by.
30. In item 29, the three photodetectors are positioned on the image planes of the target layer k and the adjacent layers (k + 1) and (k−1) on the light receiving surface side when the k layer is focused. The shape of the photodetector is the diameter D = (λ / NAI), or the light receiving area is limited by a pinhole, and the reproduction signal Ck, (k−1) layer light for the k layer photodetector. The following equation is calculated for the reproduction signal C (k−1) for the detector and the reproduction signal C (k + 1) for the photodetector in the (k + 1) layer.

Operation F≡Ck−γ × C (k−1) −γ × C (k + 1)
≒ CkR + β × C (k−1) R + β × C (k + 1) R
−γ × {C (k−1) R + β × CkR + β × C (k−2) R} −γ × {C (k + 1) R + β × CkR + β × C (k + 2) R}
β: The ratios C (k−2) R and C (k + 2) R of the crosstalk components included in each signal to the necessary signal components are sufficiently small and the frequency components are low, and can be ignored. Therefore,
F≈ (1-2γβ) × CkR + (β−γ) × C (k−1) R
+ (Β−γ) × C (k + 1) R
Here, assuming that the operation coefficient γ≡β <1,
F≈ (1-β ² ) × CkR
By using the arithmetic function of the above equation, only the signal component of the target layer is obtained.
31. In item 29, a plurality of spots are used. The spot having the same spot diameter as the defocus spot on the adjacent layer when focused on the k layer is scanned in advance on the two adjacent layers to obtain the reproduction signal, and the calculation of item 30 is performed.
32. In item 31, as shown in FIG. 18, an aperture is inserted to reduce the effective aperture of the aperture lens. That is, the effective diameter a ′ is set to [λ / (2d × NAF ² ) × a].
33. In item 31, it is divided into three optical axes and the numerical apertures of the aperture lenses of the preceding two optical systems are reduced, that is, NAF ′ = λ / (2d × NAF).
34. In item 31, integration is performed by multiplying the reproduction signal from the preceding spot by a weight function obtained by approximating the Gaussian distribution, which is the intensity distribution of the spot, to a triangular distribution. 35. In the item 30, in the weight setting circuit for setting each calculation coefficient γ (≡β), the disk recording format is arranged so that the mark recording areas are not included in the same light flux at least between the upper and lower three layers, and h (k −1) / hk, h (k + 1) / h are β (−1) and β (+1).
36. In item 1, by using a plurality of spots and focusing on each layer, recording and reproduction are performed simultaneously on two or more layers, that is, parallel recording and reproduction are performed.
37. Item 9 uses a recording medium whose transmittance increases after recording.
38. In item 1, the pre-pits such as guide grooves and addresses in each layer surface of the multilayer disk are provided in the ultraviolet curable resin layer for each layer, and light is incident from the surface of the mold using a transparent mold for each layer. Form.
39. In item 1, a quarter-wave plate layer is provided in the intermediate layer.

  The above means operates as described below.

Recording film layer whose optical properties change locally due to local light irradiation, antireflection, multiple reflection, light absorption, transfer of optical local change of recording film layer, heat insulation , Heat absorption, heat generation, or a layer for the purpose of reinforcement, or an intermediate layer film, which is a superposition of layers, has a disk in which multiple layers are stacked on an optically transparent substrate. By changing the local optical properties of each layer two-dimensionally (independently), recording corresponding to the data “1” and “0” after modulation is performed, and further, the local optical properties are changed. In a three-dimensional recording / reproducing apparatus that detects a change in reflected light amount (or transmitted light amount) by light spot irradiation on each layer and reproduces data,
1. In the disk structure, the refractive index of an optically transparent substrate is NB, and the thickness is d0. Further, the intermediate layer and the recording film layer are divided as one layer, and 1 to N layers are assigned in order from the upper layer. The distance between each layer is indicated by the distance dk between the adjacent recording film layers k-th and (k−1) -th film thickness. The film thicknesses of an arbitrary kth recording layer and intermediate layer are dFk and dMk, and the real part of the refractive index is NFk and NMk, respectively. Further, the period b [μm] of local optical property change on the plane of each layer is used. The aperture optical system uses, for example, a semiconductor laser having a wavelength of λ [μm] as a light source, is converted into parallel light by a collimator lens, and is incident on the aperture lens via a deflection beam splitter. Here, the numerical aperture of the aperture lens is NAF, the effective radius is a [mm], and the focal length is fF (≈a / NAF). The reflected light from the disk passes through the aperture lens and is guided to the light receiving image lens by the beam splitter. A change in the amount of reflected light is converted into an electrical signal by a photodetector located near the focal point of the image lens. The numerical aperture of the image lens is NAI, and the focal length is fI (≈a / NAI). When the diameter of the light receiving surface of the photodetector is D, the reflected light from the target layer when the kth layer is the target layer and focused is imaged at the focal position of the image lens. The spot diameter Uk ′ of
Uk ′ = λ / NAI = λ × (fI / a) (Expression 14)
m: Lateral magnification of light receiving optical system Next, the spot diameter U (k ± 1) ′ on the focal plane from the adjacent layer (k ± 1) th layer separated from the kth target layer by the interlayer distance d is
U (k ± 1) ′ ≈a × m ² d / fI
= NAI · m ² d (Equation 16)
From the above equation, the diameter D of the photodetector is D = Uk ′ = λ / NAI, and the amount of reflected light detected from the other layers is the transmittance δjk between the target k layer and the other j layer, and the reflection Assuming that the ratio of reflected light received from the n layer at the photodetector is In

(Equation 17) ≈I (k−1) / Ik
= Δ ² (k−1), k × α (k−1), k × (D / U (k−1) ′) ² (Equation 17.5)
By setting the disk structure and the optical system so that the above equation holds, leakage of reflected light from other layers is reduced.
2. In the term 1, the minimum value bmin of the two-dimensional period b is set to (λ / NAF), and the maximum value bmax of the two-dimensional period b is made smaller than (d × NAF).

    Further, in the light receiving optical system shown in FIG. 1, the respective optical characteristic functions (OTF) H0 (S), H1 (S) in the target layer surface where recording / reproduction is performed and in the adjacent layer surface separated by the optical distance d [μm]. ) Are shown in FIG. 4 by a straight line 13 and a straight line 14, respectively.

Where S: normalized spatial frequency Here, the optical characteristic function H1 (S) when defocus occurs at the value of the interlayer distance d, the maximum of the period b from S where H1 (S) = 0. Specifies the repetition bmax. In this way, by defining the relationship between the local optical property change period b on the layer surface, the disc structure, and the light receiving optical system, the interlayer crosstalk component can be determined from the local optical property change period b. However, by increasing the length, only the signal component of the target layer can be detected.
3. In item 1, the target layer is reproduced by using a code in which the total area of the local optical change (mark) region included in the spot diameter (2d × NAF) region in the adjacent layer is always a constant value. Only the signal component of the target layer is extracted by making the crosstalk component from the adjacent layer included at a certain time constant DC component and removing the DC component.
4). In item 1,
dk = dF (k−1) + dMk + dFk
≒ dMk (Equation 1)
In addition, the effective refractive index NMk of the intermediate layer is assumed to be the same refractive index NB as that of the substrate. The thickness d up to the Nth layer of the multi-layer disc is

For the spherical aberration amount W40, W40 = | (1 / (8 × NB)) × ((1 / NB ² ) −1) × NAF ⁴ × Δd | (Equation 3)

By combining the thickness dk and the total number N of the intermediate layers of each layer so that W40 ≦ λ / 4, the spherical aberration caused by the change in the optical distance between the layers is suppressed within an allowable value, and in each layer A diffraction limited light spot is formed. The absolute value on the right side of W40 is normally negative (when NB ≧ 1).
5. In item 1, the optical constants of the k-th recording film layer 1 are transmittance Tk, reflectance Rk, and absorption rate Ak. Here, the relationship Tk + Rk + Ak = 1 holds. The optical constant when the local optical property is changed by recording is represented by a dash symbol “′” hereinafter. Generally, an energy threshold value Eth [nJ] always exists in order to cause a thermal structure change in thermal recording. A light spot narrowed down to the diffraction limit on the recording target layer is scanned over the disk at a linear velocity V [m / s].

In order to locally generate a thermal structural change corresponding to the binary signal after modulation, the light intensity P (recording power) [mW] incident on the disc is
Here, when the linear velocity V and the irradiation time t are given, the light intensity density threshold Ith [mW / μm ² ] for the recording film of each layer is set.

Because the spot diameter is λ / NAF for the light intensity density Ik in the k layer when the k layer is focused,
Sk: 1 / e ² spot area when focused on the k layer Sk = π (0.5 × λ / NAF) ²
The light intensity Pk [mW] in the k layer is

  δk is the transmittance between the light incident surface on the disk and the kth recording layer.

However, Tn; transmittance of n layer (when n = 0, transmittance of one layer)
From the above formula, the minimum recording power Pmin necessary for recording in the k layer is
Pmin ≧ Ikth × Sk / δk (Expression 7)
Also, since recording is performed on the k layer, the light intensity density Ijk [mW] at the j layer when focusing on the k layer is Pjk = Pk × δjk
= P × δj (Equation 9)
δjk = Π / Π (= (transmittance up to j-th layer / transmittance up to k-th layer)).

    When recording on the k layer, the upper limit Pmax of the recording power is given by

Pmax = Ijth × Sjk / δj (Equation 10)
Sjk is the light spot area in the j layer when focusing on the k layer,

dn: nth layer thickness
TANφ = a / fF ≒ NAF
By setting the narrowing optical system, the disk structure, and the recording conditions so that the above equations hold simultaneously, the incident recording power is set so that stable recording can be performed on the target layer and other layers are not destroyed at that time.
6). The role of each layer is to provide information other than user data by providing a ROM (Read Only Memory) layer or a WOM (Write Once Memory) together with a layer for recording and reproducing user data.
7. As a management layer for layer data, data update and access can be performed by recording the data status of each layer, for example, the presence / absence of data, error management, effective data area, and number of rewrites (overwrite) as needed. Do it promptly.
8). In item 1, data reliability is ensured by inserting information in place of the layer in which the recording error is detected as an alternate layer.
9. In item 1, sectors and tracks are provided as the management format in each layer surface of the disk, and recording is performed in order from the 1 → k → N layer and the upper layer. However, in each layer, user data recording / reproduction is managed by recording information in all user sectors and tracks and then recording in the next layer.
10. Recording is performed in order from N → k → 1 layer and lower layers. However, in each layer, user data recording / reproduction is managed by recording information in all user sectors and tracks and then recording in the next layer.
11. In each layer, information is recorded in all user sectors and tracks and then recorded in the next layer. The order of the recording layers is set to random access to manage user data recording / reproduction.
12 The order of the layers to be recorded is random access, but after all data is recorded in the sector in one layer, the sector in the next layer is filled, the sector in all layers is filled, User data recording / reproduction is managed by recording data of the next sector.
13. In this track, random access is performed in the layer direction. In this case, user data recording / reproduction is managed by applying variable-length blocks instead of fixed block management by sector.
14 In item 1, as a light spot positioning mechanism, a two-dimensional actuator that drives the aperture lens in the layer direction and the disk radial direction, or a one-dimensional actuator that drives the aperture lens only in the layer direction and a light beam incident on the aperture lens on the disk radius. In the combination of galvanometer mirrors that deflect in the direction, the layer number detection circuit recognizes the number of the current layer by reading the layer address in the preformat part, and from the jth layer that is currently focused Recognize how many (| k−j |) layers should be spot-moved in the upper or lower (sign (k−j)) direction to the k-th target layer, which is a command from the host controller. The jump jump signal is generated in the layer jump signal generation circuit, and the AF actuator By input to the server, to focus on a target layer.
15. In item 14, the jump signal is composed of a pair of + -polarity pulses for movement between one layer, and the + -pulse is switched depending on the vertical movement direction. The first pulse is used to drive the spot in the moving direction by the moving distance, and the next polarity inversion pulse is used to stabilize the spot so that the spot does not go too far. Also, a pair of pulses of the number of moving layers is input to the driver circuit. Next, the spot number is positioned on the target layer k by detecting the layer number and confirming that j = k.
16. In item 14, when the lens is moved in the layer direction by providing a cross layer signal detection circuit that detects the in-focus detection for each recording layer using the zero cross pulse of the AF error signal and the total light amount pulse as gates A signal with the focal position crossing each layer is obtained.
17. In item 16, by generating and counting up pulses and down pulses from the zero cross pulse, the total light amount pulse, and the two kinds of pulses, it is always recognized which layer the lens is positioned on, and the lens is positioned relative to the disc. Recognize the direction of movement.
18. In item 14, when a sawtooth wave is generated from the AF actuator moving signal generation circuit so that the focal position moves at least from the uppermost layer of the disc to the lowermost layer, and the AF actuator is driven, the cross layer signal detection circuit From the upper limit of the up pulse when the focal point of the N layers is counted and the lens is moved upward, from the lower limit of the down pulse when the uppermost layer (n = 1) or the lens is moved downward By recognizing the lowermost layer (n = N) and always recognizing the focal position in the disk layer direction, layer access is possible without providing a layer address.
19. In item 5, when recording is stably performed on the k layer which is the recording target, the recording power P (light intensity) in consideration of the transmittance (ΣTn (n = 0, 1, 2,... K−1)) up to the k layer. ) Is set, recording is performed under the optimum recording power condition for the target layer.
20. In item 5, the transmissivity up to the k-th layer is set for the layer address recognition, so that the target layer is recorded under the optimum recording power condition.
21. By address recognition, the transmittance ΣTn (n = 0, 1, 2,..., K−1) up to the k layer at the time of disk shipment (or design value) and the transmittance ΣTn (n = 0, n) immediately before recording are recorded. 1,..., K−1), that is, by setting the recording power in consideration of the change G of the transmittance, the transmittance is changed due to the presence of the layers recorded up to the target layer. Even if that is the case, recording is performed under the optimum recording power condition for the target layer.
22. In Items 6 and 21, the management layer of the layer data is provided, which layer is recorded is recorded, the management layer is reproduced before recording the target layer, and the transmittance ΣT ′ ( k-1) is recognized and the change G of the transmittance is recognized, so that even if the transmittance changes due to the layers recorded up to the target layer, the target layer is taken into consideration. Recording with optimal recording power conditions.
23. In item 21, before recording on the target layer, the area to be recorded is reproduced in advance, and the transmittance change G is obtained, whereby the transmittance changes due to the layers recorded up to the target layer. Even if that is the case, recording is performed under the optimum recording power condition for the target layer.
24. In item 23, as a method of reproducing the area to be recorded in advance, the reproduction check is performed at the first rotation of the disk in the recording mode, the recording is performed at the next rotation, and the recording error is checked at the next rotation.
25. In item 23, it is not necessary to wait for rotation by using a plurality of spots and performing the reproduction check at the preceding spot.
26. In claim 25, in the reproduction check, a reproduction signal C′k (t−τ) received for the preceding spot is used. Here, τ is a time-converted distance between spots of the preceding spot and the recording spot. Here, the transmittance change G is obtained as the square root of the ratio between the reproduction signal Ck ′ in the state of focusing on the k layer as the recording target layer and the designed reproduction signal Ck at the time of shipping the disc. In the reflection optical system, a change in transmittance is obtained.
27. In item 25, in the reproduction check, the value of the reproduction signal Ck is set as a check area in advance as a check area, and a non-recording area in the layer direction is provided in the disk plane so Reduce the effect of rate variation.
28. In Item 23, with respect to the photodetector that obtains the reproduction signal, the reflection component from the target layer is specified and detected by adopting the shape of Claim 1 to obtain a more accurate transmittance change G.
29. In item 1, as a reproduction control circuit, in addition to detecting the reflected light component from the target layer, in particular, the reflected light component from the adjacent layer occupying most of the interlayer crosstalk is also detected, and the components included in each other are calculated. The reflected light component of the target layer is extracted by removing by (1).
30. In item 29, the three photodetectors are positioned on the image planes of the target layer k and the adjacent layers (k + 1) and (k−1) on the light receiving surface side when the k layer is focused. The shape of the photodetector is the diameter D = (λ / NAI), or the light receiving area is limited by a pinhole, and the reproduction signal Ck, (k−1) layer light for the k layer photodetector. The following equation is calculated for the reproduction signal C (k−1) for the detector and the reproduction signal C (k + 1) for the photodetector in the (k + 1) layer.

Operation F≡Ck−γ × C (k−1) −γ × C (k + 1)
≒ CkR + β × C (k−1) R + β × C (k + 1) R
−γ × {C (k−1) R + β × CkR + β × C (k−2) R}
−γ × {C (k + 1) R + β × CkR + β × C (k + 2) R}
β: The ratios C (k−2) R and C (k + 2) R of the crosstalk components included in each signal to the necessary signal components are sufficiently small and the frequency components are low, and can be ignored. Therefore,
F≈ (1-2γβ) × CkR + (β−γ) × C (k−1) R
+ (Β−γ) × C (k + 1) R
Here, assuming that the operation coefficient γ≡β <1,
F≈ (1-β ² ) × CkR
By using the arithmetic function of the above equation, only the signal component of the target layer is obtained.
31. In item 29, a plurality of spots are used. By scanning the spot having the same spot diameter as the defocus spot on the adjacent layer when focused on the k layer, scanning the two adjacent layers in advance of the spot, obtaining a reproduction signal, and performing the calculation of the term 30 Only the signal component of the target layer is obtained.
32. In item 31, as shown in FIG. 18, an aperture is inserted to reduce the effective aperture of the aperture lens. That is, by setting the effective diameter a ′ to [λ / (2d × NAF ² ) × a], the spot diameter of the preceding spot that focuses on the adjacent layer is set to (2d × NAF).
33. In item 31, by dividing the optical axis into three optical axes and reducing the numerical apertures of the aperture lenses of the preceding two optical systems, that is, NAF ′ = λ / (2d × NAF), the adjacent layer is focused. The spot diameter of the preceding spot to be connected is set to (2d × NAF).
34. In item 31, integration is performed by multiplying the reproduction signal from the preceding spot by a weight function obtained by approximating the Gaussian distribution, which is the intensity distribution of the spot, to a triangular distribution, so that the defocus spot effectively scans the mark row. Get the playback signal.
35. In the item 30, in the weight setting circuit for setting each calculation coefficient γ (≡β), the disk recording format is arranged so that the mark recording areas are not included in the same light flux at least between the upper and lower three layers, and h (k −1) / hk and h (k + 1) / h are set to β (−1) and β (+1), respectively, to determine weights for the upper and lower layers.
36. In item 1, by using a plurality of spots and focusing on each layer, recording and reproduction are simultaneously performed on two or more layers, that is, parallel recording and reproduction are performed, thereby increasing the transfer rate.
37. In item 9, by using a recording medium whose transmittance increases after recording, the light intensity given when recording in the lower layer is reduced, and the reflected light from the lower layer is increased, so that high-efficiency recording, high SN Perform specific regeneration.
38. In item 1, the pre-pits such as guide grooves and addresses in each layer surface of the multilayer disk are provided in the ultraviolet curable resin layer for each layer, and light is incident from the surface of the mold using a transparent mold for each layer. By forming each layer, prepits such as a guide groove for tracking and a layer address indicating the position of the layer are formed, and data is recorded and reproduced.
39. In item 1, by providing the quarter-wave plate layer in the intermediate layer, the polarization direction of the reflected light from the adjacent layer is different, so there is no interference and the crosstalk between the adjacent layers can be reduced.

  According to the present invention, a light spot narrowing optical system, a disk structure, a light detection optical system capable of stably recording and reproducing in a recording process and a reproducing process, an encoding method for suppressing crosstalk between adjacent layers, which is particularly a problem, and a cross Talk cancellation method, 3D data format, accompanying disk creation method and 3D access method can be provided, so that the light spot is narrowed down to each layer of the multi-layered disk, and data recording / reproduction with high reliability is possible. it can.

Less than,
(1) Principle of three-dimensional recording / reproducing method of the present invention (2) Three-dimensional disc format, data management (3) Device configuration (4) Access method (5) Recording control method (6) Reproduction control method (7) Disc structure The embodiment will be described in the order of the embodiment and the disc creation method.

(1) Basic principle of three-dimensional recording / reproducing FIG. 1 shows a principle of recording / reproducing of the three-dimensional recording / reproducing apparatus of the present invention. Recording film layer 1 whose optical properties change locally by local light irradiation, and antireflection, multiple reflection, light absorption, transfer of optical local change of recording film layer as an aid to the function of the recording film layer, It has a disk 4 in which layers for the purpose of heat insulation, heat absorption, heat generation or reinforcement, or an intermediate layer film 2 that is a superposition of these layers is stacked on an optically transparent substrate 3, and is narrowed down to each layer. By recording the local optical properties of each layer two-dimensionally and independently between each layer by the irradiated light spot, recording corresponding to the modulated data “1” and “0” is performed. The local optical property change is detected as a change in reflected light amount (or transmitted light amount) by light spot irradiation to each layer, and data is reproduced.

  In FIG. 1, the structure of the disk 4 is such that the refractive index of the optically transparent substrate 3 is NB and the thickness is d0. Further, the intermediate layer 2 and the recording film layer 1 are separated as a set of layers, and numbers from 1 to N are assigned in order from the upper layer (light incident side). The distance between each layer is indicated by the distance dk between the adjacent recording film layers k-th and (k−1) -th film thickness. The film thicknesses of an arbitrary kth recording layer and intermediate layer are dFk and dMk, and the real part of the refractive index is NFk and NMk, respectively. Further, the period b [μm] of local optical property change on the plane of each layer is used. The aperture optical system uses, for example, a semiconductor laser 5 having a wavelength λ [μm] as a light source, converts the light into parallel light by a collimator lens 6, and enters the aperture lens 8 through a deflection beam splitter 7. Here, the numerical aperture of the lens 8 is NAF, the effective radius is a [mm], and the focal length is fF (≈a / NAF). Each layer is irradiated with a diffraction-limited light spot 11 by focusing on each layer.

  As for the light receiving optical system, a reflection light receiving system is shown as an example. The reflected light from the disk 4 passes through the lens 8 and is guided to the image lens 9 for light reception by the beam splitter 7. A change in the amount of reflected light is converted into an electrical signal by the photodetector 10 located near the focal point of the lens 9. The numerical aperture of the image lens 9 is NAI, and the focal length is fI (≈a / NAI). Let D be the diameter of the light receiving surface of the photodetector 10. In the present invention, the parallel optical system shown in FIG. 2A is shown as an example of the optical system, but the same effect can be obtained by the diffusion optical system shown in FIG. 2B. Further, a transmitted light detection system as the light receiving optical system can achieve the same effect as the present invention.

In the three-dimensional recording / reproduction, the first problem for performing the recording / reproduction is to narrow the light spot to the diffraction limit in each layer. In the conventional optical disk, in order to protect the recording film, the light spot is generally narrowed down to the single layer recording surface over the substrate 3 by the diffraction limit. Therefore, the design specification of the aperture lens 8 is performed in consideration of the refractive index and the film thickness of the substrate 3 so that the spherical spot does not occur and the light spot is not distorted. However, in the multilayer disk 4, the influence of the film thickness of each layer cannot be ignored. For example, as shown in a known example “Kubota et al .: Optics, 14 (1985), eye pattern jitter analysis I to V in an optical disk”, As the number of layers increases, spherical aberration increases and the diffraction limit cannot be reduced. Therefore, the present invention shows a design of a focusing lens and a disk structure for obtaining a light spot in a range sufficient for recording and reproduction. In order to simplify the design method, it is assumed that the film thickness dFk of the recording film layer 1 is sufficiently smaller than the film thickness dMk of the intermediate layer 2 and can be ignored. That is,
dk = dF (k−1) + dMk + dFk≈dMk (Equation 1)
The intermediate layer 2 has the same refractive index NB as that of the substrate 3 in each layer. In this case, the thickness d up to the Nth layer of the multilayer disk is

It is.

  On the other hand, as the Rayleigh limit, a spherical aberration amount W40 = λ / 4, which guarantees 80% of the peak intensity of the narrowed spot when no aberration occurs, is given as an allowable value.

  The spherical aberration amount W40 generated by the change Δd in film thickness from the first to the Nth layer is expressed as follows.

W40 = | (1 / (8 × NB)) × ((1 / NB ² ) −1) × NAF ⁴ × Δd | (Equation 3)
Therefore, the design of the focusing lens and the disk structure are determined so that W40 ≦ λ / 4. The absolute value on the right side of W40 is normally negative (when NB ≧ 1). As an example, when a glass substrate having a refractive index NB = 1.5 is used as the substrate 3, an ultraviolet curable resin having substantially the same refractive index as that of glass is used as the intermediate layer, and NAF = 0.55 of the aperture lens 8, ( From equation (3), Δd ≦ 50 μm. here,
d0 = 1.2 mm−Δd = (1.15-1.2 mm),

By combining the intermediate layer thickness dk and the total number N so that Δd ≦ 50 μm, the aperture lens for the substrate thickness of 1.2 mm used in the conventional optical disc can be applied as it is. To the Nth layer, a light spot sufficient for recording / reproduction can be formed. As one combined solution, when the intermediate layer thickness dMk = 10 μm and the recording layer thickness dFk = 200 mm, d0 = 1.15 mm, Σdk = 10.4 μm≈100 μm, and the total number N = 10.

In (Equation 4), the spherical aberration is zero in the fifth layer, and the maximum spherical aberration occurs within the allowable value in the uppermost layer and the lowermost layer. This can be further corrected. According to wave optics, spherical aberration can be corrected by shifting the focal position. The conditions are W40 = −W20 = −0.5 × NAF ² Δz, Δz = −2 / NAF ² × W40. Here, W20 is aberration due to defocus, and Δz is defocus. In the above example, the spherical aberration Wk40 generated in the k-th layer at the interlayer distance Δdk = (k−5) × d from the fifth layer is obtained from (Equation 3), and the defocus amount Δzk for correcting this aberration. Δzk = −2 / NAF ² × Wk40.

  The lowermost layer (k = 10) may be 1.4 μm, and the uppermost layer (k = 1) may be given a defocus of −1.4 μm as an offset.

Next, the second problem for recording / reproducing is the thermal recording process. The prescribed conditions for recording are the following two terms.
(A) The recording target layer can be provided with a recording power density sufficient for recording and stable.
(B) When data is recorded on an arbitrary k layer, data on other layers should not be destroyed.

  Factors can be divided into those due to light intensity and those due to heat conduction through the layers. Here, the former will be described. The latter can be dealt with by providing the intermediate layer 2 with a heat insulating effect, but this method will be described in the section of the recording medium embodiment.

  In the present invention, as a method of satisfying these two terms, first, the disk structure and the focusing optical system are optimized.

In FIG. 1, the substrate 3 and the intermediate layer 2 have a transmittance of 100% as an example for simplification of design. The optical constants of the kth recording film layer 1 are transmittance Tk, reflectance Rk, and absorption rate Ak. Here, the relationship Tk + Rk + Ak = 1 holds. In addition, the optical constant when the local optical property is changed by recording is represented by a dash symbol “′” hereinafter. In general, in thermal recording, the heat structure of the recording film changes due to heat generation due to light absorption of the recording film and a temperature increase governed by a thermal diffusion phenomenon using this as a heat source. This corresponds to movement of the recording film due to melting in the punched recording medium, crystallization and amorphization in the phase change recording medium, and reversal of perpendicular magnetization in the magneto-optical recording medium. This thermal structural change occurs, resulting in a local optical property change. Regardless of the type of recording film, the energy threshold Eth [nJ] always exists in order for the thermal structure change to occur. In the recording process, the light spot 11 narrowed down to the diffraction limit in the recording target layer is scanned over the disk at a linear velocity V [m / s]. In order to locally generate a thermal structure change corresponding to the binarized signal after modulation, the light intensity P (recording power) [mW] applied to the disk surface is modulated at time t [s]. Here, if the linear velocity V and the irradiation time t are given, the energy threshold Eth can be discussed with the light intensity density threshold Ith [mW / μm ² ].

  In order to satisfy the term (A), the equation (5) is preferably satisfied with respect to the light intensity density Ik in the k layer when the k layer is focused.

Ik = Pk / Sk ≧ Ikth (Equation 5)
Ikth; threshold value of light intensity density in the recording layer k (mW / μm ² )
Sk: 1 / e ² spot area when focusing on the k layer
Sk = Π (0.5 × λ / NAF) ²
However, the light spot diameter narrowed down to the diffraction limit is λ / NAF.
Here, the light intensity Pk [mW] in the k layer is

δk is the transmittance between the light incident surface on the disk and the kth recording layer, and Tn is the transmittance of the n layer (when n = 0, the transmittance of up to one layer). Pk is as shown in FIG. (Equation 5) From Equation (6), the minimum recording power Pmin necessary for recording with k layers is:
Pmin ≧ Ikth × Sk / δk (Expression 7)
In general, the light intensity becomes the smallest when the lowest layer N is used, where n = 1 to N-1 is recorded and the transmittance Tn is all reduced. → Tn ′ (transmittance after recording) is there.

In order for the term (B) to hold, since recording is performed on the k layer, the light intensity density Ijk [mW / μm ² ] in the j layer when focusing on the k layer should satisfy (Equation 8). .

  Ijk = Pjk / Sjk << Ijth (Equation 8)

It is.

  When recording is performed on the k layer, the upper limit Pmax of the recording power is given by

Pmax = Ijth × Sjk / δj (Equation 10)
Sjk is the light spot area on the j layer when the k layer is focused, and can be obtained geometrically if the interlayer distance d is greater than or equal to the wavelength λ.

dn: nth layer thickness
TANφ = a / fF ≒ NAF
Here, 1 / Sjk [μm ² ] represents the areal density, as shown in FIG. The light intensity density Ijk [mW / μm ² ] is obtained from FIGS. 3a and 3b, as shown in FIG. 3c.

By setting the aperture optical system, the disk structure, and the recording conditions so that the equations (5) and (8) are satisfied simultaneously, highly reliable recording is possible in each layer. As an example, the recordable interlayer distance d is obtained for the three-layer disc shown in FIG. 10a. However, the aperture optical system has a wavelength λ = 0.78 μm, NAF = 0.55, and the optical constants of the respective layers are R1 = R2 = R3 = 0.1, T1 = T2 = T3 = 0.8, A1 = A2 = A3 = 0.1. Further, the linear velocity v = 7 m / s, the irradiation time t = 100 ns to 500 ns, and the light intensity density threshold value of the recording layer at this time is I1th = I2th = I3th = 2.53 (mW / μm ² ). . Here, the recordable interlayer distance d = d1 = d2 = d3 and the range of the recording power are obtained.

  FIG. 10b shows the recording power applied to the disk and the degree of modulation of the reproduction signal corresponding to each power when recording is not performed on other than the target recording layer and when the spot is narrowed down to each layer. Here, the degree of modulation indicates a measure of the local optical property change (mark) formed on each layer surface, and the degree of modulation tends to saturate when the mark becomes sufficiently large as the narrowed spot diameter. The vertical axis represents each layer normalized with the saturation value of the modulation degree set to 1. In the figure, the threshold power that can form a mark on the first layer is 4 mW (= Ith × S1), the second layer is 5 mW (= Ith × S2 / δ2), and the third layer (k = 3) is This determines the minimum power Pmin. From the formulas (5), (6), and (7)

It becomes.
(Equation 8) (Equation 9) (Equation 11)

  For example, when d = 2.5 μm, Pmax = 16 mW (P3max = 10 mW), and a mark with a sufficient signal can be recorded as shown in FIG. Thus, by designing, it is possible to record the target layer with high reliability without destroying other layers.

Next, the third problem for recording / reproducing is in the reproducing process. The specified conditions for reproduction are as follows.
(C) Minimize the noise component. Here, it is reduction of interlayer crosstalk noise.
(D) Maximize the signal component from the target layer.

  The 1st method for achieving the (C) term is shown.

  The first method is to optimize reproduction of the light receiving optical system in FIG. 1 to sufficiently reduce the amount of reflected light from other than the target layer, thereby reducing interlayer crosstalk and reproducing with a large SN ratio. is there. In FIG. 1, as indicated by the solid line, the amount of reflected light from the layer to be reproduced is all detected by the photodetector 10 placed on the focal point of the image lens 9. On the other hand, the reflected light from the adjacent layer spreads on the focal plane 12 of the image lens as indicated by the dotted line. Therefore, by limiting the size of the photodetector 9 as shown in FIG. 1, the reflected light from the adjacent layer can be reduced.

The k-th layer is the target layer, and the diameter at which the intensity is 1 / e ² of the peak intensity value of the light spot 11 when focused, that is, the spot diameter is Uk = (λ / NAF). Then, the reflected light from the target layer is imaged at the focal position of the image lens 9. The spot diameter Uk ′ on the focal plane 12 is
Uk ′ = mUk = m × (λ / NAF) = (NAF / NAI) × (λ / NAF) = λ / NAI = λ × (fI / a) (Expression 14)
m: Lateral magnification of light receiving optical system Next, a spot diameter U (k ± 1) ′ on the focal plane from the (k ± 1) th layer separated from the kth target layer by the interlayer distance d is obtained. The distance d ′ between the position where the reflected light from the (k ± 1) layer is focused by the image lens 9 and the focal plane is:
d ′ = Y × d = m ² × d (Equation 15)
Y: longitudinal magnification U (k ± 1) ′ = d ′ × tan φI = d ′ × a / (fI + d ′)
= M ² d × a / (fI + m ² d)
Here, if fI >> m ² d, U (k ± 1) ′ ≈a × m ² d / fI = NAI · m ² d (Equation 16)
If the diameter D of the photodetector is D = Uk ′ = λ / NAI from the above equation, the area ratio ε = (D / U (k ± 1) compared to the case where the diameter of the photodetector is not limited. ² ) Since the amount of reflected light from the adjacent layer can be reduced by ² , the change in the amount of reflected light from the target layer can be detected with a high S / N ratio.

  Actually, the amount of reflected light from the other layer to be detected takes into account the transmittance δjk between the target k layer and the other j layer and the reflectance ratio αjk. Here, assuming that the amount of interlayer crosstalk noise necessary for highly reliable signal detection is −20 dB (1/10), the following equation should generally hold.

  When the amount of reflected light received from the n layer at the photodetector 10 is In.

However, only the adjacent layer (k-1) layer with respect to the target layer k layer will be considered below. The influence from other layers can be considered in the same manner, but the value is sufficiently small.

(Equation 17) ≈I (k−1) / Ik
= Δ ² (k−1), k × α (k−1), k × (D / U (k−1) ′) ²
(Equation 17.5)
For example, assuming that λ = 0.78 μm, NAF = 0.55, fI = 30 mm (NAI = 0.075, m = 7.33, m ² = 53.8), D = Uk′≈10.4 μm
Taking FIG. 10 as an example, since δ23 = 1.25 and α23 = 1, the suppression rate of the amount of reflected light is ε × δ ² 23 × α23.

I2 / I3 = δ ² 23 × α23 × ε = δ ² 23 × α23 × (D / U2 ′) ²
= Δ ² 23 × α23 × (λ / NAI) ² / (NAI × m ² d) ²
= Δ ² 23 × α23 × (λ / NAF ² / d) ² (Equation 18)
(I2 / I3) ≦ 1/10 When d satisfying the above equation is obtained,

Here, the influence of the crosstalk from the second layer is considered, but the influence of the crosstalk from the first layer can be calculated in the same manner, and the value (I1 / I3) = 0.024 (= −32 dB) is sufficient. Small and negligible.

  In the above example, the photodetector diameter D = Uk ′ = λ / NAI, but there is a degree of freedom in design so that there is a value of crosstalk between layers including the positional deviation of the photodetector. Next, a second method for achieving the item (C) will be described.

  The second method is to define the relationship between the local optical property change (mark) period b on the layer surface, the disk structure, and the light receiving optical system. It is made longer than the change period b. That is, data on the target layer surface is reproduced with a high S / N ratio by making the frequency component of the interlayer crosstalk smaller than the data signal band. The principle of this method will be described with reference to FIGS. In order to distinguish from the first method, the diameter of the photodetector is not limited, but by using it together, a higher SN can be obtained.

  Since a diffraction-limited light spot is formed on the target layer, if the two-dimensional period b is about the spot diameter (λ / NAF), the target layer can be sufficiently decomposed. That is, if the minimum value bmin of the two-dimensional period b is (λ / NAF), the signal component can be sufficiently large. This is the condition that satisfies the term (D). In FIG. 4, when H0 (S) = 0, decomposition is impossible, and the value of b at this time is 1/2 of the spot diameter λ / NAF. On the other hand, the spot diameter in the adjacent layer is out of focus, so when the interlayer distance is d, (2d × NAF) is obtained, and the optical resolution is lowered. Therefore, if the maximum value bmax of the two-dimensional period b is made smaller than 1/2 of the spot diameter (2d × NAF) in the adjacent layer, that is, (d × NAF) using this characteristic, the signal component from the adjacent layer The frequency component of the leakage of the inter-layer crosstalk, which is smaller than the signal band (1 / bmax to 1 / bmin), can be removed using a filter or AGC (auto gain control).

  Here, a decrease in optical resolution due to defocusing, that is, a decrease in the degree of signal modulation is obtained from optical theory.

  In the light receiving optical system shown in FIG. 1, the respective optical characteristic functions (OTF) H0 (S) and H1 (S) in the target layer surface where recording / reproduction is performed and in the adjacent layer surface separated by the optical distance d [μm] are obtained. In FIG. 4, the straight line 13 and the straight line 14 are shown. The horizontal axis corresponds to the repetition frequency of the object, and the vertical axis corresponds to the degree of modulation. Here, S is a normalized spatial frequency.

S = λ × fF / (2Πa) = λ / NAF × b (Equation 20)
When there is no defocus and no aberration, the optical characteristic function H0 (S) becomes a straight line 13. In this case, the cutoff frequency at which the optical resolution is zero is S = 2. In an actual recording / reproducing apparatus, since noise components such as laser noise and amplifier noise are included and the optical system itself has aberrations other than defocusing, up to a period b corresponding to the cutoff frequency S = 2. , Difficult to detect. Therefore, the modulation degree half (−6 dB) is set as the allowable value of the modulation degree. At that time, S = 1, which defines the minimum repetition bmin of the period b.

bmin = λ / NAF (Expression 21)
On the other hand, with respect to the optical characteristic function H1 (S) in the case where defocus occurs at the value of the interlayer distance d, the maximum repetition bmax of the period b is defined from S where H1 (S) = 0.

  As the defocus d increases, the optical characteristic function H1 (S) changes in the direction of the arrow 15 and bmax can be increased.

  Thus, the frequency component of crosstalk from the adjacent layer is less than fmin (= 1 / bmax), and if an auto gain control circuit having a tracking characteristic 16 as shown in FIG. 4 is used, the adjacent crosstalk component is absorbed. it can.

(Numerical example)
The relationship between the defocus d and the wavefront aberration amount B1 is expressed by the following equation.

B1 = −d / 2 × (NAF) ²
As a numerical example, a cut-off frequency S with respect to defocus d was obtained, and bmax was obtained.

When d = 6.7 μm → bmax = 4.7 μm
B1 = −λ
When d = 10 μm → bmax = 7.9 μm
B1 = -1.5λ
Bmin = (λ / NAF) = 1.42 μm
For example, as shown in FIG. 20, a pit shown in a publicly known example “Japanese Patent Laid-Open No. 63-53722” is used for a disk using a 2-7 code, which is a variable length code, in the spot scanning direction and having a track pitch of 1.5 μm. When the edge recording method is used, when the minimum reproducible bit pitch q (μm) and the interlayer distance d are obtained, as shown in FIG.
3q = bmin = 1.42 μm
q = 0.47 μm
Here, the longest pattern repetition is 8q,
8q = 3.76μm ≦ bmax
Further, the mark period in the disk radial direction needs to be constant at a track pitch of 1.5 μm and 1.5 μm ≦ bmax. Therefore, d ≧ 5 μm is sufficient.

  Next, a third method for achieving the item (C) will be described. In the second method, the frequency component of the interlayer crosstalk noise is equal to or less than fmin. However, depending on the modulation method, the signal from the target layer varies due to the variation in local optical properties. The 2-7 modulation code used in the above example is one of them, and the power spectrum characteristic 86 of the modulation signal is shown in FIG. There are slight components below fmin. This can be suppressed by the filter and AGC as described above. However, even if such a circuit is not used, it is possible to suppress inter-layer crosstalk noise by eliminating variation in density and making the DC component constant value. Can do. The principle of the third method uses a code in which the total area of the local optical change (mark) region included in the spot diameter (2d × NAF) region in the adjacent layer is always a constant value. By doing so, the amount of interlayer crosstalk to the reproduction signal when the spot is scanned is always a constant DC value. The third method and the first method can be used in combination.

  An example is shown. The power spectrum 87 of the modulation signal in the case of using the EFM modulation system in the well-known example “Toshitada Doi, Akira Iga: Digital Audio” has a characteristic that the spectrum of the low frequency component sharply decreases as shown in FIG. Have. Therefore, the interlayer distance d may be set so that the break point 88 where the spectrum sharply decreases coincides with the cutoff frequency at which H1 (S) = 0 for the optical characteristic function H1 (S) of the adjacent layer.

For example, if q = 0.6 μm, 2.82q = 1.7 μm ≧ bmin = 1.42 μm, 10.36q = 6.2 μm ≦ bmax, the repetition period at the break point 88 is 24 μm, and the interlayer distance d = 22 μm. At this time, the occupation ratio of the mark included in the spot diameter (2d × NAF = 24 μm) in the adjacent layer is almost 50% constant, and the component of the reflected light amount from the adjacent layer included in the detected reproduction signal is always a constant value. It becomes.

Next, in FIGS. 21 and 22, the present invention is applied to the case where two-dimensional recording is performed in the layer plane. The two-dimensional recording / reproducing system is shown in Japanese Patent Application No. 3-11916 “Information Recording / Reproducing Method and Apparatus”. In the prior application, as shown in FIG. 21, for example, a combination of using 2 × 2 4 grid points as one block and recording marks at the grid points represents 2 ⁴ = 16, 4 bit data, Densify. In this case, the first and second main methods can be applied. Also, as shown in FIG. 22, the same number of marks are necessarily included in the lattice points in the 4 × 4 lattice block (one in the figure). Further, if the spot diameter (2d × NAF) in the adjacent layer includes many lattice blocks, the number of marks included in the spot and the occupied area of the marks are almost constant, and the third method is applied. it can.

  By the way, in an optical disk, a diffraction-limited light spot is formed on each recording layer surface. However, in each optical system shown in FIG. 2, when a defocus of a certain value dm occurs, the condition of the imaging system of the microscope is satisfied. An image of the recording film surface may be formed on the light receiving surface. For example, when a diffraction-limited spot is formed on the target layer and light is received, if the distance to the other layer is dm, a mark row pattern on this layer is formed on the light-receiving surface, and information on the target layer There is a possibility of crosstalk noise in the signal band on the signal. Therefore, it is desirable to design the disk structure so that the interlayer distance does not become dm.

In addition, since the light reflected from each layer is the same as the irradiation light, the reflected light interferes when the distance between the layers is reduced to a coherent distance. As a result, the crosstalk noise between the layers cannot be expressed by the ratio of the amounts of light received from the target layer and other layers on the light receiving surface. In other words, since interference occurs, worst-case interlayer crosstalk noise appears at the square root of the received light amount ratio. This effect is actually a problem in the case of adjacent layers.

  An embodiment for solving this problem is shown in FIG. The principle of this embodiment is that interference is not caused by changing the polarization direction of the light reflected from the adjacent layer. As one means for changing the polarization direction, in FIG. 27, each intermediate layer 2 is provided with a quarter-wave plate layer 201. The quarter-wave plate layer 201 has a phase difference of 90 degrees in the two-dimensional direction of the layer surface with respect to the wave of the electric field of light traveling in the depth direction of the layer, that is, the optical thickness in the two directions. The difference is changed by 1/4 wavelength. By adopting such a disk structure, for example, as shown in the figure, when the polarization direction of the irradiated light is E-polarized light, the reflected light from the layers adjacent to each other is the difference between reciprocating the quarter-wave plate layer 201. That is, since the wavelength difference is different by ½ wavelength and 180 degrees, the polarization direction is alternately orthogonal to the E polarization and the H polarization. Therefore, reflected light components between adjacent layers do not interfere with each other, and can be expressed by a simple ratio of received light amounts on the light receiving surface, thereby reducing crosstalk between layers. Further, in the light receiving system, as shown in FIG. 27, a polarization beam beam splitter 202 is inserted, and the photodetectors 203 and 204 to be detected are separated according to the polarization direction of the reflected light. By doing so, since the reflected light from the adjacent layer is not detected even if it is at least, the allowable value of the variation in the size of the photodetector can be increased in the first reproduction method described above.

Next, an apparatus for achieving the principle of the three-dimensional recording / reproducing method of the present invention shown in section (1) will be described.
(2) Three-dimensional disk format and data management FIG. 5 shows an example of the format of the multilayer disk 4. The layers are 1 to n layers from the substrate 3 on which light is incident toward the light traveling direction. The data format in the k layer is data managed by sector m obtained by dividing the disk into radiation, track l for managing the data position in the radial direction, and three addresses (l, m, n). As shown in the figure, the format of an arbitrary track l and sector m is recorded / reproduced by recording / reproduction timing, pre-format area in which address information is created in advance, and user data. It consists of a data area that records and manages the prohibition of soup stock. Also, as shown in the figure, each layer has a ROM (Read Only Memorey) layer or a WOM (Write Once Memorey) layer as well as a layer for recording / reproducing user data, and an OS (Operating System) of the host controller, or As will be described later, the recording or reproducing conditions in each layer can be preformatted at the time of disc creation or recorded at the time of shipment. As the layer data management layer, the data state of each layer, for example, the presence / absence of data, error management, effective data area, and number of rewrites (overwrite) can be recorded as needed. In addition, information can be reinserted as a replacement layer instead of the layer in which the recording error is detected.

Next, the order of recording data includes, for example, the following combinations.
(a) Recording is performed in order from the 1 → k → N layer and the upper layer. However, in each layer, information is recorded in all user sectors and tracks and then recorded in the next layer.

When performing the above data recording, it is possible to perform recording / reproduction with higher reliability by using a recording medium having a characteristic of increasing the transmittance after recording. That is, since the transmittance to the lower recording layer is increased, the light intensity necessary for recording can be sufficiently applied to the lower target layer by irradiation with light intensity substantially equal to the light intensity necessary for recording on the upper layer. In reproduction, the reflected light component from the target layer returns to the detector with almost no attenuation, so that a reproduction signal having a high S / N ratio can be obtained. An example of a recording medium having the above characteristics is a punched recording medium. When this medium is recorded, a hole is formed in the reflection film, and the reflectance is lowered, that is, the transmittance is increased.
(b) Recording is performed in order from N → k → one layer and lower layers. The rest is the same as (a).
(c) In each layer, information is recorded in all user sectors and tracks and then recorded in the next layer, but the order of the layers to be recorded is random access.
(d) The order of recording layers is random access, but after all data is recorded in the sector in one layer, the sector in the next layer is filled, and the sector in all layers is filled. After that, the next sector data is recorded.
(e) Random access is performed in the layer direction in the track. In this case, by applying variable length blocks that are data management of the magnetic disk instead of fixed block management by sector, the magnetic disk data format can be applied as it is, with the cylinder of the magnetic disk corresponding to the layer.

In the random access, for example, the information recording area may be managed by the host controller so as not to access the area recorded at the time of recording by mistake, or may be managed by the management area described above.
(3) Overall Configuration of Device FIG. 6 shows the overall configuration of the three-dimensional recording / reproducing device. In the case of recording, user data 17 is passed through a modulation circuit 18 to obtain binary data 19 after modulation. The modulated binarized data passes through the recording condition setting circuit 20 and the laser driving circuit 21 is driven so as to be intensity-modulated under the optimal recording condition at the position where the light spot is positioned, and the optical head The light intensity of the semiconductor laser in 22 is modulated and recording on the disk 4 is performed.

  On the other hand, when reproducing, the light spot is positioned at the target layer and track position on the disk, the weak light is irradiated, the intensity change of the reflected light is converted into an electric signal by the photodetector 10, and the reproduction signals 23 and 24 are reproduced. Get. The reproduction signals 23 and 24 pass through the reproduction control circuit 25, suppress interlayer crosstalk, pass through an AGC (auto gain control) circuit 26, absorb fluctuations at a frequency lower than the data band, and operate in later circuits. Adjust the signal to the absolute level.

  Thereafter, the reproduced signal passes through the waveform equalizer 27, improves waveform distortion (amplitude deterioration, phase shift) due to the data pattern, and is converted into a binary signal by the shaper 28. The shaper 28 includes one that binarizes by an amplitude slice and one that detects zero cross by differentiation.

Next, the binarized signal passes through the phase synchronization circuit 29 and performs clock extraction from the data. The phase synchronization circuit 29 includes a phase comparator 30, a low pass filter (LPF) 31, and a voltage controlled oscillator 32. By the clock generated by the phase synchronization circuit 29, the binarized signal passes through the discriminator 33 for determining “1” and “0” of the data, and is converted into the user data 17 by the decoder 34. For the above recording and reproduction, in order to position the light spot at the target layer and the target position in the layer surface by the command from the host controller, defocus and track shift signal detection 35 from the optical head 22 is performed, and the compensation circuit 36 compensates for a signal optimal for servo control, and drives the light spot positioning mechanism through the drive circuit 37.
(4) Access method As a light spot positioning mechanism, a two-dimensional actuator that drives the aperture lens 8 in the layer direction and the disk radial direction, or a one-dimensional actuator that drives the aperture lens 8 only in the layer direction and the aperture lens 8 are incident. There is a combination of galvanometer mirrors that deflect the luminous flux to be deflected in the radial direction of the disk.

  Here, in the case of performing random access for data recording / reproduction described in (2), first, a method for focusing on the target layer k will be described. In order to detect the defocus signal, the size of the reflected light spot from the target layer changes depending on the defocus. Therefore, the difference between before and after shown in the publicly known examples "JP-A-62-231738, JP-A-1-19535" is described. A dynamic defocus detection method can be used. FIG. 24a shows an AF error signal 35 obtained when the position of the aperture lens is scanned in the layer direction Z with respect to the disk surface. It can be seen that the defocus error signal for each layer and the zero cross point 105 as the in-focus position are obtained in order.

  Here, FIG. 23 shows a block diagram of the first embodiment when accessing the target layer k. A sawtooth wave 106 is generated by an AF (autofocus) actuator movement signal generation circuit 93 on the rotating disk 4 to drive the AF actuator driver 91, and the aperture lens 8 is moved in the + Z direction with respect to the disk surface (the lens on the disk). In the direction of the At this time, an AF error signal 35 is obtained in the AF detection circuit 89. This signal is detected by the pull-in point determination circuit 92 at the zero-cross point 105 and notifies the AF servo system controller 94 that the focus is on a certain layer surface. In the determination circuit 92, as shown in FIG. 24a, the AF pulse 37 shown in FIG. 24b is generated based on the slice level 103 slightly shifted from the zero slice level, and the falling edge 104 is detected, so that the lens 8 immediately passes the focal point. Is sent to the controller 94.

  The controller 94 recognizes that the focus has been pulled in by a command from the host controller, and switches the switch 97 together with the input of the above timing to connect the AF servo circuit 90 to the AF actuator driver 91 to close the servo loop. In this state, the AF servo circuit 90 drives the AF actuator so that the AF error signal obtained by the AF signal detection circuit 89 is always zero. Therefore, it is possible to stably form a diffraction limit spot in a layer even if the disk 4 swings up and down during rotation.

  Next, the layer number detection circuit 95 recognizes the current layer number by reading the layer address in the preformat section shown in FIG. In the controller 94, in any direction (sign (k−j)) from the jth layer that is currently focused to the kth target layer that is a command from the host controller, how many (| k− j |) It is recognized whether the number of layers should be spot-moved, and the jump forcing signal 107 is generated in the layer jump signal generation circuit 96 and input to the AF actuator driver.

  The jump signal 107 is composed of a pair of + -polarity pulses for movement between one layer, and the + -pulse is switched depending on the vertical movement direction. The first pulse is used to drive the spot in the moving direction by the moving distance, and the next polarity inversion pulse is used to establish that the spot does not go too far. In addition, a pair of pulses of the number of moving layers is input to the driver 91. Next, the layer number is detected, and when j = k, a spot is positioned on the target layer k. When accessing other layers for random access, a layer jump may be performed as described above.

  FIG. 25 shows a block diagram of the second embodiment when accessing the target layer k.

  The diaphragm lens 8 is moved up and down with respect to the disk surface with respect to the rotating disk 4. At this time, the AF error signal 35 is obtained, and further, the total light quantity 36 detected by the photodetector 10 and outputted from the total light quantity detection circuit 102 is focused on each recording layer as shown in FIG. 24a. Sometimes has a peak. Thus, the total light amount pulse 38 for detecting the AF pulse 37 and the total light amount pulse 38 by the slicing levels 103 and 108 in the pulsing circuit 98 in the cross layer signal detection circuit 101 shown in FIG. By detecting the falling edge, the focal point can be detected more reliably. Further, in order to recognize the direction in which the lens moves with respect to the disk, the up-pulse 109 and the down-pulse 110 are generated and counted from these two kinds of pulses by the cross-layer pulse generator 99, so You can recognize whether it is positioned in a layer.

  In FIG. 25, a sawtooth wave is generated from the AF actuator movement signal generation circuit 93 so that the focal position moves at least from the uppermost layer of the disc to the lowermost layer, and the AF actuator is driven. At this time, it is certain that it is sufficiently larger than the vertical deflection of the rotating disk. From the cross layer signal detection circuit 101, the focal points of N layers are counted, and the uppermost layer (n = 1) or the lens is moved downward from the upper limit of the up pulse 109 when the lens is moved upward. The lowest layer (n = N) is recognized from the lower limit of the down pulse 110 at the time. In response to a command from the host controller, the switch 100 may be switched immediately before the spot is focused on the target layer in order to close the servo loop. By controlling in this way, layer access can be performed without providing a layer address.

  By the way, when a medium whose transmittance and reflectance change by recording is used, the AF error signal and the total light amount are different from those in FIG. 25 in the vicinity of the recorded layer, as shown in FIG. , 124 are obtained. This indicates that the amount of light changes when the spot scans the portion where the mark exists, and the amount of light returns to the normal value when the spot is applied to the portion where the mark does not exist. As described above, since the signal fluctuates, the signal in the servo band also deteriorates, the AF servo system gain fluctuates and the AF offset occurs, and defocus occurs in the recorded layer. In such a case, the ideal AF error signal and the total light amount shown in FIG. 26 are obtained by always holding the signal of the portion where the mark is not recorded among the signal components detected on the photodetector. It is done.

  An example of this method is shown in FIG. This figure shows the AF detection circuit 89 and the total light quantity detection circuit 102 in FIGS. The front and rear photodetectors 111 and 112 in the principle diagram of the front and rear differential AF error signal detection optical system include light receiving surfaces 119 and 120 or 121 and 122, respectively. If the sizes of the light spots 113 and 114 on the front and rear light detector surfaces 111 and 112 are the same, the focal point is obtained. The sum signal for each detector is obtained by preamplifiers 115 and 116 having a band in which the spot scans the mark row, that is, a data recording / reproducing frequency band. Next, signals in the on-mark scanning portion are detected by the sample and hold circuits 117 and 118, and held during the servo band. The difference signal between the signals thus obtained is obtained as an AF error signal 35, and the sum signal as a total light quantity 36. The sample hold circuits 117 and 118 may be a peak hold for sampling the maximum point of the light amount, or an area in which no mark is recorded is provided as a sample area in advance as a format, and the sample area is recognized by a sample timing pit or the like. The signal in that area may be held.

  Here, the front-rear differential method is shown as the defocus detection method, but the astigmatism method and the image rotation method, which are other defocus detection methods, may be used.

On the other hand, after layer access to the target layer, positioning in the disk radial direction, that is, track positioning is performed on the layer surface. As shown in FIG. 20, the push-pull method, which is a well-known example, can be applied to the track deviation signal detection by providing a guide groove 39 in each layer. In this method, the diffracted light from the grooves of the layers other than the target layer is out of focus, and therefore the phase of the light wave that hits the grooves is disturbed, resulting in a uniform light quantity distribution on the photodetector. The track shift signal for the target layer is not affected. In addition, as shown in FIG. 22, a sample servo method, which is a publicly known example, can be applied by previously forming a wobble pit 40 in each track in the track direction. The spot positioning technique described above is shown in known examples "Japanese Patent Laid-Open No. 63-231738, Japanese Patent Laid-Open No. 1-19535, Japanese Patent Laid-Open No. 4-228112". The method of creating guide grooves and wobble pits on the disc will be described later.
(5) Recording Control Method Next, a recording control method that achieves the principle of the three-dimensional recording method of the present invention shown in section (1) will be described. As described in (1), in order to record stably on the k layer which is the recording target, the recording power P (light intensity) must be set in consideration of the transmittance 42 up to the k layer. Therefore, as shown in FIG. 6, the recording condition setting circuit 20 uses the address recognition 41 and the transmittance 42 up to the k layer which is the recording target. A circuit block example showing this in detail is shown in FIG. 7, and a signal example is shown in FIG.

  In FIG. 9, when the binarized signal 19 is recorded as the mark 43 on the disc, the address recognition 41 (l, m, k) is considered in consideration of the recording condition depending on the recording position and the recording state based on the data pattern. By inputting recording conditions such as recording pulse width setting and recording power setting conditions into the ROMs 44 and 45, a light intensity modulation signal P (t) 47 corresponding to the output of the D / A converter 46 is obtained. The mark in the recording state 47 can be recorded. Such a circuit configuration shown by the solid line in FIG. 7a can be applied to the following case.

  In the case of (2) (b), or in the case of (2) (a), and (2) (a) Since the transmittance 42 (ΣTn (n = 0, 1, 2,..., K−1)) is determined at the time of disc creation, if the layer address k is input, it can be handled as known.

  In cases other than the above, the transmittance 42 to the layer at the time of recording is not known. In such a case, a circuit indicated by a dotted line is added to the circuit of FIG. In the power setting ROM 45, a recording power setting value in consideration of the transmittance up to the k layer when all the layers are unrecorded is inputted.

  By the address recognition 41, the transmittance ΣTn (n = 0, 1, 2,..., K−1) up to the k layer at the time of shipment of the disc (n = 0, 1, 2,... K−1) and the transmission up to the k layer immediately before recording detected by the method described later. The rate ΣTn ′ (n = 0, 1, 2,..., K−1) 42 is input to the division circuit 47, and the change G of the transmittance is input to the gain control circuit 48 so that the optimum recording power is set. To.

  An example to which this circuit configuration can be applied is shown. (3) A third method for providing the “layer data management layer” described in section (2), reproducing and recognizing the contents before recording, and achieving the item (1) (C) When the data management in (2) Sections (c) and (d) is applied, it is known from the constant transmittance after recording in the light spot in each layer if it is known which layer is recorded. Therefore, the transmittance ΣTn ′ (n = 0, 1, 2,... K−1) 42 up to the k layer can be obtained.

  Another example is a method of obtaining a change G in transmittance by scanning a spot in advance before recording.

As a method of reproducing the area to be recorded in advance, the reproduction check is performed with the first rotation of the disk in the recording mode, the recording is performed with the next rotation, and the recording error is checked with the next rotation. The other method uses a plurality of spots as shown in FIG. Here, the latter will be described as an example. In the reproduction check, the reproduction signal C′k (t−τ) received for the preceding spot 49 is used. Here, τ is a time-converted distance between spots of the preceding spot 49 and the recording spot 51. Here, as shown in FIG. 7b, the transmittance change amount G is the difference between the reproduction signal Ck 'when focused on the k layer which is the recording target layer and the reproduction signal Ck designed at the time of shipping the disc. The square root of the ratio is obtained using the calculator 52. This is because the reproduction signal uses reflected light, and the transmittance change up to the k layer appears in the reproduction signal as a square.

However, the value of the reproduction signal Ck is set as a check area in advance as a disc format, and a non-recording area in the layer direction is provided in the disk surface, so that there are variations between disks and optical variations within the disk. It can be detected by absorption. Therefore, recording power control with high accuracy is possible. Further, as described in the first method for achieving the item (C) in section (1), the photodetector 10 that obtains the reproduction signal has the shape shown in FIG. 1 so that the reflected light from other layers can be obtained. Since the reflection component from the target layer can be detected as a reproduction signal, a more accurate transmittance change G can be obtained. As shown in FIG. 9, the recording state 53 when the gain control is not performed is different from the ideal recording state 47, but the ideal recording state is achieved by performing the recording power gain control and recording with G × P (t). 47 could be obtained.
(6) Reproduction Control Method Next, the reproduction control circuit 25 shown in FIG. 6 that achieves the reproduction method of the present invention will be described in detail. Here, in addition to the reproduction principle of reducing the interlayer crosstalk which is the first to third methods as described in the section (1), the data signal generated when the distance between the layers is further reduced to increase the density. A fourth method for suppressing the interlayer crosstalk component of the band or the interlayer crosstalk component that occurs when the optical system deviates from the ideal state will be described. In the fourth method, in addition to the detection of the reflected light component from the target layer as shown in the first method, in particular, the reflected light component from the adjacent layer occupying most of the interlayer crosstalk is also detected. The reflected light component of the target layer is extracted by removing the included component by calculation.

  Here, FIG. 17a shows an optical system. The basic configuration is the same as in FIG. 1, but the imaging surfaces of the adjacent layers (k + 1) and (k−1) on the light receiving surface side when the photodetectors 54 and 55 are focused on the k layer. Position it. However, in the arrangement of FIG. 17a, since the light is shielded from each other, half mirrors or beam splitters 56 and 57 are inserted into the imaging system as shown in FIG. 17b. The photodetectors 10, 54, and 55 have a diameter D = (λ / NAI), but a pinhole may be used as shown in FIG. 17C. The reproduction signal detected by each photodetector in this case is shown in FIG.

  Here, the reproduction signal Ck for the photodetector 10, the reproduction signal C (k−1) for the photodetector 55, and the reproduction signal C (k + 1) for the photodetector 54 are shown. A circuit for obtaining a reproduction signal is shown in FIG. However, in the system of FIG. 17, the integrating circuits 59 and 60 and the delay circuits 61 and 62 are not necessary. As shown in FIG. 14, when the distance between the adjacent layer satisfying the first to third methods is smaller than the target layer, the interlayer cross obtained when the spot 69 scans the mark array 71 on the k-layer surface. The reproduction signal 73 without talk fluctuates like the reproduction signal 72. This is because, with the scanning of the spot 69 on the surface of the k layer, the reproduction signal 64 detected by scanning the mark array 74 on the adjacent side with the spot 70 irradiated with the defocusing on the adjacent layer and the other adjacent side. This is because the component of the reproduction signal 63 for the layer is included in the reproduction signal 73 so as not to be ignored. Therefore, as shown in FIG. 13, the arithmetic circuit 66 performs the following calculation.

Ck≈CkR + β × C (k−1) R + β × C (k + 1) R
C (k−1) ≈C (k−1) R + β × CkR + β × C (k−2) R
C (k + 1) ≈C (k + 1) R + β × CkR + β × C (k + 2) R (Equation 22)
Here, CnR represents a reproduction signal component for the reflected light from only the n layer. Here, β <1 holds. From the above formula,
Operation F≡Ck−γ × C (k−1) −γ × C (k + 1)
≒ CkR + β × C (k−1) R + β × C (k + 1) R
−γ × {C (k−1) R + β × CkR + β × C (k−2) R} −γ × {C (k + 1) R + β × CkR + β × C (k + 2) R} (Equation 23)
Since C (k−2) R and C (k + 2) R are sufficiently small and have low frequency components, they can be ignored. Therefore,
F≈ (1-2γβ) × CkR + (β−γ) × C (k−1) R
+ (Β−γ) × C (k + 1) R (Equation 24)
Here, if γ≡β <1,
F≈ (1-β ² ) × CkR (Equation 25)
Thus, the crosstalk between the layers can be suppressed, and the reproduced signal 68 after the calculation matches the reproduced signal 73 as shown in FIG. An example using a plurality of spots as another configuration for achieving the fourth method will be described below. In FIG. 14, a spot 75 having the same spot diameter as the defocus spot 70 is scanned in two adjacent layers in advance of the spot 69 to obtain a reproduction signal. However, as shown in FIG. 13, delay circuits 61 and 62 corresponding to the spot interval are inserted, and the same calculation as described above is performed. An example of an optical system used for this configuration is shown in FIG. In the figure, the optical axis is divided into three parts to show the principle of the optical system, but it is also possible to use the aperture lens 8 in common. As a means for setting the spot diameters of the spots 75 and 82 focused on the preceding adjacent layer to (2d × NAF), one is to insert a stop 83 as shown in FIG. Reduce the effective aperture. That is, the effective diameter a ′ may be λ / (2d × NAF ² ) × a. Of course, the same effect can be obtained even if the numerical apertures of the aperture lenses of the preceding two optical systems are reduced by dividing the optical axis into three optical axes. That is, NAF ′ = λ / (2d × NAF).

  Up to now, the preceding spot has been limited to the spot shape 75 shown in FIG. 14, but the same effect can be obtained with, for example, the spot shape 76 shown in FIG. 15 or the three spots 77, 78, 79 shown in FIG. can get. For this purpose, integrating circuits 59 and 60 are inserted into the circuit of FIG. In FIG. 15, by integrating the reproduction signal from the preceding spot by multiplying the Gaussian distribution, which is the intensity distribution of the spot, by, for example, a weight function 80 obtained by approximating the triangular distribution, the spot 75 is effectively marked. A reproduction signal when 74 is scanned can be obtained. Also in FIG. 16, the weight function 81 may be used in consideration of the spot intensity distribution in the two-dimensional direction.

  Here, a method for obtaining β in the weight setting circuit 67 used in the arithmetic circuit will be described. As shown in FIG. 19, h (k−1) as shown in FIG. 14 is obtained by arranging the mark recording area 84 so as not to be included in the same light flux as at least the upper and lower three layers as shown in FIG. By setting / hk and h (k + 1) / h to β (−1) and β (+1), the weights for the upper and lower layers can be obtained, respectively.

In the embodiments so far, the case where recording / reproduction is basically performed for one layer has been described. However, by using a plurality of spots and focusing on each layer, recording and reproduction can be performed for two or more layers simultaneously. That is, parallel recording / reproduction is possible, and the data transfer rate can be increased. As a means for forming a plurality of spots, a plurality of optical heads 22 may be positioned on the same disk, or a plurality of light sources may be incorporated in one optical head. In addition, by using a plurality of light sources having different wavelengths, it is possible to selectively record the recording layer according to the wavelength, and further, reproduction / separation by a wavelength filter is possible.
(7) Disc Structure Example and Disc Making Method As shown in FIG. 11, the surface of a disc-shaped chemically tempered glass plate having a diameter of 130 mm and a thickness of 1.1 mm is formed by a photopolymerization method (2P method). 5 μm pitch tracking guide groove and 17 divide the circumference into 17 sectors. Prepits such as layer address, track address and sector address at the beginning of each sector in the form of uneven pits at the middle of the groove A replica substrate on which an ultraviolet curable resin layer having (this portion is referred to as a header portion) was formed.

A silicon nitride antireflection layer 402 was formed to a thickness of about 50 nm on the replica substrate 401 by using a sputtering apparatus with good uniformity and reproducibility of film thickness. Next, a recording film 403 having a composition of In ₅₄ Se ₄₃ Tl ₃ was formed to a thickness of 10 nm in the same sputtering apparatus. On this, an ultraviolet curable resin layer 404 having a tracking guide groove and pre-pits such as a layer address, a sector address, and a track address by a 2P method in which light is incident from a mold side using a transparent mold, In consideration of the heat insulation effect with the multilayer, it was formed to a thickness of 30 μm.

Subsequently, a silicon nitride antireflection layer 405 having a thickness of about 50 nm is formed in the sputtering apparatus, and a recording film 406 having a composition of In ₅₄ Se ₄₃ Tl ₃ is formed to a thickness of 10 nm. In addition, an ultraviolet curable resin layer 407 having tracking guide grooves and layer addresses, and pre-pits such as track addresses and sector addresses was formed to a thickness of 30 μm by the 2P method. Further thereon, a silicon nitride antireflection layer 408 having a thickness of about 50 nm was formed in the sputtering apparatus, and a recording film 409 having a composition of In54Se43Tl3 was formed to a thickness of 10 nm.

Similarly, on another similar replica substrate 401 ′, a silicon nitride antireflection layer 402 ′, an In ₅₄ Se ₄₃ Tl ₃ recording film 403 ′, an ultraviolet curable resin layer 404 ′, a silicon nitride antireflection layer 405 ′, An In ₅₄ Se ₄₃ Tl ₃ recording film 406 ′, an ultraviolet curable resin layer 407 ′, a silicon nitride antireflection layer 408 ′, and an In ₅₄ Se ₄₃ Tl ₃ recording film 409 ′ were sequentially formed. The two discs thus obtained were bonded together with the adhesive layer 410 with the layers 409 and 409 'side inside. The thickness of the adhesive layer 410 is about 50 μm. By creating a disc in this way, recording and reproduction can be performed from both sides with a single disc.

  In the above example of disc creation, the guide groove 39 for push-pull tracking has been described, but the wobble pit 40 used in the sample servo method can also be created by the same method as the above-described pre-pit.

  The disk produced in this example is read out by utilizing the difference in reflectivity by changing the optical constant by causing an atomic arrangement change of the atoms constituting the recording film by laser light irradiation. The atomic arrangement change here is a phase change between crystal and amorphous.

  In the disk, immediately after the recording film is formed, the recording film constituent elements have not yet reacted sufficiently and are in an amorphous state. When this disc is used as a write-once type, the recording laser beam is irradiated here for crystallization recording, or the recording film is heated in advance by Ar laser beam irradiation or flash annealing, etc. After the reaction and crystallization, amorphous recording is performed by irradiating a recording laser beam having a high power density. Here, the range of laser power suitable for crystallization recording is a range higher than the temperature at which crystallization occurs and lower than the temperature at which amorphization occurs. Further, the range of laser power suitable for amorphization recording is a range higher than the crystallization temperature and lower than the temperature at which strong deformation or hole formation occurs. In order to use this disk as a rewritable type, the recording film is heated in advance by Ar laser irradiation or flash annealing, and each element is sufficiently reacted and crystallized. Overwriting is performed by irradiating a recording laser beam modulated with a laser power suitable for amorphization.

The disk is rotated at 1800 rpm, the semiconductor laser beam (wavelength 780 nm) is kept at a power level (1 mW) at which recording is not performed, and is condensed by a lens (NA = 0.55) in the recording head and further passed through the substrate. The recording film was irradiated and the reflected light was detected to drive the head so that the center of the light spot always coincided between the tracking groove and the groove. By using a recording track in the middle of the groove, the influence of noise generated from the groove can be avoided. While performing tracking in this way, automatic focusing is performed so that the focal point is further on the recording film, and recording / reproduction is performed. After passing the recording part, the laser power was lowered to 1 mW and tracking and autofocusing were continued. Note that tracking and automatic focusing are continued during recording. This focusing can be performed independently for each of the recording film 403 and the recording films 406 and 409 in the disk.

  The case where recording is performed from the substrate side toward the lower layer at a linear velocity of 8 m / s (rotation speed: 1800 rpm, radius: 42.5 mm) is shown. First, the recording film 403 was focused and recorded by irradiating a recording pulse of 90 ns at a recording frequency of 5.5 MHz. The recording power dependence of the reproduction signal intensity at this time is shown below.

Recording power (mW) Playback signal strength (mV)
6 30
7 100
8 160
9 210
10 250
11 280
12 300
14 310
After recording on the recording film 403, the recording film 406 was further focused and recorded. The recording power dependence of the reproduction signal intensity at this time is shown below.

Recording power (mW) Playback signal strength (mV)
7 25
8 95
9 155
10 205
11 245
12 275
13 295
15 305
After recording on the recording film 403 and the recording film 406, the recording film 409 was further focused and recorded. The recording power dependence of the reproduction signal intensity at this time is shown below.

Recording power (mW) Playback signal strength (mV)
8 20
9 90
10 150
11 200
12 240
13 270
14 290
16 300
Further, after recording a signal of 3 MHz on the recording film 403, 4 MHz on the recording film 406, and 5 MHz on the recording film 409, the reproduction signal is read out by focusing on the recording films 403, 406, and 409. .

  The reproduction signal is shown by a measurement result of a CN ratio (noise component to carrier component ratio) at each carrier frequency with a resolution frequency width of 30 kHz as a measurement condition using a spectrum analyzer.

3MHz 4MHz 5MHz
Recording film 403 55 dB 23 dB 6 dB
Recording film 406 25 dB 53 dB 21 dB
Recording film 409 10 dB 23 dB 51 dB
As described above, for each layer, a signal with a CN ratio of 50 dB or more and an interlayer crosstalk from the adjacent recording film of less than −25 dB, which can be reproduced with high reliability, can be obtained.

Next, a thin film having a composition of Ge ₁₄ Sb ₂₉ Te ₅₇ is formed as a recording film 403, 406 and 409 to a thickness of 2 nm, and a thin film of ZnS is formed as an antireflection layer 402, 405 and 408 to a thickness of 50 nm. The other discs having the same structure as the above-described disc were produced. This disc has a feature that the transmittance of the layer after recording is lowered. Therefore, by recording from the layer on the substrate side, the disk having the above configuration is recorded in order from the lower layer to the upper layer on the substrate side at a linear velocity of 8 m / s (rotation speed 1800 rpm, radius 42.5 mm). Show. First, the recording film 409 was focused and recorded by irradiating a recording pulse of 90 ns at a recording frequency of 5.5 MHz. The recording power dependence of the reproduction signal intensity at this time is shown below.

Recording power (mW) Playback signal strength (mV)
7 15
8 85
9 145
10 195
11 235
12 265
13 285
15 295
After recording on the recording film 409, the recording film 406 was further focused and recorded. The recording power dependence of the reproduction signal intensity at this time is shown below.

Recording power (mW) Playback signal strength (mV)
7.5 20
8.5 90
9.5 150
10.5 200
11.5 240
12.5 270
13.5 290
15.5 300
After recording on the recording film 409 and the recording film 406, the recording film 403 was further focused and recorded. The recording power dependence of the reproduction signal intensity at this time is shown below.

Recording power (mW) Playback signal strength (mV)
8 25
9 95
10 155
11 205
12 245
13 275
14 295
16 305
Further, after recording a signal of 5 MHz on the recording film 409, 4 MHz on the recording film 406, and 3 MHz on the recording film 403, respectively, the CN at each carrier frequency of the reproduction signal read out by focusing on the recording films 403, 406, and 409 The ratio measurement results are shown below.

3MHz 4MHz 5MHz
Recording film 403 54 dB 24 dB 7 dB
Recording film 406 26 dB 52 dB 22 dB
Recording film 409 11 dB 24 dB 50 dB
As described above, for each layer, a signal with a CN ratio of 50 dB or more and an interlayer crosstalk from the adjacent recording film of less than −25 dB, which can be reproduced with high reliability, can be obtained.

  Similar results were obtained when a plastic disk such as polycarbonate and acrylic resin produced by injection molding was used as the substrate in addition to the chemically strengthened glass disk used in the above examples.

  As the recording film composition, in addition to the above In-Se-Tl system, Ge-Sb-Te system, Ge-Sb-Te-M (M is a metal element) system, In-Sb-Te system, In-Sb- Similar results can be obtained using Se, In—Se, In—Se—M (M is a metal element), Ga—Sb, Sn—Sb—Se, Sn—Sb—Se—Te, etc. Is obtained.

  Similar results can be obtained by using an In—Sb system or the like using a crystal or intercrystalline phase change in addition to the crystal or amorphous phase change as the recording film.

A recording film was prepared by spin-coating a 20-nm-diameter Bi-substituted garnet (YIG (Y ₃ Bi ₃ Fe ₁₀ O ₂₄ )) particle dispersed in an organic binder on the same substrate as in FIG. A Bi-substituted garnet having a diameter of 20 nm was prepared by a coprecipitation method, and then crystallized by heat treatment at 600 to 800 ° C. An organic binder having a refractive index of 25 was used. The film thickness of the spin-coated recording film was about 1.5 μm, and the reflectance, transmittance, and absorptance were R = 8%, T = 12%, and K = 80% at a wavelength of 530 nm, respectively. Since the volume ratio of the Bi-substituted garnet in the binder was about 60%, the rotation angle of the polarization plane of the reflected light at this time was about 0.8 degrees. The method of stacking multiple layers with an ultraviolet curable resin layer in between, the method of laminating two discs, and the recording / reproducing method were the same as in the previous embodiment. However, the wavelength of the light source is λ = 530 nm.

  An example of a recording / reproducing experiment using the information recording medium having the configuration shown in FIG. 12 will be described. FIG. 12A is a diagram showing a part of a cross-sectional view of the information recording medium, and FIG. 12B is a diagram showing a cross-sectional view of the recording layer portion.

On a disk-shaped glass substrate (411) having a diameter of 13 cm and a thickness of 1.2 mm, a laser light guide groove having a track pitch of 1.5 μm was formed by an ultraviolet curable resin layer (412) having a thickness of 50 μm. Next, the recording layer (413) was laminated by a vacuum evaporation method. As shown in FIG. 10B, the recording layer has a structure in which an Sb ₂ Se ₃ layer (414) having a thickness of 8 μm and a Bi layer (415) having a thickness of 3 μm are sandwiched. Further thereon, two sets of a 30 μm-thick UV curable resin layer (412) provided with a laser beam guide groove and a recording layer (413) were laminated. That is, three recording layers were provided. An ultraviolet curable resin layer having a thickness of 100 μm was provided on the top for the purpose of protecting the recording layer. The recording layers are referred to as a first recording layer, a second recording layer, and a third recording layer in order from the side closer to the substrate.

  Here, the track groove was U-shaped, and the width of each of the land portion and the groove portion was 0.75 μm. Recording may be performed on either the land portion or the groove portion, but in the case of this example, recording was performed on the groove portion.

  When the recording layer was irradiated with a 2.0 mW laser beam in focus and the reflectance was measured, the reflectance of the first recording layer, the second recording layer, and the third recording layer before recording was 8. It was 5%, 5.8%, and 4.4%. Recording was performed by irradiating each recording layer with a laser beam of 6.0 mW or more. The reflectances of the portions of the first recording layer, the second recording layer, and the third recording layer irradiated with the recording laser light were 18.5%, 13.0%, and 9.4%, respectively.

The reason why the reflectance of the recording layer changes before and after recording is due to alloying of the recording layer. That is, when a part of the recording layer composed of three layers of Sb ₂ Se ₃ and Bi is heated by irradiation of the recording laser beam, a diffusion reaction of Se and Bi occurs and alloying occurs. As a result, regions having different optical constants, that is, recording points are formed in the recording layer. In the case of the recording layer made of Sb ₂ Se ₃ and Bi used in this example, both the reflectance and the transmittance increase due to the alloying, and the absorption rate decreases.

Although not performed in this embodiment, if the land portion is irradiated with continuous laser light before recording, the land portion is alloyed, and the average light transmittance per recording layer increases by 10%. Accordingly, the reflectance before and after recording increases as described above, which is convenient when performing tracking or the like. Further, even when recording is performed on both the land portion and the groove portion, the average light transmittance per recording layer can be similarly increased. The recording layer is not limited to the combination of Sb ₂ Se ₃ and Bi, and may be a combination that produces an alloy by raising the temperature.

The figure which shows the principle of the recording / reproducing system of this invention (The principle figure of a 1st reproducing system). In the basic optical system configuration diagram applied to the present invention, a is an example of a parallel optical system, and b is an example of a diffusion optical system. FIG. 2 is a diagram illustrating the principle of the recording method of the present invention, in which a is a diagram showing the light intensity in each layer, b is a diagram showing the spot surface density in other layers when the focus is on the k layer, and c is the focus on the k layer. The figure which shows the power density in the other layer about the case where these are match | combined. The principle diagram of the second and third reproduction systems of the present invention. The figure which shows an example of the disk format of this invention. The whole block diagram of the three-dimensional recording / reproducing apparatus of this invention. FIG. 3 is a block diagram illustrating a recording control method of the present invention. The figure which shows RBW (Read Before Write) by a preceding beam. The figure explaining the recording control method of this invention. A diagram showing an example of a three-layer film structure and recording characteristics, a is an example of a three-layer film structure, and b is a recording characteristic. 1 is a cross-sectional view showing the structure of a phase change information recording medium used in an embodiment of the present invention. The fragmentary sectional view of the 3rd information recording medium used for this invention. The block diagram which shows the reproduction | regeneration control method of this invention. The figure explaining the reproduction | regeneration control method of this invention. The figure explaining the reproduction | regeneration control method of this invention. The figure explaining the reproduction | regeneration control method of this invention. An example of an optical system for realizing the reproduction control method of the present invention, a is a principle diagram of the optical system, and b is an actual optical system. An example of the optical system for implement | achieving the reproduction | regeneration control method of this invention. Calculation coefficient γ (≡β) check area and principle diagram. A disc structure for realizing the third reproducing method of the present invention. An example in which a two-dimensional recording / reproducing method is applied. An example in which a two-dimensional recording / reproducing method is applied. The block diagram explaining the layer access in this invention. The figure which shows the focus shift detection in each layer. The block diagram explaining the layer access in this invention. The figure which shows the focus shift detection in the recorded layer, a is a focus shift signal in the recorded layer, b is a figure which shows the focus shift detection of this invention. Explanatory drawing of the method of reducing the interference of the reflected light between the adjacent layers of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Recording layer, 2 ... Intermediate layer, 3 ... Substrate, 4 ... Disc, 5 ... Semiconductor laser, 8 ... Aperture lens, 9 ... Image lens, 10 ... Photo detector, 11 ... Light spot, 12 ... Focal plane, 13 ... optical characteristic function without aberration for the target layer, 14 ... optical characteristic function for the adjacent layer, 15 ... direction in which the characteristic function changes when defocus increases, 16 ... frequency characteristics of the AGC, 20 ... recording Condition setting circuit, 23, 24 ... reproduction signal, 25 ... reset control circuit, 26 ... AGC circuit, 35 ... AF error signal, 36 ... total light quantity, 39 ... guide groove, 40 ... wobble pit, 41 ... address recognition, 42 ... Transmission up to k layer, 43 ... Mark, 44, 45 ... ROM, 46 ... D / A converter, 47 ... Mark in ideal recording state, 49 ... Preceding spot, 51 ... Spot for recording, 52 ... Calculation , 53 ... GAINCO Recording state when no troll is performed, 54, 55 ... photodetector, 56, 57 ... beam splitter, 59, 60 ... integration circuit, 61, 62 ... delay circuit, 63, 64, 68 ... reproduction signal, 67 ... Weight setting circuit, 69... Spot focused on k layer surface, 71... Mark arrangement on k layer surface, 72, 73... Reproduction signal, 74... Mark row, 75, 76, 77, 78, 79, 82. 80, 81 ... weight function, 83 ... stop, 84 ... mark recording area, 86 ... power spectrum of modulation signal when using 2-7 modulation method, 87 ... using EFM modulation method Modulation spectrum power spectrum, 88 ... spectrum break point, 91 ... AF actuator movement signal generation circuit, 92 ... pull-in point determination circuit, 95 ... layer number detection circuit, 100 ... switch, DESCRIPTION OF SYMBOLS 01 ... Cross layer signal detection circuit, 103 ... Slice level, 105 ... Zero cross point, 109 ... Up pulse, 110 ... Down pulse, 111, 112 ... Photo detector, 113, 114 ... Light spot in front and back photo detector surface, 115, 116 ... Preamplifier, 117, 118 ... Sample and hold circuit, 119, 120, 121, 122 ... Light receiving surface, 123 ... AF error signal in the vicinity of the recorded layer, 124 ... Total in the vicinity of the recorded layer Light quantity, 401, 401 ′, replica substrate, 402, 402 ′, 405, 405 ′, 408, 408 ′, antireflection layer, 403, 403 ′, 406, 406 ′, 409, 409 ′, recording film, 404, 404 ', 407, 407' ... UV curable resin layer, 410 ... Adhesive layer, 411 ... Glass substrate, 412 ... UV curable resin layer, 413 ... Rokuso, 414 ... Sb ₂ Se ₃ layer, 415 ... Bi layer.

Claims (3)

Focusing a light spot on a first recording layer of a medium having a plurality of recording layers on which information is recorded;
Reading the address of the first layer converging the spot with the light;
Designating a second layer different from the first layer;
Recognizing the number of light spot moving layers and the moving direction from the first layer to the second layer, and generating a signal;
Inputting the signal into a means for moving a light spot;
Moving the light spot based on the input signal,
2. The layer access method according to claim 1, wherein the signal is composed of a pair of pulses having different polarities with respect to movement of the plurality of recording layers of the light spot, and the polarity is switched depending on a moving direction. In a layer access method for converging a light spot on a first layer of a medium having a plurality of recording layers on which information is recorded,
Generating a sawtooth wave from a movement signal generating circuit of the light spot moving means and driving the light spot moving means so that the focal position of the light spot moves from the uppermost layer to the lowermost layer of the recording medium. A layer access method characterized by the above. In an information recording method for recording information by irradiating a light spot on a first recording layer of a medium in which a plurality of recording layers are laminated, in the order from the top layer to the bottom layer of the plurality of recording layers or from the bottom layer to the top layer An information recording method, wherein information is recorded by moving a light spot in the following order.

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