JP2004213884A - Method for accessing layer and method for recording or reproducing information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high density by using a three-dimensional recording and reproducing method. <P>SOLUTION: A three-dimensional information recording and reproducing device has a recording medium 4 obtained by laminating a plurality of recording layers 1 on a substrate 3 and an optical system for focusing light from the substrate 3 side on each of the plurality of recording layers 1 and recording or reproducing information three-dimensionally. In the three-dimensional recording and reproducing device, λ/4≤(1/8NB)(1/NB<SP>2</SP>-1)NAF<SP>4</SP>Δd, wherein λ: wavelength of light, NB: refractive index of the substrate 3, NAF: the number of apertures of a narrowing-down lens 8 for focusing light, and Δd: a positional range in the direction of an optical axis where there are recording layers on which light should be focused is satisfied. By narrowing down a light spot to each layer of a disk with a multilayer film structure, data can be recorded and reproduced with high density and with high reliability. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

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

  A method for increasing the recording density of an optical information recording / reproducing apparatus has conventionally 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 device, and there is a limit in increasing the density on a plane.

JP-A-59-127237

JP-A-60-202545 JP-A-60-202554 JP-A-63-231738 JP-A-1-19535

  Therefore, a three-dimensional recording / reproducing method including the depth direction is indispensable as a method for achieving higher density. In three-dimensional recording / reproducing, there is a means for providing a multi-layered disk, narrowing a light spot on each layer, and recording / reproducing data, as shown in a well-known example of Japanese Patent Application Laid-Open No. 59-127237. However, in this known example, no specific disc structure and optical constants are specified, and further, a method of setting recording conditions is not described, and it is difficult to perform reliable recording. Also, 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, the known examples “JP-A-60-202545” and “JP-A-60-202554” describe a method for adjusting the film thickness and focusing for forming a diffraction-limited light spot on each layer. However, there is no clear provision for the former. In the latter, the principle of focusing is described, but the access method for actually focusing on the target layer is not described. Further, as a disc making method, a guide groove for tracking is impossible in a known example, and a method of performing laser exposure for each layer is shown. However, this method has no productivity.

  SUMMARY OF THE INVENTION It is an object of the present invention to study an optical spot focusing optical system, a disc structure, and a photodetection optical system capable of stably recording and reproducing in a recording process and a reproducing process. A method, a crosstalk canceling method, a three-dimensional data format, a disk creation method accompanying the three-dimensional data format, and a three-dimensional access method are to be examined.

In order to solve the above problems,
Recording film layer whose optical properties are locally changed by local light irradiation, and anti-reflection, multiple reflection, light absorption, transfer of optical local change of recording film layer, heat insulation to assist the function of the recording film layer , A disk in which layers for the purpose of heat absorption, heat generation or reinforcement, or an intermediate layer film which is a superposition of layers are stacked in multiple layers on an optically transparent substrate, and irradiated with a light spot focused on each layer By changing the local optical properties of each layer two-dimensionally (independently), recording corresponding to the modulated data "1" and "0" is performed. Further, in a three-dimensional recording / reproducing apparatus for reproducing data by detecting a change in the local optical property as a change in reflected light amount (or transmitted light amount) by irradiating each layer with a light spot,
1. The structure of the disk is such that the optically transparent substrate has a refractive index of NB and a thickness of d0. Further, the intermediate layer and the recording film layer are divided as one layer, and 1 to N layers are allocated in order from the upper layer. The distance between the respective layers is indicated by the distance dk between the kth and (k-1) th film thickness centers of the adjacent recording film layers. Further, the film thicknesses of the arbitrary k-th recording layer and the 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 the change of the local optical property on the plane of each layer. The focusing optical system uses, for example, a semiconductor laser having a wavelength of λ [μm] as a light source, converts the light into parallel light by a collimating lens, and causes the light to enter the focusing 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 electric 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 light receiving surface diameter of the photodetector is D, the k-th layer is the target layer, and the reflected light from the target layer when 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 the light receiving optical system Next, the spot diameter U (k ± 1) ′ at the focal plane from the adjacent layer (k ± 1) th layer away 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 equation, the diameter D of the photodetector is
D = Uk ′ = λ / NAI,
The detected amount of reflected light from other layers is represented by 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 by 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 the optical system are set so that the above equation holds.
2. Further, the minimum value bmin of the two-dimensional cycle b is set to (λ / NAF), and the maximum value bmax of the two-dimensional cycle 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 plane for recording and reproduction and in the adjacent layer plane separated by an optical distance d [μm]. 4) are shown by straight lines 13 and 14 in FIG.

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

In the disk structure of the above, the spherical aberration amount W40 is as follows: W40 = | (1 / (8 × NB)) × ((1 / NB ² ) −1) × NAF ⁴ × Δd | (Equation 3)

The thickness dk of the intermediate layer of each layer and the total number N are combined so that W40 ≦ λ / 4. Note that the absolute value of the right side of W40 is usually negative (when NB ≧ 1).
5. Further, the optical constants of the k-th recording film layer 1 are assumed to be transmittance Tk, reflectance Rk, and absorptance Ak. Here, the relationship of Tk + Rk + Ak = 1 holds. The optical constant when the local optical property is changed by the recording is hereinafter represented by a dash “′”. In general, an energy threshold Eth [nJ] always exists for a thermal structural change to occur in thermal recording. A light spot focused on the recording target layer at the diffraction limit scans the disk at a linear velocity V [m / s].

In order to locally cause 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 value Ith [mW / μm ² ] for the recording film of each layer is set.

Regarding the light intensity density Ik at the k-th layer when focusing on the k-th layer, the spot diameter is λ / NAF.
Sk; 1 / e ² spot area when focusing on the k layer Sk = π (0.5 × λ / NAF) ²
The light intensity Pk [mW] in the k-th layer is

δk is the transmittance between the light incident surface on the disk and the k-th recording layer.

Here, Tn: transmittance of n layers (transmittance of one layer when n = 0)
From equation (6), the minimum recording power Pmin required for recording on the k-th layer is:
Pmin ≧ Ikth × Sk / δk (Equation 7)
In addition, since recording is performed on the k-th layer, the light intensity density Ijk [mW] at the j-th layer when focusing on the k-th layer is as follows.

It is.

    When recording is performed on the k-th layer, the upper limit Pmax of the recording power is given by the following equation because the recording is not destroyed on the j-th layer.

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

dn; nth layer thickness TANφ = a / fF ≒ NAF
The aperture optical system, the disc structure, and the recording conditions are set so that the equations (6, 7) and (9, 10, 11) are simultaneously satisfied.
6. As a role of each layer, a ROM (Read Only Memory) layer or a WOM (Write Once Memory) is provided together with a layer for recording and reproducing user data.
7. As a layer data management layer, the data state of each layer, for example, the presence / absence of data, error management, a valid data area, and the number of rewrites (overwrites) are recorded as needed.
8. In item 1, information is entered as a replacement layer in place of the layer where a recording error is detected.
9. In item 1, sectors and tracks are provided as management formats 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 before recording in the next layer.
10. Recording is performed in order from the N → k → 1 layer and the lower layer. However, in each layer, information is recorded in all user sectors and tracks before 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 recording layers 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, and the sector in all layers is filled. The data of the next sector is recorded.
13. In this track, random access is performed in the layer direction. In this case, variable-length blocks are applied instead of fixed block management by sectors.
14． In item 1, as a light spot positioning mechanism, a two-dimensional actuator that drives a stop lens in a layer direction and a disk radial direction, or a one-dimensional actuator that drives a stop lens only in a layer direction and a light beam that enters the stop lens in a disk radius In the combination of the galvanomirror that deflects in the direction, the layer number detection circuit recognizes the number of the current layer by reading the layer address in the preformat section, and starts from the j-th layer that is currently focused. Recognize how many (| kj |) layers should be spot-moved in the upper or lower (sign (k-j)) direction up to the k-th target layer, which is a command from the host controller. Then, a jump forcing signal is generated in the layer jump signal generating circuit, and the AF actuator driver is generated. To be input to the server.
15. In the item 14, the jump signal is composed of a pair of pulses of + -polarity pulse for the movement between one layer, and the +-and --pulses are switched according to the vertical movement direction. The first pulse is used to drive the spot in the direction of movement by the moving distance, and the next polarity inversion pulse is used to stabilize the spot so as not to go too far. Also, a pair of pulses of the number of layers to be moved is input to the driver circuit. Next, the layer number is detected, and it is confirmed that j = k.
16. In Item 14, a cross-layer signal detection circuit is provided for detecting a focus point 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 above-mentioned zero-cross pulse and total light amount pulse and two kinds of pulses, it is always recognized in which layer the lens is positioned, and the lens is positioned on the disk with respect to the disk. Recognize the direction of movement.
18. Item 14. In the case where a sawtooth wave is generated from the AF actuator movement signal generation circuit and the AF actuator is driven so that the focal position moves at least from the uppermost layer of the disk to the lowermost layer, the cross layer signal detection circuit The focal point of the N layers is counted, and from the upper limit of the up pulse when the lens is moved upward, from the lower limit of the down pulse when the lens is moved to the uppermost layer (n = 1) or the lens is moved downward. , The lowermost layer (n = N), 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 as a recording target, the recording power P (light intensity) is considered in consideration of the transmittance (透過 Tn (n = 0, 1, 2,..., K−1)) up to the k layer. ) Is set.
20. In item 5, the transmittance up to the k-th layer is set for the layer address recognition.
21. By the address recognition, the transmittance ΣTn (n = 0, 1, 2,..., K−1) up to the k layer when the disk is shipped (or the design value) and the transmittance ΣT′n (n = 0, 1, 2,..., K-1), that is, the recording power is set in consideration of the transmittance change G.
22. In items 6 and 21, a management layer for 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), and the transmittance change G is recognized.
23. In item 21, before recording on the target layer, an area to be recorded is reproduced in advance, and a change G in transmittance is obtained.
24. In item 23, as a method of reproducing an area to be recorded in advance, a reproduction check is performed in the first rotation of the disc in the recording mode, recording is performed in the next rotation, and a recording error check is performed in the next rotation.
25. In item 23, the reproduction check is performed on the preceding spot using a plurality of spots.
26. In the item 25, in the reproduction check, the received reproduction signal C′k (t−τ) for the preceding spot is used. Here, τ is a time conversion of the distance between the preceding spot and the spot for recording. Here, the transmittance change G is obtained as the square root of the ratio of the reproduction signal Ck ′ in a state where the focus is on the k-th layer which is the recording target layer and the reproduction signal Ck designed at the time of shipping the disc.
27. In the item 25, in the reproduction check, the value of the reproduction signal Ck is set in advance as a check area as a disc format in an area not recorded in the layer direction on the disc surface.
28. In a twenty-third aspect, a photodetector for obtaining a reproduced signal has the same shape as that of the first aspect.
29. In item 1, as a reproduction control circuit, in addition to detecting a reflected light component from the target layer, a reflected light component from an adjacent layer that occupies most of the interlayer crosstalk is also detected, and a component included in both is calculated. Get rid of.
30. In item 29, the three photodetectors are positioned on the imaging plane of the target layer k and the adjacent layers (k + 1) and (k-1) on the light receiving surface side when focusing on the k layer. The shape of the photodetector has a diameter D = (λ / NAI), or the light receiving area is limited by a pinhole, and the reproduction signal Ck of the k-th photodetector and the light of the (k−1) layer The following calculation is performed on the reproduced signal C (k-1) for the detector and the reproduced signal C (k + 1) for the (k + 1) layer photodetector.

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 component included in each signal to the required signal component 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 arithmetic coefficient γ≡β <1,
F ≒ (1-β ² ) × CkR
By using the calculation function of the above equation, only the signal component of the target layer is obtained.
31. In section 29, a plurality of spots are used. A spot having the same spot diameter as the defocus spot on the adjacent layer when focusing on the k-th layer is scanned on two adjacent layers prior to the spot, a reproduction signal is obtained, 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 stop lens. That is, the effective diameter a ′ is set to [λ / (2d × NAF ² ) × a].
33. In the term 31, the numerical apertures of the aperture lenses of the two preceding optical systems are divided into three optical axes, that is, NAF ′ = λ / (2d × NAF).
34. In the term 31, integration is performed by multiplying a reproduction signal from the preceding spot by a weight function obtained by approximating a Gaussian distribution, which is a spot intensity distribution, to a triangular distribution. 35. In item 30, in the weight setting circuit for setting each operation coefficient γ (≡β), as a disk format, mark recording areas between at least three upper and lower layers are arranged so as not to be included in the same light flux, and h (k Let -1) / hk, h (k + 1) / h be β (-1), β (+1).
36. In Item 1, recording and reproduction are performed simultaneously on two or more layers by using a plurality of spots and focusing on each layer, that is, parallel recording and reproduction is performed.
37. In Item 9, a recording medium whose transmittance increases after recording is used.
38. In item 1, pre-pits such as guide grooves and addresses in each layer surface of the multilayer disc are provided in the ultraviolet curing resin layer for each layer, and a transparent mold is used for each layer, and light is incident from the mold surface using a 2P method. Form.
39. In Item 1, a quarter-wave plate layer is provided as an intermediate layer.

  The above means operates as follows.

Recording film layer whose optical properties are locally changed by local light irradiation, and anti-reflection, multiple reflection, light absorption, transfer of optical local change of recording film layer, heat insulation to assist the function of the recording film layer , A disk in which layers for the purpose of heat absorption, heat generation or reinforcement, or an intermediate layer film which is a superposition of layers are stacked in multiple layers on an optically transparent substrate, and irradiated with a light spot focused on each layer By changing the local optical properties of each layer two-dimensionally (independently), recording corresponding to the data "1" and "0" after modulation is performed. In a three-dimensional recording / reproducing apparatus that detects a change in reflected light amount (or transmitted light amount) by irradiating a light spot on each layer and reproduces data,
1. The structure of the disk is such that the optically transparent substrate has a refractive index of NB and a thickness of d0. Further, the intermediate layer and the recording film layer are divided as one layer, and 1 to N layers are allocated in order from the upper layer. The distance between the respective layers is indicated by the distance dk between the kth and (k-1) th film thickness centers of the adjacent recording film layers. Further, the film thicknesses of the arbitrary k-th recording layer and the 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 the change of the local optical property on the plane of each layer. The focusing optical system uses, for example, a semiconductor laser having a wavelength of λ [μm] as a light source, converts the light into parallel light by a collimating lens, and causes the light to enter the focusing 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 electric 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 light receiving surface diameter of the photodetector is D, the k-th layer is the target layer, and the reflected light from the target layer when focused is imaged at the focal position of the image lens. The spot diameter Uk 'of
Uk ′ = λ / NAI = λ × (fI / a) (Equation 14)
m; Lateral magnification of the light receiving optical system Next, the spot diameter U (k ± 1) ′ at the focal plane from the adjacent layer (k ± 1) th layer away 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 set as D = Uk ′ = λ / NAI, and the amount of reflected light from another layer to be detected is the transmittance δjk between the target k layer and another j layer, and the reflection. Assuming that the amount of light received and reflected from the n-layer by the photodetector is In as the ratio αjk of the ratio

(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 disc 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 cycle b is set to (λ / NAF), and the maximum value bmax of the two-dimensional cycle b is set to be smaller than (d × NAF).

    Further, 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 plane for recording and reproduction and in the adjacent layer plane separated by an optical distance d [μm]. 4) are shown by straight lines 13 and 14 in FIG.

Here, S is a normalized spatial frequency. Here, regarding the optical characteristic function H1 (S) in the case where defocus occurs at the value of the interlayer distance d, the maximum of the period b is larger than the S where H1 (S) = 0. Specify the repetition bmax. In this manner, by defining the relationship between the period b of the local optical property change on the layer surface, the disk structure, and the light receiving optical system, the component of interlayer crosstalk can be calculated from the period b of the local optical property change. 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) area included in the spot diameter (2d × NAF) area in the adjacent layer is always a constant value. The crosstalk component from the adjacent layer, which is sometimes included, is set to a constant DC component value, and only the signal component of the target layer is extracted by removing the DC component.
4. In item 1,
dk = dF (k-1) + dMk + dFk
≒ dMk (Equation 1)
In addition, it is assumed that the effective refractive index NMk of the intermediate layer is the same as the refractive index NB of the substrate. The thickness d up to the Nth layer of the multilayer disc is

In the disk structure of the above, the spherical aberration amount W40 is as follows: W40 = | (1 / (8 × NB)) × ((1 / NB ² ) −1) × NAF ⁴ × Δd | (Equation 3)

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

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

Regarding the light intensity density Ik at the k-th layer when focusing on the k-th layer, the spot diameter is λ / NAF.
Sk; 1 / e ² spot area when focusing on k layer Sk = π (0.5 × λ / NAF) ²
The light intensity Pk [mW] in the k-th layer is

  δk is the transmittance between the light incident surface on the disk and the k-th recording layer.

Here, Tn: transmittance of n layers (transmittance of one layer when n = 0)
From the above equation, the minimum recording power Pmin required for recording on the k-th layer is:
Pmin ≧ Ikth × Sk / δk (Equation 7)
Further, since recording is performed on the k-th layer, the light intensity density Ijk [mW] on the j-th layer when focusing on the k-th 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 is performed on the k-th layer, the upper limit Pmax of the recording power is given by the following equation because the recording is not destroyed on the j-th layer.

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

dn: nth layer thickness
TANφ = a / fF ≒ NAF
By setting the focusing optical system, the disc structure, and the recording conditions so that the above equations are simultaneously satisfied, 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. As a role of each layer, information other than user data is handled 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 of layer data, data status of each layer, for example, presence / absence of data, error management, a valid data area, and the number of rewrites (overwrites) are recorded as needed, thereby updating and accessing data. Perform promptly.
8. In item 1, data reliability is assured by inserting information as a replacement layer in place of the layer in which a recording error is detected.
9. In item 1, sectors and tracks are provided as management formats 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, management of user data recording and reproduction is performed by recording information in all user sectors and tracks and then recording information in the next layer.
10. Recording is performed in order from the N → k → 1 layer and the lower layer. However, in each layer, management of user data recording and reproduction is performed by recording information in all user sectors and tracks and then recording information 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 recording layers is random access, thereby managing the recording and reproduction of user data.
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, and the sector in all layers is filled. The recording and reproduction of the user data is managed by recording the data of the next sector.
13. In this track, random access is performed in the layer direction. In this case, management of user data recording / reproduction is performed by applying a variable-length block instead of managing a fixed block by a sector.
14． In item 1, as a light spot positioning mechanism, a two-dimensional actuator that drives a stop lens in a layer direction and a disk radial direction, or a one-dimensional actuator that drives a stop lens only in a layer direction and a light beam that enters the stop lens in a disk radius In the combination of the galvanomirror that deflects in the direction, the layer number detection circuit recognizes the number of the current layer by reading the layer address in the preformat section, and starts from the j-th layer that is currently focused. Recognize how many (| kj |) layers should be spot-moved in the upper or lower (sign (k-j)) direction up to the k-th target layer, which is a command from the host controller. Then, a jump forcing signal is generated in the layer jump signal generating circuit, and the AF actuator driver is generated. By input to the server, to focus on a target layer.
15. In the item 14, the jump signal is composed of a pair of pulses of + -polarity pulse for the movement between one layer, and the +-and --pulses are switched according to the vertical movement direction. The first pulse is used to drive the spot in the direction of movement by the moving distance, and the next polarity inversion pulse is used to stabilize the spot so as not to go too far. Also, a pair of pulses of the number of layers to be moved is input to the driver circuit. Next, the spot 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 for detecting the focal point detection for each recording layer using the zero-cross pulse of the AF error signal and the total light amount pulse as a gate, The signal at which the focal position crosses each layer is obtained.
17. In item 16, by generating and counting up pulses and down pulses from the above-mentioned zero-cross pulse and total light amount pulse and two kinds of pulses, it is always recognized in which layer the lens is positioned, and the lens is positioned on the disk with respect to the disk. Recognize the direction of movement.
18. Item 14. In the case where a sawtooth wave is generated from the AF actuator movement signal generation circuit and the AF actuator is driven so that the focal position moves at least from the uppermost layer of the disk to the lowermost layer, the cross layer signal detection circuit The focal point of the N layers is counted, and from the upper limit of the up pulse when the lens is moved upward, from the lower limit of the down pulse when the lens is moved to 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 disc layer direction, the layer can be accessed without providing a layer address.
19. In item 5, when recording is stably performed on the k layer as a recording target, the recording power P (light intensity) is considered in consideration of the transmittance (透過 Tn (n = 0, 1, 2,..., K−1)) up to the k layer. ), Recording is performed on the target layer under the optimum recording power condition.
20. In item 5, by setting the transmittance up to the k-th layer for layer address recognition, recording is performed on the target layer under the optimum recording power condition.
21. By the address recognition, the transmittance ΔTn (n = 0, 1, 2,..., K−1) up to the k layer at the time of disk shipment (or design value) and the transmittance ΔTn (n = 0, n) up to the k layer immediately before recording. By setting the recording power in consideration of the ratio of 1, 2,..., K−1), that is, the change G of the transmittance, the transmittance changes due to the presence of the layers recorded up to the target layer. Recording is performed under the optimum recording power condition on the target layer in consideration of the above.
22. In items 6 and 21, a management layer for 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), and by recognizing the change G in transmittance, even if the transmittance is changed due to the presence of a layer recorded in a layer up to the target layer, the change in the target layer is taken into account. Recording is performed under the optimum recording power condition.
23. In item 21, before recording on the target layer, the area to be recorded is reproduced in advance and the change G of the transmittance is obtained, whereby the transmittance changes due to the presence of the layers recorded in the layers up to the target layer. Recording is performed under the optimum recording power condition on the target layer in consideration of the above.
24. In item 23, as a method of reproducing an area to be recorded in advance, a reproduction check is performed in the first rotation of the disc in the recording mode, recording is performed in the next rotation, and a recording error check is performed in the next rotation.
25. In item 23, the rotation wait may not be performed by using a plurality of spots and performing the reproduction check at the preceding spot.
26. In claim 25, in the reproduction check, the received reproduction signal C'k (t-τ) for the preceding spot is used. Here, τ is a time conversion of the distance between the preceding spot and the spot for recording. Here, the transmittance change G is obtained as the square root of the ratio of the reproduction signal Ck 'in a state where the recording layer is focused on the k layer and the reproduction signal Ck designed at the time of shipping the disc. In the reflection optical system, a change in transmittance is obtained.
27. In the item 25, in the reproduction check, the value of the reproduction signal Ck is determined as a disc format by setting an area that is not recorded in the layer direction on the disc surface in advance as a check area, thereby allowing transmission between discs and within the disc. Reduce the effect of rate variation.
28. In claim 23, with respect to the photodetector that obtains the reproduction signal, the reflection component from the target layer is specified and detected, and the transmittance change G with higher accuracy is obtained by adopting the shape of claim 1.
29. In item 1, as a reproduction control circuit, in addition to detecting a reflected light component from the target layer, a reflected light component from an adjacent layer that occupies most of the interlayer crosstalk is also detected, and a component included in both is calculated. , The reflected light component of the target layer is extracted.
30. In item 29, the three photodetectors are positioned on the imaging plane of the target layer k and the adjacent layers (k + 1) and (k-1) on the light receiving surface side when focusing on the k layer. The shape of the photodetector has a diameter D = (λ / NAI), or the light receiving area is limited by a pinhole, and the reproduction signal Ck of the k-th photodetector and the light of the (k−1) layer The following calculation is performed on the reproduced signal C (k-1) for the detector and the reproduced signal C (k + 1) for the (k + 1) layer photodetector.

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 component included in each signal to the required signal component 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 arithmetic coefficient γ≡β <1,
F ≒ (1-β ² ) × CkR
By using the calculation function of the above equation, only the signal component of the target layer is obtained.
31. In section 29, a plurality of spots are used. A spot having the same spot diameter as the defocus spot on the adjacent layer when focused on the k-th layer is scanned on two adjacent layers in advance of the spot, a reproduction signal is obtained, and the operation of item 30 is performed. 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 stop lens. That is, by setting the effective diameter a ′ to [λ / (2d × NAF ² ) × a], the spot diameter of the preceding spot focused on the adjacent layer is set to (2d × NAF).
33. In item 31, by dividing the optical system into three optical axes and reducing the numerical aperture of the stop lenses of the two preceding optical systems, that is, by setting NAF ′ = λ / (2d × NAF), the focus on the adjacent layer is adjusted. The spot diameter of the preceding spot to be connected is set to (2d × NAF).
34. In item 31, by integrating 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, the defocus spot effectively scans the mark row. To obtain a reproduction signal when the operation is performed.
35. In item 30, in the weight setting circuit for setting each operation coefficient γ (≡β), as a disk format, mark recording areas between at least three upper and lower layers are arranged so as not to be included in the same light flux, and h (k By setting -1) / hk and h (k + 1) / h to β (-1) and β (+1), weights for the upper and lower layers are obtained, respectively.
36. In Item 1, the transfer speed is increased by simultaneously recording and reproducing two or more layers by using a plurality of spots and focusing on each layer, that is, by performing parallel recording and reproducing.
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 and high SN are achieved. Perform a specific regeneration.
38. In item 1, pre-pits such as guide grooves and addresses in each layer surface of the multilayer disc are provided in the ultraviolet curing resin layer for each layer, and a transparent mold is used for each layer, and light is incident from the mold surface using a 2P method. By forming, a guide groove for tracking and a prepit such as a layer address indicating the position of the layer are formed for each layer, and data is recorded and reproduced.
39. In item 1, by providing the quarter-wave plate layer in the intermediate layer, the polarization directions of the reflected light from the adjacent layers are different, so that interference is eliminated and crosstalk between the adjacent layers can be reduced.

  According to the present invention, an optical spot focusing optical system, a disc structure, and a photodetection optical system capable of stably recording and reproducing in a recording process and a reproducing process, and an encoding method for suppressing crosstalk between adjacent layers, which are particularly problematic, Since a talk cancellation method, a three-dimensional data format, a method for creating a disk, and a three-dimensional access method can be provided, a light spot can be narrowed down to each layer of a disk having a multilayer structure to record and reproduce data with high reliability. it can.

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

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

  In FIG. 1, the disk 4 has a structure in which the optically transparent substrate 3 has a refractive index of NB and a thickness of 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 the respective layers is indicated by the distance dk between the kth and (k-1) th film thickness centers of the adjacent recording film layers. Further, the film thicknesses of the arbitrary k-th recording layer and the 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 the change of the local optical property on the plane of each layer. The stop-down optical system uses, for example, a semiconductor laser 5 having a wavelength of λ [μm] as a light source, converts the light into parallel light by a collimator lens 6, and makes the parallel light enter a stop-down lens 8 via 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). By focusing each layer, each layer is irradiated with a diffraction-limited light spot 11.

  As for the light receiving optical system, a reflection light receiving system is shown as an example. Light reflected from the disk 4 passes through a lens 8 and is guided by a beam splitter 7 to an image lens 9 for receiving light. The change in the amount of reflected light is converted into an electric 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). The light receiving surface diameter of the photodetector 10 is D. In the present invention, the parallel optical system shown in FIG. 2A has been described as an example of the optical system. However, the same effect can be obtained with the diffusion optical system shown in FIG. 2B. Further, the same effects as those of the present invention can be obtained by a transmitted light detection system as the light receiving optical system.

In three-dimensional recording / reproducing, the first problem for performing recording / reproducing is to narrow the light spot to the diffraction limit in each layer. In a conventional optical disc, a light spot is narrowed down to a single-layer recording surface over the substrate 3 at a diffraction limit in order to protect a recording film. Then, 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 a spherical aberration does not disturb the light spot. However, in the multilayer disc 4, the influence of the film thickness of each layer cannot be ignored. For example, as shown in the well-known example "Kubota et al .: Optics, 14 (1985), Jitter analysis of eye pattern on optical disc I to V", As the number of layers increases, the spherical aberration increases, and it cannot be narrowed down to the diffraction limit. Therefore, in the present invention, a design of a stop lens and a disk structure for obtaining a light spot in a sufficient range for recording and reproduction will be described. In order to simplify the design method, it is assumed that the thickness dFk of the recording film layer 1 is sufficiently smaller than the 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 the substrate 3 in each layer. In this case, the thickness d of the multilayer disc up to the Nth layer is

It is.

  On the other hand, as the Rayleigh limit, a spherical aberration amount W40 = λ / 4 at which the peak intensity of the narrowed-down spot is guaranteed to be 80% when there is no aberration is given as an allowable value.

  The spherical aberration amount W40 caused by the change Δd in the 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 aperture lens and the disc structure are determined so that W40 ≦ λ / 4. Note that the absolute value of the right side of W40 is usually 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 a refractive index almost equal to that of glass is used as the intermediate layer, and NAF of the aperture lens 8 is set to 0.55, From the equation (3), Δd ≦ 50 μm. here,
d0 = 1.2 mm−Δd = (1.15-1.2 mm),

By combining the thickness dk of the intermediate layer of each layer and the total number N so that Δd ≦ 50 μm, the narrowing lens for the substrate thickness of 1.2 mm used for the conventional optical disk can be directly applied to the first lens. A light spot sufficient for recording / reproduction can be formed in each of the Nth layers from the first. As one combination solution, when the thickness dMk of the intermediate layer is 10 μm and the thickness dFk of the recording layer is 200 °, d0 = 1.15 mm, {dk = 10.4 μm ≒ 100 μm, and the total number N = 10 are possible.

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 condition is 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 at 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 Is Δzk = −2 / NAF ² × Wk40.

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

Next, a second problem for performing recording and reproduction is in a thermal recording process. The prescribed conditions for recording are the following two items.
(A) The recording target layer can be given a recording power density sufficient and stable for recording.
(B) When recorded on any k layers, data on other layers must not be destroyed.

  Factors can be classified into those based on light intensity and those based on heat conduction transmitted between layers. Here, the former will be described. The latter can be dealt with by giving the intermediate layer 2 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 for satisfying these two terms, first, the disk structure and the focusing optical system are optimized.

In FIG. 1, for simplicity of design, as an example, the substrate 3 and the intermediate layer 2 have a transmittance of 100%. The optical constants of the k-th recording film layer 1 are transmittance Tk, reflectance Rk, and absorptance Ak. Here, the relationship of Tk + Rk + Ak = 1 holds. Further, the optical constants when the local optical properties are changed by recording are hereinafter represented by dashes “′”. Generally, in thermal recording, the thermal structure of the recording film changes due to heat generated by light absorption of the recording film and a temperature rise governed by a thermal diffusion phenomenon using the heat as a heat source. This corresponds to movement of the recording film due to melting in a perforated recording medium, crystallization and amorphization in a phase change recording medium, and reversal of perpendicular magnetization in a magneto-optical recording medium. This thermal structural change results in a local optical characteristic change. Regardless of the type of recording film, an energy threshold value Eth [nJ] always exists in order for a thermal structural change to occur. In the recording process, the light spot 11 narrowed to the diffraction limit on the recording target layer scans the disk at a linear velocity V [m / s]. The light intensity P (recording power) [mW] applied to the disk surface is modulated at time t [s] in order to locally cause a thermal structure change in response to the modulated binary signal. Here, given the linear velocity V and the irradiation time t, the energy threshold Eth can be discussed by the light intensity density threshold Ith [mW / μm ² ].

  In order to satisfy the term (A), it is preferable that the expression (5) holds for the light intensity density Ik in the k-th layer when focusing on the k-th layer.

Ik = Pk / Sk ≧ Ikth (Equation 5)
Ikth; light intensity density threshold value in recording layer k (mW / μm ² )
Sk; 1 / e ² spot area when focusing on k layer
Sk = Π (0.5 × λ / NAF) ²
Here, 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 k-th recording layer, and Tn is the transmittance of the n-th layer (when n = 0, the transmittance is up to one layer). Pk is as shown in FIG. 3a. From Equations (5) and (6), the minimum recording power Pmin required to enable recording on the k-th layer is:
Pmin ≧ Ikth × Sk / δk (Equation 7)
In general, the light intensity becomes the lowest in the lowermost layer N, where n = 1 to N−1 is recorded, and when a medium in which the transmittance Tn is all reduced is used → Tn ′ (transmittance after recording). is there.

In order for the term (B) to be satisfied, since recording is performed on the k-th layer, the light intensity density Ijk [mW / μm ² ] on the j-th layer when focusing on the k-th layer may be obtained by (Equation 8). .

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

It is.

  When recording is performed on the k-th layer, the upper limit Pmax of the recording power is given by the following equation because the recording is not destroyed on the j-th layer.

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

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

By setting the focusing optical system, the disc structure, and the recording conditions so that the equations (5) and (8) are simultaneously satisfied, highly reliable recording can be performed in each layer. As an example, a 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 each layer are R1 = R2 = R3 = 0.1, T1 = T2 = T3 = 0.8, A1 = A2 = A3 = 0.1. The linear velocity v is 7 m / s, the irradiation time t is 100 ns to 500 ns, and the light intensity density threshold of the recording layer at this time is I1th = I2th = I3th = 2.53 (mW / μm ² ). . Here, a recordable interlayer distance d = d1 = d2 = d3 and a range of the recording power are obtained.

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

It becomes.
From (Equation 8), (Equation 9), and (Equation 11),

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

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

  4 shows a first method for achieving the item (C).

  The first method is to perform reproduction with a large SN ratio by optimizing the light receiving optical system in FIG. 1 to sufficiently reduce the amount of reflected light from portions other than the target layer, thereby reducing interlayer crosstalk. is there. In FIG. 1, as shown by the solid line, the amount of reflected light from the layer to be reproduced is all detected by a photodetector 10 placed at the focal point of the image lens 9. On the other hand, the reflected light from the adjacent layer spreads at the focal plane 12 of the image lens as shown 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 diameter at which the intensity is 1 / e ² of the peak intensity value of the light spot 11 when the k-th layer is the target layer and the light spot 11 is focused, that is, the spot diameter is Uk = (λ / NAF). Then, the reflected light from the target layer forms an image at the focal position of the image lens 9. The spot diameter Uk ′ on this focal plane 12 is
Uk ′ = mUk = m × (λ / NAF) = (NAF / NAI) × (λ / NAF) = λ / NAI = λ × (fI / a) (Equation 14)
m: Lateral magnification of the light receiving optical system Next, the spot diameter U (k ± 1) ′ at the focal plane from the (k ± 1) th layer separated from the kth target layer by the interlayer distance d is determined. The distance d ′ between the position where the reflected light from the (k ± 1) layer focuses on the image lens 9 and the focal plane is
d ′ = Y × d = m ² × d (Equation 15)
Y: vertical 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)
Assuming that the diameter D of the photodetector is D = Uk ′ = λ / NAI from the above equation, the area ratio ε = (D / U (k ± 1)) as compared with the case where the diameter of the photodetector is not limited. ') In ² , the amount of reflected light from the adjacent layer can be reduced, so that a change in the amount of reflected light from the target layer can be detected with a high SN ratio.

  In practice, 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 layers, and the reflectance ratio αjk. Here, assuming that the amount of interlayer crosstalk noise required for highly reliable signal detection is -20 dB (1/10), the following equation generally holds.

  When the amount of reflected light received from the n-layer in the photodetector 10 is In,

However, in the following, only the layer (k-1) adjacent to the target layer k is considered. Effects from other layers can be considered as well, but their values are small enough.

(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, when 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, δ23 = 1.25, than α23 = 1, inhibition rate of the amount of reflected light becomes ε × δ ² 23 × α23.

I2 / I3 = δ ² 23 × α 23 × ε = δ ² 23 × α 23 × (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 that satisfies the above equation is obtained,

Here, the influence of the crosstalk from the second layer is considered, but the effect 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 diameter of the photodetector is D = Uk ′ = λ / NAI. However, there is a degree of freedom in design such that the crosstalk between the layers has a certain value, including the displacement 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 period b of the change (mark) of the local optical property on the layer surface, the disc structure, and the light receiving optical system, and thereby to reduce the component of the interlayer crosstalk to the local optical property. It is made longer than the change cycle b. That is, data on the target layer surface is reproduced with a high SN ratio by making the frequency component of interlayer crosstalk smaller than the data signal band. The principle of this method will be described with reference to FIGS. Although the diameter of the photodetector is not limited to distinguish it from the first method, a higher SN can be obtained by using the photodetector together.

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

  Here, a decrease in optical resolution due to defocus, that is, a decrease in signal modulation degree 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 plane of a target layer for recording and reproduction and in the plane of an adjacent layer separated by an optical distance d [μm] are shown. FIG. 4 shows a straight line 13 and a straight line 14, respectively. 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 there is no aberration, the optical characteristic function H0 (S) becomes like a straight line 13. In this case, the cutoff frequency at which the optical resolution becomes zero is S = 2. In an actual recording / reproducing apparatus, noise components such as laser noise and amplifier noise are included, and further, since the optical system itself has aberrations other than defocus, the period b corresponding to the cutoff frequency S = 2 is not satisfied. , Difficult to detect. Therefore, half the modulation degree (-6 dB) is set as the allowable value of the modulation degree. At that time, S = 1, and the minimum repetition bmin of the cycle b is defined.

bmin = λ / NAF (Equation 21)
On the other hand, with respect to the optical characteristic function H1 (S) when defocus occurs at the value of the interlayer distance d, the maximum repetition bmax of the cycle 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 arrow 15 and bmax can be increased.

  As described above, the frequency component of the crosstalk from the adjacent layer is not more than fmin (= 1 / bmax), and if the auto gain control circuit having the 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, the cut-off frequency S with respect to the 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 disk having a constant track pitch of 1.5 .mu.m using a variable length code of 2-7 code in the spot scanning direction and a pit shown in a known example "JP-A-63-53722" is used. 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 = 3.76 μm ≦ bmax
The mark period in the disk radial direction is constant at a track pitch of 1.5 μm, and it is necessary that 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 fluctuates 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. It has a slight component below fmin. This can be suppressed by the filter and the AGC as described above. However, even without using such a circuit, it is possible to suppress the interlayer crosstalk noise by eliminating fluctuations in density and maintaining a constant DC component value. Can be. The principle of the third method uses a code in which the total area of the local optical change (mark) area included in the area of the spot diameter (2d × NAF) in the adjacent layer is always a constant value. By doing so, the amount of interlayer crosstalk to the reproduced signal when the spot is scanned always has a constant DC value. The third method and the first method can be used in combination.

  An example is shown. As shown in FIG. 4, the power spectrum 87 of the modulated signal in the case of using the EFM modulation method 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 at which 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 constant at 50%, and the component of the amount of reflected light 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 a case where two-dimensional recording is performed in a layer plane. The two-dimensional recording / reproducing method is disclosed in Japanese Patent Application No. Hei 3-11916, "Information Recording / Reproducing Method and Apparatus". In the prior application, as shown in FIG. 21, for example, 2 ⁴ = 16, 4-bit data is represented by a combination of using 4 grid points of 2 × 2 as one block and recording a mark at the grid point. Densify. In this case, the first and second schemes can be applied. In addition, as shown in FIG. 22, the same number of marks are always included in the grid points in the 4 × 4 grid block (one in the figure). Furthermore, if the spot diameter (2d × NAF) in the adjacent layer includes many lattice blocks, the number of marks included in the spot and the area occupied by the marks are almost constant, and the third method is applied. it can.

  By the way, in the 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 certain value dm is out of focus, the condition of the imaging system of the microscope is satisfied. In some cases, an image of the recording film surface is formed on the light receiving surface. For example, when a diffraction-limited spot is formed on the target layer to receive light, when the distance to another layer is dm, a mark array pattern on this layer is formed on the light-receiving surface, and information on the target layer is formed. There is a possibility that crosstalk noise in the signal band is added to the signal. Therefore, it is desirable to design the disk structure so that the interlayer distance does not become dm.

Also, since the light reflected from each layer has the same irradiation light, when the distance between the layers is reduced to about the coherent distance, the reflected lights interfere with each other. As a result, the crosstalk noise between the layers cannot be expressed by the ratio of the amount of light received from the target layer and the other layers on the light receiving surface. That is, because of interference, worst-case interlayer crosstalk noise appears at the square root of the received light amount ratio. This effect actually becomes a problem when between adjacent layers.

  An embodiment that solves this problem is shown in FIG. The principle of this embodiment is to prevent interference by changing the polarization direction of light reflected from an adjacent layer. As one means for changing the polarization direction, in FIG. 27, each intermediate layer 2 includes a １ ／ wavelength 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 electric field wave of light traveling in the depth direction of the layer, that is, the optical thickness in the two directions. Is changed by １ ／ wavelength. With such a disk structure, for example, as shown in the figure, when the polarization direction of the irradiation light is E-polarization, the reflected light from the layers adjacent to each other is different from the light traveling back and forth in the quarter-wave plate layer 201. That is, since they differ by a half wavelength and a phase difference of 180 degrees, the polarization directions are alternately orthogonal to the E-polarized light and the H-polarized light. Therefore, since the reflected light components between adjacent layers do not interfere with each other, the reflected light components can be represented by a simple light receiving amount ratio on the light receiving surface, and crosstalk between the layers can be reduced. Furthermore, 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, at least the reflected light from the adjacent layer is not detected, so that in the above-described first reproduction method, the allowable value of the variation in the size of the photodetector can be increased.

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, Data Management FIG. 5 shows an example of the format of the multilayer disk 4. There are 1 to n layers from the substrate 3 on which light enters, in the direction of travel of the light. The data format in the k-th layer is such that data is managed by a sector m which divides the disk on a radiation, a track 1 which manages a data position in a radial direction, and three addresses (l, m, n). As shown in the figure, the format of a given track l and sector m is as follows: recording / reproducing timing, a pre-format area in which address information is preliminarily prepared, and user data are recorded / reproduced. It consists of a data area that records and manages the prohibition of dashi. As shown in the figure, as a role of each layer, a ROM (Read Only Memory) layer or a WOM (Write Once Memory) is provided together with a layer for recording and reproducing user data, and an OS (Operating System) of an upper controller or As will be described later, conditions for recording or reproduction in each layer can be preformatted at the time of disc creation, or can be recorded at the time of shipment. Further, as a layer data management layer, the data state of each layer, for example, the presence or absence of data, error management, a valid data area, and the number of rewrites (overwrites) can be recorded as needed. Also, information can be re-entered as a replacement layer instead of the layer where the recording error was 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 before recording in the next layer.

In the case of performing the data recording, more reliable recording and reproduction can be performed by using a recording medium having a characteristic of increasing the transmittance after recording. That is, since the transmittance to the lower recording layer increases, the lower target layer can be given sufficient light intensity for recording by irradiating light intensity substantially equal to the light intensity required for recording on the upper layer. In the reproduction, the reflected light component from the target layer returns to the detector without being attenuated, so that a reproduced signal having a high SN ratio can be obtained. As a recording medium having the above characteristics, there is, for example, a perforated recording medium. By recording on this medium, a hole is formed in the reflective film, and the reflectance is reduced, that is, the transmittance is increased.
(b) Recording is performed in order from the lower layer to N → k → 1 layer. 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. The order of recording layers is random access.
(d) 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, and the sector in all layers is filled. After that, the data of the next sector is recorded.
(e) In the track, random access is performed in the layer direction. In this case, by applying a variable length block, which is data management of the magnetic disk, instead of the fixed block management by the sector, the cylinder of the magnetic disk can be made to correspond to the layer and the data format of the magnetic disk can be applied as it is.

In the random access, for example, the information recording area may be managed by the upper controller or may be managed by the above-mentioned management area so as not to access the area recorded at the time of recording by mistake.
(3) Overall Configuration of Apparatus FIG. 6 shows the overall configuration of a three-dimensional recording / reproducing apparatus. When recording, the user data 17 is passed through a modulation circuit 18 to obtain binarized data 19 after modulation. The modulated binary data passes through the recording condition setting circuit 20, and the laser driving circuit 21 is driven so that the intensity is modulated under the optimum 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, in the case of reproduction, a light spot is positioned on a target layer or track position on the disk, irradiated with weak light, 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 an AGC (auto gain control) circuit 26 after suppressing interlayer crosstalk through a reproduction control circuit 25, absorb fluctuations in frequencies lower than the data band, and operate in subsequent circuits. Match the signal to the absolute level.

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

Next, the binarized signal passes through a phase synchronization circuit 29 to extract a clock 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. The binarized signal is converted into the user data 17 by the decoder 34 through the discriminator 33 that determines data “1” and “0” by the clock generated by the phase synchronization circuit 29. In order to position the light spot at the target layer and the target position in the layer plane in accordance with a command from the host controller for the above recording / reproducing, a focus shift and track shift signal detection 35 from the optical head 22 is performed, and a compensation circuit is performed. By 36, a signal optimal for servo control is compensated, and the light spot positioning mechanism is driven through the drive circuit 37.
(4) Access Method As a light spot positioning mechanism, a two-dimensional actuator that drives the stop lens 8 in the layer direction and the disk radial direction, or a one-dimensional actuator that drives the stop lens 8 only in the layer direction and incident on the stop lens 8 There is a combination of a galvanomirror that deflects a light beam to be emitted in a disk radial direction.

  Here, in the case of performing random access for data recording and reproduction described in (2), first, a method of focusing on the target layer k will be described. In order to detect the defocus signal, the size of the light spot reflected from the target layer changes due to the defocus, so that the difference between before and after as shown in the known examples "JP-A-63-231738 and JP-A-1-19535" is known. 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, which is 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. For the rotating disk 4, a sawtooth wave 106 is generated by an AF (autofocus) actuator movement signal generation circuit 93, an AF actuator driver 91 is driven, and the aperture lens 8 is moved in the + Z direction with respect to the disk surface (the lens is mounted on the disk). In the direction in which At this time, the AF error signal 35 is obtained by the AF detection circuit 89. This signal detects the zero-cross point 105 in the pull-in point determination circuit 92 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 fall 104 is detected, so that the lens 8 passes immediately before the lens 8 passes the focal point. Is sent to the controller 94.

  The controller 94 recognizes that it is in the focus-in state by a command from the host controller, switches the switch 97 together with the input of the timing, connects the AF servo circuit 90 to the AF actuator driver 91, and closes 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, even if the disk 4 swings up and down during rotation, a diffraction-limited spot can be stably formed on a certain layer.

  Next, the layer number detection circuit 95 reads the layer address in the preformat section shown in FIG. 5 to recognize the number of the current layer, and sends it to the controller 94. In the controller 94, from the j-th layer that is currently focused to the k-th target layer, which is a command from the upper controller, in which (| sign (k−j)) direction, which (| k− j |) Recognizing whether the number of layers should be moved by a spot, the layer jump signal generation circuit 96 generates a jump compulsory signal 107, and inputs the signal to the AF actuator driver.

  The jump signal 107 is composed of a pair of pulses of plus and minus polarity pulses for movement between one layer, and the plus and minus pulses are switched according to the up and down movement direction. The first pulse is used to drive the spot in the direction of movement by approximately the moving distance, and the next polarity inversion pulse is used to set the spot so as not to go too far. Further, a pair of pulses of the number of layers to be moved is input to the driver 91. Next, when the layer number is detected and j = k, the spot is positioned on the target layer k. When accessing another layer for random access, a layer jump may be performed in the same manner as described above.

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

  The aperture lens 8 is moved up and down with respect to the rotating disk 4 with respect to the disk surface. At this time, the AF error signal 35 is obtained, and the total light amount 36 detected by the photodetector (detector) 10 and output from the total light amount detection circuit 102 is focused on each recording layer as shown in FIG. Sometimes has a peak. Therefore, the pulse generation circuit 98 in the cross-layer signal detection circuit 101 shown in FIG. 24C uses the AF pulse 37 and the total light amount pulse 38 for detecting the total light amount pulse 38 as gates by the slice levels 103 and 108, and outputs the AF pulse. By detecting the fall, more in-focus point detection is possible. Further, in order to recognize the direction in which the lens moves with respect to the disk, an up pulse 109 and a down pulse 110 are generated and counted by the cross-layer pulse generator 99 from these two types of pulses, so that the lens is always in any position. It can be recognized whether or not 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 disk to the lowermost layer, and the AF actuator is driven. At this time, it is certain that the vertical deflection amount of the rotating disk is sufficiently large. The focal point of the N layers is counted by the cross-layer signal detection circuit 101, 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 lowermost layer (n = N) is recognized from the lower limit of the down pulse 110 when it is made to operate. In response to a command from the host controller, the switch 100 may be switched just before the spot focuses on the target layer in order, and the servo loop may be closed. By controlling in this way, layer access can be made possible 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 amount of light near the recorded layer differ from the signal 123 shown in FIG. , 124 are obtained. This indicates that the light amount changes when the spot scans the portion where the mark exists, and returns to the normal value when the spot hits the portion where the mark does not exist. As described above, since the signal fluctuates, the signal in the servo band is also reduced, the gain of the AF servo system fluctuates, the AF offset occurs, and defocus occurs in the recorded layer. In such a case, among the signal components detected on the photodetector, by always holding the signal of the portion where no mark is recorded, the ideal AF error signal and the total light amount shown in FIG. 26 can be obtained. Can be

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

  Here, the front-rear differential method has been described as a method of detecting a focus shift, but other methods of detecting a focus shift, such as an astigmatism method and an image rotation method, may be used.

On the other hand, after accessing the target layer, positioning in the disk radial direction, that is, track positioning, is performed on the target layer. As shown in FIG. 20, a track shift signal can be detected by applying a push-pull method, which is a known example, by providing a guide groove 39 in each layer. In this method, since the diffracted light from the grooves of the layers other than the target layer is out of focus, the phase of the wave of the light that strikes the grooves is disturbed, so that the light amount distribution becomes uniform on the photodetector. , Does not affect the track shift signal for the target layer. In addition, as shown in FIG. 22, a wobble pit 40 is previously formed in each layer in the track direction, so that a known sample servo method can be applied. The spot positioning technique described above is shown in the well-known examples "JP-A-63-231738, JP-A-1-19535, and JP-A-4-228112". The method of creating guide grooves and wobbled pits on the disc will be described later.
(5) Recording Control Method Next, a recording control method for achieving 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 perform stable recording on the k layer as a 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-th layer as a recording target. FIG. 7 shows an example of a circuit block showing this in detail, and FIG. 9 shows an example of a signal.

  In FIG. 9, when the binarized signal 19 is recorded as the mark 43 on the disk, the address recognition 41 (l, m, k) is taken into consideration in consideration of the recording condition depending on the recording position and the recording state by 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 of the recording state 47 can be recorded. The circuit configuration shown by the solid line in FIG. 7A can be applied to the following case.

  In the case of (2) (b) or the third method for achieving the item (1) (C), and in the case of (2) (a), the target layer Since the transmittance 42 (ΣTn (n = 0, 1, 2,..., K−1)) is determined when the disc is created, it can be treated as known if the layer address k is input.

  In other cases, the transmittance 42 up to the layer at the time of recording is not known. In such a case, a circuit shown by a dotted line is added to the circuit of FIG. 7A. In the power setting ROM 45, a recording power setting value in consideration of the transmittance up to the k-th layer when all the layers are not recorded is input.

  By the address recognition 41, the transmittance ΔTn (n = 0, 1, 2,..., K−1) up to the k-th layer when the disc is shipped (or a design value) and the transmittance up to the k-th layer immediately before recording detected by a method described later. The rate .DELTA.Tn '(n = 0, 1, 2,..., K-1) 42 is input to the dividing circuit 47, and the transmittance change G is input to the gain control circuit 48 so that the optimum recording power is set. To

  One example to which this circuit configuration can be applied will be described. The third method for providing the “layer data management layer” described in the section (2), reproducing and recognizing the contents in advance before recording, and achieving the items (1) and (C) is described below. Applying and performing data management in sections (c) and (d) in section (2), if it is known which layer is recorded, it is known as a constant transmittance after recording in the light spot in each layer. Therefore, the transmittance ΔTn ′ (n = 0, 1, 2,..., K−1) 42 up to the k-th layer can be obtained.

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

As a method of reproducing an area to be recorded in advance, a reproduction check is performed in the first rotation of the disc in the recording mode, recording is performed in the next rotation, and a recording error check is performed in the next rotation. Another method is to use a plurality of spots as shown in FIG. Here, the latter will be described as an example. In the reproduction check, the received reproduction signal C′k (t−τ) for the preceding spot 49 is used. Here, τ is a time-converted distance between the spot between the preceding spot 49 and the recording spot 51. Here, as shown in FIG. 7B, the transmittance change G is calculated by comparing the reproduction signal Ck ′ in a state where the recording layer is focused on the k 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 reproduced signal uses reflected light, and the change in transmittance up to the k-th layer appears in the reproduced signal as a square.

However, the value of the reproduction signal Ck can be set to a disc format as a check area in advance by providing an area that is not recorded in the layer direction on the disc surface, so that variations between the discs and optical variations in the disc are reduced. Absorb and detect. Therefore, highly accurate recording power control becomes possible. Further, as described in the first method for achieving the item (C) in the section (1), the photodetector 10 for obtaining a reproduction signal has the shape shown in FIG. Can be reduced, and the reflected component from the target layer can be detected as a reproduction signal, so that the transmittance change G can be obtained with higher accuracy. As shown in FIG. 9, the recording state 53 when gain control is not performed is different from the ideal recording state 47. However, by performing gain control of the recording power and performing recording at G × P (t), the ideal recording state 53 is obtained. 47 could be obtained.
(6) Reproduction Control Method Next, the reproduction control circuit 25 shown in FIG. 6 for achieving the reproduction method of the present invention will be described in detail. Here, in addition to the principle of reproduction that reduces interlayer crosstalk, which is the first to third methods described in section (1), a data signal generated when the distance between layers is further reduced to achieve higher density. A fourth method for suppressing an interlayer crosstalk component in a band or an interlayer crosstalk component generated when a deviation from an ideal state of an optical system occurs 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, particularly, the reflected light component from an adjacent layer that occupies most of the interlayer crosstalk is also detected. The reflected light component of the target layer is extracted by removing the contained component by calculation.

  Here, the optical system is shown in FIG. 17A. The basic configuration is the same as that of FIG. 1, but the image planes 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-th layer. Position. However, in the arrangement shown in FIG. 17A, light is shielded from each other. Therefore, as shown in FIG. 17B, half mirrors or beam splitters 56 and 57 are inserted into the imaging system. The photodetectors 10, 54 and 55 have a diameter D = (λ / NAI), but pinholes may be used as shown in FIG. 17C. FIG. 14 shows a reproduced signal detected by each photodetector in this case.

  Here, a reproduced signal Ck for the photodetector 10, a reproduced signal C (k-1) for the photodetector 55, and a reproduced signal C (k + 1) for the photodetector 54 are shown. FIG. 13 shows a circuit for obtaining a reproduced signal. However, in the system of FIG. 17, the integration circuits 59 and 60 and the delay circuits 61 and 62 are not required. As shown in FIG. 14, when the distance between the adjacent layer and the target layer satisfying the first to third methods becomes smaller, the mark array 71 on the k-th layer is scanned by the spot 69 to form the interlayer cross. The reproduction signal 73 without talk fluctuates like the reproduction signal 72. This is because, along with the scanning of the spot 69 on the k-th layer surface, the reproduced signal 64 detected because the spot 70 irradiated with the defocus on the adjacent layer scans the mark array 74 on the adjacent layer, and the other adjacent adjacent layer. This is because the components of the reproduction signal 63 for the layer are included in the reproduction signal 73 to a considerable extent. Therefore, as shown in FIG. 13, the arithmetic circuit 66 performs the arithmetic operation of the following equation.

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 reproduced signal component of light reflected only from the n-th 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, interlayer crosstalk 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 above fourth method will be described below. In FIG. 14, a spot 75 having the same spot diameter as the defocus spot 70 is scanned on two adjacent layers prior to the spot 69 to obtain a reproduced signal. However, as shown in FIG. 13, the same calculation as described above is performed by inserting delay circuits 61 and 62 corresponding to the spot interval. FIG. 18 shows an example of an optical system used for this configuration. In the figure, the optical axis is divided into three in order to show the principle of the optical system, but it is also possible to use a common stop lens 8. As 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 set to λ / (2d × NAF ² ) × a. Of course, the same effect can be obtained even if the numerical aperture of the aperture lenses of the two preceding optical systems is reduced by dividing the optical system into three optical axes. That is, NAF ′ = λ / (2d × NAF).

  Up to now, the preceding spot is limited to the spot shape 75 shown in FIG. 14, but the same effect can be obtained by, 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 in the circuit of FIG. In FIG. 15, the spot 75 is effectively a mark train by integrating the reproduction signal from the preceding spot by multiplying the Gaussian distribution which is the spot intensity distribution by a weight function 80 obtained by approximating a triangular distribution, for example. It is possible to obtain a reproduced signal when scanning 74 is performed. Also in FIG. 16, the weighting function 81 may be used in consideration of the spot intensity distribution in the two-dimensional direction.

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

In the above embodiments, the case where recording and reproduction are basically performed on one layer has been described. However, by using a plurality of spots and focusing on each layer, recording and reproduction can be simultaneously performed on two or more layers. That is, parallel recording and reproduction can be performed, and the data transfer rate can be increased. As 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. Further, 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, it is possible to perform reproduction separation by a wavelength filter.
(7) Example of Disk Structure and Method of Making Disk As shown in FIG. 11, a disk-shaped chemically strengthened glass plate having a diameter of 130 mm and a thickness of 1.1 mm was coated on a surface of a chemically strengthened glass plate by photopolymerization (2P method). A guide groove for tracking at a pitch of 5 μm, and one circumference is divided into 17 sectors. Pre-pits such as layer addresses, track addresses and sector addresses are formed in the form of concave and convex pits at the beginning of each sector in the middle of the groove. (This portion is referred to as a header portion) to form a replica substrate having an ultraviolet curable resin layer having the same.

An anti-reflection layer 402 of silicon nitride was formed on the replica substrate 401 to a thickness of about 50 nm by using a sputtering apparatus having a uniform thickness and reproducibility. 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, a guide groove for tracking and an ultraviolet curable resin layer 404 having pre-pits such as a layer address, a sector address, and a track address are formed by a 2P method in which light is incident from the mold side using a transparent mold. It was formed to a thickness of 30 μm in consideration of the heat insulating effect with the multilayer.

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

Similarly, a silicon nitride anti-reflection layer 402 ', an In ₅₄ Se ₄₃ Tl ₃ recording film 403', an ultraviolet curing resin layer 404 ', a silicon nitride anti-reflection layer 405', An In ₅₄ Se ₄₃ Tl ₃ recording film 406 ′, an ultraviolet curing resin layer 407 ′, a silicon nitride anti-reflection layer 408 ′, and an In ₅₄ Se ₄₃ Tl ₃ recording film 409 ′ were sequentially formed. The two disks 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 manner, recording and reproduction can be performed from both sides with one disc.

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

  In the disk manufactured in this embodiment, the atomic arrangement of the atoms constituting the recording film is changed by irradiating a laser beam, whereby the optical constant is changed, and reading is performed using the difference in reflectance. The atomic arrangement change here is a phase change between a crystal and an amorphous.

  Immediately after the recording film is formed on the disk, the constituent elements of the recording film have not yet reacted sufficiently and are in an amorphous state. When this disc is used as a write-once type, crystallization recording is performed by irradiating the disc with a recording laser beam, or the recording film is heated in advance by Ar laser beam irradiation, flash annealing, etc. After the reaction and crystallization, the recording laser light having a high power density is irradiated to perform the amorphous recording. Here, the range of laser power suitable for crystallization recording is higher than the temperature at which crystallization occurs and lower than the temperature at which amorphization occurs. Further, the range of the laser power suitable for performing the amorphous recording is higher than the crystallization temperature and lower than the temperature at which strong deformation occurs or a hole is formed. 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 the respective elements are sufficiently reacted and crystallized. Then, a laser power suitable for crystallization is used. 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 the light is focused by a lens (NA = 0.55) in the recording head and further passed through the substrate. The recording head was driven so that the center of the light spot always coincided with the middle of the tracking grooves by irradiating the recording film with the reflected light. By setting the recording track between the grooves, the influence of noise generated from the grooves can be avoided. Recording and reproduction are performed by performing automatic tracking so as to further focus on the recording film while performing tracking as described above. After passing the portion to be recorded, the laser power was reduced to 1 mW and tracking and autofocusing were continued. Note that tracking and automatic focusing are continued during recording. This focusing can be independently performed on each of the recording films 403, 406, and 409 in the disk.

  A case will be described in which a disk having the above configuration is recorded at a linear velocity of 8 m / s (rotation speed 1800 rpm, radius 42.5 mm) in order from the substrate side to the lower layer. First, the recording film 403 was focused, and recording was performed by irradiating a recording pulse of 5.5 ns with a recording pulse of 90 ns. The dependence of the reproduction signal intensity on the recording power at this time is shown below.

Recording power (mW) Reproduction 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 was further focused on the recording film 406. The dependence of the reproduction signal intensity on the recording power at this time is shown below.

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

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

  The reproduced signal is shown by a measurement result of a CN ratio (noise component to carrier component ratio) at each carrier frequency with a decomposition 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, the CN ratio was 50 dB or more, the interlayer crosstalk from the adjacent recording film was smaller than -25 dB, and a signal capable of highly reliable reproduction was obtained.

Next, thin films having a composition of Ge ₁₄ Sb ₂₉ Te ₅₇ are formed to have a thickness of 2 nm as the recording films 403, 406 and 409, and thin films of ZnS are formed to have a thickness of 50 nm as the antireflection layers 402, 405 and 408. A disk having the same structure as that of the above-described disk was manufactured. This disc is characterized in that the transmittance of the layer after recording is reduced. Therefore, the case where recording is performed from the lower layer to the upper layer on the substrate side in order from the lower layer at a linear velocity of 8 m / s (rotation speed 1800 rpm, radius 42.5 mm) by recording from the 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 recording was performed by irradiating a recording pulse of 5.5 ns with a recording pulse of 90 ns. The dependence of the reproduction signal intensity on the recording power at this time is shown below.

Recording power (mW) Reproduction 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 was further focused on the recording film 406. The dependence of the reproduction signal intensity on the recording power at this time is shown below.

Recording power (mW) Reproduction 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 was further focused on the recording film 403. The dependence of the reproduction signal intensity on the recording power at this time is shown below.

Recording power (mW) Reproduction signal strength (mV)
8 25
9 95
10 155
11 205
12 245
13 275
14 295
16 305
After recording a signal of 5 MHz on the recording film 409, a signal of 4 MHz on the recording film 406, and a signal of 3 MHz on the recording film 403, respectively, the reproduced signal read out by focusing on the recording films 403, 406 and 409 at each carrier frequency. The measurement results of the ratio 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, the CN ratio was 50 dB or more, the interlayer crosstalk from the adjacent recording film was smaller than -25 dB, and a signal capable of highly reliable reproduction was obtained.

  Similar results were obtained when a plastic disk made of injection-molded polycarbonate or acrylic resin was used 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 are obtained using Se, In-Se, In-Se-M (M is a metal element), Ga-Sb, Sn-Sb-Se, Sn-Sb-Se-Te, and the like. Is obtained.

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

On a substrate similar to that shown in FIG. 11, a recording film was prepared by spin coating a dispersion of Bi-substituted garnet (YIG (Y ₃ Bi ₃ Fe ₁₀ O ₂₄ )) particles having a diameter of 20 nm in an organic binder. A Bi-substituted garnet having a diameter of 20 nm was prepared by a coprecipitation method, and then heat-treated at 600 to 800 ° C. to be crystallized. An organic binder having a refractive index of 25 was used. The 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 curing resin layer provided therebetween, the method of laminating two disks, and the recording / reproducing method were the same as those in the above-described embodiment. However, the wavelength of the light source is λ = 530 nm.

  An example in which a recording / reproduction experiment was performed 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 a recording layer.

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, a recording layer (413) was laminated by a vacuum evaporation method. As shown in FIG. 10 (b), the recording layer had a configuration in which an 8 μm thick Sb ₂ Se ₃ layer (414) and a 3 μm thick Bi layer (415) were sandwiched. Further, two sets of a set of an ultraviolet curable resin layer (412) having a laser light guide groove and having a thickness of 30 μm and a recording layer (413) were further laminated thereon. That is, three recording layers were provided. An ultraviolet curable resin layer having a thickness of 100 μm was provided on the uppermost part 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 and groove was 0.75 μm. Recording may be performed on either the land portion or the groove portion. In the case of this embodiment, recording was performed on the groove portion.

  Each recording layer was irradiated with a laser beam of 2.0 mW in focus, and the reflectance was measured. The reflectance of each of the first, second, and third recording layers before recording was 8.8. 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 first recording layer, the second recording layer, and the third recording layer irradiated with the recording laser beam 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 the irradiation of the recording laser beam, a diffusion reaction of Se and Bi occurs and alloys. As a result, areas having different optical constants, that is, recording points are formed in the recording layer. In the case of the recording layer composed of Sb ₂ Se ₃ and Bi used in this embodiment, both the reflectance and the transmittance increase due to alloying, and the absorption decreases.

Although not performed in the present 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%. Therefore, the reflectance before and after the recording described above increases, which is convenient when performing tracking or the like. 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, but may be any combination that generates an alloy by raising the temperature.

FIG. 1 is a diagram illustrating the principle of a recording / reproducing method according to the present invention (the principle diagram of a first reproducing method). 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. In the principle diagram of the recording method of the present invention, a is a diagram showing light intensity in each layer, b is a diagram showing spot areal densities in other layers when focusing on the k layer, and c is a diagram showing focus on the k layer. FIG. 9 is a diagram showing power densities in other layers when the values are combined. FIG. 4 is a principle diagram of the second and third reproduction systems of the present invention. FIG. 3 is a diagram showing an example of a disk format according to the present invention. 1 is an overall configuration diagram of a three-dimensional recording / reproducing apparatus according to the present invention. FIG. 2 is a block diagram illustrating a recording control method according to the present invention. The figure which shows RBW (Read Before Write) by a preceding beam. FIG. 3 is a diagram illustrating a recording control method according to the present invention. 4A and 4B show an example of a three-layer film structure and recording characteristics. FIG. FIG. 1 is a cross-sectional view showing the structure of a phase change type information recording medium used in an example of the present invention. FIG. 9 is a partial cross-sectional view of a third information recording medium used in the present invention. FIG. 2 is a block diagram illustrating a reproduction control method according to the present invention. FIG. 4 is a diagram illustrating a reproduction control method according to the present invention. FIG. 4 is a diagram illustrating a reproduction control method according to the present invention. FIG. 4 is a diagram illustrating a reproduction control method according to the present 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. 1 is an example of an optical system for realizing a reproduction control method according to the present invention. FIG. 9 is a diagram illustrating a calculation coefficient γ (≡β) check area and a principle. 11 is a disc structure for realizing a 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. FIG. 3 is a block diagram illustrating layer access according to the present invention. FIG. 4 is a diagram illustrating detection of defocus in each layer. FIG. 3 is a block diagram illustrating layer access according to the present invention. FIG. 7 is a diagram illustrating detection of a focus shift in a recorded layer, FIG. 7A is a diagram illustrating a focus shift signal in a recorded layer, and FIG. FIG. 4 is an explanatory diagram of a method for reducing interference of reflected light between adjacent layers according to the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Recording layer, 2 ... Intermediate layer, 3 ... Substrate, 4 ... Disk, 5 ... Semiconductor laser, 8 ... Focusing lens, 9 ... Image lens, 10 ... Photodetector, 11 ... Optical spot, 12 ... Focal plane, 13 ... Optical characteristic function of the target layer when there is no aberration, 14... Optical characteristic function of the adjacent layer, 15... Direction in which the characteristic function changes when defocus increases, 16... Frequency characteristic of AGC, 20. 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: transmittance up to the k-th layer, 43: mark, 44, 45: ROM, 46: D / A converter, 47: mark in an ideal recording state, 49: preceding spot, 51: recording spot, 52: calculation Vessel, 53 ... Gainco Recording state without troll, 54, 55: photodetector, 56, 57: beam splitter, 59, 60: integrating circuit, 61, 62: delay circuit, 63, 64, 68: reproduced signal, 67: Weight setting circuit, 69: spot focused on the k-layer surface, 71: mark arrangement on the k-layer surface, 72, 73: reproduced signal, 74: mark row, 75, 76, 77, 78, 79, 82: adjacent layer 80, 81: weight function, 83: stop, 84: mark recording area, 86: power spectrum of modulation signal when 2-7 modulation method is used, 87: EFM modulation method Power spectrum of the modulated signal in the case, 88 ... breakpoint of spectrum, 91 ... AF actuator movement signal generation circuit, 92 ... drop-in point determination circuit, 95 ... layer number detection circuit, 100 ... switch, 01: cross layer signal detection circuit, 103: slice level, 105: zero cross point, 109: up pulse, 110: down pulse, 111, 112: photodetector, 113, 114: light spot on front and rear photodetector surface, 115, 116: Preamplifier, 117, 118: Sample hold circuit, 119, 120, 121, 122: Light receiving surface, 123: AF error signal near the recorded layer, 124: Total error near 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)

Converging a light spot on a first recording layer of a medium having a plurality of recording layers on which information is recorded;
Reading an address of a first layer that focuses the light on a spot;
Designating a second layer different from the first layer;
Generating a signal by recognizing the number and moving direction of light spot moving layers from the first layer to the second layer;
Inputting the signal to the means for moving the light spot;
Moving the light spot based on the input signal,
The layer access method, wherein the signal is constituted by a pair of pulses having different polarities with respect to movement of the light spot between one of the plurality of recording layers, 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 generation circuit of 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, and driving the light spot moving means. A layer access method, comprising: In an information recording method for recording information by irradiating a first recording layer of a medium having a plurality of recording layers with a light spot, an order from an uppermost layer to a lowermost layer of the plurality of recording layers or an uppermost layer to a lowermost layer An information recording method, wherein the information is recorded by moving the light spot in the following order.

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