JP2003091834A - Information recorder and information reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the increase of density by using a three-dimensional recording/reproducing method. SOLUTION: A three-dimensional recording/reproducing device and an access method between layers have a special feature to satisfy the equation, λ/4<=(1/8NB) (1/NB2-1) NAF4Δd where, λ: wavelength of light NB: refractive index of a substrate 3 NAF: the number of openings of convergence lens 8 for converging a light Δd: positional range in the direction of optical axis, where the recording layer to converge the light is in existence, as to the three- dimensional recording/reproducing device provided with a recording medium 4 laminating a plurality of recording layers 1 on the substrate 3 and an optical system for three-dimensionally recording or reproducing the information by converging the light from the side of substrate 3 to each of a plurality of recording layers 1. Thus, the light spot is converged to each layer of a disk having the structure of multi-layer films, then the high density recording/reproducing operation of data is attained with high reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording device and an information reproducing device such as an optical disk, an optical tape and an optical card, and more particularly to an information recording device and an information reproducing device for high recording density.

[0002]

2. Description of the Related Art A conventional method for increasing the recording density of an optical information recording / reproducing apparatus has been to improve the recording areal density on the plane of a two-dimensional recording medium. However, the size of the 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.

[0003]

Therefore, as a method for achieving higher density, a three-dimensional recording / reproducing method including the depth direction is indispensable. In three-dimensional recording / reproducing, there is a means for recording / reproducing data by providing a disc having a multilayer film structure and narrowing a light spot on each layer, as shown in a known example "JP-A-59-127237". However, in this known example, a specific disc structure, the definition of optical constants, and the method of setting recording conditions are not described, and reliable recording is difficult. Also, regarding how to read the data,
The configuration of the light receiving optical system is unclear, and reliable reproduction is difficult.

On the other hand, in the known examples "JP-A-60-202545" and "JP-A-60-202554", a disk thickness and a focusing method for forming a diffraction-limited light spot on each layer are described. ing. However, no clear provision has been given for the former. Regarding the latter, the principle of focusing is described, but the access method for actually focusing on the target layer is not described. Furthermore, as a disc manufacturing method, a guide groove for tracking is not possible in a known example, and a method of laser exposure for each layer is shown, but in this method,
Not productive. An object of the present invention is to investigate an optical system for narrowing down an optical spot, a disc structure, and a photo-detecting optical system capable of stable recording / reproducing in a recording process and a reproducing process, and further, encoding for suppressing crosstalk between adjacent layers which is a particular problem. A method, a crosstalk canceling method, a three-dimensional data format, a disc creating method associated therewith, and a three-dimensional access method.

[0005]

In order to solve the above problems, in order to solve the above problems, a recording film layer whose optical properties are locally changed by local light irradiation, and an antireflection film and a multiplex film are added to assist the function of the recording film layer. Layer for reflection, light absorption, transfer of optical local change of recording film layer, heat insulation, heat absorption, heat generation or reinforcement, or an intermediate layer film which is a stack of layers is laminated on an optically transparent substrate. By modulating the local optical properties of each layer two-dimensionally (independently) by irradiating the light spots focused on each layer, the data “1” and “0” after modulation can be obtained. Make corresponding recordings. Furthermore, in the three-dimensional recording / reproducing apparatus for reproducing the data by detecting the change in the local optical property as a change in the reflected light amount (or the transmitted light amount) by irradiating each layer with a light spot. The disk structure 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 separated as one layer, and 1 to N layers are allocated in order from the upper layer. The distances between the respective layers are the kth adjacent recording film layer and (k-
The distance dk between the 1) th film thickness centers is shown. Further, the film thicknesses of the arbitrary k-th recording layer and the intermediate layer are dFk, dMk, and the real parts of the refractive index are NFk, NMk, respectively. Also,
Period b [μ of change of local optical properties on the plane of each layer
m]. The narrowing optical system uses, for example, a semiconductor laser having a wavelength λ [μm] as a light source, a collimator lens converts the light into parallel light, and the parallel light is incident on the narrowing lens via a deflection beam splitter. Here, the numerical aperture of the diaphragm lens is NAF, the effective radius is a [mm], and the focal length is fF (≈a / NAF). Further, the reflected light from the disk passes through the diaphragm lens and is guided to the image lens for light reception by the beam splitter. A photodetector located near the focal point of the image lens converts the change in the amount of reflected light into an electric signal. 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 at the time of focusing is imaged at the focal position of the image lens and on this focal plane. Uk '= λ / NAI = λ × (fI / a) m; Lateral magnification of the light receiving optical system Next, the adjacent layer (k
Spot diameter U (k ±) from the ± 1) th layer on the focal plane
1) 'is From the above equation, the diameter D of the photodetector is set to D = Uk ′ = λ / NAI, and the amount of reflected light from the other layers detected is the target k layer and other j layers.
Assuming that the transmittance δjk between layers and the ratio αjk of reflectance are In and the amount of reflected light received from the n layer in the photodetector is In.

[0006]

[Equation 17]

(Equation 17) ≈I (k−1) / Ik = δ ² (k−1), k × α (k−1), k × (D / U (k−1) ′) ² (Equation 17.5) Set the disk structure and optical system so that the above equation holds.

2. Furthermore, the minimum value bmi of the two-dimensional period b
When n is (λ / NAF), the maximum value bma of the two-dimensional period b
Make x smaller than (d × NAF).

Further, in the light receiving optical system shown in FIG.
Optical characteristic functions (OTFs) in the surface of the target layer for recording and reproduction and in the surface of the adjacent layer at an optical distance d [μm]
H0 (S) and H1 (S) are shown by a straight line 13 and a straight line 14 in FIG. 4, respectively.

However, S: Normalized spatial frequency Here, with respect to the optical characteristic function H1 (S) when defocus occurs at the value of the inter-layer distance d, from S where H1 (S) = 0, the above-mentioned period Define the maximum repetition b max of b. In this way, by defining the relationship between the cycle b of local optical property changes on the layer surface, the disc structure, and the light receiving optical system, the component of interlayer crosstalk can be calculated from the cycle b of local optical property changes. Also make it longer.

3. Furthermore, a code is used in which the total area of the area of the local optical change (mark) included in the area of the spot diameter (2d × NAF) in the adjacent layer is always a constant value.

4. Further, dk = dF (k−1) + dMk + dFk ≈dMk (Equation 1) and the effective refractive index NMk of the intermediate layer is the same as the substrate. The thickness d up to the Nth layer of the multilayer disc

[0013]

[Equation 2]

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

[0015]

[Equation 4]

The thickness dk of the intermediate layers and the total number N are combined so that W40 ≦ λ / 4. Note that the absolute value on the right side of W40 is usually negative (when NB ≧ 1).

5. Further, the optical constants of the kth recording film layer 1 are the transmittance Tk, the reflectance Rk, and the absorptance Ak. Here, the relationship of Tk + Rk + Ak = 1 is established. Hereinafter, the optical constant when the local optical property is changed by the recording is represented by a dash "'". In general, an energy threshold Eth [nJ] always exists in order to cause a thermal structure change in thermal recording. The light spot narrowed to the diffraction limit on the recording target layer has a linear velocity V [m / s].
Is scanning on the disk.

In order to locally generate a thermal structure change corresponding to the modulated binarized signal, the light intensity P (recording power) [mW] incident on the disk, where the linear velocity V and the irradiation time are When t is 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 in the k layer when focusing on the k layer, since the spot diameter is λ / NAF, Sk: 1 / e ² spot when focusing on the k layer Area Sk = π (0.5 × λ / NAF) ² The light intensity Pk [mW] in the k layer is

[0020]

[Equation 6]

Δk is the transmittance between the light incident surface on the disc and the kth recording layer.

However, Tn; the transmittance of the n layer (when n = 0, the transmittance of up to one layer) (Equation 6) From the equation (6), the minimum recording power Pmin required for recording in the k layer is Pmin. ≧ Ikth × Sk / δk (Equation 7) Further, since recording is performed on the k layer, the light intensity density Ijk [mW] at the j layer when focusing on the k layer is

[0023]

[Equation 9]

It is

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

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

[0027]

[Equation 11]

Dn; film thickness of the nth layer TANφ = a / fF≈NAF (Equation 6, 7) (Equation 9, 10, 11) The focusing optical system, the disc structure, and the recording conditions are set so that the equations are simultaneously satisfied. .

6. As the role of each layer, a ROM (Read Only Memory) layer or a WOM (Write Once Memory) layer is provided together with a layer for recording and reproducing user data.

7. As a management layer of layer data, the data state of each layer, for example, presence / absence of data, error management, effective data area, and number of times of rewriting (overwriting) are recorded as needed.

8. In Item 1, as an alternate layer, information is put in place of the layer in which a recording error is detected.

9. In the item 1, as a management format in each layer surface of the disc, sectors and tracks are provided, and recording is performed in order from the 1st layer to 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 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 the data is recorded in the sector in one layer, the sectors in the next layer are filled, and the sectors in all layers are filled, Record the data in the next sector.

13. In the 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 the item 1, as a light spot positioning mechanism, a two-dimensional actuator that drives the stop lens in the layer direction and the disk radial direction, or a one-dimensional actuator that drives the stop lens only in the layer direction and the light flux that is incident on the stop lens are the disk radius. In a combination of galvano mirrors that deflect in the direction,
The layer number detection circuit recognizes the number of the current layer by reading the layer address in the preformat section, and the jth layer which is currently focused is the kth target layer which is a command from the upper controller. Up to (sign (k-j)) direction up and down, how many (| k-j |) layers should be spot-moved, and the jump forcing signal is sent to the layer jump signal generation circuit. It is generated and input to the AF actuator driver.

15. In item 14, the jump signal is
The movement between layers is composed of a pair of pulses of + -polarity pulses, and + -pulses are switched depending on the vertical movement direction. The leading pulse is used to drive the spot in the moving direction by a moving distance, and the next polarity inversion pulse is used to settle so that the spot does not go too far. In addition, pulses of a pair of moving layers are input to the driver circuit. Next, the layer number is detected and j
Confirm that = k.

16. In paragraph 14, a cross layer signal detection circuit is provided which detects the focus detection for each recording layer by using the zero cross pulse of the AF error signal and the total light amount pulse as a gate.

17. In Item 16, by generating and counting an up pulse and a down pulse from the zero-cross pulse, the total light amount pulse, and two kinds of pulses, it is possible to always recognize in which layer the lens is positioned and Recognize the direction of movement.

18. In paragraph 14, the focal position moves at least from the top layer of the disc to the bottom layer,
When a sawtooth wave is generated from the AF actuator movement signal generation circuit to drive the AF actuator, the cross layer signal detection circuit counts the in-focus points of the N layers and raises when the lens is moved to the upper side. From the upper limit of the pulse, the top layer (n = 1) or
The lowermost layer (n = N) is recognized from the lower limit of the down pulse when the lens is moved to the lower side, and the focus position in the disc layer direction is always recognized.

19. In the item 5, in the case of stably recording on the k layer which is a recording target, the transmittance (ΣTn (n
= 0, 1, 2, ... K−1))
Set (Light intensity).

20. In Item 5, the transmittance up to k layers is set for layer address recognition.

21. By the address recognition, the transmittance ΣTn (n = n
The ratio of 0,1,2 ... k-1) to the transmittance ΣT'n (n = 0,1,2, ... k-1) up to the k layer immediately before recording, that is, the change G of the transmittance is considered. And set the recording power.

22. In paragraphs 6 and 21, a management layer for layer data is provided, which layer is recorded, the management layer is reproduced before recording the target layer, and the transmittance ΣT ′ ( k-1) is recognized, and the change G in transmittance is recognized.

23. In Item 21, before recording on the target layer, the area to be recorded is reproduced in advance and the change G in transmittance is obtained.

24. In item 23, as a method of reproducing the area to be recorded in advance, the reproduction check is performed at the first rotation of the disk in the recording mode, the recording is performed at the next rotation, and the recording error check is performed at the next rotation.

25. In the item 23, a plurality of spots are used and the reproduction check is performed at the preceding spot.

26. In the item 25, in the reproduction check, the received reproduction signal C′k for the preceding spot is received.
(T−τ) is used. Here, τ is a time conversion of the spot distance between the preceding spot and the recording spot. Here, the transmittance change amount G is obtained as the square root of the ratio of the reproduction signal Ck ′ in the state where the k layer which is the recording target layer is focused and the reproduction signal Ck designed at the time of shipment of the disc.

27. In the item 25, in the reproduction check, the value of the reproduction signal Ck is provided as a check area in advance as a disc format, and an area not recorded in the layer direction is provided in the disc surface.

28. In Item 23, the photodetector for obtaining the reproduced signal has the shape of Claim 1.

29. In paragraph 1, as a reproduction control circuit, in addition to detecting the reflected light component from the target layer, in particular, the reflected light component from the adjacent layer that occupies most of the interlayer crosstalk is also detected, and the components included in both are calculated. Remove by.

30. In paragraph 29, the three photodetectors are positioned on the image planes of the target layer k and the adjacent layers (k + 1) and (k-1) on the light receiving surface side when the k layer is focused. The shape of the photodetector is set to D = (λ / NAI), or the light receiving area is limited by a pinhole,
Reproduction signal Ck for the k-layer photodetector, reproduction signals C (k-1) and (k +) for the (k-1) -layer photodetector
The reproduction signal C (k + 1) for the photodetector of the 1) layer is calculated by the following equation.

Calculation 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: Ratio of the crosstalk component included in each signal to the required signal component C (k−2) ) R and C (k + 2) R are sufficiently small and the frequency components are also low, so they can be ignored. Therefore, F≈ (1-2γβ) × CkR + (β−γ) × C (k−1) R + (β−γ) × C (k + 1) R Here, when the calculation coefficient γ≡β <1, ≈ (1−β ² ) × CkR By using the arithmetic function of the above equation, only the signal component of the target layer is obtained.

31. In Item 29, multiple 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 the two adjacent layers in advance of the spot to obtain the reproduction signal, and the operation of item 30 is performed.

32. In Item 31, as shown in FIG. 18, an aperture is inserted to reduce the effective aperture for the aperture lens. That is, the effective diameter a ′ is [λ / (2
d × NAF ² ) × a].

33. In item 31, the numerical aperture of the aperture lens of the preceding two optical systems is reduced by dividing into three optical axes, that is, NAF ′ = λ / (2d × NA
F).

34. In the term 31, the reproduction signal from the preceding spot is multiplied by a weighting function obtained by approximating a Gaussian distribution, which is the intensity distribution of the spot, into a triangular distribution, and then integration is performed. 35. In the item 30, in the weight setting circuit for setting each calculation coefficient γ (≡β), at least the mark recording areas between the upper and lower three layers are arranged so as not to be included in the same light flux as the disk format, and h (k -1) / h
Let k and h (k + 1) / h be β (−1) and β (+1).

36. In Item 1, by using a plurality of spots and focusing on each layer, recording / reproduction is performed simultaneously on two or more layers, that is, parallel recording / reproduction is performed.

37. In item 9, a recording medium whose transmittance increases after recording is used.

38. In the item 1, the guide grooves in each layer surface of the multilayer disc, pre-pits such as addresses are provided in the ultraviolet curing resin layer for each layer, and a transparent mold is used for each layer to apply light from the surface of the mold by the 2P method. Form.

39. In paragraph 1, the intermediate layer is provided with a quarter-wave plate layer.

The above means operate as follows.

A recording film layer whose optical properties are locally changed by local light irradiation, and antireflection, multiple reflection, light absorption, and optical local change of the recording film layer as an aid of the function of the recording film layer. Layers for the purpose of transfer, heat insulation, heat absorption, heat generation or reinforcement, or intermediate layers that are a stack of layers are stacked on an optically transparent substrate in a multi-layered disc. By changing the local optical properties of each layer two-dimensionally (independently) by spot irradiation, recording corresponding to the modulated data "1" and "0" is performed. In the three-dimensional recording / reproducing apparatus which reproduces the data by detecting the change of (1) as the change of the reflected light amount (or the transmitted light amount) by irradiating each layer with the light spot. The disk structure 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 separated as one layer, and 1 to N layers are allocated in order from the upper layer. The distances between the respective layers are the kth adjacent recording film layer and (k-
The distance dk between the 1) th film thickness centers is shown. Further, the film thicknesses of the arbitrary k-th recording layer and the intermediate layer are dFk, dMk, and the real parts of the refractive index are NFk, NMk, respectively. Also,
Period b [μ of change of local optical properties on the plane of each layer
m]. The narrowing optical system uses, for example, a semiconductor laser having a wavelength λ [μm] as a light source, a collimator lens converts the light into parallel light, and the parallel light is incident on the narrowing lens via a deflection beam splitter. Here, the numerical aperture of the diaphragm lens is NAF, the effective radius is a [mm], and the focal length is fF (≈a / NAF). Further, the reflected light from the disk passes through the diaphragm lens and is guided to the image lens for light reception by the beam splitter. A photodetector located near the focal point of the image lens converts the change in the amount of reflected light into an electric signal. 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 at the time of focusing is imaged at the focal position of the image lens and on this focal plane. Uk ′ = λ / NAI = λ × (fI / a) (Equation 14) m; Lateral magnification of the light receiving optical system Next, the adjacent layer (d) separated from the kth target layer by the interlayer distance d ( k
Spot diameter U (k ±) from the ± 1) th layer on the focal plane
1) ′ is U (k ± 1) ′ ≈a × m ² d / fI = NAI · m ² d (Equation 16) From the above equation, the diameter D of the photodetector is D = Uk ′ = λ / NAI
Then, the amount of reflected light from the other layer to be detected is the amount of reflected light received from the n layer at the photodetector as the transmittance δjk between the target k layer and the other j layer and the reflectance ratio αjk. If In

[0065]

[Equation 17]

(Equation 17) ≈I (k−1) / Ik = δ ² (k−1), k × α (k−1), k × (D / U (k−1) ′) ² (Equation 17.5) By setting the disk structure and the optical system so that the above equation is satisfied, the leakage of reflected light from other layers is reduced.

2. In item 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.
Optical characteristic functions (OTFs) in the surface of the target layer for recording and reproduction and in the surface of the adjacent layer at an optical distance d [μm]
H0 (S) and H1 (S) are shown in FIG.
It is shown by a straight line 14.

However, S: Normalized spatial frequency Here, with respect to the optical characteristic function H1 (S) when defocus occurs at the value of the interlayer distance d, H1 (S) = 0
Therefore, the maximum repetition bmax of the cycle b is defined. In this way, by defining the relationship between the cycle b of local optical property changes on the layer surface, the disc structure, and the light receiving optical system, the component of interlayer crosstalk can be calculated from the cycle b of local optical property changes. Also, 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 region of the local optical change (mark) included in the region of the spot diameter (2d × NAF) 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 the DC component is removed to extract only the signal component of the target layer.

4. In the item 1, dk = dF (k−1) + dMk + dFk ≈dMk (Equation 1) and 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

[0072]

[Equation 2]

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

[0074]

[Equation 4]

By combining the thickness dk of the intermediate layers of each layer and the total number N so that W40 ≦ λ / 4, the spherical aberration caused by the change of the optical distance between the layers is suppressed within the allowable value. , A diffraction-limited light spot is formed in each layer. Note that the absolute value on the right side of W40 is usually negative (when NB ≧ 1).

5. In the item 1, the optical constants of the kth recording film layer 1 are the transmittance Tk, the reflectance Rk, and the absorptance Ak. Here, the relationship of Tk + Rk + Ak = 1 is established.
Hereinafter, the optical constant when the local optical property is changed by the recording is represented by a dash "'". In general, an energy threshold Eth [nJ] always exists in order to cause a thermal structure change in thermal recording. The light spot focused on the recording target layer to the diffraction limit has a linear velocity V
The disk is scanned at [m / s].

In order to locally generate a thermal structure change corresponding to the modulated binarized signal, the light intensity P (recording power) [mW] incident on the disk, where the linear velocity V and the irradiation time are When t is 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 in the k layer when focusing on the k layer, since the spot diameter is λ / NAF, Sk: 1 / e ² spot when focusing on the k layer The light intensity Pk [mW] in the area Sk = π (0.5 × λ / NAF) ² k layer is

[0079]

[Equation 6]

Δk is the transmittance between the light incident surface on the disc and the kth recording layer.

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

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

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

[0084]

[Equation 11]

Dn; thickness of the nth layer TANφ = a / fF≈NAF By setting the narrowing optical system, the disc structure, and the recording conditions so that the above equations are simultaneously satisfied, stable recording can be performed on the target layer, and At that time, the incident recording power is set so as not to destroy other layers.

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 the layer data management layer, the data state of each layer, for example, the presence or absence of data, error management, effective data area, and the number of times of rewriting (overwriting) can be recorded at any time to update and access the data. Do promptly.

8. In Item 1, as an alternate layer, by inserting information in place of the layer in which the recording error was detected,
Guarantee data reliability.

9. In the item 1, as a management format in each layer surface of the disc, sectors and tracks are provided, and recording is performed in order from the 1st layer to the upper layer. However,
In each layer, information is recorded in all user sectors and tracks, and then recorded in the next layer to manage recording and reproduction of user data.

10. Recording is performed in order from N → k → 1 layer and the lower layer. However, in each layer, information is recorded in all the user sectors and tracks, and then recorded in the next layer to manage user data recording / reproduction.

11. In each layer, information is recorded in all user sectors and tracks, and then recorded in the next layer, but the order of recording layers is random access,
It manages user data recording / playback.

12. The order of the layers to be recorded is random access, but after all the data is recorded in the sector in one layer, the sectors in the next layer are filled, and the sectors in all layers are filled, User data recording / reproduction is managed by recording the data of the next sector.

13. In the track, random access is performed in the layer direction. In this case, user data recording / reproduction is managed by applying a variable length block instead of fixed block management by sector.

14. In the item 1, as a light spot positioning mechanism, a two-dimensional actuator that drives the stop lens in the layer direction and the disk radial direction, or a one-dimensional actuator that drives the stop lens only in the layer direction and the light flux that is incident on the stop lens are the disk radius. In a combination of galvano mirrors that deflect in the direction,
The layer number detection circuit recognizes the number of the current layer by reading the layer address in the preformat section, and the jth layer which is currently focused is the kth target layer which is a command from the upper controller. Up to (sign (k-j)) direction up and down, how many (| k-j |) layers should be spot-moved, and the jump forcing signal is sent to the layer jump signal generation circuit. The target layer is focused by generating and inputting it to the AF actuator driver.

15. In item 14, the jump signal is
The movement between layers is composed of a pair of pulses of + -polarity pulses, and + -pulses are switched depending on the vertical movement direction. The leading pulse is used to drive the spot in the moving direction by a moving distance, and the next polarity inversion pulse is used to settle so that the spot does not go too far. In addition, pulses of a pair of moving layers are input to the driver circuit. Next, the layer number is detected and j
By confirming that = k, the spot is located on the target layer k.

16. In item 14, when the lens is moved in the layer direction by using a zero-cross pulse of the AF error signal and a total light amount pulse as a gate and providing a cross layer signal detection circuit for detecting focus detection for each recording layer. The signal at which the focal position crosses each layer is obtained.

17. In Item 16, by generating and counting an up pulse and a down pulse from the zero-cross pulse, the total light amount pulse, and two kinds of pulses, it is possible to always recognize in which layer the lens is positioned and Recognize the direction of movement.

18. In paragraph 14, the focal position moves at least from the top layer of the disc to the bottom layer,
When a sawtooth wave is generated from the AF actuator movement signal generation circuit to drive the AF actuator, the cross layer signal detection circuit counts the in-focus points of the N layers and raises when the lens is moved to the upper side. From the upper limit of the pulse, the top layer (n = 1) or
By recognizing the lowest layer (n = N) from the lower limit of the down pulse when the lens is moved to the lower side and always recognizing the focal position in the disc layer direction, layer access is possible without providing a layer address. Is possible.

19. In the item 5, in the case of stably recording on the k layer which is a recording target, the transmittance (ΣTn (n
= 0, 1, 2, ... K−1))
By setting (light intensity), recording is performed on the target layer under optimum recording power conditions.

20. In Item 5, the transmittance up to the k layer is set for the layer address recognition, so that recording is performed on the target layer under the optimum recording power condition.

21. By the address recognition, the transmittance ΣTn (n = n
Considering the ratio of 0,1,2 ... k-1) to the transmittance ΣTn (n = 0,1,2, ... k-1) up to the k layer immediately before recording, that is, the variation G of the transmittance. By setting the recording power, even if the transmittance changes due to the recorded layers up to the target layer, the change is taken into consideration and recording is performed on the target layer under the optimum recording power condition.

22. In paragraphs 6 and 21, a management layer for layer data is provided, which layer is recorded, the management layer is reproduced before recording the target layer, and the transmittance ΣT ′ ( By recognizing k-1) and recognizing the change G in the transmittance, even if the transmittance is changed due to the presence of a layer recorded up to the target layer, it is taken into consideration and the target layer is considered. Recording under optimum recording power conditions.

23. In the 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, so that the transmittance changes due to the presence of the layers recorded up to the target layer. However, in consideration of this, recording is performed under the optimum recording power condition for the target layer.

24. In item 23, as a method of reproducing the area to be recorded in advance, the reproduction check is performed at the first rotation of the disk in the recording mode, the recording is performed at the next rotation, and the recording error check is performed at the next rotation.

25. In the item 23, it is not necessary to wait for rotation by using a plurality of spots and performing the reproduction check at the preceding spot.

26. 26. In the reproduction check according to claim 25, the reproduction signal C'k received for the preceding spot is received.
(T−τ) is used. Here, τ is a time conversion of the spot distance between the preceding spot and the recording spot. Here, the transmittance change amount G is obtained as the square root of the ratio of the reproduction signal Ck ′ in the state of focusing on the recording target layer k layer and the reproduction signal Ck designed at the time of shipment of the disc. , In the reflective optical system, the change in transmittance is obtained.

27. In the item 25, in the reproduction check, the value of the reproduction signal Ck is transmitted as a disc format between the discs and within the disc by providing a check region in advance in the disc surface as a check region in the layer direction. Reduce the effect of rate variation.

28. In the item 23, the photodetector that obtains the reproduced signal has the shape of claim 1 to specify and detect the reflection component from the target layer, and obtain a more accurate transmittance change G.

29. In paragraph 1, as a reproduction control circuit, in addition to detecting the reflected light component from the target layer, in particular, the reflected light component from the adjacent layer that occupies most of the interlayer crosstalk is also detected, and the components included in both are calculated. The reflected light component of the target layer is extracted by removing the reflected light component.

30. In paragraph 29, the three photodetectors are positioned on the image planes of the target layer k and the adjacent layers (k + 1) and (k-1) on the light receiving surface side when the k layer is focused. The shape of the photodetector is set to D = (λ / NAI), or the light receiving area is limited by a pinhole,
Reproduction signal Ck for the k-layer photodetector, reproduction signals C (k-1) and (k +) for the (k-1) -layer photodetector
The reproduction signal C (k + 1) for the photodetector of the 1) layer is calculated by the following equation.

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: Ratio of the crosstalk component included in each signal to the required signal component C (k−2) ) R and C (k + 2) R are sufficiently small and the frequency components are also low, so they can be ignored. Therefore, F≈ (1-2γβ) × CkR + (β−γ) × C (k−1) R + (β−γ) × C (k + 1) R Here, when the calculation coefficient γ≡β <1, ≈ (1−β ² ) × CkR By using the arithmetic function of the above equation, only the signal component of the target layer is obtained.

31. In Item 29, multiple spots are used. By scanning two adjacent layers with a spot having the same spot diameter as the defocused spot on the adjacent layer when focusing on the k layer, the two adjacent layers are scanned, the 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 for the aperture lens. That is, the effective diameter a ′ is [λ / (2
d × NAF ² ) × a], the spot diameter of the preceding spot focused on the adjacent layer is (2d × NAF).
To

33. In item 31, the numerical aperture of the aperture lens of the preceding two optical systems is reduced by dividing into three optical axes, that is, NAF ′ = λ / (2d × NA
By setting F), the spot diameter of the preceding spot that focuses on the adjacent layer is set to (2d × NAF).

34. In the term 31, the reproduction signal from the preceding spot is multiplied by a weighting function obtained by approximating the Gaussian distribution, which is the intensity distribution of the spot, to a triangular distribution to perform integration, so that the defocused spot effectively scans the mark row. If so, get the playback signal.

35. In the term 30, each calculation coefficient γ (≡
In the weight setting circuit for setting β), as the disc format, at least the mark recording areas between the upper and lower three layers are arranged so as not to be included in the same light beam, and h (k−1)
By setting / hk and h (k + 1) / h to β (−1) and β (+1), the weights for the upper and lower layers are obtained, respectively.

36. In the item 1, a plurality of spots are used and focusing is performed on each layer, whereby recording and reproducing are simultaneously performed on two or more layers, that is, parallel recording and reproducing are performed to increase the transfer rate.

37. In the item 9, by using a recording medium whose transmittance increases after recording, the light intensity given at the time of recording in the lower layer is reduced, and further, the reflected light from the lower layer is increased, thereby achieving high efficiency recording and high SN. Performs ratio regeneration.

38. In the item 1, the guide grooves in each layer surface of the multilayer disc, pre-pits such as addresses are provided in the ultraviolet curing resin layer for each layer, and a transparent mold is used for each layer to apply light from the surface of the mold by the 2P method. By forming, for each layer, a guide groove for tracking,
Form pre-pits such as layer address indicating the layer position,
Record and reproduce data.

39. In Item 1, by providing the quarter-wave plate layer in the intermediate layer, the polarization direction of the reflected light from the adjacent layer is different, so that interference is eliminated and crosstalk between adjacent layers can be reduced.

[0121]

DETAILED DESCRIPTION OF THE INVENTION (1) Principle of the three-dimensional recording / reproducing method of the present invention (2) 3D disk format, data management (3) Device configuration (4) Access method (5) Recording control method (6) Regeneration control method (7) Example of disk structure and method for creating disk Embodiments will be described in this order.

(1) Basic Principle of Three-Dimensional Recording / Reproducing FIG. 1 shows the principle of recording / reproducing of the three-dimensional recording / reproducing apparatus of the present invention. The recording film layer 1 whose optical properties are locally changed by local light irradiation, and antireflection, multiple reflection, light absorption, transfer of the optical local change of the recording film layer as an aid of the function of the recording film layer, A layer 4 for heat insulation, heat absorption, heat generation or reinforcement, or an intermediate layer film 2 which is a superposition of these layers is laminated on an optically transparent substrate 3 and has a disc 4 which is narrowed down to each layer. By changing the local optical properties of each layer two-dimensionally and independently between each layer by irradiating a focused light spot, the modulated data "1", "0"
Recording is performed corresponding to the above, and further, the change in the local optical property is detected as a change in the reflected light amount (or the transmitted light amount) by irradiating each layer with a light spot, and the 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 divided as a set of layers, and the layers are numbered from 1 to N in order from the upper layer (light incident side). The distances between the respective layers are the kth adjacent recording film layer and (k-
The distance dk between the 1) th film thickness centers is shown. The film thicknesses of the arbitrary k-th recording layer and the intermediate layer are dFk and dMk, and the real parts of the refractive index are NFk and NMk, respectively. Further, the period b of the change of the local optical property on the plane of each layer
[Μm]. The narrowing optical system uses, for example, a semiconductor laser 5 having a wavelength λ [μm] as a light source, a collimator lens 6 converts the light into parallel light, and the parallel light is incident on a narrowing lens 8 via a deflecting beam splitter 7. Here, the numerical aperture of the lens 8 is NAF, the effective radius is a [mm],
The focal length is fF (≈a / NAF). By focusing each layer, each layer is irradiated with the diffraction-limited light spot 11.

Regarding the light receiving optical system, a reflection light receiving system is shown as an example. The reflected light from the disc 4 is reflected by the lens 8
The beam splitter 7 guides the light to the image lens 9 for light reception. A photodetector 10 located near the focal point of the lens 9 converts a change in the amount of reflected light into an electric signal.
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 is shown as an example of the optical system, but the same effect can be obtained with the diffusing optical system shown in FIG. 2b. Further, as the light receiving optical system, the same effect as that of the present invention can be obtained even in the transmitted light detecting system.

In three-dimensional recording / reproducing, the first problem for recording / reproducing is to narrow the light spot to the diffraction limit in each layer. With conventional optical discs,
Generally, in order to protect the recording film, the light spot is narrowed down to the single-layer recording surface over the substrate 3 by the diffraction limit. Therefore, the design specifications of the aperture lens 8 are made in consideration of the refractive index and the film thickness of the substrate 3 so that spherical aberration does not occur and the light spot is not distorted.
However, in the multilayer disc 4, the influence of the film thickness of each layer cannot be ignored, and for example, the known example “Kubota et al .: Optics, 14
(1985), Jitter analysis IV of eye pattern on optical disc ”, the spherical aberration increases as the number of layers increases, and the diffraction limit cannot be narrowed down. Therefore,
The present invention shows a design of a diaphragm lens and a disc structure for obtaining a light spot in a range sufficient for recording and reproduction. In order to simplify the design method, the film thickness dF of the recording film layer 1
It is assumed that k is sufficiently thin with respect to the film thickness dMk of the intermediate layer 2 and can be ignored. That is, dk = dF (k−1) + dMk + dFk≈dMk (Equation 1) and each of the intermediate layers 2 has the same refractive index NB as the substrate 3. In this case, the thickness d of the multilayer disc up to the Nth layer is

[0126]

[Equation 2]

It is

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

Change in film thickness from the 1st to the Nth layer Δ
The spherical aberration amount W40 caused by d is expressed as follows.

W40 = | (1 / (8 × NB)) × ((1 / NB ² ) −1) × NAF ⁴ × Δd | (Equation 3) Then, a squeezing lens so that W40 ≦ λ / 4 holds. Design and disc structure. Note that the absolute value on the right side of W40 is usually negative (when NB ≧ 1). As an example, a glass substrate having a refractive index NB = 1.5 is used as the substrate 3, an ultraviolet curable resin having a refractive index substantially equal to that of glass is used as the intermediate layer, and NAF = of the focusing lens 8 is used.
When it is set to 0.55, according to the expression (3), Δd ≦ 50 μm
Is. Here, d0 = 1.2 mm-Δd = (1.15 to 1.2 mm),

[0131]

[Equation 4]

By combining the thickness dk of the intermediate layers of each layer and the total number N so that Δd ≦ 50 μm, the focusing lens for the substrate thickness of 1.2 mm used in the conventional optical disk is applied as it is. A light spot sufficient for recording and reproduction can be formed on each of the first to Nth layers.
As one combination solution, the thickness of the intermediate layer dMk = 10 μ
m, recording layer thickness dFk = 200Å, d0 = 1.1
5 mm, Σdk = 10.4 μm≈100 μm, total number N =
10 is 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 the 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 interlayer distance Δdk = from the fifth layer
Spherical aberration Wk40 occurring at the k-th layer in (k-5) × d
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), it is 1.4 μm, and in the uppermost layer (k = 1), a defocus of −1.4 μm may be given as an offset.

The second problem for recording / reproducing is the thermal recording process. The prescribed conditions for recording are the following two terms.

(A) Sufficient and stable recording power density for recording can be given to the recording target layer.

(B) When recording on any k layer, do not destroy the data on other layers.

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

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

In FIG. 1, for simplification of the design, the substrate 3 and the intermediate layer 2 have a transmittance of 100% as an example.
Further, the optical constant of the k-th recording film layer 1 is the transmittance Tk,
The reflectance is Rk and the absorptance is Ak. Where Tk + Rk +
The relation of Ak = 1 is established. Further, the optical constant when the local optical property is changed by recording is represented by a dash symbol “′” below. Generally, in thermal recording, the thermal structure of the recording film changes due to heat generation due to light absorption of the recording film and temperature rise governed by a thermal diffusion phenomenon using this as a heat source. This corresponds to the movement of the recording film due to melting in the hole-type recording medium, crystallization and amorphization in the phase-change recording medium, and reversal of perpendicular magnetization in the magneto-optical recording medium. This thermal structure change occurs, resulting in a local optical property change. An energy threshold Eth [nJ] is always present in order for the thermal structure to change regardless of the type of recording film. In the recording process, the optical spot 11 narrowed down to the diffraction limit on the recording target layer scans the disk at the linear velocity V [m / s]. Light intensity P radiated on the disk surface in order to locally cause a thermal structure change corresponding to the modulated binarized signal.
(Recording power) [mW] is modulated at time t [s]. Here, if the linear velocity V and the irradiation time t are given, the energy threshold Eth is set to the light intensity density threshold Ith [mW / mW /
μm ² ].

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

Ik = Pk / Sk ≧ Ikth (Equation 5) Ikth; Light intensity density threshold value (mW / μ in recording layer k)
m ² ) Sk; 1 / e ² spot area when focusing on the k layer Sk = Π (0.5 × λ / NAF) ² However, the light spot diameter narrowed to the diffraction limit is λ / N
AF.

Here, the light intensity Pk [mW] in the k layer is

[0144]

[Equation 6]

Δk is the transmittance between the light incident surface on the disc and the kth recording layer, and Tn is the transmittance of the n layer (n
When = 0, the transmittance is up to 1 layer). Pk is as shown in FIG. 3a. From the equations (5) and (6), the minimum recording power Pmin required for recording on the k layer is Pmin ≧
Ikth × Sk / δk
(Equation 7) In general, the light intensity is the lowest in the lowermost layer N, where n = 1 to N-1 is recorded and a medium in which the transmittance Tn is all decreased → Tn '(after recording Transmittance).

To satisfy the condition (B), since recording is performed on the k layer, the light intensity density Ijk [mW / μm ² ] in the j layer when focusing on the k layer is (Equation 8) It should be realized.

[0147]   Ijk = Pjk / Sjk << Ijth (Equation 8)

[0148]

[Equation 9]

It is

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

Pmax = Ijth × Sjk / δj (Equation 10) Sjk is a light spot area in the j layer when focusing on the k layer, and can be geometrically obtained if the interlayer distance d is a wavelength λ or more. You can

[0152]

[Equation 11]

Dn; thickness of the nth layer TANφ = a / fF≈NAF Here, 1 / Sjk [μm ² ] represents the surface density, and FIG.
It becomes like b. From FIG. 3a and FIG. 3b, the light intensity density Ijk
[MW / μm ² ] is obtained, as shown in FIG. 3c.

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

FIG. 10b shows the recording power with which the disc is irradiated and the modulation degree of the reproduction signal corresponding to each power when the recording is performed on layers other than the target recording layer and the spot is narrowed down on each layer. There is. Here, the degree of modulation indicates a measure of the size of a local optical property change (mark) formed on each layer surface, and the degree of modulation shows a saturation tendency when the mark is as large as the narrowed spot diameter. The vertical axis represents standardization with the saturation value of the modulation degree being 1 for each layer. In the figure, the threshold power for forming a mark on the first layer is 4 mW (= Ith
× S1), 5 mW (= Ith × S2 / δ) in the second layer
2), in the third layer (k = 3), this is the minimum power Pmi
n is determined, and from (Equation 5) (Equation 6) (Equation 7),

[0156]

[Equation 12]

It becomes:

From the equations (8), (9) and (11),

[0159]

[Equation 13]

For example, when d = 2.5 μm, Pmax =
It becomes 16 mW (P3max = 10 mW), and as shown in FIG. 10b, it is possible to record a mark with a sufficient signal. In this way, by designing, it is possible to record on the target layer with high reliability without destroying other layers.

Next, the third problem for recording and reproducing is in the reproducing process. The specified conditions for reproduction are as follows.

(C) Minimize the noise component. Here, it is the reduction of interlayer crosstalk noise.

(D) Maximize the signal component from the target layer.

A first method for achieving the item (C) will be described.

The first method in FIG. 1 is to optimize the light receiving optical system to sufficiently reduce the amount of light reflected from other than the target layer, thereby reducing interlayer crosstalk and reproducing with a large SN ratio. It is something to do. In FIG. 1, as shown by the solid line, the amount of reflected light from the layer to be reproduced is detected by the photodetector 10 placed on the focal point of the image lens 9. On the other hand, the reflected light from the adjacent layer spreads on the focal plane 12 of the image lens as 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 of 1 / e ² of the peak intensity value of the light spot 11 at the time of focusing with the kth layer as the target layer, that is, the spot diameter is Uk = (λ / NA
F). Then, the reflected light from the target layer is imaged at the focal position of the image lens 9. The spot diameter Uk ′ on the focal plane 12 is Uk ′ = mUk = m × (λ / NAF) = (NAF / NAI) × (λ / NAF) = λ / NAI = λ × (fI / a) (number 14) m: Lateral magnification of light-receiving optical system Next, the spot diameter U (k ± 1) ′ on the focal plane from the (k ± 1) th layer, which is the interlayer distance d from the kth target layer, is obtained. The distance d ′ between the position where the reflected light from the (k ± 1) layer is focused 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) where fI >> m ² d, then U (k ± 1) ′ ≈ a × m ² d / fI = NAI · m ² d (Equation 16) From the above equation, the diameter D of the photodetector is D = Uk ′ = λ / NAI
If so, compared to the case where the diameter of the photodetector is not limited,
Since the area ratio ε = (D / U (k ± 1) ′) ² can reduce the reflected light amount from the adjacent layer, the change in the reflected light amount from the target layer can be detected with a high SN ratio.

Actually, the amount of reflected light from the other layer to be detected takes into consideration the transmittance δjk and the reflectance ratio αjk between the target k layer and the other j layer. Here, the amount of inter-layer crosstalk noise required for highly reliable signal detection is -2.
Assuming 0 dB (1/10), the following equation is generally satisfied.

Let In be the amount of light received and reflected from the n-layer in the photodetector 10.

[0169]

[Equation 17]

However, in the following, only the adjacent layer (k−1) layer to the target layer k layer will be considered. The influence from other layers can be considered in the same way, but the value is sufficiently small.

(Equation 17) ≈I (k−1) / Ik = δ ² (k−1), k × α (k−1), k × (D / U (k−1) ′) ² (Equation 17.5) For example, λ = 0.78 μm, NAF = 0.55, fI = 3
0 mm (NAI = 0.075, m = 7.33, m ² =
53.8), D = Uk′≈10.4 μm Taking FIG. 10 as an example, since δ23 = 1.25 and α23 = 1, the suppression rate of the reflected light amount is ε × δ ² 23 × α23.

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

[0173]

[Formula 19]

Although the influence of the crosstalk from the second layer is taken into consideration here, the influence of the crosstalk from the first layer can be calculated in the same manner, and its value (I1 / I3) = 0.024 (= − 32)
dB) and small enough to be ignored.

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

The second method is to define the relationship between the period b of the local optical property change (mark) on the layer surface, the disc structure, and the light receiving optical system so that the component of the interlayer crosstalk can be detected locally. It is set to be longer than the cycle b of changes in the physical properties.
That is, by making the frequency component of the interlayer crosstalk smaller than the signal band of the data, the data on the target layer surface is reproduced with a high SN ratio. The principle of this method will be described with reference to FIGS. Although the diameter of the photodetector is not limited in order to distinguish it from the first method, a higher SN can be obtained by using it in combination.

Since a diffraction-limited light spot is formed on the target layer, the two-dimensional period b has a spot diameter (λ / NA).
If it is about F), it can be decomposed sufficiently. That is, if the minimum value bmin of the two-dimensional period b is (λ / NAF), the signal component can be sufficiently large. This is the condition for the term (D) to hold. In FIG. 4, when H0 (S) = 0, decomposition is impossible, and the value of b at this time is the spot diameter λ / NA.
It is half of F. On the other hand, since the spot diameters in the adjacent layers are out of focus, the interlayer distance d is
(2d × NAF), and the optical resolution decreases. Therefore, using this characteristic, the maximum value bm of the two-dimensional period b
ax is 1 / of the spot diameter (2d × NAF) in the adjacent layer
If it is smaller than 2, that is, (d × NAF), the leakage of the signal component from the adjacent layer, that is, the frequency component of the interlayer crosstalk, causes the signal band (1 / bmax to 1 / bmi).
n) 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 optical characteristic function (OTF) H0 in the target layer surface for recording and reproduction and in the adjacent layer surface separated by the optical distance d [μm].
(S) and H1 (S) are shown by a straight line 13 and a straight line 14 in FIG. 4, respectively. The horizontal axis corresponds to the repetition frequency of the object, and the vertical axis corresponds to its modulation factor. Here, S is a normalized spatial frequency.

S = λ × fF / (2Πa) = λ / NAF × b (Equation 20) In the case of no defocus and 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 since the optical system itself has aberrations other than defocus, up to the cycle b corresponding to the cutoff frequency S = 2. , Difficult to detect. Therefore, the modulation factor is half (-6 dB) as the allowable value of the modulation factor. At that time,
Since S = 1, 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, H1 (S) = 0
Therefore, the maximum repetition bmax of the cycle b is defined.

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 fmin (= 1 / bmax) or less,
Adjacent crosstalk components can be absorbed by using an automatic gain control circuit having a tracking characteristic 16 as shown in FIG.

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

B1 = −d / 2 × (NAF) ^{2 As a} numerical example, the cutoff frequency S for 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 Further, bmin = (λ / NAF) = 1.42 μm For example, as shown in FIG. 20, a 2-7 code, which is a variable-length code, is used in the spot scanning direction, and the track pitch is 1.5.
For a disk having a constant μm, a known example is disclosed in JP-A-63-537
When the minimum reproducible bit pitch q (μm) and the inter-layer distance d are obtained when the pit edge recording method shown in No. 22 ”is used, the shortest pattern repetition period is 3q = bmin = 1 as shown in FIG. .42 μm q = 0.47 μm Here, the longest pattern repetition is 8q, 8q = 3.76 μm ≦ bmax, and the mark period in the disc radial direction is constant at a track pitch of 1.5 μm and 1.5 μm ≦ bmax. Need to be 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 fmin or less, but depending on the modulation method, the signal from the target layer fluctuates due to the density of changes in local optical properties. The 2-7 modulation code used in the above example is one of them, and the power spectrum characteristic 86 of the modulation signal is shown in FIG. There is a slight component below fmin. This is a filter, as mentioned above,
Although it can be suppressed by AGC, the interlayer crosstalk noise can be suppressed without using such a circuit by eliminating the variation of the density and making the DC component constant value.
The principle of the third method is that the spot diameter (2d
× NAF) local optical change (mark) included in the area
A code whose total area of the area is always constant is used. By doing so, the amount of interlayer crosstalk to the reproduction signal when the spot is scanned is always a constant DC value. The third method and the first method can be used together.

An example is shown. Well-known example "Toshida Doi, Iga
The power spectrum 87 of the modulated signal in the case of using the EFM modulation method in "Chapter: Digital Audio"
Has a characteristic that the spectrum of the low frequency component sharply decreases as shown in FIG. Therefore, the interlayer spacing d may be set so that the break point 88 where the spectrum sharply decreases coincides with the cutoff frequency at which H1 (S) = 0 for the optical characteristic function H1 (S) of the adjacent layer.

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

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

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 defocus of a certain value dm occurs, the condition of the image forming system of the microscope is changed. In some cases, the image of the recording film surface is formed on the light receiving surface when it is filled. For example, when a diffraction-limited spot is formed on the target layer to receive light, the distance to other layers is dm.
In this case, the mark row pattern on this layer is formed on the light receiving surface, and there is a possibility that the crosstalk noise in the signal band will be added to the information signal on the target layer. Therefore, the interlayer distance is dm
It is desirable to design the disk structure so that it does not become

Since the light reflected from each layer is the same as the irradiation light, when the distance between the layers is reduced to the coherence length, the reflected lights interfere with each other. As a result, the crosstalk noise between layers cannot be represented by the ratio of the amount of light received from the target layer and other layers on the light receiving surface. That is, due to the interference, the interlayer crosstalk noise appears at the square root of the received light amount ratio in the worst case. It is in the case of adjacent layers that this effect really matters.

Therefore, an embodiment for solving this problem is shown in FIG.
7 shows. The principle of this embodiment is to prevent the interference by changing the polarization direction of the light reflected from the adjacent layer. As one means for changing the polarization direction, see FIG.
In FIG. 7, the quarter wave plate layer 201 is provided in each intermediate layer 2.
The quarter-wave plate layer 201 has a phase difference of 90 degrees in the two-dimensional direction of the layer surface with respect to the wave of the electric field of the light traveling in the depth direction of the layer, that is, the optical thickness in the two directions. Is changed by a quarter wavelength. With such a disc structure, as shown in the figure, for example, when the polarization direction of the irradiation light is E-polarized light, the reflected lights from the layers adjacent to each other are different from each other by reciprocating in the quarter-wave plate layer 201. That is, the polarization directions alternate with the E-polarized light and the H-polarized light because they are different by ½ wavelength and 180 ° in phase difference. Therefore, the reflected light components between the adjacent layers do not interfere with each other, so that it is possible to reduce the crosstalk between the layers by expressing the light receiving amount ratio on the simple light receiving surface. Further, in the light receiving system, as shown in FIG. 27, a polarization beam beam splitter 202 is inserted, and the photodetectors 203 and 204 to be detected are separated according to the polarization direction of the reflected light. By doing so, at least the reflected light from the adjacent layer is not detected, and therefore, in the above-mentioned first reproducing method, it is possible to increase the allowable value of the variation in the size of the photodetector.

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 disc format, data management FIG. 5 shows an example of the format of the multi-layer disc 4.
From the substrate 3 on which light is incident, in the traveling direction of light,
1 to n layers. The data format in the k layer is a sector m that divides the disk on the radiation, a track 1 that manages the data position in the radial direction, and three or more addresses (l,
Data is managed by m, n). A given track l,
As shown in the figure, the format of the sector m includes recording / reproducing timing, a pre-formatted area in which address information is preliminarily created, user data is recorded / reproduced, and the presence / absence of data and prohibition of reading are recorded. It consists of a data area to be managed. The role of each layer is, as shown in the figure, a layer for recording and reproducing user data, a ROM (Read Only Memorey) layer, or a WOM layer.
(Write Once Memorey) is set to
S (Operating System), or as will be described later, recording or reproducing conditions in each layer may be pre-formatted at the time of disc production or recorded at the time of shipment. Further, as the layer data management layer, the data state of each layer, for example, presence / absence of data, error management, effective data area, and number of times of rewriting (overwriting) can be recorded at any time. Further, as an alternate layer, information can be reentered instead of the layer in which the recording error is detected.

Next, the data is recorded in the following combinations, for example.

(A) Recording is performed in order from the 1st layer to the kth layer to the Nth layer. However, in each layer, information is recorded in all user sectors and tracks before recording in the next layer.

When the above-mentioned data recording is performed, it is possible to perform more reliable recording / reproducing by using a recording medium having a characteristic of increasing the transmittance after recording. That is, since the transmittance up to the lower recording layer is increased, it is possible to provide the lower target layer with a sufficient light intensity for recording by irradiation with a light intensity substantially equal to the light intensity required for recording on the upper layer. Also, in reproduction, the reflected light component from the target layer returns to the detector with almost no attenuation, so that a reproduction signal with a high SN ratio can be obtained. A recording medium having the above characteristics is, for example, a perforated recording medium. When recording is performed on this medium, the reflection film has holes and the reflectance decreases, that is, the transmittance increases.

(B) Recording is performed in order from N → k → 1 layer and the lower layer. The rest is the same as (a).

(C) In each layer, information is recorded in all user sectors and tracks and then in the next layer. The order of recording layers is random access.

(D) The order of recording layers is random access. However, after all data is recorded in the relevant sector in one layer, the relevant sector in the next layer is filled, and the corresponding layers in all layers are recorded. After filling the sector, the data of the next sector is recorded.

(E) In the track, random access is performed in the layer direction. In this case, instead of the fixed block management by the sector, by applying the variable length block which is the data management of the magnetic disk, 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 host controller so as not to erroneously access the area recorded at the time of recording, or may be managed by the management area described above.

(3) Overall Configuration of Device FIG. 6 shows the overall configuration of a three-dimensional recording / reproducing device. When recording, the user data 17 is passed through the modulation circuit 18 to obtain the modulated binarized data 19. The modulated binarized data passes through the recording condition setting circuit 20 and the laser drive circuit 21 is driven so that the intensity is modulated under the optimum recording condition at the position where the light spot is located, and the optical head is driven. Two
The light intensity of the semiconductor laser in 2 is modulated, and recording on the disk 4 is performed.

On the other hand, when reproducing, a light spot is positioned on a target layer or track position on the disc, weak light is irradiated, and the intensity change of the reflected light is converted into an electric signal by the photodetector 10 to reproduce the reproduced signal. 23 and 24 are obtained. Playback signal 23, 2
4 suppresses inter-layer crosstalk through the reproduction control circuit 25, then passes through an AGC (auto gain control) circuit 26, absorbs fluctuations of a frequency lower than the data band, and outputs a signal at an absolute level which operates in a circuit later. Match.

After that, the reproduced signal passes through the waveform equalizer 27 to improve the waveform distortion (amplitude deterioration, phase shift) due to the data pattern, and the shaper 28 converts it into a binarized signal. The shaper 28 includes one that binarizes by an amplitude slice and one that detects zero-cross by differentiation.

Next, the binarized signal passes through the phase synchronization circuit 29 to extract the clock from the data. Phase synchronization circuit 2
Reference numeral 9 denotes a phase comparator 30 and a low pass filter (LPF) 3
1, a voltage controlled oscillator 32. The binarized signal is passed through the discriminator 33 for determining whether the data is “1” or “0” by the clock generated by the phase synchronization circuit 29, and is converted into the user data 17 by the decoder 34. In order to position the light spot at the target layer and the target position in the layer surface by the command from the host controller for the above recording and reproduction, the focus shift from the optical head 22 and the track shift signal detection 35 are performed, and the compensation circuit. A signal optimal for servo control is compensated by 36, and the light spot positioning mechanism is driven through the drive circuit 37.

(4) Access method As the light spot positioning mechanism, a two-dimensional actuator that drives the squeezing lens 8 in the layer direction and the disk radial direction, or a one-dimensional actuator and a squeezing lens that drives the squeezing lens 8 only in the layer direction. There is a combination of galvano mirrors that deflect the light beam incident on the beam No. 8 in the disk radial direction.

Here, in the case of performing random access for data recording / reproducing described in (2), a method of focusing on the target layer k will be described first. In order to detect the defocus signal, the size of the reflected light spot from the target layer changes depending on the defocus, and therefore the front-back difference shown in the known examples "JP-A-63-231738 and JP-A-1-19535" is used. A dynamic defocus detection method can be used. FIG. 24a shows an AF error signal 35 obtained when the position of the focusing lens is scanned in the layer direction Z with respect to the disc 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 sequentially obtained.

FIG. 23 is a block diagram of the first embodiment for accessing the target layer k. An AF (autofocus) actuator movement signal generation circuit 93 generates a sawtooth wave 106 on the rotating disk 4 to drive the AF actuator driver 91, and the focusing lens 8 is moved in the + Z direction (the lens on the disk surface) with respect to the disk surface. In the direction of getting closer to each other). At this time, the AF detection circuit 89 obtains the AF error signal 35. This signal detects the zero-cross point 105 in the pull-in point determination circuit 92,
The AF servo system controller 94 is informed that the focus is on a certain layer surface. In the determination circuit 92, as shown in FIG. 24a, the AF level 37 shown in FIG. 24b is generated by the slice level 103 slightly deviated from the zero slice level, and the trailing edge 104 is detected to immediately before the lens 8 passes the in-focus point. The timing of the controller 9
Send to 4.

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

Next, the layer number detection circuit 95 recognizes the number of the layer currently existing by reading the layer address in the preformat section shown in FIG. 5, and sends it to the controller 94. In the controller 94, from the j-th layer currently in focus to the k-th target layer which is a command from the upper controller, either the upper or lower (sign)
The number of (| k-j |) layers to be spot-moved in the (k-j) direction is recognized, and the jump forcing signal 107 is generated in the layer jump signal generation circuit 96 to perform AF actuation. Make the driver input.

The jump signal 107 is composed of a pair of pulses of + -polarity pulse with respect to the movement between one layer, and the + -pulses are switched depending on the vertical movement direction. The first pulse is used to drive the spot in the moving direction by a moving distance, and the next polarity inversion pulse is used to set the spot so that the spot does not go too far. Further, the pair of pulses of the number of moving layers is input to the driver 91. Next, the layer number is detected, and when j = k, 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 above.

A block diagram of the second embodiment for accessing the target layer k is shown in FIG.

The focusing lens 8 is moved up and down with respect to the rotating disk 4. At this time, the AF error signal 35 is obtained, and further the photodetector (detector) is used.
The total light amount 36 detected by 10 and output from the total light amount detection circuit 102 has a peak in each recording layer when focused, as shown in FIG. 24a. Therefore, the total light amount pulse 38 for detecting the AF pulse 37 and the total light amount pulse 38 is used as a gate by the pulse leveling circuit 98 in the cross layer signal detection circuit 101 shown in FIG. By detecting the trailing edge, more reliable focus detection can be performed. Further, in order to recognize the direction in which the lens moves with respect to the disc, the cross layer pulse generator 9 uses these two types of pulses.
By generating and counting the up pulse 109 and the down pulse 110 by 9, it is possible to always recognize in which layer the lens is positioned.

In FIG. 25, a sawtooth wave is generated from the AF actuator movement signal generating circuit 93 to drive the AF actuator so that the focus position moves at least from the uppermost layer to the lowermost layer of the disc. At this time, it is certain that it is sufficiently larger than the amount of vertical deflection of the rotating disk. The cross-layer signal detection circuit 101 counts the in-focus points of N layers, and moves the uppermost layer (n = 1) or the lens downward from the upper limit of the up pulse 109 when the lens is moved upward. Down pulse 1 when you let
From the lower limit of 10, recognize the bottom layer (n = N). It is sufficient to switch the switch 100 and close the servo loop immediately before the spot is focused on the layer in the target order by a command from the host controller. By controlling in this way,
It is possible to enable layer access without providing a layer address.

By the way, when a medium whose transmittance and reflectance are changed by recording is used, the AF error signal and the total light amount are as shown in FIG. 26a near the recorded layer.
Signals 123 and 124 different from those in FIG. 25 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 also drops in the signal in the servo band, the gain of the AF servo system fluctuates, the AF offset occurs, and defocus occurs in the recorded layer. In such a case, the ideal AF error signal and total light amount shown in FIG. 26 are obtained by always holding the signal of the portion where the mark is not recorded among the signal components detected by the photodetector. To be

An example of this method is shown in FIG. 26b. This figure shows the AF detection circuit 89 and the total light amount detection circuit 102 in FIGS. Front and rear photodetectors 11 in the principle diagram of the front-rear differential AF error signal detection optical system
1, 112 are light receiving surfaces 119, 120 or 121, 1
It consists of 22. If the light spots 113 and 114 on the front and rear photodetector surfaces 111 and 112 have the same size, they are in focus. The sum signal for each detector is obtained by the preamplifiers 115 and 116 having a band in which the spot scans the mark train, that is, a data recording / reproducing frequency band. Next, the sample and hold circuits 117 and 118 detect the signal in the scanning portion above the mark and hold it during the servo band. The difference signal of the signals thus obtained is used as the AF error signal 3
5, 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 light amount, or an area in which no mark is recorded is provided in advance as a sample area as a format, and the sample area is recognized by a sample timing pit or the like. The signal in that area may be held.

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

On the other hand, after the target layer is accessed, positioning in the disk radial direction, that is, track positioning is performed on the layer surface. To detect the track shift signal, a push-pull method, which is a known example, can be applied by providing a guide groove 39 in each layer as shown in FIG. In this method, the diffracted light from the groove of the layer other than the target layer is out of focus, so the phase of the wave of the light hitting the groove is disturbed, resulting in a uniform light amount distribution on the photodetector. , It does not affect the track shift signal for the target layer. Also, as shown in FIG.
By forming the wobble pit 40 in each layer in advance in the track direction, the well-known sample servo method can be applied. The technique of spot positioning described above is disclosed in the publicly known examples "JP-A-63-231738, JP-A-1-19535,"
319000034 ”. The method of creating guide grooves and wobble pits on the disc will be described later.

(5) Recording Control Method Next, a recording control method 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, which is the recording target, the recording power P (light intensity) must be set in consideration of the transmittance 42 up to the k layer. Therefore, as shown in FIG. 6, the recording condition setting circuit 20 uses the address recognition 41 and the transmittance 42 up to the k layer which is the recording target. FIG. 7 shows an example of a circuit block showing this in detail, and FIG.
Shown in.

In FIG. 9, when the binarized signal 19 is recorded as the mark 43 on the disc, the address recognition 41 (l, m, k) is considered in consideration of the difference in the recording condition depending on the recording position and the recording state according to the data pattern. ), The recording conditions, for example, the recording pulse width setting and the recording power setting condition are R
D / A converter 46 by inputting to OM44 and 45
The light intensity modulation signal P (t) 47 corresponding to the output of (1) is obtained, and the mark in the ideal recording state 47 can be recorded. The circuit configuration shown by the solid line in FIG. 7A can be applied to the following cases.

The order of recording data is (2)
In the case of (b), or in the case of (2) and (a), the transmittance to the target layer 42 (ΣTn (n = 0, 1, 2
... k-1)) was decided at the time of disc creation, so
If the layer address k is input, it can be treated as known.

In cases other than the above, the transmittance 42 to the layer at the time of recording is not known. In such a case, FIG. 7a
The circuit indicated by the dotted line is added to the circuit. Power setting RO
In M45, a recording power setting value in consideration of the transmittance up to the k layer when all layers are unrecorded is input.

By the address recognition 41, the transmittance ΣTn (n = n) at the time of shipment of the disc (or design value) up to k layers
0,1,2 ... k-1) and the transmittance ΣTn '(n = 0,1,2 ... k) up to the k layer immediately before recording detected by the method described later.
-1) 42 is input to the division circuit 47, and the change amount G of the transmittance G
Is input to the gain control circuit 48 so that the optimum recording power is set.

One example to which this circuit configuration can be applied will be shown. The third method for providing the “layer data management layer” described in section (2), reproducing and recognizing the contents in advance before recording, and achieving item (1) (C) Apply,
In the case of performing the data management in Sections (c) and (d) of (2), if it is known which layer is recorded, it is known that the constant transmittance after recording in the light spot in each layer is known. , ΣTn ′ (n = 0, 1, 2, ... k−1) 42 up to k layers can be obtained.

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

As a method of reproducing the area to be recorded in advance, the reproduction check is performed at the first rotation of the disk in the recording mode, the recording is performed at the next rotation, and the recording error check is performed at the next rotation. Another method is shown in Figure 8.
This is a method of performing reproduction check at the preceding spot 49 using a plurality of spots as shown in FIG. Here, the latter case will be described as an example. In the reproduction check, the preceding spot 4
The received reproduction signal C′k (t−τ) for 9 is used. Here, τ is a time conversion of the spot distance between the preceding spot 49 and the recording spot 51. Here, as shown in FIG. 7b, the reproduction signal Ck ′ in the state where the transmittance change amount G is focused on the k layer which is the recording target layer.
Is calculated by using the calculator 52 as the square root of the ratio of the designed reproduction signal Ck at the time of shipment of the disk. This is because the reproduction signal uses reflected light, and thus the change in transmittance up to the k layer appears in the reproduction signal as a square.

However, the value of the reproduction signal Ck is set as a disc format in advance as a check region, and a region which is not recorded in the layer direction is provided in the disc surface. It can be detected by absorbing the statistical variation. Therefore, highly accurate recording power control becomes possible. Further, regarding the photodetector 10 for obtaining the reproduction signal, as described in the first method for achieving the term (1) (C), the shape shown in FIG. 1 allows the reflected light from other layers to be reflected. Can be reduced, and the reflection component from the target layer can be detected as a reproduction signal, so that it is possible to obtain a more accurate transmittance change G. As shown in FIG. 9, the recording state 53 when the gain control is not performed
Is different from the ideal recording state 47, but the ideal recording state 47 can be obtained by performing gain control of the recording power and recording with G × P (t).

(6) Reproduction Control Method Next, the reproduction control circuit 25 shown in FIG. 6 for achieving the reproduction system of the present invention will be described in detail. Here, in addition to the principle of reproduction for reducing interlayer crosstalk, which is the first to third methods as described in section (1), a data signal generated when the distance between layers is further shortened to increase the density. A fourth method for suppressing the interlayer crosstalk component of the band or the interlayer crosstalk component generated when the optical system deviates from the ideal state will be described. In the fourth method, in addition to the detection of the reflected light component from the target layer as shown in the first method, the reflected light component from the adjacent layer that occupies most of the interlayer crosstalk is detected, and the two are mutually The reflected light component of the target layer is extracted by removing the included component by calculation.

The optical system is shown in FIG. 17a. The basic configuration is the same as that of FIG.
5 is positioned on the image plane of the adjacent layers (k + 1) and (k-1) on the light-receiving surface side when focusing on the k layer. However, in the arrangement of FIG. 17a, since the light is shielded from each other, a half mirror or beam splitters 56 and 57 are inserted in the image forming system as shown in FIG. 17b. The photodetectors 10, 54, 55 have a diameter D = (λ / NAI), but pinholes may be used as shown in FIG. 17C.
FIG. 14 shows a reproduction signal detected by each photodetector in this case.

Here, the reproduced signal Ck for the photodetector 10 and the reproduced signal C (k-1) for the photodetector 55.
And the reproduced signal C (k + 1) for the photodetector 54. A circuit for obtaining a reproduction signal is shown in FIG. However, in the system of FIG. 17, the integrating circuits 59 and 60, the delay circuit 6
No need for 1,62. As shown in FIG. 14, first to third
When the distance between the adjacent layer and the target layer satisfying the above method is smaller than the distance between the target layer and the adjacent layer, the reproduced signal 73 without the interlayer crosstalk obtained when the spot 69 scans the mark array 71 on the k-layer surface is To fluctuate. This is k
Along with the scanning of the spot 69 on the layer surface, the reproduction signal 64 that is detected because the spot 70 that is irradiated out of focus on the adjacent layer scans the mark array 74 on the adjacent layer and the reproduction of the other adjacent layer. This is because the components of the signal 63 are included in the reproduced signal 73 so much that they cannot be ignored. Therefore, as shown in FIG. 13, the arithmetic circuit 66 performs 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) However, CnR represents a reproduction signal component regarding the reflected light only from the n layer. Here, β <1 holds.
From the above equation, the calculation 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) C (k-2) R, C (k + 2) R is sufficient Since it is small and the frequency component is low, it can be ignored. Therefore, F≈ (1-2γβ) × CkR + (β−γ) × C (k−1) R + (β−γ) × C (k + 1) R (Equation 24) where γ≡β <1 , F≈ (1−β ² ) × CkR (Equation 25), interlayer crosstalk can be suppressed, and the reproduced signal 68 after calculation matches the reproduced signal 73 as shown in FIG. An example using a plurality of spots will be shown below as another configuration for achieving the above fourth method. In FIG. 14, two spots 75 having the same spot diameter as the defocus spot 70 are shown.
The two adjacent layers are scanned in advance of the spot 69 to obtain a reproduction signal. However, as shown in FIG. 13, delay circuits 61 and 62 corresponding to the spot interval are inserted to perform the same calculation as above. An example of an optical system used in this configuration is shown in FIG.
8 shows. In the figure, the optical axis is divided into three to show the principle of the optical system, but it is also possible to share the diaphragm lens 8. As means for making the spot diameters of the spots 75 and 82 focused on the preceding adjacent layer (2d × NAF), one is to insert a diaphragm 83 as shown in the figure and Make the effective aperture small. That is, the effective diameter a'is λ / (2d × NAF ² ).
It may be set to xa. Of course, the same effect can be obtained by dividing the optical axis into three optical axes and reducing the numerical aperture of the aperture stop lens of the preceding two optical systems. 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 spot shape 76 shown in FIG. 15 or the three spots 77, 78, 79 shown in FIG. The effect of is obtained. Therefore, the integrating circuits 59 and 60 are inserted in the circuit of FIG. In FIG. 15, the reproduction signal from the preceding spot is multiplied by a Gaussian distribution, which is the intensity distribution of the spot, by a weighting function 80 obtained by approximating, for example, a triangular distribution, and integration is performed. It is possible to obtain a reproduction signal when scanning 74. Also in FIG. 16, the weighting function 81 may be used in consideration of the spot intensity distribution in the two-dimensional direction.

Here, the weight setting circuit 6 used in the arithmetic circuit
A method for obtaining β will be described in Section 7. As shown in FIG. 19, as the disc format, at least three layers above and below
By arranging the mark recording areas 84 between layers so that they are not included in the same light flux, as shown in FIG. 14, h (k−
1) / hk, h (k + 1) / h to β (-1), β (+1)
Then, the weights of the upper and lower layers can be obtained respectively.

In the above-mentioned embodiments, basically, the case of recording / reproducing on one layer has been described. However, by using a plurality of spots and focusing on each layer, it is possible to simultaneously perform recording on two or more layers. Recording and reproduction can be performed, 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 into one optical head. Also, by using a plurality of light sources of different wavelengths, it is possible to selectively record the recording layer according to the wavelength,
Furthermore, it is possible to perform regeneration separation with a wavelength filter.

(7) Example of Disc Structure and Method for Making Disc As shown in FIG. 11, the surface of a disc-shaped chemically strengthened glass plate having a diameter of 130 mm and a thickness of 1.1 mm was subjected to photopolymerization method (2P method). A guide groove for tracking with a pitch of 1.5 μm, and one circumference is divided into 17 sectors, and at the beginning of each sector, the layer address, track address and sector address are formed in the form of concave and convex pits in the groove and in the middle of the groove A replica substrate on which an ultraviolet curable resin layer having pre-pits such as the above (this portion is referred to as a header portion) was formed was produced.

An antireflection layer 402 of silicon nitride having a thickness of about 50 nm was formed on the replica substrate 401 by using a sputtering apparatus having good film thickness uniformity and reproducibility. Next, in the same sputtering device, In ₅₄ Se ₄₃ T
The recording film 403 of the composition of l ₃ was formed to a thickness of 10 nm. 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 on this by a 2P method in which light is incident from the mold side using a transparent mold. In consideration of the heat insulating effect with the multilayer, the film was formed to a thickness of 30 μm.

Subsequently, an antireflection layer 405 of silicon nitride was formed in the above sputtering apparatus to a thickness of about 50 nm, and the recording film 4 having a composition of In ₅₄ Se ₄₃ Tl ₃ was formed.
06 is formed to a thickness of 10 nm, and an ultraviolet curable resin layer 407 having a guide groove for tracking and pre-pits such as a layer address, a track address and a sector address is formed thereon to a thickness of 30 μm by the 2P method. did. Further, an antireflection 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, on the other similar replica substrate 401 ', a silicon nitride antireflection layer 402', In is formed.
₅₄ Se ₄₃ Tl ₃ recording film 403 ′, ultraviolet curable resin layer 40
4 ', silicon nitride antireflection layer 405', In ₅₄ Se ₄₃
Tl ₃ recording film 406 ′, ultraviolet curable resin layer 407 ′,
Silicon nitride antireflection layer 408 ′, In ₅₄ Se ₄₃ Tl ₃
The recording film 409 'was sequentially formed. The two discs thus obtained were laminated with an adhesive layer 410 with the layers 409 and 409 'side facing inward. 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 of a single disc.

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

The disk produced in this example is one in which the atomic arrangement of the atoms constituting the recording film is changed by laser light irradiation to change the optical constant and read out by utilizing the difference in reflectance. The atomic arrangement change here is a phase change between crystalline and amorphous.

Immediately after forming the recording film on the above-mentioned disc, the constituent elements of the recording film have not reacted sufficiently and are in an amorphous state. When this disc is used as a write-once type, it is irradiated with a recording laser beam for crystallization recording, or the recording film is heated in advance by Ar laser beam irradiation, flash annealing or the like, and each element is sufficiently added. After the reaction and crystallization, the recording laser beam with high power density is irradiated to perform amorphized recording. Here, the range of laser power suitable for crystallization recording is a range higher than the temperature at which crystallization occurs and lower than the temperature at which amorphization occurs.
The range of laser power suitable for amorphization recording is higher than the crystallization temperature and lower than the temperature at which strong deformation occurs or holes are formed. In order to use this disc as a rewritable type, the recording film is heated in advance by Ar laser irradiation, flash annealing, or the like to sufficiently react and crystallize each element, and then a laser power suitable for crystallization Overwriting is performed by irradiating a recording laser beam that is modulated with a laser power suitable for amorphization.

The disk was rotated at 1800 rpm, the semiconductor laser light (wavelength 780 nm) was kept at a power level (1 mW) at which recording was not performed, and the light was condensed by the lens (NA = 0.55) in the recording head. The head was driven so that the center of the light spot was always aligned with the tracking groove and the middle of the groove by irradiating a recording film of one layer through the substrate and detecting the reflected light. The influence of noise generated from the groove can be avoided by setting the recording track in the middle of the groove. While tracking is performed in this way, automatic focusing is performed so that the focus is on the recording film, and recording / reproduction is performed. After passing the recording portion, the laser power was lowered to 1 mW and tracking and automatic focusing were continued. Note that tracking and automatic focusing are continued during recording. This focusing is performed by the recording film 403, the recording films 406 and 409 in the disc.
Each can be matched independently.

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

Recording power (mW) Reproduction signal intensity (mV) 6 30 7 100 8 160 160 9 210 10 250 250 11 280 12 300 14 310 After recording on the recording film 403, recording was further focused on the recording film 406. The recording power dependency of the reproduction signal strength 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 film 403 and the recording film 406, the recording film 409 is further focused. Recorded. The recording power dependency of the reproduction signal strength at this time is shown below.

Recording power (mW) Reproduction signal intensity (mV) 8 20 9 90 10 150 150 11 200 12 240 13 270 14 290 16 300 Also, the recording film 403 has 3 MHz and the recording film 406 has 4 MH.
The following shows the result of reading the reproduced signal by focusing on the recording films 403, 406, and 409 after recording a signal of 5 MHz on the z and the recording film 409, respectively.

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.

3 MHz 4 MHz 5 MHz 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, the CN ratio of each layer is 50 dB or more, and the interlayer crosstalk from the adjacent recording film is −25 dB. We were able to obtain a small, reliable signal that can be reproduced.

Next, recording films 403, 406 and 40
9, a thin film having a composition of Ge ₁₄ Sb ₂₉ Te ₅₇ is formed to a thickness of 2 nm, and the antireflection layers 402, 405 and 408 are formed.
Then, a ZnS thin film was formed to a thickness of 50 nm, and a disc having the same other configurations as the above was produced.
This disc is characterized in that the transmittance of the layer after recording is lowered. Therefore, by recording from the layer on the substrate side, the disc having the above-mentioned structure can be linearly moved at a linear velocity of 8 m / s (rotation speed 1
800 rpm, radius 42.5 mm), the case of recording from the lower layer to the upper layer on the substrate side is shown. First, the recording film 409 was focused on, and recording was performed by irradiating a recording pulse of 90 ns at a recording frequency of 5.5 MHz. The recording power dependency of the reproduction signal strength at this time is shown below.

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

Recording power (mW) Reproduced signal strength (mV) 7.5 20 8.5 9.5 9.5 150 150 10.5 200 11.5 240 12.5 270 13.5 290 15.5 300 Recording film 409 and After recording on the recording film 406, the recording film 403 was further focused and recorded. The recording power dependency of the reproduction signal strength 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 Further, the recording film 409 has 5 MHz, and the recording film 406 has 4 MH.
The measurement results of the CN ratio at each carrier frequency of the reproduced signal read out by focusing on the recording films 403, 406 and 409 after recording a 3 MHz signal on the z and the recording film 403 respectively are shown below.

3 MHz 4 MHz 5 MHz 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, the CN ratio is 50 dB or more for each layer, and the interlayer crosstalk from the adjacent recording film is −25 dB. We were able to obtain a small, reliable signal that can be reproduced.

Similar results were obtained by using a plastic disc such as polycarbonate or acrylic resin produced by injection molding as the substrate in addition to the chemically strengthened glass disc used in the above example.

The composition of the recording film is the above-mentioned In-Se-T.
In addition to the 1 system, Ge-Sb-Te system, Ge-Sb-Te-
M (M is a metal element) type, In-Sb-Te type, In-S
b-Se system, In-Se system, In-Se-M (M is a metal element) system, Ga-Sb system, Sn-Sb-Se system, Sn-
Similar results can be obtained by using an Sb-Se-Te system or the like.

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

As a recording film on a substrate similar to that shown in FIG.
Bi-substituted garnet (YIG (Y ₃ Bi ₃
Fe ₁₀ O ₂₄ )) particles dispersed in an organic binder were spin-coated. Bi-substituted garnet with a diameter of 20 nm was prepared by the coprecipitation method, and then 600-800
Crystallized by heat treatment at ℃. The organic binder used had a refractive index of 25. The thickness of the spin-coated recording film is about 1.5 μm, and the reflectance, transmittance, and absorption are at wavelength 5
R = 8%, T = 12%, K = 80 at 30 nm, respectively
%Met. Since the volume ratio of the Bi-substituted garnet in the binder was about 60%, the rotation angle of the plane of polarization of the reflected light at this time was about 0.8 degree. The method of stacking multiple layers with an ultraviolet curable resin layer provided therebetween, the method of laminating two discs, and the recording / reproducing method were the same as in the above-mentioned embodiment. However, the wavelength of the light source is λ = 530 nm.

An example of a recording / reproducing experiment using the information recording medium having the structure shown in FIG. 12 will be described. 12
FIG. 12A is a diagram showing a part of a sectional view of an information recording medium, and FIG. 12B is a diagram showing a sectional view of a part 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 and an ultraviolet curable resin layer (41
It was formed in 2). Next, the recording layer (413) was laminated by a vacuum vapor deposition method. The recording layer has a thickness of 8μ, as shown in FIG. 10 (b).
m Sb ₂ Se ₃ layer (414) and 3 μm thick Bi layer (415)
Was sandwiched. A UV-curing resin layer having a thickness of 30 μm and further provided with a laser light guide groove thereon.
Two sets of (412) and the recording layer (413) were laminated. That is, three recording layers were provided. An ultraviolet curable resin layer having a thickness of 100 μm was provided on the uppermost part for the purpose of protecting the recording layer. The recording layers will be referred to as a first recording layer, a second recording layer, and a third recording layer in order from the side closer to the substrate.

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

When the recording layer was irradiated with a laser beam of 2.0 mW in focus, the reflectance was measured. The reflectances of the first recording layer, the second recording layer and the third recording layer before recording were respectively , 8.5%, 5.8%, 4.4%. Recording was performed by irradiating each recording layer with a laser beam of 6.0 mW or more. The reflectance of the portions of the first recording layer, the second recording layer, and the third recording layer irradiated with the recording laser light is 18.5, respectively.
%, 13.0% and 9.4%.

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

Although not performed in this embodiment, before recording,
If the land portion is irradiated with continuous laser light, the land portion is alloyed, and the average light transmittance per recording layer is 10%.
To rise. Therefore, the above-described reflectance before and after recording increases, which is convenient when performing tracking or the like. Further, even if 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 as long as it produces an alloy by heating.

[0266]

According to the present invention, an optical system for narrowing down an optical spot capable of stable recording / reproducing in a recording process and a reproducing process, a disc structure, a photo-detecting optical system, and particularly a crosstalk between adjacent layers which is a problem is suppressed. Since it is possible to provide an encoding method, a crosstalk canceling method, a three-dimensional data format, and a method for creating a disc and a three-dimensional access method associated therewith, a light spot can be narrowed down to each layer of a disc having a multi-layered structure, with high reliability. You can record and play back data.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle of a recording / reproducing system of the present invention (a principle diagram of a first reproducing system).

FIG. 2 is a block diagram of a basic optical system applied to the present invention, where a is an example of a parallel optical system and b is an example of a diffusing optical system.

FIG. 3 is a principle diagram of the recording method of the present invention, in which a is a diagram showing light intensity in each layer, b is a diagram showing spot areal densities in other layers when the k layer is focused, and c is a diagram. The figure which shows the power density in another layer about the case where it focuses on k layer.

FIG. 4 is a diagram showing the principle of a reproducing method according to the second and third aspects of the present invention.

FIG. 5 is a diagram showing an example of a disc format of the present invention.

FIG. 6 is an overall configuration diagram of a three-dimensional recording / reproducing apparatus of the present invention.

FIG. 7 is a block diagram showing a recording control method of the present invention.

[FIG. 8] RBW (Read Before Write) with a preceding beam
FIG.

FIG. 9 is a diagram illustrating a recording control method of the present invention.

FIG. 10 is a diagram showing an example of a three-layer film structure and recording characteristics, a is an example of a three-layer film structure, and b is recording characteristics.

FIG. 11 is a sectional view showing the structure of a phase change type information recording medium used in an example of the present invention.

FIG. 12 is a partial sectional view of a third information recording medium used in the present invention.

FIG. 13 is a block diagram showing a reproduction control method of the present invention.

FIG. 14 is a diagram illustrating a reproduction control method of the present invention.

FIG. 15 is a diagram illustrating a reproduction control method of the present invention.

FIG. 16 is a diagram illustrating a reproduction control method of the present invention.

FIG. 17 is 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.

FIG. 18 shows an example of an optical system for realizing the reproduction control method of the present invention.

FIG. 19 is a diagram illustrating a calculation coefficient γ (≡β) check area and a principle.

FIG. 20 is a disc structure for realizing the third reproducing method of the present invention.

FIG. 21 is an example of applying a two-dimensional recording / reproducing system.

FIG. 22 shows an example in which a two-dimensional recording / reproducing system is applied.

FIG. 23 is a block diagram illustrating layer access according to the present invention.

FIG. 24 is a diagram showing defocus detection in each layer.

FIG. 25 is a block diagram illustrating layer access according to the present invention.

FIG. 26 is a diagram showing defocus detection in a recorded layer, a is a defocus signal in a recorded layer, and b is defocus detection of the present invention.

FIG. 27 is an explanatory diagram of a method of reducing interference of reflected light between adjacent layers of the present invention.

[Explanation of symbols]

1 ... recording layer, 2 ... intermediate layer, 3 ... substrate, 4 ... disk, 5
… Semiconductor laser, 8… narrowing lens, 9… image lens,
10 ... Photodetector, 11 ... Light spot, 12 ... Focal plane, 1
3 ... Optical characteristic function of the target layer at the time of no aberration, 14 ...
Optical characteristic function of adjacent layer, 15 ... Direction of change of characteristic function when defocus increases, 16 ... AGC frequency characteristic, 20 ... Recording condition setting circuit, 23, 24 ... Reproduction signal, 25 ... Reset Control circuit, 26 ... AGC circuit, 35
... AF error signal, 36 ... total light amount, 39 ... guide groove, 40 ...
Wobble pit, 41 ... Address recognition, 42 ... Transmissivity up to k layer, 43 ... Mark, 44, 45 ... ROM, 46
... D / A converter, 47 ... Ideal recording state mark, 49
... Preceding spot, 51 ... Recording spot, 52 ... Arithmetic unit, 53 ... Recording state without gain control, 54, 55 ... Photodetector, 56, 57 ... Beam splitter, 59, 60 ... Integrating circuit, 61 , 62 ... delay circuit,
63, 64, 68 ... Playback signal, 67 ... Weight setting circuit, 6
9 ... Spot focused on the k-layer surface, 71 ... Mark arrangement on the k-layer surface, 72, 73 ... Reproduction signal, 74 ... Mark row,
75, 76, 77, 78, 79, 82 ... Spot focused on adjacent layer, 80, 81 ... Weighting function, 83 ... Aperture,
84 ... Mark recording area, 86 ... Power spectrum of modulation signal when 2-7 modulation method is used, 87 ... Power spectrum of modulation signal when EFM modulation method is used, 88
... spectrum break point, 91 ... AF actuator movement signal generation circuit, 92 ... pull-in point determination circuit, 95 ... layer number detection circuit, 100 ... switch, 101 ... cross layer signal detection circuit, 103 ... slice level, 105
... Zero cross point, 109 ... Up pulse, 110 ... Down pulse, 111, 112 ... Photodetector, 113, 114
... light spots on front and back photodetector surfaces, 115, 116 ... preamplifiers 117, 118 ... sample and hold circuits, 1
19, 120, 121, 122 ... Light receiving surface, 123 ... AF error signal near recorded layer, 124 ... Total light amount near recorded layer, 401, 401 '... Replica substrate, 4
02,402 ', 405,405', 408,408 '
... Antireflection layer, 403, 403 ', 406, 406',
409, 409 '... Recording film, 404, 404', 40
7,407 '... UV curable resin layer, 410 ... Adhesive layer,
411 ... Glass substrate, 412 ... UV curable resin layer, 41
3 ... recording layer, 414 ... Sb ₂ Se ₃ layer, 415 ... Bi layer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Matsumoto             1-280, Higashikoigokubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Motoyasu Terao             1-280, Higashikoigokubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Okamine Shigenori             1-280, Higashikoigokubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Tetsuya Nishida             1-280, Higashikoigokubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor, J. Miyamoto             1-280, Higashikoigokubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. F term (reference) 5D029 JB02 JB13                 5D044 BC02 CC06 DE02 DE46 GK12                 5D090 AA01 BB02 BB03 BB04 CC01                       CC04 CC12 CC14 DD01 DD05                       FF05 FF12                 5D117 AA02 CC06 DD00 FF06 GG02

Claims (3)

[Claims] 1. A method of converging a light spot on a first recording layer of a medium having a plurality of recording layers on which information is recorded, and an address of the first layer converging the light spot. A step of reading, a step of designating a second layer different from the first layer, a number of light spot moving layers from the first layer to the second layer and a moving direction are recognized to generate a signal And a step of inputting the signal to a means for moving a light spot, and a step of moving the light spot based on the input signal, wherein the signal is the plurality of the light spots. The layer access method is characterized by comprising a pair of pulses having different polarities with respect to the movement of one recording layer, and switching the polarities depending on the moving direction. 2. 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, wherein a focal position of the light spot is from an uppermost layer of the recording medium. A layer access method comprising a step of generating a sawtooth wave from a movement signal generation circuit of the light spot moving means so as to move to the lowermost layer and driving the light spot moving means. 3. An information recording method for recording information by irradiating a first recording layer of a medium in which a plurality of recording layers are laminated with a light spot, in order from the uppermost layer to the lowermost layer of the plurality of recording layers, or An information recording method, wherein information is recorded by moving a light spot in order from the bottom layer to the top layer.