JP2001093189A - Multilayer type optical disk and its recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To irradiate two signal recording layers with the recording and a sufficient amount of reproducing light. SOLUTION: A second signal recording layer 5 formed in a prescribed irregular pattern by a land part which is a recess viewed from the side of a light transmission protective layer 6 and a groove part which is the part to be a projection is irradiated with a laser beam 20, the laser beam 20 is scanned in a track direction and thus, only one of the land part and the groove part is initialized to a crystal state. Then, at the time of performing recording and reproducing to the second signal recording layer 5, only the part turned to the crystal state out of the land part and the groove part is irradiated with the laser beam 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer optical disc having two signal recording layers and recording and / or reproducing information signals on each signal recording layer. The invention also relates to a recording / reproducing method for such a multilayer optical disc.

[0002]

2. Description of the Related Art As a recording medium on which an information signal is recorded,
There is an optical disk on which recording and / or reproduction (hereinafter, referred to as recording / reproduction) is optically performed. On optical discs,
For example, there are a read-only optical disk in which a pit row corresponding to an information signal is formed, a magneto-optical disk and a phase-change optical disk in which an information signal can be rewritten or additionally recorded.

[0003] In an optical disk, a signal recording layer is formed in a thin film shape on a substrate, and recording and reproduction are performed on the signal recording layer by irradiating a laser beam with a recording and reproducing device. Further, on the substrate, a groove, which is a groove formed continuously along the track, and a pit row in which a large number of pits are arranged along the track, are spirally or concentrically formed at a predetermined track pitch. Is formed. The optical disc is configured to perform recording and reproduction by irradiating a laser beam along a groove or a pit row.

One of such optical disc standards is
There is a DVD (Digital Versatile Disc). In a DVD, a single-layer DVD having only one signal recording layer is 4.7.
8.5 GB for a two-layer DVD having two GB and two signal recording layers
An optical disk having a storage capacity of B has been realized. D
VD has a storage capacity several times to several tens of times larger than that of a CD, while having an outer shape equivalent to a CD (Compact Disc) which is a standard of an optical disk that has been widely used in the past. It is expected to be used as an optical disk compatible with large capacity.

[0005]

By the way, the above-mentioned D
VD is a read-only optical disk having a pit row formed in a signal recording layer. When manufacturing this DVD, a stamper having a concavo-convex pattern inverted with respect to a desired pit row is used, and a stamper is formed on a substrate manufactured by an injection molding method.
A signal recording layer and the like are sequentially laminated to form a film. Since the production of a stamper is expensive, before producing a DVD, a prototype disk is produced using a recordable and reproducible optical disk having the same reproduction characteristics as this DVD. It is necessary to verify that it does not occur.

At this time, for verification of a single-layer DVD, a DV
An optical disk of a standard called DR is used.
The DVD-R is a so-called write-once optical disc in which writing to the signal recording layer can be performed only once, and the signal recording layer is formed of an organic dye material such as cyanine or phthalocyanine.

However, in order to verify a two-layer DVD, it is necessary to have an optical disk which has two signal recording layers, is capable of rewriting or additional recording of recorded signals, and satisfies the reproduction characteristics of the DVD standard. Become. Conventionally, such an optical disk does not exist, and a two-layer type D using a stamper is used.
Verification could only be performed after VD creation.
Therefore, as a result of the verification, if a defect is found in the recorded contents or the reproducing operation, it is necessary to newly make a stamper, and there has been a problem that the cost of manufacturing a two-layer DVD increases.

In view of the above, the present invention provides a multi-layer optical disc having two signal recording layers, capable of rewriting or appending information signals to each signal recording layer, and having sufficient recording / reproducing characteristics, and its recording. It is intended to provide a reproduction method.

[0009]

The inventor of the present invention has conducted various studies to achieve the above-mentioned object, and found that the phase change material forming the signal recording layer has a more amorphous state than a crystalline state. We paid attention to sometimes showing a large light transmittance. And 2
Of the signal recording layers of the layer, the upper signal recording layer located on the side irradiated with the recording / reproducing light is formed of a phase change material, and is not used for recording / reproducing information signals in the upper signal recording layer. By not forming the portion in a crystalline state, it has been found that the recording / reproducing light can be sufficiently incident on the signal recording layer located on the lower layer side.

That is, the multilayer optical disc according to the present invention is formed on a substrate by a first signal recording layer made of a phase change material or an organic dye material, a transparent layer, and a phase change material. A second signal recording layer and a light transmission protection layer are sequentially laminated, and the first signal recording layer and the second signal recording layer are irradiated by irradiating recording / reproducing light from the light transmission protection layer side. Are multi-layer optical discs on which information signals are recorded and / or reproduced. The second signal recording layer is formed in a predetermined concavo-convex pattern by a land portion that is a concave portion as viewed from the light transmission protection layer side and a groove portion that is a convex portion. In the second signal recording layer, as an initial state, one of the land portion or the groove portion is in a crystalline state, the other is in an amorphous state, and the other is in a crystalline state. The recording and / or reproduction of the information signal is performed.

In the multilayer optical disk having the above-described structure, the initial state of the second signal recording layer is such that only one of the lands or grooves where the information signal is recorded and / or reproduced is in the crystalline state. That this second
Can improve the transmittance of the signal recording layer for recording / reproducing light. Therefore, it is easy to irradiate the recording / reproducing light with sufficient intensity to the first signal recording layer located on the lower layer side, and the information signal can be reliably recorded. In addition, since the transmittance of the second signal recording layer is improved, at the time of reproducing the information signal with respect to the first signal recording layer, the recording / reproducing light is reflected by the first signal recording layer. It is possible to obtain a sufficient intensity and a sufficient signal modulation degree.

Further, the recording / reproducing method for a multi-layer optical disc according to the present invention comprises a first signal recording layer formed of a phase change material or an organic dye material on a substrate, a transparent layer, and a phase change material. A second signal recording layer formed and a light transmission protection layer are sequentially laminated, and the first signal recording layer and the second signal recording layer are irradiated by irradiating recording / reproducing light from the light transmission protection layer side. This is a recording / reproducing method for a multi-layer optical disc in which information signals are recorded and / or reproduced with respect to each signal recording layer. First, with respect to the second signal recording layer, which is formed in a predetermined concavo-convex pattern by a land portion which is a concave portion as viewed from the light transmission protection layer side and a groove portion which is a convex portion, By irradiating the recording / reproducing light and scanning the recording / reproducing light in the track direction, only one of the land portion or the groove portion is initialized to a crystalline state. Next, when recording and / or reproducing an information signal with respect to the second signal recording layer, a recording / reproducing light is applied only to the land portion or the groove portion which is in a crystalline state. .

Therefore, according to this method, only the lands or grooves on which recording and / or reproduction are performed are initialized to the crystalline state with respect to the second signal recording layer of the multilayer optical disc. Can be. Thereby, the transmittance of the second signal recording layer with respect to the recording / reproducing light can be improved. Therefore, at the time of recording the information signal, it becomes easy to irradiate the recording / reproducing light of sufficient intensity to the first signal recording layer located on the lower layer side, and the information signal can be reliably recorded. Further, at the time of reproducing the information signal from the first signal recording layer, it is possible to sufficiently obtain the intensity of the return light which is reflected by the recording / reproducing light reflected on the first signal recording layer and has a sufficient signal modulation degree. Can be obtained.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. Hereinafter, first, as one configuration example of the multilayer optical disc according to the present invention,
A multilayer optical disc 1 as shown in FIG. 1 will be described.

As shown in FIG. 1, a multilayer optical disc 1 is provided on a substrate 2 on which a predetermined uneven pattern is formed.
Signal recording layer 3, intermediate layer 4, and second signal recording layer 5
And the light transmission protection layer 6 are sequentially laminated.

The multilayer optical disk 1 is housed in a disk cartridge (not shown), for example, and is used detachably with respect to a recording / reproducing apparatus (not shown). In addition,
The multilayer optical disk 1 may be used without being housed in a disk cartridge, or may be configured integrally with a recording / reproducing device.

When recording / reproducing is performed on the multilayer optical disc 1, the recording / reproducing apparatus irradiates a laser beam having a wavelength of, for example, about 655 nm from the main surface side facing the outside of the light transmission protection layer 6, and Laser light is applied to the first signal recording layer 3
Alternatively, the light is emitted toward the second signal recording layer 5. At this time, as shown in FIG. 1, the laser beam is condensed by the objective lens 7 of the recording / reproducing apparatus, and is focused on the second signal recording layer 5 so as to focus on the second signal recording layer 5. Recording and reproduction are performed. When recording / reproducing is performed on the first signal recording layer 3, the laser beam condensed by the objective lens 7 passes through the second signal recording layer 5 and the intermediate layer 4 and the first signal The focus is set on the recording layer 3.

As described above, as a method of condensing a laser beam on each of the first signal recording layer 3 and the second signal recording layer 5, one objective lens 7 is used. There is a method achieved by moving the position 7 in the optical axis direction, and a method achieved by switching between these two objective lenses 7 using two objective lenses 7 having different focal lengths.

In the multilayer optical disc 1, the first signal recording layer 3 and the second signal recording layer 5 are formed of a phase change material, and the first signal recording layer 3 and the second signal recording layer 5 are formed. By irradiating each of the layers 5 with the laser beam as described above, recording and reproduction of a recording signal is performed by a so-called phase change recording method.

Specifically, when recording signals are recorded on the multilayer optical disc 1, a laser beam having a predetermined output is incident from the light transmission protection layer 6 side by the recording / reproducing apparatus, and the first signal recording layer Irradiation is performed on the third or second signal recording layer 5. As a result, one of the signal recording layers is heated to a temperature equal to or higher than the melting point at the irradiation position of the laser beam. Thereafter, the signal recording layer is cooled and becomes an amorphous state at this position. In the multilayer optical disc 1, a recording signal is recorded by forming an amorphous portion, that is, a recording mark in accordance with the recording signal.

When the recording signal recorded on the signal recording layer is erased, the multilayer optical disc 1 is irradiated with a laser beam having a weaker output than during recording, and the signal recording layer is crystallized at this irradiation position. The temperature is raised to a temperature not lower than the melting point and not lower than the temperature.
Thereby, the signal recording layer becomes a crystalline state at this irradiation position regardless of the state before irradiation.

Further, when reproducing the recording signal recorded in the signal recording layer, the multilayer optical disk 1 is irradiated with a laser beam having a weaker output than when erasing the recording signal.
At this time, the recording / reproducing device detects the return light that is reflected by the laser light and returns to the signal recording layer, and determines whether the signal recording layer is in a crystalline state or an amorphous state at the irradiation position of the laser light. The recording mark is read by utilizing the fact that the reflectivity is different, and the recording signal is reproduced. In the multilayer optical disc 1, for example, when the recording material of the first signal recording layer 3 and the second signal recording layer 5 is in a crystalline state where no recording signal is recorded, the reflectance to laser light is high. The recording and reproduction are performed in a so-called High-to-Low recording mode in which the reflectance is reduced when the recording signal is recorded in an amorphous state.

In the multilayer optical disc 1, the substrate 2
The whole is formed in a substantially disc shape with a thickness of, for example, about 1.2 mm from a hard material. As a material for forming the substrate 2, for example, polycarbonate resin, acrylic resin,
Various resin materials such as polyolefin resin and epoxy resin, and glass materials such as synthetic quartz glass can be used. Further, various metal materials such as aluminum and a stainless alloy may be used.

The substrate 2 has a predetermined concavo-convex pattern formed in a spiral shape or concentric shape on the main surface 2a on the side on which each layer is formed. That is, in the multilayer optical disc 1, when viewed from the light transmission protection layer 6 side where the laser beam is incident, a land portion which is a concave portion and a groove portion which is a convex portion are formed on the substrate 2. ing. This concavo-convex pattern is formed at a depth of, for example, about 60 nm.

In the multi-layer optical disc 1, the land and groove pattern is transferred to each layer formed on the substrate 2. Further, in the multilayer optical disc 1, tracks on which recording and reproduction are performed are formed along a concave / convex pattern formed by lands and grooves. The interval between the concavo-convex patterns is called a track pitch.
μm. Therefore, when the multilayer optical disc 1 is used as an optical disc conforming to the DVD standard, it is desirable to form the concavo-convex pattern so that the track pitch becomes 0.74 μm.

The intermediate layer 4 and the light transmission protection layer 6 are made of a first signal recording layer 3 and a second signal recording layer, respectively, made of a hard material having a light transmitting property with respect to a laser beam incident for recording and reproduction. It is formed on the signal recording layer 5 in the form of a thin film. As a material for forming the intermediate layer 4 and the light transmission protective layer 6, for example, various ultraviolet curable resins such as an acrylic acid-based ultraviolet curable resin, and resin sheets such as a polycarbonate sheet and a polyolefin sheet can be used. The thickness of the intermediate layer 4 is, for example, about 40 μm, and the thickness of the light transmission protection layer 6 is, for example, about 600 μm.

The first signal recording layer 3 and the second signal recording layer 5 are formed of a phase change material in the form of a thin film. As the phase change material, for example, InSe, SbSe, Sb
Binary alloys such as Te, ternary alloys such as InSbSe, InSbSe, quaternary alloys such as GeSbSeTe, AgInSb
A ternary alloy such as SeTe may be used. Further, nitrides or oxides of these alloys may be used.

The first signal recording layer 3 and the second signal recording layer 5 may have a structure in which a plurality of thin films having various functions are stacked. Specifically, for example,
The first signal recording layer 3 includes, from the substrate 2 side, a light reflecting layer, a first enhancement layer, a first crystallization promoting layer, a first signal recording thin film, and a second crystallization promoting layer. And a second enhancement layer may be sequentially laminated. Further, for example, the second signal recording layer 5 is formed from the side of the intermediate layer 4.
Even when the third enhancement layer, the third crystallization promotion layer, the second signal recording thin film, the fourth crystallization promotion layer, and the fourth enhancement layer are sequentially laminated. Good.

That is, in the multilayer optical disc 1, the first signal recording thin film and the second signal recording thin film are formed of the above-mentioned phase change material, and the first signal recording thin film and the second signal recording thin film are formed. The first signal recording layer 3 and the second signal recording layer 5 may be formed by having a structure in which a crystallization promoting layer and an enhancement layer are respectively laminated on both principal surfaces of the above.

The light reflection layer has a function as a reflection layer for reflecting the laser light incident from the light transmission protection layer 6 side. In the multilayer optical disc 1, since the first signal recording layer 3 is configured to have the light reflection layer, the recording laser beam can be reflected by the incident laser beam so that the recording mark can be read by the recording / reproducing apparatus. In addition, it is possible to improve the use efficiency of laser light at the time of recording. As a material for forming the light reflection layer, for example, Al, Au, Ag, C
It is desirable to use a non-ferrous metal element such as u, or a compound thereof, alone or in combination.

The enhancement layer has a function of adjusting the reflectance of the first signal recording layer 3 and the reflectance of the second signal recording layer 5, respectively. In the multilayer optical disc 1, since the first signal recording layer 3 and the second signal recording layer 5 have the enhancement layer, it is possible to adjust each signal recording layer to have a desired reflectance. it can. Therefore, the multilayer optical disc 1 reflects the first signal recording layer 3 and the second signal recording layer 5 so that the reflectivity required for a two-layer DVD, which is one of the optical disc standards, is satisfied. By adjusting the ratio, the optical disk can be used as a rewritable or write-once optical disk compatible with the dual-layer DVD standard.

As a material for forming the enhance layer, for example, ZnS, ZnS-SiO ₂ , SiO ₂ , MgF, etc. can be used alone or in combination.

The crystallization promoting layer has a function of promoting crystallization of the first signal recording thin film and the second signal recording thin film. The material for forming the crystallization promoting layer is a material which has been conventionally used as a dielectric layer (enhancement layer) in an optical recording medium and has an extinction coefficient k of 0.3 with respect to the wavelength of laser light. It has been confirmed that all of the following materials except sulfide function.

That is, the crystallization promoting layer is made of Al, Si,
Ta, Ti, Zr, Nb, Mg, B, Zn, Pb, C
nitrides, oxides, carbides, fluorides, oxynitrides, nitrocarbides, of metals such as a, La, Ge, etc.
It can be formed of a material such as an oxycarbide or a material containing these as a main component. However, materials having particularly excellent crystallization accelerating functions include Si-C, Si-C-
O, Si-C-H, Si-C-HO, Si-NO,
Si-N-H, Si-N-HO, Si-CN, Si
—C—N—O, Si—C—N—H, Si—C—N—H—
Materials having compositions such as O and Si-OH can be given. For _{example, Si-C, Si 3 N} 4, SiO 2, Al
Examples thereof include N, Al ₂ O _{3, and the} like, or a material containing these as a main component and introducing elements such as oxygen, hydrogen, and nitrogen.

In the multilayer optical disc 1, the first signal recording layer 3 and the second signal recording layer 5 each have a crystallization promoting layer, thereby promoting the generation of crystal nuclei. The crystallization speed can be improved. As a result, the multilayer optical disc 1 can obtain a sufficient overwrite erasure ratio even at a high transfer rate, leading to obtaining a good jitter value. Therefore, in the multilayer optical disc 1, recording marks can be stably formed at a high speed on the first signal recording layer 3 and the second signal recording layer 5, and a high-speed and reliable recording operation can be performed. Can be.

The material for forming the crystallization promoting layer may be a material that also functions as an enhance layer. For example, an enhancement layer formed using a ZnS-SiO ₂ mixture may be provided separately from a crystallization promoting layer in contact with the signal recording thin film, or a crystallization promoting layer formed of ZnS-SiO ₂ may be provided as a signal recording thin film. You may provide so that it may contact. That is, if a layer formed of a material that promotes crystallization of each signal recording thin film is provided so as to be in contact with each signal recording thin film of the first signal recording layer 3 and the second signal recording layer 5. , With or without enhanced layer,
Alternatively, the type of material used for the enhancement layer is not limited.

Each of the signal recording thin films of the first signal recording layer 3 and the second signal recording layer 5 has a crystallization promoting layer provided on at least one surface thereof. The crystallization speed can be improved as compared with the case where no is provided. However, when a crystallization promoting layer is provided so as to be in contact with both surfaces of each signal recording thin film, a greater crystallization promoting effect can be obtained.

In the above description, the first signal recording layer 3 and the second signal recording layer 5 are both formed of a phase change material, and recording and reproduction are performed by a phase change recording method. The present invention is not limited to such a configuration. In the multilayer optical disc 1, the first signal recording layer 3 is formed of, for example, an organic dye material such as cyanine or phthalocyanine, and is used as a write-once type signal recording layer in which recording signals can be written only once. Is also good.

The multi-layer optical disc 1 according to the present invention, as described above, irradiates the two signal recording layers, the first signal recording layer 3 and the second signal recording layer 5, with laser light. It is configured to perform recording and reproduction by performing Therefore, if the transmittance of the second signal recording layer 5 located on the upper layer side with respect to the irradiated laser light is small, a sufficient amount of laser light for performing recording and reproduction is applied to the first signal recording layer 3. It is difficult to reach.

Actually, in a conventional optical disk having two signal recording layers, the signal recording layer located on the upper layer side irradiated with the laser beam has a small transmittance, and is sufficiently sufficient for the signal recording layer on the lower layer side. It was difficult to reach a sufficient amount of laser light. In a conventional optical disk, the entire surface of the signal recording layer formed of a phase change material is in a crystalline state as an initial state.

The present inventor has paid attention to the fact that the phase change material forming the signal recording layer shows a larger light transmittance in the amorphous state than in the crystalline state, and focuses on the signal recording layer on the upper layer side. It has been found that by making a part of the layer in an amorphous state, a sufficient amount of laser light can reach the lower signal recording layer.

That is, in the multilayer optical disc 1, the second
As an initial state of the signal recording layer 5, for example, the land portion is in an amorphous state and the groove portion is in a crystalline state. Then, in the multilayer optical disc 1, when recording / reproducing on / from the second signal recording layer 5, a laser beam is applied to a groove portion whose initial state is a crystalline state. That is, in the multilayer optical disc 1, the recording of an information signal is performed by forming a recording mark in an amorphous state on a groove portion in a crystalline state.

As described above, the multilayer optical disc 1
In the signal recording layer 5, recording and reproduction are performed only on the groove portion whose initial state is a crystalline state, and
Land portions not used for recording / reproduction are in an amorphous state. Therefore, the multilayer optical disc 1 has a land portion and a groove portion in the second signal recording layer 5 as a whole.
The transmittance to laser light can be improved. Therefore, the first signal recording layer 3 located on the lower layer side can be irradiated with a laser beam having a sufficient intensity,
The information signal can be reliably recorded on the two signal recording layers. Further, since the transmittance of the second signal recording layer 5 is improved, it is possible to sufficiently obtain the intensity of the return light that is reflected by the laser light and returned to the first signal recording layer 3, and A sufficient signal modulation degree can be obtained.

Accordingly, the multi-layer optical disc 1 can rewrite or additionally record information signals on the two signal recording layers, and can be used as a multi-layer optical disc having sufficient recording and reproducing characteristics.

In the above description, the initial state of the groove portion in the second signal recording layer 5 is set to a crystalline state, and recording and reproduction of an information signal are performed on this groove portion. It is not limited to the configuration. For example, the groove portion in the second signal recording layer 5 may be in an amorphous state, the initial state of the land portion may be in a crystalline state, and the recording and reproduction of the information signal may be performed on the land portion. That is, one of the land portion and the groove portion is made to be in a crystalline state and the other is made to be in an amorphous state in accordance with a desired recording / reproducing characteristic, etc. What is necessary is just to perform reproduction.

However, it is possible to efficiently irradiate the laser beam by adopting a structure in which the initial state of the groove portion which is convex on the side where the laser beam is incident is a crystalline state and recording / reproducing is performed on the groove portion. Becomes easier.

Next, a recording / reproducing method for a multilayer optical disk according to the present invention will be described. Hereinafter, a method of performing recording and reproduction on the above-described multilayer optical disc 1 by applying the present invention will be described.

When performing recording and reproduction on the multilayer optical disc 1, it is necessary to first initialize at least the second signal recording layer 5. As shown in FIG. 2, the initial state of the second signal recording layer 5 is an amorphous state 5a immediately after the multilayer optical disc 1 is manufactured. Therefore, the laser beam 20 is irradiated at a predetermined intensity only to the groove portion in the second signal recording layer 5, and the laser beam 20 is operated in the track direction (the direction of arrow A in FIG. 2). 2, only the second signal recording layer 5 of the multilayer optical disc 1 is shown, and other components are omitted.

As a result, the groove portion of the second signal recording layer 5 is instantaneously heated to a temperature higher than the crystallization temperature and lower than the melting point at the irradiation position of the laser beam 20. Thereafter, the heated portion is cooled to be in the crystalline state 5b. In this initialization step, the laser beam 2
By irradiating 0, all the groove portions of the second signal recording layer 5 are initialized to the crystalline state 5b.

When recording an information signal on the second signal recording layer 5, only the groove portion is irradiated with the laser beam 20, and the temperature of the laser beam 20 rises to the melting point or higher at the irradiation position. Warm up. After that, the second signal recording layer 5 is cooled, becomes amorphous at this position, and a recording mark is formed.

When reproducing the information signal from the second signal recording layer 5, only the groove portion is irradiated with a laser beam 20 having an output lower than that at the time of recording. And
By detecting return light that is reflected by the laser beam 20 and returned to the second signal recording layer 5, the second signal recording layer 5 is in a crystalline state or an amorphous state at the irradiation position of the laser beam 20. It is determined whether or not it is in the state, and the recording mark is read.

According to the recording / reproducing method for the multilayer optical disc 1 according to the present invention as described above, the land portion of the second signal recording layer 5 is kept in an amorphous state, and the second signal recording is performed. Recording and reproduction on the layer 5 can be performed. Therefore, the transmittance of the second signal recording layer 5 can be improved, and sufficient laser light 20 can be applied to the first signal recording layer 3 located below the second signal recording layer 5. Irradiation becomes easy. Therefore, the information signal can be reliably recorded on the two signal recording layers.

Further, since the transmittance of the second signal recording layer 5 is improved, the laser beam 20 is reflected on the first signal recording layer 3 when reproducing the information signal from the first signal recording layer 3. A sufficient intensity of the returned light can be obtained, and a sufficient signal modulation degree can be obtained.

Therefore, by performing recording and reproduction on the multilayer optical disc 1 as described above, it is possible to reliably record and reproduce information signals on each of the two signal recording layers.

In the above description, only the method of recording / reproducing on / from the second signal recording layer 5 of the multilayer optical disc 1 has been described.
In the case where the first signal recording layer 3 is formed of a phase-change material in the same manner as the signal recording layer 5, recording and reproduction may be performed on the first signal recording layer 3 in the same manner. However, the first signal recording layer 3 does not need to improve the light transmittance with respect to the laser beam 20, so that not only the groove portion but also the entire surface may be initialized to a crystalline state. When the first signal recording layer 3 is formed of an organic dye material,
There is no need to initialize the first signal recording layer 3.

Next, the definitions of the reflectance and the transmittance of the first signal recording layer 3 and the second signal recording layer 5 for the laser beam used for recording and reproduction in the multilayer optical disc 1 will be described. 3 will be described.

FIG. 3 is a diagram schematically showing an optical path of a laser beam inside the multilayer optical disc 1. As shown in FIG. In FIG. 3, Rc indicates the reflectance of the laser beam incident on the second signal recording layer 5 when the phase change material of the second signal recording layer 5 is in a crystalline state, and Tc indicates the reflectance in this case. 5 shows the transmittance of the second signal recording layer 5. Ra indicates the reflectance of the laser light incident on the second signal recording layer 5 when the phase change material of the second signal recording layer 5 is in an amorphous state, and Ta indicates the second light in this case. Shows the transmittance of the signal recording layer 5.

Ru indicates the reflectance of the laser beam incident on the first signal recording layer 3 when the phase change material of the first signal recording layer 3 is in a crystalline state, and Rr indicates the first signal recording layer. When the phase change material of the recording layer 3 is in an amorphous state, the reflectance of the laser light incident on the first signal recording layer 3 is shown.

R′u indicates that, when the phase change material of the first signal recording layer 3 is in a crystalline state, the laser light incident from the light transmission protection layer 6 passes through the second signal recording layer 5 and the intermediate layer 4. Penetrate,
The ratio of the amount of light reflected by the first signal recording layer 3 and returned to the light transmission protection layer 6 again to the amount of light incident on the light transmission protection layer 6 is shown. R′r indicates the same ratio as R′u when the phase change material of the first signal recording layer 3 is in an amorphous state.

Although the case where the first signal recording layer 3 is formed of a phase change material is described in the description, the first signal recording layer 3 is formed of an organic dye material. In the case, Ru and R'u indicate the case where the first signal recording layer 3 is in an unrecorded state, and Rr and R '
r indicates a case where the first signal recording layer 3 is in a recording state.

Next, the definition of the reflectance and the degree of modulation in the DVD standard will be described with reference to FIG. FIG. 4 shows a signal obtained by converting a reflected light amount from a signal recording layer obtained when a recorded signal is reproduced into an electric signal and superimposing the electric signal, and is called an RF signal. This RF signal is detected as a DC signal and is based on the GND level. The reflectivity in the DVD standard means a ratio of the amount of reflected light corresponding to the highest level of the RF signal to the amount of light incident on the light transmission protection layer 6, and is represented by I14h. The modulation degree is expressed by the following equation using this I14h and the lowest level I141 of the RF signal.

Modulation degree = (I14h-I141) / I
14h × 100 (%) Note that the standard of the dual-layer DVD requires that each signal recording layer satisfy I14h ≧ 18% and a modulation factor ≧ 60%.

Next, a specific configuration example for optimizing the multilayer optical disc 1 as described above for use in verifying a two-layer DVD will be described. In order to make the multilayer optical disc 1 usable for verification of a two-layer DVD, as described above, both the first signal recording layer 3 and the second signal recording layer 5 have I14h ≧ 18%,
In addition, it is necessary to satisfy a condition of a modulation degree ≧ 60%.

In the multi-layer optical disc 1, a two-layer DV
In order to satisfy the standard of D, the second signal recording layer 5 has a layer configuration as shown in FIG. 5, for example. FIG. 5 is a schematic diagram showing the layer configuration of the multilayer optical disc 1, in which the substrate 2 and the first signal recording layer 3 are omitted. FIG.
Table 1 below shows the reflectance, transmittance, and absorptance of the second signal recording layer 5 having the layer structure shown in FIG. The characteristics shown in Table 1 are characteristics of the second signal recording layer 5 formed in a flat state.

[0065]

[Table 1]

Further, in the multilayer optical disc 1, 2
In order to satisfy the standard of the layer type DVD, the first signal recording layer 3
For example, as currently used in DVD-R,
It is formed of an organic dye material such as cyanine and phthalocyanine. On the lower layer side of the first signal recording layer 3, that is, on the substrate 2 side, for example, a light transmitting layer made of Au is formed in a thin film shape.

For an optical disc having a plurality of signal recording layers, such as the multilayer optical disc 1, a method has been established for accurately measuring the state of lamination in the groove portion of the first signal recording layer 3 formed of an organic dye material. Not.
Then, as a result of actually manufacturing such a multilayer optical disc 1 and measuring the optical characteristics of the first signal recording layer 3,
Characteristics as shown in Table 2 below were obtained.

[0068]

[Table 2]

From the results obtained as described above, the two-layer type D
In order to satisfy the VD standard and to perform good recording and reproduction on the first signal recording layer 3 as well, the average transmittance of laser light in the second signal recording layer 5 must be about 50% or more. Turned out to be necessary. Further, it has been found that the first signal recording layer 3 needs to have a reflectance of 50% or more with respect to a laser beam irradiated during recording and reproduction. With such a configuration, the multilayer optical disc 1 can sufficiently irradiate the laser light to the two signal recording layers so as to satisfy the standard of the two-layer DVD, The return light from the recording layer can be sufficiently obtained.

In the multi-layer optical disc 1, the reflectivity of each signal recording layer with respect to laser light depends on the material used for the first signal recording layer 3 and the second signal recording layer 5 and the layer configuration. Transmittance and absorption can be changed,
The characteristics are not limited to those shown in Tables 1 and 2.

The multilayer optical disk 1 is a dual-layer DV.
In order to satisfy the standard of D, it is desirable to be configured as follows.

That is, in the multilayer optical disc 1,
When the refractive index of the light transmission protection layer 6 is N _s , the depth of the groove portion of the second signal recording layer 5 is d, and the wavelength of the laser beam used for recording and reproduction is λ, the second signal recording layer 5 It is preferable that the concavo-convex pattern is formed so as to satisfy the following formula: 0.02 ≦ N _s · d / λ ≦ 0.22 (formula 1)

In the multilayer optical disc 1, the second
The transmittance of the signal recording layer 5 for the laser light in the crystalline state is T _c , the transmittance for the laser light in the amorphous state is T _a , the width of the groove portion in the second signal recording layer 5 is W _g , when the track pitch TP, the second signal recording layer _{5, 50 ≦ (1-W g} / 2TP) × T a + W g / 2TP × T c ≦ 60 ··· ( equation 2) becomes formula It is desirable that it be formed so as to satisfy the following.
Equation 2 shows a range of possible values of the average transmittance T _avg in the second signal recording layer 5. That is, the following, and _{T avg = (1-W g} / 2TP) × T a + W g / 2TP × T c [%].

Hereinafter, these equations 1 and 2 will be described.

<Explanation Regarding Equation 1> Multilayer Optical Disc 1
Is formed so as to satisfy Equation 1,
The reflectance and modulation degree of the second signal recording layer 5 with respect to the laser beam satisfy the standard of the two-layer DVD, and the signal amount of the radial push-pull signal obtained in the second signal recording layer 5 is secured. Thus, it is possible to perform stable recording and reproduction on the second signal recording layer 5.

The upper limit of Equation 1 is mainly determined by the second signal recording layer 5 in a state where the second signal recording layer 5 is in a crystalline state and lands and grooves are not formed, that is, in a flat state. 5 is determined by the maximum value of the reflectance.

The multilayer optical disc 1 can be formed, for example, by a layer configuration as shown in FIG. In addition,
FIG. 6 is a schematic diagram showing the layer configuration of the multilayer optical disc 1, in which the substrate 2 and the first signal recording layer 3 are omitted. The present inventor has confirmed that as a result of actually manufacturing the multilayer optical disc 1 having such a layer configuration, the reflectance of the second signal recording layer 5 with respect to laser light can be made 30% or more.

The following is an example of the reflectance, transmittance, and absorptance of the second signal recording layer 5 with respect to the laser light obtained when the multilayer optical disc 1 is manufactured with such a layer configuration. It is shown in Table 3.

[0079]

[Table 3]

Here, when a land portion and a groove portion are provided in the second signal recording layer 5, the reflectance I14h of the laser beam obtained in the groove portion in the second signal recording layer 5,
With respect to the average transmittance of the second signal recording layer 5, the following experiment was conducted by changing the width and depth of the groove portion in the second signal recording layer 5.

First experiment: Average transmission of the second signal recording layer 5
In this experiment, a plurality of sample disks were manufactured by changing the width of the groove portion in the second signal recording layer 5 with the configuration shown in FIG. The sample disk manufactured at this time was manufactured without the first signal recording layer 3. In each sample disk, only the groove portion in the second signal recording layer 5 was initialized to a crystalline state, and the land portion was kept in an amorphous state. The depth of the groove was set to 20 nm. Further, each sample disk performs a recording operation on a groove portion that has been initialized to a crystalline state, so that a crystal region and an amorphous region are formed in the groove portion at a ratio of 1: 1. .

FIG. 7 shows the results of measuring the laser beam transmittance of the second signal recording layer 5 for the sample disk manufactured as described above. Note that FIG. 7 shows an average value obtained by measuring the transmittance of both the land portion and the groove portion over the entire surface of the second signal recording layer 5. Here, as the average transmittance T _avg, from equation 2 described above, was calculated as _{T avg = (1-W g} / 2TP) × T a + W g / 2TP × T c. FIG. 7 also shows, for comparison, the results of a sample disk manufactured by setting both the initial state of the land portion and the groove portion to a crystalline state, such as a conventional multilayer optical disk.

As is clear from the results shown in FIG.
When the initial state of both the land portion and the groove portion of the sample disk is a crystalline state, the average transmittance of the second signal recording layer 5 does not exceed 50%. However, the sample disk according to the present invention,
It can be seen that the sample disk in which only the groove portion of the signal recording layer 5 was initialized to a crystalline state and the land portion was kept in an amorphous state exhibited an average transmittance for laser light of 50% or more. Also, from the results shown in FIG. 7, when the second signal recording layer 5 has the layer configuration as shown in FIG. 6, the average transmittance of the second signal recording layer 5 for laser light is
For example, in order to achieve 50% or more, recording is performed so that an amorphous region formed as a recording mark in the groove portion is formed to be substantially equal to or larger than a crystal region in the groove portion, and the width of the groove portion is adjusted. Can be set to about 550 nm or less.

Second experiment: laser beam in groove
In this experiment, a plurality of sample disks were manufactured by changing the width and depth of the groove portion in the second signal recording layer 5 with the configuration shown in FIG. The sample disk manufactured at this time was manufactured without the first signal recording layer 3. Further, only the groove portion in the second signal recording layer 5 was initialized to a crystalline state, and the land portion was kept in an amorphous state. Further, each sample disk performs a recording operation on a groove portion initialized to a crystalline state, and a 1: 1 ratio of a crystalline region and an amorphous region is formed in this groove portion.
In a state of being formed.

FIG. 8 shows the results of measuring the reflectivity I14h of the laser beam in the groove portion of the second signal recording layer 5 for the sample disk manufactured as described above.

From the results shown in FIG.
Satisfies the double-layer DVD standard and the second signal recording layer 5
In order to make the reflectance I14h of 18% or more, for example, the width of the groove portion of the second signal recording layer 5 is set to 550.
When it is set to nm, it is understood that the depth of the groove portion needs to be about 90 nm or less.

Here, the depth of the groove portion of the second signal recording layer 5 will be described. When recording / reproducing is performed on the second signal recording layer 5, the uneven pattern of the second signal recording layer 5 functions as a diffraction grating, and causes a part of the irradiated laser light to be diffracted. . Therefore, as the depth of the groove portion in the second signal recording layer 5 increases, the amount of return light from the second signal recording layer 5 decreases. That is, as the depth of the groove portion is reduced, the second
Of the signal recording layer can be increased.

This is clear from the results shown in FIG. 8. The deeper the groove portion, the greater the amount of diffraction of the irradiated laser beam and the lower the value of the reflectance I14h. I understand. The amount of diffraction of the irradiated laser light is such that the return light becomes minimum particularly when the depth of the groove portion is about λ / 4 with respect to the wavelength λ of the laser light.

Third experiment: In the second signal recording layer 5
Reflectivity and Degree of Modulation of RF Signal In this experiment, the layer structure shown in FIG.
A plurality of sample disks were manufactured by changing the width of the groove portion in the signal recording layer 5 of FIG. The sample disk manufactured at this time had the same configuration as in the first experiment described above. The depth of the groove was set to 20 nm.

FIG. 9 shows the results of measuring the reflectivity I14h of the laser beam in the groove portion of the second signal recording layer 5 and the modulation factor of the RF signal for the sample disk manufactured as described above.

From the results shown in FIG. 9, when the layered structure as shown in FIG.
VD standard is satisfied, and the reflectance I of the second signal recording layer 5 is
It can be seen that the width of the groove portion needs to be 500 nm or more in order for 14h to be 18% or more and the modulation degree of the RF signal to be 60% or more.

From the results of the first to third experiments described above,
For example, by setting the width of the groove portion to 550 nm and the depth of the groove portion to 90 nm, the average transmittance of the second signal recording layer 5 can be made 50% or more, and the second signal recording can be performed. 18% reflectivity I14h of layer 5
It can be seen that the above can be achieved. At this time, the refractive index N _s of the light transmission protection layer 6 is 1.53, and the wavelength λ of the laser beam used in the first experiment and the second experiment is 640 nm.
Therefore, N _s · d / λ = 0.22. And
This value is the upper limit in Equation 1.

The present inventor has set that the width of the groove portion in the second signal recording layer 5 is 550 nm, the width of the groove portion is 90 nm, and the first signal recording layer 3 has a reflectance of 70%.
With the above configuration, the multilayer optical disc 1 was actually manufactured. As a result, it was possible to realize the multilayer optical disc 1 that satisfies the standard of the dual-layer DVD and can stably and reliably record and reproduce data on the two signal recording layers. The multilayer optical disc 1 has a reflectivity I1 of the second signal recording layer 5.
4h is 18.5%, and the modulation degree of the RF signal is 71.7.
%, The radial push-pull signal was 0.11, and the average transmittance of the second signal recording layer 5 was 50%. Here, the value of the radial push-pull signal was calculated by a calculation method based on the DVD-R standard.

By the way, the lower limit in the above equation 1 is:
It is mainly determined by a radial push-pull signal that changes depending on the depth of the groove in the second signal recording layer 5. The radial push-pull signal is used as a tracking error signal for scanning a laser beam along a groove when performing recording and reproduction on the multilayer optical disc 1. The signal level required for this purpose is required to be 0.05 or more. Therefore, the second
In order to examine the relationship between the signal recording layer 5 and the obtained radial push-pull signal, the following experiment was performed.

Fourth Experiment: Radial Push-Pull Signal In this experiment, a plurality of sample disks were manufactured by changing the width and depth of the groove in the second signal recording layer 5 in the same manner as in the second experiment. did. The sample disk manufactured at this time had the same configuration as that of the above-described second experiment.

FIG. 10 shows the signal level of the radial push-pull signal obtained for the second signal recording layer 5 for the sample disk manufactured as described above. From the results shown in FIG. 10, it can be seen that the signal level of the obtained radial push-pull signal increases as the groove portion in the second signal recording layer 5 becomes deeper. In order to set the signal level to 0.05 or more, the depth of the groove in the second signal recording layer 5 is set to 10 nm.
It is understood that it is necessary to make the above.

In the third experiment, since the refractive index N _s of the light transmitting layer 6 is 1.53 and the wavelength of the laser beam is λ = 640 nm, N _s · d / λ = 0.02 Becomes This value is the lower limit in Equation 1.

In the fourth experiment, the layer structure of the multilayer optical disc 1 was set as shown in FIG. FIG. 11 is a schematic diagram showing the layer configuration of the multilayer optical disc 1, in which the substrate 2 and the first signal recording layer 3 are omitted. Table 4 below shows the reflectance, transmittance, and absorptance of the second signal recording layer 5 with respect to the laser beam, which were obtained with such a layer configuration.

[0099]

[Table 4]

The inventor of the present invention has set the groove width in the second signal recording layer 5 to 520 nm, the groove width to 10 nm, and the first signal recording layer 3 to a reflectance of 52.
The multilayer optical disc 1 was actually manufactured as a configuration showing 5% or more. As a result, the dual-layer DVD standard is satisfied,
The multilayer optical disc 1 capable of stably and reliably recording / reproducing with respect to two signal recording layers was realized. In the multilayer optical disc 1, the reflectance I14h of the second signal recording layer 5 is 18.5%, and the modulation degree of the RF signal is 6
2.5% and the radial push-pull signal is 0.0%
5. The average transmittance of the second signal recording layer 5 was 58.5%.

<Explanation Regarding Equation 2> Multilayer type optical disc 1
Is formed so as to satisfy Expression 2 described above, so that the reflectance of the first signal recording layer 3 with respect to the laser beam, that is, R'u shown in FIG. 3, satisfies the standard of the dual-layer DVD. It becomes possible.

The reflectance R′u of the first signal recording layer 3
Using the average transmittance T _{avg of} the second signal recording layer 5 and the reflectance Ru of the first signal recording layer 3 alone, the following relationship is obtained: R′u = T _avg × T _avg × Ru Can be shown.

Here, it has been experimentally confirmed that the value of Ru can be about 70%. Therefore, the first
In order for the reflectance R′u of the signal recording layer 3 to satisfy the standard of the dual-layer DVD and be 18% or more, the average transmittance T _avg of the second signal recording layer 5 should be 50% or more. There is a need to. That is, it is necessary to _satisfy 50 ≦ _Tavg .

The average transmittance T of the second signal recording layer 5
The upper limit value of _avg is mainly determined by the second signal recording layer 5
Depends on the maximum value of the transmittance Ta in the amorphous state, and also depends on the width and depth of the groove portion in the second signal recording layer 5. As a result of conducting various experiments as described above by the present inventor, the maximum value of _Tavg obtained is:
58.5%. However, by appropriately selecting the layer configuration and material of the second signal recording layer 5, T _avg can be reduced to 60%.
Upgrading to a degree is easy. Therefore,
With this value as the upper limit, T _avg ≦ 60.

[0105]

As described above, the multi-layer optical disc according to the present invention can improve the transmittance of the second signal recording layer, so that it can be used with respect to the first signal recording layer located below. However, it is easy to irradiate recording / reproducing light of sufficient intensity, and an information signal can be reliably recorded. Further, at the time of recording / reproducing an information signal with respect to the first signal recording layer, it is possible to sufficiently obtain the intensity of the returning light which is reflected by the recording / reproducing light reflected on the first signal recording layer, and has sufficient signal modulation. You can get the degree. Therefore, the information signal can be rewritten or additionally written to the two signal recording layers, and a multilayer optical disc having sufficient recording and reproducing characteristics can be realized. As a result, for example, the multi-layer optical disc according to the present invention is
By using it for verification of VD, it is not necessary to rebuild the stamper many times, and the manufacturing cost of a two-layer DVD can be reduced.

Further, according to the recording / reproducing method for a multilayer optical disc according to the present invention, the transmittance of the second signal recording layer located on the upper layer side with respect to the recording / reproducing light can be improved. Therefore, at the time of recording / reproducing an information signal, it is easy to irradiate the recording / reproducing light of sufficient intensity to the first signal recording layer located on the lower layer side, and the information signal can be reliably recorded. . In addition, it is possible to obtain a sufficient intensity of the returning light that is returned by the recording / reproducing light being reflected by the first signal recording layer, and a sufficient signal modulation degree. Therefore, the recording / reproducing operation can be reliably and stably performed on each signal recording layer of the multilayer optical disc, and sufficient recording / reproducing characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic view of a main part showing a multilayer optical disc according to the present invention.

FIG. 2 is a schematic diagram of a second signal recording layer shown for describing a recording / reproducing method according to the present invention.

FIG. 3 is a schematic diagram for explaining a reflectance and a transmittance of a multilayer optical disc according to the present invention with respect to recording / reproducing light.

FIG. 4 is a schematic diagram showing the definition of the reflectance and the degree of modulation in the DVD standard and showing an RF signal.

FIG. 5 is a diagram showing an example of a layer configuration in a multilayer optical disc according to the present invention.

FIG. 6 is a diagram showing another example of the layer configuration in the multilayer optical disc.

FIG. 7 is a view showing the average transmittance of the second signal recording layer when the width of the groove portion in the second signal recording layer is changed in the multilayer optical disc.

FIG. 8 is a diagram showing the reflectance I14h of the second signal recording layer when the width and depth of the groove portion in the second signal recording layer are changed in the same multilayer optical disc.

FIG. 9 is a diagram showing the reflectance I14h and the degree of modulation of the second signal recording layer when the width of a groove portion in the second signal recording layer is changed in the multilayer optical disc.

FIG. 10 is a diagram showing a signal level of a radial push-pull signal when the width and depth of a groove portion in a second signal recording layer are changed in the same multilayer optical disc.

FIG. 11 is a diagram showing still another example of the layer configuration in the multilayer optical disc.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 multilayer optical disc, 2 substrate, 3 first signal recording layer, 4 intermediate layer, 5 second signal recording layer, 6 light transmission protection layer, 7 objective lens

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) G11B 7/24 561 G11B 7/24 561P 7/004 7/004 Z 7/007 7/007 F Term (Reference) 5D029 JB05 JC02 MA38 WA29 WB11 WB17 WC04 WC05 5D090 AA01 BB05 BB12 CC06 CC11 CC14 DD02 EE01 EE11 GG07

Claims (8)

[Claims] A first signal recording layer formed of a phase change material or an organic dye material on a substrate; a transparent layer; a second signal recording layer formed of a phase change material; A transmission protection layer is sequentially laminated, and by irradiating recording / reproducing light from the light transmission protection layer side, recording and recording of information signals on the first signal recording layer and the second signal recording layer, respectively. And / or a multi-layer optical disc on which reproduction is performed, wherein the second signal recording layer includes a land portion that is a concave portion as viewed from the light transmission protection layer side and a groove portion that is a convex portion. It is formed in a predetermined concavo-convex pattern, and as an initial state, one of the land portion or the groove portion is in a crystalline state, the other is in an amorphous state, and the other is in a crystalline state. Information signal Multi-layered optical disc, wherein a recording and / or reproduction is performed. 2. The multilayer according to claim 1, wherein the land portion of the second signal recording layer is in an amorphous state and the groove portion is in a crystalline state as an initial state. Optical disk. 3. The unevenness pattern of the second signal recording layer is 0 when the refractive index of the light transmission protection layer is N _s , the depth of the groove portion is d, and the wavelength of the recording / reproducing light is λ. 2. The multi-layer optical disc according to claim 1, wherein the optical disc is formed so as to satisfy the following equation: 0.02 ≦ N _s · d / λ ≦ 0.22. 4. The second signal recording layer has a transmittance T _c for recording / reproducing light in a crystalline state, a transmittance T _a for recording / reproducing light in an amorphous state, and a width W of _a groove portion. _g, when the track pitch of the concavo-convex pattern and TP, 50 ≦ (1-W g / 2TP) × T a + W g / 2TP × T c ≦
2. The multilayer optical disc according to claim 1, wherein the optical disc is formed so as to satisfy the following expression: 60 (%). 5. The first signal recording layer has a reflectance of 50% with respect to recording / reproducing light incident on the first signal recording layer.
2. The multilayer optical disc according to claim 1, wherein: 6. The first signal recording layer and / or the second signal recording layer, at least on one side thereof, is contacted with a crystallization promoting layer for accelerating the crystallization speed of the signal recording layer. 2. The multilayer optical disc according to claim 1, wherein: 7. A first signal recording layer formed of a phase change material or an organic dye material on a substrate, a transparent layer, a second signal recording layer formed of a phase change material, and light. A transmission protection layer is sequentially laminated, and by irradiating recording / reproducing light from the light transmission protection layer side, recording and recording of information signals on the first signal recording layer and the second signal recording layer, respectively. And / or a recording / reproducing method for a multi-layer optical disc in which reproduction is performed, wherein a land portion, which is a concave portion as viewed from the light transmission protection layer side, and a groove portion, which is a convex portion, have a predetermined uneven pattern. By irradiating the formed second signal recording layer with recording / reproducing light and scanning the recording / reproducing light in the track direction, only one of the land portion or the groove portion is crystallized. When recording and / or reproducing the information signal with respect to the second signal recording layer, the recording / reproducing light is applied only to the land portion and the groove portion which are in the crystalline state. A recording / reproducing method for a multilayer optical disc, which comprises irradiating. 8. When the second signal recording layer is initialized, only the groove portion is initialized to a crystalline state, and information signals are recorded and / or recorded on the second signal recording layer. 8. The recording / reproducing method for a multi-layer optical disc according to claim 7, wherein when reproducing, only the groove portion is irradiated with recording / reproducing light.