JPH07254154A - Method for reproducing signal of optical disk and optical disk used therefor - Google Patents

Abstract

PURPOSE:To form 1st and 2nd regions different from each other in reflectance in a phase change material layer by forming mutually different phase states and to reproduce a signal in a limited region in a spot of reproducing light by the difference in reflectance. CONSTITUTION:At least a phase change material layer 1 is formed on a transparent substrate 10 with phase pits 2 formed in accordance with an information signal and a translucent metallic layer 3 is interposed between the layer 1 and the substrate 10. Cross talk is reduced and track density is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk signal reproducing method and an optical disk used therefor.

[0002]

2. Description of the Related Art For optical discs such as digital audio discs, so-called compact discs and video discs, an aluminum reflective film is formed on a transparent substrate on which phase pits are formed in advance in accordance with an information signal, and a protective film is formed thereon. Etc. are formed.

In such an optical disc, a signal is read out or reproduced by irradiating the disc surface with a reading light and detecting a large decrease in the amount of reflected light due to the diffraction of the light in the phase pit forming portion. There is.

By the way, in the above-mentioned optical disc, the resolution of signal reproduction is almost equal to the wavelength λ of the light source of the reproduction optical system and the numerical aperture N.V. of the objective lens. A. And the spatial frequency is 2N. A. / Λ is the reproduction limit.

Therefore, in order to realize high density in such an optical disc, the wavelength λ of the light source of the reproducing optical system, generally a semiconductor laser, is shortened or the numerical aperture N.V. A. Will need to be increased.

However, the wavelength λ of the light source and the numerical aperture N. A. However, there is a limit to the improvement of the recording medium, and it is difficult to dramatically increase the recording density.

Therefore, the applicant of the present invention utilizes the change in reflectance due to the partial phase change in the scanning spot of the reading light to determine the wavelength λ and the numerical aperture N.V. A. Has proposed a reproducing method and an optical disk for performing super-resolution reproduction capable of obtaining a resolution higher than the limit according to (Japanese Patent Laid-Open No. 3-2.
92632, JP-A-5-89511).

As shown in the schematic sectional view of FIG. 12, the basic structure of the optical disc for performing the super-resolution reproduction is such that information is recorded on the transparent substrate 10 having phase pits 2 formed by, for example, concave or convex, depending on the temperature. The phase change material layer 1 has a structure in which a phase change occurs and the reflectance changes accordingly.

In the reproduction, the reflectance is increased by utilizing the temperature distribution in the spot of the reproduction light and utilizing the change in the reflectance due to the phase change in the phase change material layer 1 in the reproduction light spot. The phase pits 2 can be detected, that is, information can be read out only partially in a limited area, that is, super-resolution reproduction below the optical limit is performed.

To further explain this, in this super-resolution reproduction, the relationship between the reproduction laser beam spot on the optical disk and the temperature due to the irradiation of this reproduction light is as shown in FIG. 13 and the scanning direction of the laser light spot L is the direction indicated by the arrow c in FIG. 13, the temperature distribution of the spot L in the stopped state is that of the spot indicated by the broken line A. The normal distribution has a peak at the center, but in the scanning state, as shown by the solid line B, the temperature distribution having a peak on the rear side of the spot in the scanning direction is used.

That is, according to this temperature distribution, in the spot L from which information is read, the relative speed between the optical disk and the spot L (that is, the linear speed of the spot on the optical disk) is selected, and the power of the irradiation light is selected. In FIG. 13, since a high temperature region S _H having a temperature higher than the melting point MP of the phase change material layer 1 and a low temperature region S _L having a temperature lower than the melting point can be formed in the spot L as shown by hatching in FIG. , Can form a partially melted liquid state.

Therefore, the phase change material layer 1 of the optical disk
However, depending on the liquid state and the crystalline or amorphous state,
If it is made of a material whose reflectance changes greatly,
Area S _HOr low temperature region S_LCan increase reflectance only at
Done, this area S_HOr S_LEither one of the
Only the phase pit 2 can be read out
Wear.

That is, in this case, as described above, a so-called FAD (Front Aperuture Detector) is used to read out the phase pits in the low temperature region S _L in the spot of the reproduction light.
When so-called RAD (Rea for reading in the high temperature region S _H
r Aperuture Detector).

Here, the optical disk used for FAD needs to be made of a material whose reflectance in the crystalline state is higher than reflectance in the liquid phase state as the phase change material layer 3 thereof. As a material, for example, a Te-based material can be considered.

However, in the case of this FAD, as shown in FIG. 13, the low temperature region S _{L serving as the} read region has a crescent shape that spreads in the track width direction, so that the recording density on one track is Although it can be improved, there is a problem that the track density cannot be increased because crosstalk occurs when the intervals between the tracks are narrowed.

On the other hand, in the high temperature region S _H , the width in the track width direction also becomes narrower than the width of the spot L. Therefore, the RAD for reading in the high temperature region S _H also improves the track density. Therefore, there is an advantage that the recording density can be further improved.

However, in the case of this RAD,
The phase change material layer 3 of the optical disk is required to have a reflectance in the liquid phase state sufficiently higher than that in the crystalline state in the low temperature region S _L.

On the other hand, at present, as the phase change material, a chalcogen-based material containing Te such as Ge ₂ Sb ₂ Te ₅ is considered to be the best in terms of crystallization speed and sensitivity.

However, Te-based materials generally have a large optical constant, specifically, an extinction coefficient k (complex refractive index: n-ik) in the crystalline state of 2 or more, and FAD is easy to design, but good. There is a problem that it is difficult to design an RAD having a high contrast.

[0020]

SUMMARY OF THE INVENTION As described above, the present invention forms the different phase states due to the above-mentioned high temperature region and the low temperature region in the reproducing light spot for the optical disc having the phase change material layer, and thus the reflectances are different from each other. The first difference
Of the phase change material layer in the signal reproduction method of the optical disc by the super resolution reproduction, in which the signal of a limited area in the reproduction light spot is reproduced by forming the area of No. 2 and the second area of the phase change material layer. It is intended to provide a signal reproducing method of an optical disc which can arbitrarily adopt the signal reproducing method of the RAD described above and further the FAD in some cases without being restricted by optical constants, and an optical disc used therefor.

[0021]

According to a first aspect of the present invention, in a reproducing light spot for an optical disc having a phase change material layer, different phase states are formed in the phase change material layer, and the reflectances are different from each other. A signal reproducing method for an optical disc, wherein a first region and a second region are formed and a signal in a limited region within a reproduction light spot is reproduced by a difference in reflectance between the first region and the second region. This is a signal reproducing method for an optical disc in which the magnitude relations of the amounts of reflected light due to different phase states are mutually inverted and reproduced.

A second aspect of the present invention is an optical disc that can be used in the above-mentioned optical disc signal reproducing method, and as shown in FIG. 1, a transparent substrate 10 having phase pits 2 formed according to information signals. At least the phase change material layer 1 and the semitransparent metal layer 3 disposed between the phase change material layer 1 and the transparent substrate 10 are formed on the top.

A third aspect of the present invention is the optical disc described above, wherein the semi-transparent metal layer 3 has a refractive index n and an extinction coefficient k.
However, with respect to the reproduction light wavelength of about 780 nm, the structure is limited to the range of 0 <n ≦ 0.6 2.5 ≦ k ≦ 5.2.

A fourth aspect of the present invention is the optical disc described above, wherein the semi-transparent metal layer 3 has a refractive index n and an extinction coefficient k.
However, the configuration is limited to the range of 0 <n ≦ 22 ≦ k ≦ 5 with respect to the reproduction light wavelength of about 532 nm.

In the fifth invention, similarly, in each of the above-mentioned optical disks, the phase change material is composed of a chalcogen-based material containing Te.

[0026]

According to the signal reproducing method of the first aspect of the present invention described above, the phase change material layer 1 of the optical disk is provided in the reproducing light spot.
In the above, since different phase states are formed and portions having different reflectances are formed, it is possible to perform super resolution reproduction in which information is read out only in one phase state described above.

In particular, in the present invention, since the original magnitude relation of the reflectance in the phase change material layer 1 is read out by externally reversing it, the optical characteristics of the phase change material layer are unique. A phase-change material, which has a reflectance higher than that in the liquid state and is to be applied to the regeneration method by FAD, is used without depending only on the constants, that is, the characteristics determined by the refractive index n and the extinction coefficient k. Since the reproducing method by RAD can be performed by the optical disc, it is possible to reduce the crosstalk and thus the track density.

On the contrary, the reproduction method by FAD can be performed by the optical disk using the phase change material whose reflectance in the liquid state is originally larger than that in the crystalline state and the reproduction method by RAD should be applied.

Further, according to the second to fourth aspects of the present invention, there is provided an optical disc which can carry out the reproducing method according to the first aspect of the present invention. In this case, by providing the semitransparent metal layer 3, 2 shows the relationship between the film thickness of the semi-transparent metal layer 3 and the reflectance of the optical disk due to the dynamic interference effect, each phase state (curve 21 in FIG. 2 shows the reflectance in the crystalline state, Since the reflectance of the liquid phase state is shown by the curve 22), it is possible to change the reflectance of the semi-transparent metal layer 3 in FIG. 2, that is, in the state where the semi-transparent metal layer is not formed. It is possible to reverse the magnitude relationship of the reflectance in each phase state of the phase change material layer itself, for example, in the crystalline state and the liquid state, by forming the semitransparent metal layer 3 and selecting the film thickness.

Therefore, according to the second to fourth aspects of the present invention, it is possible to change the reflectance and select the contrast due to the phase change without depending on only the optical characteristics of the phase change material layer 1. , An RAD reproduction method or an FAD reproduction method can be appropriately configured, and the degree of freedom in selecting a phase change material is large.

Further, according to the fifth aspect of the present invention, as described above, according to the present invention, the regeneration method is prevented from being limited only by the characteristics of the phase change material layer.
Also in D, since the chalcogen-based material containing Te is used as the phase change material, the crystallization rate and the sensitivity can be improved.

[0032]

EXAMPLES Examples of the present invention will be described. In the signal reproducing method according to the present invention, for the optical disc having the phase change material layer, the phase change material in the high temperature region S _H and the low temperature region S _L in the reproduction laser beam spot L is similar to that described in FIG. In the layer, different phase states such as a liquid state and a crystalline state are formed to form a first region and a second region having different reflectances. Then, due to the difference in these reflectances, only the signal in a limited area is reproduced within the same reproduction light spot.

In particular, according to the present invention, the magnitude relationship of the reflected light amount due to the different phase states of the phase change material layers of the optical disk is reversed and reproduced.

As described above, in order to invert the magnitude relations of the reflected light amounts due to the different phase states of the phase change material layers of the optical disc to each other and to reproduce, the optical disc used for this or the signal reproduction of the optical disc is performed. This can be realized by providing a function of generating an optical interference effect in the optical system.

The optical disc according to the present invention realizes the above-mentioned reproducing method of the present invention by utilizing the optical interference effect in the optical disc itself.

The optical disk according to the present invention is, for example, as shown in FIG. 1, a known 2P (Photo P) on a glass substrate, for example.
the semitransparent metal layer 3, the first dielectric layer 4, and the phase change material layer 1 are sequentially deposited on the transparent substrate 10 on which the concave and convex phase pits 2 are formed according to the information recording, Although not shown, a protective film may be formed on and deposited thereon.

The transparent substrate 10 is not limited to the above-mentioned example, but may have various configurations such as molding an acrylic resin, a polyolefin resin or the like.

Further, the optical disc according to the present invention, as shown in FIG. 3, for example, has a semitransparent metal layer 3, a first dielectric layer 4, and a phase change material layer 1 on a transparent substrate 10 similar to that described above. The second dielectric layer 5, the reflective film 6, and the third dielectric layer 7 may be laminated and formed, and a protective film, for example, may be formed thereon, which is not shown. .

In each of the above-mentioned optical discs, the semitransparent metal layer 3 and the first and second dielectric layers 4 and 5 are used to set the optical characteristics such as reflectance.

The first dielectric layer 3 may also serve as a separating layer for preventing undesired reactions between the semitransparent metal layer 4 and the phase change material layer 1, for example alloying.

Further, the third dielectric layer 7 can improve the mechanical strength of the laminated film of each layer on the substrate 10 and can improve the durability.

The optical disk according to the present invention has a high temperature region S _H in the reproduction laser beam spot L as described with reference to FIG.
And forming different phase states in the low temperature region S _L to form a first region and a second region having different reflectances, and the difference in the reflectances limits the reproduction laser light spot L. The phase pits of the optical disk, that is, the recorded information is read by super-resolution reproduction that reproduces the signal in the area S _H or S _L. In this case, for example, as described above, it is desirable to adopt the reproduction method by the RAD that performs the reading in the high temperature area S _H , but in some cases, the signal reproduction method of the FAD that performs the reading in the low temperature area S _L. You can also

Examples of the optical disk according to the present invention will be given. Example 1 In this example, in the case where the structure shown in FIG. 3 was adopted, the transparent substrate 10 had a track pitch of 1.6 μm, a pit depth of 120 nm, and a pit length of 0. Pit 2 having a size of 3 μm and a pit repeating period of 0.6 μm was formed.

Then, a semitransparent metal layer 3 made of Au is deposited on the transparent substrate 10 on which the pits 2 are formed, and a laminated film of ZnS and SiO ₂ (hereinafter ZnS) having a thickness of 150 nm is formed thereon. A first dielectric layer 4 made of SiO ₂ ) is deposited and a Ge layer having a thickness of 20 nm is formed on the first dielectric layer 4.
_A phase change material layer 1 made of ₂ Sb ₂ Te ₅ was deposited. Further, a Zn layer having a thickness of 35 nm is formed on the phase change material layer 1.
A second dielectric layer 5 made of S-SiO ₂ is formed, and a Dy reflection film 6 is deposited thereon to a thickness of 200 nm,
A third dielectric layer 7 made of ZnS-SiO ₂ having a thickness of 400 nm is formed on the first dielectric layer 7 by deposition.

With this structure, 21 samples of optical discs were prepared in which the film thickness of the semitransparent metal layer 3 made of Au was changed in the range of 0 to 20 nm. Then, the results of measuring the respective reflectances in the crystalline state and the liquid state regarding these samples are shown in FIG. In FIG. 2, the black circles are the crystalline state and the white circles are the measured results of the reflectances in the liquid phase.

The reflectance in this case was measured in terms of the reflectance in the crystalline state. For each sample, the phase change material layer of each sample was once completely crystallized by irradiation with a xenon (Xe) lamp, and this sample was recorded on this optical disk. It was measured by irradiating a semiconductor laser beam having a wavelength of 780 nm with a laser power of 1 mW at a linear velocity of 7 m / s. Regarding the reflectance in the liquid state, the same laser light was measured with a laser power of 2.5 mW.

As is apparent from FIG. 2, when the semitransparent metal layer 3 is not formed, that is, when the Au film thickness is 0 nm, the reflectance in the liquid state is lower than the reflectance in the crystalline state. When the thickness of the semitransparent metal layer 3 made of Au is about 5 nm or more, the relationship between the reflectance in the liquid state and the reflectance in the crystalline state is reversed. In this example, the thickness of the semitransparent metal layer 3 made of Au is 8
At -10 nm, the reflectance in the crystalline state becomes extremely small, and the difference between the reflectance in the liquid state and the reflectance in the crystalline state becomes large.
That is, the contrast becomes large.

Therefore, super-resolution reproduction by RAD can be performed by a sample having a large contrast, that is, an optical disk.

In this structure, with respect to the optical disk having the Au semi-transparent metal layer 3 having a thickness of 10 nm, laser light having a wavelength of 780 nm is irradiated as reproduction light at 9 mW, and the linear velocity is set to 7 m / s, and the signal portion thereof is set. When reproduced, the C / N of the signal was 42 dB.

Example 2 An optical disk having the same structure as in Example 1 but having the Au semi-transparent metal layer 3 having a thickness of 10 nm was produced.
Then, in this structure, 25 samples of optical disks were prepared in which the thickness of the second dielectric layer 5 made of ZnSe—SiO ₂ was changed in the range of 0 to 250 nm. Then, FIG. 4 shows the results of measuring the respective reflectances in the crystalline state and the liquid state of these samples by the same method as the samples described in Example 1. In FIG. 4, black circles are plots of the crystalline state and white circles are plots of the respective reflectance measurement results in the liquid phase state.

Comparative Example 1 An optical disk having the same structure as in Example 2 but having no semitransparent metal layer was prepared. Then, in this structure, 25 samples of optical disks in which the thickness of the second dielectric layer 5 also made of ZnS—SiO ₂ was changed in the range of 0 to 250 nm were prepared, and these samples were related. FIG. 5 shows the results of measuring the reflectance in the crystalline state and the reflectance in the liquid state by the same method as that for each sample described in Example 1. In FIG. 5, the black circles are the crystalline results, and the white circles are the plotted results of the reflectance measurements in the liquid phase.

As is clear from the comparison between FIG. 4 and FIG. 5, when the semitransparent metal layer 3 is provided, the reflectance in the liquid phase state can be increased as compared with the crystal state, and in this way, the crystal state In comparison with the above, the thickness range of the second dielectric layer 5 capable of increasing the reflectance in the liquid phase state is extremely wide, and the thermal characteristics of the disk can be widely changed. That is, for example, the structure can be formed from the slow cooling structure to the rapid cooling structure.

Example 3 In this example as well, the same configuration as that of Example 1 was used, but in this case, the semitransparent metal layer 3 was made of Cu. Even in this case, by setting the thickness of the semi-transparent metal layer 3 made of Cu to about 5 nm or more, the reflectance in the liquid phase state could be higher than the reflectance in the crystalline state. In this case, the thickness of the semitransparent metal layer 3 is set to 9
It was possible to sufficiently enhance the contrast between the liquid phase state and the crystalline state in the vicinity of -10 nm.

Then, with respect to the optical disk of the third embodiment in which the film thickness of the semitransparent metal layer made of Cu is 10 nm, the reproduction laser power is set to 9 mW and the linear velocity is set to 7 m / s, and the reproduction is performed to obtain the signal. When the portion was reproduced, the C / N of the signal was 40 dB or more.

Example 4 Also in this example, the same structure as that of Example 1 was used, but in this case, the semitransparent metal layer 3 was Pt. Also in this case, by setting the thickness of the semitransparent metal layer 3 made of Pt to about 5 nm or more, the reflectance in the liquid phase state could be higher than the reflectance in the crystal state. Even in this case, the film thickness of the semitransparent metal layer is 9 to 10
It was possible to sufficiently enhance the contrast between the liquid phase state and the crystalline state in the vicinity of nm.

Then, with respect to the optical disk in which the thickness of the semitransparent metal layer made of Pt in Example 4 was 10 nm, the reproducing laser power was set to 9 mW and the linear velocity was set to 7 m / s.
When the signal part is reproduced, the C / N of the signal is 4
It was 0 dB or more.

Example 5 Also in this example, the same structure as that of Example 1 was used, but in this case, the semitransparent metal layer 3 was made of Ag. Even in this case, by setting the thickness of the semitransparent metal layer 3 made of Ag to about 5 nm or more, the reflectance in the liquid phase state could be higher than the reflectance in the crystal state. Even in this case, the thickness of the semitransparent metal layer 3 is set to 9 to 1
It was possible to sufficiently enhance the contrast between the liquid phase state and the crystalline state near 0 nm.

Then, regarding the optical disk in which the thickness of the semi-transparent metal layer 3 made of Ag in Example 5 was set to 10 nm,
When the reproduction laser power was set to 9 mW and the linear velocity was set to 7 m / s and the signal portion was reproduced, the C / N of the signal
Was 40 dB or more.

The reproduction in each of the above-mentioned Examples 1 to 5 is
In each case, the reproduction laser light of the reproduction optical system has a wavelength of 780n.
m, the numerical aperture N.V. of the objective lens. A. Is 0.5.

Reproduction laser light used in reproduction of a general optical disk is, for example, laser light having wavelengths of 780 nm and 680 nm by a semiconductor laser, or Y.
532n in which AG laser (wavelength 1064nm) light is wavelength-converted into second harmonic by an SHG (second harmonic generation) element
m laser light.

In the optical disc according to the present invention described above,
When the configuration of FIG. 3 is adopted, the first dielectric layer 4 has a film thickness of 10 nm to 300 nm, and the phase change material layer 1 has a film thickness of 10 n.
m to 100 nm, the second dielectric layer 5 is 5 nm to 300 n
The reflective film 6 may have a thickness of 50 nm to 500 nm, and the third dielectric layer 7 may have a thickness of 10 nm to 1 μm.

The metal material of the semitransparent metal layer 3 is R
When applying the AD reproducing method, when a laser having a wavelength of 780 nm is used as the reproducing laser light, the refractive index n for this is 0 <n ≦ 0.6, and its extinction coefficient k
Is formed by a metal layer satisfying 2.5 ≦ k ≦ 5.2.

When the wavelength of the reproducing laser beam is 532 nm, the metal material of the semitransparent metal layer 1 has a refractive index n for this wavelength of 0 <n ≦ 0.6 and its extinction coefficient k. , 2.5 ≦ k ≦ 5.2.

With this structure, the reflectance in the liquid state can be 2.5 times or more the reflectance in the crystalline state, and a high C / N can be obtained.

For example, in the configuration of FIG. 3, a glass substrate
2P transparent layer with a thickness of 1.2mm
18 nm thick semi-transparent metal layer 3 on the bright substrate 10, thickness
125 nm ZnS-SiO₂First dielectric layer according to
4, Ge with a thickness of 20 nm₂ Sb ₂ Te_FivePhase change material
Material layer 1, ZnS-SiO having a thickness of 205 nm₂By the second
Dielectric layer 5, a reflection film 6 of Dy having a thickness of 150 nm,
400 nm thick ZnS-SiO₂Third dielectric by
780 for an optical disc with layers 7 deposited in sequence
Each refractive index n- quenching of crystalline state and liquid crystal state with respect to nm
Drawing the contour line of reflectance at the extinction coefficient k coordinate
And as shown in FIG.

In this case, the contrast between the reflectance in the liquid state and the reflectance in the crystalline state, that is, the reflectance in the liquid state is _RL
And the reflectance in the crystalline state is R _c , the ratio of the two is R
_{The range where L} / R _c is R _L / R _c > 3 is the range shown by hatching in FIGS. 6 and 7, that is, 0 <n ≦ 0.
6, 2.5 ≦ k ≦ 3.5.

Similarly, for example, in the structure of FIG. 3, a thickness of 1.2 m in which phase pits are formed by 2P of the glass substrate.
on the transparent substrate 10 having a thickness of 10 m, the semi-transparent metal layer 3 having a thickness of 10 nm, the first dielectric layer 4 made of ZnS—SiO _{2 having} a thickness of 70 nm, and the phase change material layer made of Ge ₂ Sb ₂ Te _{5 having} a thickness of 20 nm. 1, the second by ZnS-SiO ₂ having a thickness of 150nm dielectric layer 5, reflective layer 6 by Dy thickness 150nm, the third by ZnS-SiO ₂ having a thickness of 400nm dielectric layer 7 sequentially deposited and formed Regarding optical discs
Refractive index n of crystalline state and liquid crystal state for 32 nm
-Extinction coefficient Fig. 8 is a drawing of contour lines of reflectance at the k coordinate.
And as shown in FIG.

In this case, the contrast between the reflectance in the liquid state and the reflectance in the crystalline state, that is, the reflectance in the liquid state is R _L
And the reflectance in the crystalline state is R _c , the ratio of the two is R
_{The range where L} / R _c is R _L / R _c > 2.5 is the range shown by hatching in FIGS. 8 and 9, that is, 0 <n ≦
The range is 2,2 ≦ k ≦ 4. Becomes

Similarly, for example, in the structure of FIG. 3, a thickness of 1.2 m in which phase pits are formed by 2P on the glass substrate.
on the transparent substrate 10 having a thickness of 10 m, the semi-transparent metal layer 3 having a thickness of 10 nm, the first dielectric layer 4 made of ZnS—SiO _{2 having} a thickness of 90 nm, and the phase change material layer made of Ge ₂ Sb ₂ Te _{5 having} a thickness of 20 nm. 1, the second by ZnS-SiO ₂ having a thickness of 80nm dielectric layer 5, reflective layer 6 by Dy thickness 150 nm, the third by ZnS-SiO ₂ having a thickness of 400nm dielectric layer 7 sequentially deposited and formed Regarding optical discs
Refractive index n of crystalline state and liquid crystal state for 32 nm
-Extinction coefficient Figure 1 shows the contour line of the reflectance at the k coordinate.
0 and as shown in FIG.

In this case, the contrast between the reflectance in the liquid state and the reflectance in the crystalline state, that is, the reflectance in the liquid state is R _L
And the reflectance in the crystalline state is R _c , the ratio of the two is R
_{The range in which L} / R _c is R _L / R _c > 3 is the range shown by hatching in FIGS. 10 and 11, that is, 0 <n ≦
The range is 0.4 and 4.5 ≦ k ≦ 5.0.

In the above example, the phase change material layer 1 is made of Ge ₂ Sb ₂ Te _5. However, other Te-based chalcogens or chalcogenites and the extinction coefficient k of the crystalline state are It is also possible to use a material whose optical constant changes in two or more liquid phases.

The first, second, and third dielectric layers 4, 5, and 7 are not limited to ZnS-SiO ₂ and may be metal or semiconductor elements such as Al or Si, respectively. It is also possible to use any of the above-mentioned nitrides, oxides, and sulfides that do not absorb in the wavelength region of the reproduction laser light.

The reflective film 6 has a thermal conductivity of 0.00
4 J / (cm · K · s) to 2.2 J / (cm · K · s)
It can also be constituted by a metal element, a metalloid element, a semiconductor element and a compound thereof, or a mixture thereof having a value of.

Further, the phase pit 2 is not limited to the concave and convex pits formed by the 2P method, but may be phase pits which can be optically read by various configurations.

In addition, the structure of the optical disk according to the present invention is not limited to the above-mentioned embodiment, but can be applied to various structures.

[0076]

According to the signal reproducing method of the first aspect of the present invention described above, different phase states are formed in the phase change material layer 1 of the optical disk in the reproduction light spot, and portions having different reflectances are formed. Since it is formed, it enables super-resolution reproduction in which information is read out only in one of the above-mentioned phase states.

In particular, in the present invention, since the original magnitude relation of the reflectance in the phase change material layer 1 is externally inverted and read out, it is possible to obtain an optical characteristic of the phase change material layer. An optical disk using a phase-change material whose reflectance in the crystalline state is larger than that in the liquid state and to which the reproducing method by FAD should be applied without depending only on the constants, that is, the characteristics determined by the refractive index n and the extinction coefficient k. Since the reproducing method by RAD can be performed by the method, it is possible to reduce the crosstalk and thus improve the track density.

On the contrary, the reproduction method by FAD can be carried out by an optical disk using a phase change material, which originally has a reflectance higher than that in the crystalline state in the liquid state and to which the reproduction method by RAD should be applied.

Further, according to the optical disc of the present invention, by providing the semitransparent metal layer 3, the magnitude relationship between the reflectance in each phase state, for example, the crystalline state and the reflectance in the liquid phase state, and the relationship between the two due to the optical interference effect. Since the contrast can be selected, an optical disc applicable to the reproduction method by RAD or the reproduction method by FAD can be appropriately configured, and the degree of freedom in selecting the phase change material is large.
Even when the reproduction method by AD is adopted, for example, Te
Since it can be constituted by a chalcogen-based material containing, the crystallization rate and sensitivity can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the basic structure of an optical disc according to the present invention.

FIG. 2 is a diagram showing a relationship between a film thickness and a reflectance of a semitransparent metal layer in an optical disc according to the present invention.

FIG. 3 is a schematic cross-sectional view of an embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the reflectance and the film thickness of a second dielectric phase change material layer in a crystalline state and a liquid state used for explaining the present invention.

FIG. 5 is a diagram showing the relationship between the reflectance and the film thickness of a second dielectric phase change material layer in a crystalline state and a liquid state, which is used for explaining a comparative example.

FIG. 6 shows a crystalline state 78 of an optical disc according to the present invention.
It is a reflectance contour line with respect to the refractive index n-extinction coefficient k with respect to 0 nm.

FIG. 7 shows a liquid crystal state 78 of an optical disc according to the present invention.
It is a reflectance contour line with respect to the refractive index n-extinction coefficient k with respect to 0 nm.

FIG. 8 is a crystal state 53 of an example of an optical disc according to the present invention.
It is a reflectance contour line with respect to the refractive index n-extinction coefficient k regarding 2 nm.

FIG. 9 shows an example of an optical disc according to the present invention in a liquid phase state 53.
It is a reflectance contour line with respect to the refractive index n-extinction coefficient k regarding 2 nm.

FIG. 10 shows a crystalline state 5 of an example of an optical disc according to the present invention.
It is a reflectance contour line with respect to the refractive index n-extinction coefficient k with respect to 32 nm.

FIG. 11 is a diagram showing an example of an optical disc according to the present invention in a liquid phase state 5
It is a reflectance contour line with respect to the refractive index n-extinction coefficient k with respect to 32 nm.

FIG. 12 is a schematic cross-sectional view showing the basic structure of an optical disc.

FIG. 13 is a diagram showing a light spot and a temperature distribution used for explanation of super-resolution reproduction.

[Explanation of symbols]

 10 Transparent Substrate 1 Phase Change Material Layer 2 Phase Pit 3 Semitransparent Metal Layer 4 First Dielectric Layer 5 Second Dielectric Layer 6 Reflective Film 7 Third Dielectric Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masumi Ono 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (5)

[Claims] 1. A first phase different phase state is formed in the phase change material layer in a reproduction light spot with respect to an optical disc having a phase change material layer, and the reflectances are different from each other.
Area and the second area are formed, and the signal of a limited area in the reproduction light spot is reproduced by the difference in the reflectances. A method for reproducing a signal from an optical disk, which is characterized in that the magnitude relationship of the reflected light quantity depending on the state is reversed and reproduced. 2. A transparent substrate having phase pits formed in response to an information signal, at least a phase change material layer, and a semitransparent metal layer disposed between the phase change material layer and the transparent substrate. An optical disc comprising: 3. The semi-transparent metal layer has a refractive index n and an extinction coefficient k in the range of 0 <n ≦ 0.6 2.5 ≦ k ≦ 5.2 with respect to a reproduction light wavelength of about 780 nm. The optical disc according to claim 2, which is limited. 4. The refractive index n and the extinction coefficient k of the semitransparent metal layer are limited to a range of 0 <n ≦ 22 ≦ k ≦ 5 with respect to a reproduction light wavelength of about 532 nm. The optical disk according to claim 2. 5. The optical disk according to claim 2, 3 or 4, wherein the phase change material is a chalcogen-based material containing Te.