JP3306975B2 - Optical disc reproducing method and optical disc - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reproducing information on an optical disk for reproducing information by irradiating a laser beam, an optical disk for performing such reproduction, and a method for reproducing an optical disk particularly suitable for high-density recording. Related to optical disks.

[0002]

2. Description of the Related Art For example, an optical disc such as a digital audio disc, a so-called compact disc and a video disc, has an aluminum reflective film formed on a transparent substrate on which recording pits having irregularities are formed in advance in accordance with a signal. It is configured by forming a protective film and the like.

In such an optical disk, a signal is read out, that is, reproduced by irradiating the disk surface with readout light and detecting a large decrease in the amount of reflected light due to diffraction of light at a recording pit formation portion. I have.

In the above-mentioned optical disk, the resolution of signal reproduction is almost determined by the wavelength λ of the light source of the reproduction optical system and the numerical aperture NA of the objective lens, and the period of the formed recording pits is limited by the diffraction limit (λ / 2NA) or more, a good reproduced signal can be obtained.

Therefore, in order to increase the density of such an optical disk, first, the wavelength λ of the light source of the reproducing optical system, generally a semiconductor laser, is shortened, and the numerical aperture N of the objective lens is reduced.
It is necessary to increase A.

[0006]

However, there is naturally a limit in improving the wavelength of the light source and the numerical aperture of the objective lens. That is, for example, even if the wavelength of the light source is shortened, the recording density can be increased at most four times with the current technology. In addition, it is difficult to manufacture a lens having a small aberration when trying to increase the numerical aperture of the lens, and even if such a lens is obtained, the stability of the focus against disk vibration and skew is reduced. Problems arise. Therefore, it is actually difficult to dramatically improve the recording density of the optical disk.

On the other hand, an optical disk capable of obtaining a resolution higher than the above-mentioned limitation of the light source wavelength λ or the numerical aperture NA of the lens system is disclosed in Japanese Patent Application No. 2-94452 and Japanese Patent Application No. Hei. It was proposed in Hei 2-291773. The inventions related to these applications relate to an optical disk or a reproduction system for performing super-resolution reproduction by changing a reflectance by a partial phase change in a laser spot of a reading light.

In the present invention, the difference in reflectance between the target read recording pit and the other portion is more remarkably and stably ensured to ensure a high C / N (signal / noise ratio) or S / N.
Provided is an optical disk capable of performing super-resolution reproduction with a (sound / noise ratio).

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for reproducing an optical disk in which at least a recording layer made of a photochromic material is formed on a transparent substrate on which recording pits have been formed. With light
The recording light is reproduced by irradiating the read light with a mask generation light having a different wavelength and lowering the reflectivity of the recording layer so as to partially overlap the recording layer. Further, the present invention provides the above-mentioned reproducing method, wherein the photochromic material is represented by the following chemical formula 1.

Embedded image Or the following Chemical Formula 2

Embedded image And the wavelength of the reading light is set to 550.
nm to 700 nm, and the wavelength of the mask generation light is 4
The thickness should be greater than or equal to 00 nm and less than or equal to 550 nm.

Further, the present invention relates to an optical disc in which at least a recording layer made of a photochromic material is formed on a transparent substrate on which recording pits are formed, wherein the photochromic material of the recording layer is a reading light for reading the recording pit. Irradiation and the readout light are materials whose wavelengths are different from each other and which change into different absorption spectrum states with respect to the irradiation of the mask generation light for reducing the reflectance of the recording layer. Reproduction is performed by irradiation with the mask generation light so as to partially overlap.

The present invention also provides the optical disk as described above, wherein the photochromic material is represented by the above formula 1 or 2
And the wavelength of the readout light is 550 nm or more and 700 nm or less, and the wavelength of the mask generation light is 400 nm or more and 550 nm or less.

[0012]

In the optical disc reproducing method and the optical disc according to the present invention, since the optical disc 10 made of a photochromic material is used as the recording layer 3, the read light and the mask generation light having different wavelengths are partially overlapped on the recording layer 3. Thus, in reading or reproducing the recording by the recording pits 1, a change in the absorption spectrum of the recording layer 3 due to the reading light and a change in the absorption spectrum of the recording layer 3 due to the light generated by the mask can be used.

That is, in the spot of the readout light, particularly, for example, the reflectivity of the recording layer 3 at the portion where the mask generation light overlaps is remarkably lowered so that the readout light spot and the mask generation light spot overlap each other. For a certain recording pit, for example, reading by diffraction can be disabled. Accordingly, a region where the recording pits are optically extinguished is partially formed in the readout light spot, and for example, only one recording pit can be read out in this spot, and ultra-high resolution reproduction is not restricted by λ / 2NA. It can be carried out.

Further, according to the present invention, in the above-described optical disk reproducing method, reproduction is performed by irradiating the surface of the optical disk 10 with two beams so as to partially overlap with each other using an optical system having light sources of two different wavelengths. For example, for light of one wavelength, the reflectance can be reduced, for example, so that reading is not possible, and the reflectance can be increased, for example, so that reading is possible for light of the other wavelength,
Thereby, super-resolution reproduction can be performed by one irradiation.

Further, in the present invention, the above-mentioned photochromic material is represented by the above-mentioned chemical formula 1 or 2,
Each of the light sources of the two different wavelengths is 400
A light source of .lambda.s of .about.550 nm and a .lambda.
l using the light source of l
The absorption spectrum of the recording layer 3 can be reduced and increased, and super-resolution reproduction can be performed by one irradiation as described above.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cross-sectional view of a main part of an example of the present invention. As shown in FIG. 1, a photochromic material is formed on a transparent substrate 2 on which recording pits 1 are formed. The optical disk 10 is formed by forming the recording layer 3 having the above structure.

The optical disk 10 is not limited to the structure shown in FIG. 1, but, for example, as shown in FIG. To form a recording layer 3 made of a photochromic material via a second dielectric layer 6 and a reflective layer 4 made of Al or the like via a second dielectric layer 6.
Further, a configuration in which a protective layer 7 is provided thereon may be adopted. The provision of the first and second dielectric layers 5 and 6 facilitates setting of optical characteristics such as reflectance.

When a photochromic material, for example, a material represented by Chemical Formula 1 or Chemical Formula 2 described above is used, a recording medium having photoresponsiveness shown in the following (1) and (2) can be obtained. Symposium Papers (1992) p45-p47 ". (1) Upon irradiation with light Ls having a wavelength λs, the photochromic material changes from state A to state B. (2) When irradiated with light Ll having a wavelength λl, the photochromic material changes from state B to state A.

The state A mentioned here is a state in which the absorption spectrum of the photochromic material has a distribution having peaks at, for example, two wavelengths λs and λl, as shown in FIG. FIG.
As shown in (1), the absorption spectrum has a distribution having a peak only at the wavelength λs.

Here, when the photochromic material is irradiated, light Ls having a wavelength λs which causes a photochemical reaction to change from state A to state B is used as mask generation light, and when the photochromic material is irradiated, the photochemical reaction changes from state B to state A. By using the light L1 having the wavelength .lambda.1 to be changed as a result of the occurrence as the readout light, it is possible to repeatedly perform recording / reproducing with high resolution.

When the mask generating light Ls is forward and the readout light Ll is backward with respect to the traveling direction of the light spot, FIG.
As shown schematically, the light intensity distribution corresponding to the spot and the distribution of the reflectance at a specific wavelength, in this case λl, the mask generation light L in front of the spot of the read light Ll.
In the part overlapping with the spot s, the readout light Ll
The recording pit 1 cannot be read because the reflectance of the recording pit 1 is low. On the other hand, behind the spot of the read light Ll, the reflectivity is high because it does not overlap with the spot of the mask generated light Ls, so that the recording pit 1 can be read. In FIG. 5, the arrow S indicates the moving direction of the light spot.

Next, when the readout light Ll is in front of the traveling direction of the light spot and the mask generation light Ls is behind, the spot of the mask generation light Ls is located in front of the spot of the readout light Ll as shown in FIG. Since it does not overlap, the reflectance increases, and the recorded pits can be read.
Further, behind the spot of the reading light Ll,
Since the light spot overlaps with the spot of the mask generation light Ls, the reflectance is low, and the recording pit cannot be read. 6, parts corresponding to those in FIG. 5 are denoted by the same reference numerals, and redundant description will be omitted.

Therefore, by adopting the spot irradiation mode described in FIG. 5 or FIG. 6, even when a plurality of (two in FIG. 5 and FIG. 6) recording pits 1 enter the spot, only one pit is recorded. It is possible to reliably read data, and thereby the period of the recording pit becomes the diffraction limit (λ
/ 2NA) or more, a good reproduced signal can be obtained, and the above-mentioned transition from the state A to the state B and vice versa are reversible, so that repeated reading is possible, that is, non-destructive. Can be reproduced.

That is, when the optical disk according to the present invention is irradiated with a laser spot, as shown in FIGS. 5 and 6, when a plurality of recording pits, in this case, two recording pits 1, exist in the spot of the readout light λl. In this case, it is possible to read out only one recording pit 1 existing in the area aperture having a large reflectance which does not overlap with the spot of the mask generating light λs, and the other recording pit overlaps with the spot of the mask generating light λs. Therefore, the readout is not performed in the area mask having an extremely low reflectance.

As described above, even if a plurality of recording pits 1 are present in the spot of the reading light λ1, the reading can be performed only with respect to a single recording pit 1. That is, the reading is repeated with ultra-high resolution without being limited by the numerical aperture NA of the lens system and the wavelength λ of the reading light,
Moreover, it can be performed without destroying the recorded contents.

As an optical system for performing such reading, for example, as shown in FIG.
The light source 11 is provided so as to face the recording layer of the optical disk 10, and the light L ₁ from the light source 11 passes through the half mirrors 13 and 14 and irradiates the recording layer from the substrate side of the optical disk 10. light L ₂ is configured to be irradiated to the recording layer from the substrate side of the optical disk 10 with a predetermined minute angle α to the light L ₁ from above the light source 11, for example by the half mirror 13 from. This angle α is the half mirror 13
Is set to 45 ° ± α, for example, from the traveling direction of the light from the second light source 12 so that the respective lights L ₁ and L ₂ have a desired overlap on the recording layer of the optical disc 10. It can be made to be irradiated as a spot. The light obtained by the reflection from the recording layer can be reflected by the half mirror 14 as indicated by an arrow _Lo and detected by the light receiving element 15 such as a photodiode.

Next, each embodiment in which reproduction is performed by the above-described reproduction method using the optical disk 10 having the configuration described in FIG. 2 will be described below.

Embodiment 1 In this embodiment, a transparent substrate 2 made of a glass substrate is used, and a recording pit 1 is formed on one main surface thereof. The recording pit 1 was formed under the following conditions: a track pitch of 1.6 μm, a pit depth of about 120 nm, and a pit width of 0.3 μm. Then, the transparent substrate 2 having the pit 1
A first dielectric layer 4 made of AlN or the like having a thickness of 90 nm is formed on one principal surface, and a photochromic material is formed on the first dielectric layer 4 with a thickness of 50 nm as shown in the following chemical formula 3 (that is, the above chemical formula 1). The recording layer 3 was formed by applying an organic compound having the structural formula.

[0029]

Embedded image

A second dielectric layer 5 made of AlN or the like having a thickness of 30 nm is formed thereon as a second dielectric layer 5, and a reflective layer 6 made of Al or the like is formed thereon with a thickness of 30 nm.
And a protective layer 7 made of an acrylic resin, for example, a UV (ultraviolet) curable resin.

In the first embodiment, the readout light Ll is light obtained from, for example, a He-Ne laser having a wavelength 550 nm to 700 nm and a wavelength λl of, for example, 633 nm. The reflectance at a wavelength of 633 nm was 30%. Further, the mask generation light Ls is set to 400 nm to 550.
e.g. Ar having a wavelength λs of e.g.
The reflectance at a wavelength of 633 nm when the mask-generated light Ls was applied as light obtained from a laser, that is, in the state B, was 3%. When the power of the readout light L1 was set to 1 mW, the power of the mask generation light Ls was set to 1 mW, and the linear velocity was set to 3 m / sec, the reproduction was performed to reproduce the signal portion. 4
It was 0 dB.

Example 2 In this example, the transparent substrate 2 and the recording pits 1 were formed in the same manner as in Example 1 described above. A first dielectric film 4 made of AlN having a thickness of 180 nm is formed on one main surface of the transparent substrate 2 and a recording layer 3 made of a photochromic material is formed on the first dielectric film 4 having a thickness of 50 nm. That is, an organic compound having the structural formula shown in the above Chemical Formula 2) was formed by deposition.

[0033]

Embedded image Further, a second dielectric layer 5 having a thickness of 75 n
A second dielectric layer 5 of mN AlN, an Al reflective film 6 having a thickness of 180 nm, and a protective layer 7 made of a UV curable resin or the like were formed by deposition.

At this time, the read light Ll (λl = 633)
nm), that is, the wavelength 6 when in the state A.
The reflectance at 33 nm is 25%, and the light Ls generated by the mask is
(Λs = 458 nm), that is, state B
In this case, the reflectance at a wavelength of 633 nm was 2%. Then, the power of the read light L1 is set to 5 mW, the power of the mask generation light Ls is set to 5 mW, and the linear velocity is set to 3 m / s.
When the signal portion was reproduced by setting it to ec and reproducing it, the C / N of the signal was 40 dB.

The organic compound shown in Chemical Formula 4 has a temperature dependency shown in FIG. 8 in a reaction when the state is changed from the state A to the state B by irradiating the mask generating light Ls. By the way, the light intensity distribution and the temperature distribution when irradiating the light spot while the disk is moving are such that the temperature distribution peak comes after the light intensity peak as described in FIG. 5 and FIG.

By using this, when the readout light Ll is in front of the traveling direction of the light spot and the mask generation light Ls is behind, as shown in FIG. Since the spot does not overlap with the spot of Ls, by changing from the state B to the state A, the reflectance is increased and the recorded pits can be read. Further, behind the spot of the read light Ll, the spot overlaps with the spot of the mask generation light Ls, and further, the temperature rise due to the light spot causes a change from state A to state B, thereby lowering the reflectivity and reading the recording pits. Can not.

In reproducing the optical disk according to the present invention, it is possible to reproduce the optical disk with ultra-high resolution by utilizing the difference between the reflectance when the read light Ll is irradiated on the optical disk and the reflectance when the mask generation light Ls is irradiated. it can.

The present invention is not limited to the above-described embodiments. For example, the transparent substrate 2 is not limited to the above-mentioned glass substrate, but may be a synthetic resin substrate such as polycarbonate or polymethacrylate or a resin substrate. Various configurations can be adopted, such as forming a recording pit 1 with a stamper by applying a photopolymer.

Further, the photochromic material is not limited to the above-mentioned organic compound represented by Chemical Formula 3 or Chemical Formula 4, but may be constituted by another organic photochromic compound or an inorganic photochromic compound. As the inorganic photochromic compound, tungsten oxide, molybdenum oxide, or the like can be used.

Further, as the first dielectric film 4 and the second dielectric film 5, in addition to the above-described AlN, Si ₃ N ₄ ,
SiO, Al ₂ O ₃ , ZnS, MgF ₂ or the like can be used.

The reflective film 6 may be made of Cu, Ag, Au, Ti, or an alloy thereof, in addition to Al.

[0042]

As described above, in the present invention, a difference in reflectance is caused by a change in the absorption spectrum of the photochromic material due to the photochemical reaction of the readout light λl and the mask generation light λs, and a specific light spot in the light spot is formed. By performing reading only with respect to the recording pits, it is possible to more stably and reliably perform reading with high C / N and high stability and ultra-high resolution.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic sectional view of a main part of an embodiment of the present invention.

FIG. 2 is a schematic enlarged sectional view of a main part of another embodiment of the present invention.

FIG. 3 is a diagram showing an absorption spectrum of an example of a photochromic material used in Examples of the present invention.

FIG. 4 is a diagram showing an absorption spectrum of an example of a photochromic material used in Examples of the present invention.

FIG. 5 is an explanatory diagram showing an example of the principle of super-resolution reproduction for explaining the present invention.

FIG. 6 is an explanatory diagram showing another example of the principle of super-resolution reproduction for explaining the present invention.

FIG. 7 is a configuration diagram of an example of an optical system used in an embodiment of the present invention.

FIG. 8 is a diagram showing the temperature dependence of the photochemical reaction of the photochromic material used in the examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Recording pit 2 Substrate 3 Recording layer 4 Reflection layer 5 First dielectric layer 6 Second dielectric layer

Claims (4)

(57) [Claims] 1. A method for reproducing an optical disk in which at least a recording layer made of a photochromic material is formed on a transparent substrate on which recording pits have been formed, comprising: a reading light for reading the recording pits; Reproducing the recording pits by irradiating with a mask generating light for reducing the reflectance of the recording layer having a different wavelength so as to partially overlap the recording layer, thereby reproducing the recording pits. Method. 2. The photochromic material of the following chemical formula Or the following chemical formula And the wavelength of the readout light is 550 nm or more and 700 nm.
The wavelength of the mask generation light is 400 nm or more and 5 or less.
2. The method for reproducing an optical disk according to claim 1, wherein the thickness is 50 nm or less. 3. An optical disc in which a recording layer made of at least a photochromic material is formed on a transparent substrate on which recording pits are formed, wherein the photochromic material of the recording layer is a reading light for reading the recording pits. Irradiation, the readout light is a material having a different wavelength and a different absorption spectrum with respect to the irradiation of the mask generation light for reducing the reflectance of the recording layer, and the recording layer has An optical disc characterized in that reproduction is performed by irradiating the readout light and the mask generation light so as to partially overlap each other. 4. The photochromic material according to claim 1, wherein Or the following chemical formula Is used, and the wavelength of the readout light is 550 nm or more and 700 nm.
4. The method according to claim 3, wherein the wavelength of the mask generation light is 400 nm or more and 550 nm or less.
An optical disk according to claim 1.