JP2650559B2 - Optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk, an optical card,
The present invention relates to an optical recording medium, such as an optical tape, on which information is recorded or reproduced optically using a spot light. In particular, the spot light is substantially reduced by using a transmittance changing material to achieve high density. The present invention relates to an improvement in an optical recording medium for performing an excellent recording.

[0002]

2. Description of the Related Art As an optical recording medium, for example, a CD (compact disk) is generally used, but recently, attempts have been made to record information at a higher density. Japanese Patent Application No. 2-96926 discloses a technique for attempting such high density. According to this, a nonlinear optical layer is provided on the light incident side of the record carrier.
The beam spot diameter of the incident light is reduced by the function of the nonlinear optical layer, and as a result, high-density information recording and reproduction can be performed.

As a nonlinear optical layer, a transmittance changing material such as gallium arsenide, whose light transmittance is increased by light irradiation and whose light transmittance returns to almost the original value when the light irradiation is stopped or when another light irradiation is performed. Indium antimony or the like is used. The transmittance changing material has a non-linear transmittance characteristic with respect to the incident light intensity, for example, as shown by a graph indicated by a solid line GA in FIG. Such transmittance characteristics have an effect of substantially reducing the spot diameter of the incident light beam. For example, when the incident light intensity and the transmittance are proportional to each other as shown by a graph indicated by a dotted line GB in the same figure, the light spot diameter is reduced to about 3/4. In the case of the graph indicated by the solid line GA in the figure, the diameter of the light spot is further reduced to about 3/5.

According to the above-mentioned prior art, as shown in FIG. 12A, a transmittance changing film 1 is first formed on a main surface of a substrate 100 on which pit rows (or irregularities corresponding to guide grooves) are formed.
02 is formed. Then, a reflective film 104 and a protective film 106 are formed on the transmittance change film 102, respectively. When a light beam having a spot diameter SA as shown in FIG. 4B is incident on such an optical disc, the spot diameter SA substantially becomes S by the action of the transmittance changing film 102.
B, which is incident on the pit. For this reason, even if the track interval becomes narrow due to the increase in the density of information recording, the information can be read satisfactorily.

[0005]

However, when the transmittance changing material is used as in the above-mentioned prior art, the following problems remain. Since a non-linear optical material (transmittance changing material) layer is formed on the surface of the recording medium, it is disadvantageous in productivity and price compared to forming an aluminum reflective film and a protective film after molding like a CD or a laser disk. . Therefore, it is preferable to improve the recording density by shortening the laser wavelength as much as possible, and technical development of shortening the laser wavelength is progressing. However, there is no prospect of commercialization. On the other hand,
There is still a demand for improving the recording density, and it is necessary to form a non-linear optical material layer on the surface of the recording medium to meet the demand for improving the recording density.

However, a recording medium in which a non-linear optical material (transmittance changing material) layer is formed on the recording medium surface still has a problem that it cannot be used for a high-density reproducing apparatus or a recording / reproducing apparatus in which a laser wavelength is shortened. In other words, as with the nonlinear optical material (transmittance changing material) layer, as with the long laser wavelength, the effective light spot diameter decreases as the transmittance increases due to the increase in light intensity even for short laser wavelength light. Too much. As a result, the relationship between the light spot diameter and the pit width / track pitch is deviated, and the amplitude of the reproduced signal is reduced, the symmetry is deteriorated, and the quality of the reproduced signal is significantly deteriorated.

Accordingly, the present invention provides a non-linear optical material layer (transmittance changing material) formed on the surface of a recording medium to meet the demand for improvement in recording density, and at the same time, a recording medium having a non-linear optical material layer formed thereon. It is an object of the present invention to provide a recording medium which can be used in a high-density reproducing apparatus or a recording / reproducing apparatus in which a laser wavelength is set to a short wavelength.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a recording layer for reproducing or recording / reproducing using a spot light, and a light transmittance changes according to the intensity of irradiated light. In an optical recording medium comprising an auxiliary layer, the auxiliary layer has a specific wavelength or a wavelength band whose light transmittance changes in accordance with the intensity of irradiated light, and which is more than the specific wavelength or the wavelength band described above. An object of the present invention is to provide an optical recording medium that is a transmittance changing material that has a substantially constant light transmittance regardless of the intensity of irradiated light in a short wavelength or a wavelength band.

When reproduction or recording / reproduction is performed on the optical recording medium configured as described above using a spot light,
Specific wavelength or wavelength band (long wavelength or wavelength band)
In the spot light, since the light transmittance changes according to the light intensity, the irradiated spot light is substantially reduced to have a smaller diameter, and a wavelength or wavelength shorter than the specific wavelength or wavelength band described above. In the case of spot light having a small band diameter, the transmittance does not change in accordance with the light intensity, so that the spot light is not reduced more than necessary.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the optical recording medium according to the present invention will be described below in detail with reference to the drawings. <Basic Principle> FIGS. 1A and 2A are side views of an optical recording medium (hereinafter, referred to as an optical disk). In FIG. 1, an optical disc 1 has an auxiliary layer 3 made of a transmittance changing material formed on a main surface of a substrate 2 on which pit rows (or irregularities corresponding to guide grooves) are formed. And
On the auxiliary layer 3, a reflection film 4 and a protection film 5 are formed.

The auxiliary layer 3 has a light transmittance that changes in accordance with the intensity of the irradiated light at a specific wavelength or wavelength band (long wavelength or wavelength band), and is higher than the specific wavelength or wavelength band. It is a transmittance changing material that has a substantially constant light transmittance regardless of the intensity of irradiated light in a short wavelength or wavelength band. That is, as shown in FIG. 3, the transmittance changing material does not irradiate light at a wavelength or a wavelength band longer than a certain length, or has low light transmittance under weak light irradiation, and increases light transmittance under strong light irradiation. (Characteristic graph GH) When the light irradiation is stopped, the light transmittance substantially returns to the original state. On the other hand, the light transmittance is high in a wavelength or a wavelength band shorter than a certain length, and the light irradiation hardly changes in the light irradiation. (Characteristic graph G
L) Material.

As shown in FIGS. 1A and 2A, the optical disk 1 configured as described above has a spot light (for example, having a light intensity distribution such as a Gaussian distribution) from a spot light irradiation unit. Reproduction or recording / reproduction using a laser beam). That is, the light spot irradiated from the spot light irradiating means is incident from the substrate 2 side to the auxiliary layer 3 side which is a light transmittance changing material, and a reproducing (recording / reproducing) operation is performed.
The reflected light (or transmitted light) of the incident light is read and reproduced. Further, information is recorded while the recording layer 2 is fixedly (irreversibly) changed by the light spot.

FIG. 1A is a conceptual diagram of a part of an optical recording medium showing a state where a light spot is irradiated when a spot light X having a long laser wavelength is used, and FIG. It is an example of a light spot intensity distribution on a medium surface. When irradiating the spot light with the long laser wavelength, the auxiliary layer 3, which is a light transmittance changing material, has optical characteristics of light intensity and light transmittance as shown in the graph GH of FIG. Is substantially reduced. That is, when the spot light X (light spot diameter x) having the light intensity distribution shown in FIG. 1B is incident on the auxiliary layer 2 which is a light transmittance changing material, at the central portion where the intensity is large,
Since the light transmittance is higher than that of the peripheral portion having lower intensity, more light passes through and is transmitted. On the other hand, the light transmittance of the peripheral portion having lower intensity is lower than that of the central portion having higher intensity. 1 (B)
As shown in (2), the light is incident as a sharp light spot having a small light spot diameter (substantial light spot diameter z). As a result, high-density reproduction and recording / reproduction are performed by the light spot having a substantially small diameter z.

FIG. 2A is a conceptual diagram of a part of an optical recording medium showing a state where a light spot is irradiated when a spot light Y having a short laser wavelength is used, and FIG. It is an example of a light spot intensity distribution on an optical recording medium surface. At the time of irradiation with the spot light having the short laser wavelength, the auxiliary layer 3 which is a light transmittance changing material has optical characteristics of light intensity and light transmittance as shown in a graph GL of FIG. Is high and the transmittance does not change much even if the light intensity changes, so that the light spot diameter y used for reproduction / recording is not affected at all.

Therefore, even if the laser wavelength light is shortened, the problem that the spot diameter becomes too small and the reproduced signal is significantly deteriorated does not occur. Of course, if the laser wavelength is extremely short, the spot diameter becomes too small even if the light transmittance changing layer does not change, so that the quality of the reproduced signal may deteriorate.
The effect of the present invention is favorably produced when the relationship between the long laser wavelength and the short laser wavelength is shortened by a rate substantially equal to the rate at which the light spot is effectively reduced by the light transmittance changing layer. . That is, when the light spot is effectively halved by the light transmittance changing layer, the wavelength ratio between the short laser wavelength and the long laser wavelength is preferably approximately 、, but the allowable value allowed in recording / reproducing. It only has to be within the range. FIGS. 1 and 2 show a specific example in which the optical disk is configured as a read-only optical recording medium having a pit-shaped substrate and a reflective layer, which is the same as FIG. 4 described later.

<Auxiliary Layer as Light Transmittance Changing Material> Next, the light transmittance changing material constituting the auxiliary layer 2 will be described. The auxiliary layer 2 is a material that produces a nonlinear optical effect when the laser wavelength is long and does not produce a nonlinear optical effect when the laser wavelength is short, and is not a material that changes thermally but a material that changes optically. is there. That is, as shown in FIG. 3 described above, the light transmittance and the reflectance change when the laser wavelength is long, and the optical characteristics such as the light transmittance and the reflectance do not change when the laser wavelength is short.

[Specific Example 1] As a light transmittance changing material, about 1% of iron phthalocyanine (ligand pyridine) was mixed with urethane rubber, dissolved in a solvent DMF, and formed on a disk molded using an amorphous polyolefin material. About 80 nm in thickness by spin coating. The maximum absorption wavelength of this coating layer (auxiliary layer) was 670 nm. After an Al reflective layer was attached thereon by a sputtering method, an ultraviolet curable resin was applied by a spin coating method. This optical disc is laser-wavelength 680n
By reproducing with an optical pickup using a lens of m, NA of 0.55, it was possible to reproduce information of about 4 times the density of CD. Also, this optical disk was used with an argon laser wavelength of 488n.
A high quality reproduced signal could be obtained even with an optical pickup having an m of 0.5 and a lens NA of 0.5.

Substantially the same results were obtained when cobalt phthalocyanine (ligand pyridine) was used instead of iron phthalocyanine (ligand pyridine). Almost the same results were obtained when the ligand was piperidine (either iron phthalocyanine or cobalt phthalocyanine may be used). Substantially the same results were obtained when PMMA, PC, or PVC was used instead of urethane rubber (any combination of iron phthalocyanine of the skeleton, cobalt phthalocyanine and the ligands of pyridine and piperidine may be used). It goes without saying that glass may be used instead of amorphous polyolefin as a disc material. When glass was used as a disc material, DMSO could be used instead of DMF as a solvent.

[Specific Example 2] As a light transmittance changing material, about 1% of spiro selenazolino benzopyran exhibiting reverse photochromic was mixed with urethane rubber, dissolved in a solvent DMF, and molded using an amorphous polyolefin material. It was applied to a thickness of about 120 nm on the disk by spin coating. The maximum absorption wavelength of this coating layer (auxiliary layer) was about 620 nm.
Al was deposited thereon by sputtering, and an ultraviolet-curable resin was applied thereon by spin coating. By reproducing this optical disk using an optical pickup having a laser wavelength of 680 nm and a lens NA of 0.55, information about four times the density of a CD could be reproduced. Also, a high-quality reproduction signal could be obtained from this optical disk by using an optical pickup having an argon laser wavelength of 488 nm and a lens NA of 0.5.

As in Example 1, almost the same results were obtained by using PMMA, PC and PVC instead of urethane rubber. It goes without saying that glass may be used instead of amorphous polyolefin as a disc material.
When glass was used as the disc material, DMSO could be used instead of DMF as the solvent. Spirobenzoselenazolinoxazine may be used instead of spiroselenazolinobenzopyran. In this case,
The maximum absorption wavelength became about 650 nm. When recording / reproducing was performed using a laser wavelength of 680 nm, the sensitivity was higher than that of spiroselenazolinobenzopyran.

<Specific Configuration Example of Optical Disk> Next, a specific example of the optical disk will be described with reference to FIGS. On the optical disk, an auxiliary layer made of a light transmittance changing material is laminated before and after a layer that substantially functions as a recorded layer (in the case of a reproduction type). An auxiliary layer made of a light transmittance changing material is laminated between the layer and the layer substantially functioning as a recording layer. In the figure, a is incident light for reading, b is reflected light, and b 'is transmitted light. When the light enters through the substrate of the optical recording medium,
It is laminated on the light-emitting surface of the substrate or between the substrate and a recording film or an additional layer or a reflective film added for improving recording / reproducing characteristics. When light is incident without passing through the substrate of the optical recording medium, the light is laminated on the light incident surface of the substrate, between the reflective film and the protective film, or on the light incident surface of the reflective film.

FIG. 4 shows a specific example of a read-only optical recording medium, which has a reflective layer (see FIGS. 1 and 2 described above). The optical disk 11 is obtained by sequentially laminating a substrate 12, an auxiliary layer 13, which is a light transmittance changing material, a reflective layer 14, and a protective layer 15. The information is recorded as pits on the substrate 12, and the reflected light from the reflective layer 14 corresponding to the pits is read, so that the incident path of the reading light spot (the substrate 12 on the incident side) and the recording layer are substantially formed. Layer 1 which is a light transmittance changing material between reflective layer 14 and optically functioning reflective layer 14
3 are provided.

FIG. 5 is a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, and has a reflective layer. The optical disk 16 includes a substrate 12, a recording layer 17,
An auxiliary layer 13, a reflective layer 14, and a protective layer 15, which are light transmittance changing materials, are sequentially laminated. Information is an optical change of the recording layer 17 (or a magnetic change using the optical change).
Since the reflected light from the reflective layer 14 is read, the auxiliary layer, which is a light transmittance changing material, is provided between the reflective layer 14 and the incident path of the reading light spot (the substrate 12 on the incident side). 13 are provided. Generally, the recording layer 17 has a non-linearity that is not recorded when the light is weak.
7 is formed on the light incident side of the auxiliary layer 13. In order to further enhance the nonlinearity, it is preferable that the auxiliary layer 13 be on the light incident side. However, when the sensitivity of the recording layer is not sufficient with respect to the used laser power, it is better to set the recording layer 17 on the light incident side as shown in FIG.

FIG. 6 shows a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, in which a reflective layer is not provided. The optical disk 23 is obtained by sequentially laminating a substrate 12, an auxiliary layer 13, which is a light transmittance changing material, a recording layer 17, and a protective layer 15. Information is recorded as an optical change of the recording layer 17 and the like, and the reflected light from the recording layer 17 is read. Therefore, the information is provided between the incident path of the reading light spot (the substrate 12 on the incident side) and the recording layer 17. An auxiliary layer 13 which is a light transmittance changing material is provided.

FIG. 7 shows a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, in which an additional layer for improving characteristics is provided on a recording layer. The optical disk 18 is obtained by sequentially laminating a substrate 12, an auxiliary layer 13 as a light transmittance changing material, an enhance layer 19 as an additional layer, a recording layer 17, a heat insulating layer 20, an additional layer, a reflective layer 14, and a protective layer 15. It is. Information is recorded as an optical change in the recording layer 17 (such as a magnetic change utilizing the optical change), and the information is recorded in the reflective layer 14.
Since the reflected light from the recording layer 17 is read, the auxiliary layer 13, which is a light transmittance changing material, is placed between the incident path of the reading light spot (the substrate 12 on the incident side) and the reflection layer 14 and the recording layer 17. Is provided.

FIG. 8 is a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, and is a transmission type example. The optical disk 19 is formed by sequentially laminating a substrate 12, an auxiliary layer 13, which is a light transmittance changing material, a recording layer 17, and a protective layer 15. The information is recorded as an optical change of the recording layer 17 and the transmitted light from the recording layer 17 is read.
The incident path of the light spot for reading (the substrate 1 on the incident side)
An auxiliary layer 13 which is a light transmittance changing material is provided between 2) and the recording layer 17.

FIG. 9 shows a specific example of a read-only optical recording medium, in which reading is performed without passing through a substrate. The optical disk 24 has a substrate 12, a reflective layer 14, an auxiliary layer 13, which is a light transmittance changing material, and a protective layer 15, which are sequentially laminated. The information is recorded as pits on the substrate 12, and the reflected light from the reflective layer 14 corresponding to the pits is read, so that the read light spot is formed as an incident path (the protective layer 15 on the incident side) and a recording layer. Reflective layer 14 that functions substantially
And an auxiliary layer 13 which is a light transmittance changing material.

FIG. 10 shows a specific example of a read-only optical recording medium, in which an additional layer for improving characteristics is provided. The optical disk 21 includes a substrate 12, a dielectric layer 22, which is an additional layer,
An auxiliary layer 13, which is a light transmittance changing material, a dielectric layer 22, which is an additional layer, a reflective layer 14, and a protective layer 15, are sequentially laminated. The information is recorded as pits on the substrate 12, and the reflected light from the reflective layer 14 corresponding to the pits is read, so that the incident path of the reading light spot (the substrate 12 on the incident side) and the recording layer are substantially formed. Functioning reflective layer 14
And an auxiliary layer 13 which is a light transmittance changing material.

The optical recording medium according to the present invention is shown in FIGS.
In any of the configurations shown in the above, the reproduction spot diameter is substantially reduced, and high-density reproduction and high-density recording / reproduction can be performed. Then, it can be used as it is even in a high-density reproducing apparatus using a spot light having a shortened wavelength.

[0030]

As described above in detail, in the optical recording medium according to the present invention, the recording layer for reproducing or recording / reproducing using the spot light, and the light transmittance changes according to the intensity of the irradiated light. In an optical recording medium comprising an auxiliary layer, the auxiliary layer has a specific wavelength or wavelength band, the light transmittance of which changes according to the intensity of the irradiated light, and the specific wavelength or wavelength. Since it is a transmittance changing material whose light transmittance is almost constant irrespective of the intensity of irradiated light in a wavelength or a wavelength band shorter than the band, when reproducing or recording / reproducing using a spot light, a specific wavelength or In the case of spot light in a wavelength band (long wavelength or wavelength band), the light transmittance changes in accordance with the light intensity, so that the irradiated spot light is substantially reduced to have a smaller diameter. Wavelength The spotlight small diameter short wavelength or wavelength band than the wavelength band, the change in transmittance in accordance with the intensity of light does not occur, not be reduced more than necessary spot light. Therefore, it can be used in a high-density reproducing apparatus or recording / reproducing apparatus in which the wavelength of the spot light is shortened while responding to the demand for the improvement of the recording density by the auxiliary layer made of the transmittance changing material.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical recording medium according to the present invention. FIG. 1 (A) shows an optical recording showing a state where a light spot is irradiated when a spot light X having a long laser wavelength is used. FIG. 2B is a conceptual diagram of a part of the medium, and FIG. 2B is an example of a light spot intensity distribution on the optical recording medium surface.

FIG. 2 is a diagram showing an embodiment of an optical recording medium according to the present invention. FIG. 2A shows an optical recording state in which a light spot is irradiated when a spot light Y having a short laser wavelength is used. FIG. 2B is a conceptual diagram of a part of the medium, and FIG. 2B is an example of a light spot intensity distribution on the optical recording medium surface.

FIG. 3 is a view showing characteristics of an auxiliary layer (light transmittance changing material) of the optical recording medium according to the present invention.

FIG. 4 is a specific example of a read-only optical recording medium, which has a reflective layer.

FIG. 5 is a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, in which a reflective layer is provided.

FIG. 6 is a specific example of an additional recordable optical recording medium or a rewritable optical recording medium, which is an example having no reflective layer.

FIG. 7 is a specific example of an additional recordable optical recording medium or a rewritable optical recording medium, in which a recording layer is provided with an additional layer for improving characteristics.

FIG. 8 is a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, which is a transmission type example.

FIG. 9 is a specific example of a read-only optical recording medium, in which reading is performed without passing through a substrate.

FIG. 10 is a specific example of a read-only optical recording medium, in which an additional layer for improving characteristics is provided.

FIG. 11 is a diagram showing characteristics of an auxiliary layer (light transmittance changing material) in a conventional optical recording medium.

FIG. 12A is a diagram showing a conventional optical recording medium.
(B) is an example of the light spot intensity distribution on the optical recording medium surface.

[Explanation of symbols]

1,11,16,18,19,21,23,24 Optical disk (optical recording medium) 12 Substrate 13 Auxiliary layer (light transmittance changing material) 14 Reflective layer 17 Recording layer 19,20,22 Additional layer X Long wavelength Spot light Y Spot light of short wavelength x Diameter of spot light of long wavelength y Diameter of spot light of short wavelength z Diameter of spot light of long wavelength substantially reduced

Claims (1)

(57) [Claims] 1. An optical recording medium comprising: a recording layer for reproducing or recording / reproducing using spot light; and an auxiliary layer whose light transmittance changes according to the intensity of irradiated light. At a specific wavelength or wavelength band, the light transmittance changes according to the intensity of the irradiated light, and at a wavelength or wavelength band shorter than the specific wavelength or wavelength band, regardless of the intensity of the irradiated light. An optical recording medium comprising a transmittance changing material having a substantially constant light transmittance.