JPH05242524A - Optical recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] With the current device that uses spot light with a long wavelength, the diameter of the spot light can be made substantially smaller to enable high-density recording, and a spot light with a short wavelength is used. The present invention provides an optical recording medium that can be used as it is in future devices. [Structure] An optical recording medium 1 in which a recording layer 2 for reproducing or recording / reproducing by using spot light and an auxiliary layer 3 whose light transmittance changes according to the intensity of irradiated light are laminated. The light transmittance of the auxiliary layer 3 changes in accordance with the intensity of the irradiated light in a specific wavelength / wavelength band (characteristic graph GH), and a wavelength / wavelength band shorter than the specific wavelength / wavelength band described above. Then, it is formed of a transmittance changing material having a substantially constant light transmittance (characteristic graph GL) regardless of the intensity of the irradiated light.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical disc, an optical card,
The present invention relates to an optical recording medium such as an optical tape in which information is optically recorded or reproduced by using spot light, and in particular, a transmittance changing material is used to substantially reduce the spot light and achieve high density. The present invention relates to an improvement of an optical recording medium for performing various recordings.

[0002]

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

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

According to the above-mentioned conventional technique, as shown in FIG. 12 (A), the transmittance changing film 1 is first formed on the main surface of the substrate 100 on which pit rows (or irregularities corresponding to guide grooves) are formed.
02 is formed. Then, the reflective film 104 and the protective film 106 are respectively formed on the transmittance changing film 102. When a light beam having a spot diameter SA as shown in FIG. 3B is incident on such an optical disc, the spot diameter SA is substantially S due to the action of the transmittance changing film 102.
It is reduced to B, and this will enter the pit. Therefore, even if the track interval is narrowed due to the high density of information recording, the information can be read out satisfactorily.

[0005]

However, when the transmittance changing material is used as in the above-mentioned prior art, the following problems remain. Since the non-linear optical material (transmissivity changing material) layer is formed on the surface of the recording medium, it is disadvantageous in terms of productivity and price as compared with the case where the aluminum reflective film and the protective film are formed 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 technological development for shortening the laser wavelength is progressing. However, there is no prospect of commercialization. On the other hand,
The demand for higher recording density is still present, and it is necessary to meet the demand for higher recording density by forming a non-linear optical material layer on the surface of a recording medium.

However, a recording medium having a non-linear optical material (transmissivity changing material) layer formed on the surface of the recording medium has a problem that it cannot be used as it is in a high-density reproducing apparatus or recording / reproducing apparatus in which the laser wavelength is a short wavelength. In other words, the effective optical spot diameter becomes smaller when the transmittance increases with increasing light intensity for short laser wavelength light as well as for the nonlinear optical material (transmittance changing material) layer for long laser wavelength. Too much. As a result, the relationship between the light spot diameter and the pit width / track pitch is deviated, and the reproduction signal amplitude is reduced and the symmetry is deteriorated, resulting in a remarkable deterioration of the reproduction signal quality.

Therefore, according to the present invention, while the non-linear optical material layer (transmission factor changing material) is formed on the surface of the recording medium to meet the demand for the improvement of the recording density, at the same time, the non-linear optical material layer is left as it is. The present invention provides a recording medium that can be used in a high-density reproducing apparatus or recording / reproducing apparatus in which the laser wavelength is a short wavelength.

[0008]

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

When reproducing or recording / reproducing using spot light on the optical recording medium having the above-mentioned structure,
Specific wavelength or wavelength band (long wavelength or wavelength band)
In the spot light, since the light transmittance changes according to the intensity of the light, the spot light irradiated is substantially reduced and its diameter becomes smaller, and the wavelength or wavelength shorter than the specific wavelength or wavelength band described above. With spot light having a small band diameter, the transmittance does not change according to the intensity of the light, so the spot light is not reduced more than necessary.

[0010]

An embodiment of an optical recording medium according to the present invention will be described in detail below 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 disc). 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
A reflective film 4 and a protective film 5 are formed on the auxiliary layer 3.

The auxiliary layer 3 has a light transmittance which changes according to the intensity of the irradiated light at a specific wavelength or wavelength band (long wavelength or wavelength band), and more than the specific wavelength or wavelength band described above. It is a transmittance changing material that has a substantially constant light transmittance regardless of the intensity of the irradiated light in a short wavelength or a wavelength band. That is, as shown in FIG. 3, the transmittance changing material does not emit light at a wavelength or wavelength band longer than a certain length, or has low light transmittance when weak light irradiation is used, and increases light transmittance when strong light irradiation is used. (Characteristic graph GH), when the light irradiation is stopped, the light transmittance returns to the original value. On the other hand, the light transmittance is high at a wavelength or a wavelength band of a certain length or less, and the light transmittance hardly changes by the light irradiation. (Characteristic graph G
L) Material.

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

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. FIG. 1B shows the optical recording. It is an example of a light spot intensity distribution on the medium surface. During irradiation with the spot light having this 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 by a graph GH in FIG. The light spot diameter used for 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 that is the light transmittance changing material,
Since the light transmittance is higher than that of the peripheral area where the intensity is low, more light is transmitted and transmitted. On the other hand, the light transmittance is lower in the peripheral area where the intensity is lower than that in the central area where the intensity is high. Is less transmitted through, as shown in Fig. 1 (B).
As shown in, the light is incident as a sharp light spot with a small light spot diameter (substantial light spot diameter z). As a result, high-density reproduction and recording / reproduction can be performed by a light spot having a substantially small diameter z.

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

Therefore, even if the laser wavelength light becomes short, the spot diameter becomes too small and the reproduced signal does not significantly deteriorate. Of course, if the laser wavelength becomes extremely short, the spot diameter becomes too small even if the light transmittance changing layer does not change, so 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 about 1/2, but the allowable value for recording / reproduction is acceptable. It should be in the range of. 1 and 2 are specific examples in which the optical disk is configured as a read-only optical recording medium having a pit-shaped substrate / reflection layer, and are the same as those in FIG. 4 described later.

<Auxiliary Layer as Light Transmittance Change Material> Next, the light transmittance change material constituting the auxiliary layer 2 will be described. The auxiliary layer 2 is a material that produces a non-linear optical effect when the laser wavelength is long and does not produce a non-linear optical effect when the laser wavelength is short, and is not a thermally changing material but an optically changing material. is there. That is, as shown in FIG. 3 described above, the material is a material whose light transmittance and reflectance change when the laser wavelength is long and whose optical characteristics such as light transmittance and 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 molded on a disk using an amorphous polyolefin material. Was applied by a spin coating method to a thickness of about 80 nm. The maximum absorption wavelength of this coating layer (auxiliary layer) was 670 nm. After depositing an Al reflective layer on this by a sputtering method, an ultraviolet curable resin was applied by a spin coating method. This optical disc has a laser wavelength of 680n
By reproducing with an optical pickup using a lens of m, NA 0.55, it was possible to reproduce information having a density about 4 times that of a CD. In addition, this optical disc is used with an argon laser having a wavelength of 488n.
It was possible to obtain a high-quality reproduced signal even with an optical pickup having a lens having a lens NA of 0.5.

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

[Specific Example 2] As a light transmittance changing material, about 1% of spiroselenazolinobenzopyran exhibiting reverse photochromic was mixed with urethane rubber, dissolved in a solvent DMF, and molded using an amorphous polyolefin material. About 120 nm was applied onto the disk by spin coating. The maximum absorption wavelength of this coating layer (auxiliary layer) was about 620 nm.
Al was deposited thereon by a sputtering method, and an ultraviolet curable resin was applied thereon by a spin coating method. By reproducing this optical disk using an optical pickup having a laser wavelength of 680 nm and a lens NA of 0.55, it was possible to reproduce information having a density about four times that of a CD. Further, 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.

Similar results as in Example 1 were obtained even when PMMA, PC or PVC was used instead of urethane rubber. It goes without saying that glass may be used instead of the amorphous polyolefin as the disk material.
When glass was used as the disk material, DMSO could be used instead of DMF as the solvent. Spirobenzoselenazolino oxazine may be used instead of spiro selenazolino benzopyran. In this case,
The maximum absorption wavelength became about 650 nm. The sensitivity was higher than that of spiroselenazolinobenzopyran when recording / reproducing using a laser wavelength of 680 nm.

<Specific Configuration Example of Optical Disc> Next, a specific example of the optical disc will be described with reference to FIGS. An optical disc has an auxiliary layer made of a light transmittance changing material laminated before and after a layer that substantially functions as a recorded layer (in the case of a reproducing type), and also has an incident position of a reading light spot and a recording layer. An auxiliary layer made of a light transmittance changing material is laminated between the layer and the layer that substantially functions as (for recording type). In the figure, a is incident light for reading, b is reflected light, and b'is transmitted light. The auxiliary layer made of the light transmittance changing material has a structure in which when light is incident through the substrate of the optical recording medium,
It is laminated on the light emitting surface of the substrate or between the substrate and the recording film or an additional layer or reflective film added to improve recording / reproducing characteristics. When light is incident on the optical recording medium without passing through the substrate, it is laminated on the light incident surface of the substrate, between the reflection film and the protective film, or on the light incident surface of the reflection 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 comprises a substrate 12, an auxiliary layer 13, which is a light transmittance changing material, a reflective layer 14, and a protective layer 15, which are sequentially stacked. Since information is recorded as pits on the substrate 12 and the reflected light from the reflective layer 14 corresponding to the pits is read, it is substantially used as the incident path of the optical spot for reading (the substrate 12 on the incident side) and the recording layer. Auxiliary layer 1 which is a light transmittance changing material between the reflective layer 14 and the reflective layer 14
3 is provided.

FIG. 5 is a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, which is an example having a reflective layer. The optical disc 16 includes a substrate 12, a recording layer 17,
The auxiliary layer 13, which is a light transmittance changing material, the reflective layer 14, and the protective layer 15 are sequentially laminated. Information is an optical change of the recording layer 17 (or a magnetic change utilizing 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 incident path of the reading light spot (the substrate 12 on the incident side) and the reflective layer 14. 13 are provided. In general, 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 enhance the non-linearity, the auxiliary layer 13 should be located on the light incident side. However, when the sensitivity of the recording layer is not sufficient with respect to the laser power used, 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 type optical recording medium and a rewritable type optical recording medium, in which no reflective layer is provided. The optical disk 23 comprises a substrate 12, an auxiliary layer 13, which is a light transmittance changing material, a recording layer 17, and a protective layer 15, which are sequentially stacked. Information is recorded as an optical change in the recording layer 17, and the reflected light from the recording layer 17 is read, so that the information is recorded 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 is a specific example of an additional recordable optical recording medium and a rewritable optical recording medium, and shows an example in which an additional layer for improving characteristics is provided in the recording layer. The optical disc 18 is formed by sequentially laminating a substrate 12, an auxiliary layer 13 which is a light transmittance changing material, an enhancement layer 19 which is an additional layer, a recording layer 17, a heat insulating layer 20 which is an additional layer, a reflection layer 14 and a protective layer 15. Is. Information is recorded as an optical change (such as a magnetic change utilizing the optical change) of the recording layer 17, and 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 provided between the incident path (the incident side substrate 12) of the reading light spot and the reflective layer 14 / recording layer 17. Is provided.

FIG. 8 shows a concrete example of an additional recordable type optical recording medium and a rewritable type optical recording medium, and is a transmission type example. The optical disc 19 comprises a substrate 12, an auxiliary layer 13, which is a light transmittance changing material, a recording layer 17, and a protective layer 15, which are sequentially laminated. Information is recorded as an optical change of the recording layer 17 and the transmitted light from the recording layer 17 is read,
Incident path of reading light spot (incident side substrate 1
The 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, which is an example of reading without passing through a substrate. The optical disk 24 is formed by sequentially laminating a substrate 12, a reflective layer 14, an auxiliary layer 13 which is a light transmittance changing material, and a protective layer 15. Information is recorded as pits on the substrate 12, and the reflected light from the reflection layer 14 corresponding to the pits is read, so that the information is recorded as the incident path of the light spot for reading (the protective layer 15 on the incident side) and the recording layer. Substantially functional reflective layer 14
An auxiliary layer 13 which is a light transmittance changing material is provided between the above and.

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 disc 21 includes a substrate 12, a dielectric layer 22 as an additional layer,
The auxiliary layer 13, which is a light transmittance changing material, the dielectric layer 22, which is an additional layer, the reflective layer 14, and the protective layer 15, are sequentially laminated. Since information is recorded as pits on the substrate 12 and the reflected light from the reflective layer 14 corresponding to the pits is read, it is substantially used as the incident path of the optical spot for reading (the substrate 12 on the incident side) and the recording layer. Layer 14 that functions as a function
An auxiliary layer 13 which is a light transmittance changing material is provided between the above and.

The optical recording medium according to the present invention is shown in FIGS.
With any of the configurations described in 1), the reproduction spot diameter is substantially reduced, and high-density reproduction and high-density recording / reproduction are possible. Further, it can be used as it is in a high-density reproducing apparatus using spot light whose wavelength is shortened.

[0030]

As described above in detail, the optical recording medium according to the present invention has a recording layer for reproducing or recording / reproducing by using spot light, and a light transmittance changing according to the intensity of the irradiated light. In the optical recording medium comprising an auxiliary layer, the auxiliary layer has a light transmittance that changes in accordance with the intensity of the irradiated light at a specific wavelength or wavelength band, and the specific wavelength or wavelength specified above. Since it is a transmittance changing material whose light transmittance is almost constant at wavelengths shorter than the band or in the wavelength band, regardless of the intensity of the irradiated light, when reproducing or recording / reproducing using spot light, In the spot light of the wavelength band (long wavelength or wavelength band), the light transmittance changes according to the intensity of the light, so that the spot light irradiated is substantially reduced and its diameter is reduced. Wavelength or 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 for a high-density reproducing apparatus or a recording / reproducing apparatus in which the wavelength of spot light is shortened as it is while satisfying the demand for improvement of recording density by the auxiliary layer made of the transmittance changing material.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an embodiment of an optical recording medium according to the present invention. FIG. 2A is an optical recording showing a state where a light spot is irradiated when a spot light Y with a short laser wavelength is used. A conceptual diagram of a part of the medium, FIG. 1B is an example of the light spot intensity distribution on the surface of the optical recording medium.

FIG. 3 is a diagram 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 is an example having a reflective layer.

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

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 type optical recording medium and a rewritable type optical recording medium, in which an additional layer for improving characteristics is provided in a recording layer.

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

FIG. 9 is a specific example of a read-only optical recording medium, and is an example of reading 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 surface of the optical recording medium.

[Explanation of symbols]

1,11,16,18,19,21,23,24 Optical disc (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 Short wavelength spot light x Long wavelength spot light diameter y Short wavelength spot light diameter z Substantially reduced long wavelength spot light diameter

Claims (1)

[Claims] 1. An optical recording medium comprising a recording layer for reproducing or recording / reproducing by utilizing spot light, and an auxiliary layer whose light transmittance changes according to the intensity of irradiated light, wherein the auxiliary layer comprises: The light transmittance changes according to the intensity of the irradiated light at a specific wavelength or wavelength band, and regardless of the intensity of the irradiated light at a wavelength or wavelength band shorter than the specific wavelength or wavelength band described above. An optical recording medium comprising a transmittance changing material having a substantially constant light transmittance.