JPH11120621A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medium which permits recording and reproducing for any specification of lasers even when the wavelength of a laser light or the numerical aperture of the optical system are changed, by forming grooves having specified depth on a substrate and recording, reproducing and erasing information in the lands and grooves with violet or red laser light. SOLUTION: This optical recording medium is a phase transition type optical disk using 6 material which reversibly changes between a noncrystalline state and a crystalline state. The depth of grooves in the recording layer 4 is specified to 40 to 70 nm in order to obtain high compatibility. When violet laser light of 400 nm wavelength is used, signals of a high level can be obtd. by a push-pull method and three-spot method by controlling the depth of the grooves to 33 to 70 nm. When red laser of 680 nm wavelength is used, also signals of a high level can be obtd. by controlling the depth of the grooves to 40 to 113 nm. The track pitch is preferably 0.30 to 0.50 nm and the thickness of a light- transmitting layer 6 is preferably 10 to 177 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of recording and reproducing with light of various wavelengths, for example, an optical recording medium having a recording layer which reversibly changes between an amorphous state and a crystalline state. Regarding the medium.

[0002]

2. Description of the Related Art As an optical recording medium used as a high-density information recording medium, a so-called phase-change type optical disk using a material that reversibly changes between an amorphous state and a crystalline state for a recording layer is mentioned. Can be Compared to a magneto-optical disk, this phase-change type optical disk does not require a magnetic field generating means in the recording / reproducing device, and thus has many advantages such as the miniaturization of the recording / reproducing device. .

In this phase change type optical disk, the recording layer is in a crystalline state in an initialized state. When recording an information signal on this phase change optical disk, the recording layer is irradiated with a laser beam having a strong power. Thus, the portion irradiated with the laser beam is heated to a temperature equal to or higher than the melting point of the material forming the recording layer. After that, the part irradiated with laser light is rapidly cooled,
This part is in an amorphous state. As described above, in the phase-change optical disk, an information signal is recorded by forming a recording mark in an amorphous state.

In this phase change optical disk,
When erasing the information signal recorded on the recording layer, the erasing is performed by crystallizing a non-crystalline recording mark. Specifically, by irradiating a laser beam weaker than the laser beam irradiated during recording, the temperature of the recording layer is equal to or lower than the melting point,
The temperature rises above the crystallization temperature. Then, by gradually cooling the recording layer, the portion irradiated with the laser light
It becomes a crystalline state regardless of the previous state.

Further, in the phase-change type optical disk, when the information signal recorded on the recording layer is reproduced, the recording layer is irradiated with the weakest laser beam. At this time, the reflectance of the irradiated laser beam changes depending on whether the irradiated portion is in a crystalline state or an amorphous state. This is due to the difference between the optical constant in the crystalline state and the optical constant in the non-crystalline state. Then, by detecting the reflectance, the information signal can be reproduced.

In this phase change type optical disk, a dielectric layer is formed on a transparent substrate on which a concavo-convex pattern is formed, and the above-described recording layer is formed on the dielectric layer.
It has a configuration in which a dielectric layer is further formed on this recording layer, and a reflective layer is formed on this dielectric layer.

[0007] In the phase-change optical disk thus configured, recording and reproduction are performed by irradiating the recording layer with the above-described laser light from the transparent substrate side. At this time, the irradiated laser beam has a predetermined spot diameter. In this phase-change optical disk, the irregularities (the convex portions are called lands and the concave portions are called grooves) formed on the substrate have a width substantially equal to the spot diameter. The recording and reproduction are performed by irradiating a laser beam.

In such a phase change type optical disk,
In order to achieve higher density recording, it is conceivable to reduce the spot diameter of the laser beam used for recording, reproduction, and erasing. That is, by reducing the spot diameter of the laser beam to be irradiated, many irregularities can be formed on the substrate, and high-density recording can be achieved.

Here, the spot system d can be expressed as d = K · λ / NA (K is a proportional constant), where λ is the wavelength of the laser beam and NA is the numerical aperture of the lens used. Therefore, it can be seen that the spot diameter d can be reduced by shortening the wavelength of the laser light used or increasing the numerical aperture of the lens used.

Specifically, shortening of the wavelength of laser light has been studied with the physical properties of the material used as the main factor.
６００600 nm is being put to practical use. In order to increase the numerical aperture NA, for example, a method using a second group lens or the like is used. As described above, with the shortening of the wavelength of the laser beam and the improvement of the numerical aperture NA, high-density recording has been promoted in the field of optical discs.

More specifically, an optical disk currently in practical use, for example, a DVD (Digital Video Disk) as an example of a ROM (Read Only Memory) disk, has a wavelength λ of 650 nm and a numerical aperture NA of 0.6. It is reproduced using some kind of optical system, in which case the recording capacity is
It is 4.7 GB including the reduction of the redundancy.

[0012]

By the way, in an optical disk, a standard for recording and reproduction is determined by defining a wavelength λ of a laser beam, a numerical aperture NA and the like to predetermined values. This standard will be updated as high-density recording is promoted. That is, as the high density recording is promoted, the wavelength λ of the laser beam becomes shorter, and the numerical aperture N
The standard is updated so that A becomes larger.

As described above, since the wavelength of the laser beam used differs when the standard is updated, there is a problem that the optical disc after the update cannot be recorded and reproduced with the standard before the update. On the contrary, there is a problem that the optical disc before the update cannot be recorded and reproduced with the updated standard.

Therefore, the present invention provides an optical recording medium that can record and reproduce data in any standard before and after updating, even if the standard for recording and reproducing such as the wavelength of a laser beam and the numerical aperture of an optical system is updated. The purpose is to provide.

[0015]

An optical recording medium according to the present invention, which has achieved the above-mentioned object, comprises a recording layer on a substrate on which lands and grooves are formed, and the groove has a depth of 4 inches.
It is characterized in that recording / reproducing and erasing are performed on lands and grooves using laser light having a wavelength of 0 to 70 nm and 400 to 680 nm.

In the optical recording medium according to the present invention having the above-described structure, by setting the depth of the groove to 40 to 70 nm, any laser light having a wavelength of 400 to 680 nm can be used. Is also recorded and reproduced well.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the optical recording medium according to the present invention will be described below in detail with reference to the drawings. Here, as an example of the optical recording medium according to the present invention, an example in which the present invention is applied to an optical disk which is a disk-shaped recording medium will be described. It is also applicable to such recording media.

As shown in FIG. 1, the optical disk shown in this embodiment has a reflection film 2, a first dielectric film 3, a recording film 4, and a second dielectric film 5 on one main surface 1a of a substrate 1. , And the light transmitting film 6 are sequentially laminated. Also, this substrate 1
As shown in FIG. 2, an uneven pattern is formed on one main surface 1a on which the reflective film 2 is formed. This uneven pattern
It is formed in a concentric or spiral shape. Here, a convex portion formed by the concave and convex pattern is called a land 7, and a concave portion formed by the adjacent land 7 is a groove 8.
Call.

In this optical disk, the substrate 1 is obtained by molding a synthetic resin such as polycarbonate, for example, and has an uneven pattern formed on one principal surface by this molding. The substrate 1 has, for example, a diameter of 12 cm and a thickness of 0.3 to 1.2 mm. In this optical disk, the depth h of the groove formed on one main surface 1a of the substrate 1 as shown by h in FIG. 2 is 40 to 70 nm.

The reflection film 2 formed on one main surface 1a of the substrate 1 is made of, for example, a metal material mainly composed of Al, and is formed on the substrate 1 by a thin film forming method such as a sputtering method or an ion beam sputtering method. Formed by In this optical disk, the first dielectric film 3 and the second dielectric film 5 are made of, for example, a material such as ZnS—SiO _{2 and} formed by a thin film forming method such as a sputtering method.

In this optical disk, the recording film 4
Is formed of, for example, a chalcogen compound or a simple chalcogen, and is formed by a thin film forming method such as a sputtering method.

Further, in this optical disc, the light transmitting film 6 formed on the second dielectric film 5 may be formed in the same manner as the light transmitting layer of this type of optical recording medium. Further, as a material constituting the light transmitting layer 6, it is preferable that the transmittance is 90% or more, and for example, UV resin, polycarbonate, or the like can be used. However, in this optical disc, the thickness of the light transmitting layer 6 is t,
The light transmission layer 6 is formed so as to satisfy the following expressions (1) and (2), where Δt is the variation in the thickness.

10 (μm) ≦ t ≦ 177 (μm) Expression (1) Δt ≦ ± 5.26 (λ / NA ⁴ ) Expression (2) The optical disk configured as described above is: By irradiating a predetermined laser beam to the recording layer, an information signal can be recorded / reproduced and erased.

In this optical disc, the recording layer 4 is in a crystallized state as an initialized state. Specifically, the recording layer 4 is irradiated with a strong laser beam. As a result, in the recording layer 4, the laser power is converted into thermal energy in the irradiated portion, and the temperature is increased. At this time, the irradiated portion is heated to a temperature below the melting point and above the crystallization point. Then, by gradually cooling the recording layer 4, the recording layer 4 is cooled.
Is in a crystalline state.

When recording an information signal on the phase change optical disk, the recording layer 4 is irradiated with a laser beam having a higher power. As a result, the portion irradiated with the laser light is heated to a temperature higher than the melting point of the material forming the recording layer 4. Thereafter, the portion irradiated with the laser beam is rapidly cooled, so that the portion becomes non-crystalline. As described above, in the phase-change optical disk, the information signal is recorded by forming the non-crystalline recording mark on the recording layer 4 in the crystalline state.

In this phase change optical disk,
The erasing of the information signal recorded on the recording layer 4 is performed by crystallizing a non-crystalline recording mark.
Specifically, by irradiating a laser beam used when the recording layer 4 was initialized, that is, a laser beam weaker than the laser beam irradiated at the time of recording, the temperature of the recording layer 4 was lowered to the melting point or lower, and the crystallization temperature was lowered. The temperature rises above. Then, by gradually cooling the recording layer 4, the portion irradiated with the laser beam becomes a crystalline state regardless of the previous state.

Further, in this phase change type optical disk, when reproducing the information signal recorded on the recording layer 4, the recording layer 4 is irradiated with the weakest laser beam. At this time, the reflectance of the irradiated laser beam changes depending on whether the irradiated portion is in a crystalline state or an amorphous state. This is due to the difference between the optical constant in the crystalline state and the optical constant in the non-crystalline state. Then, by detecting the reflectance, the information signal can be reproduced.

On the other hand, a characteristic required for this optical disk is that a so-called tracking servo can be accurately performed. When performing this tracking servo, a push-pull method or a three-spot method (also called a three-beam method) is used.

Here, the push-pull method is a method in which reflected light of laser light applied to a groove or a land is received by a two-part light receiving element, and a signal based on the amount of light received by each light receiving element is output. This is a method of detecting a tracking error based on a signal output difference. That is, when the laser light is accurately on the track, the signals output from the two light receiving elements have the same level and there is no output difference. On the other hand, when the laser light is at a position shifted from the track, the signal levels output from the two light receiving elements are different, and an output difference is generated.

Here, the three-spot method refers to a method in which three laser beams formed of a zero-order light and ± first-order lights formed by a diffraction grating are tracked by ± v with respect to the zero-order light. In this method, a tracking error is detected by irradiating light in a direction perpendicular to the direction, detecting reflected light of ± primary light, and detecting a difference in signal output based on the reflected light. That is, when the zero-order light is at the correct position on the track, there is no difference in the signal output based on the reflected light of the ± first-order light. On the other hand, when the zero-order light is at a position shifted from the track, a difference occurs in the signal output based on the reflected light of the ± first-order light.

Further, in an optical disk, it is necessary to accurately detect a so-called cross track signal. The cross-track signal is for detecting the number of tracks crossed by the irradiated laser light, and is performed by detecting reflected light of the irradiated laser light. That is, since the degree of modulation is different between the reflected light when irradiating the groove and the reflected light when irradiating the land, the number of tracks traversed must be detected by detecting the reflected light of the irradiated laser light. Can be.

As described above, it is desirable that the output level of the optical disk be high, regardless of whether the push-pull method or the three-spot method is employed, and that the cross-track signal be high. In this optical disc, when the refractive index of the light transmitting layer 6 is N and the wavelength of the laser beam to be irradiated is λ, the depth h of the groove is set to around λ / 8 / N, so that the push-pull method is used. The level of the output signal becomes higher. Also,
Similarly, by setting the depth h of the groove near λ / 4 / N, the modulation degree of the reflected light can be detected with high sensitivity, and the cross-track signal can be detected at a high level.

Specifically, when a laser beam having a wavelength of 680 nm is irradiated, the depth h of the groove is set to 40 to 1
By setting it to 13 nm, a high-level signal can be output in the push-pull method and the three-spot signal, and a high-level cross-track signal is also output. When a laser beam having a wavelength of 400 nm is irradiated, the groove depth h is 33 to 70 n.
If m, a high-level signal can be output in the push-pull signal and the three-spot signal, and a high-level cross-track signal can be output.

For this reason, in this optical disc, by setting the groove depth h to 40 to 70 nm, 400 to 70 nm is obtained.
Using any one of the laser beams having a wavelength of 680 nm, the tracking error can be detected with high accuracy by the push-pull method and the three-spot method, and the cross-track signal can be detected with high accuracy.

In such an optical disc, the width of the land 7, that is, the track pitch is 0.30 to 0.49.
μm is preferred. By setting the track pitch in this range, the above-described signal can be detected with higher accuracy.

Here, the case where recording / reproducing is performed on an optical disk by using laser beams having various spot diameters will be specifically described.

As a standard for performing recording and reproduction on an optical disk, a standard using a laser beam having a wavelength of 650 nm and using an optical system having a numerical aperture NA of 0.85 has been proposed.
The "first generation" standard. Further, as a standard for performing recording / reproducing, a laser beam having a wavelength of 500 nm and an optical system having a numerical aperture NA of 0.85 are used.
"2nd generation" standard. Further, as a standard for performing recording and reproduction, a laser using a laser beam having a wavelength of 400 nm and an optical system having a numerical aperture NA of 0.85 is used.
The "third generation" standard. As described above, when the wavelength is shortened in the order of the first generation, the second generation, and the third generation, the spot diameter of the laser beam is correspondingly reduced.

Therefore, the optical disks of each generation have a groove width and a land width corresponding to the spot diameter. For this reason, the groove and the land become narrower in the order of the first generation, the second generation, and the third generation.

Specifically, the first generation optical disk has a track pitch of 0.49 μm and a linear density of 0.21 μm.
μm / bit. Therefore, the recording capacity is 8.0 GB when the redundancy is 25%. The second-generation optical disk has a track pitch of 0.38 μm and a linear density of 0.16 μm / bit, and therefore has a recording capacity of 13.5 GB when the redundancy is 25%. . The third-generation optical disk has a track pitch of 0.30 μm and a linear density of 0.13 μm / bit. Therefore, when the redundancy is 25%, 21.1 GB is used.
Recording capacity.

Here, the redundancy means a ratio of data such as an error correction code added to actual data to the entire data.

In the first-generation optical disk, the second-generation optical disk, and the third-generation optical disk, the recording / reproducing and erasing can be performed at any wavelength by setting the groove depth to 40 to 70 nm.

For example, when recording / reproducing a first generation optical disk according to a second generation standard, the track pitch is 0.4
Since the recording density is 9 μm and the linear density is 0.16 μm, the recording capacity is 10.5 GB. When the first generation optical disc is recorded and reproduced according to the third generation standard, the track pitch is 0.49 μm and the linear density is 0.13 μm, so that the recording capacity is 12.9 GB.

As described above, the optical disk according to the present invention
By setting the depth h of the groove to 40 to 70 nm,
Any laser light having a wavelength in the range of 400 to 680 nm can be used for recording and reproduction. That is, this optical disc has upward compatibility.
In other words, when the standard is updated for high-density recording, even if the optical disc is compatible with the standard before the update,
Recording and reproduction can be performed according to the updated standard.

[0044]

As described above in detail, the optical disk according to the present invention can be used as long as the laser beam has a wavelength of 400 to 680 nm by setting the groove depth to 40 to 70 nm. Even a laser beam having a wavelength can be recorded and reproduced and erased.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part showing an example of an optical disk according to the present invention.

FIG. 2 is a perspective view of a main part showing a substrate of the optical disc.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 substrate, 2 reflective layer, 3 first dielectric layer, 4 recording layer, 5 second dielectric layer, 6 light transmitting layer

Claims (6)

[Claims] A recording layer provided on a substrate on which lands and grooves are formed, wherein the depth of the grooves is 40 to 70 nm;
An optical recording medium which is recorded / reproduced and erased from / to lands and grooves using a laser beam having a wavelength of 680 nm. 2. The optical recording medium according to claim 1, wherein the track pitch is 0.3 to 0.5 μm. 3. An optical system having a light transmitting layer on one main surface of the recording layer, wherein the wavelength of the laser light emitted from the light transmitting layer side is λ, and the laser light has a numerical aperture of NA. when recording reproducing and erasing the recording layer, a thickness of the light transmission layer 3～177Myuemu, claim 1, wherein the thickness unevenness of the light transmissive layer is ± 5.26λ / NA ⁴ Optical recording medium. 4. The optical recording medium according to claim 3, wherein the numerical aperture satisfies NA ≧ 0.7. 5. The optical recording medium according to claim 3, wherein said optical system is a two-group lens. 6. The optical recording medium according to claim 1, wherein the recording layer is made of a material that reversibly changes between an amorphous state and a crystalline state.