JP2001035011A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mask layer capable of surely recording and reproducing information without rupturing the information to be recorded and the recorded information when information signals are optically recorded and reproduced in high density (super high resolution). SOLUTION: In an optical disk wherein a mask layer 4A whose temperature and light transmittance are increased as irradiation optical intensity of a laser beam L is increased and a recording layer 6 for recording and reproducing information signals are laminated and film-formed on a transparent disk substrate 2 and the diameter of an optical spot of the laser beam L projected from the transparent disk substrate 2 side is made incident on the recording layer 6 being changed to a substantially reduced diameter of the optical spot by passing through the mask layer 4A, the mask layer 4A is so formed that the best mask effect is obtained when the laser beam has the greatest irradiation optical intensity by which recorded information recorded in the recording layer 6 can be repeatedly reproduced without rupturing the recorded information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk capable of optically recording and reproducing information signals at a high density (super-resolution), in particular, to repeatedly reproduce information recorded on a recording layer without destroying the information. The present invention relates to an optical disk having a mask layer formed thereon.

[0002]

2. Description of the Related Art Generally, an optical disk is known as a recording / reproducing medium capable of recording / reproducing a large amount of information signals and having a short access time. There is a demand for further high-density recording / reproducing (super-resolution recording / reproducing) using. Recording and reproduction in the following description means recording an information signal, reproducing an information signal, and reproducing while recording an information signal. For example, the following method has been proposed as a method for optically recording and reproducing an information signal on an optical disk at a high density.

That is, this method includes (a) shortening the wavelength of a recording / reproducing laser beam, (b) increasing the NA (numerical aperture) of a lens focused on an optical disk, and (c) information signal. A multi-layered recording layer, (d) multiplex recording by changing the wavelength of the laser beam to be recorded, and (e) forming a mask layer to substantially reduce the light spot diameter of the laser beam. And other methods. Among these methods, a method of forming a mask layer to substantially reduce the spot diameter of a laser beam is described in, for example, JP-A-5-12673, JP-A-5-12715, and JP-A-5-28498. JP-A-5-2853
No. 5, JP-A-5-73961, and the like.

FIG. 6 is an enlarged sectional view showing a conventional optical disk, FIG. 7 is a diagram showing the relationship between the temperature of a mask layer and light transmittance in the conventional optical disk, and FIG. It is a schematic diagram of the intensity distribution of light incident on the layer and the intensity distribution of light transmitted through this mask layer,
(A) shows the light intensity distribution in the rotation direction of the optical disk,
FIG. 9B is a diagram showing the intensity distribution of light in the radial direction of the optical disk, and FIG. 9 shows a light spot of the laser light incident on the mask layer and a light absorption, the temperature rises and the transmittance increases in the conventional optical disk. FIG. 10 is a diagram showing the relationship between the rising light spot transmitted through the mask layer and FIG. 10 is a diagram showing the relationship between the output of the semiconductor laser device and noise.

A conventional optical disk D3 having the above-described mask layer is formed, for example, as shown in FIG. 6, and has a disk-shaped transparent disk substrate (hereinafter referred to as a transparent substrate) 2
The mask layer 4, the recording layer 6, and the protective layer 8 are formed by sequentially laminating and forming a film thereon. The transmittance of the mask layer 4 is small when the laser light L is not irradiated from the transparent substrate 2 side or when the light intensity of the laser light L from the transparent substrate 2 side is low. When the light intensity of the laser light L of the
Is chemically changed by optically absorbing light and raising the temperature, the light transmittance is increased as shown in FIG. 7, and the spot diameter transmitted through the mask layer 4 is substantially reduced as shown in FIG. It becomes smaller in size.

That is, in the light intensity distribution characteristics of the laser light L shown in FIGS. 8A and 8B, the intensity distribution of the light transmitted through the mask layer 4 is different from the intensity distribution of the light incident on the mask layer 4. This effect makes it possible to record and reproduce small pits using this effect. FIG. 9 shows the state of the light spot of the laser light appearing on the optical disk surface when this function is used. At this time, the state shown in FIG. 8A corresponds to the state in the rotation direction of point B described later in FIG. 9, while the state shown in FIG. This corresponds to the radial state at point B.

As shown in FIG. 9, when a laser beam of a constant intensity is continuously irradiated in a spot shape while rotating the optical disk in the direction of the arrow, for example, point B on the optical disk is
Light having an intensity obtained by integrating the light intensity from point A to point B of the circular light spot 10 is applied. The temperature rises by the heat obtained by subtracting the heat lost by heat conduction and radiation from the heat converted by absorbing the light, thereby increasing the transmittance of the mask layer. Therefore, the portion where the transmittance increases in the light spot 10 is behind the spot diameter (the downstream side) in the rotation direction of the optical disc, and the spot diameter of the laser beam is substantially reduced.

In FIG. 9, a hatched area C in the light spot 10 indicates a mask transmitted light spot transmitted through the mask layer, and an area D excluding this area C is a mask layer. 2 shows a light spot that does not pass through. Thus, by forming the mask layer,
The spot diameter of the laser beam is substantially reduced, and high-density optical disk recording / reproduction becomes possible.

[0009]

By the way, the mask layer 4
In the conventional optical disc D3 formed with the laser beam L, the spot diameter of the laser beam L is substantially reduced due to the mask effect of the mask layer 4, and the information signal can be recorded and reproduced at a high density (super-resolution). Problems have arisen.

That is, at the time of reproduction of the conventional optical disc D3 having the mask layer 4 formed thereon, the reproducing light intensity of the laser beam L at which the mask effect is best is obtained without destroying the recorded information recorded on the recording layer 6 without destruction. In the case where a rewritable phase change material is used as the recording material of the recording layer 6 when reproducing with good / N, the irradiation light intensity of the laser beam L at the time of reproduction is increased.
The recorded information recorded in the amorphous state gradually crystallizes, and the recorded information is easily destroyed.

In the case where the recording layer 6 is of a write-ones type in which recording is performed in a crystallized state even with a phase change material, the intensity of the irradiation light of the laser beam that destroys the recorded information recorded on the recording layer 6 is much higher. .

Here, the relationship between the output of a semiconductor laser device used for recording and reproduction of a general optical disk and noise is high when the output is low as shown in FIG. The noise of the semiconductor laser device is a relative noise intensity RI
N (dB / Hz) and is as follows: RIN (dB / Hz) = {(AC part of output) ² / (DC part of output) ² } × {1 / (measurement bandwidth)} In the reproduction of a general optical disk, the relative noise intensity R
It is said that the allowable value of IN (dB / Hz) is -130 dB / Hz or less, preferably -140 dB / Hz or less. FIG. 10 shows a case where the maximum output of the semiconductor laser element is 5 mw, and the relative noise intensity RIN (dB / dB) is set every 1 mw.
Hz), the output of a semiconductor laser device used for recording and reproduction on an optical disk is generally 30 mw or more. When an optical disc is reproduced with an output of several mW or less using a semiconductor laser element having an output of 30 mW or more, the noise level is higher than that shown in FIG.

In the case of a rewritable optical disk using a phase-change material as a recording material for the recording layer 6, the recording layer 6, which can be reproduced continuously and repeatedly without destroying the recorded information recorded on the recording layer 6, is irradiated. Reproduction laser power is 0.7
１1 mw or less. The reproducing laser power at this time is generally one third of the output of the semiconductor laser element in consideration of the loss in the optical system. In other words, if the reproducing laser power is 0.7 to 1 mw or less, the output of the semiconductor laser element is 2.1 to 3 mw or less. As can be seen from the example of FIG. 10, when the output of the semiconductor laser device is equal to or less than 2.1 to 3 mw, an output close to an allowable noise level is used.
Therefore, if the output of the semiconductor laser element is made smaller than this, the noise level will be further increased.

On the other hand, among the above-mentioned publications, for example, Japanese Patent Laid-Open No. Hei 5-73661 discloses that a temperature range in which recorded information is not destroyed during reproduction can be set by using In for a mask layer. I have. At this time, it is described that the optical constant of the mask layer needs to largely change in a temperature range at the time of reading (that is, a temperature range in which recorded information is not destroyed). However, the above-mentioned publication discloses a method of increasing the output of a semiconductor laser at a temperature as high as possible even at a temperature at which recorded information recorded on a recording layer does not break down, and reducing noise caused by the output of a semiconductor laser element. Is not described at all.

Therefore, there is a demand for an optical disk having a mask layer on which recorded information is not destroyed even when the optical disk is reproduced continuously and repeatedly.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a mask layer on a transparent disk substrate, on which the temperature is increased and the light transmittance is increased when the intensity of the irradiation light of laser light is increased. And a recording layer for recording and reproducing an information signal are laminated and formed into a film, and the light spot diameter of the laser light irradiated from the transparent disk substrate side is substantially reduced by transmitting through the mask layer. In an optical disc having a light spot diameter formed so as to be incident on the recording layer, the mask layer has a maximum irradiation light intensity of the laser beam that can repeatedly reproduce the recorded information recorded on the recording layer without destroying the information. And an optical disk formed so as to have the best mask effect.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the optical disk according to the present invention will be described below in detail with reference to FIGS.
For convenience of explanation, the same reference numerals are given to the same constituent members as those shown in the conventional example, and will be described.

FIG. 1 is an enlarged sectional view showing an optical disk according to the present invention, FIG. 2 is an enlarged sectional view showing a modified example in which the optical disk according to the present invention is partially modified, and FIG. FIG. 4 is a diagram showing a mask material for reproducing a mask layer, FIG. 4 is a diagram showing a spectral transmittance characteristic of a thermochromic mask layer in an optical disc according to the present invention, and FIG. 5 is applied to an optical disc according to the present invention. FIG. 2 is a configuration diagram illustrating a recording / reproducing optical system device.

An optical disc D1 according to the present invention shown in FIG.
Is that a mask layer (reproducing mask layer) 4A on a disk-shaped transparent disk substrate (hereinafter, referred to as a transparent substrate) 2 having a higher temperature and a higher light transmittance when the irradiation light intensity of the laser beam L is increased. A dielectric film 6A, a phase change material film 6B, a dielectric film 6C, Al (aluminum) as a recording layer 6 on which the information signal is recorded and reproduced on the mask layer 4A.
Films 6D are sequentially laminated and formed, and a protective layer 8 is further formed on the recording layer 6. The recording and reproducing laser light L is incident from the transparent substrate 2 side, and the information signal is recorded and reproduced only from one side.

An optical disc D2 of a modification according to the present invention shown in FIG. 2 is prepared by removing the protective layer 8 from the structure of the optical disc D1 shown in FIG. Are bonded to each other via an adhesive layer 40, with the recording layers 6 facing each other and the recording layers 6 facing each other. Therefore, this bonded optical disc has a structure capable of recording and reproducing information signals from both sides.

Here, the components of the optical disks D1 and D2 will be described in detail.
Is formed in a disk shape using a transparent resin material such as a polycarbonate resin or an acrylic resin, or a transparent glass plate, and has a central hole (not shown) formed in the center.

Next, as in the conventional example, the temperature of the mask layer 4A and the light transmittance increase as the intensity of the irradiation light of the laser beam L increases, as in the conventional example. This is a reproducing mask layer that exerts a mask effect when reproducing the optical disk D1 (or D2), and has a mask effect with the maximum irradiation light intensity of laser light that can be repeatedly reproduced without destroying the recorded information recorded on the recording layer 6. The characteristic is that the sensitivity of the mask effect is improved by forming a thin film of the mask layer 4A so as to obtain the best.

That is, in the present embodiment, thermochromic is used as a reproducing mask material of the mask layer (reproducing mask layer) 4A, and as shown in FIG. GN2, using BHPE (bishydroxyphenylethane) as a color developer, and using a color former (G
N2) and a developer (BHPE) in a weight ratio of about 1: 2 at the same time using a binary vapor deposition machine by using a binary vapor deposition machine.
A is thinly applied.

At this time, the composition of the color former (GN2) and the developer (BHPE) is set to approximately 1: 2 by weight% as described above in correspondence with the wavelength of the laser beam L to be used. ,
The spectral transmittance characteristic of the mask layer (reproducing mask layer) 4A is, as shown in FIG.
5 nm. The wavelength at which the irradiation light intensity becomes minimum when the same mask effect is produced on the optical disk on which the mask layer 4A is formed is the time when irradiation is performed at the maximum absorption wavelength. In this example, the nominal is 635 nm, substantially 640-645.
nm semiconductor laser element was used. As a result, the sensitivity can be improved by 3 to 4% as compared with the conventional semiconductor laser device having a nominal laser wavelength of 650 nm and substantially 660 nm.

Further, in the conventional example, the transmittance of the mask layer 4 (FIG. 6) is set to several percent, but in the present embodiment, the transmittance of the mask layer 4A is set to ten and several percent. When the transmittance of the mask layer 4A is increased, the change in transmittance of the mask layer 4A with respect to the change in irradiation light intensity is increased. In other words, the mask layer 4A absorbs the laser beam L and changes to be transparent. However, when the mask layer 4A is thick, it is necessary to change from the incident side to the output side of the laser beam L so as to be transparent. This is because many laser beams L are required. In the present embodiment, the irradiation light intensity at which the mask effect occurs can be reduced by 10% or more by reducing the film thickness of the mask layer 4A to make the transmittance 10% or more.

The mask layer 4A using the thermochromic is colored by the reaction between the coloring agent (GN2) and the developing agent (BHPE). The coloring layer (GN2) and the developing agent (B
And (HPE) at a ratio of about 1: 2 by weight%, the color state is most efficiently obtained. That is, the mask layer 4
A is formed by vapor deposition as described above.
A good colored state can be obtained when the film thickness of A is the thinnest.

Next, as the recording layer 6 formed on the mask layer 4A, a phase change material, a magneto-optical material, an organic material, or the like is used. The recording layer 6 of this embodiment uses a phase change material, and this recording layer 6 is composed of a plurality of laminated films. To describe this recording layer 6 in detail, from the side closer to the mask layer 4A, the ZnS—SiO ₂ dielectric film 6A, AgInSbTe
Phase change material film 6B, ZnS-SiO ₂ dielectric film 6C, A
1 (aluminum) films 6D are sequentially laminated and attached.

The protective layer 8 provided on the recording layer 6
As the material 40, a photopolymer or the like is used.

The recording / reproducing optical system device 20 applied to the optical disk D1 (or D2) according to the present invention formed as described above will be briefly described with reference to FIG.

The recording / reproducing optical system device 20 has a wavelength of 64
Semiconductor laser element 2 that emits laser light L of 0 nm
2, a collimator lens 24 for converting the laser light L from the semiconductor laser element 22 into parallel light, and a polarizing prism 26
, A quarter-wave plate 28, and the laser light L
An objective lens 30 having an NA (numerical aperture) of 0.6 to converge the light to 1 (or D2) and a condensing light for condensing the reflected light from the optical disk D1 (or D2) branched by the polarizing prism 26 It mainly comprises a lens 32, a cylindrical lens 34 for obtaining focus information and tracking information from the reflected light, and a photodetector 36 for detecting condensed light. The recording information of the optical disk D1 (or D2) is recorded and reproduced by detecting the reflected light from D1 (or D2).

At this time, the recording / reproducing optical system device 20 can switch the irradiation light intensity of the laser beam L emitted from the semiconductor laser element 22 between recording and reproducing when separately recording and reproducing the information signal. Good, the irradiation light intensity during recording is approximately 1
5 mw, and the reproducing irradiation light intensity is set to 0.85 mw to 0.95 mw as the maximum irradiation light intensity as described later. When recording and reproducing information signals are performed at the same time, the recording and reproducing optical system device 20 may have two systems for recording and reproducing.

Next, information signals were recorded / reproduced by the recording / reproducing optical system device 20 using the optical disk D1 (or D2) according to the present invention.

First, as Comparative Example 1 of the present invention, AgInSb was used as a recording material for a recording layer without forming a mask layer.
When a Te phase change material is used, the recording and reproducing conditions are such that the wavelength of the laser beam L is 640 nm, the NA (numerical aperture) of the objective lens 30 is 0.6, and the linear velocity is 3.5.
In the case of m / s, unless the reproducing power is set to 0.7 mw or less, the recorded information recorded on the recording layer will be destroyed.

As a comparative example 2, when a mask layer having a transmittance of about 60% with respect to the entire irradiation light intensity is used, depending on characteristics such as the heat conduction characteristics of the mask layer, a reproducing power of 1 mw or more is used. In this case, if the same location is continuously reproduced for a long time, the recorded information recorded on the recording layer is destroyed.

Next, at the time of reproduction of the optical disk D1 (or D2) according to the present invention, the mask layer 4A is formed in advance with a reduced thickness to increase the transmittance, and the laser wavelength of the semiconductor laser element 22 is increased. Is about 640 nm, and the maximum irradiation light intensity of the laser light that produces the best masking effect is 0.85 mw to 0.95 mw. It was confirmed that the recorded information recorded on the recording layer 6 was not destroyed, and that the C / N during reproduction was good. At this time, the maximum irradiation light intensity of the laser light is set to 0.85 mw.
By setting the value to 0.95 mw, the relative noise intensity RIN (dB / H
It was confirmed that z) was also within the allowable value. In other words, when the mask layer 4A is present, light is absorbed by the mask layer 4A, so that the recorded information recorded on the recording layer 6 is not destroyed.

The wavelength at which the maximum absorption occurs is 648 nm.
It was also confirmed that the use of the coloring agent GN608 (trade name of Yamamoto Kasei Co., Ltd.) having a lower melting point than that of the coloring agent GN2 and the developing agent BHPE can further reduce the irradiation light intensity.

The mask layer 4A is not thermochromic.
When a phase change material such as In, TeGe, or Sb is used, the irradiation light intensity at the time of reproduction at which the mask effect is maximized is further larger than that of the thermochromic case, and recorded information is greatly destroyed by repeated reproduction. .

[0038]

In the optical disk according to the present invention described in detail above, a mask layer which increases the temperature and increases the light transmittance when the intensity of the irradiation of the laser beam is increased, and the information signal is recorded on the transparent disk substrate. The recording layer is formed by laminating a recording layer to be read and played back, and the light spot diameter of the laser beam L irradiated from the transparent disk substrate side becomes a substantially reduced light spot diameter by transmitting through the mask layer. In an optical disk adapted to be incident on the
Since the mask effect was formed at the maximum irradiation light intensity of the laser beam which can be repeatedly reproduced without destroying the recorded information recorded on the recording layer, the C / N at the time of reproduction was improved, and the semiconductor laser element was improved. Noise due to the output can also be kept within the tolerance.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing an optical disc according to the present invention.

FIG. 2 is an enlarged sectional view showing a modified example in which the optical disk according to the present invention is partially modified.

FIG. 3 is a view showing a mask material for reproducing a mask layer in the optical disc according to the present invention.

FIG. 4 is a diagram showing a spectral transmittance characteristic of a thermochromic mask layer in the optical disc according to the present invention.

FIG. 5 is a configuration diagram showing a recording / reproducing optical system device applied to the optical disc according to the present invention.

FIG. 6 is an enlarged sectional view showing a conventional optical disc.

FIG. 7 is a diagram showing a relationship between a temperature of a mask layer and a light transmittance in a conventional optical disc.

FIG. 8 is a schematic diagram of an intensity distribution of light incident on a mask layer and an intensity distribution of light transmitted through the mask layer in a conventional optical disc.

FIG. 9 is a diagram showing a relationship between a light spot of a laser beam incident on a mask layer and a light spot transmitted through the mask layer, which absorbs light and raises the temperature to increase the transmittance, in a conventional optical disc. .

FIG. 10 is a diagram showing the relationship between the output of a semiconductor laser device and noise.

[Explanation of symbols]

 D1: optical disk according to the present invention; D2: optical disk of a modification according to the present invention; 2: transparent disk substrate (transparent substrate); 4A: mask layer (reproducing mask layer); 6: recording layer; , 40 ... Protective layer, L ... Laser light.

Claims (1)

[Claims] 1. A transparent disk substrate comprising: a mask layer, which increases in temperature and increases light transmittance when the intensity of laser light is increased, and a recording layer for recording and reproducing information signals. The light spot diameter of the laser light emitted from the transparent disk substrate side is transmitted through the mask layer to have a substantially reduced light spot diameter and is incident on the recording layer. The optical disc according to claim 1, wherein the mask layer is formed so that a mask effect is best at a maximum irradiation light intensity of the laser beam that can repeatedly reproduce the recorded information recorded on the recording layer without destroying the information.