JP2001006176A - Initialization method of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an initialization method of an optical disk capable of initializing a layer to be used for the recording and reproduction of information without melting a mask layer so much. SOLUTION: An optical disk D includes, a layer 6 to be used for the recording and reproduction of information, and a mask layer 4 which exhibits a masking effect in which a light transmittance increases as an intensity of irradiated light increase. These two layers are formed in a layered structure. A spot diameter of light that passes through the mask layer 4 is configured to be substantially reduced as compared to a spot diameter of light incident on the mask layer 4. In an initialization method of such as optical disk, upon initialization of the layer to be used for the recording and reproduction of information, laser light in a wavelength band which is different from that used for the recording and reproduction and exhibits less absorption in the mask layer 4 is used. Thus, the layer to be used for the recording and reproduction of information can be initialized without melting the mask layer so much.

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 at a high density, and more particularly to digital data such as data of a computer, a facsimile signal, a digital audio signal and a digital video signal. The present invention relates to a method for initializing an optical disk capable of recording at high density. In this specification, the term “recording / reproducing” means recording, reproducing, and reproducing while recording.

[0002]

2. Description of the Related Art In general, an optical disk is known as a recording medium capable of recording a large amount of information and having a short access time. However, with the development of an information society, higher density recording is desired. I have. As a method for optically recording and reproducing information at high density, for example, the following methods have been proposed. That is, this method includes shortening the wavelength of the recording / reproducing laser beam, increasing the NA (numerical aperture) of the lens focused on the optical disk, increasing the number of recording layers for recording information, and recording. There are methods such as multiplex recording by changing the wavelength of laser light, and forming a mask layer to substantially reduce the light spot diameter. Among them, a method of forming a mask layer to substantially reduce the spot diameter is described in, for example, Japanese Patent Application Laid-Open No. 5-12673.
JP-A-5-12715, JP-A-5-28498, JP-A-5-28535, JP-A-5-739
No. 61 and JP-A-8-315419.

An optical disk having a mask layer is formed, for example, as shown in FIG. As shown in the figure, the optical disc D is formed by sequentially laminating a mask layer 4, a layer for recording and reproducing information, for example, a recording layer 6 and a protective layer 8, on a transparent substrate 2. A guide groove 10 is formed on the surface of the transparent substrate 2 on the mask layer 4 side. In the case of a read-only optical disk, a reflection layer is provided instead of the recording 6,
Pits and the like are formed on the surface of the transparent substrate 2.

Then, a laser beam L for recording or reproduction is irradiated from the transparent substrate 2 side. Generally, a phase change material, a photochromic material, a thermochromic material, or the like is used as a material of the mask layer 4. When the mask layer 4 is not irradiated with the laser beam L or when the laser beam L is weak, the transmittance is small, and when the light intensity is increased, the mask layer 4 may optically or absorb light to increase the temperature. As a result, the light transmittance increases. The relationship between the temperature of the thermochromic material and the light transmittance is shown in FIG. 6, and when the light intensity incident on the mask layer increases,
The intensity of the absorbed light increases, the temperature of the mask layer increases,
Light transmittance increases. Due to such characteristics, the spot diameter transmitted through the mask layer is substantially reduced as shown in FIG. That is, FIG. 7 is a diagram schematically illustrating an example of the intensity distribution of light incident on the mask layer and the intensity distribution of light transmitted through the mask layer. The intensity distribution of light transmitted through the mask layer is narrowed. Thus, it is possible to record and reproduce small pits using this effect. FIG. 8 shows a state of a light spot appearing on the optical disk surface when this function is used.

FIG. 8 is a diagram showing a relationship between a light spot incident on the mask layer and a light spot transmitted through the mask layer, which absorbs light and raises the transmittance as the temperature rises.
When light of a constant intensity is continuously irradiated while rotating the optical disc, for example, point B on the optical disc becomes light spot 1
Light of an intensity obtained by integrating the light intensity from point A to point B of No. 2 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 part where the transmittance increases is
In the direction of rotation of the optical disk, the spot diameter is behind (the downstream side) the spot diameter, and the spot diameter is substantially reduced. In the figure, the hatched area C indicates a light spot transmitted through the mask layer, and the circular area D excluding this area C indicates a light spot not transmitted through the mask layer. Thus, by forming the mask layer,
The spot diameter is substantially reduced, and recording and reproduction of a high-density optical disk can be performed.

[0006] Generally, a rewritable recording layer material includes a magneto-optical recording material in addition to a phase-change type recording material. A phase change type recording material that records information by utilizing change is preferable. Immediately after forming such a recording material by a vacuum evaporation method or a sputtering method (as depo. State), at least a part thereof is in an amorphous state or in a metastable crystalline state. Such an as depo. State is different from a state after repeated rewriting, and when recording is performed, there is a possibility that a difference in recording / erasing / reproduction characteristics such as recording sensitivity depending on the number of recording repetitions and a recording location may occur. .

Therefore, stable recording can be performed by previously setting the recording layer to a uniform crystalline state, and this processing is called initialization. Conventionally, as a means for this initialization, a laser beam emitted from a high-power semiconductor laser element is irradiated to a recording layer as an oblong beam spot as shown in JP-A-7-161038, or Initialization is performed by a combination of laser light irradiation and flash light irradiation. The laser beam used in this case is disclosed in JP-A-7-161038,
As described in JP-A-212918, laser light having a wavelength close to the wavelength band of laser light used for recording and reproduction is generally used.

[0008]

When the above-described optical disk with a mask layer is initialized, there are the following problems. That is, when the mask layer absorbs light and becomes high temperature, it melts, and the melt moves from the position where the film was formed, causing partial thickness unevenness, and as a result, uneven light transmittance. In particular, at the time of initialization, an area much larger than the spot diameter at the time of recording and reproduction is simultaneously irradiated and heated, so that the movement of the melt is more likely to occur.
For example, a recording layer using a thermochromic material has a thickness of 150
It melts near ℃ and becomes liquid. Since the spot diameter used for recording / reproducing is about 1 μm, even if the mask layer is melted, it is unlikely to move even if the mask layer is melted. When the layer is melted, the melted mask material moves, causing partial thickness unevenness. In this case, in order to minimize the movement of the melt, it is conceivable to initialize with a spot diameter as large as the recording spot diameter, but this takes too much time for initialization, Not practical. The present invention focuses on the above problems, and has been made to solve the problems effectively. The purpose of the present invention is to initialize a layer for recording and reproducing information without melting the mask layer so much. It is an object of the present invention to provide a method of initializing an optical disk capable of performing the above.

[0009]

According to the present invention, a layer for recording and reproducing information and a mask layer having a mask effect of increasing light transmittance when the intensity of irradiation light is increased are formed by laminating the mask layer. In the method for initializing an optical disc, wherein the diameter of the transmitted light spot is substantially smaller than the diameter of the light spot incident on the mask layer, when initializing the layer for recording and reproducing the information, Different from the wavelength band of the laser beam to be used, a laser beam having a wavelength band with a small absorption in the mask layer is used. Thereby, the absorption energy of the laser beam for initialization in the mask layer is reduced, and this temperature rise is suppressed, and therefore, it is possible to prevent the mask layer from melting.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk initialization method according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a spot shape when an optical disk is irradiated with a laser beam for initialization, FIG. 2 is a graph showing spectral characteristics of a mask layer made of a thermochromic material, and FIG. FIG. 4 is a graph showing the reproduction characteristics of an optical disk initialized by the method of the present invention. The optical disk has exactly the same structure as that described above with reference to FIG. 5, and includes a transparent substrate 2, a mask layer 4, a layer (for example, a recording layer) 6 for recording and reproducing information, and a protective layer 8 For example, a guide groove 10 is formed on the side surface of the mask layer 4 of the transparent substrate 2.

Although the disk shown in FIG. 5 is a single-plate disk, the method of the present invention is also effective for a bonded optical disk or a two-layer optical disk. As a material of the mask layer 4, a thermochromic material, a photochromic material, a phase change material, or the like is used. In this example, a thermochromic material composed of two components, an electron-donating color compound and an electron-accepting color developer, was used. The thermochromic material used was about 1
It melts at 70 ° C and becomes liquid. FIG. 2 shows the spectral characteristics of the mask layer. The transmittance of the light greatly varies depending on the wavelength of the laser light. Here, the wavelength of the laser light used for recording and reproduction is about 635 nm. The mask layer 4 absorbs the laser beam of this wavelength and becomes high in temperature. Therefore, the transmittance is greatly reduced.

As a material of the recording layer 6, a phase change material is used. The temperature at which the transmittance of the mask layer 4 increases is set lower than the temperature at which recording or erasing is performed in the recording layer. More specifically, the recording layer 6 is composed of a ZnS—SiO ₂ dielectric layer, an AgInSbT
e phase change material layer, ZnS-SiO ₂ dielectric layer, are stacked in multiple layers in the order of Al layer. As a material of the protective layer 8, a photopolymer or the like is used. When the optical disk D is initialized as described above, the initialization laser beam output from the initialization device forms an initialization light spot 20 having a shape as shown in FIG. That is, the light spot 20 is formed in a narrow, substantially rectangular shape and has a track pitch L1 of about 0.74 μm, whereas the long axis (length) L of the initialization light spot 20 is different.
2 is about 120 μm, and many at a time, for example, 40 to 5
About 0 tracks can be initialized (light is irradiated a plurality of times in the initialization). In the figure, 10
Is a guide groove. Here, in the method of the present invention, laser light in a wavelength band in which light absorption by the mask layer 4 is small is used as the initialization laser light. Specifically, FIG.
When the wavelength of the laser light used for recording and reproduction is 635 nm to 650 nm as described above, the wavelength of the laser light for initialization is 750 nm or more, more specifically, about 780 n.
m, about 830 nm or 1300 nm. Alternatively, it is in the range of 460 nm to 530 nm, more specifically, 488 nm to 51 which is the wavelength of the argon ion laser light.
4.5 nm. In these wavelength bands, the mask layer 4
Has a high transmittance of about 90% or more, so that light energy is easily transmitted and the temperature does not rise so much. That is, this is a wavelength band in which the mask layer 4 is very difficult to melt.

That is, the laser beam for initialization used in the method of the present invention is hardly absorbed by the mask layer 4, the temperature rise of the mask layer 4 is small and the material of the mask layer 4 does not melt, and the mask material 4 No movement occurs. Further, since there is almost no absorption in the mask layer 4, the same laser light used for initialization of an optical disk without a mask layer can be used for the initialization. Incidentally, Japanese Patent Application Laid-Open No. 9-21291
No. 8 discloses that the wavelength of the laser beam of the initialization device is 810n.
m, the wavelength of the laser beam for reading information is 680 nm
Is written. The purpose of this prior art is as d
In the case where the reflectivity in the epo. state is low, the fact that the reflectivity increases when the wavelength is set to 810 nm is used, and the purpose of the present application and the disc structure and disc material to be initialized are different. The purpose of the present application is different from that of the prior art described above.
The purpose is to initialize a phase-change optical disc with a mask layer that tends to melt and move when heated to a high temperature without moving the mask layer.

Here, an optical disk with a mask layer initialized by the method of the present invention, an optical disk with the above optical disk initialized by a conventional method (laser light having the same wavelength as the recording / reproducing laser light), and an optical disk without a mask layer The recording / reproducing characteristics of the optical disk in which the optical disk was initialized by the conventional method were evaluated, and the evaluation results will be described. For this evaluation, the recording / reproducing device 21 shown in FIG. 3 was used. This recording / reproducing device 21
Is a laser element 22 for generating a laser beam LR for reproduction.
And a collimator lens 24 for converting the laser light LR into parallel light
, Grating 26, polarizing prism 28, 1 /
A four-wavelength plate 30, an objective lens 32 for condensing the laser light L on the optical disc D, and a condensing lens 3 for condensing the reflected light from the optical disc D branched by the polarizing prism 28
4, a cylindrical lens 36 for obtaining focus information and tracking information from the reflected light, and a photodetector 38 for detecting the condensed light. The information recorded on the optical disc D is reproduced by detecting the reflected light from the optical disc D. The recording / reproducing conditions here are such that the wavelength of the laser beam LR is 6
35 nm, NA of the objective lens 32 condensed on the optical disk
(Numerical aperture) is 0.6.

FIG. 4 is a graph showing evaluation results for each optical disk. As is clear from the figure, the C of the optical disk with the mask layer initialized by the method of the present invention is used.
The / N characteristic shows much better characteristics than the C / N characteristic of the optical disk in which the optical disk without the mask layer is initialized by the conventional method. Further, with respect to an optical disk in which a mask layer-attached optical disk has been initialized by a conventional method, the characteristics of the optical disk cannot be obtained due to severe deterioration of the mask layer. Here, the reproducing power of the optical disk with the mask layer is about 1.1.
mW, and the reproduction power of the optical disk without the mask layer was about 0.7 mW. The optimum reproduction power of the optical disk with the mask layer is the reproduction power at which the effect of the mask layer is maximized. Note that the wavelength of the recording / reproducing laser beam and the wavelength of the initialization laser beam described in the present embodiment are merely examples, and may be variously changed according to the spectral characteristics of the material of the mask layer. Of course.

[0016]

As described above, according to the optical disk initialization method of the present invention, the following excellent operational effects can be exhibited. Since the initialization is performed using the laser light in the wavelength band where the absorption in the mask layer is small, the layer for recording and reproducing information can be initialized without melting the mask layer so much.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a spot shape when an optical disk is irradiated with a laser beam for initialization.

FIG. 2 is a graph showing spectral characteristics of a mask layer made of a thermochromic material.

FIG. 3 is a diagram showing a recording / reproducing device.

FIG. 4 is a graph showing the reproduction characteristics of an optical disc initialized by the method of the present invention.

FIG. 5 is a diagram showing an optical disc having a mask layer.

FIG. 6 is a graph showing the relationship between the temperature of a thermochromic material and the light transmittance.

FIG. 7 is a diagram schematically illustrating an example of an intensity distribution of light incident on a mask layer and an intensity distribution of light transmitted through the mask layer.

FIG. 8 is a diagram showing a state of a light spot appearing on an optical disk surface.

[Explanation of symbols]

Reference numeral 2 denotes a transparent substrate, 4 denotes a mask layer, 6 denotes a layer for recording and reproducing information (recording layer), 8 denotes a protective layer, 10 denotes a guide groove, 20 denotes a light spot for initialization, and D denotes an optical disk.

Claims (1)

[Claims] An information recording / reproducing layer is formed by laminating a mask layer having a mask effect of increasing light transmittance when the intensity of irradiation light is increased, and a diameter of a light spot passing through the mask layer is determined by the mask. In the method for initializing an optical disc, which is made to be substantially smaller than the diameter of the light spot incident on the layer, when the layer for recording and reproducing the information is initialized, what is the wavelength band of the laser beam used for recording and reproduction? A method for initializing an optical disk, characterized in that a laser beam in a wavelength band having less absorption in the mask layer is used.