JPH10261243A - Initialization method for phase transition type optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly perform the initialization of a phase transition type optical disk. SOLUTION: This initialization device irradiates the beam spot converged in an elliptic shape with an objective lens 17 on an optical disk 7 and the reflected light from the optical disk 7 is directed toward a focusing servo mechanism 18 by a beam splitter 14. At this time, an abnormal oscillation is generated by the return light to a laser device 12 and a recording layer is inhomogeneously crystallized. In order to resolve this, an initialization is performed by arranging the objectivelens 17 whose numerical aperture is 0.55 so that a beam waist departs from the position of the recording layer of the optical disk 7 by 2μm or more. Moreover, the initialization is performed by arranging the objective lens 17 whose numerical aperture is not larger than 0.50 so that the beam waist becomes the position of the recording layer of the optical disk 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable phase-change optical recording medium such as an optical disk, an optical card, an optical tape, etc., capable of recording / erasing / reproducing information by a phase change between an amorphous state and a crystalline state. Related to the initialization method.

[0002]

2. Description of the Related Art Optical information recording media have attracted attention because of their high density and large capacity, and have been used in various applications. For example, a read-only optical disk includes a compact disk and a CD-ROM dedicated to data reproduction, and is widely used in the music field, computer field, game field, and the like. In addition, write-once optical disks that can be recorded only once are used in fields in which data security is particularly important, such as a document filing system and a data filing system.

In addition, a rewritable optical disk capable of erasing and re-recording recorded information is capable of restoring and updating data and can be used repeatedly by rewriting, so that it is expected to contribute to expanding the use of optical disks. Is done. As such a rewritable optical disk,
Up to now, magneto-optical disks and phase-change optical disks have been put to practical use, and are used for data files and the like.

A rewritable optical disk utilizing a phase change generally uses an amorphous state as a recording state and a crystalline state as an erasing state. Recording, erasing, and reproduction of such a phase-change optical disk are performed by irradiating a laser beam, and there are two irradiation methods and a one-beam overwriting method.

In the two-beam system, for example, recording / reproducing is performed by using a small circular beam spot having a beam diameter of about 1 μm, and erasing is performed by an elliptical elongated beam having a disk radius of about 1 μm and a circumferential direction of about 10 μm. Perform at the spot. In the one-beam overwrite method, recording, erasing, and reproduction are performed by using only a small circular beam spot having a beam diameter of about 1 μm and changing the intensity.

As a recent irradiation system, a one-beam overwrite system is mainly used rather than a two-beam system. When recording / erasing / reproducing is performed by the one-beam overwrite method, it is required that the crystallization speed of the recording layer of the phase-change optical disk be high.

FIG. 1 shows an example of a typical layer structure of a phase change optical disk. In this example, a first protective layer 2, a recording layer 3, a second protective layer 4, a reflective heat radiation layer 5, and a protective coat layer 6 made of resin are sequentially laminated on the disk substrate 1. As the material of the protective layer, the first protective layer 2 and the second protective layer 4
In both cases, a mixture of ZnS and SiO ₂ , AlN, SiN and the like are used. The material of the recording layer 3 is GeTeS
b, InSbTe, AgInSbTe, etc. are used. As a material of the reflective heat radiation layer 5, a metal such as Al, Ag, Ni, or an alloy thereof is used.

[0008] Such a phase-change type optical disk performs recording and erasing by utilizing the fact that the recording layer reversibly changes phase between an amorphous state and a crystalline state by light irradiation, and the difference in the reflectance between the two. Playback is performed using. That is, the portion of the recording layer irradiated with the laser beam of the recording power is heated to a temperature equal to or higher than the melting point and then rapidly cooled, whereby the recording layer material is made amorphous and a recording mark corresponding to a recording signal is formed. You. The portion of the recording layer irradiated with the laser beam of the erasing power is heated to a temperature higher than the crystallization temperature and then gradually cooled, whereby the material of the recording layer is crystallized and the recording mark (recording signal) is erased. You.

As a method of forming the recording layer, a sputtering method is mainly used. In this case, the recording layer immediately after formation is in an unstable amorphous state. There is a problem in terms of gender. for that reason,
2. Description of the Related Art Conventionally, “initialization” for crystallizing the entire recording layer of a manufactured phase-change optical disc has been performed.

As a method of initialization, there are a method of irradiating a high-power laser beam to the disk surface of a phase change optical disk and a method of heating using a lamp or the like. Various initialization apparatuses employing these methods are available. Has been produced. In particular, since a method using laser light is excellent in controllability of initialization, an initialization device that irradiates a disk surface with laser light is often used.

A general initialization apparatus includes a disk supporting means for rotatably supporting an optical disk to be initialized, a laser device for emitting a laser beam, and a laser beam emitted from the laser device as a beam spot having a predetermined cross section. An optical system for directing the optical disk supported by the disk support means on a predetermined optical path, a focus servo mechanism for adjusting a beam waist (focus of laser light) to a recording layer position of the optical disk, and an irradiation position of the beam spot. And a moving mechanism for moving the optical disk in the radial direction.

The optical system is configured such that, for example, a laser beam is shaped into an elliptical spot, and the optical disk is irradiated with a beam spot in a state where its long axis is orthogonal to the track of the optical disk. In addition, the focus servo mechanism adjusts the focus of the laser light (adjusts the beam waist to the position of the recording layer) using, for example, the laser light reflected from the optical disk.

Such an initialization device is disclosed in Japanese Patent Laid-Open No. 4-216.
No. 323, and the configuration is as shown in FIG. That is, the laser device (semiconductor laser) 1
The laser light 8 emitted from the light source 2
The light is converted into parallel light by the polarization beam splitter 14 and the λ / 4 plate 15, bent by the mirror 16, condensed by the objective lens 17, and irradiated on the surface of the optical disk 7. Also,
The laser light reflected from the optical disk 7 is bent by the mirror 16, passes through the λ / 4 plate 15, is bent by the polarization beam splitter 14, and travels to the focus servo mechanism 18.

According to Japanese Patent Application Laid-Open No. 4-216323, a semiconductor laser beam is shaped into an elliptical spot and irradiated on a recording layer of a phase-change type optical disk, thereby generating the laser beam from the recording layer during initialization. It is said that the deformation of the substrate due to the generated heat and the occurrence of warpage and cracks due to the thermal distortion of each laminated film can be prevented.

[0015]

However, when initialization is performed using the above-described initialization device, there has been a problem that uniform initialization is not performed.

When using a phase-change type optical disk, first, address information recorded on the disk substrate is reproduced in advance, and the position where information is recorded / erased / reproduced is determined / determined.・ Erasing / reproducing. This address information is different from a normal information recording / erasing / reproducing portion, and is previously formed as minute unevenness on the substrate. In order for this minute uneven portion to be accurately reproduced as a recording signal of address information, the recording layer laminated on this portion needs to be uniformly initialized.

Therefore, if the address information portion is non-uniformly initialized, it becomes impossible to accurately reproduce the address information. Even if an attempt is made to record, erase, or reproduce information using the address information of this portion, It is determined as a defective part. As a result, the information recording capacity of the phase-change optical disc decreases.

The present invention has been made in view of such a problem of the prior art. When an initialization apparatus having a configuration as shown in FIG. 2 is used, the initial state of a phase change optical recording medium is reduced. It is an object of the present invention to be able to perform the conversion uniformly.

[0019]

The present inventors have made intensive studies to solve the above-mentioned problems. As a result, the reason why uniform initialization is not performed by the initialization device shown in FIG. It was found that a very small high-energy portion having a width of about 1 μm was generated in the major axis direction of the elliptical laser beam spot. That is, the portion of the recording layer which is irradiated with the high energy portion of the laser beam spot is in a high heat state exceeding the crystallization temperature and melts, so that it is in an amorphous state and is not initialized.

Investigation into the cause of the occurrence of the above-mentioned high-energy portion revealed that when the laser beam was emitted with the optical disk 7 removed from the initialization device, the above-mentioned high-energy portion was lost. Turned out not to occur. Therefore, although the return light to the laser device 12 is prevented by the polarizing beam splitter 14, the effect is not sufficient, and the reflected light from the optical disk 7 enters the laser device 12 due to the birefringence of the disk substrate, resulting in an abnormal condition. We concluded that oscillation was occurring.

Furthermore, it has been found that even if the laser oscillates abnormally due to the birefringence of the disk substrate, it can be properly initialized depending on the amount of light converging by the objective lens. That is, a diameter of 120 mm and a thickness of 1.
An initialization device conventionally used for a 2 mm optical disk is usually provided with an objective lens having a numerical aperture of 0.55, and the objective lens is moved to focus the laser beam on the position of the recording layer. Initialization.
From the original idea of reviewing this, the present inventors have found an appropriate range of the amount of light to be reduced by the objective lens, and have completed the present invention.

That is, according to the first aspect of the present invention, a laser beam from a semiconductor laser is converted into parallel light by a collimator lens, and the parallel light is condensed into an elliptical shape by an objective lens to form a beam spot on a phase-change optical recording medium. A phase change by an initialization device including an optical system that irradiates a reflected light from a phase-change optical recording medium onto a surface and separates the reflected light from the optical path by a beam splitter installed on an optical path of the parallel light and directs the reflected light to another direction. Axis (Wd) of the beam spot at the position of the recording layer of the phase-change type optical recording medium
Is a phase-change-type light, wherein initialization is performed with respect to the major axis (Wd _0.55 ) of a beam waist when an objective lens having a numerical aperture of 0.55 is used, in a state satisfying the following expression (1). A method for initializing a recording medium is provided.

Wd ≧ 1.1 × Wd _0.55 ‥‥ (1) According to a second aspect of the present invention, the laser light from the semiconductor laser is collimated by a collimator lens, and the parallel light is condensed into an ellipse by an objective lens. Irradiates the reflected beam from the phase-change optical recording medium onto the surface of the phase-change optical recording medium, and redirects the reflected light from the optical path by a beam splitter installed on the optical path of the parallel light in another direction. In a method for initializing a phase-change optical recording medium by an initialization device having an optical system, an objective lens having a numerical aperture of 0.55 is arranged such that a beam waist deviates from a recording layer surface of the phase-change optical recording medium by 2 μm or more. A method for initializing a phase-change optical recording medium, characterized in that the initialization is performed.

According to a third aspect of the present invention, a laser beam from a semiconductor laser is collimated by a collimator lens, and the collimated light is condensed into an elliptical spot by an objective lens. And a phase-change-type initialization device including an optical system that redirects reflected light from the phase-change-type optical recording medium from the optical path by a beam splitter installed on the optical path of the parallel light and directs the reflected light in another direction. In the method for initializing an optical recording medium, initialization is performed by using an objective lens having a numerical aperture of 0.50 or less and adjusting the beam waist to the position of the recording layer of the phase-change optical recording medium. An object of the present invention is to provide a method for initializing a recording medium.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to specific examples. As a phase change type optical recording medium, a phase change type optical disk having a layer configuration shown in FIG. 1 was manufactured.

That is, the outer diameter is 120 mm and the inner diameter is 15 m
m, a disc-shaped substrate with a thickness of 1.2 mm and a spiral groove of 1.6 μm formed on a polycarbonate disk substrate 1, a ZnS-SiO layer having a thickness of 200 nm
The first protective layer consisting of _2, a recording layer 3 made of SbTeGe thickness 30 nm, a second protective layer 4 made of ZnS-SiO ₂ having a thickness of 40 nm, a reflective heat dissipation layer 5 composed mainly of Al with a thickness of 150nm Laminated sequentially by sputtering method,
The protective coat layer 6 was formed by applying and curing an ultraviolet curable resin on the reflective heat dissipation layer 5.

The obtained phase-change type optical disk 7 was set in an initialization apparatus shown in FIG. 2 and was initialized under various conditions shown in Examples 1 and 2 below. This initialization device includes a disk support device 11, a laser device 12, a collimator lens 13, a polarization beam splitter 14, a λ / 4 plate 15
, A mirror 16, an objective lens 17, a focus servo mechanism 18, and a moving table 19.

The disk support device 11 rotatably supports the optical disk 7 and has a motor for rotating the optical disk. The laser device 12 has a wavelength of 810
It is a semiconductor laser that emits laser light of nm. The collimator lens 13 converts the laser light emitted from the laser device 12 into parallel light. The mirror 16 bends the optical axis of the parallel light from the collimator lens 13 by 90 ° and directs the light toward the optical disk 7 attached to the disk support device 11.

The objective lens 17 is arranged between the mirror 16 and the optical disk 7, and is movable in the optical axis direction by a focus servo mechanism 18. The objective lens 17 has a numerical aperture of 0.55, 0.53, 0.50,.
Seven types of 48, 0.45, 0.40, and 0.30 were prepared.

The polarization beam splitter 14 is disposed between the collimator lens 13 and the mirror 16, and directs the reflected light from the optical disk 7 to the focus servo mechanism 18. The λ / 4 plate 15 is arranged between the polarization beam splitter 14 and the mirror 16 to unify the polarization directions of the beams. The focus servo mechanism 18 is arranged at a position where the reflected light from the polarization beam splitter 14 is incident, and moves the objective lens 17 in the optical axis direction based on the reflected light from the optical disc 7. The moving table 19 is fixed with constituent members other than the disk support device 11 and integrally moves them at an appropriate pitch in the radial direction of the optical disk 7.

Therefore, according to this initialization device, the laser light which has been converted into parallel light by the collimator lens 13 is condensed by the objective lens 17 on the recording layer surface of the rotating disk 7 to form an elliptical beam spot. (Here, an elliptical shape having a short axis of about 2 μm and a long axis of about 100 μm). In addition, since the beam spot moves at a predetermined pitch in the radial direction of the optical disk 7 by the movement of the moving table 19, the entire recording layer of the optical disk 7 is automatically initialized. The focus servo mechanism 18 controls the focal point (ie, beam waist) of the laser light to a predetermined position. (Embodiment 1) First, the rotation speed (initial linear velocity) of the disk 7 and the moving amount of the moving table 19 (initialization pitch: the amount of movement in the disk radial direction per rotation of the disk) by the disk support device 11 are shown. The optimum conditions were examined by changing each of them. As a result, the linear velocity was 6.0 m / s, and the pitch was 50.
The condition was μm / rotation.

When the beam waist B (the focal point of the laser beam 8) is moved to the recording layer position 30 by moving the objective lens 17 by the focus servo mechanism 18 (FIG. 3), the beam waist B is moved ahead of the recording layer position 30 (protection). (FIG. 4; defocus on the "+" side with respect to the recording layer position 30), the position before the recording layer position 30 (substrate 1).
Side) (FIG. 5; defocus on the “−” side with respect to the recording layer position 30), it was examined how the initialization state changes.

That is, the defocus distance is set in the following Table 1.
The initialization was performed by setting each of the values shown in (1), and the disk 7 after initialization was examined for defects (ID errors) in the address information portion on the entire surface. The optimum condition of the power (initialization power) of the laser beam irradiated for each defocus distance was examined, and the initialization was performed with the initialization power of the optimum condition.

Here, in the phase-change type optical disk manufactured this time, address information portions are recorded in advance at approximately 1.3 million locations on the surface of the disk substrate 1 as minute irregularities. is there. And, in each address information part,
The same three pieces of the same address information are continuously formed. Therefore, of the three pieces of address information formed consecutively in each address information part, the error is reproduced when one is not reproduced, the error is reproduced when two are not reproduced, and the error is reproduced when two are not reproduced. The case where the error was not performed was regarded as error 3, and the occurrence rate of each error in the surface of the substrate 1 was calculated.

The results are shown in Table 1 below.

[0036]

[Table 1]

From the results shown in Table 1, when the defocus distance at the time of initialization is 0 (that is, the beam waist B is adjusted to the recording layer position 30 as in the conventional method),
It can be seen that the rate of occurrence of ID errors is higher than in other cases, and that the initialization is not uniform in the conventional method.
In addition, as the defocus distance (absolute value) increases, the occurrence rate of the ID error decreases, and the initialization may be performed uniformly by removing the beam waist B from the recording layer position 30. I understand.

When the defocus distance is 1 μm, the rate of occurrence of ID errors is higher than when the defocus distance is 2 μm or more, and the beam waist B is shifted from the recording layer position 30 to the substrate 1 side or to the protection. 2 μm on coat 6 side
It can be seen that the effect of uniform initialization is increased by separating from the above.If the defocus distance is too large, the energy density of the narrowed portion is too low, and the efficiency of the initialization is deteriorated, and the processing is performed. Speed decreases. In this example, it was found that it is appropriate to set the defocus distance to 5 μm or less in terms of processing speed.

Therefore, in the initialization by the initialization device having the optical system shown in FIG. 2, an objective lens having a numerical aperture of 0.55 is used to record a beam waist (focal point of a laser beam) on a phase-change optical recording medium. By arranging and performing initialization so as to deviate from the layer position by 2 μm or more and 5 μm or less, initialization can be performed uniformly and the processing efficiency of initialization can be secured. (Embodiment 2) Next, the beam waist B is set at the recording layer position 30.
In accordance with the above, the objective lens 17 used was changed in numerical value (NA) to each of the values shown in Table 2 below, and how the state of initialization changed was examined. That is, in the same manner as in Example 1, the respective ID error occurrence rates were measured.
The optimum condition of the initializing power was checked for each objective lens, and the initialization was performed with the initializing power of the optimum condition.

[0040]

[Table 2]

From the results shown in Table 2, when the numerical aperture of the objective lens is 0.55, the ID is larger than when the numerical aperture of the objective lens is less than 0.55.
It can be seen that the error occurrence rate is large and the initialization is not uniform in the conventional method. The numerical aperture is 0.50
It can be seen that the following effect can be substantially obtained in which the initialization is performed uniformly. Example 3 Next, using an objective lens having a numerical aperture of 0.55, the major axis (Wd) of the elliptical beam spot at the recording layer position when the defocus distance was ± 2 μm and ± 5 μm was measured. And using the same objective lens,
The ratio of the measured value (Wd) to the major axis of the elliptical beam spot at the recording layer position 30 (ie, beam waist Wd _0.55 ) when just focused (W =
Wd / Wd _0.55 ) was calculated.

Further, the numerical aperture (NA = 0.55 / W) of the objective lens in which the major axis (Wd) of the beam spot in each defocused state becomes the beam waist was calculated. Table 3 shows the results.

[0043]

[Table 3]

From the results shown in Table 3, the major axis (Wd) of the beam spot at the recording layer position is as follows with respect to the major axis (Wd _0.55 ) of the beam waist when using an objective lens having a numerical aperture of 0.55. When initialization is performed in a state that satisfies equation (1),
It can be seen that the initialization is performed uniformly in the same manner as the initialization in “a numerical aperture of 0.55 and a defocus distance of 2 μm or more” and “initial focus state with a numerical aperture of 0.50 or less”.

Wd ≧ 1.1 × Wd _0.55 ‥‥ (1) Further, initialization is performed in the just focus state, which corresponds to “the numerical aperture is 0.55 and the defocus distance is 2 μm or more and 5 μm or less” in the first embodiment. It can be understood that the range of the numerical aperture of the objective lens required for the above is from 0.29 to 0.50.

That is, in the initialization by the initialization device having the optical system shown in FIG. 2, an objective lens having a numerical aperture of 0.29 or more and 0.50 or less is used, and the beam waist is adjusted to the phase change type optical recording medium. By performing the initialization in accordance with the recording layer position, the initialization can be performed uniformly, and the processing efficiency of the initialization can be secured.

[0047]

According to the present invention, when the phase change type optical recording medium is initialized, the unevenness of the recording layer caused by the abnormal oscillation of the laser beam caused by the reflected light from the phase change type optical recording medium. Crystallization is eliminated. Therefore, the phase change type optical recording medium can be initialized uniformly and in a good state, and the productivity can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a layer configuration of a phase-change optical recording medium used in an example.

FIG. 2 is a schematic configuration diagram showing an initialization device used in the embodiment.

FIG. 3 is a schematic diagram showing a relationship (just focus state) between a beam waist (focus of a laser beam) and a recording layer position in Example 1.

FIG. 4 is a schematic diagram showing a relationship between a beam waist (focus of a laser beam) and a recording layer position (a defocused state of “+”) in Example 1.

FIG. 5 is a schematic diagram showing a relationship between a beam waist (focus of a laser beam) and a recording layer position (a defocused state of “−”) in Example 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 disk substrate 2 first protective layer 3 recording layer 4 second protective layer 5 reflective heat dissipation layer 6 protective coat layer 7 phase-change optical disk (phase-change optical recording medium) 8 laser beam 11 disk support device 12 laser device (semiconductor laser) 13) Collimator lens 14 Polarizing beam splitter 15 λ / 4 plate 16 Mirror 17 Objective lens 18 Focus servo mechanism 19 Moving table 30 Recording layer position B Beam waist

Claims (3)

[Claims] 1. A laser beam from a semiconductor laser is collimated by a collimator lens, and a beam spot obtained by converging the parallel light into an elliptical shape by an objective lens is applied to the surface of a phase-change optical recording medium. Method for initializing a phase-change type optical recording medium by an initialization apparatus including an optical system for redirecting reflected light from an optical recording medium from the optical path by a beam splitter installed on the optical path of the parallel light and directing the reflected light in another direction Wherein the major axis (Wd) of the beam spot at the recording layer position of the phase-change optical recording medium is as follows with respect to the major axis (Wd _0.55 ) of the beam waist when using an objective lens having a numerical aperture of 0.55. A method for initializing a phase-change optical recording medium, wherein the initialization is performed in a state satisfying the following equation (1). Wd ≧ 1.1 × Wd _0.55 ‥‥ (1) 2. A laser beam from a semiconductor laser is made parallel by a collimator lens, and a beam spot obtained by converging the parallel light into an ellipse by an objective lens is applied to the surface of a phase-change optical recording medium. Method for initializing a phase-change type optical recording medium by an initialization apparatus including an optical system for redirecting reflected light from an optical recording medium from the optical path by a beam splitter installed on the optical path of the parallel light and directing the reflected light in another direction Wherein the initialization is performed by disposing an objective lens having a numerical aperture of 0.55 so that the beam waist deviates from the recording layer surface of the phase change optical recording medium by 2 μm or more. Method. 3. A laser beam from a semiconductor laser is converted into parallel light by a collimator lens, and a beam spot obtained by converging the parallel light into an ellipse by an objective lens is applied to the surface of a phase-change optical recording medium. Method for initializing a phase-change type optical recording medium by an initialization apparatus including an optical system for redirecting reflected light from an optical recording medium from the optical path by a beam splitter installed on the optical path of the parallel light and directing the reflected light in another direction 2. The method for initializing a phase-change optical recording medium according to claim 1, wherein the beam waist is initialized according to the position of the recording layer of the phase-change optical recording medium using an objective lens having a numerical aperture of 0.50 or less.