JPH08263879A - Optical recording medium and optical recording and reproducing method - Google Patents

Abstract

PURPOSE: To execute recording or reproducing while stably executing control of an optical system, such as focus servo and tracking servo, by providing a side where the light of a mask layer is incident with a half-reflection layer. CONSTITUTION: This optical recording medium 10 is constituted by successively laminating the half-reflection layer 14, the mask layer 12 and a recording layer 13 on a transparent substrate 11. As a result, the side of the mask layer 12 where the light is made incident is provided with the half-reflection layer 14 and, therefore, the irradiation light of the optical recording medium 10 is partly passed and partly reflected by the half-reflection layer 14. The control signals of the optical system for recording or reproducing are consequently made possible by this reflected light. Then, the quantity of the reflected light for detecting the control signals of the optical system is made larger than heretofore and, therefore, the control of the optical system, such as focus servo and tracking servo, is stably executable.

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 high density information and an optical recording and reproducing method.

[0002]

2. Description of the Related Art In recent years, a super-resolution light reproducing technique has been proposed for recording / reproducing an area smaller than a recording spot determined by the diffraction limit of light in an optical disk device and a medium.
For example, Japanese Patent Application Laid-Open No. 5-225611 discloses an optical recording medium provided with a layer including a light absorption center that causes a nonlinear light absorption phenomenon such as saturable absorption characteristics as a mask layer. Further, Japanese Patent Application Laid-Open Nos. 5-242524 and 5-266478 disclose super-resolution reproducing methods using the same non-linear optical phenomenon and inverse photochromism. Here, reverse photochromism is
It is a phenomenon that changes to a colored state by a thermal reaction and changes to a decolored state by a photochromic reaction.

Further, the present inventors have proposed a super-resolution reproducing technique using a photochromic mask layer or a thermochromic mask layer (Japanese Patent Application No. 6-265687).
FIG. 2 is a plan view showing a super-resolution optical recording medium utilizing the non-linear light absorption phenomenon of saturable absorption characteristics. FIG. 3 is a sectional view showing such a super-resolution optical recording medium. Referring to FIG. 3, the optical recording medium 10 includes a transparent substrate 11 and a mask layer 12.
And the recording layer 13. The reproducing beam spot 1 irradiated from the transparent substrate 11 side has a Gaussian energy distribution with a high energy density in the central portion, and therefore the mask layer 1 irradiated with this reproducing beam spot 1
In No. 2, the transmittance is high in the central portion due to the non-linear light absorption phenomenon, and the masked state is maintained around it with the low transmittance. Therefore, as shown in FIG. 2 and FIG. 3, the transmittance of the mask layer is increased in a region smaller than the spot size in the reproduction beam spot 1, and an effective super-resolution spot 1a is formed. Information on the recording layer 13 is read out through the effective super-resolution spot 1a with improved transmittance. Therefore, only the recording mark 2 located in the effective super-resolution spot 1a is read out, and the recording mark 3 masked by the mask layer 12 is not read out. In this way, high-density recording / reproduction can be performed.

In the mask layer shown in FIGS. 2 and 3, a saturable absorbing dye is used, and the effective super-resolution spot is formed at the center of the reproduction beam spot. However, including the case where a photochromic mask layer or a thermochromic mask layer is used, the transmittance of the mask layer is increased on the side opposite to the scanning direction of the reproduction beam spot, that is, in the latter half of the reproduction beam spot. An effective super-resolution spot may be formed in the latter half of the beam spot.

[0005]

As described above, in the method of obtaining the super-resolution effect by using the mask layer, the recording marks which are not read out are protected from the light so as to prevent crosstalk. Must be masked. Therefore, the transmittance of the mask layer must be set to be sufficiently low, and the reproduction light is absorbed by the mask layer having such a low transmittance, that is, the large absorption, and the reflectance of the irradiation light is Becomes smaller. Usually, in order to stably record and reproduce an optical disc, an optical system control such as a focus servo and a tracking servo is performed. Such an optical system control is performed by detecting the reflected light of the light irradiated on the optical recording medium. It is generally done. Therefore, when the reflectance of the irradiation light is reduced by the mask layer, the reflected light cannot be sufficiently detected, and the control of the optical system such as the focus servo and the tracking servo becomes unstable.

An object of the present invention is to provide an optical recording medium and an optical recording / reproducing method capable of stably controlling an optical system such as a focus servo and a tracking servo in a super-resolution optical recording medium having a mask layer. is there.

[0007]

The optical recording medium of the present invention comprises:
An optical recording medium in which recording or reproduction is performed by irradiation of light, and a control signal of an optical system for recording or reproduction is detected by the reflected light thereof. It includes a mask layer that gives an image effect, and a semi-reflective layer that is provided on the light incident side of the mask layer and that allows a part of the light applied to the optical recording medium to pass therethrough and reflects a part of the light.

The optical recording / reproducing method of the present invention is an optical recording / reproducing method using the above-mentioned optical recording medium of the present invention, wherein a tracking / focus error signal is detected by reflected light from the semi-reflective layer to record or reproduce information. It is characterized by performing.

The mask layer in the optical recording medium of the present invention is
It gives a super-resolution effect when recording or reproducing on the information recording layer, and in a part of the reproducing light spot, absorption of the reproducing light is small, that is, the transmittance is improved to form an effective super-resolution spot. Is a mask layer for. Such a mask layer can be formed of a chromic material such as a saturable absorptive material, a photochromic material, and a thermochromic material whose light absorption intensity (transmittance) changes by light absorption. The mask layer may be provided above or below the information recording layer.

In the present invention, the semi-reflective layer is provided above the mask layer, that is, on the incident side of the light with which the optical recording medium is irradiated. The reflectance of the semi-reflective layer is preferably 5% or more, more preferably 10 to 20%.

The semi-reflective layer can be formed of, for example, a dielectric film having a refractive index larger than that of the substrate, and may be a single layer film or a laminated film in which a plurality of layers are laminated. . It can also be formed of a metal thin film or the like. It can be said that the dielectric film is a more desirable material than the metal thin film because the recording efficiency and the reproducing efficiency are less likely to decrease due to the light absorption.

When grooves, pits, etc. are required for tracking servo, etc., such grooves, pits, etc. are formed in the semi-reflective layer.

[0013]

According to the present invention, the semi-reflective layer is provided on the side of the mask layer on which light is incident. A part of the irradiation light to the optical recording medium is reflected by this semi-reflective layer, so that the control signal of the optical system for recording or reproduction can be detected by this reflected light. Therefore, according to the present invention, the amount of reflected light for detecting the control signal of the optical system can be increased more than in the past, so that the control of the optical system such as the focus servo and the tracking servo can be stably performed. It will be possible.

[0014]

FIG. 1 is a sectional view showing an optical recording medium of an embodiment according to the present invention. With reference to FIG. 1, an optical recording medium 10
Is formed by laminating a semi-reflective layer 14, a mask layer 12 and a recording layer 13 in this order on a grooved transparent substrate 11 (not shown in the figure) made of glass or polycarbonate. There is. Mask layer 12
For this purpose, a chromic mask layer is used which causes a chromic reaction upon irradiation with reproducing light, and as a result, the transmittance of the mask layer is improved. Further, as the recording layer 13,
Various optical recording materials such as known magneto-optical materials and phase-change type materials can be used, but TbFeCo-based magneto-optical materials are used here. When the recording layer 13 is thin and the amount of reflected light is insufficient, a reflective layer for reflecting the light passing through the recording layer 13 may be further provided on the recording layer 13.

In this example, a spiropyran-based chromic material having the following molecular structure was used as the chromic material contained in the mask layer. FIG. 4 is a diagram showing an absorption spectrum of this spiropyran-based chromic material.

[0016]

Embedded image

In FIG. 4, (1) is before light irradiation, (2)
The absorption spectra are shown after irradiation with 350 nm light, (3) after irradiation with 500 nm light or after heat treatment. As is clear from FIG. 4, the spiropyran-based material having the above molecular structure has absorption in the ultraviolet wavelength range in the decolored state, and changes to a colored state having absorption in the visible light wavelength range upon irradiation with ultraviolet rays (UV). To do. This colored state is visible light (VIS)
It is well known that not only the photochromic reaction by irradiation but also the thermal reaction changes the state to the decolorized state.

The semi-reflective layer can be formed of a dielectric multilayer film or a high-reflectance metal thin film as described above. In this embodiment, Ti having a larger refractive index than the transparent substrate is used.
An N film was formed by a sputtering method and used as a semi-reflective layer. As the transparent substrate 11, a glass disk substrate was used, on which grooves were formed with a track pitch of 1.2 μm. This glass disk substrate 11
On top of which TiN with a thickness of 0.1 μm was formed by sputtering.
The semi-reflective layer 14 was formed by forming a film. The semi-reflective layer 14 is provided with irregularities that reflect the shape of the groove of the glass disk substrate 11.

The mask layer 12 was formed to have a film thickness of 0.3 μm by mixing the above chromic dye molecules with polystyrene resin, dissolving them in cyclohexanone, and spin coating. As a resin to be mixed, a resin other than polystyrene may be used, or only a dye may be used to form a thin film. Furthermore, the mask layer can be formed by a method other than coating, for example, by vacuum-depositing a dye. The thickness of the mask layer is preferably set smaller than the depth of focus of the reproducing laser spot (about 1 μm).

The recording layer 13 is formed by the sputtering method.
It was formed as a thin film of the above-mentioned magneto-optical material. If necessary, a reflective layer may be provided below the recording layer 13 as described above, or a protective layer made of an ultraviolet curable resin or the like may be provided.

The optical recording medium sample of the example was prepared as described above, and for comparison, the medium sample of the comparative example prepared in the same manner as the above example except that the semi-reflective layer 14 was not provided was also prepared. .

The medium samples of the above Examples and Comparative Examples were first recorded by the magnetic field modulation method. For the media samples of the examples, recording was performed after the transmittance of the mask layer was entirely improved. For recording, a semiconductor laser with a wavelength of 630 nm was used, the spot diameter was focused to 1.2 μm, the relative speed was 1.4 m / s, the frequency was 700 kHz, and the recording power was 5.
It was performed in mW.

Reproduction by super-resolution reproduction was tried on the medium samples of Examples and Comparative Examples recorded as described above. For the control of the optical system, the astigmatism method was used for the focus servo and the push-pull method was used for the tracking servo. During playback, the mask layer coloring beam (3 m
W) was scanned in advance of the reproduction beam (2 mW) to reduce the transmittance of part of the mask layer in advance, and then reproduction was performed. As the colored light, an Ar laser light that emits an ultraviolet laser having a wavelength of 360 nm has a spot diameter of 2.5 μm.
It was focused on m and used. As the reproducing light, the same semiconductor laser light as the recording light was condensed to the same spot diameter and used.

Upon reproduction, super-resolution reproduction was performed by improving the transmittance of the mask layer in a portion corresponding to a part of the reproduction spot and forming a super-resolution spot. First, when only the focus servo was operated and the tracking error signal was detected, the output voltage of the medium sample of the example was four times that of the medium sample of the comparative example.
From this, it was confirmed that in the medium sample of the example, the optical system control signal of higher output voltage was obtained in the medium sample of the comparative example.

Next, when the tracking servo was performed while the tracking error signal was detected and the reproduction was performed, the tracking servo was not stably obtained in the medium sample of the comparative example, and the reproduction output could not be confirmed. It was On the other hand, in the medium sample of the example, stable tracking could be performed, and the reproduction output could be confirmed.

As is clear from the above, in the medium sample of the embodiment according to the present invention, the control signal of the optical system can be detected with a sufficient output, and the focus servo and the tracking servo can be reproduced while being stably performed. You can

Although the optical system control at the time of reproduction is described in the above embodiment, the present invention can be applied to the recording, for example, when the transmittance of the mask layer is low at the recording.

In the above embodiments, magneto-optical recording was described as an example, but the present invention is applicable to phase-change type optical recording materials, write-once type optical recording, and recording media by pit formation such as compact discs. It can also be applied to other optical recording media such as the reproduction-only optical recording medium.

The optical recording medium of the present invention can be applied to various focus / tracking servo systems.
In particular, the three-beam tracking servo system is more useful.

[0030]

According to the present invention, in a super-resolution optical recording medium having a mask layer, recording or reproduction can be performed while stably controlling the optical system such as focus servo and tracking servo.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an optical recording medium of an embodiment according to the present invention.

FIG. 2 is a plan view for explaining a super-resolution optical recording medium using a mask layer.

FIG. 3 is a sectional view showing an example of a conventional optical recording medium.

FIG. 4 is a diagram showing an absorption spectrum of a chromic material used in Examples.

[Explanation of symbols]

 1 ... Reproduction beam spot 1a ... Effective super-resolution spot 2 ... Recording mark to be read 3 ... Masked recording mark 10 ... Optical recording medium 11 ... Transparent substrate 12 ... Mask layer 13 ... Recording layer 14 ... Semi-reflective layer

Claims (2)

[Claims] 1. Recording or reproduction is performed by light irradiation,
An optical recording medium in which a control signal of an optical system for recording or reproduction is detected by the reflected light, and an information recording layer, and a mask layer which gives a super-resolution effect when recording or reproducing the information recording layer. An optical recording medium provided with a semi-reflective layer which is provided on a light incident side with respect to the mask layer and which allows a part of light applied to the optical recording medium to pass therethrough and reflects a part thereof. 2. An optical recording / reproducing method, wherein the optical recording medium according to claim 1 is used to detect a tracking / focus error signal by reflected light from the semi-reflective layer to record or reproduce information. Method.