JPH05205314A - Optical disk - Google Patents

Abstract

PURPOSE:To execute ultraresolution reproduction by creating phase pits on a transparent substrate, superposing an La-material layer thereon, reading out by the heat of reading out light, changing the reflectivity within a light spot and restoring the initial state after the passage of the reading out light. CONSTITUTION:The phase pits 1 are formed at a prescribed track pitch, pit depth and width on the glass substrate 2. A material which is a material to be changed in the reflectivity by generating an optical constant change in the high-temp. region within the light spot by the heat of the reading out light, is low in heat conduction, can be heated up to >=500 deg.C on a disk surface in spite of use of a laser and has >=795 deg.C m.p. is selected for the material layer 3 to be superposed thereon. Such material includes La, Y, Ce, etc., alone or the alloys thereof. The reflectivity is greatly increased in the high-temp. region within the scanning light spot of the reading out light and the reading out by, for example, diffraction, is made possible. The optical disk which obviates the deterioration in signals at the time of repetitive reading out and does not require any initiating means is obtd. according to this constitution. In addition, the recording density is exceedingly increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an optical disk suitable for high density recording, which is formed by forming a material layer whose reflectance changes with temperature on a transparent substrate having phase pits formed thereon. Regarding

[0002]

2. Description of the Related Art For optical discs such as digital audio discs (so-called compact discs) and video discs, an aluminum reflective film is formed on a transparent substrate on which phase pits are formed in advance according to an information signal, and an aluminum reflective film is formed thereon. It is configured by forming a protective film or the like.

In such an optical disc, a signal is read (reproduced) by irradiating the disc surface with a reading light and detecting a large decrease in the amount of reflected light due to the diffraction of the light in the phase pit forming portion. ing.

By the way, in the optical disc as described above, the resolution of signal reproduction is almost determined by the wavelength λ of the light source of the reproduction optical system and the numerical aperture NA of the objective lens, and the spatial frequency 2NA / λ is the reproduction limit.

Therefore, in order to achieve high density in such an optical disc, it is necessary to shorten the wavelength λ of the light source (for example, semiconductor laser) of the reproducing optical system or increase the numerical aperture NA of the objective lens. Will be needed.

[0006]

However, the wavelength λ of the light source is
There is a limit to the improvement of the numerical aperture NA of the objective lens and the objective lens, and it is difficult to dramatically increase the recording density by this.

Therefore, the applicant of the present invention can obtain a resolution higher than the above-mentioned limits by the wavelength λ and the numerical aperture NA by utilizing the reflectance change due to the partial phase change in the scanning spot of the reading light. (See Japanese Patent Application Nos. 2-94452 and 3-249511).

The inventions according to these applications relate to an optical disk or a reproducing system thereof for performing super-resolution reproduction by changing the reflectance by a partial phase change in the laser spot of the reading light.

In the present invention, a super-resolution reproducing system utilizing a partial reflectance change by using the temperature dependence of the optical constant of the present material is adopted without further phase change, and a substance accompanying the phase change is adopted. No deterioration due to movement, and more stable and reliable Stable and reliable high C / N (S / S) by making the difference in reflectance between the target read phase pit and other parts noticeable.
N) is provided to provide an optical disk capable of performing super-resolution reproduction.

[0010]

The present invention, as shown in the schematic sectional view of the essential portion of FIG. 1, is a material whose reflectance can be changed by temperature change on a transparent substrate 2 on which phase pits 1 are formed. The layer 3 is formed, and when the reading light is irradiated, the reflectance of the material layer 3 changes depending on the temperature distribution in the scanning spot of the reading light, and the reflectance is returned to the initial state when the temperature is lowered after reading. Return to the configuration.

In another aspect of the present invention, the material layer 3 is made of lanthanoid.

[0012]

In the optical disc according to the present invention, when the material layer 3 reads or reproduces the recording by the phase pit 1, the temperature distribution in the scanning spot of the reading light is used to generate a high temperature region in the spot. Thus, for example, the reflectance in the material layer 3 is remarkably increased, for example, so that the phase pits in this high temperature region can be read out by, for example, diffraction.

That is, it is possible to form a region in which the phase spot optically appears in the read light spot and read only, for example, one phase spot in this spot, and to perform super-resolution reproduction not restricted by λ / 2NA. To do.

As described above, according to the present invention, since it is possible to optically read an information signal without being melted, even if the information signal is repeatedly read, the signal is not deteriorated, and therefore, it is used for a large number of times of repeated reading. Is possible, and by doing this,
In addition, the initial state is formed in a normal state without taking special heat treatment and cooling steps and without providing means for taking this step, that is, initialization means.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1 which is a schematic cross-sectional view of a basic structure of the essential part of the present invention, a transparent substrate 2 having phase pits 1 formed thereon is subjected to a temperature change. A material layer 3 whose reflectance can be changed is formed.

When the reading light, for example, a laser beam is irradiated on the material layer 3, the reflectance partially increases in a high temperature region within the scanning spot of the reading light of the material layer 3 and the post-reading temperature is increased. The reflectance is returned to the initial state in a state where the value is lowered.

In the example shown in FIG. 1, the material layer 3 is formed directly on the transparent substrate 2. For example, FIG. 2 shows a schematic enlarged cross-sectional view of the main part thereof. As described above, the material layer 3 is formed on the transparent substrate 2 having the phase pits 1 via the first dielectric layer 4, the second dielectric layer 5 is further formed thereon, and the reflection is performed on the second dielectric layer 5. In the case where the film 6 is further provided, a protective film (not shown) is formed on the film 6, and the optical characteristics such as reflectance are set by the first and second dielectric layers 4 and 5. You can

Example 1 In this example, a glass 2P substrate was used as the transparent substrate 2 when the configuration described in FIG. 2 was adopted. The 2P referred to here is a photopolymer method.

In this example, the track pitch P is 1.6 μm, the pit depth is about 120 nm, and the pit width W is W.
= 0.3 μm. Then, on the main surface of the transparent substrate 2 having the pits 1, Al having a thickness of 90 nm is formed.
A first dielectric film 4 made of N was deposited, and a 17 nm thick Tb simple metal was used as the material layer 3 on the first dielectric film 4. The thermal conductivity of this material layer 3 is 0.024 J / cm.
sec · deg, melting point is 1356 ° C.

Further, a second dielectric layer 5 of AlN having a thickness of 90 nm is deposited and formed thereon as a second dielectric film 5, and an Al reflection film 6 having a thickness of 180 nm is further formed thereon. It was deposited on.

As the material of the transparent substrate 2, acrylic resin, polyolefin resin, glass or the like can be used.

As the material layer 3, a material satisfying the following conditions is used. That is, due to the heat of the reading light, a temperature gradient between the high temperature region and the low temperature region is partially generated in the reading light spot, and the reflectance changes due to the change of the optical constant in the high temperature region. Also has a small thermal conductivity that can raise the temperature to 500 ° C. or higher on the disc surface, and a melting point of 795 ° C. or higher is required to avoid deterioration due to melting.

If the above conditions are satisfied, Y,
La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, T
Examples include simple substances such as b, Dy, Ho, Er, Tm, Yb, and Lu, or alloys of two or more of these.

As the dielectric films 4 and 5, Al,
Examples thereof include nitrides, oxides, and sulfides of metals such as Si and semiconductor elements, and any compound that does not absorb in the semiconductor laser wavelength region may be used.

Further, the reflection film 6 may be made of any metal such as Al and Au, which has a good reflectance and thermal conductivity.

With respect to the optical disk thus formed, the reproduction power was set to 9 mW, the linear velocity was set to 6 m / s, and the reproduction was performed to reproduce the signal portion. The C / N of the signal was It was 35 dB. Then, the optical disc according to the present invention is reproduced with super-resolution by utilizing the temperature distribution in the scanning spot on the optical disc upon reproduction.

That is, a case where the optical disk according to the present invention is irradiated with a laser spot will be described with reference to FIG.
In FIG. 3, the horizontal axis indicates the position of the spot in the scanning direction. Looking at the state where the optical disk is irradiated with the laser light spot L by laser irradiation, in this case, the light intensity is shown by the broken line A in FIG. The distribution shows a distribution, and at this time, the above-mentioned high temperature region Px and low temperature region Pz relatively occur in the spot L. On the other hand, the reflectance distribution corresponding to the temperature distribution in the material layer 3 corresponds to the scanning speed of the laser spot L and is slightly delayed with respect to the scanning direction of the spot L indicated by the arrow C, and is reflected by the solid line B in the figure. Becomes a rate distribution,
Information can be read at the portion where the reflectance is increased in this reflectance distribution.

Further, in the above embodiment, the transparent substrate 2
Although the phase pit 1 is formed on the upper side, the present invention can be applied to other optical readable recording pits.

[0029]

According to the present invention, since the signal can be read out without melting, deterioration due to melting, for example, a decrease in signal output due to non-uniformity of the film thickness due to flow does not occur, so that the durability against repetition is increased. The optical disc has a high recording density that can be improved and can be applied to applications in which the number of repetitions is large.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an essential part showing the configuration of an example of an optical disc.

FIG. 2 is a schematic cross-sectional view of a main part showing the configuration of the embodiment.

FIG. 3 is a diagram showing a relationship between a light intensity distribution of a laser spot and a temperature distribution (reflectance) of an optical disc.

[Explanation of symbols]

 1 Phase Pit 2 Transparent Substrate 3 Material Layer 4 First Dielectric Layer 5 Second Dielectric Layer 6 Reflective Film

Claims (2)

[Claims] 1. An optical disk comprising a transparent substrate on which recording pits that can be optically read according to an information signal are formed, and a material layer whose reflectance changes with temperature is formed on the transparent substrate. 2. The optical disc according to claim 1, wherein the material layer is made of lanthanoid.