JPH04123334A - Optical recording medium and its recording and reproducing method - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an erroneous signal due to a flaw on the surface of a medium with a simple constitution by successively laminating an optical recording layer which can be punched with irradiaion of recording light, a polarization plane rotating layer, and a light reflecting layer on a transparent substrate. CONSTITUTION:When an optical recording layer 3 of an optical recording medium 1 is irradiated with recording light 21 stronger than reproducing light, this layer 3 is punched in the irradiated part to form a hole part 31, and a signal is recorded. When this hole part 31 is irradiated with reproducing light 21, this light 21 is transmitted through the hole part 31 and a polarization plane rotating layer 4 and is reflected by a light reflecting layer 5. Since reflected light has the plane of polarization rotated while being transmitted back and forth through the polarization plane rotating layer 4, the light 22 has a polarized light component which has the plane of polarization perpendicular to the surface of paper, and this component is reflected by a polarizing beam splitter 13 and is detected as signal light 23 by a photodetector 14 and the signal is reproduced. Thus, the occurrence of an erroneous signal due to a flaw on the surface of the optical recording medium 1 is prevented, and information is recorded and reproduced with a high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which additional information can be optically recorded and reproduced, and a recording and reproducing method thereof.

[Conventional technology]

In recent years, demands for improved recording density and reliability have increased for magnetic recording media, which are widely used in various fields, and optical recording media have been proposed as an alternative.
Some of them have been put into practical use as optical cards, optical tapes, etc.

One of the recording methods for such an optical recording medium is a write-once recording method. In this method, an optical recording medium is constructed by providing a thin film-like optical recording layer on a substrate, which has appropriate reflection and absorption ability for recording and reproducing light, and a part of this optical recording layer is irradiated with recording light to form holes. A signal is recorded by forming (perforating) a portion, and the recorded signal is reproduced by irradiating reproduction light onto this and detecting a change in the amount of reflected light depending on the presence or absence of an optical recording layer. This type of optical recording medium is free from erroneous erasure or falsification of recorded information, and is suitable as a means for storing various types of information.

A problem with such optical recording media is the generation of erroneous signals due to scratches on the surface of the medium. In other words, the reflectance of the optical recording layer is usually set relatively high, and the signal is reproduced from the difference in the amount of reflected light by taking advantage of the decrease in the reflectance of the recorded area, but if there is a scratch on the surface of the medium. If this occurs, this scratch will scatter the reproduction light, reducing the amount of light that enters the photodetector, which may cause it to be mistakenly read as a signal even though no signal is recorded there. Normally, there is no recording. Since focused light is used as the reproduction light, the medium surface is in a defocused state, but due to constraints on the medium thickness and objective lens design, the beam diameter there is only a few hundred micrometers at most, and the width is a few pm or more. If there are large scratches or a large number of small scratches, it is not possible to completely prevent the effects of the scratches, and although error detection codes are usually added to the recorded signal to perform error correction, There is also a limit to the correction ability when a large number of erroneous signals occur in succession.

Therefore, as a method to prevent the generation of erroneous signals due to scratches on the medium surface, a method is proposed in which a resin having a refractive index similar to that of the transparent substrate is applied to the surface and cured to repair the scratches (Japanese Unexamined Patent Publication No. 63-1
06947), a method of recording and reproducing by immersing the medium in a liquid having a refractive index similar to that of a transparent substrate (see Japanese Patent Application Laid-Open No. 1-143018), etc.
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[Problem to be solved by the invention]

However, although these methods are highly effective as means for preventing the generation of false signals due to scratches on the media surface, they have many problems in practice. Maintenance such as replenishment is time-consuming, and repair must be carried out in a controlled environment to prevent adhesion of dust, so it is not a method that can be easily used by media users at any time. Method 2 requires a liquid filling section inside the recording/reproducing device, which increases the size and weight of the device, requires time and effort for liquid replenishment and quality control, and also makes it difficult to move the medium at high speeds due to the viscosity of the liquid. This poses a problem in that the data transfer speed becomes slow.

The present invention has been made in view of the above-mentioned important problems, and it is an object of the present invention to prevent the generation of erroneous signals due to scratches on the surface of a medium with a simple configuration without requiring special equipment that requires time and effort to maintain. The purpose of the present invention is to provide an optical recording medium and a recording/reproducing method for the same.

[Means to solve the problem]

A first aspect of the present invention is an optical recording device characterized in that an optical recording layer that can be perforated by recording light irradiation, a polarization plane rotation layer, and a light reflection layer are sequentially laminated on a transparent substrate. It is a medium.

Further, the second aspect of the present invention is to record a signal by perforating a part of the optical recording layer by irradiating the recording light to form a hole, and to add linearly polarized reproduction light having a lower output than the recording light. The recorded signal is reproduced by detecting the rotation of the polarization plane of the light transmitted through the polarization plane rotation layer and reflected by the light reflection layer in the hole formed in the optical recording layer. This is a characteristic recording and reproducing method for an optical recording medium.

<Function> The optical recording medium of the present invention has a structure in which an optical recording layer that can be perforated by recording light irradiation, a polarization plane rotation layer, and a light reflection layer are sequentially laminated on a transparent substrate. In areas where no signal is recorded, linearly polarized reproduction light that enters the optical recording layer from the transparent substrate side is partially absorbed by the optical recording layer and partially reflected while the polarization plane remains unchanged. . on the other hand,
At a location where a signal is recorded, that is, a location where a hole is formed in the optical recording layer, the reproduction light passes through the hole and the polarization plane rotation layer and is reflected by the light reflection layer. undergoes rotation of the plane of polarization while passing through the polarization plane rotation layer. Therefore, the recorded signal can be reproduced by detecting the rotation of the polarization plane of the reflected light. When reproducing a signal recorded using this keyaki, even if there is a scratch on the surface of the medium, this will only scatter a part of the reproduced light and will not cause a rotation of the plane of polarization, so no erroneous signal will be generated. Therefore, by using the optical recording medium and the recording/reproducing method of the present invention,
With a simple configuration, generation of erroneous signals due to scratches on the medium surface can be prevented.

<Example> The present invention will be described in detail below using an example with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the optical recording medium of the present invention;
FIG. 2 is an explanatory diagram showing an optical configuration in an embodiment of the recording/reproducing method for an optical recording medium of the present invention.

First, the optical recording medium of the present invention will be explained.

The optical recording medium 1 is composed of a transparent substrate 2, an optical recording layer 3, a polarization plane rotation layer 4, a light reflecting layer 5, and a protective layer 6.

The transparent substrate 2 may be made of any material as long as it has good transparency and optical isotropy for recording/reproducing light, and substrates such as glass, acrylic resin, polycarbonate resin, etc. can be used.

The optical recording layer 3 has appropriate reflection/absorption ability for the wavelength of recording/reproduction light from an appropriate light source such as a semiconductor laser, and can form (perforate) holes by irradiation with recording light. Any material that can form a thin film may be used, including low melting point metals, alloys, and inorganic compounds such as tellurium, cyanine,
Organic pigments such as squalirium, phthalocyanine, naphthoquinone, and anthraquinone can be used.

The polarization plane rotation layer 4 functions to rotate the polarization plane (vibration plane of the electric field vector of light) when linearly polarized light is transmitted in the thickness direction of this layer, and the rotation direction of the polarization plane is It is necessary to be independent of the direction in which the light travels. A typical example of such an effect is the so-called magneto-optical Faraday effect, and materials that have this effect include, for example, Co
Fe! 04, NdFeOs, Y, Fes 01
! , GdxFes O, and the like are known. The polarization plane rotation layer 4 is provided by directly forming a film using a vacuum film forming method such as high frequency sputtering, or by dispersing the fine powder in a suitable solvent together with a suitable binder resin, coating, and drying. I can do it. However, in order to utilize the magneto-optical Faraday effect, it is desirable to magnetize the polarization plane rotation layer 4 in a direction perpendicular to the film surface when forming it. The thickness of the polarization plane rotation layer 4 is preferably in the range of 1 μm to 10 μm, since it is advantageous to be thicker in order to increase the rotation angle of the polarization plane, but as it becomes thicker, loss due to light diffusion and scattering increases. It is preferable.

For example, the polarization rotation ability of Y, -, Cex F 6% O+t is on the order of 2 to 4 x 10' de g/cm (Journal of the Japan Society of Applied Magnetics vol. 1 .13.No, 2,16
3-166 (19B9)), therefore, if a layer with a thickness of 5 ym in which this is dispersed in a binder resin at a volume fraction of 50% is used, a rotation angle of 10 to 20 deg of the plane of polarization can be obtained.

The light reflecting layer 5 may be made of any material as long as it has a high reflectance for the wavelength of the recording/reproducing light, such as AI, Ag, or C.
A vapor deposited film such as R or a plating film can be applied. Further, the polarization plane rotation layer 4 and the light reflection layer 5 are made of C which exhibits the magneto-optic Kerr effect.
, dTbFe or the like may be used instead.

The protective layer 6 is provided for the purpose of protecting the optical recording layer 3, polarization plane rotation layer 4, and reflective layer 5 from external physical and chemical stimulation, and its material and thickness are not particularly limited. The light reflecting layer 5 may be made sufficiently thick and may be used as a substitute for the protective layer 6.

Next, a method for recording and reproducing an optical recording medium according to the present invention will be explained.

The light emitted from the light source 11 is converted by a polarizer 12 into linearly polarized light having a plane of polarization parallel to the plane of the paper, passes through a polarized beam splinter 13, and enters the optical recording layer 3 of the optical recording medium 1. When no signal is recorded on the optical recording medium l,
A part of the reproduction light 21 is absorbed by the optical recording layer 3 and a part is absorbed by the light source 1.
However, like the reproduction light 21, this reflected light 22 is linearly polarized light with a plane of polarization parallel to the plane of the paper, so it passes through the polarization beam splinter 13 and is detected by the photodetector 14. No light is detected in (Figure 2 (a))
, recording light 2 stronger than the reproduction light is applied to the optical recording layer 3 of the optical recording medium 1.
1, the irradiated area is perforated, a hole 31 is generated, and a signal is recorded. When the hole 31 is irradiated with the reproduction light 21, the reproduction light 21 passes through the hole 31 and the polarization plane rotation layer 4 and is reflected by the light anti-resistance layer 5,
The light then passes through the transparent substrate 2 and enters the polarizing beam splitter 13 as reflected light 22. At this time, the reflected light 22 undergoes rotation of the polarization plane while passing through the polarization plane rotation layer 4 back and forth, so it has a polarization component having a polarization plane perpendicular to the plane of the paper.
This component is reflected by the polarizing beam splitter 13 and becomes a signal light 23, which is detected by the photodetector Fi 14 and the signal is reproduced (FIG. 2(b)).

When the transmittance of the optical recording layer 3 is high, the transmitted light passes through the polarization plane rotation layer 4.
The reflected light 22 generates a polarized light component having a plane of polarization perpendicular to the plane of the paper, and the light with considerable intensity enters the photodetector 14 even in unrecorded areas. The transmittance of the recording layer 3 is as low as possible, preferably 1
It is best to set it to 0% or less.

As described above, the polarization beam splitter 13 separates the rotated polarization plane component of the reflected light 22 and the photodetector 14 detects the component, which prevents the generation of erroneous signals due to scratches on the surface of the optical recording medium 1. It can be prevented. In other words, since scratches do not rotate the plane of polarization of light, in unrecorded areas, no light enters the photodetector 14 regardless of the presence or absence of scratches, so it is impossible for an erroneous signal to occur. Furthermore, in the area where the signal is recorded, unless a scratch on the surface scatters all of the reproduced light 21 and reflected light 22, the signal light 23 will enter the photodetector 14, although the intensity will be weakened. , can play the signal.

〔effect〕

As described in detail above, by using the optical recording medium and the recording and reproducing method thereof of the present invention, it is possible to record and reproduce information with high reliability, which is hardly affected by scratches on the surface of the medium.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the optical recording medium of the present invention;
FIGS. 2(a) and 2(b) are explanatory diagrams showing an optical configuration in an embodiment of the recording/reproducing method for an optical recording medium of the present invention. 1... Optical recording medium 2... Transparent substrate 3...
・Optical recording layer 31... Holes 4 of the optical recording layer...
・Polarization plane rotation layer 5...Light reflective layer 6...Protective layer 11...Light source 2...Polarizer 3...Polarized beam splinter 4...Photodetector 1...Recording light or Reproduction light 2...Reflected light 23...Signal light frame Application by Toppan Printing Co., Ltd. Representative Kazuo Suzuki Figure (b)

Claims (2)

[Claims] (1) An optical recording medium characterized in that an optical recording layer that can be perforated by recording light irradiation, a polarization plane rotation layer, and a light reflection layer are sequentially laminated on a transparent substrate. (2) A method for recording and reproducing an optical recording medium in which an optical recording layer that can be perforated by recording light irradiation, a polarization plane rotation layer, and a light reflection layer are sequentially laminated on a transparent substrate, the method comprising: recording light; A signal is recorded by perforating a part of the optical recording layer by irradiation to form a hole, and this is then irradiated with linearly polarized reproduction light of lower output than the recording light to form a hole in the optical recording layer. A method for recording and reproducing an optical recording medium, characterized in that a recorded signal is reproduced by detecting rotation of a polarization plane of light transmitted through a polarization plane rotation layer and reflected by a light reflection layer in a hole.