JP2737612B2 - optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk for recording high-density information.

[0002]

2. Description of the Related Art In recent years, optical disks capable of recording high-density information have been researched and developed by various methods. As one of the means, a method of recording a signal, which was conventionally recorded only on either the land portion or the glove portion, on both the land portion and the groove portion has been studied. At this time, crosstalk between adjacent signals may increase more than before. To prevent this, in the magneto-optical medium, the interference film thickness between the land and groove is changed, and the Kerr rotation angle is wavelength-dependent. Japanese Patent Application Laid-Open No. 64-10446 discloses a method of reducing crosstalk by reproducing the land and the groove with light having different wavelengths. FIG. 3 shows the basic structure of this optical disk, and FIG. 4 shows its function. As shown in FIG. 3, the optical disc has an interference layer 9 (having a thickness different from that of the land 4) between the substrate 1 and the recording layer 3 (magneto-optical medium). In this case, d1 is formed, and in the groove portion 5, d2) is formed. Due to the difference in the thickness of the interference layer, as shown in FIG. 4, the wavelength dependence of the Kerr rotation angle enhanced by the interference layer in the land portion and the groove portion is different. Utilizing this fact, the light of wavelength λ1 is used for the light beam 6 for reproducing the land 4 and the light of wavelength λ2 is used for the light beam 7 for reproducing the groove 5, so that the light from the adjacent recording area can be read. The signal intensity from the reflected light is weakened, and crosstalk can be reduced.

[0003]

However, the above-mentioned method for reading recorded information uses the enhancement effect of the Kerr rotation angle due to the interference layer of the magneto-optical medium, and therefore cannot be realized with another recording medium, for example, a phase change medium. . Further, since a certain signal intensity exists even in a wavelength region where the enhancement effect of the Kerr rotation angle is weak, the effect of reducing the crosstalk is not so large.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an optical disk capable of recording and reproducing high-density information with little crosstalk between a land portion and a groove portion regardless of a recording medium.

[0005]

The optical disk of the present invention comprises:
On a transparent substrate, light Di which is formed the light modulating film of the reproduction light
A light modulating film, wherein the light modulating film is a light modulating medium excluding a magneto-optical medium.
In the optical disc , which is a film, a film having different wavelength dependences of transmittance or reflectance at a land portion and a groove portion is formed on a front surface or a back surface of the light modulation film. Further, the above-mentioned film in which the transmittance or the reflectance shows different wavelength dependency is a dielectric multilayer film in which the land portion and the groove portion have different film thicknesses.

[0006]

When two kinds of dielectric materials having different refractive indices are alternately stacked with a quarter of the effective film thickness of a certain wavelength, one is obtained at the wavelength.
It is well known that a reflectance close to 00% can be obtained. Further, by changing the thickness of the laminated film in the middle or by changing the laminating order, it is possible to modulate the wavelength dependence of the reflectance or the transmittance of the dielectric multilayer film. By taking a multilayer structure with desired modulation and changing the basic film thickness between the land and the groove, the peak wavelength of the reflectance or the transmittance can be changed between the land and the groove. By using light of a different wavelength that becomes the peak wavelength of the reflectance or the transmittance for reproduction of the land portion and the groove portion, the reflection amount of the signal component from the adjacent signal recording area is reduced, and the crosstalk is suppressed. be able to.

[0007]

FIG. 1 is a diagram showing a cross-sectional structure of an optical disk showing an embodiment of the present invention.

This optical disk has a dielectric multilayer film 2 between a substrate 1 and a recording layer 3. The material of the substrate 1 is polycarbonate, and the recording layer 3 is made of a layer change medium GeS.
bTe was used. The dielectric multilayer film 2 is formed of alumina having a refractive index of 1.68 and amorphous silicon having a refractive index of 3.8. Generally, a dielectric H having a large refractive index and a dielectric L having a small refractive index each having an effective film thickness of １ ／ of the wavelength λ are HLHLHLHLLLHLHLHL.
FIG. 2 shows the wavelength dependence of the transmittance when the layers are stacked in the order of H.

In this embodiment, the dielectric H is made of amorphous silicon and the dielectric L is made of alumina. The effective film thickness of each layer of the land 4 is １ ／ of the wavelength λ1 , and
The effective thickness of each layer of the groove portion 5 was set to １ ／ of the wavelength λ2. As a signal recording / reproducing light, a light beam 6 having a wavelength λ1 (here, 680 nm) was used for the land portion 4, and a light beam 7 having a wavelength λ2 (here, 780 nm) was used for the groove portion 5. Accordingly, even if the peripheral portion of the light beam 6 irradiating the land portion 4 enters the groove portion 5,
Since the transmittance of the dielectric multilayer film 2 at the wavelength λ1 in the portion 5 is almost 0% as shown in FIG.
Of the signal recorded in the land portion 4 as crosstalk is greatly reduced. This mechanism is
The same applies to the groove 5.

In the embodiment described above, the dielectric multilayer film is provided on the light incidence side of the recording medium. However, according to the requirements of the present invention, the dielectric multilayer film is provided on the light non-incidence side of the recording medium. Arrange a dielectric multilayer film,
A configuration in which the wavelength of the reproduction light is adjusted to the peak of the reflectance is also possible.

In the present invention, the reflectivity and transmittance of the dielectric multilayer film are used as means for reducing crosstalk. Therefore, the present invention can be applied to both a layer change medium for modulating light intensity and a magneto-optical medium for modulating Kerr rotation angle. Function can be realized.

In the above embodiment, the HLHLHLHLHLHLHLHLH type structure has been described as the layer structure of the dielectric multilayer film. However, the layer structure can be formed appropriately in consideration of the characteristics required for the medium. Further, as the dielectric used for the dielectric multilayer film, other materials such as SiO ₂ can be used depending on the wavelength used. In the above embodiment, the wavelengths are set to 680 nm and 780 nm.

[0013]

According to the optical disk of the present invention, regardless of the type of recording medium, there is little crosstalk between the land and the groove, and high-density information recording and reproduction can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of the present invention.

FIG. 3 is an explanatory view showing a conventional high-density optical disk.

FIG. 4 is an explanatory view showing the principle of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Dielectric multilayer film 3 Recording layer 4 Land part 5 Groove part 6 Light beam 7 Light beam 8 Objective lens 9 Interference layer

Claims (2)

(57) [Claims] 1. An optical disk having a light modulation film for reproduction light formed on a transparent substrate , wherein the light modulation film is a magneto-optical medium.
In an optical disc which is a light modulating film excluding a body , a land portion and a groove portion are formed on a surface or a back surface of the light modulating film.
An optical disc, characterized in that a film whose transmittance or reflectance exhibits different wavelength dependence is formed. 2. The film according to claim 1, wherein the film having different wavelength dependences of the transmittance or the reflectance is a dielectric multilayer film having a different thickness between a land portion and a groove portion. Optical disk.