JPH08167147A - Optical disk - Google Patents

Abstract

PURPOSE: To decrease crosstalk when signals recorded in lands and grooves of an optical disk are reproduced, and to improve the recording track density. CONSTITUTION: Grooves (3) having depth about 1/8 to 1/4 of the wavelength of laser light are formed on a disk in such a manner that the land (2) between the grooves (3) has the same width as the groove (3). Such a material is used for the recording film (6) that gives the same phase of amplitude reflectance of laser beam both in and out of the recorded mark (4) formed and that gives 0 to 16 ratio of the intensity reflectance of laser beam in the area out of the recorded mark (4) to in the area in the recorded mark (4). By this method, crosstalk when signals recorded in lands (2) and grooves (3) are reproduced can be effectively decreased and the recording track density can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and is particularly suitable for application to recording and reproducing a signal on a land and a groove on the disk.

[0002]

2. Description of the Related Art Conventionally, in an optical disc, a wobbled groove is previously formed on the disc as a guide groove in accordance with address information or the like, and a desired signal is recorded in the groove based on the wobble information at the time of recording / reproducing. There is something to play.

[0003]

By the way, in such an optical disc, in order to improve the recording track density, signals are recorded on both the groove and the land between the grooves, thereby ensuring a wide recording area. Possible things are proposed. However, when reproducing such an optical disk, crosstalk from adjacent grooves or lands becomes a problem.

As a solution to such a problem, when the reflectance in the recording mark of the optical disk is 0 [%], about λ / 6.
A phase change type optical disc having a groove depth (where λ is a light source wavelength) has been proposed. In this phase-change optical disc, when signals are recorded on the lands and the grooves, the signal crosstalk between the lands and the grooves is small, and recording / reproduction with a high track density is possible.

However, if the reflectance within the recording mark is set to 0%, for example, the selection range of the material selected as the recording film is limited, and it is difficult to diversify the disk structure.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose an optical disk capable of reducing crosstalk when reproducing a signal recorded in a land and a groove and improving the recording track density. To do.

[0007]

In order to solve such a problem, in the present invention, a recording film formed on a disk is irradiated with laser light to change the state of the recording film to record a desired signal. In an optical disc that reproduces a desired signal by detecting a change in the reflectance of the laser beam due to a change in the state of the recording film, the depth on the disc is about 1 wavelength of the laser beam.
A groove formed of / 8 to 1/4 is formed so that the width of the groove and the land between the grooves are equal to each other,
As the recording film, the phases of the amplitude reflectance of the laser light inside and outside the recording mark to be formed are equal, and the ratio of the intensity reflectance of the laser light inside the recording mark to the intensity reflectance of the laser light outside the recording mark is the same. Select materials that are 0 or more and 16 or less,
A desired signal is recorded and reproduced in each of the groove and the land.

[0008]

Function: The depth on the disk is about 1/8 of the wavelength of the laser light
The groove (3) of about 1/4 to 1/4 is formed so that the width of the groove (3) and the land (2) between the groove (3) are equal. As the recording film (6), the phase of the amplitude reflectance of the laser beam inside and outside the recording mark (4) to be formed is the same, and the recording mark (4) with respect to the intensity reflectance of the laser beam outside the recording mark (4). A material is selected so that the ratio of the intensity reflectance of the laser light within the range is 0 or more and 16 or less. As a result, it is possible to realize the optical disk (1) capable of reducing the crosstalk when reproducing the signals recorded in the land (2) and the groove (3) and improving the recording track density.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 generally indicates a phase change type optical disk according to an embodiment of the present invention. In the optical disc 1, as so-called land / groove recording, signals are recorded and reproduced on the recording marks 4 formed on the lands 2 and the grooves 3 (FIG. 1A).

As shown in FIG. 1B, the optical disk 1
Has a recording film 6 formed on a substrate 5, and the recording film 6 is a protective film 7.
Protected by. Further, the groove 3 has a depth d, and the width of the land 2 and the groove 3 is selected to be 1: 1.
In the phase-change optical disc 1, the recording film 6 is irradiated with laser light to reversibly change the recording film 6 between an amorphous phase and a crystalline phase, and the laser light changes according to the state of the recording film 6. The signal is recorded and reproduced by detecting the change in the reflectance of the.

In this optical disc 1, as the recording film 6,
A material having the following characteristics is selected. As shown in FIG. 2, the amplitude reflectance of the laser light inside the recording mark 4 is rr _in , and the amplitude reflectance of the laser light outside the recording mark 4 is rr.
_out . The amplitude reflectance rr _in in the recording mark 4,
The amplitude reflectance rr _out outside the recording mark 4 is calculated by the following equations (1) and (2), respectively.

[Equation 1]

[Equation 2] When expressed by, φ _{in of} the equation (1) and φ _out of the equation (2) are phase terms of the amplitude reflectance, respectively.

When the real part and the imaginary part are represented by Re [] and Im [], respectively, the phase φ _in of the amplitude reflectance of the laser light inside the recording mark 4 and the amplitude reflectance of the laser light outside the recording mark 4 are shown. Phase φ
_out is the following equations (3) and (4), respectively.

(Equation 3)

[Equation 4] In the recording film 6, the phase difference Δφ of the complex amplitude reflectance inside and outside the recording mark 4 is expressed by the following equation (5).

(Equation 5) It has been selected as a material that satisfies the conditions of.

Further, the recording film 6 has the recording mark 4 with respect to the intensity reflectance of the laser beam outside the recording mark 4, as will be described later.
The material is selected as a material whose intensity reflectance of laser light is within the range of 0 or more and 16 or less, and the groove depth d is about λ / 8 ~
It is set between λ / 4.

Here, light source wavelength λ = 780 [nm], objective lens numerical aperture 0.53, recording mark length 1.3 [μm], mark width
0.8 [μm], land width and groove width are 0.8
[Μm] (track pitch is 0.8 [μm]), the phase difference of the complex amplitude reflectance inside and outside the recording mark 4 Δφ = φ _in −φ
Under the condition of _out = 0, various intensity reflectance ratios R _in /
FIG. 3 shows an experimental result of the crosstalk amount with respect to the groove depth d with R _out as a parameter.

Here, R _in is the intensity reflectance of the laser light inside the recording mark 4, R _out is the intensity reflectance of the laser light outside the recording mark 4, and the intensity reflectance R _in is rr _in · rr _in ^*
The intensity reflectance R _out is calculated as follows: rr _out · rr _out ^*
Calculated by " ^* " Is a parameter indicating a complex conjugate. The intensity reflectance ratio R _in / R _out is selected as the parameter because the crosstalk is uniquely determined with respect to the intensity reflectance ratio R _in / R _out under the condition of the phase difference Δφ = 0. .

As can be seen from the experimental results of FIG. 3, the intensity reflectance ratio R _in / R _out is _in the range of 0 ≦ R _in / R _out ≦ 16, and the groove depth d is between approximately λ / 8 and λ / 4. Therefore, crosstalk of -30 [dB] or less, which is practically no problem, can be obtained. Further, under the condition of the intensity reflectance ratio R _in / R _out = 0 (R _in = 0), about λ
The optimum groove depth d is / 8 to λ / 7, and the optimum groove depth d increases as the intensity reflectance ratio R _in / R _out increases. Under the condition of the intensity reflectance ratio R _in / R _out = 16, about λ / 4 is the optimum groove depth d.

Therefore, in the optical disc 1, the recording film 6 is selected as a material such that the phase difference Δφ of the complex amplitude reflectance inside and outside the recording mark 4 is Δφ = 0 as described above, and the intensity reflectance ratio is selected. R _in / R _out is 0 ≦ R _in / R _out ≦ 16
It has been selected as a material within the range. Further, the groove depth d is selected between λ / 8 and λ / 4.

The track pitch 0.8 [μm] in the optical disc 1 is the same as that of a conventional system (for example, light source wavelength 780 [nm], objective lens numerical aperture 0.53, track pitch approximately 1.5 [μm]) for recording signals on lands or grooves. About 1
/ 2. In other words, the optical disk 1 has twice the recording track density of the conventional system.

According to the above structure, in the land / groove recording in which the width ratio of the land 2 and the groove 3 is 1: 1,
As the recording film 6, the phase difference Δφ of the amplitude reflectance of the laser light inside and outside the recording mark 4 is “0”, and the intensity reflectance ratio R _in
Recording on land 2 and groove 3 by selecting a material whose / R _out is _in the range of 0 ≤ R _in / R _out ≤ 16 and setting the groove depth d in the range of approximately λ / 8 to λ / 4. It is possible to effectively reduce crosstalk when reproducing the generated signal, and to realize the optical disk 1 having a recording track density that is about double.

Further, according to the above-mentioned structure, it is not necessary to limit the material for the recording film 6 to the intensity reflectance in the recording mark 4 of 0%, so that the selection range of the material of the recording film 6 is enlarged. Therefore, the structure of the disk can be further diversified.

In the above embodiment, the case where the present invention is applied to the phase change type optical disk 1 has been described.
The present invention is not limited to this, and the recording film 6 is irradiated with laser light to change the state of the recording film to record a desired signal, and the change in the reflectance of the laser light due to the change in the state of the recording film 6 is detected. As long as it is an optical disk that reproduces a desired signal, it can be applied to other optical disks. In this case, as the recording film 6, a material that does not change the phase of the amplitude reflectance of the laser light inside and outside the recording mark 4 is selected.

In the above embodiment, the case where the present invention is applied to the phase change type optical disk 1 has been described.
The present invention is not limited to this, and can be applied to a write-once type optical disk that can be rewritten only once. In this case, as the recording film 6, a material that does not change the phase of the amplitude reflectance of the laser light inside and outside the recording mark 4 is selected.

[0024]

As described above, according to the present invention, a groove having a depth of about ⅛ to ¼ of the wavelength of the laser beam is formed on the disk, and the width between the groove and the land between the grooves. Of the laser light inside and outside the recording mark to be formed as a recording film, and the phase of the amplitude reflectance of the laser light inside and outside the recording mark is equal to the intensity reflectance of the laser light outside the recording mark. The ratio of light intensity reflectance is 0
By selecting a material of 16 or less, it is possible to realize an optical disk capable of reducing crosstalk when reproducing a signal recorded in a land and a groove and improving a recording track density.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an optical disk according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a phase difference in amplitude reflectance inside and outside a recording mark of an optical disc and an intensity reflectance ratio according to an example.

FIG. 3 is a phase difference Δφ = 0 between amplitude reflectance inside and outside a recording mark.
FIG. 9 is a characteristic curve diagram showing experimental results of crosstalk amount with respect to groove depth using various intensity reflectance ratios R _in / R _out as parameters under the condition of.

[Explanation of symbols]

1 ... Optical disk, 2 ... Land, 3 ... Groove, 4
...... Record mark, 5 ... Substrate, 6 ... Recording film, 7 ... Protective film.

Claims (2)

[Claims] 1. A recording film formed on a disk is irradiated with a laser beam to change the state of the recording film to record a desired signal, and the reflectance of the laser beam due to the change of the state of the recording film. Of the optical disc for detecting the change in the desired signal and reproducing the desired signal, the depth on the disc is about 1/8 of the wavelength of the laser beam.
To 1/4 of the groove are formed such that the width of the groove and the land between the grooves are equal, and the phase of the amplitude reflectance of the laser light inside and outside the recording mark is formed as the recording film. Are equal, and the ratio of the intensity reflectance of the laser light inside the recording mark to the intensity reflectance of the laser light outside the recording mark is 0 or more 16
An optical disk characterized by selecting the following materials, and recording and reproducing the desired signal in each of the groove and the land. 2. The recording film is made of a phase change medium which reversibly changes its state between an amorphous phase and a crystalline phase by irradiating the recording film with the laser beam. The optical disk according to claim 2.