JPH0384748A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To provide a higher recording density and smaller crosstalks by adequately adjusting the depth of guiding grooves according to the sectional shape and pitch of the guiding grooves. CONSTITUTION:The guiding grooves 4 are formed to have the depth d1 of (lambda/10n to lambda/16n)X(1.5 to 1.6) when the sectional shape of the guiding grooves 4 is formed to an approximately triangular shape, the pitch P of the refractive index to 1.0 to 1.5 mum and the wavelength of light for reproducing as lambda and the refractive index of a transparent substrate 2 as (n). Many tracks can be arranged in the recording of a specified area and the recording density in the direction where the guiding grooves are arranged is increased when the track pitch is diminished. The wavelength of the light for recording/reproducing is shortened and the pitch length of prepits and add-on pits is shortened as the track pitch is smaller and, therefore, the recording density can be increased in the direction along the guiding grooves as well. On the other hand, the crosstalks are decreased when the guiding grooves of the smaller pitch are formed in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information recording medium, and particularly to the size, shape, and arrangement of guide grooves formed on the signal surface of a transparent substrate.

[Conventional technology]

Conventionally, guide grooves are arranged at a constant pitch.

An optical information recording medium is known in which a thin film layer including at least a recording film or a reflective film is laminated on the signal surface of a transparent substrate having prepit rows formed along the guide grooves.

This optical information recording medium records/reproduces signals by tracking a light spot having a diameter approximately equal to the pitch (track pitch) of the guide grooves along the guide grooves.

Conventionally, in this type of optical information recording medium, the track pitch has been adjusted to 1.6 μm based on the wavelength of the semiconductor beam used (830 nm) and the numerical aperture (0.5) of the objective lens. Further, in order to maximize the tracking signal level, the depth of the guide groove is set to λ/8n, where λ is the wavelength of the reproduction light and n is the refractive index of the transparent substrate.

[Problem to be solved by the invention]

By the way, in this type of optical information recording medium.

Increasing recording density has become one of the most important technical issues, and to address this, we are working to reduce the track pitch, narrow the width of pre-pits and add-on pits, and
Shortening the wavelength of the reproduction light and reducing the diameter of the optical spot are being considered.

However, the light beam formed with a track pitch of 1.0 to 1.5 μm and a guide groove depth of λ/8n (where λ is the wavelength of the recording/reproducing light and n is the refractive index of the transparent substrate) When information is recorded/reproduced on an information recording medium, compared to an optical information recording medium formed with a track pitch of 1.6 μm, crosstalk from adjacent tracks increases and the CN ratio of the reproduced signal deteriorates. It turned out that there was a problem.

The present invention was made to solve the above-mentioned drawbacks of the prior art, and its purpose is to provide an optical information recording medium with high recording density and low crosstalk.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention provides optical information in which a thin film layer including at least a recording film or a reflective film is laminated on the signal surface of a transparent substrate having guide grooves and pre-pit arrays arranged at a constant pitch. In the recording medium, the cross-sectional shape of the guide groove is approximately triangular, and the pitch of the guide groove is 1.0 to 1.
．． 5 μm, the wavelength of the reproducing light is λ, and the refractive index of the transparent substrate is n, the depth of the guide groove is (λ/10n~λ/16n)X(1,5~1,6
) was formed.

Further, as another means for achieving this object, in a similar optical information recording medium, the cross-sectional shape of the guide groove is approximately trapezoidal, and the pitch of the guide groove is 1.0-1.5 μm.
Also, the wavelength of the reproduction light is λ.

When the refractive index of the transparent substrate is n, the depth of the guide groove is λ/10n to λ/16n.

[Operation] By reducing the track pitch, a large number of tracks can be arranged in a recording area of a constant area, and the recording density in the direction in which the guide grooves are arranged can be increased. In addition, as the track pitch becomes smaller, the wavelength of recording/reproducing light becomes shorter, and the pit length of pre-pits and add-on bits becomes shorter, so the recording density also increases in the direction along the guide groove. be able to.

On the other hand, it has been confirmed through experiments by the inventors that crosstalk can be reduced by forming the depth of the guide groove with a small pitch according to its cross-sectional shape as described above.

Further, when the depth of the guide groove is adjusted to the above value, the tracking signal level decreases, but at least a signal level of 60% or more required for stable tracking control can be secured.

It was confirmed by the same experiment conducted by the inventors that there was no problem in signal recording/reproduction.

Therefore, it is possible to provide an optical information recording medium with high recording density and low crosstalk.

〔Example〕

First, a first embodiment of the present invention will be described based on FIGS. 1 to 3. FIG. 1 is a plan view of the optical information recording medium according to the first embodiment, FIG. 2 is an enlarged plan view of the main part of this optical information recording medium, and FIG. 3 is an enlarged sectional view of the main part of this optical information recording medium. be.

As shown in these figures, the optical information recording medium of this embodiment has a disk-shaped transparent substrate 2 with a center hole 1 in the center.
A thin film layer 3 including at least a recording film is laminated on the signal surface 2a of the recording medium.

The transparent substrate 2 can be made of any known transparent hard material such as glass or plastic.

The signal surface 2a is formed by an appropriate method depending on the material of the transparent substrate 2. For example, when the transparent substrate 2 is made of glass or thermosetting plastic material, the signal surface 2a is formed by a desired method depending on the material of the transparent substrate 2. Preformat pattern (guide groove 4
The signal surface 2a can be formed by spreading a photocurable resin between the mold and the mold in which the inverted pattern of the pre-pit rows 5) is formed, and transferring this resin layer onto the transparent substrate 2. Further, when the transparent substrate 2 is formed of a thermoplastic material, the signal surface 2a can be formed on one side when the transparent substrate 2 is injection molded.

On the signal surface 2a of the transparent substrate 2, as shown in FIGS. 1 and 2, a spiral or concentric guide groove 4 is formed around the center hole 1, and adjacent guide grooves 4 are formed around the center hole 1.
A pre-pit row 5 is formed between them.

The cross-sectional shape of the guide groove 4 is approximately triangular, as shown in FIG. 3, and the cross-sectional shape of each prepit 6 constituting the prepit row 5 is approximately trapezoidal, as shown in the same figure. be done. Here, the term "nearly triangular" is a general term for grooves whose opening width gradually becomes narrower from the opening to the bottom, and which has no flat surface at the bottom, and also includes grooves whose edges are not formed in an acute angle shape. It will be done. Also, what is a trapezoid?
A general term for grooves that have a flat bottom, and includes grooves that do not have sharp edges.

The guide groove 4 has a line width W of 0.4 to 0.5 μm, and a pitch p of 1.0 to 1.5 μm. In addition, the depth dl is the wavelength of the reproduction light λ, and the transparent substrate 2
When the refractive index of is n, (λ/10n to λ/16n)
X (1,5-1.6) is formed.

On the other hand, the width S of the pre-pit 6 is equal to the width S of the reproduction light spot 7.
is formed to have a diameter of φ/3 to φ/4, and its depth D is λ, where the wavelength of the reproduction light is λ.

When the refractive index of the transparent substrate 2 is n, λ/3.3n~λ
/3.8n.

The thin film layer 3 can be formed using an appropriate heat mode recording material depending on the type of optical information recording medium, such as a perforated type, magneto-optical type, or phase change type. Also, regarding the film structure of this thin film layer 3.

It can be adjusted as appropriate depending on the recording film material.

For example, a perforated recording film can be formed with a two-layer structure of an underlayer film for improving recording sensitivity and a recording film, and a magneto-optical recording film can be formed with an enhancement film, a magneto-optical recording film, and a protective film. It can have a four-layer structure consisting of one reflective film and one reflective film.

Next, a second embodiment of the present invention will be described based on FIG. 4.

FIG. 4 is an enlarged sectional view of a main part of an optical information recording medium according to a second embodiment, as shown in this figure.

In the optical information recording medium of this embodiment, the guide groove 4 has a substantially trapezoidal cross-sectional shape. The meaning of the substantially trapezoidal shape is the same as that explained in the first embodiment.

The depth d2 of this guide groove 4 is λ/10 n to λ, where λ is the wavelength of the reproduction light and n is the refractive index of the transparent substrate.
/16n.

In addition, the line width and pitch of the guide grooves 4, the width and depth of the pre-pits 6, the substrate material, the means for forming the signal surface, etc. are formed in the same manner as in the optical information recording medium of the first embodiment.

FIG. 5 shows the optical information recording medium of the first embodiment type (track pitch is 1.0 to 1.5 μm, the cross-sectional shape of the guide groove is approximately triangular) when the depth of the guide groove is varied. Shows changes in add-on pit crosstalk level. However, during measurement, the signal is written with the center position of the light spot off-track by 0.1 μm in one direction from the center of the land portion, and then off-track by 0.1 μm in the opposite direction to this off-track direction. The tracked light spot (wavelength: 780 nm) was focused by an objective lens with NA of 0.55, and signals were read out.

As is clear from this figure, in the optical information recording medium of the first embodiment type, the depth of the guide groove is λ/17nX (1,5~
1.6) The following and the guide groove depth is λ/9nX
(1,5~1.6) or more, about -30d
There is a crosstalk of about B, whereas the guide groove depth is (λ/10n to λ/16n)X (1,5 to 1.6).

Crosstalk is reduced to about -32 to -32.5 dB.

Due to the design of the recording/reproducing device, if the crosstalk exceeds -30 dB, it becomes difficult to read out a normal signal, but since the optical information recording medium of the first embodiment has a crosstalk of -32 dB or less, variations are taken into account. Even if it does, the crosstalk is 130
Stable recording/reproduction can be performed without exceeding dB.

Furthermore, as shown in this figure, the track pitch is 1.6μ.
In a conventional optical information recording medium in which the guide groove has a substantially triangular cross-sectional shape and a depth of λ/8n, the crosstalk level of the add-on pit is -33.5m.
It can be suppressed to about dB. However, the measurement conditions at this time were that the wavelength of the reproduction light was 830 nm and the NA of the objective lens was 0.50.

FIG. 6 shows the optical information recording medium of the second embodiment type (track pitch is 1.0 to 1.5 μm, the cross-sectional shape of the guide groove is approximately trapezoidal) when the depth of the guide groove is varied. The test conditions showing the change in the crosstalk level of the add-on bits are the same as in the case of the first embodiment type described above.

As is clear from this figure, in the optical information recording medium of the first embodiment type, the depth of the guide groove is λ/17n or less, and the depth of the guide groove is λ/11n or more. While there is a crosstalk of about -30dB,
The depth of the guide groove is λ/10n to λ/16n,
It can be seen that the crosstalk has decreased to about -32 dB, and that the same effect as the optical information recording medium of the first example is achieved.

Furthermore, as shown in this figure, the track pitch is 1.6μ.
m, the cross-sectional shape of the guide groove is approximately trapezoidal, and its depth is λ
/ 8n, the wavelength of the reproduction light is 830nm, and the NA of the objective lens is 0.
．． 50, the crosstalk level of add-on bits can be suppressed to about -33.5 dB.

FIG. 7 shows changes in the tracking signal level when the depth of the guide groove is variously changed for the optical information recording medium of the first embodiment type.

As is clear from this figure, in the optical information recording medium of the first embodiment type, the depth of the guide groove is approximately λ/8nX (1
, 5 to 1.6), the tracking signal level reaches its maximum, and the depth of the guide groove is set to λ/16 n
, 5 to 1, 6), the tracking signal level drops to about 65%. However, in general recording/playback devices, the tracking signal level is 60
% or more, normal tracking control can be performed, so set the depth of the guide groove to (λ/10n to λ/16n)
(1.5 to 1.6) does not cause any problem in signal recording/reproduction.

FIG. 8 shows changes in the tracking signal level when the depth of the guide groove is variously changed for the optical information recording medium of the second embodiment type.

As is clear from this figure, also in the optical information recording medium of the second embodiment type, the depth of the guide groove is λ/10n~
By forming it to λ/16n, a tracking signal level of 65% or more can be ensured.

Figure 9 shows the modulation degree when the pre-pit depth is varied for an optical information recording medium formed with a track pitch of 1.5 μm and an optical information recording medium formed with a track pitch of 1.6 μm. However, for optical information recording media with a track pitch of 1.6 μm, the wavelength is 7
For an optical information recording medium with a track pitch of 1.6 μm, signals are reproduced using an optical head equipped with a reproduction light of 80 nm and an objective lens with an NA of 0.55.

Signals were reproduced using a reproduction light having a wavelength of 830 nm and an optical head equipped with an objective lens having an NA of 0.50.

As is clear from this figure, the track pitch is 1.6μ
The optical information recording medium formed to have a pre-pit depth of λ
/4n (where λ is the wavelength of the reproduction light and n is the refractive index of the transparent substrate), the degree of modulation of the reproduced signal becomes maximum (
(approximately 85%), whereas the track pitch is 1.5μ
In the optical information recording medium formed to have a pre-pit depth of λ/3.3n to λ/3.8n, the modulation degree of the reproduced signal becomes maximum (approximately 80 to 85%).

Based on this test result, the track pitch has been narrowed, and the wavelength of the reproduction light used has been shortened accordingly, resulting in a large NA.
For optical information recording media in which signals are reproduced using an optical head equipped with an objective lens, the pre-pit depth is λ
/4n (where λ is the wavelength of the reproduction light and n is the refractive index of the transparent substrate).

In the above embodiments, only a write-once type optical information recording medium has been described, but the present invention can be implemented in the same manner also for a read-only optical information recording medium.

Furthermore, in the above embodiments, an optical disk using the so-called on-land recording method, in which signals are recorded between adjacent guide grooves, was explained as an example, but an optical disc using the so-called in-group recording method, in which signals are recorded overlappingly on the guide grooves, was explained as an example. The same method can be applied to optical discs as well.

Furthermore, although the above embodiments have been described using an optical disk as an example, the present invention can be implemented in the same manner with other optical information recording media such as an optical card.

〔Effect of the invention〕

As explained above, in the optical information recording medium of the present invention, the depth of the guide groove is appropriately adjusted according to the cross-sectional shape and pitch of the guide groove, so that crosstalk becomes excessive and the tracking signal level becomes too low. Therefore,
An optical information recording medium with high recording density and low crosstalk can be provided.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining the first embodiment of the present invention, in which FIG. 1 is a plan view of an optical information recording medium, FIG. 2 is an enlarged plan view of main parts, and FIG. is an enlarged sectional view of the main part. FIG. 4 is an enlarged sectional view of a main part of an optical information recording medium according to a second embodiment. 5 to 9 are diagrams for explaining the present invention in detail, and FIGS. 5 and 6 are graphs showing the relationship between guide groove depth and add-on pit crosstalk, and FIG. FIG. 8 is a graph showing the relationship between guide groove depth and tracking signal level, and FIG. 9 is a graph showing the relationship between track pitch, pit depth, and modulation degree. 2...Transparent substrate, 2a...Signal surface 2a
, 3... thin mm, 4... guide groove, 5...
...Pre-pit row, 601. ...Pripit,
7... Light spot for reproduction. Fig. 1 Fig. 4 Fig. 4 Indoor groove III) Depth (nm) <Xt, S~1. b) Figure: Depth of the indoor groove (nm) Figure 8: Depth of the inner groove of τ

Claims (6)

[Claims] (1) In an optical information recording medium in which a thin film layer including at least a recording film or a reflective film is laminated on a signal surface of a transparent substrate having guide grooves and pre-pit arrays arranged at a constant pitch, a cross section of the guide grooves is provided. The depth of the guide groove is ( An optical information recording medium characterized in that it is formed to have a size of λ/10n to λ/16n)×(1.5 to 1.6). (2) In an optical information recording medium in which a thin film layer including at least a recording film or a reflective film is laminated on a signal surface of a transparent substrate having guide grooves and pre-pit arrays arranged at a constant pitch, a cross section of the guide grooves is provided. The depth of the guide groove is λ, where the shape is approximately trapezoidal, the pitch of the guide groove is 1.0 to 1.5 μm, the wavelength of the reproduction light is λ, and the refractive index of the transparent substrate is n. An optical information recording medium characterized in that the optical information recording medium is formed to have an angle of /10n to λ/I6n. (3) The optical information recording medium according to claim 1 or 2, wherein the pre-pit rows are formed between adjacent guide grooves. (4) The optical information recording medium according to claim 1 or 2, wherein the pre-pit row is formed to overlap the guide groove. (5) A thin film layer containing at least a recording film or a reflective film is laminated on the signal surface of a transparent substrate having guide grooves arranged at a constant pitch and pre-pit rows formed between adjacent guide grooves. In the on-land recording type optical information recording medium, the cross-sectional shape of the guide groove is approximately triangular, the pitch of the guide groove is 1.0 to 1.5 μm, and the wavelength of the reproduction light is λ, and the transparent substrate An optical information recording medium characterized in that the depth of the guide groove is (λ/10n to λ/16n)×(1.5 to 1.6), where n is the refractive index of the guide groove. (6) A thin film layer containing at least a recording film or a reflective film is laminated on the signal surface of a transparent substrate having guide grooves arranged at a constant pitch and pre-pit rows formed between adjacent guide grooves. In the on-land recording type optical information recording medium, the cross-sectional shape of the guide groove is approximately trapezoidal, the pitch of the guide groove is 1.0 to 1.5 μm, and the wavelength of the reproduction light is λ, and the transparent substrate An optical information recording medium characterized in that the guide groove has a depth of λ/10n to λ/16n, where n is the refractive index of the optical information recording medium.