JP2000276769A - Information recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable errors to be decreased and stable performance to be maintained by using a recording medium having a fluctuation in the reflection factor of the recording medium to laser light having a wavelength shifted within the range of specified values with the wavelength of laser light as the center being within the range of specified values with the factor of reflection to the laser light of a predetermined wavelength as the center as an information recording medium. SOLUTION: This recording medium is the one that has a fluctuation in the reflection factor of laser light having the wavelength shifted within the range of ±3% with the wavelength of laser light as the center being within the range of ±10% with the reflection factor of laser light having the predetermined wavelength as the center. As a substrate, a plastic substrate is used and the surface of a side to form a recording layer is coated with a base paint layer while using polymethyl methacrylate or acrylic acid/methacrylic acid copolymer, for example. A tracking guide is arranged on the substrate, the recording layer containing coloring matters capable of recording and reproducing information with laser light is formed thereon and a reflecting layer composed of a metal is formed thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium capable of recording (writing) and reproducing (reading) information using a laser beam having a high energy density, and more particularly to a laser used for recording and reproducing information. The present invention relates to an information recording medium having a stable and excellent performance with a small variation in performance with respect to a variation in light wavelength, and an optical information recording / reproducing method for recording and reproducing information on and from the medium by light.

[0002]

2. Description of the Related Art In recent years, information recording media using high energy density beams such as laser beams have been developed and put into practical use. This information recording medium is called an optical disk, and is used as a video disk, an audio disk, a large-capacity still image file, a large-capacity computer disk memory, and the like.

The optical disk has a basic structure such as a disk-shaped substrate made of glass, synthetic resin, or the like, and a metal or metalloid such as Bi, Sn, In, Te, etc. provided on the disk-shaped substrate; A recording layer made of a dye such as quinone. Incidentally, the surface of the substrate on which the recording layer is provided is usually provided with a view to improving the flatness of the substrate, improving the adhesive force with the recording layer, or improving the sensitivity of the optical disc.
An intermediate layer made of a polymer substance is often provided.

For the purpose of improving the durability of the information recording medium, a protective layer is provided on the recording layer, or the recording layer is formed on at least one of the two disc-shaped substrates as a disk structure. And an air sandwich structure in which the two substrates are joined via a ring-shaped inner spacer and a ring-shaped outer spacer so that the recording layer is located on the inside and forms a space. . In an optical disk provided with such a protective layer or an optical disk having an air sandwich structure, the recording layer does not come into direct contact with the outside air, and information is recorded and reproduced by laser light transmitted through the substrate. This has the advantage that it does not suffer physical or chemical damage, or dust adheres to its surface and does not hinder the recording and reproduction of information.

[0005] Recording of information on the optical disk and reproduction of information from the optical disk are usually performed by the following method. Recording of information is performed by irradiating the optical disk with a laser beam. The irradiated portion of the recording layer absorbs the light and locally raises the temperature, causing a physical or chemical change (for example, a pit change). Generation) occurs,
Information is recorded by changing its optical properties.
The reproduction of information is also performed by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected light or transmitted light corresponding to a change in the optical characteristics of the recording layer.

[0006] As a recording material for forming the recording layer of such an information recording medium, metals and dyes are known as described above. Information recording media using dyes have advantages in the characteristics of the recording medium itself, such as high sensitivity compared to recording materials such as metals, and in addition, the recording layer can be easily formed by a coating method. It has the great advantage above. However, a recording layer made of a dye generally has a drawback that it is difficult to obtain a low reflectance or a high C / N.

[0007] Recording of information on a recording layer made of a dye is performed by forming pits in the dye recording layer.
As described above, dyes have high sensitivity, but require relatively large recording power to form complete pits. That is, since a large recording power is required to obtain a recording signal with a high C / N, it is often difficult to say that the sensitivity is really high. Further, in order to improve the low reflectance, which is a drawback of the dye recording layer, when a reflective layer is provided,
There is a problem that formation of pits in the dye recording layer becomes more difficult.

Further, the dyes used in the dye recording layer generally change in reflectance and transmittance depending on the wavelength of laser light used for recording and reproducing information. The dye that is used is such that the change in reflectance falls within a specific range (for example, a range of ± 10%) centered on the reflectance at a predetermined (predetermined) wavelength of the laser light. The range of wavelength variation was very narrow, generally within about ± 2% around a predetermined (predetermined) wavelength. That is, if the wavelength of the laser beam used for recording and reproducing information deviates from the range of about ± 2%, the reflectance of the dye recording layer of the information recording medium greatly changes. Therefore, when the wavelength of the laser beam used for recording or reproducing information slightly deviates from a predetermined (predetermined) wavelength, the reflectivity of the dye recording layer of the information recording medium is greatly reduced. In some cases, errors in reproduction may occur, and in severe cases, recording and / or reproduction of information may become impossible.

[0009]

According to the present invention, a recording layer containing a dye is provided on a substrate, the fluctuation of the performance is small with respect to the fluctuation of the wavelength of laser light used for recording and reproducing information, Errors during recording and reproduction are reduced, stable and excellent performance, the allowable range of the wavelength of the laser beam used is wide, and there are few things that become off-grade,
Another object of the present invention is to provide an information recording medium that can be manufactured with high productivity. Further, the present invention provides a method for recording information on the information recording medium with almost no error by light.
An object of the present invention is to provide an optical information recording / reproducing method for reproducing.

[0010]

According to the present invention, there is provided a dye recording layer capable of recording and reproducing information with a laser beam of a predetermined wavelength on a disk-shaped substrate provided with a tracking guide on the surface thereof, An optical information recording / reproducing method comprising: irradiating the laser beam on the information recording medium on which the reflective layer composed of the protective layer and the protective layer are laminated in this order to record the information; and then reproducing the recorded information. In the information recording medium, a change in the reflectance of the recording medium with respect to a laser beam having a wavelength shifted within a range of ± 3% around the wavelength of the laser beam is the predetermined value. An information recording / reproducing method is characterized by using a recording medium within a range of ± 10% with respect to a reflectance to a laser beam having a wavelength.

The preferred embodiments of the information recording medium used in the present invention are as follows. 1) An information recording medium in which a shift range of a laser beam having a wavelength shifted around the wavelength of the laser beam is within a range of ± 5%. 2) The dye in the recording layer is a cyanine dye, an azulenium dye, a squarylium dye, a phthalocyanine dye, a pyrylium dye, a thiopyrylium dye, an indophenol dye, an indoaniline dye, a triphenylmethane dye, or a quinone dye. Reflection of the recording medium with respect to a laser beam having a wavelength that is selected from an aminium-based dye, a diimmonium-based dye, a metal complex salt-based dye, and the like and is shifted within a range of ± 3% around the wavelength of the laser light. An information recording medium comprising one or more dyes capable of changing the rate within a range of ± 10% around the reflectance for the laser light having the predetermined wavelength.

3) The recording layer further comprises a metal complex dye in an amount of from 0.001 to 1 mol part of the above dye or dye mixture.
An information recording medium containing 0.2 mole parts. 4) An information recording medium in which the thickness of the recording layer is in the range of 500 to 2000 °. 5) The reflection layer is made of Au, Ag, Cu, Pt, Cr, Ti,
It is made of at least one metal or alloy selected from the group consisting of Al and stainless steel.

6) The thickness of the reflection layer is 500-2000 °
Information recording medium in the range of. 7) An information recording medium in which a protective layer is provided on a reflective layer. 8) An information recording medium in which the material of the substrate is polycarbonate, polyolefin or cell cast polymethyl methacrylate. 9) The predetermined wavelength of the laser light is 780 to 830
Information recording medium in the range of nm.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The information recording medium of the present invention has a basic structure in which a recording layer containing one or more dyes having specific properties and a reflective layer are sequentially provided on a disc-shaped substrate.

The substrate is preferably a substrate made of plastic, and this plastic can be arbitrarily selected from various materials used as substrates for conventional information recording media. Substrate optical properties, flatness,
From the viewpoints of workability, handling, stability over time, and production cost, examples of the substrate material include acrylic resins such as cell cast polymethyl methacrylate and injection molded polymethyl methacrylate; polyvinyl chloride, vinyl chloride copolymer, and the like. Epoxy resin, polycarbonate resin, amorphous polyolefin and polyester. Preferred are polycarbonate, polyolefin and cell cast polymethyl methacrylate.

An undercoat layer may be provided on the surface of the substrate on which the recording layer is provided, for the purpose of improving flatness, improving adhesion, improving solvent resistance of the substrate, and preventing deterioration of the recording layer. Good. As a material of the undercoat layer, for example, polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleic anhydride copolymer, polyvinyl alcohol,
N-methylol acrylamide, styrene / sulfonic acid copolymer, styrene / vinyl toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, Polymeric substances such as ethylene / vinyl acetate copolymer, polyethylene, polypropylene and polycarbonate; organic substances such as silane coupling agents; and inorganic oxides (SiO ₂ , Al ₂ O
₃ ) and inorganic substances such as inorganic fluorides (MgF ₂ ).

The undercoat layer is prepared, for example, by dissolving or dispersing the above-mentioned materials in an appropriate solvent to prepare a coating solution, and then applying the coating solution to the substrate by a coating method such as spin coating, dip coating, or extrusion coating. It can be formed by coating on the surface. The thickness of the undercoat layer is generally in the range of 0.005 to 20 μm, preferably
It is in the range of 1 to 10 μm.

A tracking guide is provided on the substrate (or undercoat layer). That is, a pre-groove layer and / or a pre-pit layer are generally provided for the purpose of forming irregularities representing information such as tracking grooves or address signals. As a material for the pregroove layer and the like, a mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester and tetraester and a photopolymerization initiator can be used.

In order to form the pre-groove layer, first, a mixed solution comprising the above-mentioned acrylate and the polymerization initiator is applied onto a precisely formed master (stamper). After mounting, a method of curing the liquid layer by irradiating ultraviolet rays through the substrate or the matrix to fix the substrate and the liquid layer, and then peeling the substrate from the matrix, a method can be used. A substrate on which a pre-groove layer is formed is obtained by the method. The thickness of the pre-groove layer is generally in the range of 0.05 to 100 μm, preferably 0.1 to 100 μm.
It is in the range of 1 to 50 μm. When the substrate material is plastic, pregrooves and / or prepits may be provided directly on the substrate by injection molding or extrusion molding.

On a tracking guide provided on a substrate, a recording layer containing a dye capable of recording (writing) and reproducing (reading) information by a laser beam is provided, and a recording layer made of metal is further provided thereon. The layers are provided, and constitute the information recording medium of the present invention. The present invention is particularly characterized in that the dye in the recording layer and the reflective layer are provided on the dye recording layer.

That is, the dye of the recording layer of the information recording medium of the present invention has a reflectance of the information recording medium with respect to a laser beam having a wavelength shifted within a range of ± 3% around the wavelength of the laser beam. Can be set to fall within a range of ± 10% around the reflectance for the laser light having the predetermined wavelength.

Further, in the information recording medium of the present invention,
The change in the reflectance of the information recording medium with respect to the laser light having a wavelength shifted within a range of ± 5% around the wavelength of the laser light is caused by the reflection with respect to the laser light having the predetermined wavelength. It is preferable to be within a range of ± 10% around the rate.

In the present specification, the reflectance of the information recording medium is a value measured by a normal specular reflection measurement method.

In an information recording medium having a recording layer containing a dye as described above and a reflective layer provided thereon,
Even if the reflectivity of the medium changes due to a change in the reflectivity of the dye, etc., if the changed reflectivity is within a range of ± 10% of a predetermined reflectivity, an error in recording and reproducing information is substantially reduced. Does not occur. However, the laser light generally used for recording and reproducing information varies in a range of about ± 3% around the set wavelength, and the dye of the dye responds to the change in the wavelength of the laser light. The reflectance fluctuates, and accordingly, the reflectance of the recording layer of the information recording medium also fluctuates. As in the case of a conventionally known information recording medium, when the reflectance greatly changes (for example, more than ± 10%) in response to a very small change in the wavelength of the laser beam (for example, in a range of ± 2%), An error will occur when recording or reproducing information.

In the information recording medium of the present invention, the change in the reflectance of the information recording medium with respect to the laser light having a wavelength shifted within a range of ± 3% around the wavelength of the laser light used for recording / reproduction. Are manufactured so as to be within a range of ± 10% around the reflectance with respect to the laser light having the predetermined wavelength. In other words, the variation range of the reflectance is the reflection at the predetermined wavelength. Since the range of the variation of the wavelength of the laser beam falling within the range of ± 10% of the ratio is a wide range of ± 3% of the predetermined wavelength of the laser beam used for recording and reproduction. In addition, even when a laser beam having a wavelength that is generally used for recording and reproducing information is used, the recording and reproduction of information can be reliably performed without errors.

In the information recording medium of the present invention, the center of the wavelength of the laser beam having the predetermined wavelength is ± 5%.
% (Particularly within the range of ± 10%), the change in the reflectance of the information recording medium with respect to the laser light having a wavelength shifted from the reflectance with respect to the laser light having the predetermined wavelength. Is preferably within a range of ± 10% from the center.

In the information recording medium of the present invention, although the influence is not so large as the reflectance of the dye, the fluctuation of the transmittance with respect to the fluctuation of the wavelength of the laser beam also affects the performance of the information recording medium.

Dyes having the above-mentioned properties used in the recording layer of the information recording medium of the present invention include, for example, cyanine dyes, azurenium dyes and squalilium dyes,
Selected from phthalocyanine dyes, pyrylium dyes, thiopyrylium dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, quinone dyes, aminium dyes, diimmonium dyes, metal complex salt dyes (ie, And the reflectance of the information recording medium with respect to the laser light having a wavelength shifted within a range of ± 3% around the wavelength of the laser light. ± 1 around the reflectance for the laser light of the predetermined wavelength.
It is a dye that can be brought into the range of 0%, and may be a single dye or a mixture of two or more dyes.

As a single dye having the above-mentioned properties, for example, a dye represented by the following formula (I) can be mentioned.

[0030]

Embedded image

The dye represented by the formula (I) is 740-
For a wavelength in the range of 870 nm (805 nm ± 8%), when gold is laminated as a reflective layer, the reflectance is 74%.
% To 90% (82% ± 10%).

When a cyanine dye is used, it is preferable to use the above metal complex dye or an aminium / diimmonium dye together as a quencher.
In this case, it is preferable that a metal complex salt dye or the like is contained as a quencher in an amount of 0.001 to 0.2 mol part based on 1 mol part of the total dye.

The recording layer is formed by dissolving the dye and, if desired, a binder in a solvent to prepare a coating solution, and then applying the coating solution to the substrate surface to form a coating film and then drying. Can be performed.

Solvents for preparing the dye coating solution include esters such as ethyl acetate, butyl acetate and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; dichloromethane;
-Dichloroethane, halogenated hydrocarbons such as chloroform, ethers such as tetrahydrofuran, ethyl ether and dioxane, ethanol, alcohols such as n-propanol, isopropanol and n-butanol, amides such as dimethylformamide, and the like, 2,2,3 Fluorinated solvents such as 3-tetrafluoropropanol can be exemplified. In addition, these non-hydrocarbon organic solvents,
As long as the content is within 50% by volume, it may contain a hydrocarbon solvent such as an aliphatic hydrocarbon solvent, an alicyclic hydrocarbon solvent, or an aromatic hydrocarbon solvent.

Various additives such as an antioxidant, a UV absorber, a plasticizer and a lubricant may be further added to the coating solution according to the purpose.

When a binder is used, the binder may be
For example, cellulose derivatives such as gelatin, nitrocellulose and cellulose acetate; natural organic high molecular substances such as dextran, rosin and rubber; and hydrocarbon resins such as polyethylene, polypropylene, polystyrene and polyisobutylene, polyvinyl chloride and polyvinylidene chloride , Vinyl resins such as polyvinyl chloride / polyvinyl acetate copolymer, acrylic resins such as polymethyl acrylate and polymethyl methacrylate, polyvinyl alcohol, chlorinated polyolefin, epoxy resin, butyral resin, rubber derivatives, phenol / formaldehyde Synthetic organic polymer substances such as a precondensate of a thermosetting resin such as a resin can be used.

Examples of the coating method include a spray method, a spin coating method, a dip method, a roll coating method, a blade coating method, a doctor roll method, and a screen printing method. In order to form a favorable alignment state of the dye, it is preferable to use a spin coating method. Further, at the time of spin coating, the rotation speed of the spinner is set to 500 to 500.
0r. p. m. And the drying time is 1-60.
It is preferable to carry out in a range of seconds in order to promote good orientation of the dye.

When a binder is used in combination as a material for the recording layer, the ratio of the dye to the binder is generally 0.01 to 9%.
9% (weight ratio), preferably 1.0 to 95%
% (Weight ratio).

The thickness of the dye recording layer is generally from 200 to 30.
00 °, preferably in the range of 500-2000 °.

In the information recording medium of the present invention, a reflection layer is provided on the recording layer. By providing the reflective layer, the effect of improving the reflectance, the S / N at the time of reproducing information, and the effect of improving the sensitivity at the time of recording can be obtained.

As a material of the reflection layer, Mg, Se, Y,
Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W,
Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, I
r, Pt, Cu, Ag, Au, Zn, Cd, Al, G
a, In, Si, Ge, Te, Pb, Po, Sn, Bi
And metal and semimetals. Further, an alloy such as stainless steel may be used. In the present invention,
High thermal conductivity at a temperature of 400K, at least 10
It is preferable to provide a reflective layer made of a metal of w / mk or more. Thereby, the heat when the dye recording layer is irradiated with the laser beam can be rapidly transmitted to the reflection layer.
Among these, Au, Ag, Cu, Pt, Al, Cr,
Ni and stainless steel are particularly preferred. These substances may be used alone, in combination of two or more, or as an alloy.

The reflection layer can be formed on the dye recording layer, for example, by vapor deposition, sputtering or ion plating of a light-reflective substance. The thickness of the reflective layer is generally in the range of 100-3000 °, preferably in the range of 500-2000 °.

On the reflective layer, a protective layer is provided for the purpose of physically and chemically protecting the recording layer and the entire information recording medium. This protective layer also has the effect of increasing the scratch resistance and moisture resistance on the side of the substrate where the recording layer is not provided.

Examples of materials used for forming the protective layer include inorganic substances such as SiO, SiO ₂ , Si ₃ N ₄ ,
MgF ₂ , SnO _{2 and the} like can be given. Examples of the organic substance include a thermoplastic resin, a thermosetting resin, a UV-curable resin, and the like, and a UV-curable resin is preferable. In the present invention, a remarkable effect can be obtained when the above substance is provided by coating. This is particularly effective when the organic substance is provided by coating.

That is, it can also be formed by dissolving a thermoplastic resin, a thermosetting resin, or the like in an appropriate solvent to prepare a coating solution, applying the coating solution, and drying. In the case of a UV-curable resin, it can also be formed by preparing a coating solution as it is or by dissolving it in an appropriate solvent, applying the coating solution, and irradiating with UV light to cure. UV curable resins include (meth) acrylate oligomers such as urethane (meth) acrylate, epoxy (meth) acrylate, and polyester (meth) acrylate, monomers such as (meth) acrylate, and further photopolymerization. Usual UV curable resins such as initiators can be used. These coating solutions further contain an antistatic agent, an antioxidant,
Various additives such as a V absorbent may be added according to the purpose. In the present invention, it is preferable to use a UV curable resin.

The thickness of the protective layer is generally 0.1 to 100 μm.
m.

In addition to the above, the protective layer can be formed, for example, by laminating a film obtained by extrusion of a plastic on the dye recording layer via an adhesive layer. Alternatively, it may be provided by a method such as vacuum deposition, sputtering, or coating.

[0048]

[Example 1] The following structural formula:

[0049]

Embedded image

Is dissolved in 2,2,3,3-tetrafluoropropanol to form a coating solution for a recording layer (dye concentration:
2.0% by weight). Disc-shaped polycarbonate substrate provided with a tracking guide (outer diameter: 130 m
m, inner diameter: 15 mm, thickness: 1.2 mm, track pitch: 1.6 μm, groove depth: 800 °). p.
m. And dried for 30 seconds to a film thickness of 1300
The dye recording layer of Å was formed. Au is placed on the dye recording layer.
Was subjected to DC sputtering to form a reflection layer having a thickness of 1300 °.

On the reflective layer, a UV curable resin (trade name: 3070, manufactured by Three Bond Co.) was used as a protective layer by spin coating at a rotational speed of 850 rpm. p. m. After coating at a speed of, an ultraviolet ray was irradiated from a high-pressure mercury lamp and cured to form a protective layer having a thickness of 3 μm. Thus, an information recording medium comprising a substrate, a recording layer, a reflective layer and a protective layer was manufactured.

The obtained information recording medium was subjected to a wavelength of 780 nm using a spectrophotometer according to the following evaluation method.
At m, 805 nm and 830 nm, fresh reflectance and C / N were measured. Table 1 shows the results.

[Evaluation of Information Recording Medium] A semiconductor laser beam of a predetermined wavelength (805 nm) was used for the information recording medium, at a constant linear velocity of 1.3 m / sec, at a recording power of 6 mW, and at a modulation frequency of 720 kHz. A single signal (duty: 33%) was recorded.

(Reflectance) The fresh reflectance obtained above corresponds to the reflectance in the area where no pits are formed on the information recording medium after recording. .

(C / N) The information recorded under the above conditions is
Read power 0.5m using laser light of wavelength 780nm
At W and a constant linear velocity of 1.3 m / sec, the ratio (C / N) of the carrier and noise output levels was measured with a spectrum analyzer (RBW: 10 kHz, VBW: 100 Hz).

[Comparative Example 1] A dye was represented by the following structural formula:

[0057]

Embedded image

And a dye concentration of 2.7.
The coating solution for the recording layer was prepared by changing the coating solution to 5% by weight, and the number of revolutions at the time of coating by the spin coating method was 1,000 rpm. p. m. An information recording medium was manufactured in the same manner as in Example 1 except that the above was changed.

Example 1 of the obtained information recording medium
The evaluation was performed in the same manner as in the above. Table 1 shows the results.

[0060]

[Table 1] Table 1 {Reflectance C / N} ────────────────────────────────── Laser wavelength 780 nm 805 nm 830 nm 780 nm ────────── {Example 1 79% 82% 85% 52dB Comparative Example 1 67% 80% 91% 51dB} ────────────────────────────────

As is clear from the results shown in Table 1, when the wavelength of the laser beam fluctuates 805 nm ± about 3%, the reflectance of the information recording medium obtained in Comparative Example 1 is -80%. While the value fluctuated in the range of 16.3% to + 13.8%, the reflectance of the information recording medium obtained in Example 1 was -3.7% to + 3.7%, compared to 82%. , And the variation range of the reflectance is extremely small. Also,
For C / N, a predetermined wavelength (805 nm)
The information recording medium obtained in Example 1 is superior to the information recording medium obtained in Comparative Example 1 when reproduction is performed with a shorter laser beam having a wavelength of 780 nm.

[0062]

According to the information recording medium of the present invention, the fluctuation of the reflectance with respect to the fluctuation of the wavelength of the laser beam used for recording and reproducing information is small, and the error in recording or reproducing information is reduced. An information recording medium which has excellent performance, and has a remarkably excellent effect that it can be manufactured with high productivity with few off-grades due to the wide allowable range of the wavelength of laser light used.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masao Yabe 200 Fujinaka Film Co., Ltd., Fujinomiya-shi, Shizuoka Prefecture (72) Inventor Mitsuru Sawano 200 200 Onakazato Fujinaka City, Fujinomiya-shi, Shizuoka Fuji Photo Film Co., Ltd.

Claims (1)

[Claims] 1. A dye recording layer capable of recording and reproducing information with a laser beam of a predetermined wavelength, a reflective layer made of metal, and a protective layer on a disk-shaped substrate provided with a tracking guide on the surface. After recording the information by irradiating the laser light on the information recording medium laminated in this order,
An optical information recording / reproducing method for reproducing recorded information, comprising: as an information recording medium, a laser beam having a wavelength shifted within a range of ± 3% around the wavelength of the laser beam. An information recording / reproducing method using a recording medium in which the variation of the reflectance of the recording medium is within a range of ± 10% around the reflectance for the laser beam of the predetermined wavelength. .