JP2001325727A - Optical information recording/reproducing method of write once optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that an error rate is increased with the enlargement of the succeeding recoding mark or the deviation of the center position to the front side for time-wise continuously formed recording marks adjacent to each other by the generation of the thermal interference due to the remaining heat in the formation process of the preceding recording mark affecting the formation process of the succeeding recording mark. SOLUTION: The problem is solved in such a manner that the inequality of (1/21)Pw<Pb<(1/14)Pw is satisfied when a laser power (recording power) at the time of forming the recording mark is taken as Pw and a laser power (bias power) at the time of forming the space is taken as Pb, and further, when a laser power (reproduction power) at the time of reproducing the recording information is taken as Pr, the inequality of (1/21)Pw<Pr<(1/7)Pw is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing method for a write-once optical recording medium, and more particularly to a recording / reproducing method using a large-capacity optical information recording medium.

[0002]

2. Description of the Related Art With the advent of the advanced information age, optical recording media have been attracting attention as recording media capable of handling various types of information. Optical recording media are classified into read-only optical recording media on which information cannot be written, write-once optical recording media on which information can be written only once, and rewritable optical recording media on which information can be rewritten any number of times. . Of these optical recording media, write-once optical recording media are suitable as storage media for public documents and important documents because information once recorded cannot be falsified. As one of such write-once optical recording media, for example, a CD-R (Compact Disc Recordable) which is a write-once CD is known.

A write-once type CD-R has a light absorbing layer made of an organic dye on a substrate, and can obtain an output signal conforming to the CD format when reproducing information. On the CD-R substrate, a pre-groove is formed in advance in a spiral or concentric shape for tracking. To record information on the CD-R, the organic dye constituting the light absorbing layer is decomposed or deteriorated by irradiating a laser beam along the pre-groove. As a result, a portion where the optical characteristics have changed due to a cavity or alteration is formed as a so-called recording mark in the recording light irradiation portion of the light absorbing layer in the pre-groove. When the reproduction light is irradiated along the pre-groove, a difference occurs in the light reflectance between the portion where the recording mark is formed and the portion where the recording mark is not formed. Is read.
The wavelength of the laser beam used for recording / reproducing a CD-R is usually 770 nm to 830 nm.

[0004] In recent years, there has been a demand for further increasing the storage capacity of a medium.
A method has been proposed in which the recording density is increased by shortening the wavelength of a laser beam used in recording and reproduction to reduce the beam spot diameter. DVDs (digital versatile discs) and DVD-Rs (digital versatile discs-recordable) have been proposed as high-density recording media according to this method (for example, Electronic Technology p10 August 1996). The wavelength of the laser beam used for recording / reproducing the DVD-R is 630 nm to 660 nm.

[0005] A pre-groove for tracking is formed in a spiral or concentric shape on a DVD-R substrate, and land pre-pits for address signals are provided between adjacent pre-grooves (lands). Are formed at intervals. The track pitch of the pre-groove of the DVD-R is 0.7 μm to 0.8 μm, which is extremely dense as compared with the track pitch of 1.6 μm of the CD-R.

[0006]

Therefore, in a DVD-R, even if adjacent recording marks formed successively in time are spatially separated from each other, the residual heat in the process of forming the preceding recording mark can be reduced. Causes a problem of affecting the subsequent formation process of recording marks, that is, a problem of thermal interference. The subsequent recording mark becomes large or its center position shifts forward due to the thermal interference effect. When such a recording mark is read, so-called jitter becomes large, which leads to an increase in the error rate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to enable accurate reproduction of recording marks and land prepits and to reduce jitter and error rates of recording signals. It is an object of the present invention to provide an optical information recording / reproducing method that can perform the above.

[0008]

According to the present invention, there is provided an optical information recording / reproducing method for a write-once optical recording medium comprising a light absorbing layer and a light reflecting layer provided on a substrate having pregrooves and prepits formed between the pregrooves. The following inequality (1/21) Pw <Pb, where Pw is a laser power (recording power) for forming a recording mark and Pb is a laser power (bias power) for forming a space. <(1/14) Pw (1) is satisfied, and when the laser power (reproduction power) for reproducing the recorded information is Pr, the following inequality (1/21) Pw <Pr <(1 / 7) Pw (2) an optical information recording and reproducing method, characterized by satisfying the, also the laser power to Pb _3TS, the more space 4T shape for forming the 3T space The laser power at the time of when the Pb _4TS, optical information recording and reproducing, characterized by satisfying the following inequality _{(1/21) Pw <Pb 3TS <} Pb 4TS <(1/14) Pw (3) Is the way.

FIG. 6 schematically shows changes in laser power in the recording / reproducing method of the present invention. FIG. 6 is a diagram showing the relationship between each laser power (vertical axis) and irradiation time (horizontal axis).
In FIG. 6, Pr is a reproducing power, and it is preferable that no decomposition or deterioration occurs even when the recording layer is repeatedly irradiated.
Pw is a recording power, and forms a portion where optical characteristics are changed, that is, a so-called recording mark, by decomposing or altering the organic dye in the recording layer. Pb is a bias power, which is a laser power irradiated when forming a space, and is a minimum laser power that can read a land pre-pit signal when forming a space during recording.
Further, Pb can be changed depending on the length of the space at the time of formation.

The write-once optical recording medium of the present invention is preferably formed such that c <a when the groove depth of the pre-groove is a and the maximum depth of the pre-pit is c. Since the bottom surface of the pre-pit is formed to be higher than the bottom surface of the pre-groove, the amount of light reflected from the pre-pit is smaller than the amount of light reflected from the pre-groove. Therefore,
Even if a part of the pre-pit is included in the reproduction light spot, it is prevented from being recognized as a part of the recording pit, and the recording pit can be appropriately reproduced regardless of the presence or absence of the pre-pit adjacent to the recording pit. it can. Therefore, the optical recording medium of the present invention can reduce jitter and block error rate. Considering that the function of the pre-pit cannot be obtained if the bottom surface of the pre-pit is too high, the depth c of the pre-pit is particularly preferably 50% to 98% of the maximum depth a of the pre-groove.

Further, it is preferable that the pre-pits are formed such that an edge of the pre-pits in a direction perpendicular to the pre-grooves projects from a bottom surface of the pre-pits. That is, when the depth of the edge of the prepit from the land surface in the direction perpendicular to the pregroove is b, it is preferable to form the prepit so as to satisfy b ≦ c <a.

FIGS. 2 and 3 are a schematic perspective view and a partially enlarged sectional view, respectively, of a sectional structure when the substrate is cut along a plane perpendicular to the longitudinal direction of the pre-groove (pre-groove direction) and including the pre-pits. In FIG. 3, in FIG. 3, the maximum depth a of the pre-groove 22 and the edges 23 and 2 of the pre-pit 21 are shown.
The depth b of 3 ′ and the depth (maximum depth) c of the central portion of the pre-pit 21 satisfy the inequality (1). The depth b of the edge of the prepit is 20% to 1% of the maximum depth c of the prepit.
00% is preferred.

Further, as shown in FIG.
A is the length of the edge 23 on the pregroove 22 side, B is the length of the edge 23 ′ on the pregroove 22 ′,
Let C be the length (maximum length) at the center of
It is preferable to form pre-pits so as to simultaneously satisfy 0 <A ≦ C and 0 <B ≦ C.

In the present invention, the lengths A and B of both edges 23 and 23 'of the prepit need not necessarily be the same.

For the substrate of the optical recording medium of the present invention, any material having light transmittance can be used. For example, a transparent resin material such as a polycarbonate resin or a polymethyl methacrylate resin can be used. The substrate can be manufactured, for example, by injection molding the transparent resin material using an injection molding machine equipped with a stamper on which a preformat pattern is formed. -Polymerization) method. The spacing between the tracking pre-grooves formed on at least one surface of the substrate is preferably 0.7 μm to 0.9 μm in order to increase the recording density. The groove depth of the pre-groove is set to 100 nm to 2 nm in order to obtain a reproduced signal amplified by utilizing the light interference effect.
It is desirable to set it to 50 nm.

The light absorbing layer of the optical recording medium of the present invention can be constituted by using a cyanine-based organic dye, an azo-based organic dye, or a dye obtained by mixing these organic dyes.
The light absorption layer can be formed by spin coating, vapor deposition, or the like, and a spin coating method using a solvent is particularly preferable. As a solvent used at the time of film formation, for example, ethyl cellosolve, methyl cellosolve, methanol, and tetrafluoropropanol can be used. The thickness of the light absorbing layer to be formed is preferably 20 nm to 200 nm. Further, a singlet oxygen quencher or the like may be contained in the light absorbing layer in order to prevent light deterioration of the cyanine dye used in the light absorbing layer.

In the optical recording medium of the present invention, the light reflection layer can be made of a metal such as Au, Ag, Cu, Al or an alloy containing them as a main component.
A film can be formed by sputtering, ion plating, or the like. The thickness of the light reflecting layer is 0.02 μm
０．５0.5 μm is preferred.

In the optical recording medium of the present invention, a protective layer can be further formed on the light reflecting layer. For the protective layer, an ultraviolet curable resin, an epoxy resin, an acrylic resin, a silicone resin, a urethane resin, or the like can be used. The thickness of the protective layer is preferably 0.1 μm to 100 μm, and 4 μm to 1 μm.
0 μm is even more preferred.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the optical recording medium according to the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic sectional view of one write-once optical recording medium according to the present invention. The write-once optical recording medium 100 includes a light absorbing layer 2 and a light reflecting layer 3 on a light transmitting substrate 1.
And a protective layer 4 are sequentially laminated. FIG. 5 shows a light-transmitting substrate made of injection-molded polycarbonate having a groove width of 320 nm, a groove depth of 170 nm, a track pitch of 0.74 μm, and a pregroove formed in a spiral shape having a diameter of 120 mm and a thickness of 0.6 mm. A substrate having a shape was used. Next, on the surface of the substrate having a pre-groove,
An azo organic dye represented by the following formula (I) was applied as a light absorbing layer to a thickness of 120 nm by spin coating. When applying the metal-containing azo organic dye, tetrafluoropropanol was used as a solvent.

[0021]

Embedded image

On this light absorbing layer, a silver target was attached to a sputtering device, and a silver reflecting layer was formed to a thickness of 120 nm. Further, on the silver reflection layer, a UV-curable resin SD-1700 (manufactured by Dainippon Ink and Chemicals) as a protective layer.
Was formed into a film having a thickness of 7 μm by spin coating. After forming the protective layer, the protective layer was cured by irradiating it with ultraviolet light having a predetermined light intensity using an ultraviolet irradiator.

The write-once optical recording medium manufactured as described above was irradiated with a laser beam having a wavelength of 635 nm by Pw = 8 mW, P
b _3TS = 0.4 mW, Pb _4TS = 0.45 mW, Pr =
The recording / reproducing characteristics were evaluated at 0.7 mW. Table 1 shows the results. 8.5% jitter, 8ECC (Error
The maximum value of the number of errors in the Correct Code) block was 60, and a good value was obtained. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

(Embodiment 2) A laser beam having a wavelength of 635 nm is irradiated with Pw = 8.0 mW, Pb _3TS = 0.5 mW, and Pb _4TS =
Example 1 except that 0.55 mW and Pr = 0.7 mW were used.
Recording and reproduction characteristics were evaluated in the same manner as described above. Table 1 shows the results. Jitter is 8.8%, 8ECC (Error Corr
ect Code) The maximum value of the number of errors in the block was 72, and a good value was obtained. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

(Embodiment 3) Pw = 9.5 mW, Pb _3TS = _{0.5 mW} , Pb _4TS =
Recording and reproduction characteristics were evaluated in the same manner as in Example 1 except that 0.6 mW and Pr = 0.6 mW were used. Table 1 shows the results.
Shown in Jitter is 7.1%, 8ECC (Error Correc
t Code) The maximum number of errors in a block is 31.
Good values were obtained. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

(Embodiment 4) A laser beam having a wavelength of 650 nm is irradiated with Pw = 9.5 mW, Pb _3TS = 0.5 mW, and Pb _4TS =
The recording / reproducing characteristics were evaluated in the same manner as in Example 1 except that 0.6 mW and Pr = 1.0 mW were used. Table 1 shows the results.
Shown in Jitter is 6.9%, 8ECC (Error Correc
t Code) The maximum number of errors in a block is 28,
Good values were obtained. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

(Embodiment 5) FIG. 1 is a schematic sectional view of one write-once optical recording medium according to the present invention. The write-once optical recording medium 100 includes a light absorbing layer 2 and a light reflecting layer 3 on a light transmitting substrate 1.
And a protective layer 4 are sequentially laminated. A method for manufacturing the write-once optical recording medium 100 will be described below.

First, a glass master used for manufacturing the light-transmitting substrate 1 was manufactured as follows. First, a polished flat glass substrate was prepared, and a photoresist reactive to ultraviolet rays was uniformly applied on the glass substrate to a predetermined thickness. As the photoresist, a mixed material of a polymer of cresol novolak resin and a photosensitive agent of naphthoquinonediazide was used. Next, a glass substrate is placed on a turntable of an exposure apparatus (not shown), and two types of laser beams are irradiated on the photoresist while rotating the glass substrate.
Each laser beam was used to expose a pattern corresponding to the pregroove and prepit. At this time, the irradiation was performed with the irradiation position of the pre-pit laser light shifted from the irradiation position of the pre-groove laser light by 1/2 track in the track width direction. Also, the laser power of the prepit and pregroove laser beams was adjusted so that the width and depth of the prepit and pregroove became desired values. Next, the exposed photoresist was developed using a developing solution. Irregularities corresponding to pregrooves and prepits were formed in the photoresist. Thus, a glass master having desired dimensions of pregrooves and prepits was produced.

Next, a nickel stamper was produced by performing nickel electroforming on the glass master. Then, the produced stamper was mounted on a mold of an injection molding machine, and a polycarbonate resin was injected and filled into the mold to produce a light-transmitting substrate 1. The manufactured light transmitting substrate 1 had a track pitch of 0.80 μm and a groove width of 0.35.
A pre-groove for tracking of μm was concentrically formed, and a pre-pit having a shape as shown in FIGS. 2, 3 and 4 was provided at a predetermined position of the land. The maximum depth a of the pre-groove 22 in FIG. 3 is 150 nm, the depth b at both edges 23 and 23 ′ of the pre-pit 21 in the direction perpendicular to the pre-groove 22 is 120 nm, and the maximum depth c of the pre-pit 21 is 145 nm. Met. In FIG. 4, the length A of one edge 23 of the prepit 21 in the pregroove direction is 150 nm, the length B of the other edge 23 ′ in the pregroove direction is 150 nm, and the length of the prepit 2 is 150 nm.
The length (maximum length) C in the pre-groove direction at the center of No. 1 was 250 nm.

Next, the light absorbing layer 2 is formed on the surface of the substrate 1 on which the pregrooves and prepits are formed as described above.
A cyanine dye as a film having a thickness of 20
Coated at 0 nm. When applying a cyanine dye,
Using tetrafluoropropanol as a solvent, a cyanine dye solvent was used. Next, Ag was formed as a light reflecting layer 3 on the light absorbing layer 2 to a thickness of 0.1 μm by a sputtering method. Further, the light absorbing layer 2 and the light reflecting layer 3
A UV curable resin was formed to a thickness of 7 μm by a spin coating method as a protective layer 4 for protecting. Protective layer 4
Was formed, and then the protective layer 4 was cured by irradiating ultraviolet rays of a predetermined light intensity using an ultraviolet irradiator. Thus, a write-once optical recording medium 100 having the laminated structure shown in FIG. 1 was obtained.

The write-once optical recording medium 100 manufactured as described above was irradiated with a laser beam having a wavelength of 635 nm by Pw = 8.
_{5mW, Pb 3TS = 0.4mW, Pb} 4TS = 0.45m
Recording and reproduction characteristics were evaluated with W and Pr = 0.7 mW. Table 1 shows the results. 8.6% jitter, 8E
The maximum value of the number of errors in the CC (Error Correct Code) block was 63, and a good value was obtained. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

Embodiment 6 In FIG. 3, the maximum depth a of the pre-groove 22 is 150 nm, the depth b at the edge 23 of the pre-pit 21 and the maximum depth c of the pre-pit 21 are both 140 nm. The length A of the edge 23 of the prepit 21 in the direction perpendicular to the pregroove.
Example 5 except that the length B of the other edge 23 ′ and the length C of the center (maximum length) of the prepit were all 200 nm. Similarly, a write-once recording medium was manufactured.

The write-once optical recording medium 100 manufactured as described above was irradiated with a laser beam having a wavelength of 635 nm at Pw = 8.
_{5mW, Pb 3TS = 0.4mW, Pb} 4TS = 0.45m
Recording and reproduction characteristics were evaluated with W and Pr = 0.7 mW. Table 1 shows the results. 8.7% jitter, 8E
The maximum value of the number of errors in the CC (Error Correct Code) block was 69, and a good value was obtained. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

(Comparative Example 1) A laser beam having a wavelength of 635 nm was irradiated with Pw = 8 mW, Pb _3TS = 0.2 mW, and Pb _4TS = 0.
Recording and reproduction characteristics were evaluated in the same manner as in Example 1 except that 2 mW and Pr = 0.7 mW. Table 1 shows the results. Jitter is 8.3%, 8ECC (Error Correct Co
de) The maximum value of the number of errors in the block was 57, and a good value was obtained. The land pre-pit signal, which is an address signal, could be recognized well during reproduction, but could not be recognized during recording.

(Comparative Example 2) A laser beam having a wavelength of 635 nm was irradiated with Pw = 8 mW, Pb _3TS = 0.8 mW, and Pb _4TS = 0.
The recording / reproducing characteristics were evaluated in the same manner as in Example 1 except that 8 mW and Pr = 0.7 mW were used. Table 1 shows the results. Jitter is 10.5%, 8ECC (Error Correct
The maximum number of errors in the Code) block was 210, which was bad. Also, a land pre-pit signal which is an address signal at the time of recording and reproduction was well recognized.

(Comparative Example 3) A laser beam having a wavelength of 650 nm was irradiated with Pw = 9.5 mW, Pb _3TS = 0.5 mW, and Pb _4TS =
Recording and reproduction characteristics were evaluated in the same manner as in Example 1 except that 0.6 mW and Pr = 0.2 mW were used. Table 1 shows the results.
Shown in The jitter is 8.5, 8 ECC (Error Correct
The maximum value of the number of errors in the (Code) block was 63, and a good value was obtained. The land pre-pit signal, which is an address signal, could be recognized well during recording, but could not be recognized during reproduction.

[0037]

[Table 1]

[0038]

According to the optical information recording / reproducing method of the present invention, the laser power (recording power) for forming a recording mark is Pw, and the laser power (bias power) for forming a space is Pb. The following inequality (1/21) Pw <Pb <(1/14) Pw (1) is satisfied, and the laser power (reproducing power) for reproducing recorded information is Pr. By satisfying (1/21) Pw <Pr <(1/7) Pw (2), good recording / reproducing characteristics can be obtained.

Further, the optical information recording / reproducing method of the present invention comprises:
It can be used as a DVD-R recording / reproducing method.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a cross-sectional structure of an optical recording medium according to the present invention.

FIG. 2 is a schematic perspective view of a cross-sectional structure when a substrate is cut along a plane perpendicular to a pregroove and including a prepit.

FIG. 3 is a partially enlarged view of a cross-sectional structure when the substrate is cut along a plane perpendicular to the pregroove and including a prepit.

FIG. 4 is a schematic view of a pre-pit formed on a substrate of an optical recording medium according to the present invention as viewed from above.

FIG. 5 is a schematic perspective view of a cross-sectional structure of a conventional DVD-R substrate.

FIG. 6: each laser power (vertical axis) and irradiation time (horizontal axis)
FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light absorption layer 3 Light reflection layer 4 Protective layer 21 Prepit 22, 22 'Pregroove 23, 23' Prepit edge 100 Optical recording medium

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takuya Hayashi 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Koji Takazawa 1-188 Ushitora, Ibaraki City, Osaka Hitachi (72) Inventor Mitsuru Ito 1-88 Ushitora, Ibaraki-shi, Osaka F-term (reference) 5D029 WA17 WA28 WB11 WB17 WD07 WD11 5D090 AA01 BB03 CC01 CC04 DD03 DD05 EE02 EE13 FF15 GG10 KK03

Claims (7)

[Claims] An optical information recording / reproducing method for a write-once optical recording medium comprising a light absorbing layer and a light reflecting layer provided on a pre-groove and a substrate having pre-pits formed between the pre-grooves. When the laser power (recording power) at the time of forming is Pw and the laser power (bias power) at the time of forming the space is Pb,
When the following inequality (1/21) Pw <Pb <(1/14) Pw (1) is satisfied, and the laser power (reproduction power) for reproducing recorded information is Pr, the following inequality (1) is satisfied. / 21) An optical information recording / reproducing method for a write-once optical recording medium, wherein Pw <Pr <(1/7) Pw (2) is satisfied. 2. The write-once optical recording according to claim 1, wherein c <a when a maximum depth of said pre-groove of said write-once optical recording medium is a and a maximum depth of said pre-pit is c. An optical information recording / reproducing method for a medium. 3. The write-once optical recording medium according to claim 2, wherein b ≦ c <a, where b is a depth of an edge of said prepit in a direction perpendicular to said pregroove of said write-once optical recording medium. An optical information recording / reproducing method for an optical recording medium. 4. The ratio c / a of the maximum depth c of the pre-pit to the maximum depth a of the pre-groove of the write-once optical recording medium is 0.50 to 0.98.
4. The optical information recording / reproducing method for a write-once optical recording medium according to claim 3, wherein 5. The ratio b / c of the depth b of the edge portion of the prepit to the maximum depth c of the prepit in the write-once optical recording medium is 0.20 to 1.00.
The optical information recording / reproducing method of the write-once optical recording medium according to the above. 6. The length of one pre-groove side edge of the pre-pits of the write-once optical recording medium in the pre-groove direction is A, and the length of the other pre-groove side edge in the pre-groove direction is B. 4. The write-once type according to claim 2, wherein 0 <A ≦ C and 0 <B ≦ C are satisfied at the same time, where C is a length in the pre-groove direction at the center of the pre-pit. An optical information recording / reproducing method for an optical recording medium. 7. The laser power for forming the 3T space Pb _3TS, the laser power for forming the above space 4T is taken as Pb _4TS, following inequality _{(1/21) Pw <Pb 3TS <} Pb _2. The optical information recording / reproducing method according to claim 1, wherein _4TS <(1/14) Pw (3) is satisfied.