JPH04243019A - Information recording medium - Google Patents

Abstract

PURPOSE:To make uniform C/N of wobbling RF reproduced signals in prepit and pregroove area by making the track amplitude in the prepit which forms a wobbling track larger than the amplitude of the pregroove area. CONSTITUTION:In a disk-type substrate 11 of an optical disk having a center hole 12, there are provided wobbling tracks comprising a prepit area 13 and a pregroove 14 in a sine curve along the center line of the helical virtual truck. The track amplitude in the prepit 13 is made larger by >=10nm than that in the pregroove area 14, which prevents decrease in C/N of RF reproduced signals in the prepit 13 in the inner area. Thus, uniform C/N of wobbling RF reproduced signals is obtd. in the prepit and pregroove area. Thus, the obtd. recording medium has little read out error for wobbling RF reproduced signals in the prepit area.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an information recording medium on which information can be recorded, reproduced, or erased using a high-energy-density laser beam. The present invention relates to an information recording medium having a wobbling track consisting of a pre-groove section and a pre-groove section.

0002

2. Description of the Related Art Information recording media (optical disks) are known in which information is recorded by changing the reflectance and the like in response to light by irradiating the medium with a laser modulated based on recorded information. Such optical discs generally have a basic configuration in which a recording layer capable of recording the above information is provided on a disc-shaped substrate made of plastic or the like.

[0003] In the above recordable optical disk, a track consisting of spiral pre-pits and pre-grooves is preformed on the substrate surface in order to guide laser beam irradiation. Such pre-pits and pre-grooves are formed by embossing the surface of the substrate or by injection molding the substrate.

[0004] Also, wobbling is applied to the tracks of spiral pre-pits and pre-grooves (that is, substantially sinusoidal tracks and no tracks), and the wobbling period at that time is used as absolute time data, or the wobbling period is set to FM. Optical discs are also known that are made to be (frequency) modulated so that absolute addresses on the disc can be detected (for example, Japanese Patent Laid-Open No. 1-317239).

The wobbling amplitude (magnitude of amplitude) obtained from the wobbled pre-pits and pre-grooves is, for example, about ±30 nm when the track pitch is 1.6 μm, and the wobbling period is set by the pickup (optical head). For example, the spatial frequency (fundamental frequency) is set to 22.05 kHz so that the frequency does not directly respond.

[0006] Recently, such optical discs are provided with a partial ROM in which the system and data are pre-pitted on the inner circumference side from which the drive starts reading, and the user uses the system and data only for reading (playing). A standard has been proposed in which data and programs created by the user are recorded and saved in the pregroove on the outer periphery. In this standard, address management is performed using not only the pre-pit section but also the pre-groove section, so the absolute time from the inner track is managed by wobbling the track to indicate an FM (frequency) modulation signal. It is like that. Also, this wobbling amplitude is
Generally, it is about ±30 nm.

[0007] The wobbling amplitude of such an optical disc is the same in both the pre-pit section and the pre-groove section, and the wobbling amplitude is set so that the degree of modulation of the wobbling RF reproduction signal (reproduction carrier signal) of the pre-groove track is optimized. ing.

[0008]

However, according to studies by the present inventors, the information recording medium obtained by the conventional method as described above has a track pitch of 1.6 μm, and pre-pits and pre-grooves are It has become clear that the C/N of the RF reproduction signal when wobbling at 30 nm (that is, when the pre-pit and pre-groove have the same wobbling amplitude) has a lower value in the pre-pit part than in the pre-groove part. This is thought to be because the pits in which information is recorded intermittently are more likely to become noise during reproduction of the wobbling RF reproduction signal than the grooves in which the laser is guided continuously, resulting in a lower C/N. That is, compared to the pre-groove section, the noise level is generally higher in the pre-pit section due to the wraparound of the pit reproduction signal of the pre-pit. Therefore, even if the level of the wobbling RF reproduction signal is the same, the C/N value decreases and reading errors are more likely to occur.

The present invention improves the above-mentioned problems, and provides an information recording medium in which the C/N of the wobbling RF reproduction signal in the pre-pit portion and the pre-groove portion is made uniform, and there are fewer errors in reading the wobbling RF reproduction signal in the pre-pit portion. The purpose is to provide

0010

[Means for Solving the Problems] The above object is to provide a virtual track spirally set on a disk-shaped substrate at regular intervals in the radial direction along the circumference, and a pre-pit portion and a pre-pit portion formed along the virtual track. Information in which a wobbling track consisting of a pregroove section for guiding an optical head during recording, reproduction, or erasing is formed in a substantially sinusoidal shape, and a recording layer on which information can be recorded by a laser is provided on the substrate. This can be achieved by using an information recording medium characterized in that the amplitude (WP) at the pre-pit portion of the wobbling track is larger than the amplitude (WG) at the pre-groove portion of the wobbling track.

Preferred embodiments of the information recording medium of the present invention are as follows.

1) The information recording medium described above, wherein the difference between the amplitude (WP) of the pre-pit portion of the wobbling track and the amplitude (WG) of the pre-groove portion is 10 nm or more.

2) The information recording medium described above, wherein the difference between the amplitude (WP) of the pre-pit portion of the wobbling track and the amplitude (WG) of the pre-groove portion is 16 to 36 nm.

3) The information recording medium described above, wherein the amplitude (WP) of the pre-pit portion of the wobbling track is in the range of 66 to 106 nm.

4) The information recording medium described above, wherein the amplitude (WG) of the pregroove portion of the wobbling track is in the range of 40 to 80 nm.

5) The above-mentioned information recording medium, wherein the pre-pits of the wobbling track have a shape with a half width in the range of 450 to 650 nm and a depth in the range of 90 to 280 nm.

6) The information recording medium as described above, wherein the pregroove of the wobbling track has a shape with a half width in the range of 400 to 600 nm and a depth in the range of 30 to 190 nm.

[0018]

[Function] The information recording medium of the present invention increases the level of the wobbling RF reproduction signal by increasing the wobbling amplitude of the pre-pit section to reduce the increase in the noise level of the wobbling signal due to the wraparound of the reproduction signal due to the pits of the pre-pit section. This makes it possible to make the C/N and error of the wobbling RF reproduction signal comparable to those of the pregroove section.

The information recording medium of the present invention will be described below with reference to FIGS. 1 to 3.
This will be explained in detail with reference to.

FIG. 1 is a plan view showing an optical disk having a wobbling track according to the present invention. The optical disc 10 has an inner pre-pit portion 13 on the surface of a disc-shaped substrate 11 having a hole 12 in the center and on the inner circumference side of the substrate outside the hole.
, and an outer peripheral pregroove 14 is provided on the outside thereof. Further, a recording layer 15 is provided on the inner pre-pit portion 13 and the outer pre-groove portion 14 . In some cases, the recording layer is formed only on the outer circumferential pregroove portion 14. If desired, a reflective layer, a protective layer, etc. may be provided on the recording layer.

The track consisting of the inner pre-pit portion 13 or the outer pre-groove 14 is a virtual track (not shown in FIG. 1) that is set spirally from the inner circumferential side of the substrate surface toward the outer circumference at a track pitch of 1.6 μm. A laser spot formed on the re-disk by laser irradiation moves along this track to record and reproduce information.

[0022] On the inner circumferential side of the optical disc, there is a partial ROM that the user uses for system and data playback only.
An area is provided in the pre-pit section 13, and an outer pre-groove section 14 is formed on the outer circumferential side of the pre-pit section 13, which is used for recording and storing programs and data created by the user. In order to manage addresses and absolute time from the inner circumference using a wobbling track consisting of a pre-pit section and a pre-groove section, the track is wobbled in a manner that indicates an FM (frequency) modulation signal (approximately a sinusoidal curve). formed).

FIGS. 2 and 3 show the pre-pit portion and pre-groove portion wobbling in the sinusoidal curve, respectively.

In FIG. 2, a pre-pit 17 is shown that wobbles in a substantially sinusoidal shape with respect to the virtual track center line 16. The amplitude of the curve is WP.

In FIG. 3, the pregroove 18 wobbles in a substantially sinusoidal shape with respect to the virtual track center line 16.
It is shown. The amplitude of the curve is WG.

The management of the address and the absolute time from the inner circumference are performed by a wobbling track consisting of a pre-pit section and a pre-groove section formed by wobbling as described above. In the present invention, the amplitude of such a wobbling track is, for example, ±60 nm (WP) at the pre-pit portion and ±30 nm (WP) at the pre-groove portion.
nm (WG), and the amplitude (WP) of the wobbling track in the pre-pit portion is set to be larger than the amplitude (WG) of the wobbling track in the pre-groove portion.

In order to record an RF reproduction signal on such an optical disk, pits are first formed on the substrate at the time of molding in the pre-pit portion, and pits are formed on the recording layer provided above in the pre-groove portion. It is done by forming. In such optical discs, the C/N of the RF reproduction signal is affected by slight differences in pickup operating conditions, slight differences in the depth and half-width of pre-pits and pre-grooves, and even differences in the material of the recording layer. Although there may be slight fluctuations due to
Since the C/N of the pre-pit portion and that of the pre-groove portion are relatively unchanged, errors in reading the reproduced signal are extremely reduced.

In the optical disc of the present invention, the difference between the amplitude (WP) of the pre-pit portion and the amplitude (WG) of the pre-groove portion of the wobbling track formed on the substrate is preferably 10 nm or more, and further, 16-3
It is preferably in the range of 6 nm. Further, the amplitude (WP) of the prepit portion is preferably in the range of 66 to 106 nm. Also, the amplitude of the pregroove part (W
G) is preferably in the range of 40 to 80 nm.

Further, regarding the shapes of the pre-pits and pre-grooves formed on the substrate, the half width of the pre-pits is in the range of 450 to 650 nm, and the depth is in the range of 90 to 2.
Preferably, the width is in the range of 80 nm, the half width of the pregroove is in the range of 400 to 600 nm, and the depth is preferably in the range of 30 to 190 nm.

Next, a method of detecting a wobbling RF reproduction signal using a wobbling track will be explained with reference to FIG.

FIG. 4 is a block diagram showing an example of a method for detecting a wobbling RF reproduction signal using a wobbling track.

The illustrated reproduction optical system includes a laser diode 41, a lens 42, and a beam splitter 4.
4 and push-pull detector 45 are built in. In this reproduction optical system, when the wobbling track 43 in the pre-pit area is irradiated with a laser beam through the lens 42 of the pickup and the laser beam is tracked (moved while irradiating) the wobbling track 43, as the wobbling track 43 moves, the laser beam radially shifted from the beam spot position. This shift is detected by the push-pull detector 45, and the detected output is input to the differential amplifier 46, where the tracking error component (It component) and the wobbling signal component (
Iw component). 47 is a 10 to 30 kHz band pass filter, which detects the wobbling signal component (Iw component: 22.05 kHz). An RF reproduction signal 48 is obtained from this wobbling signal component.

The information recording medium of the present invention can be manufactured, for example, as follows.

The disc-shaped resin substrate used in the present invention can be arbitrarily selected from various materials used as substrates for conventional information recording media. In terms of substrate optical properties, flatness, processability, handling, stability over time, manufacturing cost, etc., examples of substrate materials include acrylic resins such as cell cast polymethyl methacrylate and injection molded polymethyl methacrylate; Examples include vinyl chloride resins such as vinyl chloride and vinyl chloride copolymers; epoxy resins; polycarbonate resins, amorphous polyolefins, and polyesters. Preferably, mention may be made of polycarbonate, polyolefin and cell-cast polymethyl methacrylate.

The pregroove and prepit are formed on the substrate.

The method for forming pre-grooves and pre-pits on the substrate can be carried out, for example, as follows. This will be explained with reference to FIG.

FIG. 5 is an explanatory diagram for explaining the manufacturing process of the optical disc substrate.

[0038] The cleaned and polished glass original plate 50 has
A photoresist layer 51 is formed by coating and drying, and is cut by exposure to a laser 54 through a cutter lens 53 to form a latent image 52 such as a pregroove or prepit. Next, the latent image is developed to form an image 55 of pre-grooves, pre-pits, etc., a Ni conductive film 56 is formed thereon, and then a Ni electroforming film 57 is formed by Ni plating.
Then, the Ni electroforming 57 is peeled off from the glass original plate to create a Ni stamper 58. Using a Ni stamper as a mold for injection molding, an optical disk substrate (replica) 59, which is the disk-shaped substrate, is created.

A method for forming wobbling tracks in the cutting process will be described in detail with reference to FIG. 6.

FIG. 6 is a schematic diagram of a cutting device (original plate exposure device) used in the cutting process.

Laser beam 6 emitted from light source 61
2 is optically modulated by the AO converter 63 using pre-pit and pre-groove signals. The laser beam 62 is reflected by a reflecting mirror 64, deflected by an AO deflector 65 at an angle 66 at a wobbling frequency, and is incident on a condenser lens 67. The laser beam 62 incident on the condensing lens is controlled to focus on the resist layer surface of the resist original plate, and is exposed in the form of pre-pits and pre-grooves. At this time, since the exposure beam is deflected by the AO deflector by the above angle, a sinusoidal wobbling track is formed at the above wobbling frequency. That is, since the amount of wobbling amplitude is determined by the angle 66 that changes with the AO deflector, the input wobbling signal 68 to the AO deflector
By setting and switching the amplitude to the optimum value when forming the pre-pit portions and when forming the pre-groove portions, it is possible to cut the original plate with the amount of wobbling amplitude changed.

[0042] A substrate (replica) on which such pre-pits and pre-grooves are formed is obtained by coating the above-mentioned stamper with a liquid mixture consisting of the above-mentioned acrylic ester and polymerization initiator, and then coating the substrate on this coating liquid layer. After being placed on the substrate, the liquid layer may be cured by irradiation with ultraviolet rays through the substrate or the matrix to fix the substrate and the liquid phase, and then the substrate may be peeled off from the matrix.

An undercoat layer may be provided on the surface of the substrate for the purpose of improving planarity, improving adhesive strength, improving solvent resistance of the substrate, and preventing deterioration of the recording layer. Examples of materials for the undercoat layer include polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, styrene/maleic anhydride copolymer, polyvinyl alcohol, N-methylolacrylamide, styrene/sulfonic acid copolymer, and styrene/sulfonic acid copolymer.
Vinyl toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate/vinyl chloride copolymer, ethylene/vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate, etc. Examples include polymeric substances; organic substances such as silane coupling agents; and inorganic substances such as inorganic oxides (SiO2, Al2 O3, etc.) and inorganic fluorides (MgF2).

The undercoat layer is prepared by, for example, dissolving or dispersing the above substance in a suitable solvent to prepare a coating solution, and then applying this coating solution to the substrate surface by a coating method such as spin coating, dip coating, or extrusion coating. It can be formed by The thickness of the undercoat layer is generally 0.
It is in the range of 0.005 to 20 μm, preferably 0.01 to 20 μm.
The range is 10 μm.

A recording layer is provided on the substrate. The material of the recording layer is not particularly limited, and metals, dyes, etc. commonly used in recording layers of optical discs can be used. Examples of metals include Te, In, Sn, and Pb.
, Bi, and metal oxides and metal sulfides. Examples of pigments include cyanine pigments, phthalocyanine pigments, pyrylium/thiopyrylium pigments, azulenium pigments, squarylium pigments, N
Examples include metal complex dyes such as i, Cr, naphthoquinone/anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallylmethane dyes, aluminum/diimmonium dyes, and nitroso compounds. be able to.

The recording layer is formed, for example, by vacuum evaporation, sputtering or ion plating of the metal, or by dissolving the dye and, if desired, a binder in a solvent to prepare a coating solution. This can be done by coating the surface of the substrate to form a coating film and then drying it.

The recording layer may be a single layer or a multilayer, but its layer thickness is generally in the range of 0.01 to 10 μm, preferably in the range of 0.02 to 1 μm. Furthermore, the recording layer may be provided not only on one side of the substrate but also on both sides.

A reflective layer may be provided on the recording layer. By providing a reflective layer, in addition to the effect of improving reflectance, it is possible to obtain the effects of improving S/N during information reproduction and improving sensitivity during recording.

[0049] The light-reflecting substance that is the material of the reflective layer is a substance that has a high reflectance to laser light, and examples thereof include Mg, Se, Y, Ti, Zr, Hf, V, Nb, and Ta.
, Cr, Mo, W, Mn, Re, Fe, Co, Ni, R
u, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn
, Cd, Al, Ga, In, Si, Ge, Te, Pb,
Mention may be made of metals and semimetals such as Po, Sn, and Bi. Among these, preferred are Au, Ag,
They are Cu, Pt, Al, Cr and Ni. These substances may be used alone, or in combination of two or more or as an alloy.

The reflective layer can be formed on the recording layer by, for example, vapor deposition, sputtering or ion plating of the above-mentioned light reflective material. The thickness of the reflective layer is generally in the range of 10 to 300 nm.

A protective layer is provided on the reflective layer 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 scratch resistance and moisture resistance on the side of the substrate where the recording layer is not provided.

Examples of materials used for the protective layer include inorganic materials such as SiO, SiO2, SiN4, M
Examples include gF2, SnO2, and the like. Also,
Organic substances include thermoplastic resins, thermosetting resins, UV
Examples include curable resins, preferably UV curable resins. In the present invention, remarkable effects can be obtained when the above-mentioned substance is provided by coating. This is particularly effective when the organic substance is applied by coating.

That is, it can also be formed by dissolving a thermoplastic resin, a thermosetting resin, etc. in a suitable solvent to prepare a coating solution, and then applying this coating solution and drying it. In the case of a UV curable resin, it can also be formed by preparing a coating liquid as it is or by dissolving it in an appropriate solvent, applying this coating liquid, and curing it by irradiating it with UV light. Examples of UV-curable resins include oligomers of (meth)acrylate such as urethane (meth)acrylate, epoxy (meth)acrylate, and polyester (meth)acrylate, monomers such as (meth)acrylic acid ester, and photopolymerization initiators. Conventional UV curable resins such as UV curable resins can be used. Various additives such as antistatic agents, antioxidants, and UV absorbers may be further added to these coating liquids depending on the purpose. In the present invention, it is preferable to use a UV curable resin. The thickness of the protective layer generally ranges from 0.1 to 100 μm.

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

[0055]

[Examples] Examples and comparative examples of the present invention will be described below. However, these examples do not limit the invention.

[Example 1] Wobbling pre-pit (
A disc-shaped polycarbonate substrate (outer diameter: 130 mm) provided with a wobbling track consisting of a wobbling pre-pit part) and a wobbling pre-groove (pre-groove part of a wobbling track).
, inner diameter: 15mm, thickness: 1.2mm, track pitch: 1.6μm, wobbling pre-pit (recording signal:
RF signal, area: 23-36mm, amplitude (WP): 43
nm, half width: 0.6 μm, depth: 110 nm) and wobbling pregroove (area: 36-58 mm,
Amplitude (WG): 30 nm, half width: 0.6 μm, depth:
80 nm) was fabricated by injection molding using a stamper as a mold, which was fabricated using the wobbling track forming method shown in FIG. 5 and the track cutting method shown in FIG. 4.

The following dyes:

[Chemical formula 1] 3.25 g of 2,2,3,3-tetrafluoropropanol, ethyl cellosolve and tetrachloroethylene (
A dye recording layer coating solution was prepared by dissolving the dye in a mixed solvent having a solvent composition of 75:20:5 (volume ratio). The coating solution was applied onto the disk-shaped polycarbonate substrate at a rotation speed of 200 rpm by spin coating, and then the speed was increased by 50 rpm per second to 1000 rpm.
After holding the substrate at a speed of 2,000 rpm for 10 seconds, the substrate was further dried by rotating at a speed of 2,000 rpm for 1 minute to form a recording layer having a thickness of 120 nm.

A reflective layer having a thickness of 130 nm was formed on the dye recording layer by sputtering Au. moreover,
On the reflective layer, ultraviolet curing resin (product name: 3070, manufactured by Three Bond Co., Ltd.) was applied by spin coating at a rotation speed of 2.
After coating at a speed of 00 rpm, the rotation speed is 1500 rpm.
This was leveled for 10 seconds and then cured by irradiation with ultraviolet rays to form a protective layer with a thickness of 2 μm.

In this manner, an information recording medium consisting of a substrate having wobbling tracks, a recording layer, a reflective layer and a protective layer was manufactured.

[Comparative Example 1] An information recording medium was manufactured in the same manner as in Example 1 except that the amplitudes of the wobbling pre-pits and wobbling pre-grooves on the substrate were both 30 nm. .

[Evaluation of Information Recording Medium] The information recording medium obtained above had an oscillation wavelength of 780 nm and a lens numerical aperture (
NA): Laser power (recording power) when recording using a pickup with a semiconductor laser of 0.5
The RF signal was recorded at 7 mW and linear velocity: 1.3 m/s, and a reproducing optical system was used to detect the wobbling RF reproduced signal using the wobbling track shown in Figure 4. :7
80 nm, lens numerical aperture (NA): 0.5, linear velocity: 1.3 m/sec, and reproduction power: 0.5 mW
The C/N (C: carrier, N: noise) of the RF reproduction signal of wobbling pre-pits and wobbling pre-grooves was measured under the following conditions.

As the above measurement results, FIG. 7 shows a graph of C/N, FIG. 8 shows a graph of C (carrier), and FIG. 9 shows a graph of N (noise).

As is clear from FIG. 7, in the optical disc of the present invention of Example 1, the C/N of the RF reproduction signal is high and approximately the same in both the inner pre-pit portion and the outer pre-groove portion. However, in a conventional optical disc (Comparative Example 1) in which the wobbling pre-pits and wobbling pre-grooves have the same amplitude, the C/N of the RF reproduction signal at the inner pre-pit portion is low, so the difference between the inner pre-pit portion and the outer pre-groove portion is low. The C/N is different and reading errors are likely to occur. Furthermore, from FIGS. 8 and 9, it can be seen that the optical disc of the present invention of Example 1 has a higher C/N because the C (carrier) of the inner pre-pit portion is larger than that of the optical disc of Comparative Example 1.

[0064]

According to the present invention, since the wobbling track is formed so that the wobbling amplitude of the pre-pit track is larger than the wobbling amplitude of the pre-groove track, the C/N of the wobbling RF reproduction signal is reduced.
can be made uniform, and errors in reading the wobbling RF reproduction signal at the pre-pit portion can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an optical disc having a wobbling track according to the present invention.

FIG. 2 is a plan view showing wobbling pre-pits of the optical disc of the present invention.

FIG. 3 is a plan view showing a wobbled pregroove of the optical disc of the present invention.

FIG. 4 is a block diagram illustrating an example of a method for detecting a wobbling RF reproduction signal using a wobbling track.

FIG. 5 is an explanatory diagram for explaining the manufacturing process of an optical disc substrate.

FIG. 6 is a schematic diagram of a cutting device (original plate exposure device) used in the cutting process.

FIG. 7 is a graph showing the C/N of the RF reproduction signal in the inner pre-pit portion and the outer pre-groove portion of the optical disc obtained in Example 1 according to the present invention and Comparative Example 1;

FIG. 8 is a graph showing C (carrier) of the RF reproduction signal in the inner pre-pit portion and outer pre-groove portion of the optical disc obtained in Example 1 according to the present invention and Comparative Example 1.

FIG. 9 is a graph showing N (noise) of the RF reproduction signal in the inner pre-pit portion and outer pre-groove portion of the optical disc obtained in Example 1 according to the present invention and Comparative Example 1;

[Explanation of symbols]

10 Optical disc 11 Disc-shaped substrate 12 Hole 13 Inner pre-pit part 14 Outer pregroove section 15 Recording layer 16 Virtual track center line 17 Wobbling pre-pit

Claims (1)

[Claims] [Claim 1] A wobbling track consisting of a pre-pit section and a pre-groove section is formed in a substantially sinusoidal shape along a virtual track set spirally at constant intervals in the radial direction along the circumference. In an information recording medium in which a recording layer on which information can be recorded by a laser is provided at least on the pregroove of a disc-shaped substrate, the amplitude (WP) at the pre-pit portion of the wobbling track is
An information recording medium characterized in that the amplitude (WG) is larger than the amplitude (WG) in a pregroove portion of a wobbling track.