JPH09180279A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress birefringent abnormality in the vicinity of an embossed pit and to obtain a high quality regenerative signal even when a ZCAV(zone constant angular velocity) system is adopted by setting the depth of the embossed pit formed on a transparent substrate to the range of prescribed values. SOLUTION: The optical disk to which a recording format is set, is constituted laminating a recording part 2 on a main surface of the substrate 1. The substrate 1 is a disk like transparent substrate, and a guide groove 3 is carved on the surface of the side provided with the recording part 2 corresponding to the track of the recording format, and further, the minute embossed pit 4 is carved corresponding to an address pit. Particularly, the depth d of the embossed pit 4 is made the range of λ/3.3n-λ/2.7n when a read laser wavelength is defined λ, and the refractive index of the substrate is n. The upper limit of the pit depth is set from the point that the birefringent abnormality in the vicinity of the embossed pit is suppressed, and a noise caused by the fact that the birefringent abnormality affects an MO signal adjacent to the address pit, is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk, and more particularly to a magneto-optical disk in which address signals and the like are written by embossed pits.

[0002]

2. Description of the Related Art In a magneto-optical recording system, the temperature of a magnetic thin film is partially raised above a Curie point or a temperature compensation point, and the coercive force in this portion is eliminated to magnetize the magnetic thin film in the direction of an externally applied recording magnetic field. It is based on the principle of reversing the direction of an image, and is being put to practical use in an optical file system, an external storage device of a computer, a recording device for audio and video information, and the like.

As a magneto-optical disk used in this magneto-optical recording system, a recording magnetic layer having a large magneto-optical effect and having an easy axis of magnetization in the direction perpendicular to the film surface on one main surface of a transparent substrate made of polycarbonate or the like. Layer (for example, a rare earth-transition metal alloy amorphous thin film), a reflective layer, and a dielectric layer are laminated to form a recording portion, and in order to prevent corrosion of the recording portion, an ultraviolet curable resin is formed on the recording portion. There is known one formed so as to cover a protective layer made of, for example.

In such a magneto-optical disk, spiral or concentric tracks are set on the disk, and information signals are written along this track. This track is allocated to a plurality of sectors having a fixed capacity. Each sector is provided with an address area indicating the physical address (address) of the sector on the disk at the head portion, and the area other than this area is a data area into which a data signal is written by the user.

The track and address pits formed in the address area are usually formed as an uneven shape on the transparent substrate. That is, the tracks are engraved as spiral or concentric continuous grooves, and the address pits are engraved as minute embossed pits.

By the way, the method of arranging the sectors on the track is selected corresponding to the method of controlling the rotational speed of the disk.

As the disc rotation speed control system, there are a system in which the angular velocity of the disc is constant (CAV system) and a system in which the linear velocity is constant (CLV system). Of these, the former system is the disc. The advantage is that the rotation speed control is easy.

In the CAV method, when the recording frequency is constant, the outer track and the inner track have the same number of bytes, and therefore the same number of sectors. in this case,
The angular range occupied by one sector is equal on the outer circumference side and the inner circumference side, and the address areas attached to the beginning of the sectors are arranged in the radial direction.

Here, in such a sector format, the physical sector length becomes shorter and the recording density in the sector becomes higher toward the inner circumference side. Although there is a space on the outer peripheral side in terms of space, the number of bytes that can be recorded on the inner peripheral side is limited, and the recording density cannot be sufficiently increased. Therefore, the CAV method is disadvantageous for high density recording on the disc.

Therefore, the ZCAV system (ZoneCAV system) has been proposed as a system for effectively utilizing the space on the outer peripheral side. In this ZCAV system, tracks are divided into blocks in the radial direction (zoning), and recording / reproduction is performed at a constant angular velocity and a constant recording frequency within a track group (zone) corresponding to one block. The angular velocity and recording frequency of the disc are controlled so that the linear density becomes substantially constant between zones. As described above, in the ZCAV system, since the outer and inner zones have substantially constant linear densities, high density recording can be achieved on the entire disc.

[0011]

In the ZCAV method, the angular range occupied by one sector in the zone is the same on the outer and inner sides, and the address areas of the sectors are arranged in the radial direction. On the other hand, when you look at each other,
The line length of the sector group formed by arranging the sectors in the zone in the radial direction is substantially constant. In this case, since the angular range occupied by the sector group becomes wider toward the inner circumference side, a positional relationship in which the adjacent areas are displaced from each other in the address area occurs.

Here, if the address areas are in such a positional relationship that they are displaced, the influence of the address pits on the reproduced signal becomes a problem.

That is, the address pits in the address area are formed as embossed pits on the transparent substrate.
Around the pits, the resin flow is discontinuous due to the anchor effect of the pits at the time of molding the substrate, so that stress in the substrate remains and birefringence anomaly occurs due to the stress.

When the address areas are arranged in the radial direction, the address pits in the address area and the magneto-optical signal (MO signal) in the data area are not adjacent to each other.
Therefore, the birefringence abnormality around the address pit hardly affects the reproduction signal obtained from the data area.

However, if the address areas are not arranged in the radial direction and have a shifted positional relationship, the address pits of the address area and the MO signals of the data area may be adjacent to each other. In such a case, the birefringence anomaly around the address pit affects the MO signal, causing a problem of giving spike-like noise to the reproduced waveform.

Therefore, the present invention has been proposed in view of such a conventional situation, and suppresses the birefringence abnormality around the embossed pits, and when the ZCAV system is adopted, a good reproduction signal is obtained from the data area. It is an object of the present invention to provide an optical disc that can obtain

[0017]

In order to achieve the above object, an optical disk of the present invention is an optical disk in which at least a recording layer is formed on a transparent substrate having embossed pits formed thereon. It is characterized in that the pit depth is in the range of λ / 3.3n to λ / 2.7n, where λ is the reading laser wavelength and n is the refractive index of the substrate.

When the depth of the embossed pits formed on the substrate is within the above range, the internal stress around the embossed pits is reduced and birefringence abnormality is suppressed. Therefore, even when the embossed pit and the data signal recorded in the recording portion are adjacent to each other on the disc, the data signal is reproduced well.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an optical disk according to the present invention will be described below.

The optical disk of this embodiment is a ZCAV
It is a magneto-optical disk to which the method is applied. First, the recording format of this magneto-optical disk will be described with reference to FIGS.

This magneto-optical disk has a disk surface,
A plurality of concentric tracks are set, and the plurality of tracks are divided into blocks in the radial direction. As shown in FIG. 1, the track groups divided into blocks are alternately formed as data fields 10 and buffer fields 11. Here, one data field and 1/2 of the buffer fields on both sides of the data field correspond to one zone 12.

The data field 10 is an area where an information signal is recorded on the recording magnetic layer by the user, and each track in the data field 10 is allocated to a plurality of sectors 13 having a fixed capacity. . In each sector 13, an address area 14 representing the physical address (address) of the sector 13 on the disk is provided at the head portion, and the area other than this area is a data area 15 in which a data signal is written by the user.
It is said.

The arrangement of the sectors 13 is such that the number of sectors per track is equal in the zone 12, that is, the sectors 13 are arranged on the outer and inner tracks.
So that the angular range occupied by the
When the two are viewed from each other, the length of the sector group formed by arranging the sectors 13 in the radial direction in the zone 12 is set to be substantially constant. Therefore, although the address area 14 provided at the head of the sector 13 is arranged in the radial direction in the zone 12,
As shown in FIG. 3, the adjacent zones 12 have a shifted positional relationship in the address area 14. That is,
In this format, adjacent zones 14 have areas where address areas 14 and data areas 15 are arranged in the radial direction. The arrangement of the address areas 15 on the entire disc is shown in FIG.

The magneto-optical disk in which such a recording format is set is constructed by laminating the recording portion 2 on one main surface of the substrate 1 as shown in FIG.

The substrate 1 is a disk-shaped transparent substrate having a thickness of about several millimeters, and a guide groove (groove) 3 corresponding to the track of the above-mentioned recording format is formed on the surface on which the recording section 2 is provided. The minute embossed pits 4 are engraved corresponding to the address pits of the address area.

Here, in this magneto-optical disk, in particular,
The depth d of the embossed pits 4 is λ / 3.3n to λ, where λ is the reading laser wavelength and n is the refractive index of the substrate.
The range is /2.7n.

The upper limit of the pit depth λ / 2.7n is to suppress the birefringence anomaly around the address pit, and to reduce the noise caused by the birefringence anomaly affecting the MO signal adjacent to the address pit. It is set from.

First, in FIG. 4, the depth of the address pits and
The relation of the byte error rate of the reproduction signal obtained from the data area is shown. In this way, the bit error rate increases as the depth of the pit increases, and can be suppressed to a small value by decreasing the depth of the pit.

Here, the correction limit of the error correction code (ECR) of the magneto-optical recording / reproducing system is a byte error rate of 10 ^-3 or less, and the byte error rate can be suppressed in such a range as the depth of the pit. Is less than or equal to λ / 2.7n. That is, in order to obtain a good reproduced signal from the data area, the depth of the address pit formed on the substrate needs to be λ / 2.7n or less.

However, the depth of the address pit also affects its signal strength. From the standpoint of light wave interference, the signal intensity is highest when the pit depth is λ / 4n. If the signal strength of this address pit becomes too large, the signal leaks into the tracking error signal, and tracking and the number of cross tracks cannot be accurately detected.

To show this, FIG. 5 shows the relationship between the depth of the address pit and the amount of leakage of the signal into the tracking error signal.

Here, the amount of leakage into the tracking error signal was examined by detecting the track cross signal obtained when the reproducing light spot was scanned across the track. When the reproduction light spot is scanned across the track, as shown in FIG. 6, a reproduction waveform having an amplitude corresponding to the number of grooves and lands which the reproduction light spot straddles is obtained. The leakage of the address pits is observed as spike-like noise that is superimposed on the reproduced waveform. The ratio B / A × 100 (%) of the noise magnitude B to the amplitude A of the reproduced waveform is the leakage amount of the tracking error signal of the address signal.

As shown in FIG. 5, the amount of leakage into the tracking error signal increases as the pit depth approaches λ / 4n. In order to suppress the amount of leakage into the tracking error signal within the practical range (40% or less), the depth of the address pit needs to be λ / 3.3n or more.

From the above results, in order to suppress noise on the reproduced signal due to birefringence anomaly around the address pit and leakage of the address signal into the tracking error signal, the depth of the address pit is λ / 3. 3n to λ / 2.7
It has been found that it is necessary to set the range to n, and by setting the depth of the address pit to this range, a high quality reproduction signal can be obtained from the data area without sacrificing access reliability.

In this magneto-optical disk, the depth of the address pits 4 is regulated in this way, but as the material of the transparent substrate 1 on which the pits are formed, any of those normally used in magneto-optical disks is used. It is possible. In particular,
In addition to plastic materials such as acrylic resin, polycarbonate resin, polyolefin resin, and epoxy resin, glass is also used. In the former case, the guide groove 3 and the embossed pits 4 are formed in an uneven shape by injection molding, and in the latter case by the photopolymer method (2P method).

Of these, substrates generally used for magneto-optical disks are polycarbonate, polymethylmethacrylate, glass, etc., and the refractive index n of these substrates is 6
It is about 1.59 at 80 nm. When reproduction is performed on a magneto-optical disk using such a substrate with read light having a wavelength of 680 nm, the depth of the address pit may be set to 0.130 to 0.158 μm.

A recording portion is formed on such a transparent substrate.

As shown in FIG. 3, the recording section 2 has a four-layer structure including, for example, a recording magnetic layer 5, dielectric layers 6, 7 and a reflective layer 8, and a first dielectric layer 6 is formed on a substrate 1. , The recording magnetic layer 5, the second dielectric layer 7, and the reflective layer 8 are laminated in this order.

Of these, the first dielectric layer 6 and the second dielectric layer 6
For the dielectric layer 7, an oxide or a nitride can be used, but a nitride is more preferable because oxygen in the dielectric layer may adversely affect the recording magnetic layer. Silicon nitride, aluminum nitride, or the like is preferable as a substance that does not transmit the laser light and can sufficiently transmit the used laser light.

The recording magnetic layer 5 is an amorphous magnetic thin film having an easy magnetization direction in a direction perpendicular to the film surface, and is excellent in magneto-optical characteristics and has a large coercive force at room temperature. It is desirable to have a Curie point near 200 ° C. As a recording material satisfying such conditions, a rare earth-transition metal alloy amorphous thin film and the like can be mentioned, and among them, a TbFeCo type amorphous thin film is preferable. An additive element such as Cr may be added to the recording magnetic layer for the purpose of improving corrosion resistance.

The reflective layer 8 is preferably composed of a film having a high reflectance that reflects 70% or more of the laser light at the boundary with the second dielectric layer, and a non-magnetic metal vapor deposition film is suitable. Further, it is desirable that this reflective layer is a thermally good conductor, and in consideration of availability, film formation, and the like,
Aluminum is suitable.

Further, a protective layer may be formed on the recording portion 2. This protective layer is for isolating the recording portion from water and oxygen in the atmosphere, and an ultraviolet curable resin such as an acrylic ultraviolet curable resin is used.

The magneto-optical disk having such a structure is ZC
Information is recorded and reproduced by the AV method. That is, in the zone, the angular velocity is constant and the recording frequency is constant, that is, the recording and reproducing are performed by the CAV method, and when the zones are viewed, the angular velocity and the recording frequency are controlled so that the linear density becomes substantially constant between the zones. In this magneto-optical disk, since the depth of the address pits is within a predetermined range, it is possible to accurately access the target sector and to obtain a reproduced signal with less noise from the data area, thus achieving good recording and reproducing. The characteristics can be obtained.

The present invention is not limited to the magneto-optical disk,
Although it can be applied to various types of optical discs, particularly in magneto-optical discs, since the data signal is detected by utilizing the magneto-optical effect (Kerr effect, Faraday effect) that is easily affected by birefringence anomaly, the effect of the present invention is remarkable. To be demonstrated.

[0045]

As is apparent from the above description, the optical disc of the present invention has an embossed pit depth of λ, where λ is the reading laser wavelength and n is the refractive index of the substrate.
Since it is in the range of /3.3n to λ / 2.7n, noise due to birefringence abnormality around the embossed pits is suppressed, and leakage of the embossed pit signal into the address tracking error signal is reduced. Therefore, even when adopting a format such as the ZCAV system in which an area where the embossed pit and the data signal recorded in the recording area are adjacent to each other on the disc is adopted, a reproduction signal with high quality has high access reliability. You get it without sacrificing it.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a format of an optical disc to which the present invention is applied.

FIG. 2 is a schematic diagram showing how the address areas of the optical disc are arranged.

FIG. 3 is a cross-sectional view showing one structural example of an optical disc to which the present invention is applied.

FIG. 4 is a characteristic diagram showing the relationship between the depth of embossed pits and the bite error rate.

FIG. 5 is a characteristic diagram showing the relationship between the depth of embossed pits and the amount of leakage into a tracking error signal.

FIG. 6 is a schematic diagram for explaining an amount of leakage into a tracking error signal.

[Explanation of symbols]

 1 transparent substrate 2 recording part 3 guide groove 4 address pit 10 data field 11 buffer field 12 zone 13 sector 14 address area

Claims (3)

[Claims] 1. An optical disc in which at least a recording layer is formed on a transparent substrate on which embossed pits are formed, where the depth of the embossed pits is when the reading laser wavelength is λ and the refractive index of the substrate is n. , Λ / 3.3n to λ
An optical disc having a range of /2.7n. 2. The optical disc according to claim 1, wherein the recording layer is a recording magnetic layer having a magneto-optical effect. 3. The optical disc according to claim 1, wherein the reading laser wavelength is approximately 680 nm.