JPH05234143A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium capable of stable tracking even in the case of narrowed track pitch, reducing cross talk, capable of attaining high density and ensuring high productivity by forming a common wobbling pit and a non-recording region in which groove recording cannot be carried out between the centers of adjacent tracks. CONSTITUTION:Wobbling pits 14 are stepwise arranged from the inner part of an optical recording medium 10 toward the rear ends of tracks 17. The tracking of a track 18b is carried out with a differential signal generated from wobbling pits 15a, 15b. Grooves 22 are formed in a data region 13 and bit extension is inhibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the recording of information by light,
The present invention relates to an optical recording medium for reproducing or erasing, and more particularly to an optical recording medium capable of high density recording.

[0002]

2. Description of the Related Art Conventionally, there are optical recording media in which a tracking guide groove is formed on a substrate and tracking is performed by a push-pull method, and tracking is performed by a sample servo system.

In an optical recording medium of the sample servo system, it has been studied to reduce the track pitch to increase the recording density. For example, Japanese Patent Laid-Open No. 1733932/1993 provides a groove only in a data recording area. An optical recording medium having the above structure is disclosed. That is, this optical recording medium 1
As shown in FIG. 12, a main part of 00 is a pair of wobblings which are provided outside and inside the center 102 of the track through which the laser spot 101 passes by a predetermined width and are also spaced by a predetermined distance in the track direction. Pit 10
It is composed of a servo area 106 having 4 and 105 and a data area 109 in which bits are formed and data is recorded. The servo area 106 and the data area 109 constitute one sector 110. Here, the upper side of the paper is the outside of the optical recording medium, and the lower side of the paper is the inside of the optical recording medium. Further, in the servo area, a clock pit 112 for generating a clock signal and the like are formed in the center 102 of the track. Wobbling pit 104, 105
Is composed of a concave portion or a convex portion formed on the substrate, and
A groove 114 is formed in the data area 109. A recording layer and a protective layer are laminated on the substrate.

When the laser spot 101 is applied to the wobbling pits 104 and 105, the amount of reflected light is reduced by diffraction and a signal is detected. When the laser spot 101 passes through the center of the track 102, the intensities of the signals 120 and 121 generated by the wobbling pits 104 and 105 become equal, as shown in FIG. When the laser spot 101 is displaced from the center 102 of the track to the outer side, that is, the upper side of the paper surface, the signal 120 from the wobbling pit 104 becomes larger than the signal 121 from the wobbling pit 105 as shown in FIG.

On the other hand, when the laser spot 101 is displaced inward from the center 102 of the track, that is, to the lower side of the drawing, the wobbling pit 10 is formed as shown in FIG.
The signal 121 from 5 is larger than the signal 120 from the wobbling pit 104. In the tracking servo circuit, the magnitudes of the signals 120 and 121 are sampled and held, and then the difference between them is obtained by a differential amplifier.
The deviation from 2 can be detected, and the tracking error signal can be obtained. The servo area 106 is controlled so that the difference between the signals 120 and 121 becomes zero, and this state is held in the data area 109. Tracking is performed by repeating this operation for each sector 110.

When a magneto-optical recording material is used for the recording layer, information is recorded by irradiating a laser in the data area 109 to heat the recording layer and at the same time apply a magnetic field from the outside to reverse the magnetization of the recording layer. This is done by forming a reversed magnetic domain. At this time, a groove 114 is formed in the data area 109.
Is provided, the heat conduction is blocked by the side wall portion of the groove 114, and it is possible to prevent the inverted magnetic domain, which is a bit, from spreading in the lateral direction.

[0007]

However, since the tracking is performed by the sample servo system,
When the track pitch is reduced, when recording / reproducing is performed on the track 102, a signal from the wobbling pit 114 of the adjacent track 103 is mixed, and accurate tracking cannot be performed. That is, the wobbling pits 105 and 114 are formed at positions that are separated from the centers of the tracks 102 and 103 by a predetermined width inward or outward, and the radial intervals are two adjacent tracks 1.
It is narrower than the distance between the centers of 03 and 102. Therefore, when the track pitch is reduced, part of the laser spot 101 is also irradiated on the wobbling pit 114 of the adjacent track 103. As a result, the size of the signal from the wobbling pit 104 changes from the original size, and an offset occurs in the tracking by the amount of the change, and recording / reproduction is performed with the laser spot 101 deviated from the track center and normal recording is performed. Recording / playback will not be possible. Therefore, there is a problem that the track pitch cannot be made too small.

Further, when manufacturing a master for producing a substrate used for such an optical recording medium by injection molding, a laser beam for cutting is used as the center of the track, that is, from the position a in FIG. It is necessary to deflect to the positions of d and d, which complicates the structure of the deflector and also deteriorates reproducibility, resulting in a problem that productivity is reduced.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a common wobbling pit and groove between the centers of tracks adjacent to each other, thereby providing a track. An object of the present invention is to provide an optical recording medium that can perform stable tracking even with a small pitch, has a small crosstalk, enables high density, and has high productivity.

[0010]

In order to achieve this object, in the sample servo type optical recording medium of the present invention, the first servo track is provided between the centers of the first and second tracks adjacent to each other.
Further, a common wobbling pit used for tracking the second track or a wobbling pit and a groove having the same position in the track direction are provided.

[0011]

In the optical recording medium of the present invention having the above structure,
Since the heat conduction is blocked by the groove formed between the centers of the first and second tracks adjacent to each other, the magnetic domain does not spread and crosstalk does not increase. Also, when performing tracking by the sample servo method, the wobbling pits between the centers of two adjacent tracks are the same,
That is, since it is common to two adjacent tracks,
Alternatively, since the positions in the track direction are the same, it is possible to perform stable tracking without generating unnecessary signals. Further, when the master is manufactured, the deflection amount of the laser beam required for exposing the wobbling pits and the grooves may be the same, so that the deflector is simplified and the reproducibility is improved, so that the productivity is increased.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

Optical recording medium 10 to which the present invention is preferably applied.
Is the servo area 12 and the data area 1 as shown in FIG.
3 are alternately formed in the track direction, and wobbling pits 14 are provided in the servo area 12.

The wobbling pit 14 is formed at a position separated from the center of the track 17 arranged in a spiral shape or a concentric shape by a predetermined width inward and outward. For example, the wobbling pit 15a has a track 18
The wobbling pit 15b is equidistant from the center of the track a and the center of the track 18b, and is equidistant from the center of the tracks 18b and 18c, and is separated from each other by a predetermined distance in the track direction. The other wobbling pits 14 are similarly formed. Therefore, the wobbling pit 15a
Is separated from the center to the inside of the track 18a, and is separated from the center to the outside of the track 18b, which is a common wobbling pit for the tracks 18a and 18b.

Here, from the outer periphery, that is, from the upper side of the paper surface to the inner periphery, that is, from the lower surface of the paper surface, the wobbling pits 14 are sequentially arranged at predetermined intervals behind the track, that is,
It is arranged on the right side of the paper with a shift. Therefore, the wobbling pits 15b arranged in the area sandwiched by the tracks 18b, 18c are located between the wobbling pits 15a, 15c arranged on both sides of the area sandwiched by the tracks 18b, 18c in the track direction. By arranging the wobbling pits 14 in this way, when the laser spot 40 travels along an arbitrary track 17, the signal from the wobbling pit 14 located outside the track 17 is always located inside the track 17. It occurs before the signal from 14. As a result, as will be described later, it is possible to identify which side the laser spot 40 deviates from the track 17.

The wobbling pit 14 is used for the optical recording medium 1.
The data area 13 is sequentially shifted from the outer circumference to the inner circumference of 0 by a predetermined distance in the track direction.
The start position and the end position of are also different depending on the track 17, and are sequentially shifted from the outer circumference to the inner circumference in the track direction. As a result, the lengths of the servo areas 12 and the data areas 13 are substantially constant, and the data areas 13 can be efficiently arranged according to the arrangement of the wobbling pits 14.

Further, in the data area 13, a groove 22 is formed between adjacent tracks 17. This groove 2
The portion sandwiched between 2 becomes a recording area 20 in which bits are recorded. In the servo area 12, clock pits 24 and sector marks, addresses and the like (not shown) are recorded in advance along the center of the track 17.

As shown in FIG. 2, the wobbling pits 14 are formed as concave pits in a transparent substrate 30 made of a resin such as acrylic or polycarbonate, or glass. On the substrate 30, a protective layer 31 made of a transparent oxide or nitride such as SiO ₂ or SiN, a recording layer 34 made of a rare earth transition metal amorphous alloy such as TbFeCo, and a protective layer 36 such as SiN are formed by the sputtering method. It is produced by well-known thin film forming means such as vacuum deposition method and laminated. The protective layers 31 and 36 function to protect the recording layer 34 from oxidation and the like.

The groove 22 is formed in the substrate 30 so as to have a predetermined width and substantially equal to the depth of the wobbling pit 14, as shown in FIG. 3 which is a sectional view in the radial direction. In this embodiment, the sidewall of the groove 22 is formed so as to be substantially vertical to the surface of the substrate 30.

When producing a master for producing the substrate 30 used in the optical recording medium 10 by injection molding, the laser beam for cutting is from the track center, that is, the position b'in FIG. Only by deflecting to the position of a ′, the structure of the deflector is simplified, and at the same time, the reproducibility is improved and the productivity is increased.

Tracking by the sample servo system will be described below with reference to FIGS. 1, 4 and 5.

When the laser spot 40 moves in the center of the track 18b in FIG. 1, the detection signals 42a and 42b generated by the wobbling pits 15a and 15b are equal in magnitude as shown in FIG. 4A. When the laser spot 40 moves from the center of the track 18b to the outside, that is, in the upward direction of the paper surface, the laser spot 40 moves away from the wobbling pit 15b, and 15a
Since the position moves closer to, the detection signal 42a becomes larger than 42b, as shown in FIG.

On the contrary, the laser spot 40 has the track 18
When the laser spot 40 moves inward from the center of b, that is, in the downward direction of the paper surface, the laser spot 40 approaches the wobbling pit 15b and moves away from 15a. Therefore, as shown in FIG. 4 is better
It becomes larger than 2a. Similarly, laser spot 4
When 0 moves from the center of the adjacent track 18c to the outside, that is, in the upward direction of the paper surface, the detection signal 42b generated by the wobbling pit 15b is larger than the detection signal 42c generated by the wobbling pit 15c, as shown in FIG. 4D. On the contrary, when moving inward, that is, in the downward direction of the paper surface, the detection signal 42c becomes larger than 42b as shown in FIG.

Such detection signals 42a, 42b, 42
Tracking is performed by the tracking servo circuit shown in FIG. That is, when the laser spot 40 moves along the track 18b, the detection signals of the optical detector 50 of the optical head are detected in the order of 42a and 42b, and are amplified by the amplifier 52. Amplified detection signal 42
a and 42b are timing signal generation circuits 54 in the order in which they are generated.
Is sampled by the first and second sample and hold circuits 56 and 57 in accordance with the timing signal generated by the above, and held for a predetermined time. Then, the detection signal 42a sampled and held by the first and second sample and hold circuits 56 and 57 by the differential amplifier 60,
Obtain the difference signal of 42b. This difference signal is the detection signal 42a,
When 42b is in the state of FIG. 4 (b), it is positive, and in the case of FIG. 4 (c), it is negative.

Similarly, when the laser spot 40 moves along the track 18c, the photodetector 50 of the optical head detects detection signals in the order of 42b and 42c,
It is amplified by the amplifier 52. Amplified detection signal 42b,
42c is sampled by the first and second sample hold circuits 56 and 57 in accordance with the timing signals generated by the timing signal generation circuit 54 in the order of generation, and is held for a predetermined time. Then, the detection signals 42b, 4 which are sampled and held by the first and second sample and hold circuits 56, 57 by the differential amplifier 60 are held.
Obtain a difference signal of 2c. This difference signal is the detection signals 42b, 4
When 2c is in the state of FIG. 4 (d), it is positive, and in the case of FIG. 4 (e), it is negative.

That is, when the laser spot 40 is shifted outward from the center of the tracks 18b and 18c, the difference signal is positive,
When the tracks 18b and 18c deviate inward from the center, the difference signal becomes negative. As you can see, track 17
Since the detection signal 42a is generated from the outer wobbling pit 14 and the detection signal 42b is generated from the inner wobbling pit 14, the detection signals 42a and 42b generated first and next are sequentially sampled, and the difference signal By using as a tracking error signal,
Regardless of the track 17, a positive signal is output as a tracking error signal when the laser spot 40 deviates from the center of the track to the outside, and a negative signal when the laser spot 40 deviates to the inside. Stable tracking can be realized by controlling the actuator of the objective lens so that the tracking error signal becomes zero.

For recording information, for example, when a magneto-optical recording material is used for the recording layer 34, as shown in FIG.
4 is irradiated with a laser beam 40 of a constant output from the substrate 30 side to heat the same, and at the same time a magnetic field is applied to align the magnetization of the recording layer 34 in a certain direction, and then the direction of the applied magnetic field is reversed and modulated by information. By irradiating the recording layer 34 with the laser beam 40 and heating it, the magnetization of the recording layer 34 is reversed to form the bit 68 composed of the reversed magnetic domain as shown in FIG.

At this time, as shown in the sectional view of FIG.
The recording layer 69 on the sidewall portion of the groove 22 is thinner than the flat portion 70, and the heat conduction is low. Therefore, the spread of the bit 68 is suppressed at the side wall portion of the groove 22. Therefore, the width of the bit 68 becomes the width of the recording area 20. Here, by making the sum of the track pitch and the width of the groove 22 substantially equal to the spot diameter of the laser beam 40 to be irradiated, the recording region 20 of the adjacent track is not irradiated with the laser beam 40 at the time of reproduction, so that crosstalk occurs. The track pitch can be made smaller than the spot diameter of the laser beam 40 without increasing the size, and the density can be increased.

Although one embodiment of the present invention has been described in detail with reference to FIGS. 1 to 7, the present invention can be implemented in other modes. For example, the material of the recording layer 34 is not limited to a magneto-optical recording material such as a rare earth transition metal amorphous alloy, a multilayer film of PtCo, PdCo, etc., an oxide magnetic material such as magnetic garnet, etc. Alternatively, a phase change material such as GeTeSb may be used.

A reflective layer made of a metal such as Al may be provided on the protective layer 36. Substrate 30, protective layers 31, 3
6. The material and film thickness of the reflective layer are also not particularly limited. The film thickness of the recording layer 34 is also not particularly limited. The depth of the wobbling pit 14 is also not particularly limited. Further, the wobbling pit 14 may be formed in a convex shape from the substrate 30. Further, the protective layers 31 and 36 are not always necessary, and one or both of them may not be provided.

The position, shape, size, etc. of the wobbling pits 14 are not particularly limited as long as they are between adjacent tracks. For example, wobbling pit 14
As for the position in the track direction, as shown in FIG. 1, it is not necessary to shift toward the rear of the track 17 toward the inner circumference, and the arrangement thereof is not particularly limited. For example, as shown in FIG. 8, the inner circumference may be displaced toward the front of the track 17.

Further, it is not necessary to dispose one common wobbling pit 14 between adjacent tracks 17, and for example, as shown in FIG. 9, if the positions in the track direction are the same, a plurality of wobbling pits 14 are provided. It may be composed of pits 79a and 79b. The plurality of pits 79a, 79
b may overlap as shown in FIG. 9 or may be separated.

The wobbling pits 14 are formed on the substrate 3
The pits are not limited to the concave or convex pits provided at 0, and pits made of a metal film of Al, Ta, Cr or the like may be provided on the substrate to be formed. As a result, the wobbling pit 14 can be formed even on a glass substrate or the like that is difficult to injection mold. Also, wobbling pit 14
May also be formed by heat treatment.

Further, in the same optical recording medium, the track pitch and the width of the recording area do not have to be constant and may change. That is, the recording area width and the track pitch may be reduced toward the outer circumference of the optical recording medium. At this time, the wobbling pits 14 do not need to be equidistant from the centers of the adjacent tracks, but may be located at the centers of either track.

The width, depth and shape of the groove 22 are not particularly limited. For example, the shape of the groove 22 is shown in FIG.
It may be V-shaped as in (a) or trapezoidal as in (b). Also, the depth of the groove 22 is not particularly limited. For example, the laser wavelength is λ, the refractive index of the substrate 30 is
Assuming that the depth of the groove 22 is λ / (4n), the groove 22
Since the reflectivity in the area is minimized, even if the spread of the bit is not suppressed by the sloped portion of the groove 22 and spreads to the bottom of the groove 22, the influence on the crosstalk becomes very small. Further, if the depth of the groove 22 is λ / (2n), the reflectance of the groove 22 does not decrease, so that the amount of reflected light does not fluctuate due to the fluctuation of the width of the groove 22 and the generation of noise can be suppressed. .. Further, by making the depth of the groove 22 deeper than λ / (2n), the effect of blocking heat conduction is increased, and the increase in crosstalk can be further suppressed. At this time, the depth of the groove 22 is λ / (4n) + mλ / (2n), where m is an integer, or
By setting mλ / (2n), the effect when the depth of the groove 22 described above is λ / (4n) or λ / (2n) is also obtained.

The wobbling pit 14 and the groove 22 do not have to have the same depth. For example, as shown in FIG. 11, the depth of the wobbling pit 14 is λ / (4n) and the groove 22
The depth of λ / (2n) may be deeper than the wobbling pit 14.

Further, the starting position and the ending position of the groove 22 are not particularly limited, and the positions in the track direction may be the same as shown in FIG. 9, for example.

The shape of the optical recording medium does not have to be circular, and when applied to an optical card or the like, the shape of the non-recording area or the recording area may be linear.

[0039]

As is clear from the above description,
According to the optical recording medium of the present invention, by providing a common wobbling pit and groove between the centers of adjacent tracks, stable tracking can be performed even with a small track pitch, and crosstalk is small. Higher density is possible. Furthermore, when making the master,
Since the deflection amount of the laser beam required for exposing the wobbling pit and the groove may be the same, the deflector can be simplified and the reproducibility can be improved, resulting in high productivity.

[Brief description of drawings]

FIG. 1 is a main part plan view showing the configuration of an embodiment of an optical recording medium of the present invention.

FIG. 2 is a cross-sectional view of an essential part in the track direction showing the configuration of the optical recording medium of the present invention.

FIG. 3 is a cross-sectional view of essential parts in the radial direction showing the configuration of the optical recording medium of the present invention.

4 (a) to (e) are explanatory views showing signals generated by wobbling pits in the optical recording medium of the present invention.

FIG. 5 is a block diagram showing an embodiment of a tracking servo circuit.

FIG. 6 is a plan view showing the shape of a recorded bit.

FIG. 7 is a sectional view showing a shape of a recorded bit.

FIG. 8 is a main part plan view showing another embodiment of the optical recording medium of the present invention.

FIG. 9 is a main part plan view showing another embodiment of the optical recording medium of the present invention.

10 (a) and 10 (b) are cross-sectional views of essential parts showing another embodiment of the optical recording medium of the present invention.

FIG. 11 is a cross-sectional view of essential parts showing another embodiment of the optical recording medium of the present invention.

FIG. 12 is a main-portion plan view showing the configuration of a conventional optical recording medium.

13A to 13C are explanatory diagrams showing signals generated by wobbling pits in a conventional optical recording medium.

[Explanation of Codes] 10 Optical Recording Medium 12 Servo Area 13 Data Area 14 Wobbling Pit 17 Track 22 Groove

Claims (1)

[Claims] 1. A plurality of tracks are provided, and a plurality of servo areas and data areas are alternately provided on each track, and in the servo areas, a predetermined width is provided inside and outside the center of the track, and a predetermined distance is also provided in the track direction. Used for tracking the first and second tracks between the centers of the first track and the second track that are adjacent to each other in the optical recording medium in which the wobbling pits are provided at positions apart by An optical recording medium having a common wobbling pit or wobbling pits and grooves at the same position in the track direction.