JPH09198717A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To put a land-groove recording system magneto-optical disk capable of high speed access and also suitable for mass production, to practical use by making the optical disk contain a circular arc or an ellipsoidal arc in a part of a wall surface of a boundary between a land part and a groove part. SOLUTION: The circular arc and the ellipsoidal arc are contained in a part of the wall surface of the boundary between the land part and the groove part. Then, this part is a header information common to the land part and the groove part. In this constitution, a groove exists in a header area as well. The groove width of the header area and the groove width of a data area are the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk capable of high density recording, and more particularly to an optical disk which can be accessed at high speed and is suitable for mass production.

[0002]

2. Description of the Related Art An optical disk capable of storing high-density data and capable of processing information at high speed has attracted attention as a computer memory. The optical density of 5.25-inch and 3.5-inch ISO-type optical disks and phase-change type optical disks have a recording density of 4 to 5 times higher than that of the first generation, and it is expected that their spread will be further accelerated in the future. Has been done.

Recently, rewritable optical disks of 120 mm in diameter and 86 mm in diameter are beginning to appear. Furthermore, recently, a standard for SD (DVD) (digital video disc) has been established, and application of the optical disc to the multimedia field is surely considered. In order to guide the laser beam emitted from the optical pickup of the recording / reproducing device along the information sequence, that is,
A guide for tracking is formed in a spiral shape with a concave or convex shape. This concave or convex guide is called a guide groove. Further, the guide groove will be described in detail. In the ISO standard, the concave portion, that is, the far side when viewed from the pickup is called a land, and conversely, the convex portion, that is, the near side when viewed from the pickup is called a groove. Since information is written on either the land or the groove, the distance from the center of the land or groove to the center of the adjacent land or groove is called the track pitch.

In addition to the guide groove on the optical disc, a preformat signal represented by address information for data management such as a track number, a sector number, a frame number, a chapter number, etc. is convex when seen from the pickup. Are formed in advance as a row of marks, that is, a pit row. The preformat signal area of these address information is called a header area, and the address information is also called header information. In this way, the optical disc is divided into a user area and a header area, which are used by the user for recording and reproducing information.

The width W of the groove is the width W above the groove.
If the width of the top and the bottom of the groove is Wbottom, then W = (W
top + Wbottom) / 2. The height from the bottom of the groove to the top of the groove, that is, the step between the land and the groove is also referred to as the groove depth. Taking the land recording system as an example, these actual dimensions are such that the groove width is 0.3 to 0.6 μm, and the groove depth is λ where the wavelength of the recording / reproducing laser beam is λ and where the substrate refractive index is n. For example, λ / (10 · n) to λ / (6 · n).

The standard track pitch was 1.6 μm, but recently, it has been reported that the track pitch should be narrowed in order to record information at a higher density.
m and 1.0 μm have been reported. However, in the case of an optical pickup equipped with an objective lens having a numerical aperture (NA) of 0.5 to 0.6, if the track pitch is narrower than 1.4 μm, the information written in adjacent tracks will be read simultaneously (called optical crosstalk). However, since the tracking error signal required for tracking becomes extremely small, accurate tracking becomes difficult.

Incidentally, a land-groove recording system has been proposed as another approach for recording information at a high density. This is to increase the recording density by halving the track pitch by recording information on both the land and the groove, whereas the conventional information was recorded on only one of the land and the groove. It is a thing. For example, the distance from the center of a land (or groove) to the center of an adjacent land (or groove) is 1.4μ.
In the case of m, by recording on both the land and the groove, the track pitch becomes 0.7 μm and the recording density can be increased.

In this system, if the groove depth is set to an appropriate value, the information in the user area of the land (groove) track may leak during reproduction of the information in the user area of the adjacent groove (land) track. Due to
It is possible to prevent the problem that signals are mixed by being reproduced at the same time, that is, optical crosstalk. In addition, the tracking error signal shows the distance between the centers of lands (or grooves).
Needless to say, a sufficient size can be secured because it is 1.4 μm. Thus, regarding the user area,
A technique suitable for the land-groove recording method has been proposed.

However, since the optical crosstalk in the header area formed as a pit row has not been disclosed so far, the present inventors have found that the optical crosstalk in the header area can be theoretically suppressed. The crosstalk-free conditional expression that expresses is derived analytically. The results are shown below. Note that d _G is the step between the land and groove, d _P is the depth of the pit, n is the refractive index of the optical disk substrate, P ′ and Q ′ are the track pitch p, the reproduction laser beam wavelength λ, and the objective. It is a function depending on the lens NA and the pit width W _P.

Pit on land P '. [Cos (4πnd _G / λ) {1-cos (4πnd _P / λ)} -sin (4πnd _G / λ) sin (4πnd _P / λ)] + Q' ・ { 1-cos (4πnd _P / λ)} = 0 (1) Regarding pits on the groove P ′ · [cos (4πnd _G / λ) {1-cos (4πnd _P / λ)} −sin (4πn ( −d _G ) / λ) sin (4πnd _P / λ)] + Q ′ · {1-cos (4πnd _G / λ)} = 0 (2) That is, the formulas (1) and (2) are simultaneously calculated. If the pit depth d _P and the pit width W _P that satisfy the above conditions are selected, crosstalk can be made mutually free even if the pits formed on both the land and the groove are reproduced. Two means are possible for this. One is a method of setting the pit depth d _P = λ / (4n). By doing this, sin (4πnd _P / λ) = 0
Therefore, Eqs. (1) and (2) are the same and are satisfied at the same time. The other method is to reverse the concave-convex relationship between the land pits and the groove pits. That is, a pit is formed on the land and a groove, that is, a hill is formed on the groove so that its height is the same as the pit depth when viewed from the pickup, or vice versa. Form hills and pits on the grooves. This way (2)
Sin (4πnd _P / λ) = sin (4πn (-d _G ) / of the formula
λ) holds, and in this case as well, Eqs. (1) and (2) are the same and are satisfied at the same time.

In practice, however, it is not possible to form a pit or a hill satisfying the above conditions in each of the land portion and the groove portion after forming a step between the land portion and the groove portion which is free from optical crosstalk. It is difficult to think from the stamper manufacturing process that is indispensable to.

[0012]

Therefore, there is no suitable proposal as to what kind of form should be used for the header area of the land / groove recording system, which prevents the land / groove recording system from being put into practical use. This is one of the biggest reasons. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a header area in an excellent form that enables high-speed access and practical use of a land-groove recording type magneto-optical disk that is also excellent in mass production. To do.

[0013]

In order to solve the above-mentioned problems, the present inventors have found that a part of the wall surface of the boundary between the land portion and the groove portion includes an arc or an elliptic arc, or the arc and the elliptic arc. The present invention has been found to be able to provide a high-density recording optical disk that enables high-speed access and is also excellent in mass production by including both.

[0014]

1 is an explanatory view showing an optical disc according to the present invention. That is, the structure is such that a part of the wall surface at the boundary between the land portion and the groove portion includes both an arc and an elliptic arc, and this portion is common header information for the land portion and the groove portion. This structure also has a groove in the header area. The groove width of the header area and the groove width of the data area are the same.

FIG. 2 shows an optical disk according to a fourth aspect of the present invention. The groove width of the header area and the groove width of the data area are different, and the latter is larger than the former. With this configuration, the carrier level of the reproduced signal in the circular arc or elliptic arc portion (header mark) of the header area increases, so the reproduction error rate of the header mark can be kept low, or the size of the header mark can be reduced to a higher level. It has the effect of increasing the density.

FIG. 3 shows an optical disk according to claim 6 of the present invention, wherein the groove center in the header area and the groove center in the data area do not coincide. Even with this configuration, as in the optical disc shown in FIG. 2, the carrier level of the reproduction signal of the header mark increases, so that the reproduction error rate of the header mark is suppressed to a low level, or the size of the header mark is reduced. It has the effect of increasing the density.

Next, a magneto-optical disk having the shape shown in FIG. 3 is prepared. In this disc, the step difference between the land and groove and the depth of the header mark are both 50 nm, and the land width and groove width in the data area are approximately equal to 0.6 μm.
There are two types, m and 0.7 μm, and the groove width in the header area is 0.3 μm (land width is 0.9 μm) and
0.4 μm (land width 1.0 μm). The width W _{HM of the} header mark is 0.3, 0.4, 0.5 for the above two types and
Prepare four types of 0.6 μm. In addition, a magneto-optical recording / reproducing device is separately prepared. This device has a laser beam wavelength of 680 nm, an objective lens NA 0.55, and an objective lens pupil diameter D.
And an optical pickup with a ratio D / W = 0.85 of the laser beam diameter W (the diameter that becomes 1 / e ² of the central intensity as a Gaussian beam) when entering the objective lens and a wavefront aberration of 0.055λ (rms). .

A magneto-optical disk of each shape is set in a magneto-optical recording / reproducing apparatus and is reproduced while being rotated. The relationship between the header mark width W _HM and the change in the carrier level of the reproduced signal at the header mark portion is measured. This is shown in FIG. As shown in Fig. 4, the larger the pit width, the better.
It can be seen that 0.4 μm to 0.6 μm is desirable. The same applies to the disk having the structure shown in FIGS. 1 and 2.

Next, a magneto-optical disk having the same steps as those described above except that the level difference between the land and the groove and the depth of the header mark is 200 nm and 280 nm, and the track count signal (push-pull method) is prepared. Measure. This is shown in FIG. For comparison, as shown in FIG. 6, a track count signal of a boundary pit type magneto-optical disk in which a header area has no groove and pits are formed on a boundary between a land track and a groove track is also shown.
Here, it is desirable that the track count signal be large, but if it becomes too large, it adversely affects the focusing servo and is disadvantageous for high-speed access, so 0.35-0.7 is desirable. As shown in FIG. 5, in the boundary pit method, the track count signal when the light spot does not cross the pit is very small. However, in the method of the present invention, the track count signal is large even when the light spot does not cross the pit. Signal is obtained, especially when the land / groove step and header mark depth are 100 to 25
It can be seen that a track count signal level of about 0 nm is good. The same can be said for land and groove widths of 0.7 μm. The same tendency also applies to the disk having the structure shown in FIGS.

The above is a description of the case where the land portion is engraved in the same depth as the groove portion in an arc or elliptic arc shape. On the contrary, the groove portion is arced or formed at the same height as the land portion. The same effect can be obtained when the elliptical arc-shaped projection is provided.

[0021]

As described above, according to the present invention, it is possible to realize high-speed access, and at the same time, it is possible to put the land-groove recording type magneto-optical disk excellent in mass production into practical use. Can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an optical disc according to the present invention.

FIG. 2 is an explanatory diagram showing an optical disc according to claim 4 of the present invention.

FIG. 3 is an explanatory diagram showing an optical disc according to claim 6 of the present invention.

FIG. 4 is a graph showing the relationship between the header mark width W _HM and the change in the carrier level of the reproduced signal at the header mark portion.

FIG. 5 is a graph showing a relationship between a step difference between a land and a groove and a track count signal.

FIG. 6 is an explanatory diagram showing a header area and a data area of a boundary pit type magneto-optical disk.

Claims (9)

[Claims] 1. An optical disc, wherein a part of a wall surface of a boundary between a land portion and a groove portion includes an arc or an elliptic arc, or includes both an arc and an elliptic arc. 2. Including an arc or an elliptical arc, or
The optical disc according to claim 1, wherein the region formed by including both the circular arc and the elliptical arc is a header region. 3. The optical disc according to claim 1, wherein information is recorded on both the land portion and the groove portion. 4. Including an arc or an elliptical arc, or
2. The optical disc according to claim 1, wherein a groove width in an area formed by including both an arc and an elliptic arc is different from a groove width in an area where the arc or the elliptic arc does not exist. 5. Including an arc or an elliptical arc, or
5. The optical disk according to claim 4, wherein the groove width in the area where the arc and the elliptic arc do not exist is larger than the groove width in the area configured to include both the arc and the elliptic arc. 6. Including an arc or an elliptical arc, or
2. The optical disc according to claim 1, wherein a groove center in a region including both an arc and an elliptic arc does not coincide with a groove center in a region where the arc or the elliptic arc does not exist. 7. The optical disk according to claim 1, wherein the length of the arc or elliptic arc in the direction perpendicular to the track is in the range of 0.4 to 0.6 μm. 8. The difference between the land portion and the groove portion is 110 to 22.
The optical disk according to claim 1, wherein the optical disk has a thickness of 0 nm or a range of 230 to 330 nm. 9. The optical disk according to claim 7, wherein the distance between the center of the land and the center of the groove adjacent to the land is 0.7 μm or less.