JPH02210628A - Optical disk - Google Patents

Abstract

PURPOSE:To stabilize an error signal in the entire recording area by making the quantity of deflection from the center of the virtual track of wobble bits, formed deflecting left and right from the center of a virtual track requiring a bit modulation degree and a tracking number difference signal, a smaller at a disk inside part than the wobble width quantity on a disk outer peripheral side. CONSTITUTION:A replica substrate made of polycarbonate is used as the disk substrate 11 of the optical disk and wobble bits 12 and 13 which are formed within a range of 30-40mm in inner peripheral side disk radius are formed so that the wobble width from the virtual track center 14 is 7p/32 of bit track pitch (p). Further, the wobble width is varied stepwise to p/4 within a range of 40-60mm in outer peripheral side disk radius. Then the bit modulation degree and tracking error signals from wobble pits essential to the optical disk for sample servos for the virtual track are made stable and excellent in the entire recording area.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc, and in particular, to an optical disk in which the difference in pit modulation degree from tracking pits on which information can be optically recorded and reproduced is evened out within a recording area. The present invention relates to an optical disk for a sample servo system suitable for use as a support.

[Conventional technology]

There are two tracking methods for optical discs that can record information: a continuous groove servo method and a sample servo method. These methods are described, for example, in "Nikkei Electronics J, December 16, 1986 issue, pages 163 to 1.
This is described in the paper titled ``Dual system of continuous groove method and sample servo method'' on page 70.

The continuous groove servo method is a method that has been developed in the past, but the sample servo method has been actively developed recently because of its good tracking stability.

FIG. 2(a) is a plan view schematically showing a disk substrate in a conventional sample servo system, and FIG. 2(b) is a partially enlarged view of FIG. 2(a).

In FIG. 2(a), the disk substrate 11 is a replica substrate made of plastic or the like, and in the sample servo system, as shown in FIG. 2(b).

Tracking sample marks 12 and 13 are provided at various locations on the tracks of the disk substrate 11.

The sample marks 12 and 13 are formed as wobble pits wobbled left and right symmetrically from a virtual track center 14, and the running position of the recording/reproducing head is detected and set by setting the point where the amount of reflected light from the wobble pits is the same as the track center 14.

Further, 15 is a clock pit for tracking and detecting data bits.

In FIG. 2(b), the pit length of pits 12, 13°15 is about 90 ns on the time axis, and the disk radius is 30 ns.
m m , 0 at disk rotation speed 1800 rpm
．． 5μm, 1.0μm for disk radius 60mm
becomes. In addition, the optical depth of the pit 12°13.15 is λ/4 (λ; reading laser wavelength, usually 830 mm
). Approximately 1,000 to 3,000 pits are required around the circumference of the disc, and usually 1,376 pits are required.
It is a separate place. Other parts are sector address part 1
6 (approximately 30 locations around the circumference), and the disk substrate 11
There is only a pit above.

The wobble width of the wobble pits 12 and 13 is formed at a position approximately ±P/4 of the track pitch P from the virtual track center 14. However, as mentioned above, the length of the pit is different between the inner and outer circumferences, so the pit modulation degree is different as a result, and the modulation degree due to the pit is dependent on the relationship between the inner circumference of the recording area and the outer circumference of the recording area. Become. This occurs because the amount of reflected light from the pits that enters the reproducing head is proportional to the pit length. In order to solve this phenomenon, it is possible to increase the pit length at the inner periphery where the disk radius is small, but with this method, the pit period is shorter at the inner periphery compared to the outer periphery, so in the worst case If the length is increased, there will be a problem that adjacent pits will be connected to each other.

[Problem to be solved by the invention]

In the above conventional technology, when forming pits in constant angular velocity (CAV) mode, the inner circumferential pit size becomes smaller.
No consideration has been given to the decrease in the pit modulation degree, and when attempting to obtain the modulation degree of the inner pit, a problem has arisen in that the tracking error signal at the outer periphery decreases.

An object of the present invention is to provide an optical disc that can stably obtain a pit modulation degree and a tracking error signal over the entire circumference within a recording area.

[Means to solve the problem]

The above purpose is to calculate the wobble width Wi at the inner circumference of the disk and the wobble width Wi at the inner circumference of the disk, which is formed by wobble pits that are swung left and right from the center of the virtual track that requires the pit modulation degree and tracking error signal. The relationship with the wobble width Wo at the outer periphery is expressed as Wi<Wo
This is achieved as a configuration formed as follows.

FIG. 3(a) shows the relationship between the amplitude of the wobble pit, the degree of pit modulation, and the tracking error signal (p indicates the track pitch, and r indicates the disk radius). The modulation degree and tracking error signal here are determined from the pit modulation characteristic obtained when the reproducing head passes over and between pits.

In the waveform diagram of FIG. 3(b), the waveform A is the waveform obtained when the head passes over the pit, and the waveform B is the waveform obtained when the head passes between the pits, where (Vs/Vg) is the pit modulation degree, and (Vt
/Vg) is the tracking error signal. Note that the pit width in the figure is approximately 0.6 μm. Also, the reproducing head beam spot diameter is approximately 1.0 μm, and the track pitch p is 1.
．． It is 5 μm.

According to FIG. 3(a), as the wobble width of the wobble pit increases, the pit modulation degree decreases and the tracking error signal increases. Also.

The difference in disk radius has almost no effect on the tracking error signal, but it has a large effect on the degree of pit modulation, and as the disk radius r becomes smaller, the degree of modulation becomes smaller.

The present invention utilizes the relationship shown in FIG.

In other words, even if the wobble width is p/4, the modulation degree at the outer periphery of the disk sufficiently satisfies the standard value of 0.4 or more, so a tracking error signal is obtained (approximately 0.15 or more).
Define the cutting conditions as follows.

Also, if the inner circumferential side is cut under these conditions, the modulation degree on the inner circumferential side cannot be obtained as described above.

Increase the wobble width of the inner wobble pit from p/4 to approximately 3p.
By changing to /16, both the modulation degree and the tracking error signal can be satisfied even on the inner circumferential side.

In this way, by forming pits with different wobble widths within the recording area, it is possible to keep both the pit modulation degree and the tracking error signal within the standard.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to FIG.

FIG. 1 is a schematic plan view and partially enlarged view showing an embodiment of a disk substrate of an optical disk according to the present invention, in which (a) is a plan view, (b) and (c) are partially enlarged views, respectively.

Hereinafter, an example in which the present invention is applied to a CD-RAM optical disc having a recording area of 30 to 60 mm in radius will be described with reference to FIG. 1. The optical disk substrate 11 shown in FIG. 1 is a replica substrate made of polycarbonate, and its inner diameter 12 is 15 mm and outer diameter is 130 mm.
mm, and the thickness t is 1.2 mm. In addition, the pit formation specifications are pit width w', 0.6 μm, optical pit depth λ
/4 (λ; reading laser wavelength is 830 nm), and the track pitch p is 1.5 μm.

In this embodiment, the wobble width from the virtual track center of the wobble pit formed in the inner disk radius range of 30 to 40 mm is 7p/32 of the track pitch p,
In the range of outer disk radius from 40 to 60 mm, the wobble width was changed stepwise to p/4.

By making the wobble width of the wobble pit formed in the region with a small pit modulation smaller than p/4 as in this embodiment, the pit modulation in the entire region can be kept within the standard. Furthermore, the tracking error signal can also be satisfied.

Next, as a second example, in the above example, the wobble width was changed stepwise, but the inner disk radius was changed to 30
m m, the track pitch p is 7p/32. radius 60
In m m, let it be p / 4, and the area in between is 7
The p was continuously changed from p/32 to p/4, and the same results as in the above example were obtained.

In the above description of each embodiment, the present invention has been described in detail for the case where the disk dimensions and bit dimensions are the same, but the present invention is not limited to these, and the point is to form wobble pits within the recording area. The positions may not be the same, but may be formed at different positions so that a good pit modulation degree and tracking error signal can be obtained.

〔Effect of the invention〕

According to the present invention described above, there is an effect that the pit modulation degree and tracking error signal from the pits from the wobble pits, which are essential for the optical disk for sample servo, can be stably obtained as good signals within the entire recording area. .

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view and partially enlarged view showing an embodiment of a disk substrate of an optical disk of the present invention, FIG. 2 is a schematic plan view and partially enlarged view of a disk substrate according to the prior art, and FIG. 3 is a wobble FIG. 3 is a diagram showing the relationship between the wobble width of a pit, the degree of pit modulation, and a tracking error signal. 11...Disk board, 12.13...Wobble pit, 14...Virtual track center, 15...Clock pit, 16...Sector address. Collected drawings

Claims (1)

[Claims] 1. A sample servo that tracks a recording/reproducing head by forming wobble pits on the disk surface that are swung left and right from the center of a virtual track, and tracking the head based on the signal strength from the wobble pits. What is claimed is: 1. An optical disk for use in an optical system, characterized in that an amplitude of the wobble pit from the center of a virtual track changes within a recording area. 2. The formation positional relationship of the wobble pits is such that the relationship between the wobble width Wo of the pits at the outer periphery where the disk radius is large and the wobble width Wi at the inner periphery area where the radius is small is the distance from the virtual track center. 2. The optical disc according to claim 1, wherein Wi<Wo and the change thereof is configured to change stepwise or continuously.