JPH09251667A - Disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the modulation degree of a pit signal to be almost flat by increasing the width dimension of the pit provided at least on the innermost peripheral side of a disk in the radial direction than the length in the peripheral direction of the disk. SOLUTION: Wobble pits 82, 83, clock pit 84 and sector address part 85 are formed on a disk substrate 81. Among these pits, the width dimension of the pit provided at least on the innermost peripheral side of the disk in the radial direction is made longer than the length in the peripheral direction of the disk. Meanwhile, it is preferrable for these pits that the widths of the pits provided at the inner peripheral side of the disk in the radial direction are almost equal to the widths of the pits provided at the outer peripheral side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc on which information (signal) can be recorded or reproduced, and particularly, the pit signal modulation degree (tracking error signal and bit modulation degree when reproducing pits) is made substantially flat. It's about disks.

[0002]

2. Description of the Related Art As a tracking system in an information recording / reproducing apparatus using an optical disk, there are a continuous servo system and a sample servo system. 1 for these methods
"Dual Feature of Continuous Groove Method and Sample Servo Method" described on pages 163 to 170 of Nikkei Electronics published on December 15, 986, and Showa 62
It is described in "Optical Disc Standardization Trend Explanatory Meeting Materials" issued by the Optoelectronic Industry and Technology Promotion Association's Optical Disc Roundtable and Information Processing Society of Japan Information Standards Investigation Committee published on December 3, 2012. The continuous groove servo method is a method that has been developed for a long time. On the other hand, the sample servo method is a method that has been actively developed recently because attention is paid to its good tracking stability.

An optical disk used for a conventional sample servo type recording / reproducing apparatus will be described with reference to FIG.

FIG. 2 shows a schematic plan view of an optical disk and a partially enlarged view thereof. As shown in the figure, tracks 17 and 1 are placed on a reading surface 16 of a disk substrate 11 of the optical disk.
8 are provided. An optical head (not shown) of the recording / reproducing apparatus travels on the tracks 17 and 18.
In the sample servo method, tracking sample marks 12 and 13 are provided on tracks 17 and 18 respectively. The sample marks 12 and 13 are formed as wobble bits which are distributed in the disc radial direction with the tracks 17 and 18 as the center.

The above-mentioned optical head has a wobble bit 12,
Tracks 17 and 1 indicate that the amount of reflected light from
8, and this point is set as the traveling position. The tracks 17 and 18 indicated by broken lines are examples of arrangement, and a large number of tracks 17 and 18 are actually provided. In the locally enlarged view of FIG. 2, wobble bit 1 in another track is shown.
2, 13 are also described. Also clock bit 14
Is provided for detecting a data bit (not shown) which is recorded later by the recording / reproducing apparatus. Further, the disk substrate 11 is a replica substrate made of plastic or glass.

The lengths of the wobble bits 12 and 13 and the clock bit 14 in the disk circumferential direction, that is, the bit length 1 is 90 ns when converted into the running time of the optical head. The actual size of the bit length l is about 0.5 μm when the disc radius r is 30 mm and the optical disc rotation speed is 1800 rpm. Further, when the disc radius r is 60 mm, the bit length 1 is about 1.0 μm.

On the other hand, the optical depth of these bits is
If the wavelength of the reading laser used in the optical head is λ, it is λ / 4. Here, the wavelength λ is usually selected to be 830 nm. The sample mark area provided with such bits is 1000 to 3 per one rotation (one track).
000 locations are required, usually 1376 locations. Further, there are 32 portions other than the sample mark area, that is, 32 sector address portions 15 in one track. The sector address portion 15 is provided with a bit (not shown) indicating an address.

The wobble bits 12 and 13 and the clock bit 14 of the optical disk corresponding to such a sample servo system are finely squeezed on a master such as a plastic or glass on which a photoresist film is formed, like a video disk or a compact disk. It is formed by irradiating the cutting laser beam and developing the irradiated master. The irradiation power P _B of the cutting laser light by the cutting machine is represented by P _B = Jv, where V is the linear velocity at an arbitrary point on the reading surface of the master optical disc, and J is the irradiation density of the laser light. Controlled to meet.

FIG. 3 shows a bit width (hereinafter referred to as a bit width) W in the radial direction of the disk with respect to the bit length 1 in this case.
Shows the measured values. As can be seen from FIGS. 2 and 3, the bit width W increases as the bit length 1 increases in the ordinary cutting machine. Therefore, in the sample servo type optical disc which is rotated at a constant angular velocity and used, as shown in FIG.
3 and the bit length l of the clock bit 14 are different between the inner circumference side and the outer circumference side of the optical disc. Similarly, the bit width W also differs between the inner and outer circumferences. Furthermore, when the bit length 1 formed on the reading surface of the optical disc is smaller than the beam spot diameter of the cutting laser light, the shorter the bit length 1 is, the narrower the formed bit width W is.

[0010]

In the above prior art,
When the optical disk master is manufactured, the bit length 1 and the width W are formed differently on the inner and outer circumferences of the optical disk. That is, the bit on the outer peripheral side becomes large. For this reason, there occurs a phenomenon that the bit signal modulation degree (tracking error signal and bit modulation degree) changes within the range of the recording area on the reading surface during reproduction of the optical disc. That is, the prior art has not considered this point.

An object of the present invention is to provide a disk having a pit signal modulation degree that is substantially flat.

[0012]

The above object is a disk having a plurality of pits, and the width dimension in the disk radial direction of at least the innermost pit of the pits in the disk radial direction is determined by the disk This is achieved by making the length longer than the circumferential length.

[0013]

FIG. 4 shows experimental data showing the relationship between the bit area and the bit signal modulation factor (tracking error signal and bit modulation factor). According to FIG. 4, the tracking error signal and the bit modulation degree each have a maximum value with respect to the bit area, and in the vicinity of this maximum value, these changes (differential values) with respect to changes in the bit area are small.

Therefore, in order to make the tracking error signal and the bit modulation degree substantially constant with little variation, it is effective to set a bit in the bit area corresponding to these maximum values. The bit length 1 in the disk circumferential direction differs between the inner and outer circumferences in the disk radial direction, and the bit length lo on the outer circumference side is longer than the bit length li on the inner circumference side. As a result, a means for forming pits on the master disc as Wi> Wo while maintaining the pit area substantially constant in the relationship between the pit width Wi and the pit width Wo of the inner peripheral side pits in the disc radial direction (hereinafter referred to as "means A) ”) is adopted to make the inner peripheral side bit width Wi longer than the outer peripheral side bit width Wo, the inner peripheral side bit area and the outer peripheral side bit area can be made substantially the same. it can.

It is preferable that the bit length lo and the bit width Wi are set to the same size, and the bit length li and the bit width Wo are set to the same size. Further, in FIG.
A bit area (1 × W) of about 0.35 μm ² is preferable because the tracking error signal becomes almost constant. Furthermore, when the track interval Tr is sufficiently large, it is possible to employ a bit area located between the maximum value of the tracking error signal and the maximum value of the bit modulation degree.

Further, FIG. 5 shows experimental data showing the relationship between the bit width W and the tracking error signal. Here, the bit length 1 is about 0.5 to 1.0 μm. As can be seen from FIG. 5, the tracking error signal also has the maximum value with respect to the bit width W, and the change amount with respect to the change of the bit width W is small near this maximum value. Therefore, in order to keep the tracking error signal constant with little variation, there is an optimum value for the bit width (the value of the bit width corresponding to the maximum value of the tracking error signal). Means for forming pits on a master disc (hereinafter referred to as "means (B)"), with the relationship between the pit width Wi of the inner pit and the pit width Wo of the outer pit being WiＷWo.
It is sufficient to make the bit width W almost constant around the optimum value by adopting. Then, in FIG. 5, the optimum value of the bit width W is about 0.5 μm. Although not shown,
As will be described later, it has been confirmed that the pit modulation degree becomes substantially constant by making the pit width W substantially constant near the optimum value.

The measurement data of FIGS. 4 and 5 are as follows. Regarding the bit forming specifications, the numerical aperture NA of the objective lens (which will be described later) is about 0.7, and the beam spot diameter φ, which is the diameter at which the laser light intensity drops to 1 / e ² of the spot center, is about 0.9 μm. , The track pitch Tr is 1.
5 μm, the bit length 1 is about 0.5 to 1.0 μm, and the optical bit depth (λ / 4) is about 13 when a polycarbonate having a refractive index of about 1.59 is used as the disk substrate.
0.0 nm. Also, regarding the reproduction optical system specifications, N
A is about 0.5, the laser wavelength λ is about 830 nm, the laser beam diameter φ is about 1.5 μm, and the beam cross-sectional area is about 1.8 μm ² .

Here, a pit forming method will be described.
First, since the rotating means rotates the master with the linear velocity at the radial position on the surface as the predetermined value v, the position of the master on which the bit is formed is updated. The laser irradiating means irradiates the position of the master disk on which the bit is to be formed with the cutting laser light, so that the bit is formed on the master disk. Since the irradiation power control means controls the irradiation power of the cutting laser light by a function (J ₁ v + J ₀ ′), the size of the formed bit is changed according to the position in the disk radial direction.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic plan view and a partially enlarged view of a sample servo type optical disk according to a first embodiment of the present invention. In Figure 1, the disk substrate 1 is made of poly Capo sulfonate (PC), an inner diameter phi ₁ of the hole 6 provided in its center 15 mm, outer phi ₀ of the disc substrate 1 is 130 mm, the thickness t is 1.2mm The data area 7 has a radius r in the range of 30 to 60 mm. The track pitch Tr is 1.5 μm and the optical bit depth (λ /
4), assuming that the refractive index of PC is about 1.59, about 130.
0 nm. Here, the laser wavelength λ is 830 nm. A helium cadmium (He-Cd) laser generator having a laser wavelength λ ₀ of 441.6 nm is used as a laser light source for cutting. A positive resist is used as the photoresist. Reference numeral 5 in the figure denotes a sector address portion similar to 15 in FIG.

The local enlarged view shown at the bottom of FIG. 1 shows a part (r) of a track at a radius r = 30 mm on the horizontal axis side.
30) and a part (r60) of the track at a radius r = 60 mm, and the vertical axis represents the means (A) and the means (B) employed.

Here, 2 and 3 are wobble bits similar to 12 and 13 in FIG. 2, and 4 is a clock bit similar to 14 in FIG. First, the case where the above-described means (A) is employed will be described. In this case, the relationship between the bit width Wi = W ₁ of the r30 portion and the bit width Wo = W ₂ of the r60 portion is set as W ₁ > W ₂ . The bit is formed by setting approximately 0.7μm inner circumferential side bit width W _1, the outer peripheral side bit width W ₂ of about 0.35 .mu.m in this example was approximately 0.35 .mu.m ² constant bit area .

Now, a method of forming a bit having a predetermined area will be described. Generally, the bit size is proportional to the irradiation power P of the laser beam at the time of cutting. Further, as shown in FIG. 3, when bits are formed by the conventional irradiation power control method (P _B = Jv), the inner peripheral side bit width Wi becomes narrower and the outer peripheral side bit width Wo becomes wider. Therefore, a method of setting the irradiation power P to a constant J ₀ ≒ 2.7 mJ is adopted as the irradiation power control method, and cutting is performed on the rotated disk master. As a result, the bit area becomes almost constant, and the bit width relationship is W
_1> W ₂ become. As a result, the tracking error signal and the bit modulation degree are each about 40 in the recording area.
%, About 70% and a constant optical disk can be manufactured.

In the first embodiment described [0024] above, although the bit area as 0.35 .mu.m ² constant, sufficient tracking error signal and the bit modulation even bit area 0.2 to 0.8 [mu] m ² was obtained It was The bit area at this time corresponds to 10 to 45% of the reproduction light beam area of 1.8 μm ² .

The case of controlling the magnitude of the irradiation power P has been described as the irradiation power control method, but a constant bit area can be obtained by controlling the bit cutting time T.

Conventional bit cutting time T ₀ = 90
FIG. 7 shows a time chart for the bit cutting times T _A , T _B , and T _D after correction (control) for ns.
In FIG. 7, the horizontal axis represents time, and the vertical axis represents irradiation ON of the cutting laser light. The conventional bit cutting time T ₀ is shown by a broken line. Also, in this time chart, wobble bit 2 from the left side
The bit cutting time T ₀ , the wobble bit 3 time T ₀ , and the clock bit 4 time T ₀ are described in this order. FIG. 7A shows the bit cutting time T _A at r30.
This indicates 120 ns.

FIG. 7B shows the radius r = 45 m of the optical disk.
It shows the bit cutting time T _B = 85 ns in a part (r45 part) of the track at m. Figure 7
(C) Bit cutting time T _D = 5 at r60
0 ns. Thus, even when the time T ₀ is corrected to the times T _A , T _B , and T _{D according} to the value of the radius r of the optical disk, a substantially constant bit area (0.35 μm ² ) can be obtained.

Next, referring to FIG.
The case where is adopted will be described. In this case, r30
Part bit width Wi = W ₃ and r60 part bit width Wo = W ₄
Is set such that W ₃ ≒ W ₄ . In this example, the bit was formed by setting W ₃ ≈W ₄ ≈0.5 μm.

Now, a method of forming a bit having a predetermined bit width W will be described with reference to FIG. FIG. 6 shows the laser irradiation power P with respect to the disk radius r for each irradiation power control method. The broken line in the figure shows the conventional irradiation power control method (P _B = Jv), and the solid line shows the irradiation power control method (P = J ₀ ) of the present invention used when a bit having a predetermined area is manufactured. It is shown. Then, the alternate long and short dash line in FIG. 6 shows the irradiation power control method (P = J ₁ v + J ₀ ′) of the present invention, which is used to make the bit width W constant in the recording area this time.
Here, J ₁ and J ₀ ′ are laser beam irradiation densities. In this method (P = J ₁ v + J ₀ ), J ₁ ≒ 0.65 m
Cutting was performed on the master disc rotated by setting J, J ₀ ′ ≒ 1.7 mJ. When cutting is performed in this manner, the bit width W becomes substantially constant, and the bit width relationship becomes W ₅ ≈W ₄ . As a result, it was possible to manufacture an optical disk in which the tracking error signal and the bit modulation degree were approximately constant at about 35 to 40% and about 60 to 80% in the recording area.

By controlling the bit cutting time T, a substantially constant bit width W could be obtained. This is applied to the case of FIG.
Bit cutting time T _A at the section is 120 ns, r4
Bit cutting time T _B in the 5th part is 105 ns, r
The bit cutting time T _{D for} 60 copies is 90 ns. As described above, the conventional bit cutting time T _{0 is changed according} to the value of the radius r of the optical disk to the time T _A , T _B , T.
Even when the correction is performed with _D , a substantially constant bit width (0.5 μm) can be obtained.

Further, in the above embodiments, on the reading surface of the optical disk, the bit is circular or the bit length l rather than the bit width W.
However, even if the beam spot diameter of the cutting laser light in the disk circumferential direction (track direction) is made smaller than the shortest bit and the bit width W forms a bit longer than the bit length 1, W can be made constant at the inner and outer circumferences. This embodiment is shown in FIG.

Similar to FIG. 2, FIG. 8 is a schematic plan view and a partially enlarged view of the optical disk, in which 81 is a disk substrate, 82 and 83 are wobble bits, 84 is a clock bit, and 85 is a sector address. It is a department. This Figure 8
Also in this embodiment, it is possible to obtain an optical disc having a substantially constant bit signal modulation accuracy. Furthermore, the same effect can be obtained even if the beam spot diameter at the time of cutting is narrowed down by using an optical system so that it becomes equal to the minimum bit length.

Now, the cutting machine used for forming the bits of the optical disc of the present invention will be briefly described with reference to an example.

FIG. 9 is a configuration diagram of a cutting machine used in the present invention. In the illustrated cutting machine, when forming a bit, first, the glass master disk 28 having the photoresist film 29 on the reading surface is rotated around the rotation center axis 30 by using a rotating means (not shown). Further, the head moving unit 25 including the optical deflector 26 and the objective lens 27 is moved in the radial direction as the glass master 28 rotates. Here, the movement of the head moving unit 25 is equivalent to one track pitch in one rotation.
In such an operation state of the mechanical system, the helium-cadmium (He-Cd) laser generator 21 emits the laser light 20.
Is output. The laser light 20 passes through the irradiation power controller 22, the mirror 23, the collimator lens 24, the light modulator 31, the collimator lens 32, and the mirror 33, and sequentially enters the head moving unit 25. The laser beam 20 ′ incident on the head moving section 25 is irradiated on a photoresist film 29 via an optical deflector 26 and an objective lens 27. As a result, cutting is performed and bits are formed.

The control of the laser irradiation power P (P = J ₁ v + J ₀ ′) described in FIG. 6 and the like is performed by the irradiation power controller 22. The linear velocity v was set based on the position of the head moving unit 25 detected by a potentiometer (not shown) and based on the detected value (however, the method is not limited to this). Further, the optical modulator 31 controls the irradiation on / off of the laser light 20 for cutting (modulation) at the timing shown in the bit cutting time T _C of FIG. 7.
I do. Then, the laser light 20 ′ modulated by the optical modulator 31 is deflected by the optical polarizer 26. This deflection is performed only when the wobble bit is formed, and is performed in order to irradiate the cutting laser beam at a symmetrical position in the disk radial direction around the track.

[0036]

According to the present invention, since the bit signal modulation degree can be made substantially constant (flat), a high quality optical disc can be provided.

[Brief description of drawings]

FIG. 1 is a schematic plan view and a partially enlarged view of an optical disc of an embodiment according to the present invention.

FIG. 2 is a schematic plan view and a partially enlarged view of a conventional optical disk to which a sample servo method is applied.

FIG. 3 is a characteristic diagram for explaining the present invention.

FIG. 4 is a characteristic diagram for explaining the present invention.

FIG. 5 is a characteristic diagram for explaining the present invention.

FIG. 6 is a characteristic diagram for explaining the present invention.

FIG. 7 is a characteristic diagram for explaining the present invention.

FIG. 8 is a schematic plan view and a partially enlarged view of an optical disc of an embodiment according to the present invention.

FIG. 9 is a configuration diagram showing an example of a cutting machine used for forming bits of the optical disc of the present invention.

[Explanation of symbols]

1, 11, 81 ... disk substrate, 2, 3, 12, 13,
82, 83 ... Wobble bit, 4, 14, 84 ... Clock bit, 5, 15, 85 ... Sector address part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoji Ishigaki, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Hitachi, Ltd. Home Appliances Research Laboratory (72) Inventor Yukio Fukui 292 Yoshida-cho, Totsuka-ku, Yokohama, Hitachi, Ltd. Home Appliances Research Co., Ltd. In-house

Claims (2)

[Claims] 1. A disc having a plurality of pits,
A disk characterized in that at least the pit of the pits provided on the innermost side in the disk radial direction has a width dimension in the disk radial direction longer than a length in the disk circumferential direction. 2. The disk according to claim 1, wherein the width of the pits provided on the inner peripheral side in the radial direction of the disk is substantially equal to the width of the pits provided on the outer peripheral side.