JP2713974B2 - disk - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk on which information (signal) can be recorded or reproduced, and more particularly to a pit signal modulation degree (a pit modulation for reproducing a tracking error signal and a pit). Degree) is about a flat disk.

[Conventional technology]

A tracking method in an information recording / reproducing apparatus using an optical disk includes a continuous servo method and a sample servo method. These systems are described on page 163 of Nikkei Electronics, published on December 15, 1986.
"Dual feature of continuous groove method and sample servo method" described on page 70, "Optical Industry Technology Promotion Association Optical Disc Roundtable" and Information Processing Society of Japan, published on December 3, 1987 It is described in the "Optical Disc Standardization Trend Briefing Material" by the Standards Research Committee. 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 disc used in a conventional sample servo type recording / reproducing apparatus will be described with reference to FIG.

FIG. 2 shows a schematic plan view of the optical disk and a partially enlarged view thereof. As shown, tracks 17, 18 are provided on a reading surface 16 of a disk substrate 11 of the optical disk. An optical head (not shown) of the recording / reproducing apparatus travels on the tracks 17, 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 pits, which are arranged in the radial direction of the disk around the tracks 17 and 18. The optical head described above has a wobble pit 12,1
A point where the amount of reflected light from 3 becomes the same is detected as the center of the tracks 17 and 18, and this point is set as a running position. The tracks 17, 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, the wobble pits 12 and 13 in other tracks are also described. The clock pit 14 is provided for detecting a data pit (not shown) recorded later by the recording / reproducing apparatus. Further, the disk substrate 11 is a replica substrate made of plastic, glass, or the like.

The length of the wobble pits 12, 13 and the clock pit 14 in the circumferential direction of the disk, that is, the pit length l is 90 ns in terms of the running time of the optical head. The actual size of the pit length l is 30 mm for the disk radius r and the number of rotations of the optical disk is
If it is 1800 rpm, it will be about 0.5 μm. Also, the disc radius r
Is 60 mm, the pit length 1 is about 1.0 μm. On the other hand, the optical depth of these pits is λ / 4, where λ is the wavelength of the reading laser used in the optical head. Here, the wavelength λ is usually selected to be 830 nm. The sample mark area in which such pits are provided requires 1000 to 3000 locations per rotation (one track), and usually 1376 locations. Also, the portion other than the sample mark area, that is, the sector address portion 15 is on one track.
There are 32 places. The sector address section 15 is provided with a pit (not shown) indicating an address.

The wobble pits 12 and 13 and the clock pit 14 of an optical disk compatible with such a sample servo method are used for cutting narrowly squeezed on a master made of a photoresist film-formed plastic or glass, similarly to a video disk or a compact disk. It is formed by irradiating a laser beam and developing the irradiated master. The irradiation power P _B of the cutting laser light by the cutting machine is expressed as follows: the linear velocity at an arbitrary point on the reading surface of the master optical disc is set to v, and the irradiation density of the laser light is set to J.
Is controlled so as to satisfy P _B = Jv.

FIG. 3 shows measured values of the pit width (hereinafter, referred to as pit width) W in the radial direction of the disk with respect to the pit length 1 in this case. As can be seen from FIGS. 2 and 3, in a normal cutting machine, the pit width W increases as the pit length 1 increases. Accordingly, in an optical disk of the sample servo system used by rotating at a constant angular velocity, as shown in FIG. 2, the pit lengths l of the wobble pits 12, 13 and the clock pit 14 are on the inner and outer peripheral sides of the optical disk. And will be different. Similarly, the pit width W differs between the inner and outer circumferences. Furthermore, if the pit length l formed on the reading surface of the optical disc is smaller than the beam spot diameter of the cutting laser beam, the shorter the pit length l, the smaller the formed pit width W.

[Problems to be solved by the invention]

In the above-mentioned conventional technology, when producing an optical disc master,
The pit length l and the pit width W are formed differently on the inner and outer circumferences of the optical disc. That is, the pits on the outer peripheral side become large. For this reason, a phenomenon occurs that the pit signal modulation degree (tracking error signal and pit modulation degree) changes within the range of the recording area on the reading surface during reproduction of the optical disk. 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 which is substantially flat.

[Means for solving the problem]

An object of the present invention is to provide a disk having a plurality of pits, wherein a pit area calculated from a product of a width of the pit in a disk radial direction and a length in a disk circumferential direction is provided on an inner circumferential side in the disk radial direction. Achieved by making the pits substantially equal to the pits provided on the outer circumference, and making the width of the pits provided on the inner circumference in the disk radial direction wider than the width of the pits provided on the outer circumference. Is done.

[Action]

FIG. 4 shows experimental data indicating the relationship between the pit area and the pit signal modulation (the tracking error signal and the pit modulation). According to FIG. 4, the tracking error signal and the pit modulation degree each have a maximum value with respect to the pit area, and the change (differential value) with respect to the change in the pit area is small near the maximum value. Therefore, in order to make the tracking error signal and the pit modulation degree almost constant with little variation,
It is effective to set a pit in a pit area corresponding to these maximum values. Moreover, pit length l of the disk circumferential direction is different in the inner periphery of the disk radial direction is longer than the pit length li of pit length l ₀ is the inner circumferential side of the outer peripheral side. As a result, the relationship between the pit width Wi of the inner pit in the radial direction of the disc and the pit width Wo of the outer pit is determined by Wi> Wo while forming the pit on the disc master while maintaining the pit area almost constant (hereinafter referred to as "Wo"). If the inner pit width Wi is made longer than the outer pit width W ₀ by adopting the “means (A)”), the inner pit area and the outer pit area become substantially the same. can do. The pit length l ₀ and the pit width Wi have the same dimensions, and the pit length li and the pit width W ₀
Are preferably set to the same dimensions. In addition, the fourth
In the figure, it is preferable to set the pit area (1 × W) to about 0.35 μm ² because the tracking error signal becomes almost constant. Further, when the track interval Tr is sufficiently large, a pit area located between the maximum value of the tracking error signal and the maximum value of the pit modulation degree can be adopted.

FIG. 5 shows experimental data representing the relationship between the pit width W and the tracking error signal. Here, the pit length 1 is about 0.5 to 1.0 μm. As can be seen from FIG. 5, the tracking error signal also has a maximum value with respect to the pit width W, and a change in the pit width W is small near this maximum value. Therefore, in order to keep the tracking error signal constant with little variation, the pit width has an optimum value (the pit width value corresponding to the maximum value of the tracking error signal). The relationship between the pit width Wi of the inner pit and the pit width Wo of the outer pit is determined by using Wi ≒ Wo as a means for forming a pit on the master disc (hereinafter referred to as “means (B)”). It is only necessary to make the width W substantially constant near the optimum value. And
In FIG. 5, the optimum value of the pit width W is approximately 0.5 μm. Although not shown, it has been confirmed that the pit modulation degree becomes substantially constant by making the pit width W substantially constant near the optimum value, as described later.

The measurement specifications in FIGS. 4 and 5 are as follows. Regarding the pit formation specifications, the numerical aperture NA of the objective lens (described later) is about 0.7, and the beam spot diameter φ, which is the diameter at which the intensity of the laser light decreases to 1 / e ² of the spot center, is about 0.
9 μm, track pitch Tr is 1.5 μm, pit length l is about 0.5
The optical pit depth (λ / 4) is about 130.0 nm when polycarbonate having a refractive index of about 1.59 is used as the disk substrate. The reproducing optical system had an NA of about 0.5, a laser wavelength λ of about 830 nm, a laser beam diameter φ of about 1.5 μm, and a beam cross section of about 1.8 μm.
a m ^2.

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

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic plan view and a partially enlarged view of a sample servo optical disk according to a first embodiment of the present invention. In FIG. 1, the disk substrate 1 is made of polycarbonate (PC), the inner diameter φi of the hole 6 provided in the center thereof is 15 mm, the outer diameter φo of the disk substrate 1 is 130 mm, the thickness t is 1.2 mm, Area 7 has a radius r of 30-60 m
m. Also, assuming that the track pitch Tr is 1.5 μm and the optical pit depth (λ / 4) is that the refractive index of the PC is about 1.59,
It is about 130.0 nm. Here, the laser wavelength λ is 830 nm. As a laser light source for cutting, helium cadmium (He-C) having a laser wavelength λc of 441.6 nm is used.
d) A laser generator is used. A positive resist is used as the photoresist. 5 in the figure is the second
This is the same sector address section as 15 in FIG.

The local enlarged view shown in the lower part of FIG. 1 shows a part of a track at a radius r = 30 mm (r30 part) and a part of a track at a radius r = 60 mm (r60 part) on the horizontal axis side, The side shows the adopted means (A) and means (B).

Here, 2 and 3 are wobble pits similar to 12 and 13 in FIG. 2, and 4 is a clock pit similar to 14 in FIG. First, the case where the above-described means (A) is employed will be described. Pit width of r30 parts in this case Wi = W ₁ and r60
The relationship with the pit width W ₀ = W ₂ is to set W ₁ > W ₂ . Incidentally, the inner peripheral side pit width W ₁ is approximately in the present embodiment 0.7μ
The pits were formed by setting the outer pit width W ₂ to about 0.35 μm, and the pit area was kept constant at about 0.35 μm ² .

Now, a method for forming a pit having a predetermined area will be described. Generally, the pit size is proportional to the irradiation power P of the laser beam at the time of cutting. Also, as shown in FIG. 3, when pits are formed by the conventional irradiation power control method (P _B = Jv), the inner peripheral side pit width Wi becomes narrower and the outer peripheral side pit width W ₀ 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 pit area becomes substantially constant, and the relationship between the pit widths becomes W ₁ > W ₂ . As a result of this,
It is possible to manufacture an optical disc in which the tracking error signal and the pit modulation degree are constant at about 40% and about 70%, respectively, in the recording area.

In the first embodiment described above, the pit area is set to 0.
Was 35 [mu] m ² constant, but even pit area 0.2 to 0.8 [mu] m ² sufficient tracking error signal and pit modulation factor is obtained. The pit area at this time is a reproduction light beam area of 1.8 μm ²
10 to 45% of the total.

Although the case where the magnitude of the irradiation power P is controlled as the irradiation power control method has been described, a constant pit area can also be obtained by controlling the pit cutting time T.

Pit cutting time T _A after correction for conventional pit cutting time Tc = 90ns (control), T _B, shows a time chart in FIG. 7 for T _D. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the irradiation of the cutting laser light. Conventional pit cutting time T _C is shown in broken lines. Further, in this time chart, the pit cutting time of the wobble pits 2 from the left T _C, the time T _C of the wobble pits 3, the clock pit 4
They were listed in order of the time T _C. FIG. 7A shows the pit cutting time T _A = 120 ns in the r30 part.

Figure 7 (b) is a pit cutting time T _B in the portion of the track in the radial r = 45 mm of the optical disc (r45 parts)
= 85 ns. FIG. 7C shows the pit cutting time T _D = 50 ns in the r60 part. As described above, even when the time T _C 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 pit area (0.35 μm ² ) can be obtained.

Next, a case where the above-mentioned means (B) is employed in FIG. 1 will be described. In this case, the relationship between the pit width W ₀ = W ₄ of the pit width Wi = W ₃ of r30 parts r60 parts are used for setting the W ₃ ≒ W _4. In this embodiment, W ₃ ≒ W ₄ ≒ 0.5
Pits were formed at a setting of μm.

Now, a method of forming a pit having a predetermined pit 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 dashed line in the figure indicates the conventional irradiation power control method (P _B = Jv), and the solid line indicates the irradiation power control method (P = J ₀ ) of the present invention used for forming a pit having a predetermined area. It is shown. The dashed line in FIG. 6 indicates the pit width W in the recording area this time.
It was used to constant shows the irradiation power control method of the present invention _{(P = J 1 v + J} 0 '). Here, J ₁ and J ₀ ′ are irradiation densities of laser light. This method _{(P = J 1 v + J} 0)
In the above, cutting was performed on the master disc that was rotated by setting J ₁ ≒ 0.65 mJ and J ₀ ≒ 1.7 mJ. When cutting is performed in this manner, the pit width W becomes substantially constant, and the relationship between the pit widths is W ₃ ≒ W ₄ . As a result, it was possible to produce an optical disk in which the tracking error signal and the pit modulation degree were approximately constant at about 35 to 40% and about 60 to 80%, respectively, in the recording area.

It should be noted that a substantially constant pit width W could be obtained by controlling the pit cutting time T. Describing this by adapts the case of Figure 7, the pit cutting time T _D of the pit cutting time T _B is 105 ns, r60 parts of the pit cutting time T _A is 120 ns, r45 parts at r30 parts and 90ns Become. As described above, the conventional pit cutting time T _C is calculated according to the value of the radius r of the optical disk.
Even when the correction is made to T _A , T _B , and T _D , a substantially constant pit width (0.5 μm) can be obtained.

In the above embodiments, the pit is circular or the pit length l is longer than the pit width W on the reading surface of the optical disk. However, the beam spot diameter of the cutting laser beam with respect to the disk circumferential direction (track direction) is described. Is smaller than the shortest pit, and the pit width W is the pit length l
Even when a longer pit is formed, the pit width W can be made constant at the inner and outer circumferences. This embodiment is shown in FIG.

FIG. 8 shows a schematic plan view and a partially enlarged view of the optical disk as in FIG.
Reference numerals 83 and 83 denote a wobble pit, 84 a clock pit, and 85 a sector address portion. In the embodiment shown in FIG. 8, an optical disk having a substantially constant pit signal modulation degree can be obtained. Further, the same effect can be obtained even if the beam spot diameter at the time of cutting is narrowed down using an optical system so as to be equal to the minimum pit length.

Now, a cutting machine used for forming pits on an optical disc according to 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 pits, first, a photoresist film 29 is formed on the reading surface.
Is rotated around a rotation center axis 30 using a rotating means (not shown). Further, a head moving unit 25 including an optical deflector 26 and an objective lens 27 is provided.
Is moved in the radial direction with the rotation of the glass master. Here, the movement of the head moving unit 25 is one rotation.
This corresponds to the track pitch. In such an operation state of the mechanical system, the helium cadmium (He-Cd) laser generator 21 outputs a laser beam 20. This laser beam 20 is irradiated with an irradiation power controller 22, a mirror 23, a collimator lens 24,
The light enters the head moving unit 25 through the optical modulator 31, the collimating lens 32, and the mirror 33. 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 pits are formed.

The control of the laser irradiation power P (P
= J ₁ v + J ₀ ′) is performed by the irradiation power controller 22. The linear velocity v was set based on the position of the head moving section 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 at the timing shown in the pit cutting time T _C of Figure 7 performs irradiation on the laser beam 20 for cutting, the control of irradiation off (modulation). Then, the laser beam 20 ′ modulated by the optical modulator 31 is deflected by the optical deflector 26. This deflection is performed only when wobble pits are formed, and is used to irradiate a laser beam for cutting to a symmetric position in the disk radial direction centering on a track.

〔The invention's effect〕

According to the present invention, the pit signal modulation degree can be made substantially constant (flat), so that a high quality disc can be provided.

[Brief description of the drawings]

1 and 8 are a schematic plan view and a local enlarged view of an optical disk according to an embodiment of the present invention, respectively. FIG. 2 is a schematic plan view and a local enlarged view of a conventional optical disk to which a sample servo system is applied. FIG. 7 to FIG. 7 are characteristic diagrams for explaining the present invention, and FIG. 9 is a configuration diagram showing an example of a cutting machine used for forming pits on the optical disk of the present invention. 1,11,81: disk substrate, 2,3,12,13,82,83 ... wobble pit, 4,14,84 ... clock pit, 5,15,85 ... sector address section.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Ishigaki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Home Appliances Research Laboratory, Hitachi, Ltd. (72) Yukio Fukui 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa (56) References JP-A-54-141604 (JP, A) JP-A-60-145535 (JP, A) JP-A-64-88325 (JP, A)

Claims (4)

(57) [Claims] 1. A disc having a plurality of pits,
The pit area calculated from the product of the width of the pit in the disk radial direction and the length in the disk circumferential direction is the pit provided on the inner circumferential side of the disk radial direction and the pit provided on the outer circumferential side. A disk characterized by being equal in: 2. A disk having a plurality of pits, wherein a pit area calculated from a product of a width of the pit in a disk radial direction and a length of the disk in a disk circumferential direction is provided on an inner peripheral side in a disk radial direction. Wherein the pits are equal to the pits provided on the outer peripheral side, and the width of the pits on the inner peripheral side is wider than the width of the pits on the outer peripheral side. 3. The disk according to claim 1, wherein the pit area is 0.2 μm ² or more and 0.8 μm ² or less. 4. The disk according to claim 1, wherein a ratio of the pit area to a light irradiation area of the disk is 10% or more and 45% or less.