JP2000187887A - Optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a recording and reproducing characteristic by forming a groove and a land in helical form on a substrate and forming prepits while leaving one part of the inner peripheral side or the outer peripheral side of the land, thereby obtaining a stable preformat signal to reproduce prepit information correctly. SOLUTION: A groove 2 and a land 3 and prepits 4 are formed on a substrate 1. The prepit 4 is formed while leaving one part of the land 3 without making it to be in a ladder shape having a form connecting adjacent grooves with each other. Since the cross-sectional shape of the prepit 4 becomes asymmetric with respect to the center T2 of the track of the groove 2, it generates a preformat signal in a push-pull signal. When a track pitch is defined as Tp, the groove width Wp of the prepit 4 is regulated within a specific range of 0.45 μm<=Wp<=(Tp-0.1). Moreover, the preformat signal is prevented from leaking into an RF signal and the push-pull signal by regulating the length Lp of the prepit 4 within a specified range of 0.4 μm<=Lp<=1.0 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writable optical disk, and more particularly to a method of accurately reproducing preformat information and improving the accuracy of controlling the rotational speed of the disk.

[0002]

2. Description of the Related Art In a writable optical disk, a synchronization signal and address information (hereinafter, referred to as preformat information) for position search are previously formed on a substrate as phase grooves. As a method of forming the preformat information as a phase groove, there are a method of meandering the groove (hereinafter, referred to as wobble) and a method of changing the length, interval, and position of the discontinuous groove (hereinafter, referred to as prepit). When the interval between recording groove tracks (hereinafter, referred to as track pitch) is narrowed to increase the recording capacity of an optical disc, a sufficient C / N (Carrier to Noise) method is used in a method of wobbling the groove.
Ratio) cannot be obtained, and the recording capacity is limited. Therefore, in the optical disk disclosed in JP-A-9-17029, as shown in FIG. 10, prepits 4 are formed on the lands 3 between the grooves 2. The pre-pits 4 have a ladder shape in which adjacent grooves 2 are connected to each other. As a method for reproducing the pre-pit 4, there is a method shown in FIG.
As shown in the figure, a four-division type light receiver 21 is arranged, and the output (A + B) of the adder 22 and the output (C + D) of the adder 23 are subtracted by the subtracter 24, thereby dividing the optical disk into two in the radial direction. Is detected as a difference signal of the light receiving output of the light receiving element.

When pre-pits 4 exist on lands 3 located on the left and right sides of the groove 2, pre-format information is read out at the same time, causing interference (hereinafter referred to as crosstalk). As shown in FIG. 12, the optical disk disclosed in Japanese Patent Publication No. 17029 prepares two patterns of EVEN (even number) and ODD (odd number) as patterns of preformat information formed by prepits 4. The EVEN pattern and the ODD pattern have the sync sy and ID information necessary for the servo, but the positions of the sync sy and the ID recorded by the EVEN pattern and the ODD pattern are shifted by 180 degrees. Of the two patterns, the pre-pits are usually recorded using the EVEN pattern, and while the lands are being recorded in a spiral shape, the positions of the sync sy and the ID of the recording pattern are likely to overlap between adjacent lands. ODD
Recording is performed by switching to the pattern, and when the position of the sync sy of the ODD pattern and the position of the ID are likely to overlap, the pattern is switched to the EVEN pattern to solve the problem of crosstalk.

[0004]

Problems to be Solved by the Invention
As shown in Japanese Patent Application Laid-Open Publication No. H10-260, a method of preparing two patterns of EVEN (even number) and ODD (odd number) as patterns of preformat information and switching and using the pattern when an arrangement in which crosstalk occurs is used. It is effective for solving the problem of crosstalk, but it is effective to switch between two patterns while detecting the arrangement where crosstalk occurs, that is, the presence of prepits in the lands located on the left and right sides of the groove during master exposure. It is technically very difficult to do. That is, if there is no error in the number of rotations of the disk, the position where crosstalk occurs is obtained by calculation and E
It is possible to encode a pre-pit pattern of pre-format information in which the VEN and ODD patterns are switched, but since the number of revolutions of the master exposure is generally as small as 0.1% or less, it has an error. , The position where the crosstalk occurs cannot be calculated. Therefore, it is necessary to detect the position where the crosstalk occurs while monitoring the fluctuation of the rotational speed, and to switch the pattern between the EVEN and the ODD to perform the exposure. However, since the length of the pre-pit in the track direction is short, on the order of submicron, an error in the number of rotations must be detected at least in the order of ns. There is a problem that an error occurs in the detection.

Although not described in detail in Japanese Patent Application Laid-Open No. Hei 9-17029, as a method for reproducing preformat information formed by prepits, there is a method using a push-pull signal (difference signal). The principle is shown in FIG.
And FIG. FIG. 13 shows a waveform of a push-pull signal in a portion formed in a ladder shape. Since the groove section in the radial direction of the pre-pit portion formed in a ladder shape is asymmetric, the track center T2 of the pre-pit 4 is arranged at a position shifted by s from the track center T1 of the groove 2. Therefore, when a signal is reproduced by performing tracking, a peak having a magnitude A is generated in the push-pull signal as shown in FIG. If the presence or absence or the position of the peak of the size A is detected, the preformat information formed by the prepits can be reproduced. However, as shown in section A of FIG. 10 and FIG.
When the pre-pits 4 exist on the lands 3 located on the left and right sides of the groove 2, no peak is generated in the push-pull signal because the groove cross-sectional shape of the pre-pit portion is symmetric. For this reason, when phase pits are present on the lands 3 located on the left and right sides of the groove 2, there is a problem that the preformat information formed by the phase pits cannot be detected, and reproduction is performed with a push-pull signal. In some cases, it is necessary to prepare two patterns of the preformat formed by the prepits 4, EVEN and ODD, and to use the patterns when the arrangement is such that crosstalk occurs.

The present invention solves such a problem and provides a writable optical disk capable of accurately reproducing preformat information and accurately controlling the number of rotations of a disk even when prepits are formed alongside adjacent tracks. The purpose is to do so.

[0007]

An optical disc according to the present invention is a writable optical disc in which grooves and lands are spirally formed on a substrate and preformat information is formed as prepits on the lands. Are formed leaving a part on the inner circumference or outer circumference side of the land.

The groove width Wp of the prepit is 0.45 μm ≦ Wp ≦ (TP−
0.1) μm is good.

The length Lp of the pre-pit is set to 0.4 μm.
≦ Lp ≦ 1.0 μm.

Another optical disk according to the present invention is characterized in that, in a writable optical disk in which a groove is formed in a spiral shape, the center of the groove is moved in the radial direction in accordance with preformat information and recorded. I do.

The amount of movement a in the radial direction of the center of the groove is preferably 60 nm ≦ a ≦ 100 nm.

Further, it is desirable that the groove is wobbled in each of the optical disks. This wobble amplitude aw
Is preferably 10 nm ≦ aw ≦ 30 nm.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substrate of the optical disk of the present invention has groups, lands and prepits. The pre-pits are formed by connecting adjacent grooves without forming a ladder shape, leaving a part of the land. Therefore, even if the prepits are arranged side by side on the adjacent track, the cross-sectional shape is asymmetric with respect to the track center of the groove, so that a preformat signal can be generated as the push-pull signal.

The groove width Wp of the pre-pit is 0.45 μm.
By setting m ≦ Wp ≦ (track pitch−0.1) μm, pre-pit information can be accurately reproduced. Further, the length Lp of the pre-pit is set to 0.4 μm ≦ Lp ≦
By setting the range to 1.0 μm, it is possible to prevent the pre-format signal from leaking into the push-pull signal, and to accurately reproduce the pre-pit information to obtain good recording / reproducing characteristics.

[0015]

1 shows an optical disk substrate according to an embodiment of the present invention, wherein FIG. 1A is a plan view, FIG.
(C) is BB sectional drawing. As shown in FIG.
Has a group 2, a land 3 and a pre-pit 4.
The pre-pits 4 are formed by connecting adjacent grooves 2 without forming a ladder shape and leaving a part of the lands 3.
Even if the pre-pits 4 are arranged side by side on adjacent tracks as shown in FIG. 1, the cross-sectional shape is asymmetric with respect to the track center T2 of the groove 2, so that the peak of the push-pull signal (pre-format signal) Occurs.
Here, the groove width of the groove 2 is Wg, the groove width of the prepit 4 is Wp, the groove depth of the groove 2 and the prepit 4 is Dp, and the length of the prepit 4 is Lp.

A method of manufacturing the optical disk substrate will be briefly described. A large number of plastic substrates of an optical disk are copied from a mold called a stamper by an injection molding method. The stamper is manufactured as shown in the manufacturing process of FIG.
First, a resist master production step (a) in which a photoresist film 11 is applied to a glass substrate 10 and dried,
Resist master 12 having a photoresist film 11 formed thereon
Is exposed by a focused laser beam 13 to form a latent image 14.
Master exposure step (b) for forming a resist, and developing the exposed resist master 12 to form a group 2 on the photoresist film 11
And a developing step (c) for forming a groove pattern 15 constituting the pre-pits 4, a conductive film processing step (d) for sputtering a Ni film 16 on the surface of the resist master 12 having the groove pattern 15 formed thereon, A Ni electroforming step (e) of laminating a Ni layer 17 on the substrate 16, and a peeling and cleaning step (f) of removing and cleaning the Ni electroformed plate 17 from the resist master 12 and polishing the back surface and processing the inner and outer diameters. By stamper 18
Is formed.

In the master exposure step of manufacturing the stamper, as shown in FIG. 3, a laser beam 13 is condensed on the resist master 12 while rotating and laterally moving the resist master 12, thereby forming a groove pattern 15 on the resist master 12. Is formed spirally.
When the groove pattern 15 is formed on the resist master 12 in this manner, the groove 2 and the prepit 4 are exposed with a laser beam, and the optical axis is adjusted so that the distance between the spots at the focal point becomes a desired distance. I have.

The result of examining the dependency of the pre-format signal (hereinafter referred to as LPP signal) on the pre-pit groove width by the pre-pit 4 will be described. Substrate 1 has groove depth Dp
= 400 °, groove groove width Wg = 0.34 µm (half width), prepit length Lp = 0.50 µm, track pitch = 0.75 µm, and substrate 1 was prepared in which the groove width Wp of prepit 4 was changed. A phase change recording material and a thin film such as a reflective film were formed on the substrate 1 to produce a writable optical disk. In this optical disc, a pickup having an objective lens NA (numerical aperture) = 0.6 and a wavelength of 650 nm is used.
FIG. 4 shows the result of evaluating the LPP signal at a linear velocity of 3.5 m / s. The LPP signal is a sum signal of the push-pull signal A shown in FIG. 13 and the groove 2 (hereinafter, referred to as an RF signal).
Divided by. As shown in FIG. 4, if the use value for accurately reproducing the preformat information is LPP ≧ 0.15, the appropriate groove width Wp of the prepit 4 is 0.45 μm.
It turns out that it is good if it is above. On the other hand, in order to form the land 3 while leaving a part thereof, the groove width Wp of the pre-pit 4 must be equal to or less than the track pitch and the manufacturing margin at the time of manufacturing the master is taken into consideration (track pitch TP-0.1 μm).
m) = 0.65 μm is preferred.

Next, the result of an examination on the dependence of the LPP signal on the prepit length Lp will be described. The groove Wg, the groove depth Dp, and the track pitch are the same as those described above, the groove width Wp of the prepit 4 is set to 0.50 μm, the substrate 1b having the changed prepit length LP is manufactured, and an optical disk is manufactured.
FIG. 5 shows the result of evaluating the PP signal. As shown in FIG. 5, it is understood that the proper length LP of the pre-pit 4 corresponding to LPP ≧ 0.15 needs to be 0.4 μm or more. However, when the length Lp> 1.0 μm of the pre-pit 4 is
It has been found that the leakage of the PP signal causes noise in the RF signal and the push-pull signal, thereby deteriorating the recording / reproducing characteristics. As a result, the length Lp of the pre-pit 4 is 0.4
１．０1.0 μm was found to be most suitable.

In the above embodiment, the case where the pre-pits 4 are formed in the group 2 has been described. As shown in FIG.
The case where the pre-pit corresponding portion 2a corresponding to the pre-pit 4 of the group 2 is formed shifted from the track center T1 by a will be described.

In this case, when the reproduction beam tracking the groove 2 passes through the pre-pit corresponding portion 2a,
A push-pull signal corresponding to the shift amount a is generated. Further, even if these are formed on the adjacent track, the cross-sectional shape is asymmetric with respect to the center of the track, so that a peak occurs in the push-pull signal, so that an LPP signal can be obtained.
In the method of manufacturing the optical disk master, grooves of group 2 can be cut by deflecting one laser beam. Therefore, since a laser beam for pre-pits is not required, there is also an advantage that the optical system of the master exposure machine is simplified.

The result of examining the dependence of the LPP signal on the shift amount a by the pre-pit corresponding portion 2a will be described. The shape of the substrate 1a has a groove depth Dg = 400 °, a groove groove width Wg = 0.34 μm (half width), a length corresponding to the pre-pit length Lp = 0.40 μm, and a track pitch =
The substrate 1a as shown in FIG. 6 was manufactured by moving the condensing spot using an optical deflector during exposure of the master to 0.75 μm. FIG. 7 shows an evaluation result of the LPP signal by the optical disk using the substrate 1a. Deviation a
Was determined from the amplitude of the push-pull signal when the tracking was turned off and the amplitude of the push-pull signal generated when passing through the pre-pit corresponding portion 2a when the groove 2 was turned on. As shown in FIG.
It can be seen that an appropriate shift amount a corresponding to ≧ 0.15 needs to be 60 nm or more. On the other hand, it was found that when the shift amount a was 100 nm or more, noise was generated in the RF signal and the push-pull signal due to the leakage of the LPP signal, and the recording / reproducing characteristics deteriorated. From this result, the shift amount a at which the preformat information can be accurately reproduced and good data recording characteristics are obtained is in the range of 60 nm ≦ a ≦ 100 nm.

Next, as shown in FIG. 8, the result of forming and evaluating a prepit 4 and a wobbled groove 2 on a substrate 1b will be described. The substrate 1b can control the spindle rotation speed of the recording / reproducing apparatus from the synchronization signal by the pre-pits 4 and the wobble signal of the groove 2, and can more accurately control the spindle rotation speed.

The shape of the substrate 1b is such that the groove depth Dp = 40
0 °, groove groove width Wg = 0.34 μm, pre-pit 4
Groove width Wp = 0.50 μm, pre-pit length Lp = 0.4
0 μm, and the wobble frequency was 140 kHz. FIG. 9 shows the result of examining the dependence of the wobble C / N on the wobble amplitude aw. The wobble amplitude aw was obtained from the amplitude ratio of the push-pull signal at the time of tracking ON / OFF as in the case of the shift amount a. If wobble C / N> 35 dB is specified with reference to the CD-R standard, the wobble amplitude aw needs to be 10 nm or more as shown in FIG. on the other hand,
When the wobble amplitude aw is 30 nm or more, the wobble C
Although / N can be sufficiently obtained, it has been found that the wobble signal leaks into the RF signal and the recording characteristics (jitter) deteriorate. Therefore, by setting the wobble amplitude aw in the range of 10 nm to 30 nm, the wobble signal can be reproduced and good recording characteristics can be obtained.

[0025]

As described above, according to the present invention, the pre-pits are formed while leaving a part of the inner circumference or the outer circumference of the land. Therefore, even when the pre-pits are formed on both sides of the groove, the push-pull signal is generated. , A stable preformat signal can be obtained.

Further, by restricting the pre-pit groove width Wp to a certain range, the pre-pit information can be accurately reproduced.

Further, since the length Lp of the pre-pit is regulated to a certain range to prevent the pre-format signal from leaking into the RF signal and the push-pull signal, the pre-pit information can be accurately reproduced, and good recording and reproduction characteristics can be obtained. Obtainable.

Further, by recording the preformat information by moving the center of the groove in the radial direction without forming the prepit on the land, the preformat signal can be recorded even if the preformat information is formed side by side on the adjacent track. Can be obtained reliably.

By setting the amount of movement a in the radial direction of the center of the groove within a certain range, it is possible to prevent the preformat signal from leaking into the RF signal and the push-pull signal, and to accurately reproduce the prepit information. Good recording and reproducing characteristics can be obtained.

Also, by wobbling the groove, the spindle rotation speed of the recording / reproducing apparatus can be controlled by the pre-pits and the wobbled groove, and the rotation speed control of the optical disk can be performed accurately.

By limiting the amplitude aw of the wobble to a certain range, it is possible to reproduce a wobble signal and obtain good recording characteristics, and to accurately control the rotation speed of the optical disk by the prepit signal and the signal of the wobbled groove. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical disc substrate according to an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of the stamper of the embodiment.

FIG. 3 is an explanatory view showing a master exposure step.

FIG. 4 is a change characteristic diagram of an LPP signal with respect to a change in a pre-pit groove width Wp.

FIG. 5 is a change characteristic diagram of an LPP signal with respect to a change in a prepit length LP.

FIG. 6 is a plan view showing an optical disc substrate according to a second embodiment.

FIG. 7 is a change characteristic diagram of an LPP signal with respect to a change in a group shift amount a.

FIG. 8 is a plan view showing an optical disc substrate according to a third embodiment.

FIG. 9 shows wobble C / with respect to a change in wobble amplitude aw.
FIG. 9 is a graph showing a change characteristic of N.

FIG. 10 is a plan view showing a conventional optical disc substrate.

FIG. 11 is a block diagram showing a conventional pre-pit reproducing section.

FIG. 12 is a layout diagram of a pre-pit according to a conventional example.

FIG. 13 is an explanatory diagram showing the principle of phase bit reproduction.

FIG. 14 is an explanatory diagram showing reproduction of a phase bit according to a conventional example.

FIG. 15 is an explanatory diagram showing an example in which a phase bit cannot be reproduced.

[Explanation of symbols]

 1 substrate 2 groove 3 land 4 pre-pit

Claims (7)

[Claims] 1. A writable optical disk in which grooves and lands are spirally formed on a substrate and preformat information is formed as prepits on the lands, wherein the prepits are part of the inner or outer periphery of the lands. An optical disk characterized in that the optical disk is formed by leaving a pattern. 2. The groove width Wp of the pre-pit is 0.45 μm ≦ Wp ≦ (TP
The optical disk according to claim 1, wherein the optical disk has a thickness of -0.1) μm. 3. The pre-pit length Lp is 0.4 μm.
The optical disk according to claim 1, wherein ≤ Lp ≤ 1.0 m. 4. A writable optical disk having a spiral groove formed thereon, wherein the center of the groove is moved in the radial direction in accordance with preformat information and recorded. 5. An amount of movement a in the radial direction of the center of the groove.
5. The optical disk according to claim 4, wherein satisfies 60 nm ≦ a ≦ 100 nm. 6. The optical disc according to claim 1, wherein the groove is wobbled. 7. An amplitude aw of the wobble is 10 nm ≦
7. The optical disk according to claim 6, wherein aw ≦ 30 nm.