JP4223932B2 - Optical disc, optical disc evaluation method, and optical disc evaluation apparatus - Google Patents

Description

  The present invention relates to an optical disc for recording / reproducing information, an optical disc evaluation method, and an optical disc evaluation apparatus.

Optical discs capable of high-density recording of information (for example, a single-sided single-layer storage capacity of 4.7 GB) (for example, DVD-ROM, a read-only optical disc, rewritable + RW (ECMA-337), DVD-RAM (ECMA -330) and DVD-RW (ECMA-338)).
In these optical discs, information is recorded and reproduced by condensing laser light on a transparent substrate on which an information recording layer is formed. Information is recorded / reproduced along guide grooves called grooves formed in the information recording layer of the optical disc.
At this time, a physical address is used to specify a spatial position where information is recorded / reproduced. In + RW, the physical address is determined using groove wobble modulation (hereinafter referred to as “wobble modulation”) that causes the groove to vibrate in the radial direction. That is, the wobble phase is changed corresponding to the information to be recorded. In the wobble modulation, the recording track of the optical disk is not cut off, so that the area for recording user information on the optical disk can be increased (that is, the format efficiency is high). In addition, by adopting the wobble modulation method, it becomes easy to make rewritable + RW compatible with a read-only DVD-ROM.
As an evaluation index of the quality of the wobble signal when this groove wobble is optically reproduced, there is a narrow band signal to noise ratio (NBSNR) of the wobble signal. This evaluates the ratio between the amplitude of the carrier carrying the wobble signal and the amplitude of the noise. The higher the NBSNR, the higher the demodulation rate of the wobble signal. This NBSNR is also called Carrier to Noise Raitio (CNR).
In addition, by suppressing the phase difference between the reflected light from the recording mark (non-crystal) and non-recording mark (crystal) on the optical disk from -π / 3 to + π / 3, crosstalk with the data of the adjacent track is reduced. The technology is disclosed (see Patent Document 1).
JP2003-132535A

In an optical disc using wobble modulation for forming a physical address, a signal including user data is usually recorded on the modulated groove. In this case, since the recorded signal and the wobble signal are overlapped, when the wobble signal is reproduced, the recorded signal leaks as noise, and the wobble signal is difficult to reproduce accurately.
In particular, in an optical disc of a system in which signals are recorded on both the land and groove tracks, the wobble signal is leaked from both the land and the groove, so that the wobble signal is greatly reduced.
In order to solve the above problems, the present invention provides an optical disc, an optical disc evaluation method, and an optical disc evaluation device capable of suppressing the leakage from a recorded signal to a wobble signal and enabling accurate reading of the wobble signal. With the goal.

  A. In order to achieve the above object, an optical disk according to the present invention includes a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous by heating by light irradiation, and the boundary between the land and the groove. Is characterized in that the absolute value of the phase difference of the reflected light from the recording layer in each of the crystalline state and the amorphous state is 15 degrees or less.

The physical address can be generated by converting the vibration (wobble) at the boundary between the land and the groove into a signal (for example, a radial push-pull signal) by an optical pickup or the like. The intensity of the electric signal varies depending on the level difference between the land and the groove.
The crystalline state and the amorphous state correspond to the non-recording location and the recording location of information on the recording layer, and are formed in lands and grooves. When information (data) is recorded on the optical disc, the data signal is mixed in the wobble signal when the optical disc is reproduced. Further, when the phase difference of the reflected light from these becomes large, it is optically equivalent to a change in the level difference between the land and the groove, which causes a decrease in the S / N ratio of the radial push-pull signal. Become. For this reason, mixing the data signal with the wobble signal is reduced by setting the range of the phase difference to -15 to +15 deg.

  B. In order to achieve the above object, an optical disk according to the present invention includes a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous by heating by light irradiation, and the boundary between the land and the groove. The position of the optical disk vibrates at a predetermined spatial period, and the difference between the vibration components of the reflected light from the land before and after the information recording on the land (Cw1L-Cw0L) and before and after the information recording on the groove The absolute value | (Cw1L-Cw0L)-(Cw1G-Cw0G) | of the difference in the vibration component difference (Cw1G-Cw0G) of the reflected light from the groove is 1.5 dB or less.

  Limiting the range of | (Cw1L-Cw0L)-(Cw1G-Cw0G) | reduces the mixing of the data signal into the wobble signal. Since it is not always easy to measure the phase difference of light, a parameter that can be detected relatively easily by frequency analysis of reflected light is used as an evaluation parameter.

  C. In order to achieve the above object, an optical disk evaluation method according to the present invention includes a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous by heating by light irradiation, and the land and groove. Is a method for evaluating an optical disk in which the position of the boundary of the optical disk vibrates at a predetermined spatial period, wherein the vibration component Cw0L of the reflected light from the land is measured by irradiating light onto the land of the rotating optical disk before information recording. Measuring step, a second measuring step of measuring the vibration component Cw0G of the reflected light from the groove by irradiating light to the groove of the rotating optical disc before the information recording, and a step of recording information on the optical disc And irradiating light onto the land of the rotating optical disk after information recording, and measuring the vibration component Cw1L of the reflected light from the land. A third measurement step, a fourth measurement step of measuring the vibration component Cw1G of the reflected light from the groove by irradiating the groove of the rotating optical disk after the information recording, and before and after the information recording The difference (Cw1L-Cw0L) between the difference in vibration component of reflected light from the land (Cw1L-Cw0L) and the difference in vibration component of reflected light from the groove before and after information recording (Cw1G-Cw0L)-( Cw1G-Cw0G)) is calculated.

  In this optical disk evaluation method, parameters that can be easily calculated from the vibration component of the reflected light are used, so that the optical disk can be easily evaluated.

  Here, each of the first to fourth measurement steps may include a signal multiplication step of multiplying a signal based on the reflected light from the optical disk by two. The vibration component can be easily extracted even when modulation (wobble modulation) is involved in the vibration of the boundary between the land and the groove.

  C. In order to achieve the above object, an optical disk evaluation apparatus according to the present invention includes a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous by heating by light irradiation, and the land and groove. An optical disk evaluation apparatus for evaluating an optical disk whose boundary position vibrates at a predetermined spatial period, a rotating mechanism for rotating the optical disk, a recording light source for recording information on the optical disk, and reproduction for reproducing the optical disk A light source for light, light moving means for moving the light emitted from the light source for reproduction along a track in the land and the groove, and reflected light emitted from the light source for reproduction and reflected from the recording layer of the optical disk Receiving light receiving element and vibration component extraction for extracting the vibration component by frequency analysis of the signal output from the light receiving element The difference between the vibration component of reflected light from the land before and after information recording (Cw1L-Cw0L) and the difference between the vibration component of reflected light from the groove before and after information recording (Cw1G-Cw0G) A calculation unit that calculates ((Cw1L-Cw0L)-(Cw1G-Cw0G)).

  Since the optical disk evaluation apparatus uses parameters that can be easily calculated from the vibration component of the reflected light, the optical disk can be easily evaluated.

  Here, the optical disk evaluation apparatus may further include a signal multiplying unit that doubles a signal output from the light receiving element. The vibration component can be easily extracted even when modulation (wobble modulation) is involved in the vibration of the boundary between the land and the groove.

  According to the present invention, it is possible to provide an optical disc, an optical disc evaluation method, and an optical disc evaluation device that can prevent a recorded signal from leaking into a wobble signal and accurately read out the wobble signal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
A. Configuration of Optical Disk Device First, an optical disk device will be described.
FIG. 1 is a block diagram showing the basic configuration of the optical disc apparatus 10.
The optical disk apparatus 10 includes a controller 11, an optical pickup head PUH, a photodetector PD, a preamplifier 12, a servo circuit 13, a semiconductor laser driving circuit LDD, a recording signal processing circuit 14, an RF signal processing circuit 15, and an address signal processing circuit 16.
The optical pickup head PUH has a semiconductor laser that emits laser light and an actuator that controls the irradiation position of the laser light emitted from the semiconductor laser. This semiconductor laser may have two for recording and reproduction as required, or may be used for both recording and reproduction.
Information is recorded on and reproduced from the optical disc by focusing the laser beam emitted from the semiconductor laser of the optical pickup head PUH on the information recording layer of the optical disc rotated by a rotation mechanism (not shown). The light reflected from the recording surface of the optical disk during reproduction of the optical disk passes through the optical system of the optical pickup head PUH again, and is converted into an electric signal for detection by a photodetector (light detector) PD.

In the photodetector PD, the light receiving area is divided into two or more, and a signal is output corresponding to each divided area. Here, a signal obtained by adding the signals output from the divided elements is called a sum signal, and a signal obtained by subtraction is called a difference signal. A sum signal to which high-frequency information such as user information is added is called an RF signal. A signal obtained by subtracting a signal from each element arranged in the optical radius (radial) direction of the optical disc is referred to as a radial push-pull signal.
FIG. 2 is a block diagram showing an example of the light receiver PD divided into four parts. A signal obtained by adding all four elements A, B, C, and D is a sum signal, and is output from the arithmetic element 23.
A signal obtained by adding the signals from the two elements A and B and the two elements C and D by the calculation elements 21 and 22 respectively and then subtracting the added signals is a difference signal, which is output from the calculation element 24. This difference signal is a so-called radial push-pull signal representing a difference in signal output in the radial direction.

The detection electrical signal from the photodetector PD is amplified by the preamplifier 12 and output to the servo circuit 13, the RF signal processing circuit 15, and the address signal processing circuit 16.
The servo circuit 13 generates servo signals such as focus, tracking, and tilt, and outputs each signal to the focus, tracking, and tilt actuators of the optical pickup head PUH.

The RF signal processing circuit 15 reproduces information such as recorded user information by mainly processing the sum signal among the detected signals. As a demodulation method at this time, there are a slice method and a PRML method.
The address signal processing circuit 16 processes the detected signal to read physical address information indicating the recording position on the optical disc and output it to the controller 11. Based on this address information, the controller 11 reads information such as user information at a desired position or records information such as user information at a desired position. At this time, the user information is modulated by the recording signal processing circuit 14 into a signal suitable for optical disc recording. For example, modulation laws such as (1,10) RLL and (2,10) RLL are applied.

B. Optical Disk (1) Structure of Optical Disk FIG. 3 is a schematic diagram showing the configuration of the optical disk.
The optical disc has a track T in a data recording area MA (information recording area) of the information recording layer on the transparent substrate, and information is recorded / reproduced along the track T. The track T in FIG. 3 is a spiral type continuously connected from the inside to the outside of the optical disk. In addition to this, the track T includes a concentric circle formed from a plurality of concentric circles.
FIG. 4 is an enlarged view in which the track T of the optical disk D is enlarged. As shown in FIG. 4, the track T is formed by irregularities (guide grooves) of the information recording layer. This concave side is called a groove G, and the convex side is called a land L. FIG. 4 shows a land / groove type optical disc in which information is formed as a recording mark in both the land L and the groove G.

(2) Recording signal to optical disc A thermal recording type information recording medium is used for the information recording layer of the optical disc as a recordable / rewritable one. The thermal recording type information recording medium records information by heating and cooling the information recording medium, and a phase change medium is known as a representative one.
In a phase change medium, information is recorded using a difference in physical properties (for example, a difference in reflectance) due to a difference in phase of the medium (for example, a difference between amorphous and crystal). In the optical disk apparatus 10 using the phase change medium, for example, the entire surface of the medium is crystallized by initialization, and an amorphous recording mark is formed by irradiating the laser beam with a strong intensity. The medium is melted by the strong laser beam, and then the laser beam irradiation is weakened, the medium is rapidly cooled, and the recording mark is formed by amorphization. When reproducing information, the medium is irradiated with a certain level of weak laser light, and changes in absolute reflectivity (hereinafter referred to as `` reflectance '') or phase of complex reflectivity (hereinafter referred to as `` phase '' “)” Is converted into an electrical signal and read.
The amount of change in reflectance and phase between the amorphous part and the crystal part can be adjusted by the type, layer structure and composition of the information recording medium used for the information recording layer.

C. Wobble signal (1) Relationship between wobble signal and push-pull FIG. 5 is a diagram showing the state of the track T of the optical disk as viewed from above in comparison with the reproduction signal. As shown in FIG. 5A, the track T of the optical disk meanders slightly in the radial direction. Such a track T is called a wobble track WT.
When the focused beam spot BS is scanned along the wobble track WT, the wobble frequency is higher than the bandwidth of the tracking servo signal, so the beam spot travels substantially straight through the center of the wobble track WT. . At this time, the sum signal hardly changes (see FIG. 5B), and only the radial difference signal, that is, the radial push-pull signal changes in accordance with the wobble (see FIG. 5C). This is called a wobble signal. The wobble signal is used for adjusting the rotation frequency of the spindle, recording clock reference, recording physical address information, and the like.

(2) Wobble signal (fundamental wave and modulation component)
In an optical disc, information such as physical address information indicating a physical position in an information recording area of the optical disc is recorded by modulating the wobble signal.
That is, physical address information is recorded by phase-modulating the wobble applied to the track T.
FIG. 6 is a schematic diagram illustrating a wobble signal that is not phase-modulated and a phase-modulated wobble signal. (A) represents an unmodulated wobble signal, and (B) and (C) represent a modulated wobble signal. (B) is an example of a wobble signal obtained by modulating the entire track T, and (C) is an example in which a modulation area is provided in a part of the track T and the other part is a non-modulation area. Here, phases different by 180 degrees are given to adjacent regions (first and second phase regions).

(3) Frequency Characteristic of Wobble Signal FIG. 7 is a graph showing the frequency characteristic of a single frequency wobble signal that is not modulated. The wobble signal has a peak (maximum intensity) at the carrier frequency f0, and other portions are noise components. The peak value at the carrier frequency f0 corresponds to the amplitude Wa of the wobble signal shown in FIG.
On the other hand, NBSNR (or CNR), which is an index for evaluating the performance of a wobble signal, can be measured by obtaining a difference between a peak value and a noise level value as shown in FIG. Since the value of the peak and the value of the noise level are expressed in dB (logarithm), taking these differences substantially corresponds to taking these ratios. That is, NBSNR is an S / N (signal / noise) ratio for a wobble signal.
When NBSNR becomes too small, it becomes difficult to demodulate the wobble signal. This is the same whether the noise level increases or the peak value decreases.

(4) Wobble signal amplitude change factor The amplitude Wa of the wobble signal read out as an electrical signal from the optical pickup head PUH is not only the wobble amplitude W of the groove G, but also the depth of the groove G, the brightness of the groove G (light reflection) Rate).
The relationship between the amplitude Wa of the wobble signal and each factor will be described below. Here, the optical disk and the optical disk apparatus 10 used in this example have an optical disk substrate thickness of 0.6 mm on one side, a track pitch of 0.68 μm, land groove recording, the objective lens of the optical disk apparatus 10 has an NA of 0.65, and the wavelength λ of the laser beam. Is 405 nm. However, almost the same results as below can be obtained under other conditions.

  FIG. 8 is a graph showing the relationship between the wobble amplitude W of the groove G of the optical disc D and the wobble signal amplitude Wa. As can be seen from FIG. 8, the amplitude Wa of the wobble signal increases almost linearly with respect to the wobble amplitude W of the groove G. This relationship generally holds when the amplitude of the groove G is sufficiently small with respect to the track pitch.

  FIG. 9 is a graph showing the relationship between the reflectance R of the optical disc D and the wobble signal amplitude Wa. As can be seen from FIG. 9, the amplitude Wa of the wobble signal increases almost linearly with respect to the reflectance R of the optical disk. For example, when the crystalline / amorphous state of the recording layer constituting the track T is changed by signal recording and the reflectance R is changed, the amplitude Wa of the wobble signal is changed.

FIG. 10 is a graph showing the relationship between the depth d of the groove G of the optical disc D and the amplitude Wa of the wobble signal. As can be seen from FIG. 10, the amplitude Wa of the wobble signal periodically changes corresponding to the depth d of the groove G (the step between the land L and the groove G). When the depth d of the groove G approaches λ / 8, the amplitude Wa of the wobble signal increases, and when the depth d of the groove G approaches λ / 4, the amplitude of the wobble signal decreases. Note that λ is the wavelength of the reproduction light.
The amplitude of the wobble signal changes even when the phase of the light reflected from the information recording layer changes, not the depth of the groove G. This is because the phase difference has the same meaning as the change in the depth d from an optical viewpoint. The change in the phase of the reflected light from the information recording layer occurs, for example, when the crystalline / amorphous state of the track T is changed by recording a signal. For example, when the wavelength λ of the laser is 405 nm, the change in the phase αdeg can be converted into the change Δd in the depth d by the following equation (1).
Δd = α / 360 × 405/2 Equation (1)

(5) Leakage of recording signal into wobble signal FIG. 11 is a diagram showing the groove G and the wobble signal before recording the signal. (A1) and (A2) are perspective views showing the cross-sectional states of the groove G and land L of the optical disc, respectively. (B1) and (B2) are graphs showing temporal changes in the wobble signal due to the reflected light from the groove G and the land L, respectively.
Here, the depth d of the groove G is set to λ / 6, which is generally considered to have the smallest leakage from the adjacent track (as described above, the amplitude of the wobble signal is λ / 8 is maximum, and λ / 4 is minimum).

FIG. 12 is a diagram illustrating a groove G and a wobble signal after recording a signal such as user data. (A1) and (A2) are perspective views showing the cross-sectional states of the groove G and land L of the optical disc, respectively. (B1) and (B2) are graphs showing temporal changes in the wobble signal due to the reflected light from the groove G and the land L, respectively.
When a signal is recorded on the optical disc D, the recording signal component leaks into the wobble signal. For this reason, as seen in (B1) and (B2), the noise component of the wobble signal increases.

Here, it is assumed that the phase of the reflected light from the recording mark (non-crystal) is ahead of the phase of the reflected light from the non-recording mark (crystal). For this reason, the intensity of the wobble signal at the time of reproduction of the groove G and land L differs.
That is, in the reproduction of the groove G, the height of the groove G is apparently increased and approaches λ / 4, so that the amplitude Wa of the wobble signal is reduced and the performance (S / N ratio) of the wobble signal is lowered. In the reproduction of the land L, the depth of the land L is apparently shallow and approaches λ / 8, so that the amplitude Wa of the wobble signal is increased and the performance (S / N ratio) of the wobble signal is improved.
Further, when a signal is recorded on both the groove G and the land L adjacent thereto, and the signal recorded on the groove G is reproduced, the wobble from the groove G is leaked due to leakage of the recording signal from the land L. Signal performance (S / N ratio) is further reduced.

  Contrary to the above assumption, when the reflected light from the non-recording mark (crystal) is ahead of the phase of the reflected light from the recording mark (non-crystal), the performance of the wobble signal from the groove G (S / N ratio) is improved, and the performance (S / N ratio) of wobble from the land L is lowered.

FIG. 13 is a diagram showing a groove G and a wobble signal after recording a signal such as user data. (A1) and (A2) are perspective views showing the cross-sectional states of the groove G and land L of the optical disc, respectively. (B1) and (B2) are graphs showing temporal changes in the wobble signal due to the reflected light from the groove G and the land L, respectively.
Here, it is assumed that the light reflected by the recording mark (non-crystal) has a higher intensity (the reflectance R is larger) and the phase is equal to the light reflected by the non-recording mark portion (crystal).
When a signal is recorded on this optical disc, the recording signal component leaks into the wobble signal. However, since the phases of the reflected light from the recording mark (non-crystal) and the non-recording mark portion (crystal) are equal, the apparent depth G of the groove G does not change. For this reason, the amplitude Wa of the wobble signal is increased by the increase in the reflectance R in both the groove G and the land L. In other words, the wobble performance is not significantly reduced in either track T.
Further, when a signal is recorded on both the groove G and the land L adjacent thereto and the signal recorded on the groove G is reproduced, the groove G depth is always maintained at λ / 6. Leakage is suppressed to a minimum, and a decrease in the performance (S / N ratio) of the wobble signal from the groove G is suppressed.

FIG. 14 is a graph showing the relationship between the NBSNR of the wobble signal after signal recording and the phase difference of reflected light between the crystal and the amorphous of the recording medium.
In FIG. 14, a reference line having an NBSNR of 25 dB is drawn. This is based on the fact that it has been found from our experiments that the NBSNR of the wobble signal is 25 dB or more and that information such as address information can be extracted from the wobble signal. From FIG. 14, it can be seen that the NBSNR of 25 dB corresponds to a phase difference of about 15 deg.
Therefore, it can be seen that the optical disc preferably has a phase difference of 15 degrees or less between the crystal and the amorphous phase in order to suppress the performance deterioration of the wobble signal due to signal recording. If the phase difference between the reflected light from the crystalline and non-crystalline phases is within 15 deg, the wobble signal performance is sufficiently high even after recording the signal, and the reliability can be maintained.

(6) Frequency characteristic of wobble signal Next, the frequency characteristic of the wobble signal will be described.
FIGS. 15A and 15B are graphs showing the frequency characteristics of the wobble signals in FIGS. 12B1 and 12B2, respectively. The wobble signal has a peak at the wobble frequency, and the value of this peak corresponds to the amplitude of the wobble signal. Here, the peak value before recording on the groove G is Cw0G, the peak after recording is Cw1G, the peak value before recording on the land L is Cw0L, and the peak after recording is Cw1L.
As can be seen from FIG. 15, the peak decreases in the groove G due to signal recording (FIG. 15A), but the peak increases in the land L (FIG. 15B). That is, after the signal is recorded in the groove G, the NBSNR of the wobble signal from the groove G decreases.

FIGS. 16A and 16B are graphs showing the frequency characteristics of the wobble signals of FIGS. 13B1 and 13B2, respectively.
As can be seen from FIG. 16, the peak value of the track T of either the groove G or the land L is slightly increased by signal recording. As a result, a sufficiently high NBSNR can be obtained even after the signal recording in any of the tracks T of the groove G and the land L.

As can be seen from FIG. 15, if there is a phase difference between the crystal reflectance and the amorphous reflectance of the medium, the change in the wobble signal amplitude Wa caused by recording the signal differs between the land L and the groove G. Here, the difference γ (evaluation index) between the land L and the groove G of the wobble signal amplitude Cw due to signal recording can be obtained by the following equation (2).
γ = (Cw1L-Cw0L)-(Cw1G-Cw0G) ...... Formula (2)
Here, Cw0L and the like have the following meanings.
Cw0L: Peak value [dBm] of the wobble signal from the land track LT before signal recording
Cw1L: Peak value [dBm] of the wobble signal from the land track LT after signal recording
Cw0G: Peak value [dBm] of the wobble signal from the groove track GT before signal recording
Cw1G: Peak value [dBm] of the wobble signal from the groove track GT after signal recording
If γ is 0, it means that there is no phase difference between the reflected light from the crystal of the medium and the non-crystal, and if γ is large, there is a phase difference between the reflected light from the crystal of the medium and the non-crystal. It means big.

The optical disc preferably satisfies the following formula (3).
-1.5 [dB] <(Cw1L-Cw0L)-(Cw1G-Cw0G) <1.5 [dB] ...... Equation (3)
Expression (3) indicates that the absolute value of the difference between the land L and the groove G of the amplitude Cw of the wobble signal by recording the signal on the optical disc is as small as 1.5 [dB]. This is true when the phase difference between the complex reflectances of the amorphous region and the crystalline region of the medium is 15 deg or less, and the wobble NBSNR is maintained at 25 dB or more even after signal recording. For this reason, the optical disk satisfying the expression (3) has little leakage from the recording signal, and can stably read information from the wobble signal even after the signal is recorded.
FIG. 17 is a graph showing the relationship between γ in equation (2) and the NBSNR of the wobble signal.
In FIG. 17, a reference line with an NBSNR of 25 dB is drawn as in FIG. From FIG. 17, it can be seen that the NBSNR of 25 dB corresponds to γ of ± 1.5.
If γ is within ± 1.5, the performance of the wobble signal is sufficiently high even after the signal is recorded, and the reliability can be maintained.

Note that it is possible to expand the range of the amplitude Cw of the wobble signal of the optical disk as compared with the equation (3). For example, the equation (4) may be applied to the difference in the amplitude Cw.
-2.0 [dB] <(Cw1L-Cw0L)-(Cw1G-Cw0G) <2.0 [dB] ...... Equation (4)
For example, the optical pickup head PUH to be used is limited (whether the optical pickup head with good light detection performance is used) or the wobble amplitude W is increased to use the optical disc in which the difference in the amplitude Cw is expressed by the equation (4). The wobble signal can be detected.

(Optical disk evaluation method)
Next, an optical disk evaluation method will be described.
FIG. 18 is a flowchart showing an example of an optical disc evaluation procedure.
(1) The land track LT on which no signal is recorded is reproduced (ST1), and the wobble signal amplitude Cw0L or a value corresponding thereto is measured (ST2).
(2) A signal is recorded on the reproduced land track LT (ST3), and the wobble signal amplitude Cw1L of the land track LT on which the signal is recorded, or a value corresponding thereto is measured (ST4).

(3) The optical pickup head PUH is moved from the land L to the groove G (ST5), and the wobble signal amplitude Cw0G of the groove G of the track T where no signal is recorded, or a value corresponding thereto is measured (ST6).

(4) A signal is recorded on the reproducing groove track GT (ST7), and the wobble signal amplitude Cw1G of the recorded groove track GT or a value corresponding thereto is measured (ST8).

(5) A measurement value is input to the equation (2), and an amplitude difference is calculated (ST9). If this value is -1.5 dB or more and 1.5 dB or less, it is accepted, otherwise it is rejected (ST10).

As can be seen from the above description, the wobble signal amplitude value Wa or the “similar value” can be used for the evaluation of the optical disc. That is, either the wobble signal amplitude value Wa itself shown in FIGS. 12 and 13 or the peak value Cw of the frequency characteristic shown in FIGS. 15 and 16 can be used for the evaluation of the optical disc.
In the above wobble signal evaluation method, even if the phase of the medium is not directly measured, it is possible to know the state of the phase on the optical disk simply by recording the signal at the track T2 (land L, groove G), and the evaluation is easy. And its accuracy is high. As described above, by using this determination method, it is possible to relatively easily select an optical disc in which a recording signal leaks into the wobble.

(Optical disk evaluation device)
Next, an optical disk evaluation apparatus will be described.
FIG. 19 is a block diagram showing the configuration of the optical disc evaluation apparatus 10a according to the first embodiment of the present invention.
The optical disk evaluation apparatus 10a includes a controller 11, an optical pickup head PUH, a photodetector PD, a preamplifier 12, a servo circuit 13, a semiconductor laser driving circuit LDD, a recording signal processing circuit 14, an RF signal processing circuit 15, an address signal processing circuit 16, and a radial. A push-pull signal amplitude measurement circuit 17 and an evaluation data generation circuit 18 are included.
The optical disk evaluation apparatus 10a is configured by adding a radial push-pull signal amplitude measurement circuit 17 and an evaluation data generation circuit 18 to the optical disk apparatus 10.

  The radial push-pull signal amplitude measuring circuit 17 measures the radial push-pull signal amplitude Wa of the signal detected by the photodetector PD and amplified by the preamplifier 12. Instead of the radial push-pull signal amplitude measuring circuit 17, it is also possible to perform a frequency analysis using a radial push-pull signal frequency characteristic measuring circuit and measure the peak value Cw.

The evaluation data generation circuit 18 generates data to be recorded as an evaluation signal for recording the evaluation signal. The evaluation data generation circuit 18 can be constituted by, for example, a memory that directly stores data or a random number generator that generates random data.
In the optical disk evaluation apparatus 10a, the unrecorded track T is reproduced, and the amplitude information of the reproduced signal is measured using the radial push-pull signal amplitude measuring circuit 17 (or the radial push-pull signal frequency characteristic measuring circuit).
Further, the evaluation data generated by the evaluation data generation circuit 18 is recorded on the track T. Next, the track T is reproduced, and the amplitude information of the reproduced signal is measured using a radial push-pull signal amplitude measuring circuit 17 (or a radial push-pull signal frequency characteristic measuring circuit). Finally, the evaluation means included in the controller 11 calculates the γ value of Expression (2), and evaluates the optical disk.

(Example)
FIG. 20 is a cross-sectional view showing a layer configuration example of an optical disc medium D0 having a relative reflectance phase difference of 15 d [deg] or less, which is one embodiment of the present invention. The optical disc medium D0 is composed of polycarbonate (PC) as a substrate (cover layer), Ag alloy as a reflective film, GeSbTe as a recording layer, and various protective layers.
In the layer configuration of the optical disk medium D0 in FIG. 20, the complex reflectance of the crystal is -0.26988-i0.20006, and the complex reflectance of the amorphous is -0.37330-i · 0.19520. Therefore, the absolute reflectance of the crystal is 11.29%, and the absolute reflectance of the amorphous is 17.74%. The phase of the crystal is 217 [deg], the phase of the non-crystal is 208 [deg], and the phase difference between the two is 9 [deg]. Here, when the optical disk medium D0 is applied to the optical disk device, the S / N of the wobble signal is 37.8 dB for both the land and groove when the signal is not recorded, and the land is 26.5 dB after the signal is recorded on the self track and the adjacent track. The groove becomes 26.0 dB, and the wobble signal can be stably read from both the land and the groove track.

FIG. 21 is a table showing the evaluation results of the optical disc medium D0 shown in FIG.
That is, the table of FIG. 21 shows values of γ and each Cw when the optical disk medium D0 is applied to the evaluation apparatus which is one of the embodiments of the present invention. Γ of the optical disk medium D0 is 1.1 [dB]. This is less than 1.5 [dB] in absolute value, and when applied to Equation (3), it can be determined that the wobble signal of the optical disc medium B can be read stably.

FIG. 22 is a cross-sectional view showing a layer configuration example of an optical disc medium Dx having a relative reflectance phase difference exceeding 15 d [deg], which is a comparative example of the present invention.
In the layer configuration of the optical disc medium A, the complex reflectance of the crystal is -0.27529-i0.20912, and the complex reflectance of the amorphous is -0.43662-i0.12907. Therefore, the absolute reflectance of the crystal is 11.95%, and the absolute reflectance of the amorphous is 20.73%. Further, the phase of the crystal is 217 [deg], the phase of the non-crystal is 196 [deg], and the phase difference between them is 21 [deg]. Here, when the optical disk medium Dx is applied to the optical disk device, the S / N of the wobble signal is 37.8 dB for both the land and the groove when the signal is not recorded, and after the signal is recorded on the self track and the adjacent track, the land is 29.5 dB. The groove becomes 18.5 dB, and the wobble signal cannot be read stably on the groove track.

FIG. 23 is a table showing the evaluation results of the optical disc medium Dx shown in FIG.
That is, the table of FIG. 23 shows values of γ and each Cw when the optical disk medium Dx is applied to the evaluation apparatus which is one of the embodiments of the present invention. The absolute value of γ of the optical disk medium Dx is 2.5 [dB]. This exceeds 1.5 [dB], and when it is applied to the equation (3), it can be determined that it is difficult to read a stable wobble signal of the optical disk medium A.

As can be seen from a comparison between FIGS. 22 and 24, in the optical disc media D0 and Dx, the basic multilayer structure is not changed, and the thickness of each layer is slightly different. That is, by changing the layer thickness, the phase difference of the complex reflectance can be adjusted to be within 15d [deg] in absolute value. It is also possible to adjust the phase difference of the complex reflectivity by changing the basic configuration and the constituent material (refractive index n) of the multilayer structure.
In the present example and the comparative example, the optical disc apparatus used was an apparatus having a light source wavelength of 405 nm and an objective lens NA of 0.65. The amplitude of the wobble signal of the optical disc media D0 and Dx is 0.05 (5%) when normalized by the tracking error signal amplitude. Even if the wavelength λ of the light source, the NA of the objective lens, and the amplitude of the wobble signal change, the optical disc D can be evaluated based on the equation (2).

(Second Embodiment)
Next, as a second embodiment, an optical disk and a method for evaluating the optical disk when phase modulation is applied to the wobble signal will be described. Here, the phase modulation is a method of recording a signal by changing the wobble phase according to the region and assigning it to a code as shown in FIGS. 6 (B) and 6 (C).

FIG. 24 is a graph showing the frequency characteristics of an unmodulated single frequency wobble signal, and corresponds to FIG. The frequency characteristic has a peak at the carrier frequency f0 of the wobble signal, and the other part is a noise component. As shown in FIG. 24, NBSNR (or CNR), which is an index for evaluating the performance of a wobble signal, can be measured by obtaining a difference between a peak value Cw and a noise level value.
FIG. 25 is a graph showing frequency characteristics of a wobble signal in wobble (see FIG. 6B) subjected to binary phase modulation with a phase difference between codes of about 180 degrees. The frequency characteristic rises in the vicinity of the carrier frequency, but due to the influence of the modulation component, peaks occur on both sides of the carrier frequency, and its peripheral part also rises. Therefore, it is difficult to obtain an accurate value of the wobble NBSNR as in the case of FIG.
FIG. 26 is a graph showing the frequency characteristics of the wobble signal in the wobble (see FIG. 6C) when the modulation area and the non-modulation area exist at a ratio of 1: 4. Since the non-modulation region exists for a long time, the frequency characteristic has a peak at the carrier frequency, but the peak value decreases due to the influence of the modulation component, and the peripheral portion also rises. Accordingly, in this case as well, it is difficult to obtain an accurate value of the wobble NBSNR as in the case of FIG.

A double NBSNR can be used to measure the NBSNR of such a modulated wobble signal. This double NBSNR is a difference between the peak value Cw appearing at twice the wobble carrier frequency and the noise level from the frequency characteristic resulting from double the wobble signal.
Here, the multiplication by 2 means to square the signal. When the signal is squared, the phase modulation component disappears and the fundamental component appears at twice the frequency.

FIGS. 27, 28, and 29 correspond to FIGS. 24, 25, and 26, respectively, an unmodulated single frequency wobble signal, a wobble signal that is subjected to binary phase modulation with a phase difference of about 180 degrees, and partially Shows the frequency characteristics of each of the wobble signals after multiplication (modulation area and non-modulation area in a ratio of 1: 4) after multiplication.
27 to 29, all signals have a simple frequency characteristic having only one peak. This is because only the carrier component of the wobble signal is extracted by multiplying the wobble signal by two. Therefore, by using the peak value Cw ′ appearing at twice the carrier frequency in the frequency characteristic after doubled, the amount of change in wobble signal amplitude due to signal recording and the difference between the land L and groove G are obtained. be able to.
That is, by multiplying the signal by two, the phase component due to the phase modulation disappears, and the sub-peak caused by the presence of a plurality of phases disappears. Therefore, the NBSNR can be easily obtained.

Further, when the amplitude of the wobble signal is Wa, the peak value Cw of the frequency characteristic of the unmodulated wobble is expressed by the following equation (5).
Cw [dBm] = 20 × log (Wa / C) ...... Formula (5)
Since the wobble signal amplitude becomes the square of Wa after being multiplied by 2, the peak value Cw ′ of the frequency characteristic of the wobble after being multiplied by 2 is expressed by the following equation (6).
Cw '[dBm] = 20 × log (Wa / C) ²
= 2 × 20 × log (Wa / C) = 2 × Cw …… Formula (6)
From this relationship, the change amount of the wobble signal amplitude Cw after the multiplication by 2 and the difference γ ′ between the land L and the groove G can be calculated by the following equation (7).
γ '= (Cw'1L-Cw'0L) − (Cw'1G-Cw'0G)
= (2 x Cw1-2 x Cw0L)-(2 x Cw1G-2 x Cw0G) = 2 x γ Equation (7)
Here, Cw′0L and the like are defined as follows.
Cw'0L: Peak value of the double wobble signal at the land track LT before signal recording [dBm]
Cw'1L: Peak value of the double wobble signal at the land track LT after signal recording [dBm]
Cw'0G: Peak value of the double wobble signal on the groove track GT before signal recording [dBm]
Cw'1G: Peak value of doubled wobble signal on the groove track GT after signal recording [dBm]

The optical disk preferably satisfies the following formula (8).
-3.0 [dB] <(Cw'1L-Cw'0L)-(Cw'1G-Cw'0G) <3.0 [dB] ...... Equation (8)
Equation (3) shows that the absolute value of the difference between the land L and the groove G of the double wobble signal amplitude by recording the signal on the optical disc is as small as 3.0 [dB]. This means that the absolute value of the difference between the land L and the groove G of the amplitude of the wobble signal before the multiplication by 2 is as small as 1.5 [dB]. As a result, the wobble NBSNR is maintained at 25 dB or more even after signal recording. For this reason, the optical disk satisfying Expression (8) has little leakage from the recording signal, and can stably read information from the wobble signal even after the signal is recorded.

(Optical disk evaluation device)
Next, the optical disk evaluation apparatus will be described.
FIG. 30 is a block diagram showing a configuration of an optical disc evaluation apparatus 10b according to the second embodiment of the present invention.
The optical disk evaluation apparatus 10b includes a controller 11, an optical pickup head PUH, an actuator, a photodetector PD, a preamplifier 12, a servo circuit 13, a semiconductor laser driving circuit LDD, a recording signal processing circuit 14, an RF signal processing circuit 15, and an address signal processing circuit 16. A radial push-pull signal amplitude measuring circuit 17, an evaluation data generating circuit 18, and a doubler circuit 19.
The optical disk evaluation apparatus 10b is configured by adding a double circuit 19 to the optical disk evaluation apparatus 10a.

FIG. 31 is a block diagram showing the internal configuration of the double circuit 19. As shown in FIG. 27, the double circuit 19 includes a low noise amplifier 191, a band pass filter 192, and a multiplier circuit 193.
The band pass filter 192 removes low frequency noise and high frequency noise from the radial push-pull signal amplified by the low noise amplifier 191.
The multiplier circuit 193 doubles the frequency by squaring the amplitude of the radial push-pull signal that has passed through the bandpass filter 192. Note that it is possible to double only the frequency without changing the amplitude.

  The electrical signal detected by the photodetector PD is amplified by the preamplifier 12 and output to the servo circuit 13, the RF signal processing circuit 15, the address signal processing circuit 16, and the double circuit 19. The output of the doubler circuit is output to the radial push-pull signal amplitude measuring circuit 17 or the radial push-pull signal frequency characteristic measuring circuit.

  In this optical disk evaluation apparatus 10b, reproduction is performed on an unrecorded track T, and amplitude information of the reproduction signal is measured using the radial push-pull signal amplitude measurement circuit 17 or the radial push-pull signal frequency characteristic measurement circuit. Further, the evaluation data generated by the evaluation data generation circuit 18 is recorded on the track T. Next, the track T is reproduced, and the amplitude information of the reproduced signal is measured by using the radial push-pull signal amplitude measuring circuit 17 or the radial push-pull signal frequency characteristic measuring circuit. Finally, the evaluation means included in the controller 11 calculates the γ ′ value of equation (7), and evaluates the optical disk.

(Other embodiments)
Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.

It is a block diagram showing the basic composition of an optical disk device. It is a block diagram which shows the example of the light receiver divided into 4 parts. It is a schematic diagram showing the structure of an optical disk. It is the enlarged view to which the track | truck of the optical disk was expanded. It is a figure showing the state which looked at the track of the optical disk from the top in contrast with the reproduction signal. It is a schematic diagram showing a wobble signal that is not phase-modulated and a phase-modulated wobble signal. It is a graph which shows the frequency characteristic of the wobble signal of the single frequency which is not modulated. It is a graph which shows the relationship between the wobble amplitude of the groove | channel of an optical disk, and a wobble signal amplitude. It is a graph which shows the relationship between the reflectance of an optical disk, and a wobble signal amplitude. It is a graph which shows the relationship between the depth of the groove | channel of an optical disk, and the amplitude of a wobble signal. It is a figure showing a groove and a wobble signal before recording a signal. It is a figure showing a groove and a wobble signal after recording signals, such as user data. It is a figure showing the groove | channel G and the wobble signal after recording signals, such as user data. It is a graph showing the relationship between the NBSNR of the wobble signal after signal recording and the phase difference of the reflected light between the crystal and non-crystal of the medium. It is a graph which shows the frequency characteristic of the wobble signal of FIG. It is a graph which shows the frequency characteristic of the wobble signal of FIG. It is a graph showing the relationship between (gamma) and NBSNR of a wobble signal. It is a flowchart showing an example of the evaluation procedure of an optical disk. It is a block diagram showing the structure of the optical disk evaluation apparatus based on this invention. It is sectional drawing which shows the layer structural example of the optical disk medium which is an Example of this invention. 21 is a table showing evaluation results of the optical disc medium shown in FIG. It is sectional drawing which shows the layer structural example of the optical disk medium which is a comparative example of this invention. It is a table | surface showing the evaluation result of the optical disk medium shown in FIG. It is a graph which shows the frequency characteristic of the wobble signal of the single frequency which is not modulated. It is a graph which shows the frequency characteristic of the wobble signal in the wobble which performed the binary phase modulation whose phase difference between codes is about 180 degrees. It is a graph which shows the frequency characteristic of the wobble signal in a wobble when a modulation area | region and a non-modulation area | region exist in the ratio of 1: 4. It is a graph which shows the frequency characteristic of the wobble signal of the single frequency which is not modulated. 6 is a graph showing frequency characteristics of a wobble signal subjected to binary phase modulation with a phase difference of about 180 degrees. It is a graph which shows the frequency characteristic of the wobble signal which performed partial modulation. It is a block diagram showing the structure of the optical disk evaluation apparatus based on this invention. It is a block diagram showing the internal structure of a 2 times multiplication circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical disk apparatus, 10a, 10b ... Optical disk evaluation apparatus, 11 ... Controller, 12 ... Preamplifier, 13 ... Servo circuit, 14 ... Recording signal processing circuit, 15 ... Signal processing circuit, 16 ... Address signal processing circuit, 17 ... Radial push Pull signal amplitude measurement circuit, 18 ... evaluation data generation circuit, 19 ... multiplication circuit, PUH ... optical pickup head, LDD ... semiconductor laser drive circuit, PD ... photo detector

Claims (6)

It includes a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous by heating by light irradiation, the position of the boundary between the land and the groove vibrates, and the vibration is modulated by predetermined information. An optical disc,
An optical disc characterized in that an absolute value of a phase difference of reflected light from a recording layer in each of a crystalline state and an amorphous state is 15 degrees or less. It includes a land and a groove that have a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous when heated by light irradiation, and the position of the boundary between the land and the groove vibrates, and the vibration is modulated by predetermined information. An optical disc,
The difference between the vibration components of the reflected light from the land before and after the information recording on the land (Cw1L-Cw0L) and the difference between the vibration components of the reflected light from the groove before and after the information recording on the groove (Cw1G- An optical disc characterized in that an absolute value | (Cw1L-Cw0L)-(Cw1G-Cw0G) | of a difference of Cw0G) is 1.5 dB or less. An evaluation method of an optical disc including a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous by heating by light irradiation, and the boundary position between the land and the groove vibrates at a predetermined spatial period. There,
A first measurement step of irradiating light onto a land of a rotating optical disc before information recording and measuring the vibration component Cw0L of reflected light from the land;
A second measuring step of measuring the vibration component Cw0G of the reflected light from the groove by irradiating the groove of the rotating optical disc before the information recording;
Recording information on the optical disc;
A third measurement step of irradiating the land of the rotating optical disc after information recording with light to measure the vibration component Cw1L of the reflected light from the land;
A fourth measuring step of measuring the vibration component Cw1G of the reflected light from the groove by irradiating the groove of the rotating optical disc after the information recording;
The difference (Cw1L-Cw0L) of the vibration component of the reflected light from the land before and after the information recording and the difference (Cw1G-Cw0G) of the vibration component of the reflected light from the groove before and after the information recording (( Cw1L-Cw0L)-(Cw1G-Cw0G));
An optical disc evaluation method comprising: 4. The optical disk evaluation method according to claim 3, wherein each of the first to fourth measurement steps includes a signal multiplication step of multiplying a signal based on reflected light from the optical disk by two. An optical disc that evaluates an optical disc that includes a land and a groove having a recording layer made of an optical material that undergoes a phase transition from crystal to amorphous upon heating by light irradiation, and in which the position of the boundary between the land and the groove vibrates at a predetermined spatial period An evaluation device,
A rotating mechanism for rotating the optical disc;
A recording light source for recording information on the optical disc;
A reproduction light source for reproducing the optical disk;
A light moving means for moving the light emitted from the reproduction light source in the land and along the track in the groove;
A light receiving element that receives reflected light emitted from the reproducing light source and reflected from the recording layer of the optical disc;
A vibration component extraction unit for extracting a component of the vibration by performing frequency analysis on a signal output from the light receiving element;
The difference (Cw1L-Cw0L) of the vibration component of the reflected light from the land before and after the information recording and the difference (Cw1G-Cw0G) of the vibration component of the reflected light from the groove before and after the information recording (( Cw1L-Cw0L)-(Cw1G-Cw0G))
An optical disk evaluation apparatus comprising: 6. The optical disk evaluation apparatus according to claim 5, further comprising a signal multiplier for multiplying a signal output from the light receiving element by two.

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