WO2011108192A1

WO2011108192A1 - Optical disc evaluation method and optical disc evaluation device

Info

Publication number: WO2011108192A1
Application number: PCT/JP2011/000671
Authority: WO
Inventors: 智山下
Original assignee: Ｊｖｃ・ケンウッド・ホールディングス株式会社
Priority date: 2010-03-05
Filing date: 2011-02-07
Publication date: 2011-09-09
Also published as: TW201203230A; JP2011187102A

Abstract

An optical disc evaluation unit (100) comprises a rotation control unit (2) that rotates an optical disc (D), further comprising an information recording face (D2), at a rotation speed slower than the rotation speed of playing the information that is recorded on the information recording face (D2); a light source (3) for projecting light upon the information recording face (D2) of the rotating optical disc (D); a detector (11) that detects a quantity of reflected light from the information recording face (D2); and a radial push-pull signal determination unit (26) that evaluates a wave form of a value based on the quantity that is detected by the detector (11).

Description

Optical disk evaluation method and optical disk evaluation apparatus

The present invention relates to a technique for detecting defects such as the shape of the information recording surface of an optical disc.

Conventionally, in an optical disc manufacturing process, whether or not there is a defect such as a shape or size on the information recording surface of the manufactured optical disc is determined by the following method. First, the manufactured optical disk is rotated at a rotation speed when reproducing information recorded on the information recording surface. Then, the information recording surface of the optical disk is irradiated with light, focus control is performed, the reflected light amount reflected from the optical disk is detected while gradually changing the light irradiation position in the radial direction of the optical disk, and the radial push-pull based on the amount is detected. Get a signal.

When the waveform of the obtained radial push-pull signal is evaluated and a disturbance of the waveform is detected, it is determined that there is a possibility that a defect such as a shape exists in a portion corresponding to the disturbance on the information recording surface. Finally, the part determined to have a defect is observed with an atomic force microscope or the like, and it is determined whether or not a defect such as a shape exists in the part. The information recording surface is a pit, groove, or land.

JP 2000-31344 A

There is a wobble used as position information on the information recording surface of the optical disc. Therefore, the tracking error signal, which is the original signal of the radial push-pull signal, includes a signal corresponding to a pit, a groove, or a land (hereinafter referred to as “push-pull signal”) and a signal corresponding to a wobble (hereinafter referred to as “push-pull signal”). , Described as “wobble signal”). In the tracking error signal, the frequency of the wobble signal is very high compared to the frequency of the push-pull signal.

Therefore, when determining whether there is a defect such as a shape on the information recording surface, the value of the high frequency component is markedly reduced by a low pass filter for the purpose of removing the wobble signal that is the high frequency component of the tracking error signal. Reduce. Then, the waveform of the radial push-pull signal corresponding to the pit, groove, or land is evaluated.

Next, the relationship between the actual rotation center C of the optical disc D and the center C ′ of the track T will be described with reference to FIG. FIG. 1 is a diagram showing the relationship between the rotation center C of the actual optical disc D and the center C ′ of the track T. As shown in FIG. 1, the rotation center C and the center C ′ of the track T do not coincide with each other as shown in FIG. 1 due to various alignment accuracy at the time of creating a stamper as a master disk of the optical disk D. That is, the actual optical disc D has a so-called “eccentric R”. Therefore, as shown in FIG. 1, the information recording surface of the optical disc D has a portion A (hereinafter referred to as “sparse portion A”) in which the number of tracks traversed by the circular light L irradiated without tracking control is small. And a portion B (hereinafter referred to as “dense portion B”) in which the number of tracks traversed by the light L is large.

As the eccentricity R increases, the frequency of the portion corresponding to the dense portion B of the tracking error signal increases. Then, the value of the portion corresponding to the dense portion B of the push-pull signal is greatly reduced from the original value by the low-pass filter for removing the wobble signal. For this reason, even if a defect such as a shape exists in the dense portion B, the waveform disturbance is hidden in the radial push-pull signal. That is, for the portion corresponding to the dense portion B, it is difficult to detect the disturbance of the waveform of the radial push-pull signal. Therefore, it is difficult for the dense portion B to specify a portion where a defect may exist.

Also, an optical disc with a high information transfer speed has a high rotation speed at the time of reproduction, so that the rotation speed when judging whether or not there is a defect on the information recording surface is also high. In particular, for an optical disc whose information recording surface is miniaturized in order to increase the recording capacity, the frequency of the tracking error signal corresponding to the dense portion B is high. Therefore, in the same manner as described above, it is difficult to detect the disturbance of the radial push-pull signal waveform in the portion corresponding to the dense portion B, and it is not possible to specify a portion where a defect may exist. Have difficulty.

An object of the present invention is to provide an optical disk evaluation method and an optical disk evaluation apparatus that can identify a portion where a defect in the form of an information recording surface of an optical disk may exist.

In order to solve the above problems and achieve the above object, an optical disk evaluation method according to the present invention provides an optical disk having an information recording surface at a rotation speed slower than the rotation speed when reproducing information recorded on the information recording surface. Rotating, irradiating the information recording surface of the rotated optical disc with light, detecting a reflected light amount reflected from the information recording surface, and calculating a tracking error signal based on the reflected light amount And a step of reducing the high frequency component of the tracking error signal, and determining whether a ratio or level difference between the maximum amplitude level and the minimum amplitude level in the waveform of the signal with the reduced high frequency component is within a predetermined value. Steps.

The optical disk evaluation apparatus of the present invention includes a rotation control unit that rotates an optical disk having an information recording surface at a rotation speed slower than a rotation speed when reproducing information recorded on the information recording surface; A light source for irradiating the information recording surface with light; a detection unit for detecting a reflected light amount reflected from the information recording surface; a low-pass filter for reducing a high-frequency component of a tracking error signal based on the reflected light amount; and the high-frequency component And a push-pull signal determination unit that determines whether or not the ratio or level difference between the maximum amplitude level and the minimum amplitude level in the waveform of the signal with reduced noise is within a predetermined value.

The present invention can provide an optical disk evaluation method and an optical disk evaluation apparatus that can identify a portion where a defect such as a shape of an information recording surface of an optical disk may exist.

It is a figure which shows the relationship between the rotation center of an optical disk, and the center of a track | truck. It is a block diagram of the optical disk evaluation apparatus of this Embodiment. It is a figure for demonstrating a tracking error signal. It is a figure which shows the characteristic of the low pass filter of FIG. It is a figure for demonstrating defects, such as the shape of the information recording surface of an optical disk. It is a figure which shows the relationship between defects, such as the shape of the information recording surface of an optical disk, and the waveform of a radial push pull signal. It is a perspective view containing the cross section of an optical disk. It is a figure for demonstrating that a tracking error signal is a signal containing a wobble signal and a low-pass filter reduces the value of the high frequency component of a tracking error signal remarkably. It is a flowchart which shows each step of operation | movement of the optical disk evaluation apparatus of this Embodiment. It is a flowchart which shows each step of the deformation | transformation operation | movement of the optical disk evaluation apparatus of this Embodiment. It is a figure which shows the radial push pull signal of a comparative example. It is a figure which shows the radial push pull signal of an Example.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

First, the configuration of the optical disk evaluation apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 2 is a configuration diagram of the optical disc evaluation apparatus 100 of the present embodiment. In FIG. 2, the optical disc D to be evaluated is also displayed. The optical disc D is an optical disc immediately after manufacture, and includes a substrate D1, an information recording surface D2 provided on the substrate D1, and a transparent substrate D3 provided on the information recording surface D2. The information recording surface D2 is a pit, a groove, or a land, and is formed in a spiral shape.

The optical disk evaluation apparatus 100 according to the present embodiment is an apparatus that identifies a portion where a defect such as the shape of the information recording surface D2 of the optical disk D may be present. As shown in FIG. 1, rotation controller 2, light source 3, optical power controller 4, collimator lens 5, polarizing beam splitter 6, quarter-wave plate 7, objective lens 8, and condenser lens 9 The cylindrical lens 10, the detection unit 11, the first addition unit 12, the second addition unit 13, the third addition unit 14, the fourth addition unit 15, the first subtraction unit 16, and the focus control unit 17. A first actuator 18, a fifth adder 19, a second subtractor 20, a wobble detection circuit 21, a low-pass filter 22, a radial push-pull signal generator 23, a tracking controller 24, a second Acti Having a eta 25, a radial push-pull signal determination unit 26, a reproduction signal evaluation unit 27, an output unit 28.

Spindle motor 1 rotates optical disc D. The rotation control unit 2 controls the spindle motor 1 so as to rotate the optical disc D at a predetermined rotation speed that is lower than the rotation speed when reproducing the information recorded on the information recording surface D2. The light source 3 is composed of a semiconductor laser, and emits light L that is linearly polarized light and has a divergence. The optical power control unit 4 controls the light source 3 so that the power of the light L emitted from the light source 3 is smaller than the power for reproducing the information recorded on the information recording surface D2. Hereinafter, “when reproducing information recorded on the information recording surface D2” may be referred to as “during reproduction”.

The collimating lens 5 converts the divergent light L from the light source 3 into parallel light. The polarization beam splitter 6 reflects the light from the collimating lens 5 toward the quarter-wave plate 7 side. Further, the polarization beam splitter 6 transmits the light from the quarter-wave plate 7 toward the condenser lens 9. The quarter-wave plate 7 converts the light from the polarization beam splitter 6 into circularly polarized light and directs it to the objective lens 8. The quarter-wave plate 7 converts the light from the objective lens 8 into linearly polarized light and directs it to the polarizing beam splitter 6.

The objective lens 8 collects the light from the quarter-wave plate 7 on the information recording surface D2 through the transparent substrate D3 of the optical disc D. The objective lens 8 makes the light from the information recording surface D2 parallel light and directs it toward the quarter-wave plate 7. The condensing lens 9 converges the light from the polarization beam splitter 6 and directs it to the cylindrical lens 10. The cylindrical lens 10 further converges the light from the condenser lens 9 and collects it in the detection unit 11.

With the above components, the light L emitted from the light source 3 passes through the collimating lens 5, the polarizing beam splitter 6, the quarter wavelength plate 7, and the objective lens 8 in this order, and the information recording surface D2 of the optical disc D. To be collected. Then, the light is reflected by the information recording surface D2, passes through the objective lens 8, the quarter-wave plate 7, the polarization beam splitter 6, the condensing lens 9, and the cylindrical lens 10 in that order, and passes to the detection unit 11. Collected.

The detection unit 11 detects light from the cylindrical lens 10. The detection unit 11 includes four light receiving units as in the conventional optical pickup detector. That is, the detection unit 11 includes a first light receiving unit 11A, a second light receiving unit 11B, a third light receiving unit 11C, and a fourth light receiving unit 11D. As shown in FIG. 2, each light receiving portion is arranged counterclockwise. The longitudinal direction of the set of the first light receiving unit 11A and the fourth light receiving unit 11D and the longitudinal direction of the set of the second light receiving unit 11B and the third light receiving unit 11C are substantially orthogonal to the track direction. is doing. That is, the longitudinal direction of both sets is substantially the radial direction of the optical disc D.

Each light receiving unit of the detecting unit 11 outputs a signal having a current value corresponding to the amount of received light. In the following, the current signal output by the first light receiving unit 11A is described as “current signal Ia”, the current signal output by the second light receiving unit 11B is described as “current signal Ib”, and the third light receiving unit 11C outputs The current signal to be output is referred to as “current signal Ic”, and the current signal output from the fourth light receiving unit 11D is referred to as “current signal Id”.

The first addition unit 12 adds the current signal Ib from the second light receiving unit 11B and the current signal Id from the fourth light receiving unit 11D. The second addition unit 13 adds the current signal Ia from the first light receiving unit 11A and the current signal Ic from the third light receiving unit 11C. The third addition unit 14 adds the current signal Ia from the first light receiving unit 11A and the current signal Ib from the second light receiving unit 11B. The fourth addition unit 15 adds the current signal Ic from the third light receiving unit 11C and the current signal Id from the fourth light receiving unit 11D.

The first subtractor 16 subtracts the value obtained by the first adder 12 from the value obtained by the second adder 13 to calculate the focus error signal “(Ia + Ic) − (Ib + Id)”. The focus control unit 17 causes the first actuator 18 to perform focus control based on the focus error signal calculated by the first subtraction unit 16. The first actuator 18 performs focus control according to the control of the focus control unit 17.

The fifth adder 19 adds the value obtained by the third adder 14 and the value obtained by the fourth adder 15 to calculate the RF signal “(Ia + Ib + Ic + Id)”. The second subtractor 20 subtracts the value obtained by the fourth adder 15 from the value obtained by the third adder 14 to calculate the tracking error signal “(Ia + Ib) − (Ic + Id)”.

The tracking error signal calculated by the second subtraction unit 20 will be described with reference to FIG. FIG. 3 is a diagram for explaining the tracking error signal. In FIG. 3, the detection unit 11 including the first light receiving unit 11A, the second light receiving unit 11B, the third light receiving unit 11C, and the fourth light receiving unit 11D is also displayed.

FIG. 3A shows a state in which the light L is collected at the center of the concave portion of the track T by the objective lens 8. The value of (Ia + Ib) is equal to the value of (Ic + Id), and the tracking error signal “ The value of (Ia + Ib) − (Ic + Id) ”is 0. FIG. 3B shows a state where the tracking is shifted by half of the track T, and the value of (Ia + Ib) and the value of (Ic + Id) are the most different, and the tracking error signal “(Ia + Ib) − (Ic + Id)”. "Is the maximum negative value.

FIG. 3C shows a state in which the light L is collected at the center of the convex portion of the track T by the objective lens 8. The value of (Ia + Ib) is equal to the value of (Ic + Id), and the tracking error signal The value of “(Ia + Ib) − (Ic + Id)” is 0. FIG. 3D shows a state where the tracking is shifted by half of the track T. The value of (Ia + Ib) and the value of (Ic + Id) are the most different, and the tracking error signal “(Ia + Ib) − (Ic + Id)” is shown. "Is the maximum positive value.

When the wavelength of the light L is λ, when n is a positive number, the tracking error signal is not always “0” unless the groove depth of the track is “n × λ / 4”. When m is an odd number, the tracking error signal has the maximum amplitude when the depth of the groove of the track is “m × λ / 8”.

Return to Figure 2. The wobble detection circuit 21 detects wobble based on the tracking error signal calculated by the second subtraction unit 20.

Next, the low-pass filter 22 will be described with reference to FIG. FIG. 4 is a diagram illustrating the characteristics of the low-pass filter 22. As shown in FIG. 4, the low-pass filter 22 has a characteristic of remarkably reducing the value of a high frequency component equal to or higher than the cutoff frequency Fc. That is, the low-pass filter 22 significantly reduces the value of the high frequency component equal to or higher than the cutoff frequency Fc in the tracking error signal calculated by the second subtracting unit 20.

Return to Figure 2. The radial push-pull signal generator 23 calculates a radial push-pull signal by dividing the tracking error signal whose high-frequency component is reduced by the low-pass filter 22 by the RF signal calculated by the fifth adder 19 and normalizing it. The tracking control unit 24 causes the second actuator 25 to perform tracking control based on the radial push-pull signal calculated by the radial push-pull signal generation unit 23. The second actuator 25 performs tracking control according to the control of the tracking control unit 24.

Next, the radial push-pull signal determination unit 26 will be described, but before that, defects such as the shape of the information recording surface D2 of the optical disc D will be described with reference to FIG. FIG. 5 is a diagram for explaining defects such as the shape of the information recording surface D2 of the optical disc D. FIG. 5A shows a cross section of an optical disc D that does not have a shape or other defect on the information recording surface D2. FIG. 5B shows a cross section of the optical disc D having the first defect df1 in which the groove depth of the track T is relatively shallow on the information recording surface D2. FIG. 5C shows a cross section of an optical disc D having a second defect df2 in which the groove shape of the track T is different from the others on the information recording surface D2. The structure of the information recording surface D2 will be described again with reference to FIG.

Next, the relationship between the defect such as the shape of the information recording surface D2 of the optical disc D and the waveform of the radial push-pull signal will be described with reference to FIG. FIG. 6 is a diagram showing the relationship between a defect such as the shape of the information recording surface D2 of the optical disc D and the waveform of the radial push-pull signal. FIG. 6A is a diagram showing a waveform Pw of the radial push-pull signal for the optical disc D having the cross section of FIG. 5A, and there is no disturbance of the waveform Pw.

FIG. 6B is a diagram showing the waveform Pw of the radial push-pull signal for the optical disc D having the cross section of FIG. 5B, and the waveform Pw shows the first defect df1 in FIG. There is a corresponding first disturbance dis1 whose amplitude level is relatively small compared to other parts. FIG. 6C is a diagram showing the waveform Pw of the radial push-pull signal for the optical disc D having the cross section of FIG. 5C. The waveform Pw shows the second defect df2 in FIG. Correspondingly, there is a second disturbance dis2 whose shape is different from the other parts and whose amplitude level is relatively small compared to the other parts.

As is clear from FIGS. 5 and 6, there is a correlation between the defect such as the shape of the information recording surface D2 of the optical disc D and the waveform of the radial push-pull signal. Therefore, the radial push-pull signal determination unit 26 in FIG. 2 determines (evaluates) whether there is a disturbance in the waveform of the radial push-pull signal calculated by the radial push-pull signal generation unit 23, and determines the maximum amplitude level and the minimum amplitude. When a waveform disturbance is detected by determining whether or not the amplitude level ratio or level difference is within a predetermined value, a shape is formed on the portion of the information recording surface D2 corresponding to the waveform disturbance based on the above correlation. It is determined that there may be defects such as.

The reproduction signal evaluation unit 27 evaluates the reproduction signal based on the RF signal calculated by the fifth addition unit 19. Specifically, the reproduction signal evaluation unit 27 performs error rate, CNR (Carrier-to-Noise-Ratio), jitter, SAM (Sequence-Amplitude-Margin), PRSNR (Partial-Response-Signal-Noise-Ratio), MLSE (Maximum-Likelihood-Sequence-Error), modulation. Degree, asymmetry, β, etc. are evaluated.

The output unit 28 outputs and displays the results obtained by the radial push-pull signal determination unit 26 and the reproduction signal evaluation unit 27 on a display device (not shown) outside the optical disk evaluation device 100 of the present embodiment.

Next, the structure of the information recording surface D2 of the optical disc D will be described with reference to FIG. FIG. 7 is a perspective view including a cross section of the optical disc D. FIG. As shown in FIG. 7, the information recording surface D2 of the optical disc D has a groove D21, a land D22, a recording film D23, a recording mark D24, and a wobble D25. The wobble D25 is used when controlling the focal position of light on the information recording surface D2 of the optical disc D.

As described above, the radial push-pull signal determination unit 26 detects defects such as the shape and size of the information recording surface D2 of the optical disc D to be evaluated by detecting the disturbance of the waveform of the radial push-pull signal. By the way, the push-pull signal that is the source of the radial push-pull signal is included in the tracking error signal calculated by the second subtracting unit 20. Since the tracking error signal is a signal based on the amount of reflected light reflected from the information recording surface D2, the tracking error signal includes a push-pull signal and a wobble signal corresponding to the wobble D25. Therefore, in order to detect defects such as the shape and size of the information recording surface D2, it is necessary to remove the wobble signal included in the tracking error signal. The low pass filter 22 significantly reduces the value of the high frequency component in the tracking error signal in order to remove the wobble signal included in the tracking error signal.

Next, the tracking error signal calculated by the second subtracting unit 20 is a signal including a wobble signal, and the low pass filter 22 significantly reduces the value of the high frequency component of the tracking error signal. 8 will be used for explanation. FIG. 8 is a diagram for explaining that the tracking error signal is a signal including a wobble signal and that the low-pass filter 22 significantly reduces the value of the high frequency component of the tracking error signal.

8A to 8D are tracking error signals when the rotational speed of the optical disc D is the rotational speed at the time of reproduction. More specifically, FIG. 8A is a diagram showing a tracking error signal when the eccentricity is relatively large, and FIG. 8B is a diagram showing a tracking error signal when the eccentricity is relatively small. . FIG. 8C is a diagram illustrating a tracking error signal in which a high-frequency component is reduced and a wobble signal is removed by the low-pass filter 22 with respect to the tracking error signal when the eccentricity illustrated in FIG. 8A is relatively large. FIG. 8D shows a tracking error signal in which the high-frequency component is reduced by the low-pass filter 22 and the wobble signal is removed with respect to the tracking error signal when the eccentricity shown in FIG. 8A is relatively small. is there. FIG. 8E shows a tracking error signal in which the high-frequency component is reduced by the low-pass filter 22 when the eccentricity is relatively large and the rotation speed of the optical disc D is a predetermined rotation speed lower than the rotation speed during reproduction. FIG.

As is clear from a comparison between FIG. 8B and FIG. 8D, when the eccentricity is relatively small, even if the rotational speed of the optical disc D is the rotational speed during reproduction, the low-pass filter 22 is substantially Only the wobble signal can be removed. On the other hand, as is clear from comparing FIG. 8A and FIG. 8C, when the eccentricity is relatively large and the rotational speed of the optical disc D is the rotational speed at the time of reproduction, the low-pass filter 22 Not only the wobble signal but also the value of the push-pull signal BP corresponding to the dense portion B where the number of tracks traversed by light is large is reduced. Therefore, even if a defect such as a shape exists in the dense portion B, the waveform disturbance is hidden in the push-pull signal BP corresponding to the dense portion B, and the waveform disturbance of the radial push-pull signal is detected. Have difficulty.

Therefore, in the present embodiment, the rotation control unit 2 controls the spindle motor 1 so as to rotate the optical disc D at a predetermined rotation speed that is lower than the rotation speed when reproducing the information recorded on the information recording surface D2. To do. That is, the rotation control unit 2 controls the spindle motor 1 so as to rotate the optical disc D at a speed slower than the rotation speed during reproduction.

Thereby, the number of tracks in which light crosses the dense portion B per unit time can be reduced as compared with the case where the optical disc D is rotated at the rotation speed during reproduction. That is, the time axis of the tracking error signal becomes longer, and the frequency of the portion corresponding to the dense portion B of the push-pull signal can be reduced. Then, as shown in FIG. 8E, the low-pass filter 22 can substantially remove only the wobble signal even if the eccentricity is relatively large. That is, for the dense portion B, the value of the push-pull signal after being processed by the low-pass filter 22 is substantially the original value. As a result, when a defect such as a shape exists in the dense portion B, the radial push-pull signal determination unit 26 determines that the ratio or level difference between the maximum amplitude level and the minimum amplitude level in the radial push-pull signal waveform is within a predetermined value. By determining whether or not, it is possible to detect waveform disturbance.

In the present embodiment, the light power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 is smaller than the power for reproducing the information recorded on the information recording surface D2. . The light source 3 emits even though the rotation speed of the optical disc D at the time of evaluation when judging whether or not a defect such as a shape exists on the information recording surface D2 is lower than the rotation speed at the time of reproduction. If the power of light is the same as that during reproduction, the following problems occur. That is, since the heating time in each unit time of the recording film D23 in FIG. 7 due to light irradiation is longer than before, the temperature of each part of the recording film D23 rises, and the recording film D23 crystallizes or melts for recording. Signals can be fatally damaged. Therefore, in the present embodiment, in order to prevent the recording film D23 from being damaged, the optical power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 becomes smaller than the power during reproduction.

Next, the operation of the optical disk evaluation apparatus 100 of the present embodiment will be described with reference to FIG. FIG. 9 is a flowchart showing each step of the operation of the optical disc evaluation apparatus 100 of the present embodiment.

The operator places the optical disk D to be evaluated on a mounting unit (not shown) of the optical disk evaluation apparatus 100, and the optical recording apparatus D has a defect such as a shape on the information recording surface D2 of the optical disk D. Give instructions to check whether or not In response to the instruction, the optical power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 is smaller than the power during reproduction. The light source 3 emits light having a predetermined power smaller than the power at the time of reproduction according to the control of the optical power control unit 4 (S1).

The rotation control unit 2 controls the spindle motor 1 so as to rotate the optical disc D at a predetermined rotation speed that is slower than the rotation speed during reproduction. The spindle motor 1 rotates the optical disc D at a lower speed than the rotation speed during reproduction according to the control of the rotation control unit 2 (S2). Focus control is performed under the control of the focus control unit 17, and tracking control is not performed (S3).

The radial push-pull signal determination unit 26 evaluates the waveform of the radial push-pull signal calculated by the radial push-pull signal generation unit 23 (S4). Specifically, the radial push-pull signal determination unit 26 determines whether there is any disturbance in the waveform of the radial push-pull signal (S4). When the radial push-pull signal determination unit 26 detects a waveform disturbance whose ratio or level difference between the maximum amplitude level and the minimum amplitude level is greater than a predetermined value in the waveform of the radial push-pull signal, the radial push-pull signal determination unit 26 specifies the position of the waveform disturbance. Based on this, a site where a defect such as the shape of the information recording surface D2 of the optical disc D is identified (S4). The output unit 28 outputs and displays the result obtained by the radial push-pull signal determination unit 26 on a display device (not shown) outside the optical disk evaluation apparatus 100 (S5).

Since the determination result of whether or not there is a disturbance in the radial push-pull signal waveform is displayed on the display device, the operator can check whether there is a defect such as a shape on the information recording surface D2 of the optical disc D to be evaluated. You can know whether or not. In addition, when there is a disturbance in the waveform of the radial push-pull signal, information for identifying a site where a defect such as the shape of the information recording surface D2 of the optical disc D is displayed on the display device. The site to be observed can be known with an atomic force microscope or the like.

As described above, in this embodiment, when inspecting whether or not a defect such as a shape exists on the information recording surface D2 of the optical disc D, the rotation control unit 2 rotates the optical disc D at the speed of reproduction. The spindle motor 1 is controlled to rotate at a slower predetermined rotational speed. Thereby, even if the eccentricity of the optical disk D is large, the low-pass filter 22 can substantially remove only the wobble signal, and as a result, the radial push-pull signal determination unit 26 also performs the radial push for the dense portion B. The disturbance of the pull signal waveform can be detected.

Further, in the present embodiment, the optical power control unit 4 controls the light source 3 so that the power of light emitted from the light source 3 is smaller than the power at the time of reproduction. Thereby, damage to the recording film D23 of the optical disc D can be prevented.

Note that the optical disk evaluation apparatus 100 of the present embodiment may operate as shown in FIG. FIG. 10 is a flowchart showing each step of the deformation operation of the optical disc evaluation apparatus 100 of the present embodiment.

That is, the rotation control unit 2 controls the spindle motor 1 so that the optical disc D rotates at the rotation speed during reproduction. The spindle motor 1 rotates the optical disk D at the rotation speed at the time of reproduction according to the control of the rotation control unit 2 (S11). Next, the optical power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 becomes the power at the time of reproduction. The light source 3 emits light having power during reproduction in accordance with the control of the optical power control unit 4 (S12).

Next, the focus control unit 17 performs focus control, the tracking control unit 24 performs tracking control, and the reproduction signal evaluation unit 27 evaluates the reproduction signal based on the RF signal calculated by the fifth addition unit 19. (S13). For example, the reproduction signal evaluation unit 27 evaluates error rate, CNR, jitter, SAM, PRSNR, MLSE, modulation degree, asymmetry, β, and the like. Next, the optical power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 becomes a predetermined power smaller than the power so far, for example, 80% of the power so far. To do. The light source 3 emits light with small power according to the control of the optical power control unit 4 (S14).

The rotation control unit 2 controls the spindle motor 1 so that the optical disk D rotates at a predetermined rotation speed slower than the rotation speed until then, for example, 60% of the rotation speed until then. The spindle motor 1 rotates the optical disc D at a low speed according to the control of the rotation control unit 2 (S15).

After the focus control is performed by the control of the focus control unit 17 and the tracking control is not performed, the radial push-pull signal determination unit 26 evaluates the waveform of the radial push-pull signal calculated by the radial push-pull signal generation unit 23. (S16). Specifically, the radial push-pull signal determination unit 26 determines whether the ratio or the level difference between the maximum amplitude level and the minimum amplitude level is within a predetermined value with respect to the waveform of the radial push-pull signal. It is determined whether or not there is a disturbance (S16). When the radial push-pull signal determination unit 26 detects the waveform disturbance of the radial push-pull signal, the radial push-pull signal determination unit 26 identifies the position of the waveform disturbance, and based on this, there is a defect such as the shape of the information recording surface D2 of the optical disc D. The site | part which is present is specified (S16). The output unit 28 outputs and displays the result obtained by the radial push-pull signal determination unit 26 on a display device (not shown) outside the optical disk evaluation apparatus 100 (S17).

Hereinafter, examples and comparative examples of the present invention will be described. For convenience of explanation, a comparative example will be described first, followed by an example.

(Comparative example)
In the comparative example, the optical power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 becomes 1.0 mW at the time of reproduction, and the rotation control unit 2 controls the linear velocity when the optical disc D is reproduced. The spindle motor 1 was controlled to rotate at 7.8 m / s. At that time, the radial push-pull signal generator 23 obtained the radial push-pull signal shown in FIG. FIG. 11 is a diagram illustrating a radial push-pull signal of the comparative example.

Assuming that the track pitch of the optical disk D is Tp and the eccentric amount of the optical disk D is Ro, the number n that the light emitted from the light source 3 crosses the track when the optical disk D rotates 1/2 is expressed by the following equation (1). It is represented by

n = Ro / Tp (1)
Therefore, at a position away from the center r of the optical disc D, assuming that the linear velocity when the optical disc D rotates is v, the average frequency Fave of the radial push-pull signal is expressed by the following equation (2).

Fave = 2 × n × v / (2 × π × r) (2)
Since the optical disc D is eccentric, as shown in FIG. 1, the light L crosses the information recording surface of the optical disc D with the sparse portion A having a small number of tracks traversed by the irradiated light beam L. There is a dense portion B with a large number of tracks. The frequency of the portion corresponding to the dense portion B of the radial push-pull signal is the maximum frequency Fmax of the radial push-pull signal, and the coefficient F is k. Is represented by

Fmax = k × Fave (3)
The coefficient k when the track pitch Tp of the optical disk D is 0.32 μm, the eccentricity Ro of the optical disk D is 60 μm, the linear velocity v is 7.8 m / s, and the eccentricity Ro is 60 μm is Since it is 1.6, the maximum frequency Fmax of the radial push-pull signal at a position 24 mm (r) away from the center of the optical disc D is 31 kHz according to the above equations (1) to (3). Since the cutoff frequency Fc at which the low-pass filter 22 significantly reduces the signal value was 30 kHz, the maximum frequency Fmax of the radial push-pull signal was larger than the cutoff frequency Fc.

Therefore, as shown in FIG. 11, the envelope of the radial push-pull signal has a drum shape, and the minimum amplitude level (peak-to-peak) P2 of the radial push-pull signal with respect to the maximum amplitude level (peak-to-peak) P1 of the radial push-pull signal. The ratio was greater than 3 dB. That is, the value of the radial push-pull signal corresponding to the dense portion B is greatly reduced from the original value. As a result, the radial push-pull signal determination unit 26 cannot detect the waveform disturbance in the portion corresponding to the dense portion B of the radial push-pull signal.

Note that the coefficient k is specified by an experiment, for example.

(Example)
In the embodiment, the optical power control unit 4 controls the light source 3 so that the power of the light emitted from the light source 3 is 0.5 mW, which is half of that during reproduction, and the rotation control unit 2 reproduces the optical disc D. The spindle motor 1 was controlled to rotate at 3.9 m / s, which is 1/2 of the linear velocity at the time. At that time, the radial push-pull signal generator 23 obtained the radial push-pull signal shown in FIG. FIG. 12 is a diagram illustrating a radial push-pull signal according to the embodiment.

The coefficient k when the track pitch Tp of the optical disk D is 0.32 μm, the eccentricity Ro of the optical disk D is 60 μm, the linear velocity v is 3.9 m / s, and the eccentricity Ro is 60 μm is Since it is 1.6, the maximum frequency Fmax of the radial push-pull signal at a position 24 mm (r) away from the center of the optical disc D is 16 kHz according to the above equations (1) to (3). Since the cutoff frequency Fc of the low-pass filter 22 was 30 kHz, the maximum frequency Fmax of the radial push-pull signal was smaller than the cutoff frequency Fc.

Therefore, as shown in FIG. 12, the ratio of the minimum amplitude level (peak-to-peak) P2 of the radial push-pull signal to the maximum amplitude level (peak-to-peak) P1 of the radial push-pull signal is smaller than 1 dB. That is, the value of the radial push-pull signal corresponding to the dense portion B is substantially the original value. As a result, the radial push-pull signal determination unit 26 determines whether the ratio or level difference between the maximum amplitude level and the minimum amplitude level is within a predetermined value in the portion corresponding to the dense portion B of the radial push-pull signal. As a result, the disturbance of the waveform could be detected. That is, by determining a predetermined linear velocity (rotational speed) so that the maximum frequency Fmax of the radial push-pull signal is smaller than the cutoff frequency of the low-pass filter 22, it corresponds to the dense portion B of the radial push-pull signal. In this part, the waveform disturbance can be detected. Then, the radial push-pull signal determination unit 26 determines whether the ratio between the minimum amplitude level and the maximum amplitude level of the radial push-pull signal whose high frequency component is reduced by the low-pass filter 22 is equal to or less than a predetermined value (for example, 1 dB). By making the determination, it is possible to detect waveform disturbance.

Further, although a radial push-pull signal was obtained over 1 hour, no damage to the recording film D23 of the optical disc D was detected. This is considered to be because the power of light emitted from the light source 3 was ½ of that during reproduction.

In the present embodiment described above, when inspecting whether or not a defect such as a shape is present on the information recording surface D2 of the optical disc D, the rotation control unit 2 determines the optical disc D from the rotational speed at the time of reproduction. The spindle motor 1 is controlled to rotate at a slow predetermined rotation speed. The rotational speed at that time may be determined such that the ratio (P2 / P1) of the minimum amplitude P2 of the radial push-pull signal to the maximum amplitude P1 of the radial push-pull signal is not more than a predetermined value. The predetermined value is 3 dB, for example.

Further, the power of light emitted from the light source 3 is preferably controlled as follows. That is, assuming that the ratio of the rotation speed of the optical disk D at the time of inspection to the rotation speed of the optical disk D at the time of reproduction is Rr, the rate of decrease in the power of the light emitted from the light source 3 at the time of inspection It is desirable to be between about Rr times and 1/2 of Rr times. For example, when the power of light emitted from the light source 3 during reproduction is 1.0 mW and the rotation speed of the optical disc D during inspection is ½ of the rotation speed during reproduction, the light emitted from the light source 3 during inspection It is desirable that the power of the power is 0.5 mW to 0.75 mW.

Further, when the optical disk D is a reproduction-only optical disk, when inspecting whether or not there is a defect such as a shape on the information recording surface D2 of the optical disk D, the rotation control unit 2 moves the optical disk D to the information recording surface. The spindle motor 1 is controlled to rotate at a predetermined rotational speed that is slower than the rotational speed at the time of reproducing the information recorded in D2.

Further, the radial push-pull signal determination unit 26 evaluates the waveform of the radial push-pull signal calculated by the radial push-pull signal generation unit 23, and detects the waveform disturbance. However, the radial push-pull signal determination unit 26 may evaluate the waveform of the tracking error signal whose high-frequency component has been reduced by the low-pass filter 22 and detect the waveform disturbance.

100 optical disk evaluation device, 1 spindle motor, 2 rotation control unit, 3 light source, 4 optical power control unit, 5 collimating lens, 6 polarization beam splitter, 7/4 wavelength plate, 8 objective lens, 9 condensing lens, 10 Cylindrical lens, 11 detection unit, 12 1st addition unit, 13 2nd addition unit, 14 3rd addition unit, 15 4th addition unit, 16 1st subtraction unit, 17 focus control unit, 18 1st actuator, 19th 5th Addition unit, 20 second subtraction unit, 21 wobble detection circuit, 22 low pass filter, 23 radial push-pull signal generation unit, 24 tracking control unit, 25 second actuator, 26 radial push-pull signal determination unit, 27 reproduction signal evaluation unit 28 output unit, L light, D optical disk, D2 information recording surface.

The present invention can be used in a technique for detecting defects such as the shape of the information recording surface of an optical disc.

Claims

Rotating an optical disk having an information recording surface at a rotation speed slower than a rotation speed when reproducing information recorded on the information recording surface;
Irradiating the information recording surface of the rotated optical disc with light;
Detecting the amount of reflected light reflected from the information recording surface;
Calculating a tracking error signal based on the amount of reflected light;
Reducing high frequency components of the tracking error signal;
Determining whether the ratio or level difference between the maximum amplitude level and the minimum amplitude level in the waveform of the signal with reduced high-frequency components is within a predetermined value.
The optical disk evaluation method according to claim 1, wherein when irradiating light on the information recording surface, light having a predetermined power smaller than a power for reproducing information recorded on the information recording surface is irradiated.
A rotation control unit that rotates an optical disk having an information recording surface at a rotation speed slower than a rotation speed when reproducing information recorded on the information recording surface;
A light source for irradiating the information recording surface of the rotated optical disc with light;
A detection unit for detecting a reflected light amount reflected from the information recording surface;
A low-pass filter that reduces high-frequency components of the tracking error signal based on the reflected light amount;
An optical disc evaluation apparatus comprising: a push-pull signal determination unit that determines whether a ratio or level difference between a maximum amplitude level and a minimum amplitude level in a waveform of a signal with reduced high-frequency components is within a predetermined value.