JP3939183B2 - Focus offset evaluation method and focus offset evaluation apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, for example, records information on an optical disc having discrete pit areas and evaluates the focus offset of an optical pickup device or an optical integrated unit mounted on an optical disc device that reproduces the recorded information. The present invention relates to a method and a focus offset evaluation apparatus.
[0002]
[Prior art]
Conventionally, in an optical disc apparatus equipped with a diffraction grating that diffracts reflected light from an optical disc toward a light receiving element, an RF signal (disc reading signal) obtained from an embossed pit signal on the optical disc or jitter detected based on the RF signal Or, focus error signal and track cross signal are monitored. In many cases, the focus offset is evaluated based on the jitter or the focus error signal and the track cross signal.
[0003]
In the method of monitoring jitter, the fact that the jitter is minimized at the best focus offset is used, and the focus offset is obtained based on this jitter.
[0004]
On the other hand, in the method of monitoring the focus error signal and the track cross signal, the amount of deviation of the envelope of the track cross signal obtained from the eccentricity of the optical disc from the zero cross point of the focus error signal obtained from the surface deflection of the optical disc is evaluated. Thus, the focus offset is obtained.
[0005]
Furthermore, the focus offset may be evaluated by observing the tracking error signal with the focus servo control turned on and utilizing the fact that the focus offset is the best at the point where the amplitude of the tracking error signal is maximum. .
[0006]
By the way, in an optical disc playback apparatus using a read-only optical disc such as a CD (compact disc), a CD-ROM (read only memory), and a DVD (digital versatile disc) -ROM, there is an emboss pit on the optical disc. The focus offset can be evaluated by detecting an RF signal and detecting jitter from the RF signal.
[0007]
As for MD (mini-disc), CD-type and DVD-type rewritable optical disc playback / recording apparatuses, for example, for MD, there is a reproduction-only high-reflection optical disc composed of pits. For -R (recordable) / RW (rewritable), there is a CD-ROM, and for the DVD system, there is a DVD-ROM. Therefore, as described above, the focus offset can be evaluated by using a ROM disk and detecting jitter using an RF signal.
[0008]
Even if the optical disk is not a reproduction-only optical disk, the focus offset can be evaluated by observing the focus error signal and the track cross signal as described above. Further, it is possible to evaluate the focus offset by detecting the amplitude of the tracking error signal in a state where the focus servo control is on.
[0009]
Also, in an optical pickup device mounted on an optical disk device for a magneto-optical disk, the servo signal detection light-receiving element and the magneto-optical signal detection light-receiving element in servo control are often independent. If such a light-receiving element for detecting a magneto-optical signal is mounted, it is possible to evaluate the focus offset by detecting jitter of the magneto-optical signal.
[0010]
However, a magneto-optical signal cannot be detected in an optical pickup device in which a magneto-optical signal detection light-receiving element is not yet mounted, or in an optical integrated unit in which a magneto-optical signal light-receiving element is not mounted. Therefore, the focus offset cannot be evaluated based on jitter or the like. Therefore, evaluate the focus offset from the focus error signal and track cross signal detected by the light receiving element for servo signal detection, or evaluate the focus offset by detecting the amplitude of the tracking error signal while the focus servo control is on. Will do.
[0011]
At present, an optical integrated unit incorporated in the optical pickup device as described above has been developed to be compatible with all optical discs. This optical integrated unit is composed of a semiconductor laser, a light receiving element that converts the return light reflected by the optical disk of the laser light emitted from the semiconductor laser into an electrical signal, and a diffraction element that diffracts the return light into the light receiving element. It has been Further, as the optical integrated unit, there is further developed a unit that is equipped with a beam splitter for separating the return light so that the return light does not easily return to the light emitting point of the semiconductor laser.
[0012]
Furthermore, the optical integrated unit is not provided, and the semiconductor laser, the light receiving element that converts the return light reflected by the optical disk from the laser light emitted from the semiconductor laser, and the return light are diffracted into the light receiving element. There is also an optical pickup device in which the diffraction element is arranged independently. As such an optical pickup device, devices corresponding to various types of optical disks have been developed.
[0013]
In recent years, in order to increase the capacity and density of writable optical discs, phase change optical discs and magneto-optical discs that record data in both lands and grooves or only in the grooves have appeared. Some of these discs have clock information, address information, etc. registered in pits and wobbles. Furthermore, the numerical aperture of the optical system tends to increase in order to reduce the diameter of the light spot collected on the optical disk.
[0014]
[Problems to be solved by the invention]
In an optical disc in which the data reproduction / recording area is configured by embossed pits, the focus offset of the optical pickup device and the optical integrated unit can be accurately evaluated by actually detecting jitter from the RF signal.
[0015]
However, since an RF signal cannot be detected in an optical disc in which the data reproduction / recording area is not configured with embossed pits, the above-described method for monitoring the zero cross point and the track cross signal of the focus error signal and the focus servo control are on. The focus offset is evaluated by a method of monitoring the amplitude of the tracking error signal.
[0016]
Incidentally, in recent years, with the increase in the density of optical discs, in an optical disc reproducing / recording apparatus in which the numerical aperture of the objective lens has increased, the inclination (change rate) of the focus error signal at the zero cross point becomes larger. For this reason, it becomes difficult to evaluate the focus offset with the same accuracy as in the past, and there arises a problem that the variation of the measured value becomes large.
[0017]
In addition, in the method of evaluating the focus offset based on the amplitude fluctuation of the tracking error signal, there is a difference between the focus offset at the land and the focus offset at the groove in the optical disk having a track in which the data reproduction / recording area is a land and a groove. In some cases, the focus offset cannot be evaluated by the land and the groove alone. For this reason, the subject that the dispersion | variation in evaluation of a focus offset becomes large arises with respect to both a land and a groove.
[0018]
Further, even if the data reproduction / recording area is an optical disc having a track composed only of grooves, the tracking error signal includes information other than the groove and the groove. For this reason, it becomes difficult to evaluate the focus offset from the information of only the groove. Therefore, even if the focus offset is evaluated due to the amplitude variation of the tracking error signal, the focus offset is not evaluated from the information of only the groove, and there arises a problem that the dispersion of the focus offset evaluation becomes large.
[0019]
As described above, in the prior art, it is very difficult to evaluate the optical pickup device and the optical integrated unit related to the optical disk with higher density and higher numerical aperture with the same accuracy as the conventional optical disk.
[0020]
SUMMARY OF THE INVENTION An object of the present invention is to provide a focus offset evaluation method and a focus offset evaluation apparatus that can evaluate the focus offset of an optical pickup apparatus with high accuracy.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, the focus offset evaluation method of the present invention irradiates an optical recording medium with laser light emitted from a semiconductor laser included in an optical pickup device or an optical integrated unit,
The reflected light of the laser beam from the optical recording medium is diffracted toward the light receiving element by a diffraction grating,
A focus error signal and tangential push-pull signal information are generated from an electrical signal output by the light receiving element that receives the reflected light,
By applying a predetermined focus bias signal to the focus error signal, a predetermined focus bias is set,
Obtain sample information consisting of the focus bias and tangential push-pull signal information generated when the focus bias is set,
The focus offset of the optical pickup device or the optical integrated unit is evaluated based on the relationship between the focus bias obtained from the sample information and the tangential push-pull signal information.
[0022]
In the present invention, a predetermined focus bias signal is applied to the focus error signal to set a predetermined focus bias in the optical pickup device or the optical integrated unit, and the tangential push-pull signal generated when the focus bias is set. Sample information comprising information and the focus vice is obtained. Based on the relationship between the focus bias based on the sample information and the tangential push-pull signal information, the focus offset of the optical pickup device or the optical integrated unit is evaluated. As described above, the present invention sets the focus bias to the optical pickup device or the optical integrated unit by applying the focus bias signal to the focus error signal, and uses the characteristics of the tangential push-pull signal information corresponding to the focus bias. Thus, the focus offset of the optical pickup device or the optical integrated unit can be evaluated.
[0023]
Further, the focus offset evaluation method of one embodiment obtains a plurality of sample information by applying a plurality of different focus bias signals to the focus error signal,
Based on the relationship between the focus bias obtained from the plurality of pieces of sample information and the tangential push-pull signal information, the focus offset of the optical pickup device or the optical integrated unit is evaluated.
[0024]
In the focus offset evaluation method of this embodiment, the relationship between the focus bias and the tangential push-pull signal information can be obtained more accurately by obtaining the plurality of pieces of sample information. Therefore, the focus offset of the optical pickup device or the optical integrated unit can be evaluated with higher accuracy.
[0025]
Also, the focus offset evaluation method according to an embodiment uses the extreme value of the tangential push-pull signal information based on the relationship between the focus bias obtained from the plurality of pieces of sample information and the tangential push-pull signal information. The focus bias corresponding to this extreme value is determined as the focus offset of the optical pickup device or the optical integrated unit.
[0026]
The focus offset evaluation method of this embodiment obtains the extreme value of the tangential push-pull signal information and specifies that the focus bias corresponding to this extreme value is the focus offset of the optical pickup device. Thereby, the focus offset of the optical pickup device or the optical integrated unit can be accurately evaluated.
[0027]
In one embodiment, the tangential push-pull signal information is at least one of the amplitude of the tangential push-pull signal and the jitter of the clock signal generated from the tangential push-pull signal.
[0028]
In the focus offset evaluation method of this embodiment, the amplitude of the tangential push-pull signal as the tangential push-pull signal information or the jitter of the clock signal generated from the tangential push-pull signal, or both, The focus offset of the optical pickup device can be accurately evaluated.
[0029]
Further, in the focus offset evaluation method according to one embodiment, the tangential push-pull signal information includes a positive component amplitude and a negative component amplitude of the tangential push-pull signal, and the positive component amplitude has a maximum value. Find the bias and the focus bias where the amplitude of the negative component is a maximum value,
An average value of the focus bias at which the positive component amplitude becomes a maximum value and the focus bias at which the negative component amplitude becomes a maximum value is specified as the focus offset of the optical pickup device.
[0030]
In the focus offset evaluation method of this embodiment, the positive and negative component amplitudes of the tangential push-pull signal are adopted as the tangential push-pull signal information, and the positive component amplitude of the tangential push-pull signal is maximized. This is effective when the focus bias differs from the focus bias that maximizes the amplitude of the negative component of the tangential push-pull signal, and the accuracy can be improved when specifying the focus offset of the optical pickup device or the optical integrated unit.
[0031]
In the focus offset evaluation method according to an embodiment, the tangential push-pull signal information is an absolute value of a difference between a positive component amplitude and a negative component amplitude of the tangential push-pull signal. The focus bias having the extreme value is specified as the focus offset of the optical pickup device or the optical integrated unit.
[0032]
In the focus offset evaluation method of this embodiment, the absolute value of the difference between the positive component amplitude and the negative component amplitude of the tangential push-pull signal is adopted as the tangential push-pull signal information, and the tangential push-pull signal Effective when the focus bias that maximizes the amplitude of the positive component is different from the focus bias that maximizes the amplitude of the negative component of the tangential push-pull signal.When specifying the focus offset of the optical pickup device or the optical integrated unit, The accuracy can be improved.
[0033]
In the focus offset evaluation method according to an embodiment, the tangential push-pull signal information is jitter of a clock signal generated from the tangential push-pull signal, and a focus bias at which the jitter becomes a minimum value is obtained. The bias is specified as the focus offset of the optical pickup device or the optical integrated unit.
[0034]
In the focus offset evaluation method of this embodiment, the jitter of the clock signal is adopted as the tangential push-pull signal information, and the focus bias at which the jitter becomes a minimum value is the focus offset of the optical pickup device or the optical integrated unit. Identify.
[0035]
The focus offset evaluation method according to an embodiment obtains three or more pieces of sample information by applying three or more different focus bias signals to the focus error signal, and obtains the information from the three or more pieces of sample information. The focus offset of the optical pickup device or the optical integrated unit is evaluated based on the relationship between the focus bias and the tangential push-pull signal information.
[0036]
In the focus offset evaluation method of this embodiment, the focus offset of the optical pickup device or the optical integrated unit is evaluated based on the relationship between the focus bias obtained from three or more pieces of sample information and the tangential push-pull signal information. Thereby, reliable evaluation becomes possible.
[0037]
In the focus offset evaluation method according to an embodiment, two or more different change amounts are set as the change amount for changing the focus bias.
[0038]
In the focus offset evaluation method of this embodiment, two or more different amounts of change are set as the amount of change for changing the focus bias. Therefore, the closer the tangential push-pull signal information is to the extreme value, the less the amount of change in the focus bias. The extremum of the tangential push-pull signal information can be easily obtained, and as a result, the evaluation of the focus offset of the optical pickup device and the optical integrated unit is facilitated.
[0039]
Further, the focus offset evaluation method of one embodiment sets a threshold value of tangential push-pull signal information,
The amount of change in the focus bias is set based on the result of comparing the tangential push-pull signal information in the sample information with the threshold value.
[0040]
In the focus offset evaluation method of this embodiment, the setting of the change amount of the focus bias is performed based on the result of comparing the tangential push-pull signal information with the threshold value. The amount of change in focus bias can be set. As a result, the closer the tangential push-pull signal information is to the extreme value, the smaller the amount of change in the focus bias can be reduced, making it easier to obtain the extreme value of the tangential push-pull signal information. It is easy to evaluate the focus offset of the unit.
[0041]
In the focus offset evaluation method according to an embodiment, two or more different threshold values are set as the threshold value.
[0042]
In the focus offset evaluation method of this embodiment, by setting two or more different threshold values as the threshold value, it is possible to finely set the amount of change in focus bias according to the tangential push-pull signal information. As a result, the closer the tangential push-pull signal information is to the extreme value, the smaller the amount of change in the focus bias can be reduced, making it easier to obtain the extreme value of the tangential push-pull signal information. It is easy to evaluate the focus offset of the unit.
[0043]
Further, the focus offset evaluation method according to an embodiment includes the optical pickup device and the optical integration based on the sample information obtained by changing the focus bias in either the positive or negative direction from the initial value of the focus bias. Evaluate the unit's focus offset.
[0044]
In the focus offset evaluation method of this embodiment, the method of changing the focus bias can be simplified.
[0045]
Further, the focus offset evaluation method according to an embodiment includes sample information obtained by changing the focus bias in either the positive or negative direction from the initial value of the focus bias, and the positive or negative value from the initial value. From the sample information obtained by changing the focus bias in the other direction, the focus offset of the optical pickup device and the optical integrated unit is evaluated.
[0046]
In the focus offset evaluation method of this embodiment, since the focus bias is changed in both positive and negative directions from the initial value, sample information in a range covering both positive and negative sides of the initial value can be obtained. Therefore, it becomes easy to obtain sample information suitable for evaluating the focus offset.
[0047]
Also, in the focus offset evaluation method of one embodiment, the focus bias corresponding to the target value of the tangential push-pull signal information among the plurality of sample information is the focus offset of the optical pickup device or the optical integrated unit. Is identified.
[0048]
In the focus offset evaluation method of this embodiment, the target value of the tangential push-pull signal information is selected from among a plurality of focus biases included in a plurality of sample information by setting the target value to an extreme value or a predetermined range sandwiching the extreme value. The focus bias corresponding to the target value of the tangential push-pull signal is specified as the focus offset of the optical pickup device or the optical integrated unit. Accordingly, it is easy to obtain a focus bias that specifies the focus offset.
[0049]
The focus offset evaluation method according to an embodiment calculates a focus bias at which the tangential push-pull signal information is an extreme value based on the plurality of pieces of sample information by numerical calculation processing, and calculates the calculated focus bias. The focus offset of the optical pickup device or the optical integrated unit is specified.
[0050]
In the focus offset evaluation method of this embodiment, a focus bias at which the tangential push-pull signal information becomes an extreme value is calculated by numerical calculation processing based on the plurality of pieces of sample information. Therefore, according to this focus bias, the focus offset can be specified accurately.
[0051]
Further, the focus offset evaluation method according to an embodiment is based on the relationship between the focus bias obtained from the plurality of sample information and the tangential push-pull signal information.
Sample information whose rate of change in the tangential push-pull signal information with respect to the change in the focus bias is equal to or less than a predetermined value is specified, and the focus bias included in the sample information is a focus offset of the optical pickup device or the optical integrated unit Is identified.
[0052]
In the focus offset evaluation method of this embodiment, sample information that falls below a predetermined value is specified using the fact that the rate of change of tangential push-pull signal information with respect to a change in focus bias is the minimum, and this sample information Is specified as the focus offset of the optical pickup device or the optical integrated unit. Thereby, the focus offset can be specified accurately.
[0053]
The focus offset evaluation method according to an embodiment estimates an extreme value of the tangential push-pull signal information and a focus bias corresponding to the extreme value based on the plurality of pieces of sample information, and further includes the tangential Set a predetermined value for push-pull signal information,
Among sample information having a focus bias larger than the focus bias corresponding to the set extreme value, sample information having tangential push-pull signal information closest to the predetermined value and a focus bias corresponding to the extreme value Selecting sample information having tangential push-pull signal information closest to the predetermined value among sample information having a small focus bias;
The average value of the focus bias of the selected two pieces of sample information is calculated, and the average value is specified as the focus offset of the optical pickup device or the optical integrated unit.
[0054]
In the focus offset evaluation method of this embodiment, the average value of the focus bias of the two sample information can be a good approximation to the focus bias corresponding to the actual extreme value of the tangential push-pull signal information. The focus offset can be identified efficiently.
[0055]
The focus offset evaluation method according to an embodiment evaluates the focus offset of the optical pickup device or the optical integrated unit based on the sample information obtained by irradiating the laser beam to one track of the optical storage medium. To do.
[0056]
In the focus offset evaluation method of this embodiment, the focus offset of the optical pickup device or the optical integrated unit is evaluated based on the sample information obtained by irradiating the laser beam to one track of the optical storage medium. The focus offset can be evaluated efficiently.
[0057]
The focus offset evaluation method according to an embodiment evaluates the focus offset of an optical pickup device or an optical integrated unit based on sample information obtained by irradiating two tracks of the optical storage medium with laser light, respectively. To do.
[0058]
In the focus offset evaluation method of this embodiment, the focus offset of the optical pickup device or the optical integrated unit is evaluated based on sample information obtained by irradiating the two tracks of the optical storage medium with laser light. Therefore, the focus offset can be evaluated with high accuracy.
[0059]
In addition, the focus offset evaluation apparatus according to an embodiment is based on an electrical signal output from a light receiving element that receives reflected light from an optical recording medium irradiated with a laser beam from a semiconductor laser included in an optical pickup apparatus or an optical integrated unit. A focus error signal generating means for generating a focus error signal that is a control signal for focus servo control for the optical pickup device;
Tracking error signal generating means for generating a tracking error signal to be a control signal for tracking servo control;
A focus bias means for setting a focus bias by applying a focus bias signal to the focus error signal;
Tangential push-pull signal information generating means for generating tangential push-pull signal information obtained from the electrical signal output by the light receiving element;
Tangential push-pull signal detection means for detecting tangential push-pull signal information generated by the tangential push-pull signal generation means;
A focus offset that specifies the focus offset of the optical pickup device or the optical integrated unit based on the relationship between the focus bias set by the focus bias means and the tangential push-pull signal information obtained when the focus bias is set. Specific means.
[0060]
In the focus offset evaluation apparatus of this embodiment, the focus error signal generation means outputs an electrical signal output by a light receiving element that receives reflected light from an optical recording medium irradiated with a laser beam from a semiconductor laser included in an optical pickup device. On the basis of this, a focus error signal that is a control signal for focus servo control for the optical pickup device is generated. The tracking error signal generation unit generates a tracking error signal.
The focus bias unit applies a focus bias signal to the focus error signal to set a focus bias. On the other hand, the tangential push-pull signal information generating means generates tangential push-pull signal information obtained from an electrical signal output from the light receiving element. The focus offset specifying means has a relationship between the focus bias set by the focus bias means and the tangential push-pull signal information obtained by the tangential push-pull signal detection means when the focus bias is set. Based on this, the focus offset of the optical pickup device or the optical integrated unit is specified.
[0061]
As described above, in the focus offset evaluation apparatus of this embodiment, the focus bias is set in the optical pickup device or the optical integrated unit by applying the focus bias signal to the focus error signal, and the tangential push-pull corresponding to the focus bias is set. The focus offset of the optical pickup device and the optical integrated unit can be evaluated using the characteristics of the signal information.
[0062]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on illustrated embodiments.
[0063]
Embodiments of a focus offset evaluation apparatus and a focus offset evaluation method according to the present invention evaluate a focus offset of an optical pickup device included in an optical disc apparatus that performs recording and reproduction on a predetermined optical disc as an optical recording medium. . As an example of the optical disk, an optical disk having a clock area composed of embossed pits and composed of land tracks and groove tracks is employed. In the focus offset evaluation apparatus and the focus offset evaluation method of this embodiment, a change in the amount of reflected light when a light spot follows the tangential direction of a track is detected as a TPP (tangential push-pull) signal. In the present invention, there are various types of optical disks to be applied. In this embodiment, a magneto-optical disk is employed. In the description of this embodiment, as an example, an optical pickup device including an optical integrated unit in which a semiconductor laser, a light receiving element, and a hologram element serving as a diffraction grating are integrated is adopted. A wide variety of other configurations can be employed.
[0064]
First, with reference to FIG. 1, the structure of an optical pickup device as an object for which the embodiment evaluates a focus offset and an optical integrated unit 11 provided in the optical pickup device will be described. The optical pickup device is built in an optical disk device (not shown).
[0065]
The optical integrated unit 11 includes a stem 13, a cap 12 placed on the stem 13 and welded, and a hologram element 3 placed on the upper surface of the cap 12 so as to cover the opening 12 </ b> A of the cap 12. In the cap 12, the semiconductor laser 1 is attached to a base portion 41 placed on the stem 13. A light receiving element 2 for servo signal detection is placed on the upper surface of the base 41. The hologram element 3 has a diffraction grating 14 formed on the upper surface thereof, and the diffraction grating 14 is disposed on an optical axis J extending from the light emitting point of the semiconductor laser 1 via the opening 12A. ing.
[0066]
Further, in the optical pickup device, a collimator lens 4, a polarization beam splitter 7, and an objective lens 5 are disposed on the optical axis J extending from the light emitting point of the semiconductor laser 1 of the optical integrated unit 11.
[0067]
As shown in FIG. 1, the laser light emitted from the semiconductor laser 1 passes through the hologram element 3 having the diffraction grating 14, the collimating lens 4, the polarization beam splitter 7, and the objective lens 5 and is irradiated onto the magneto-optical disk 6. The The reflected light reflected by the magneto-optical disk 6 is diffracted by the diffraction grating 14 and enters the light receiving element 2 for servo signal detection.
[0068]
On the other hand, the reflected light signal reflected by the polarization beam splitter 7 passes through the Wollaston prism 8, is then condensed by the condenser lens 9, and enters the light receiving element 10 for detecting the magneto-optical signal, and magneto-optically. A signal is detected.
[0069]
The optical integrated unit 11, the collimating lens 4, the polarizing beam splitter 7, the objective lens 5, the Wollaston prism 8, the condenser lens 9, and the light receiving element 10 constitute an optical pickup device.
[0070]
The arrangement of the semiconductor laser 1, the servo signal detecting light receiving element 2, and the hologram element 3 in the optical integrated unit 11 can be variously set in addition to the arrangement shown in FIG. Further, in FIG. 1, for understanding of the structure, the cap 12 shows a cross section and shows the structure inside the cap 12. The servo signal detecting light receiving element 2 is disposed at a position separated from the semiconductor laser 1 by a predetermined dimension in the radial direction of the track of the magneto-optical disk 6. Further, the hologram element 3 is arranged so that the approximate center of the diffraction grating 14 is positioned on the optical axis J extending from the light emitting point of the semiconductor laser 1.
[0071]
Note that the optical integrated unit 11 has a focus offset caused by a dimensional error, a characteristic error, and an assembly adjustment error of each part that occur in actual production.
[0072]
Therefore, when the optical components other than the optical integrated unit 11 in FIG. 1 are configured to be fixed under ideal conditions or conditions very close thereto, the focus offset caused only by the optical integrated unit 11 that will actually occur is evaluated ( Measurement).
[0073]
Even if there is no focus offset due to the optical integrated unit 11, in the optical pickup device equipped with the optical integrated unit 11, dimensional errors, characteristic errors, Due to the assembly adjustment error, there is a considerable focus offset due to the optical pickup device. In this case, it is possible to evaluate the focus offset of the optical integrated pickup itself that will actually occur.
[0074]
Therefore, as described above, the present invention can evaluate the focus offset of the entire optical pickup device including the optical integrated unit 11, and the optical pickup device originated only from the optical integrated unit 11 constituting the optical pickup device. The focus offset can be evaluated.
[0075]
(Optical integrated unit)
FIG. 2 shows a state in which the diffraction grating 14 and the servo signal detection light-receiving element 2 on the hologram element 3 of the optical integrated unit 11 to be evaluated in this embodiment are viewed from above to below.
[0076]
The diffraction grating 14 has a circular or elliptical shape when viewed from above to below. The diffraction grating 14 is divided from the center of the diffraction grating 14 in the track radial direction (X direction) through the center of the diffraction grating 14 through the center of the diffraction grating 14 and into the track tangential direction (Y direction). The dividing line 14b that divides the outer periphery is divided into three regions I, II, and III.
[0077]
Reflected light from the magneto-optical disk 6 is incident on each of the three divided regions I, II, and III of the diffraction grating 14, and the reflected light is received by each light receiving portion of the light receiving element 2 for servo signal detection. A fine groove is formed so as to diffract toward 2a to 2d. The light receiving element 2 receives the reflected light diffracted by the grooves of the diffraction grating 14.
[0078]
In the description of this embodiment, the light receiving element 2 for servo signal detection includes, as an example, four light receiving portions 2a to 2d that form a to d segments. Of the reflected light 15 from the magneto-optical disk 6 that has entered the diffraction grating 14, the diffracted light 15a by the region I is incident on both the light receiving portions 2a and 2b. The diffracted light 15b from the region II is incident on the light receiving portion 2c. The diffracted light 15c from the region III is incident on the light receiving portion 2d.
[0079]
In this embodiment, a focus error signal detection method using the Foucault method is employed as the focus servo control. The light receiving element 2 for detecting the servo signal is used for detecting a focus error signal.
[0080]
The light receiving element 2 receives the light 15a diffracted in the region I of the diffraction grating 14 by the light receiving portions 2a and 2b. A difference (B−A) between the output signal A obtained from the light receiving unit 2a and the output signal B obtained from the light receiving unit 2b is defined as a focus error signal FES. Focus servo is applied at the zero cross point of the focus error signal FES. That is, this zero cross point is set as the target value of the focus servo.
[0081]
The diffracted light 15a from the region I of the diffraction grating 14 is incident on the center position between the light receiving part 2a and the light receiving part 2b of the light receiving element 2 for servo signal detection, and forms a point image on the light receiving element 2. Under ideal conditions, the focus offset is zero. When deviating from this ideal condition, an offset occurs in the focus error signal and defocusing occurs.
[0082]
The tracking servo control employs a method of detecting a tracking error signal TES using a push-pull method. The tracking error signal TES as a push-pull signal is a difference between output signals C and D (C−D) obtained from the light receiving portions 2c and 2d on which the lights 15b and 15c diffracted in the regions II and III of the diffraction grating 14 are incident. ). Tracking servo is applied at the zero cross point of this tracking error signal. That is, this zero cross point is set as a tracking servo target value.
[0083]
That is, when the position of the laser beam focused on the disk track is shifted from the center line of the disk track, a tracking offset occurs. When tracking servo is applied in a state where this tracking offset is generated, the laser beam follows the track at a position shifted from the center line of the disk track. In order to avoid this, it is necessary to remove the tracking offset before or immediately after applying the tracking servo.
[0084]
In this embodiment, as an example of the magneto-optical disk 6, as shown in FIG. 3A, a magneto-optical disk 6 including lands 18 and grooves 19 is used. 16 and a clock area 17 periodically arranged independently of the data recording area 16. The clock area 17 is a concave pit P1 at a position adjacent to the land 18 in the data recording area 16, and is a convex pit P2 at a position adjacent to the groove 19 in the data area 16.
[0085]
Further, the TPP signal is generated from the electric signals A, B, C, and D detected from the servo signal detecting light receiving element 2 divided into four in a state where the focus servo and the tracking servo are applied. As shown in FIG. 3A, when the light spot 20 on the surface of the magneto-optical disk 6 moves in the tangential direction of the track, the amount of reflected light changes. This change in the amount of reflected light is detected as a TPP signal defined by the above equation (1).
[0086]
TPP = (A + B)-(C + D) (1)
As shown in FIG. 3B, the TPP signal has an S-shaped curve when the vertical axis is the signal amplitude and the horizontal axis is the position in the track tangent direction of the light spot 20. In this embodiment, as shown in FIG. 3C, a clock signal 23 is generated at the zero-cross point 22 of the TPP signal 21.
[0087]
As shown in FIG. 3A, when the light spot 20 is being tracked by the land 18, the light spot from the data recording area 16 is located when the light spot 20 is at the boundary between the data area 16 and the clock area 17. The reflected light amount of 20 is the maximum. Further, when the light spot 20 is at the center of the clock region 17, the amount of reflected light from the light spot 20 is minimized. Therefore, the TPP signal has an S-curve as shown in FIG.
[0088]
Although not shown, when the light spot 20 is tracked by the groove 19, the reflection of the light spot 20 from the data recording area 16 when the light spot 20 is at the boundary between the data recording area 16 and the clock area 17. The amount of light is minimized. On the other hand, when the light spot 20 is in the center of the clock region 17, the reflected light amount of the light spot 20 is maximized. Therefore, in this case, the polarity of the S-shaped curve of the TPP signal is opposite to that of the S-shaped curve of the TPP signal shown in FIG. Also, as in this case, when the light spot 20 is tracked to the groove 19, the clock signal 23 is generated at the zero cross point 22 of the S-shaped curve of the TPP signal 21.
[0089]
Although details will be described later, the value of the clock signal 23 varies in the time axis direction depending on various conditions such as a mark length error in the clock region 17, defocusing, disc tilt, and the like. In FIG. 3D, an envelope 24 shows the rise time distribution of the clock signal 23 with the horizontal axis as the time axis and the vertical axis as the frequency. The width 25 of the envelope 24 is the jitter of the clock signal 23.
[0090]
Next, the relationship between the defocus state (or the state in which the focus bias is set from the just focus state) generated in the optical pickup apparatus including the optical integrated unit 11 and the TPP signal will be described.
[0091]
First, in FIGS. 1 to 3, ideal conditions in the optical pickup device are cases where the following conditions (1) to (6) are satisfied.
[0092]
(1) The light spot focused by the objective lens 5 is condensed at the center of the track on the magneto-optical disk 6 and there is no track offset.
[0093]
(2) The center of the diffraction grating 14 passes through the optical axis extending from the light emitting point of the semiconductor laser 1.
[0094]
(3) The optical axis of the reflected light from the magneto-optical disk 6 passes through the center of the diffraction grating 14.
[0095]
(4) The diffraction efficiencies of the regions I to III of the diffraction grating 14 are equal.
[0096]
(5) There is no variation in efficiency in converting the optical signals of the light receiving portions 2a to 2d of the light receiving element 2 into electric signals.
[0097]
(6) The diffracted light from the region I of the diffraction grating 14 is collected as a point at the central portion between the light receiving portions 2a and 2b of the light receiving element 2.
[0098]
Under this ideal condition, the electrical signals output from the light receiving units 2a to 2d are equal, and as a result, the positive component and the negative component of the TPP signal are equal and maximum. Furthermore, even if the focus bias is not set, the just focus state is obtained, and as a result, the jitter of the clock signal is optimized. Details of this will be described later.
[0099]
However, there is almost no ideal condition that satisfies all of the above conditions in production. For example, the fact that the center of the diffraction grating 14 and the rotation center of the diffraction grating 14 completely coincide with each other physically. difficult. As a result, the light spot condensed on the light receiving element 2 is not a point image but a slightly blurred image. Therefore, the position of the hologram element 14 is adjusted in the assembly adjustment stage so that the light spot is not defocused with respect to the light receiving element 2.
[0100]
However, in reality, since there are dimensional tolerances, assembly adjustment errors, and the like of each component, it is difficult to completely remove the focus deviation with respect to the light receiving element 2, and the focus deviation with respect to the light receiving element 2 often remains slightly. Therefore, the balance of the electrical signals detected from the light receiving portions 2a to 2d of the light receiving element 2 is lost, and the amplitude of the TPP signal and the jitter of the clock signal deviate from the best values (details will be described later).
[0101]
The present invention accurately evaluates the focus offset in the optical pickup device and the optical integrated unit by using the TPP signal information such as the amplitude of the TPP signal and the jitter of the clock signal, and determines whether the product is a good product or a defective product. An evaluation method and an evaluation apparatus for determination are provided.
[0102]
Next, in FIG. 4, the light spot on the magneto-optical disk 6 follows the center of the land 18 and the components (for example, the diffraction grating 14 and the light receiving element 2) of the optical integrated unit 11 are arranged under ideal conditions. In this case, the reflected light 15 is shown when the above conditions are satisfied (that is, when the above conditions (1) to (5) are satisfied). Further, in FIG. 6, due to the tolerance of the components (diffraction grating 14, light receiving element 2) of the optical integrated unit 11, the light spot condensed on the light receiving element 2 is slightly blurred even in the minimum aperture state. The reflected light 15 in the state is shown.
[0103]
First, a state 1 shown in FIG. 4A is a just focus state. In this state 1, the reflected light 15 is condensed as a point image at an intermediate position between the light receiving portions 2a and 2b. As a result, the output signal A and the output signal B of the light receiving element 2 are equal, and the sum signal (A + B + C + D) of the output signals A to D is maximized. As a result, the TPP signal is reproduced most stably. The waveform of the TPP signal 21 in this state 1 is shown in FIG. As will be described in detail later, as a result, the clock signal generated by the TPP signal is most stable and the jitter of the clock signal is minimized.
[0104]
Next, state 2 shown in FIG. 4B is a state in which the objective lens 5 approaches the magneto-optical disk 6 from the state 1 and is defocused. In this state 2, the reflected light 15 forms a point image below the surface of the light receiving element 2. Therefore, the reflected light 15 becomes a light spot 15 a having a blurred shape while maintaining the shape of the diffraction grating 15 on the light receiving element 2. The waveform of the TPP signal 21 in this state 2 is shown in FIG.
[0105]
Next, State 3 shown in FIG. 4C is a state in which the objective lens 5 is defocused away from the magneto-optical disk 6 from State 1. In this state 3, the reflected light 15 forms a point image before (above) the light receiving element 2. Therefore, the reflected light 15 becomes a light spot 15 a having a blurred shape in a state where the shape of the diffraction grating 15 is reversed on the light receiving element 2. The waveform of the TPP signal 21 in this state 3 is shown in FIG.
[0106]
As shown in FIGS. 5B and 5C, in the state 2 and the state 3, since defocusing is performed, the amplitude of the TPP signal 21 is the TPP signal 21 in the state 1 shown in FIG. Becomes smaller than the amplitude of. However, in the signals A to D output from the light receiving units 2a to 2d, A + B = C + D is always established. Therefore, the amplitude ratio between the positive component T + and the negative component T− of the amplitude of the TPP signal 21 is not broken even in the above state 2 and state 3.
[0107]
Next, in the state 1 shown in FIG. 6A, the spots 15a, 15b, and 15c of the reflected light 15 are blurred on the light receiving element 2 even if the irradiation light is in a just-focus state on the magneto-optical disk 6. For this reason, the balance of the signals A and B output from the light receiving units 2a and 2b is lost. This unbalance is eliminated by rotating and adjusting the diffraction grating 14 in the assembly adjustment stage of the optical integrated unit 11 in advance. The waveform of the TPP signal 21 in this state 1 is shown in FIG.
[0108]
Next, state 2 shown in FIG. 6B is a state in which the objective lens 5 approaches the magneto-optical disk 6 from state 1 and is defocused. In this state 2, the reflected light 15 forms a point image below the surface of the light receiving element 2. For this reason, the reflected light 15 becomes light spots 15a to 15c having a blurred shape while maintaining the shape of the diffraction grating 14 on the light receiving portions 2a to 2d. If the reflected light 15 diffracted by the diffraction grating 14 is focused 2 below the surface of the light receiving element 2, as shown in FIG. 6B, the light spot 15a protrudes from the light receiving portions 2a and 2b. Even if not, the light spots 15b and 15c may protrude from the light receiving portions 2c and 2d. In this case, the signals A to D output from the light receiving units 2a to 2d have a relationship of A + B> C + D, and the amplitude of the TPP signal 21 is expressed by the positive component T + as shown in FIG. Becomes larger than the negative component T−.
[0109]
On the other hand, State 3 shown in FIG. 6C is a state where the objective lens 5 is defocused away from the magneto-optical disk 6 from State 1, contrary to State 2. In this state 3, the reflected light 15 forms a point image in front of the light receiving element 2. For this reason, the reflected light 15 becomes spots 15 a to 15 c that are blurred on the light receiving element 2 in a state where the shape of the diffraction grating 14 is reversed. In this case, as shown in FIG. 6C, even if the light spots 15b and 15c do not protrude from the light receiving portions 2c and 2d, the light spot 15a may protrude from the light receiving portions 2a and 2b.
[0110]
As a result, the signals A to D output from the light receiving units 2a to 2d have a relationship of (A + B) <(C + D), and the amplitude of the TPP signal 21 obtained from the equation (1) is as shown in FIG. In addition, the positive component T + is smaller than the negative component T−. In addition, since the defocusing is performed in the states 2 and 3 shown in FIGS. 6B and 6C, the amplitude of the TPP signal in the states 2 and 3 shown in FIGS. 7B and 7C is as shown in FIG. It is smaller than the amplitude of the TPP signal in the state 1 shown in FIG.
[0111]
As can be seen from the description with reference to FIGS. 4 and 5 and FIGS. 6 and 7 described above, the arrangement of the components (for example, the diffraction grating 14 and the light receiving element 2) of the optical integrated unit 11 is ideal. In any of the entered conditions (FIG. 6), the amplitude of the TPP signal 21 is maximized when the irradiation light is in a just-focused state on the magneto-optical disk 6.
[0112]
Then, when the focus bias is set and defocused by applying the focus bias signal to the focus error signal from the state where the amplitude of the TPP signal 21 is the maximum (just focus state), the amplitude of the TPP signal 21 becomes small. Become. Further, when a tolerance condition for the arrangement of components (for example, the diffraction grating 14 and the light receiving element 2) is added to this defocused state, the behaviors of the positive component and the negative component of the amplitude of the TPP signal are also different. And the balance is broken.
[0113]
Further, when defocusing is performed from the just-focus state, the clock signal generated from the TPP signal becomes unstable, and as a result, the jitter of the clock signal increases.
[0114]
Therefore, for example, with a focus bias device 36 as shown in FIG. 9, the focus bias signal is applied to the focus error signal FES, so that the focus bias is set and defocused. As a result, as shown in FIGS. 8A, 8B, 8C, and 8D, the amplitude of the TPP signal, the positive component and the negative component of the amplitude of the TPP signal (or the jitter of the clock signal) are changed. ) Is monitored. Then, a search is made for a focus bias that optimizes the amplitude of the TPP signal and the positive component and negative component (or jitter of the clock signal) of the TPP signal.
[0115]
From the focus bias detected as a result of this search, the focus offset of the optical integrated unit 11 and the optical pickup device equipped with the optical integrated unit can be specified. The present invention utilizes this phenomenon.
[0116]
(Focus offset evaluation device)
Next, a focus offset evaluation apparatus that is an embodiment of the present invention and that evaluates the focus offset of an optical pickup apparatus built in an optical disc apparatus and having an optical integrated unit will be described. The basic configuration of this focus offset evaluation apparatus will be described with reference to FIGS.
[0117]
First, the configuration of the focus offset evaluation apparatus will be described with reference to FIG. The focus offset evaluation apparatus includes a servo signal generation circuit 32 as a focus error signal generation unit and a TPP signal information generation unit, a focus bias device 36 as a focus bias unit, and a search circuit 34 as a focus offset specifying unit. .
[0118]
The magneto-optical disk 26 shown in FIG. 9 is controlled by a spindle motor 27 by a predetermined type of rotational drive such as CLV (constant linear velocity) or CAV (constant angular velocity).
[0119]
A reflected light signal from the magneto-optical disk 26 is detected by an optical pickup device 29 having an optical integrated unit 30. As described with reference to FIG. 2, the signals A to D output from the light receiving portions 2a to 2d of the light receiving element 2 are constituted by the differential amplifiers 101, 102, and 103 shown in FIG. The servo signal generation circuit 32 is supplied. The servo signal generation circuit 32 generates servo signals such as a focus error signal FES and a tracking error signal TES, and a TPP signal, as shown in FIG. 9, based on the signals A to D.
[0120]
The generated focus error signal FES is supplied to the focus servo circuit 31a of the servo signal processing circuit 31, and the focus servo circuit 31a performs focus servo control. That is, the focus servo circuit 31a controls the focus of the optical pickup device 29.
[0121]
The tracking error signal TES is supplied to the tracking servo circuit 31b of the servo signal processing circuit 31, and the tracking servo circuit 31b performs tracking servo control. That is, the tracking servo circuit 31b controls tracking of the optical pickup device 29.
[0122]
The TPP signal generated by the servo signal generation circuit 32 is supplied to a PLL (Phase Locked Loop) circuit 33. The PLL circuit 33 generates a clock signal and simultaneously generates a synchronous clock signal. (Details will be described later).
[0123]
The TPP signal is input to a TPP signal amplitude information detection circuit 34a of a search circuit 34 as a focus offset specifying means, and the detection circuit 34a detects amplitude information of the TPP signal. The detection circuit 34a inputs the amplitude information of the TPP signal to the control circuit 34b. The control circuit 34b controls the focus bias device 36 based on the amplitude information of the TPP signal. With this control, the focus bias device 36 applies a focus bias voltage to the focus error signal FES output from the servo signal generation circuit 32.
[0124]
On the other hand, in the search circuit 34, the sample information storage circuit 34c associates the amplitude information of the TPP signal from the control circuit 34b with the focus bias set by the focus bias device 36 and the track to be measured. And store it as sample information.
[0125]
The search circuit 34 derives an optimum focus bias at which the amplitude information of the TPP signal is optimum (for example, extreme value) based on the sample information stored in the storage circuit 34c. The focus offset of the optical pickup device 29 having the integrated unit 30 is specified.
[0126]
The search circuit 34, servo signal processing circuit 31, focus bias device 36, servo signal generation circuit 32, PLL circuit 33, spindle motor drive circuit 28, and spindle motor 27 constitute a focus offset evaluation device. In FIG. 9, reference numeral 35 denotes a decoder / encoder circuit that functions as a decoder and an encoder.
[0127]
Next, FIG. 10 shows a modification of the focus offset evaluation apparatus shown in FIG. This modification differs from the embodiment of FIG. 9 in that the search circuit 34 of FIG. 9 includes a jitter detection circuit 37.
[0128]
In this modification, a clock signal and a synchronous clock signal are supplied from the PLL circuit 33 to the jitter detection circuit 37, and the jitter of the clock signal can be detected by the jitter detection circuit 37. The search circuit 34 of this modification derives a focus bias that minimizes the jitter detected by the jitter detection circuit 37.
[0129]
More specifically, the clock signal is a signal generated by the TPP signal supplied to the PLL circuit 33 at the zero cross point of the TPP signal by an edge detection unit (not shown) included in the PLL circuit 33. In the PLL circuit 33, the TPP signal is fed back through a frequency dividing circuit (not shown) included in the PLL circuit 33, and further, the phase adjustment circuit (not shown) adjusts the phase of the clock signal. By doing so, a synchronous clock signal is generated. The synchronous clock signal and the clock signal are supplied to the jitter detection circuit 37, and the jitter detection circuit 37 detects the jitter of the clock signal with respect to the synchronous clock signal.
[0130]
In this modification, in addition to the TPP signal amplitude information shown in FIG. 9, the jitter of the clock signal and the focus bias are stored in the storage circuit 34c as sample information in association with each other. The search circuit 34 obtains an optimum focus bias that minimizes the jitter based on the sample information. Then, this focus bias is specified as the focus offset of the optical pickup device 29.
[0131]
(First embodiment of focus offset evaluation method)
Next, a focus offset evaluation method using the focus offset evaluation apparatus will be described.
[0132]
A first embodiment of the focus offset evaluation method of the present invention will be described with reference to the flowchart shown in FIG. In the first embodiment, first, the focus bias device 36 does not apply the focus bias signal to the focus error signal FES, and the direction of an arbitrary polarity from the initial state where the focus bias is not set (step S1). A relatively large focus bias signal for generating a relatively large focus bias is applied to the focus error signal FES (step S5). Thereby, the focus servo circuit 31a controls the focus of the optical pickup device 29 based on the focus error signal to which the focus bias signal is applied.
[0133]
Next, from a state in which a relatively large focus bias signal is applied to the focus error signal FES, a focus bias signal for generating a relatively small focus bias is applied to the focus error signal in a stepwise manner in a direction opposite to the polarity direction. Thus, the focus bias is set in steps (steps S7 to S9).
[0134]
Further, TPP signal information (for example, the amplitude of the TPP signal and the jitter of the clock signal) is detected at each focus bias. Then, the focus bias and the TPP signal information corresponding to the focus bias are stored as sample information in the storage circuit 34c (step S6). Then, a focus bias corresponding to the best TPP signal information is detected from the collected sample information (step S10). The best TPP signal information is, for example, TPP information that maximizes the amplitude of the TPP signal or TPP signal information that minimizes the jitter. Then, the focus bias corresponding to the detected best TPP signal information is specified as the focus offset of the optical pickup device 29 and the optical integrated unit 30.
[0135]
FIG. 12A shows the relationship between the focus bias and the amplitude of the TPP signal corresponding to steps S5 to S9 in the flowchart shown in FIG. 11, and FIG. 12B shows the steps S5 to S9. The relationship between the focus bias corresponding to 1 and the jitter of the clock signal is shown. In FIG. 12, the focus bias Fn indicates the nth focus bias. In the initial state where n = 0, F ₀ = 0.
[0136]
More specifically, first, the initial state F in which the focus bias is not set in step S1. ₀ After = 0, the focus servo is turned on in step S2, and the tracking servo is turned on in step S3. Next, in step S4, the tracking offset is removed. As a result, the light spot follows the center of the track, and the TPP signal information is detected. Subsequently, in step S5, the focus bias is set to the initial state F. ₀ To width F _A A predetermined value F shifted in a certain polarity direction ₁ Set to. This focus bias F ₁ If it is too small compared with the focus offset of the optical pickup device 29, the extreme value of the TPP signal information cannot be detected, and the accuracy for obtaining the optimum focus bias is deteriorated. Therefore, as shown in FIG. 12, the first focus bias F ₁ The focus bias is F ₁ To F ₀ It is desirable that the value be sufficiently large so that it can be inferred that the amplitude of the TPP signal or the extreme value of the jitter of the clock signal is within the range that is changed stepwise in the direction of = 0.
[0137]
Subsequently, in step S6, the amplitude Tn of the TPP signal when the focus bias is Fn or the jitter Jn of the clock signal is measured and stored as sample information (Fn, Tn) or (Fn, Jn). .
[0138]
Next, in step S7, n = n + 1 is set, and in step S8, it is determined whether or not it is the k-th sample information. If not, in step S9, the focus bias Fn is changed to the previous bias. F _n-1 And a predetermined addition amount α. As a result, the focus bias is changed to F in FIG. ₁ To F ₀ Change the direction. And it returns to step S6 again.
[0139]
That is, the measurement of the sample information is repeated until the focus bias becomes (F1 + kα), and k pieces of sample information are stored in the sample information storage circuit 34c. After that, although details will be described later, in step S10, a focus bias at which the TPP signal information becomes an extreme value is obtained from the stored sample information. The obtained focus bias is set as the focus offset of the optical pickup device 29.
[0140]
(Second Embodiment of Focus Offset Evaluation Method)
Next, a second embodiment of the focus offset evaluation method of the present invention will be described with reference to the flowchart of FIG.
[0141]
In the second embodiment, first, as the first stage (steps S12 to S19), the focus bias signal is applied from the initial state where the focus bias signal is not applied to the focus error signal and the focus bias is not set. As a result, the focus bias is increased stepwise in a predetermined increment in the predetermined polarity direction and applied to the focus error signal. As a result, the focus bias is increased stepwise. Then, the TPP signal information (the amplitude of the TPP signal, the jitter of the clock signal) is detected with the focus bias set in each step. The focus bias and the corresponding TPP signal information are stored as sample information in the sample information storage circuit 34c.
[0142]
Next, as the second stage (steps S20 to S24), the initial focus bias of the first stage is returned to the initial state again, and the focus bias is increased in a stepwise manner with a predetermined increment in the direction opposite to the polarity. As described above, the focus bias signal is applied to the focus error signal. Thereby, TPP signal information is detected with the focus bias set in each step. The focus bias and the corresponding TPP signal information are stored as sample information in the sample information storage circuit 34c.
[0143]
From the sample information collected by applying the focus bias signal to the focus error signal so that the focus bias is set in a stepwise manner from the initial state to the forward and reverse bipolar directions by the first and second stages, the best is obtained. A focus bias corresponding to the TPP signal information is derived (step S25). The best TPP signal information is, for example, TPP signal information in which the amplitude of the TPP signal is maximum or the jitter is minimum.
[0144]
Then, the focus bias corresponding to the best TPP signal information is specified as the focus offset of the optical pickup device 29 (or the optical integrated unit 30).
[0145]
14A shows the relationship between the focus bias corresponding to steps S16 to S24 in the flowchart of FIG. 13 and the amplitude of the TPP signal, and FIG. 14B shows the focus bias corresponding to steps S16 to S24. And the jitter of the clock signal.
[0146]
The flowchart of FIG. 13 will be described in more detail. Steps S12 to S15 in FIG. 13 are the same steps as steps S1 to S4 in FIG.
[0147]
Subsequently, in step S16, the amplitude Tn of the TPP signal or the jitter Jn of the clock signal when the focus bias is Fn is measured. The Fn and the amplitude Tn or jitter Jn corresponding to the Fn are stored in the sample information storage circuit 34c as sample information (Fn, Tn) or (Fn, Jn). Next, in step S17, n = n−1, and in step S18, it is determined whether n has become a negative number k. If it is determined in this step S18 that n = k, the process proceeds to step S20, and if it is determined that n is not a negative number k, the process proceeds to step S19. In this step S19, the previous focus bias F _n-1 A value obtained by subtracting the predetermined value α from is defined as Fn. The focus bias Fn is a negative value, and the absolute value is the previous F _n-1 Than the predetermined value α.
[0148]
Thus, in steps S17 to S19, the focus bias Fn is subtracted stepwise by the predetermined value α. If it is confirmed in step S18 that k + 1 pieces of sample information have been acquired, the process proceeds to step S20, where n = 0. As a result, Fn = F ₀ = 0 and set to the initial state.
[0149]
Next, it progresses to step S21, sets it as n = n + 1, and progresses to step S22. In this step S22, the focus bias Fn is set to the previous focus bias Fn. _n-1 And a predetermined value α. Thereby, the focus bias Fn = F ₀ From = 0, the focus bias is increased in the positive direction.
[0150]
In step S23, the amplitude Tn of the TPP signal or the jitter Jn of the clock signal at the focus bias Fn is measured, and the set of the focus bias Fn and the amplitude Tn or the jitter Jn is set as sample information (Fn, Tn) or This is stored in the sample information storage circuit 34c as (Fn, Jn).
[0151]
Next, the process proceeds to step S24, where it is determined whether or not n = j (j> 0). If it is determined that n = j, the process proceeds to step S25, where it is determined that n has not reached j. Then, the process returns to step S21. Thus, the focus bias Fn is F ₀ The above measurement is repeated j times until reaching + jα, and j pieces of sample information are stored in the sample information storage circuit 34c.
[0152]
Accordingly, (j + k + 1) pieces of sample information are stored in the sample information storage circuit 34c.
[0153]
In step S25, a focus bias value at which the amplitude of the TPP signal is maximized or a focus bias value at which jitter is minimized is obtained from the stored sample information. The value of the focus bias is specified as the focus offset of the optical pickup device 29 having the optical integrated unit 30.
[0154]
(Third embodiment of focus offset evaluation method)
Next, a third embodiment of the focus offset evaluation method of the present invention will be described with reference to FIGS.
[0155]
In this third embodiment, the manner of changing the focus bias is the same as that of the first embodiment described above, but as the TPP signal information, the amplitude of the positive component and the amplitude of the negative component of the TPP signal are individually measured. This is different from the first embodiment described above.
[0156]
That is, in the third embodiment, the focus bias that maximizes the amplitude of the positive component of the TPP signal and the focus bias that maximizes the amplitude of the negative component of the TPP signal are obtained, and the average of the two focus biases is obtained. Calculate the value. The average value is used as the focus offset of the optical pickup device 29 having the optical integrated unit 30.
[0157]
FIG. 15 shows a flowchart of the evaluation method of the third embodiment, and FIG. 16 shows how to change the focus bias in the evaluation method of the third embodiment and the amplitude of the positive component of the TPP signal with respect to the change of the focus bias. And the change in the amplitude of the negative component.
[0158]
In the third embodiment, steps S27 to S31 in the flowchart of FIG. 15 are the same steps as steps S1 to S5 in the flowchart of FIG. 11 of the first embodiment, and a description thereof will be omitted.
[0159]
In step S32 following step S31, the amplitude T of the positive component of the TPP signal when the focus bias is Fn. _{+ N} And negative component amplitude T _-N Is measured by the detection circuit 34a of the search circuit 34, and the positive component amplitude T of the focus bias Fn, TPP signal. _{+ N} , Negative component amplitude T _-N Sample information (Fn, T _{+ N} , T _-N ).
[0160]
The next steps S33 to S35 are the same as steps S7 to S9 in FIG. 11 of the first embodiment, and k pieces of sample information are acquired.
[0161]
Next, proceeding to step S36, the amplitude T of the positive component of the TPP signal. _{+ N} Focus bias F that maximizes _{+ N} And the amplitude T of the negative component of the TPP signal _-N Focus bias F that maximizes _-N And ask. This focus bias F _{+ N} And focus bias F _-N The details of how to find out will be described later.
[0162]
Next, the process proceeds to step S37, and the focus bias F _{+ N} And focus bias F _-N That is, the average value Fm = (F _{+ N} + F _-N ) / 2 is calculated, and the average value Fm is specified as the focus offset of the optical pickup device 29 on which the optical integrated unit 30 is mounted.
[0163]
(Fourth Embodiment of Focus Offset Evaluation Method)
Next, a fourth embodiment of the focus offset evaluation method of the present invention will be described with reference to FIGS.
[0164]
In the fourth embodiment, as shown in FIG. 18, the method of changing the focus bias is the same as that of the first embodiment described above, and as the TPP signal information, the positive component amplitude and negative component of the TPP signal are used. The point of individually measuring the amplitude is the same as in the third embodiment described above. On the other hand, the fourth embodiment is different from the third embodiment in that the absolute value of the difference between the positive component amplitude and the negative component amplitude of the TPP signal is calculated.
[0165]
In the fourth embodiment, a focus bias is obtained such that the absolute value of the difference between the amplitude of the positive component and the amplitude of the negative component of the TPP signal becomes a predetermined value, and this focus bias is used as the focus offset of the optical pickup device 29. To do. For example, when the waveform amplitude of the positive component and the waveform amplitude of the negative component of the TPP signal are equal, a focus bias is obtained such that the absolute value of the difference between the amplitude of the positive component and the amplitude of the negative component is “0”. The focus bias is used as the focus offset of the optical pickup device 29.
[0166]
When the waveform amplitude of the positive component and the waveform amplitude of the negative component of the TPP signal are close to the same condition, the absolute value of the difference between the amplitude of the positive component and the amplitude of the negative component is narrow near “0”. A focus bias that falls within the range is obtained, and the focus bias is specified as the focus offset of the optical pickup device 29.
[0167]
In the example shown in FIG. 8C, the vertical axis represents the difference between the amplitude of the positive component and the negative component of the TPP signal, the horizontal axis represents the focus bias, and the positive component and the negative component when the focus bias is changed. It shows how the difference in components changes. In the fourth embodiment, the relationship between the absolute value of the difference between the positive component amplitude and the negative component amplitude of the TPP signal and the focus bias as shown in FIG. 18 is used.
[0168]
In the fourth embodiment, steps S39 to S43 in FIG. 17 are the same as steps S1 to S5 shown in FIG.
[0169]
Next, the process proceeds to step S44, where the amplitude T of the positive component of the TPP signal when the focus bias is Fn. _{+ N} And negative component amplitude T _-N Measure. This measurement is performed by, for example, the TPP signal amplitude information detection circuit 34a of the search circuit 34. And the amplitude T of this positive component _{+ N} And negative component amplitude T _-N ΔTn = | T as the absolute value of the difference between _{+ N} -T _-N | Is calculated. Then, a set (Fn, ΔTn) of the focus bias Fn and the ΔTn is stored as sample information, for example, in the sample information storage circuit 34c.
[0170]
Next, the process proceeds to step S45, where it is determined whether or not the absolute value ΔTn of the difference is equal to or smaller than a predetermined value κ near “0”. If the absolute value ΔTn exceeds the predetermined value κ, step S46 is performed. If the absolute value ΔTn is equal to or smaller than the predetermined value, the process proceeds to step S48.
[0171]
In step S46, n = n + 1 is set, and the process proceeds to step S47 where the previous focus bias F is set. _n-1 A value obtained by adding a predetermined value α to (F _n-1 + Α) is set to Fn, and the process returns to step S44. By repeating this routine, a condition that satisfies step S45 is obtained. The predetermined value κ is a small value in the vicinity of “0”, but if it is too small, there may be a case where sample information in the vicinity of ΔTn = 0 or ΔTn = 0 cannot be detected. Therefore, the predetermined value κ is set to a value larger than the change amount of ΔTn corresponding to the predetermined amount α to be added to the focus bias.
[0172]
Finally, in step S48, the focus bias Fn at which ΔTn is 0 or close to 0 is specified, and the specified focus bias is specified as the focus offset of the optical pickup device 29 on which the optical integrated unit 30 is mounted. A method for specifying the focus bias will be described later. Further, instead of the absolute value of the difference between the positive component amplitude and the negative component amplitude of the TPP signal, a difference between the positive component amplitude and the negative component amplitude of the TPP signal may be employed.
[0173]
(Fifth Embodiment of Focus Offset Evaluation Method)
Next, a fifth embodiment of the focus offset evaluation method of the present invention will be described with reference to FIG. 19, FIG. 20, and FIG.
[0174]
In the focus offset evaluation method of the fifth embodiment, steps S50 to S54 in the flowchart of FIG. 19 are the same as steps S1 to S5 of the flowchart shown in FIG. (2) is different from the first embodiment.
[0175]
(1) Three increments α, β and γ as the amount of change in focus bias.
[0176]
(2) The above three increments are changed with two threshold values of TPP signal information set in advance as a boundary.
[0177]
In the fifth embodiment, as shown in FIGS. 21A and 21B, as the amplitude of the TPP signal as the TPP signal information and the jitter of the clock signal approach the extreme value, the increment of the focus bias is set to γ. , β, α are set so as to decrease in this order. That is, α <β <γ. The point that sample information is acquired at each focus bias is the same as in the above-described embodiment.
[0178]
In the fifth embodiment, the number of pieces of sample information in the vicinity of the extreme value of the TPP signal information is increased as compared with the previous embodiment, and the measurement accuracy of the focus bias at which the TPP signal information becomes the extreme value is improved. It is. The focus bias thus obtained is specified as the focus offset of the optical pickup device 29 on which the optical integrated unit 30 is mounted.
[0179]
More specifically, in the fifth embodiment, as shown in FIG. 21 (A), TPP signal amplitude threshold is T _B And this T _B Larger than T _A Two of these are set. And the amplitude of the TPP signal is T _B In the following, the increment of the focus bias is γ, and the amplitude of the TPP signal is the threshold T _B And the threshold value T _A In the following, it is assumed that the increment is β smaller than γ. Further, the amplitude of the TPP signal is the threshold value T _A Is exceeded, the increment is α smaller than β.
[0180]
Further, as shown in FIG. 21B, a threshold value J is used as the jitter threshold value of the clock signal. _A And this J _A Greater than threshold J _B These two threshold values may be set. In this case, the jitter of the clock signal is the threshold value J _B When it is equal to or greater than this, the increment of the focus bias is γ, and the jitter is the threshold J _B Below the threshold J _A Is greater than, the increment of the focus bias is β. Further, the jitter is the threshold J _A In the following cases, the increment is α.
[0181]
The threshold value T _A And J _A Is a value close to the extreme value, and the increment α is a value that can decompose the vicinity of the extreme value as shown in FIGS. 21 (A) and (B).
[0182]
If it demonstrates with reference to the flowchart of FIG. 19, step S50 to S55 of this flowchart is the same process as step S1 to step S6 of FIG.
[0183]
Next, the process proceeds to step S56, where the measured amplitude Tn of the TPP signal and the first threshold value T of the amplitude of the TPP signal. _A And the amplitude Tn of the TPP signal is equal to the first threshold T _A If so, the process proceeds to step S62. Alternatively, the jitter Jn of the measured clock signal and the first threshold value J of the jitter _A And the jitter Jn is the first threshold value J _A If so, the process proceeds to step S62.
[0184]
On the other hand, the amplitude Tn of the TPP signal is equal to the first threshold value T. _A If larger, the process proceeds to step S57 in FIG. Alternatively, the jitter Jn is the first threshold value J _A If smaller, the process proceeds to step S57 in FIG.
[0185]
In step S57, the amplitude Tn of the TPP signal is set to the second threshold T _B It is determined whether or not the amplitude Tn is equal to or less than the threshold value T _B If not, the process proceeds to step S58, and the amplitude Tn is the threshold value T. _B If so, the process proceeds to step S60.
[0186]
Alternatively, the jitter Jn is the second threshold value J _B Whether or not the jitter Jn is equal to or greater than the threshold value J _B If it is above, the process proceeds to step S58 where the jitter Jn is the threshold value J. _B If so, the process proceeds to step S60.
[0187]
In step S60, n = n + 1 and the process proceeds to step S61, where the previous focus bias F _n-1 The value obtained by adding the increment γ to ( _n-1 With + γ) as Fn, the process returns to step S55 of FIG. On the other hand, in step S58, n = n + 1 is set, and the process proceeds to step S59 where the previous focus bias F is set. _n-1 The value obtained by adding the increment β to (F _n-1 + Β) is set to Fn, and the process returns to step S55 in FIG.
[0188]
On the other hand, when the process proceeds from step S56 to step S62, n = n + 1 and m = m + 1 are set, and the process proceeds to step S64 to determine whether m = k. If it is determined in step S64 that m = k, the process proceeds to step S65. If it is determined that m = k is not satisfied, the process returns to step S55.
[0189]
In step S65, the focus bias that maximizes the amplitude of the TPP signal is specified from the at least (k + 1) pieces of sample information stored in step S55. Alternatively, the focus bias that minimizes the jitter is specified. Details of the method for specifying the focus bias will be described later. Then, it is determined that the specified focus bias is a focus offset of the optical pickup device 29.
[0190]
Thus, according to the fifth embodiment, as shown in FIG. 21A or FIG. 21B, when specifying the extreme value of the TPP signal information, the first estimated to be close to the extreme value. Threshold T _A , J _A And a second threshold T that is estimated to be far from the extreme value _B , J _B And set. Then, the measured TPP signal information is compared with the first and second threshold values, and the increment of the focus bias is reduced as the measured TPP signal information approaches the extreme value. Therefore, the extreme value of the TPP signal information can be searched efficiently and accurately.
[0191]
(Method for specifying the focus bias at which the TPP signal information is the optimum value)
Next, a method for specifying the focus offset of the optical pickup device from the sample information consisting of the set of the focus bias and the TPP signal information stored in the first to fifth embodiments shown in FIGS. 11 to 21 described above. explain.
[0192]
First, the first method is a method of specifying the TPP signal information that is the best target value among the stored sample information as the focus offset of the optical pickup device. For example, sample information in which the amplitude of the TPP signal is maximum or the jitter of the clock signal is minimum is specified, and the focus bias of the sample information is specified as the focus offset of the optical pickup device.
[0193]
In the first method, the increment α as the change amount of the focus bias described in FIGS. 11 to 21 is sufficiently reduced so that the value in the vicinity of the extreme value of the TPP signal information can be resolved, thereby reducing the focus offset. Measurement accuracy can be increased. If the increment α is large, a value near the extreme value of the TPP signal information may not be acquired.
[0194]
As an example, a method of acquiring the amplitude of the TPP signal as TPP signal information in the measurement flowchart shown in FIG. 11 and identifying the focus bias that optimizes the TPP signal information will be described with reference to FIG.
[0195]
First, immediately before step S10 in FIG. ₁ To F _k The k pieces of sample information for the k focus biases up to are stored in the sample information storage circuit 34c.
[0196]
Next, in step S68 of FIG. 22, n = 1 is set, and in step S69, T _n > T _n-1 And T _n > T _{n + 1} It is determined whether or not the condition that is satisfied. If the above condition is satisfied, the process proceeds to step S73. If the above condition is not satisfied, the process proceeds to step S70 and T _n <T _{n + 1} Whether or not the above condition is satisfied is determined. If satisfied, the process proceeds to step S71, and if not satisfied, the process proceeds to step S72. In step S71, n = n + 1 is set, and in step S72, n = n-1 is set, and the process returns to step S69.
[0197]
In step S73, Tn satisfying the condition in step S69 is determined as the extreme value (maximum value) of the amplitude of the TPP signal, and the focus bias Fn corresponding to this Tn is specified as the focus bias of the optical pickup device.
[0198]
In the first method, the TPP signal information includes not only the amplitude of the TPP signal but also the amplitude of the positive component, the amplitude of the negative component, and the difference between the amplitude of the positive component and the amplitude of the negative component. The jitter of the clock signal can be adopted. The first method is applicable not only to the first embodiment but also to the second to fifth embodiments.
[0199]
In particular, in the measurement method of the fifth embodiment shown in FIGS. 19 to 21, the focus bias increments β and γ are increased to some extent and α is sufficiently small, so that the measurement accuracy is not lowered, and Measurement time can be shortened.
[0200]
Next, a second method for specifying the focus bias at which the TPP signal information is an extreme value will be described. In the second method, the focus bias at which the TPP signal information becomes an extreme value (best) is calculated based on the measured and stored sample information.
[0201]
As shown in FIG. 23, this second method is similar to the method of the first embodiment described above, in which the focus bias is set, the amplitude of the TPP signal is measured, and based on the stored sample information, the least square method or the like is used. Using an approximation method, the relationship between the focus bias and the amplitude of the TPP signal is calculated as a parabola that becomes a quadratic curve. Then, the focus bias at the apex of the parabola is specified as the focus offset of the optical pickup device.
[0202]
More specifically, first, only k pieces of sample information are acquired immediately before step S10 in FIG. 11 in the first embodiment, and in the next step S10, an approximation method such as a least square method is used from the acquired sample information. The parabola that becomes the quadratic curve is calculated, and further, the sample information (F that is the apex of the parabola) _A , T _A ) And the sample information (F _A , T _A ) Focus bias F _A Is the focus offset of the optical pickup device. Note that not only the relationship between the focus bias and the amplitude of the TPP signal, but also the relationship between the focus bias and the jitter of the clock signal draws a curve close to a quadratic curve. Therefore, this second method can be adopted even when the jitter of the clock signal is adopted instead of the amplitude of the TPP signal. According to the second method, the vicinity of the best point of the focus bias can be calculated from less sample information than in the first method, and the measurement time can be shortened.
[0203]
Next, a third method for specifying the focus bias at which the TPP signal information is an extreme value will be described with reference to FIGS.
[0204]
This third method is a method for determining from the sample information obtained by measuring and storing the amplitude of the TPP signal that the focus bias at the point where the rate of change of the amplitude of the TPP signal is a predetermined value or less is the focus offset of the optical pickup device. It is.
[0205]
In the third method, for example, steps S75 to S79 in the flowchart of FIG. 25 are the same as steps S1 to S5 of FIG. 11 of the first embodiment, and m = 0 is set in the next step S80. Next, it progresses to step S81 and sample information is measured like step S6 of FIG. In step S82, n = n + 1 and m = m + 1 are set. In step S83, the focus bias F is set. _n = F _n-1 + Α. Next, the process proceeds to step S84 to determine whether m = 3. If m = 3, the process proceeds to step S85, and if m = 3, the process returns to step S81. Thus, as shown in FIG. 24, the sample information (T _n-2 , F _n-2 ), (T _n-1 , F _n-1 ), (T _n , F _n ).
[0206]
Next, in step S85, the change amount ΔT of the amplitude of the TPP signal from the sample information of the three points. _n-1 , ΔT _n Is calculated. And that ΔT _n And ΔT _n-1 The absolute value of the difference between and a predetermined sufficiently small value ΔT _A It is determined whether or not _A If not, the process proceeds to step S86 and ΔT _A If not, the process returns to step S80.
[0207]
In step S86, the sample information (T _n-1 , F _n-1 ) TPP signal amplitude T _n-1 Focus bias F corresponding to _n-1 And this focus bias F _n-1 Is the focus offset of the optical pickup device.
[0208]
As described above, this third method specifies sample information in which the amount of change in the TPP signal amplitude falls within a predetermined minimum range, and specifies the focus bias of this sample information as the focus offset of the optical pickup device. In the third method, the jitter of the clock signal may be adopted instead of the amplitude of the TPP signal. In addition, this third method is applied to the measurement method of the fifth embodiment described with reference to FIGS. 19 to 21, thereby further improving accuracy and shortening the measurement time when specifying the focus offset of the optical pickup device. I can plan.
[0209]
Next, a fourth method for specifying the focus bias at which the TPP signal information is an extreme value will be described with reference to FIGS.
[0210]
As shown in FIG. 27, the fourth method uses an amplitude T of a predetermined TPP signal. _A And set the amplitude T _A Is an example in which the average value Fc of the two focus biases Fa and Fb across the point where the amplitude of the TPP signal is maximum on the focus bias axis is specified as the focus offset of the optical pickup device.
[0211]
In the fourth method, steps S88 to S96 in the flowchart shown in FIG. 26 are the same as steps S1 to S9 in the flowchart shown in FIG. 11, and k pieces of sample information are measured and stored by step S95.
[0212]
Next, proceeding to step S97, the set amplitude T is selected from the stored sample information. _A And sample information (Fa, Ta), (Fb, Tb) at two points that have the amplitude of the TPP signal closest to and sandwiching the extreme value of the amplitude of the TPP signal on the focus bias axis. In step S98, the average value of Fa and Fb (Fa + Fb) / 2 = Fc is calculated, and this Fc is specified as the focus bias at which the amplitude of the TPP signal is maximum Tc. Then, it is determined that the specified focus bias Fc is a focus offset of the optical pickup device.
[0213]
Note that this fourth method is applicable not only to the first embodiment but also to the second to fifth embodiments, and a method for measuring TPP signal information shown in each embodiment. By combining these, measurement accuracy and measurement time can be shortened. Furthermore, it is possible to combine any one of the first to fourth methods with any one of the first to fifth embodiments, whereby the extreme value of the TPP signal information can be reduced. It can be extracted more easily. Accordingly, it is possible to improve the measurement accuracy and shorten the measurement time.
[0214]
In the first to fifth embodiments described above, an arbitrary track (for example, a groove track) is selected, and the focus offset of the optical pickup device is evaluated with only that track as a measurement target. When both the land track and the groove track are included, both the tracks are selected and the focus offset is evaluated. Then, the optimum focus offset obtained in each track and the measured track are stored correspondingly, whereby the optimum focus offset in the land track and the optimum focus offset in the groove track can be specified.
[0215]
Further, in the above-described embodiment, the optical system has been described as a one-beam type, but a sub-beam generating diffraction grating is provided between the diffraction grating 14 for diffracting the servo signal light receiving element 2 and the semiconductor laser 1. The present invention can also be applied to an optical system that is installed and is compatible with a multi-beam system of three beams or more.
[0216]
In the above embodiment, the optical integrated unit 11 in which the semiconductor laser 1, the servo signal light receiving element 2 and the hologram element 3 are integrated has been described. Further, an optical path separation type optical integrated unit equipped with a beam splitter is provided. The present invention can also be applied to an optical pickup device in which each component is arranged separately.
[0217]
Furthermore, the present invention can also be applied to an integrated optical pickup device in which the objective lens and each component are integrated.
[0218]
Further, a magneto-optical disk having embossed pits other than the magneto-optical disk described in the above embodiment, and a DVD-type optical disk having a clock area and other data areas other than the embossed pits whose reflectivity changes and other data areas. The present invention can also be applied to write-once and phase change optical disks. Furthermore, regardless of the configuration and structure of the data recording area and the other areas, the present invention can be applied by measuring TPP signal information along the data recording area and the other areas.
[0219]
In other words, according to the present invention, the TPP signal may be acquired from the optical signal from the optical disk that forms not only the embossed pits but also the pits having changed reflectivity regardless of the shape of the diffraction grating and the type of the optical disk. Then, by changing the focus bias using the TPP signal and measuring TPP signal information corresponding to the change, the focus offset of the optical pickup device and the optical integrated unit can be evaluated.
[0220]
Further, according to the present invention, if the optical disk has an embossed pit or an area of a pit other than the embossed pit that changes in reflectance, the pit is used regardless of the data recorded in the data recording area of the land and groove or only the groove. Regardless of the area configuration, pit shape, length, number, width, and depth, and optical disk reflectivity, it can stably detect the clock signal or edge signal reproduced by the TPP signal and TPP signal. The focus offset of the optical pickup device and the optical integrated unit can be measured, and the focus offset can be evaluated stably.
[0221]
【The invention's effect】
As is clear from the above, in the focus offset evaluation method of the present invention, a predetermined focus bias signal is applied to the focus error signal to set a predetermined focus bias in the optical pickup device or the optical integrated unit. Sample information consisting of the tangential push-pull signal information generated when setting is set and the focus bias is obtained. Based on the relationship between the focus bias based on the sample information and the tangential push-pull signal information, the focus offset of the optical pickup device or the optical integrated unit is evaluated. As described above, the present invention sets the focus bias to the optical pickup device or the optical integrated unit by applying the focus bias signal to the focus error signal, and uses the characteristics of the tangential push-pull signal information corresponding to the focus bias. Thus, the focus offset of the optical pickup device or the optical integrated unit can be evaluated accurately and stably.
[0222]
In addition, the focus offset evaluation method according to an embodiment can obtain the relationship between the focus bias and the tangential push-pull signal information more accurately by obtaining a plurality of pieces of sample information. Therefore, the focus offset of the optical pickup device or the optical integrated unit can be evaluated with higher accuracy.
[0223]
The focus offset evaluation method according to an embodiment obtains an extreme value of the tangential push-pull signal information and specifies that a focus bias corresponding to the extreme value is a focus offset of the optical pickup device. Thereby, the focus offset of the optical pickup device or the optical integrated unit can be accurately evaluated.
[0224]
In the focus offset evaluation method of one embodiment, the amplitude of the tangential push-pull signal as the tangential push-pull signal information, the jitter of the clock signal generated from the tangential push-pull signal, or both are used. Thus, the focus offset of the optical pickup device and the optical integrated unit can be accurately evaluated.
[0225]
Also, in the focus offset evaluation method of one embodiment, the positive component amplitude and negative component amplitude of the tangential push-pull signal are adopted as the tangential push-pull signal information, and the positive component amplitude of the tangential push-pull signal is adopted. This is effective when the focus bias that maximizes the focus bias differs from the focus bias that maximizes the amplitude of the negative component of the tangential push-pull signal, and can improve accuracy when specifying the focus offset of the pickup device or optical integrated unit. .
[0226]
In the focus offset evaluation method according to an embodiment, the absolute value of the difference between the positive component amplitude and the negative component amplitude of the tangential push-pull signal is adopted as the tangential push-pull signal information, and the tangential push-pull signal information is used. Effective when the focus bias that maximizes the amplitude of the positive component of the signal is different from the focus bias that maximizes the amplitude of the negative component of the tangential push-pull signal, and identifies the focus offset of the optical pickup device or integrated optical unit. In this case, the accuracy can be improved.
[0227]
Also, in the focus offset evaluation method of one embodiment, the jitter of the clock signal is adopted as the tangential push-pull signal information, and the focus bias at which this jitter becomes a minimum value is the focus offset of the optical pickup device or the optical integrated unit. It can be specified that there is.
[0228]
In the focus offset evaluation method according to the embodiment, the focus offset of the optical pickup device or the optical integrated unit is evaluated based on the relationship between the focus bias and the tangential push-pull signal information based on three or more pieces of sample information. Thereby, reliable evaluation becomes possible.
[0229]
Further, in the focus offset evaluation method of one embodiment, since two or more different amounts of change are set as the amount of change for changing the focus bias, the change in the focus bias becomes closer to the extreme value of the tangential push-pull signal information. The amount can be reduced, and the extreme value of the tangential push-pull signal information can be easily obtained. As a result, the evaluation of the focus offset of the optical pickup device and the optical integrated unit is facilitated.
[0230]
In the focus offset evaluation method according to an embodiment, the setting of the change amount of the focus bias is performed based on a result of comparing the tangential push-pull signal information with a threshold value. Accordingly, it is possible to set a change amount of the focus bias in response. As a result, the closer the tangential push-pull signal information is to the extreme value, the smaller the amount of change in the focus bias can be reduced, making it easier to obtain the extreme value of the tangential push-pull signal information, resulting in the optical pickup device and the optical integration. It is easy to evaluate the focus offset of the unit.
[0231]
Further, in the focus offset evaluation method of one embodiment, by setting two or more different threshold values as the threshold value, the focus bias change amount according to the tangential push-pull signal information is finely set. Yes. As a result, the closer the tangential push-pull signal information is to the extreme value, the smaller the amount of change in the focus bias can be reduced, making it easier to obtain the extreme value of the tangential push-pull signal information. It is easy to evaluate the focus offset of the unit.
[0232]
In one embodiment, the focus offset of the optical pickup device is evaluated based on sample information obtained by changing the focus bias in either the positive or negative direction from the initial value of the focus bias. In the focus offset evaluation method of this embodiment, the method of changing the focus bias can be simplified.
[0233]
In the focus offset evaluation method of one embodiment, since the focus bias is changed in both positive and negative directions from the initial value, sample information in a range covering both positive and negative sides of the initial value can be obtained. Therefore, it becomes easy to obtain sample information suitable for evaluating the focus offset.
[0234]
Further, in the focus offset evaluation method of one embodiment, the target value of the tangential push-pull signal information is set to an extreme value or a predetermined range sandwiching the extreme value, so that among the multiple focus biases included in the multiple sample information The focus bias corresponding to the target value of the tangential push-pull signal information selected from the above is specified as the focus offset of the optical pickup device or the optical integrated unit. Accordingly, it is easy to obtain a focus bias that specifies the focus offset.
[0235]
In one embodiment, the focus offset evaluation method calculates a focus bias at which the tangential push-pull signal information has an extreme value by numerical calculation processing based on the plurality of pieces of sample information. Therefore, according to this focus bias, the focus offset can be specified accurately.
[0236]
Also, in the focus offset evaluation method of one embodiment, sample information that is less than or equal to a predetermined value is specified using the fact that the rate of change of tangential push-pull signal information with respect to a change in focus bias is minimized, and this The focus bias included in the sample information is specified as the focus offset of the optical pickup device or the optical integrated unit. Thereby, the focus offset can be specified accurately.
[0237]
In the focus offset evaluation method of one embodiment, the average value of the focus biases of the two sample information may be a good approximation to the focus bias corresponding to the actual extreme value of the tangential push-pull signal information. And focus offset can be identified efficiently.
[0238]
In one embodiment, the focus offset evaluation method evaluates the focus offset of the optical pickup device or the optical integrated unit based on the sample information obtained by irradiating the laser beam to one track of the optical storage medium. Therefore, the focus offset can be evaluated efficiently.
[0239]
In the focus offset evaluation method according to an embodiment, the focus offset of the optical pickup device or the optical integrated unit is evaluated based on sample information obtained by irradiating the two tracks of the optical storage medium with laser light, respectively. To do. Therefore, the focus offset can be evaluated with high accuracy.
[0240]
In the focus offset evaluation apparatus according to the embodiment, the focus bias is set to the optical pickup device or the optical integrated unit by applying the focus bias signal to the focus error signal, and the tangential push-pull signal information corresponding to the focus bias is set. Using this characteristic, the focus offset of the optical pickup device or the optical integrated unit can be evaluated.
[Brief description of the drawings]
FIG. 1 is a diagram showing a structure of an optical pickup device and an optical integrated unit as evaluation targets in an embodiment of a focus offset evaluation device and evaluation method of the present invention.
FIG. 2 is a diagram showing a diffraction grating, a shape and arrangement of a light receiving element, and a circuit of the light receiving element of the optical integrated unit.
3A is a schematic diagram showing a track shape of the magneto-optical disk used in the embodiment, and FIG. 3B is a waveform diagram of a TPP signal obtained from the track. 3 (C) is a waveform diagram of the clock signal obtained from the TPP signal, and FIG. 3 (D) is a distribution diagram showing the distribution of the clock signal on the time axis.
FIGS. 4A, 4B, and 4C show the optical system, the diffraction grating, and the light receiving element in a just-focused and defocused state when the optical component arrangement is ideal. It is a schematic diagram which shows the shape of a light spot.
5A to 5C are TPP signal waveform diagrams corresponding to FIGS. 4A to 4C. FIG.
6 (A), 6 (B), and 6 (C) show the optical system, the diffraction grating, and the light receiving element in the just focus and defocus states when there is an error in the arrangement of optical components. It is a schematic diagram which shows the shape of a light spot.
7A to 7C are TPP signal waveform diagrams corresponding to FIGS. 6A to 6C. FIG.
FIGS. 8A to 8D show the focus bias as the horizontal axis, the amplitude of the TPP signal, the amplitude of the positive and negative components of the TPP signal, the difference between the positive and negative components of the TPP signal, It is a characteristic view with the jitter of the clock signal as the vertical axis.
FIG. 9 is a block diagram showing a configuration of an embodiment of a focus offset evaluation apparatus of the present invention.
FIG. 10 is a block diagram showing a configuration of a modification of the embodiment shown in FIG. 9;
FIG. 11 is a flowchart showing a first embodiment of a focus offset evaluation method according to the present invention.
FIGS. 12A and 12B are schematic diagrams showing how the amplitude of the TPP signal and the jitter of the clock signal as TPP signal information are measured by changing the focus bias in the first embodiment. It is a typical graph.
FIG. 13 is a flowchart showing a second embodiment of the focus offset evaluation method of the present invention.
FIGS. 14A and 14B are schematic diagrams showing how the amplitude of the TPP signal and the jitter of the clock signal as TPP signal information are measured by changing the focus bias in the second embodiment. It is a typical graph.
FIG. 15 is a flowchart showing a third embodiment of the focus offset evaluation method of the present invention.
FIG. 16 is a schematic graph showing how the positive component and the negative component of the amplitude of the TPP signal as TPP signal information are separately measured by changing the focus bias in the third embodiment.
FIG. 17 is a flowchart showing a fourth embodiment of the focus offset evaluation method of the present invention.
FIG. 18 is a schematic graph showing how the absolute value of the difference between the positive component and the negative component of the TPP signal amplitude as TPP signal information is measured by changing the focus bias in the fourth embodiment. .
FIG. 19 is a (partial) flowchart showing a fifth embodiment of the focus offset evaluation method of the present invention;
FIG. 20 is a flowchart (remainder) showing the fifth embodiment.
FIGS. 21A and 21B are schematic diagrams showing how the amplitude of the TPP signal and the jitter of the clock signal as TPP signal information are measured by changing the focus bias in the fifth embodiment. It is a typical graph.
FIG. 22 is a flowchart showing a first method that can be applied to the first to fifth embodiments and that specifies a focus bias at which TPP signal information has an optimum value.
FIG. 23 is a schematic graph showing a second method that can be applied to the first to fifth embodiments and that specifies a focus bias at which the TPP signal information has an optimum value.
FIG. 24 is a schematic graph showing a third method that can be applied to the first to fifth embodiments and that specifies a focus bias at which TPP signal information has an optimum value.
FIG. 25 is a flowchart showing the third method.
FIG. 26 is a flowchart showing a fourth method that can be applied to the first to fifth embodiments and that specifies a focus bias at which the TPP signal information has an optimum value.
FIG. 27 is a schematic graph showing the fourth method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Light receiving element for servo signal detection,
3 ... Hologram element, 4 ... Collimating lens, 5 ... Objective lens,
6, 26 ... Magneto-optical disk, 7 ... Polarizing beam splitter,
8 ... Wollaston prism, 9 ... Condensing lens,
10: Light-receiving element for detecting magneto-optical signal, 11: Optical integrated unit,
12 ... Cap, 13 ... Stem, 14 ... Diffraction grating,
15, 20 ... light spot,
16 ... Data recording area, 17 ... Clock area, 18 ... Land,
19 ... groove, 21 ... TPP signal,
22: Zero cross point of TPP signal, 23: Clock signal,
24: Distribution characteristic of clock signal in time axis direction,
25: Jitter of clock signal, 27 ... Spindle motor,
28 ... Spindle motor drive circuit, 29 ... Optical pickup device,
30 ... Optical integrated unit, 32 ... Servo signal generation circuit,
31 ... Servo signal processing circuit, 31a ... Focus servo circuit,
31b ... tracking servo circuit, 32 ... servo signal generation circuit,
33 ... PLL circuit, 34 ... search circuit,
34a ... TPP signal amplitude information detection circuit, 34b ... control circuit,
34c ... Sample information storage circuit, 35 ... Decoder / encoder circuit,
36: Focus bias device, 37: Jitter detection circuit.

Claims (20)

Irradiating an optical recording medium with laser light emitted from a semiconductor laser of an optical pickup device or an optical integrated unit;
The reflected light of the laser beam from the optical recording medium is diffracted toward the light receiving element by a diffraction grating,
A focus error signal and tangential push-pull signal information are generated from an electrical signal output from the light receiving element that receives the reflected light,
By applying a predetermined focus bias signal to the focus error signal, a predetermined focus bias is set,
Obtain sample information including the focus bias and tangential push-pull signal information generated when the focus bias is set,
A focus offset evaluation method, wherein a focus offset of the optical pickup device or the optical integrated unit is evaluated based on a relationship between the focus bias obtained from the sample information and the tangential push-pull signal information. The focus offset evaluation method according to claim 1,
By applying a plurality of different focus bias signals to the focus error signal, a plurality of sample information is obtained,
A focus offset evaluation method for evaluating a focus offset of the optical pickup device or the optical integrated unit based on a relationship between the focus bias obtained from the plurality of sample information and the tangential push-pull signal information . In the focus offset evaluation method according to claim 2,
Based on the relationship between the focus bias obtained from the plurality of sample information and the tangential push-pull signal information, an extreme value of the tangential push-pull signal information is obtained, and the focus bias corresponding to the extreme value is the above-described focus bias. A focus offset evaluation method characterized by specifying a focus offset of an optical pickup device or an optical integrated unit. In the focus offset evaluation method according to claim 3,
The focus offset evaluation method, wherein the tangential push-pull signal information is at least one of an amplitude of a tangential push-pull signal or jitter of a clock signal generated from the tangential push-pull signal. In the focus offset evaluation method according to claim 3,
The tangential push-pull signal information is the amplitude of the positive component and the negative component of the tangential push-pull signal, and the focus bias where the amplitude of the positive component becomes a maximum value and the amplitude of the negative component becomes a maximum value. Find the focus bias and
An average value of a focus bias at which the positive component amplitude is a maximum value and a focus bias at which the negative component amplitude is a maximum value is specified as a focus offset of the optical pickup device or the optical integrated unit. Focus offset evaluation method. In the focus offset evaluation method according to claim 3,
The tangential push-pull signal information is an absolute value of a difference between the positive component amplitude and the negative component amplitude of the tangential push-pull signal, and the focus bias at which the absolute value of the difference becomes an extreme value is the optical pickup device. A focus offset evaluation method, characterized in that the focus offset is specified. In the focus offset evaluation method according to claim 3,
The tangential push-pull signal information is the jitter of the clock signal generated from the tangential push-pull signal, and a focus bias that minimizes the jitter is obtained. A focus offset evaluation method characterized by specifying an offset. In the focus offset evaluation method according to claim 2,
Three or more pieces of sample information are obtained by applying three or more different focus bias signals to the focus error signal, and the focus bias and the tangential push-pull signal information obtained from the three or more pieces of sample information. And a focus offset evaluation method for evaluating the focus offset of the optical pickup device or the optical integrated unit. The focus offset evaluation method according to claim 8,
2. A focus offset evaluation method, wherein two or more different change amounts are set as the change amount for changing the focus bias. In the focus offset evaluation method according to claim 9,
Set the threshold for tangential push-pull signal information,
A focus offset evaluation method, comprising: setting a change amount of the focus bias based on a result of comparing tangential push-pull signal information in the sample information with the threshold value. The focus offset evaluation method according to claim 10,
A focus offset evaluation method, wherein two or more different threshold values are set as the threshold value. In the focus offset evaluation method according to claim 2,
The focus offset of the optical pickup device or the optical integrated unit is evaluated based on sample information obtained by changing the focus bias in either the positive or negative direction from the initial value of the focus bias. Focus offset evaluation method. In the focus offset evaluation method according to claim 2,
Sample information obtained by changing the focus bias in either the positive or negative direction from the initial value of the focus bias, and the focus bias in the positive or negative direction from the initial value. A focus offset evaluation method, wherein the focus offset of the optical pickup device or the optical integrated unit is evaluated from the sample information obtained in this way. In the focus offset evaluation method according to claim 2,
A focus offset evaluation method for identifying a focus bias corresponding to a target value of tangential push-pull signal information among the plurality of pieces of sample information as a focus offset of the optical pickup device or the optical integrated unit. . In the focus offset evaluation method according to claim 2,
Based on the plurality of pieces of sample information, a focus bias at which the tangential push-pull signal information becomes an extreme value is calculated by numerical calculation processing, and the calculated focus bias is calculated as a focus offset of the optical pickup device or the optical integrated unit. A focus offset evaluation method characterized by specifying. In the focus offset evaluation method according to claim 2,
Based on the relationship between the focus bias obtained from the plurality of sample information and the tangential push-pull signal information, a sample in which the change rate of the tangential push-pull signal information with respect to the change of the focus bias is a predetermined value or less. A focus offset evaluation method characterized by identifying information and identifying that a focus bias included in the sample information is a focus offset of the optical pickup device or the optical integrated unit. In the focus offset evaluation method according to claim 2,
Based on the plurality of sample information, the extreme value of the tangential push-pull signal information and a focus bias corresponding to the extreme value are estimated, and further, a predetermined value of the tangential push-pull signal information is set,
Among sample information having a focus bias larger than the focus bias corresponding to the set extreme value, sample information having tangential push-pull signal information closest to the predetermined value and a focus bias corresponding to the extreme value Selecting sample information having tangential push-pull signal information closest to the predetermined value among sample information having a small focus bias;
A focus offset evaluation method characterized in that an average value of focus biases of the two selected sample information is calculated, and this average value is specified as a focus offset of the optical pickup device or the optical integrated unit. The focus offset evaluation method according to any one of claims 1 to 17,
A focus offset evaluation method, comprising: evaluating a focus offset of the optical pickup device or the optical integrated unit based on the sample information obtained by irradiating the laser beam onto one track of the optical storage medium. The focus offset evaluation method according to any one of claims 1 to 17,
A focus offset evaluation method comprising: evaluating a focus offset of an optical pickup device or an optical integrated unit based on sample information obtained by irradiating two tracks of the optical storage medium with laser light, respectively. Control of focus servo control for the optical pickup device based on an electrical signal output from a light receiving element that receives reflected light from an optical recording medium irradiated with a laser beam from a semiconductor laser included in the optical pickup device or an optical integrated unit Focus error signal generation means for generating a focus error signal to be a signal;
Tracking error signal generating means for generating a tracking error signal to be a control signal for tracking servo control;
A focus bias means for setting a focus bias by applying a focus bias signal to the focus error signal;
Tangential push-pull signal information generating means for generating tangential push-pull signal information obtained from the electrical signal output by the light receiving element;
Tangential push-pull signal detection means for detecting tangential push-pull signal information generated by the tangential push-pull signal generation means;
A focus offset that specifies the focus offset of the optical pickup device or the optical integrated unit based on the relationship between the focus bias set by the focus bias means and the tangential push-pull signal information obtained when the focus bias is set. A focus offset evaluation apparatus comprising a specifying unit.

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