JP4131148B2 - Phase adjustment method for optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a phase adjustment method for adjusting the phase of an optical system in an optical pickup device that reads information recorded on an optical disc by irradiating the optical disc with light in a predetermined wavelength range and detecting return light. .
[0002]
[Prior art]
Conventionally, optical disks have been widely used as recording media for recording large-capacity data such as image data and audio data. The optical disc includes a signal recording layer on a disc substrate formed into a disk shape by a resin material such as polycarbonate, and the recording layer is concentrically or spirally formed on the signal recording layer along a recording track. Information signals are recorded and / or reproduced (hereinafter referred to as recording / reproduction) by irradiating the optical disc apparatus with laser light. Optical discs are roughly classified into read-only optical discs, phase change optical discs, magneto-optical discs, and the like, depending on the recording / reproducing method.
[0003]
In a read-only optical disc, a physical concavo-convex shape called a pit is formed in advance in the signal recording layer according to the recording data, and the return light reflected from the signal recording layer by the laser beam irradiated along the recording track Reproduction is performed by detecting a change in the amount of light.
[0004]
A phase change optical disc uses an organic dye material for a signal recording layer, and a recording mark is formed on the signal recording layer by irradiating a laser beam modulated in accordance with recording data. To be recorded. When reproducing this phase change type optical disk, a laser beam having a weaker output than that at the time of recording is irradiated along the recording track, and the reflectance is reduced between the part where the recording mark is formed and the part where the recording mark is not formed. The recorded information signal is obtained by detecting the change in the return light quantity due to the difference between the two.
[0005]
A magneto-optical disk uses a magnetic material for a signal recording layer, and an information signal is recorded by applying an external magnetic field along with laser light irradiation. Two recording systems for the magneto-optical disk are known, an optical modulation system and a magnetic field modulation system.
[0006]
In the optical modulation method, a pulsed laser beam modulated in accordance with an information signal to be recorded in a state where a predetermined bias magnetic field is applied to a signal recording layer that has been magnetized in a predetermined direction and initialized. Is irradiated along the recording track. As a result, a recording mark having a magnetization direction corresponding to the bias magnetic field is formed on the portion of the signal recording layer heated by irradiation with the laser beam, and recording is performed.
[0007]
In the magnetic field modulation method, a signal recording layer of a magneto-optical disk is irradiated with laser light at a predetermined output along a recording track, and an external magnetic field modulated in accordance with an information signal to be recorded is applied. As a result, a recording mark having a magnetization direction corresponding to the modulated external magnetic field is formed in the portion heated by the laser beam irradiation, and recording is performed.
[0008]
On the other hand, when reproducing a magneto-optical disk, laser light is irradiated along the recording track with a weaker output than that during recording, and the return light from the signal recording layer is detected. At this time, since the polarization plane of the laser light rotates in the signal recording layer due to the so-called magnetic Kerr effect, the presence or absence of the recording mark can be detected by detecting the difference in the amount of the return light, and the recorded information signal is can get.
[0009]
As described above, it is necessary to irradiate laser light when performing recording / reproduction on various types of optical disks. Therefore, an optical disk apparatus that performs recording / reproduction with respect to the optical disk as described above irradiates the optical disk with laser light corresponding to a recording signal at the time of recording, or the laser light irradiated at the time of reproduction reflects to the optical disk and returns. An optical pickup device that detects the return light, converts the detected return light into an electrical signal, and outputs an RF signal is mounted.
[0010]
Such an optical pickup device reliably performs recording / reproduction with respect to an optical disc, for example, in order to avoid a situation in which an optical disc that can be reproduced by a specific optical disc device cannot be reproduced by another optical disc device. Must be aligned for each apparatus. As a technique for adjusting the phase of the optical system in the optical pickup device as described above, the following technique has been conventionally employed.
[0011]
That is, a predetermined adjustment optical disc is reproduced by an optical disc apparatus, and an RF signal obtained by converting return light from the optical disc into an electrical signal is observed by an optical pickup mounted on the optical disc apparatus. Then, the phase of the optical system is adjusted so that the CNR (Code Noise Ratio), which is the ratio between the information signal and the noise, is maximized by rotating the half-wave plate provided in the optical system of the optical pickup. adjust.
[0012]
[Problems to be solved by the invention]
By the way, in recent years, the amount of data handled by computer devices and various video and audio devices has increased dramatically, and optical disks used as recording media in these devices are also required to have a large capacity and thus a high recording density. In addition, there is a demand for higher transfer rates in optical disk devices.
[0013]
Therefore, in recent years, a recording / reproducing technique based on a magnetically induced super resolution (MSR) method has attracted attention as a technique for achieving a higher recording density in a magneto-optical disk. In the magnetic super-resolution method, recording / reproduction is performed using a magneto-optical disk having a signal recording layer having a plurality of magnetic layers having different magnetic characteristics depending on temperature, so that it is narrower than the spot diameter of the laser beam to be irradiated. Recording / reproduction with respect to the recording mark is enabled. In such a magnetic super-resolution system, a high laser output is required at the time of reproduction, and the laser output at the time of reproduction for a conventional magneto-optical disk is about 1.5 mW, for example, about 4.5 mW. Three times as much laser output is required.
[0014]
In order to realize a high transfer rate of the optical disc apparatus, it is necessary to drive the optical disc at a high speed and increase the output of the laser beam corresponding to the high speed rotation.
[0015]
However, when the output of the laser beam is increased in this way, the noise component included in the laser beam itself increases, and the influence of the noise component on the RF signal obtained by converting the return light from the optical disc becomes significant. Further, when the output of the laser light is increased, minute scratches generated on the reading surface of the optical disk, optical phase distortion components generated on the disk substrate itself formed of polycarbonate, etc., the signal recording layer The influence of an optical phase distortion component caused by physical distortion or an optical phase distortion component accompanying a temperature change on the RF signal becomes significant.
[0016]
Therefore, in order to cope with higher recording density and higher transfer rate, it is important to adjust the phase of the optical system in the optical pickup device with high accuracy to prevent the deterioration of the RF signal due to the factors described above. It is.
[0017]
However, as described above, the conventional phase adjustment method for adjusting the rotation angle of the wave plate while observing the CNR has problems as described below.
[0018]
The first problem is that the change in CNR is slow with respect to the rotation angle of the wave plate. That is, there is a wide angle region in which no change in the CNR is recognized even when the wave plate is rotated, and high-precision phase adjustment cannot be performed. Therefore, the optical phase variation increases for each optical pickup device. For this reason, when an optical pickup device whose phase is adjusted by a conventional method is used, an optical disc that can be reproduced by a specific optical disc device cannot be reproduced by another optical disc device, and the compatibility between optical disc devices is remarkably high. It will be damaged.
[0019]
The second problem is that in the conventional method, when the optical pickup device is phase-adjusted, the optical phase distortion component (disk orientation) generated in the disk substrate is not taken into consideration. The direction of the disk is considered to be the direction of the optical phase generated when the resin material that is the raw material of the disk substrate is formed by injection molding or the like, and generally exists radially from the center of the disk. is there. The influence of the orientation of the disk on the RF signal becomes more prominent as the pits and recording marks become finer as the recording density increases, and the output of the laser beam increases, leading to a deterioration in error rate. was there.
[0020]
Therefore, the present invention has been made in view of the above-described conventional situation, and an object thereof is to provide a phase adjustment method capable of accurately and reliably adjusting an optical phase in an optical pickup device. To do.
[0021]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an optical pickup device for adjusting the phase of an optical pickup that reads information recorded on the optical disc by irradiating the optical disc with light in a predetermined wavelength range and detecting return light. In the phase adjustment method for adjusting the phase of the optical system in the apparatus, a reading operation is performed at a position of the phase abnormality region by the optical pickup device with respect to a predetermined adjustment optical disk having a phase abnormality region where the phase abnormality occurs. The phase compensation mechanism provided in the return optical system of the optical pickup device is adjusted so that the change in the output signal level obtained at this time is minimized.
[0022]
Unlike the conventional method of adjusting the phase of the optical system in the optical pickup device while observing the CNR, the phase adjustment method configured as described above differs from the output signal (RF obtained at the position of the phase abnormal region of the adjustment optical disk). The phase of the optical system is adjusted based on the change in signal level. Since the RF signal changes abruptly in the phase abnormality region of the optical disc, the phase position to be adjusted can be determined with extremely high accuracy by adjusting the phase based on the RF signal. In addition to this point, since the phase is adjusted using a predetermined adjustment optical disk, it is possible to effectively suppress variations in the phase of each optical pickup device.
[0023]
In addition, since the phase is adjusted using the phase abnormality region of the adjustment optical disc, the optical system of the optical pickup device after adjustment has an optical phase distortion component (disc It is possible to adjust the phase according to the direction.
[0024]
Note that the phase abnormal region used when adjusting the phase includes the above-mentioned wrinkle among the recording tracks in which the amount of return light is normal near the physical ridge generated on the information reading surface of the adjustment optical disc. It is desirable to select a recording track that exists at a position closest to the part. By performing the reading operation for phase adjustment at the position of such a phase abnormal region, the change that occurs in the RF signal can be obtained most greatly, so that it becomes easy to determine the phase position to be adjusted.
[0025]
Further, as the phase abnormality region used when adjusting the phase, it is desirable to select a region where a change in the output signal level in a sine wave shape can be obtained when the reading operation is performed.
[0026]
The output of the RF signal can be obtained with different waveforms depending on the physical shape of the buttocks, etc., but by selecting a phase abnormal region where a level change of a sine wave shape can be obtained and performing phase adjustment at this position, RF The largest change in the signal is obtained, and it becomes easy to determine the phase position to be adjusted. In addition, by determining the phase abnormality region of the adjustment optical disc that performs phase adjustment based on the output waveform of the RF signal in this way, the shape of the physical collar portion generated on the adjustment optical disc is visually checked. Thus, it is not necessary to set a phase abnormality region in advance, and phase adjustment can be realized using only various signal processing techniques.
[0027]
Note that, as described above, in the vicinity of the physical ridge generated on the information reading surface of the adjustment optical disc, the recording track where the amount of return light is normal is positioned closest to the ridge. When an existing recording track is selected, the output waveform of the obtained RF signal has a sine wave shape.
[0028]
In order to minimize the change in the output signal level, it is desirable to rotate the half-wave plate provided as the phase compensation mechanism around the optical axis. For example, an optical pickup device that employs an elliptical polarization detection method as a method for following a recording track (tracking) includes a half-wave plate as a phase compensation mechanism. Therefore, it is possible to adjust the output level change of the RF signal to be minimum by rotating the half-wave plate. However, the structure and members of the phase compensation mechanism of the optical pickup device that adjusts the phase according to the present invention are not particularly limited.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention relates to a phase adjustment method for an optical pickup device that reads information recorded on an optical disk. Therefore, first, an optical disc apparatus 10 as shown in FIG. 1 will be described as an example of an optical disc apparatus equipped with an optical pickup device to which the present invention is applied.
[0030]
The optical disk apparatus 10 described below is an apparatus that performs recording / reproduction with respect to a magneto-optical disk of a magnetic super-resolution system, but the present invention is not particularly limited with respect to the type of optical disk and the recording / reproduction system. However, it is widely applicable when adjusting the phase of an optical system in an optical pickup device that reads information recorded on the optical disc by irradiating the optical disc with light in a predetermined wavelength range and detecting return light. Of course there is.
[0031]
As shown in FIG. 1, the optical disk apparatus 10 includes a spindle motor 11 that rotationally drives the magneto-optical disk 50 at a predetermined angular velocity or linear velocity, an optical pickup 12 that irradiates the magneto-optical disk 50 with laser light, A bias magnet 13 for applying a predetermined bias magnetic field to the magnetic disk 50, a binarization unit 14 for binarizing an RF signal output from the optical pickup 12, and recording / reproduction with respect to the magneto-optical disk 50 are performed. Operation of the signal processing unit 15 that performs various types of signal processing on signals to be performed, an ODC (Optical Disk Controller) unit 16 that inputs and outputs signals between the host device 100 connected to the outside, and the operation of the entire optical disk device 10 A control unit 17 for controlling the power, a power control unit 18 for controlling the output of the laser light applied to the optical pickup 12, and a bias magnet. And it includes a magnet controller 19 to control the intensity of the magnetic field to be applied by 3.
[0032]
The optical pickup 12 has an optical system that irradiates the magneto-optical disk 50 with laser light and detects return light that is reflected from the signal recording layer of the magneto-optical disk 50 and returned. . In addition to the optical system, various electrical / electronic circuits are incorporated in the optical pickup 12, and the return light is subjected to photoelectric conversion and current-voltage conversion, and the voltage changes according to the change in the amount of the return light. The RF signal is output to the binarization unit 14. In addition, a focus servo signal and a tracking servo signal indicating the defocus amount and the detracking amount with respect to the recording track of the beam spot of the laser beam irradiated to the magneto-optical disk 50 based on the detected return light by the electric / electronic circuit are obtained. These are generated and output to the signal processing unit 15. The focusing technique and tracking technique employed in the optical disc apparatus 10 are not particularly limited, but it is assumed that the so-called elliptical polarization method is adopted in the optical disc apparatus 10 according to the present example.
[0033]
The optical pickup 12 is movable in the radial direction of the magneto-optical disk 50 by a drive mechanism (not shown), and can irradiate laser light to any position on the magneto-optical disk 50. Since this drive mechanism and the above-described electric / electronic circuit may be configured in the same manner as in the past, detailed description thereof is omitted here. Details of the optical system of the optical pickup 12 will be described later.
[0034]
The bias magnet 13 is disposed at a position facing the optical pickup 12 via the magneto-optical disk 50, and applies a bias magnetic field having a predetermined intensity to the magneto-optical disk 50 during recording and reproduction. In the bias magnet 13, the strength of the applied magnetic field is controlled by the magnet control unit 19.
[0035]
The binarization unit 14 performs a process of encoding an information signal recorded on and reproduced from the magneto-optical disk 50 into a binary value of “0” and “1”. The binarization unit 14 performs binarization processing on the RF signal output from the optical pickup 12 when the magneto-optical disk 50 is reproduced, and outputs the binarized signal to the signal processing unit 15 and the ODC unit 16. In recording, the signal input from the signal processing unit 15 is binarized, and the processed signal is output to the signal processing unit 15.
[0036]
The signal processing unit 15 performs laser beam focus control and tracking control on the optical pickup 12 based on the focus servo signal and tracking servo signal output from the optical pickup 12. In addition, the signal processing unit 15 controls the rotational drive of the magneto-optical disk 50 and controls the positioning of the optical pickup 12 by controlling the spindle motor 11 and controlling the drive mechanism that drives the optical pickup 12. . Further, the signal processing unit 15 outputs a signal indicating the strength of the external magnetic field applied by the bias magnet 13 to the magnet control unit 19.
[0037]
The ODC unit 16 performs input / output processing of various signals with respect to the host device 100 connected to the outside, and encoding / decoding processing of information signals for recording / reproducing with respect to the magneto-optical disk 50. Further, the ODC unit 16 switches the operation mode in the binarization unit 14 or changes the laser light according to the type of the magneto-optical disk 50 to be recorded and reproduced and the content of the recording / reproduction request input from the host device 100. A clock signal used as the light emission timing is generated.
[0038]
The control unit 17 is connected to each unit of the optical disc device 10 and has a function of centrally controlling the operation of the entire optical disc device 10 by comprehensively controlling the operation of each unit. The control unit 17 is configured by combining various semiconductor chips such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), for example, according to an operation program recorded in the ROM, for example. The operation of the entire apparatus 10 is controlled.
[0039]
The power control unit 18 has a function of controlling the output of the laser beam irradiated by the optical pickup 12, and the output of the laser beam is optimal according to the type and recording / reproducing characteristics of the magneto-optical disk 50 that performs recording / reproducing. The control is performed so that the output of the laser beam is optimized in accordance with the operation state such as the recording operation and the reproducing operation with respect to the magneto-optical disk 50 or the initialization operation.
[0040]
The magnet control unit 19 controls the voltage value output to the bias magnet 13 in accordance with the signal input from the signal processing unit 15, thereby controlling the intensity of the external magnetic field applied to the magneto-optical disk 50. To do.
[0041]
The optical disk apparatus 10 configured as described above performs recording / reproduction with respect to the magneto-optical disk 50 by the magnetic super-resolution method. The optical disk apparatus 10 may be configured to be able to perform recording / reproduction on not only the magneto-optical disk 50 but also various other optical disks. Further, some of the above-described units (for example, the binarization unit 14, the signal processing unit 15, and the control unit 17) may be integrally configured.
[0042]
Next, an example of an optical system provided in the optical pickup 12 will be described with reference to FIG.
[0043]
As shown in FIG. 2, the optical system provided in the optical pickup 12 includes a semiconductor laser 30 as a light source for emitting laser light, a collimator lens 31, a beam splitter 32, a mirror 33, an objective lens 34, and 1 A quarter-wave plate 35, a half-wave plate 36, a condenser lens 37, a polarization beam splitter 38, a first photodetector 39, and a second photodetector 40 are provided.
[0044]
In this optical system, the laser light emitted from the semiconductor laser 30 is converted into parallel light by the collimator lens 31, passes through the beam splitter 32, and is reflected by the mirror 33 toward the main surface of the magneto-optical disk 50. The laser beam reflected by the mirror 33 is converged by the objective lens 34 and applied to the signal recording layer of the magneto-optical disk 50. The return light reflected and returned from the signal recording layer becomes an elliptically polarized beam whose polarization plane is slightly rotated in accordance with the magnetization state of the signal recording layer at the position of the beam spot.
[0045]
The return light is converted into parallel light by the objective lens 34, reflected by the mirror 33 and incident on the beam splitter 32, reflected by the reflecting surface of the beam splitter 32, and constituted by each part after the quarter wavelength plate 35. To the detected signal system.
[0046]
The return light that has passed through the quarter-wave plate 35 enters the half-wave plate 36, is converted into a beam composed of an s-polarized beam and a p-polarized beam, and is collected by the condenser lens 37 and then the polarized beam. The light enters the splitter 38. The return light incident on the polarization beam splitter 38 is separated by the polarization plane of the polarization beam splitter 38 into a p-polarized beam traveling straight and an s-polarized beam whose traveling direction is deflected by 90 °. These p-polarized beam and s-polarized beam enter the first photodetector 39 and the second photodetector 40, respectively.
[0047]
Here, as schematically shown in FIG. 2, the first photodetector 39 and the second photodetector 40 are each configured by a photodiode having a light receiving portion divided into four. In the drawing, the four light receiving portions in the first photodetector 39 and the second photodetector 40 are respectively represented by light receiving portions 39A, 39B, 39C, 39D and light receiving portions 40A, 40B, 40C, 40D. Show. In the figure, the dividing lines between the light receiving portions 39A, 39D and the light receiving portions 39B, 39C and the dividing lines between the light receiving portions 40A, 40D and the light receiving portions 40B, 40C are recorded on the recording track of the magneto-optical disk 50. The dividing line between the light receiving units 39A and 39B and the light receiving units 39C and 39D and the dividing line between the light receiving units 40A and 40B and the light receiving units 40C and 40D correspond to the direction orthogonal to the recording track. is doing.
[0048]
In the optical pickup 12, a focus error signal EF = (A + C) − (B + D) is obtained by performing an addition / subtraction operation on the outputs A to D from the light receiving units 39A to 39D in the first photodetector 39 to obtain a focus servo circuit. To output a focus servo signal. Further, the tracking error signal ET = (A + D) − (B + C) is obtained by adjusting each output and supplied to the tracking servo circuit to output the tracking servo signal. Further, the outputs A to D from the light receiving units 39A to 39D in the first photodetector 39 and the outputs A ′ to D ′ from the light receiving units 40A to 40D in the second photodetector 40 are added and subtracted. As a result, an RF signal (A + B + C + D) − (A ′ + B ′ + C ′ + D ′) is obtained and output. The optical pickup 12 includes the above-described addition / subtraction operation circuit, focus servo circuit, and tracking servo circuit, which are not shown in FIG.
[0049]
In the optical pickup 12 configured as described above, the quarter-wave plate 35 and the half-wave plate 36 have a function as a phase compensation mechanism.
[0050]
By the way, the optical disk apparatus 10 is an apparatus that performs recording / reproduction with respect to the magneto-optical disk 50 by the magnetic super-resolution method. Is also considered large. Therefore, the noise component included in the laser light itself is increased compared to that during normal recording / reproduction, and the influence of this noise component on the RF signal obtained by converting the return light from the optical disc becomes significant. Further, when the output of the laser light is increased, minute scratches generated on the reading surface of the optical disk, optical phase distortion components generated on the disk substrate itself formed of polycarbonate, etc., the signal recording layer The influence of an optical phase distortion component caused by physical distortion or an optical phase distortion component accompanying a temperature change on the RF signal becomes significant.
[0051]
For this reason, it is important to adjust the phase of the optical system in the optical pickup 12 with high accuracy in order to suppress the influence of the above-described factors and obtain a high-quality reproduction signal. Therefore, a specific example of a technique for adjusting the phase of the optical system of the optical pickup 12 described above by applying the present invention will be described below.
[0052]
At this time, an adjustment optical disk 60 as shown in FIG. 3 is prepared. The adjustment optical disk 60 has the same configuration as the magneto-optical disk 50 to be recorded and reproduced by the optical pickup 12. FIG. 3 is a plan view of the adjustment optical disc 60 as seen from the main surface side. The adjustment optical disc 60 has a chucking hub 62 formed at the center of a disc-shaped signal recording surface 61.
[0053]
In addition, as shown in FIG. 4, the adjustment optical disk 60 is physically scratched on the disk substrate or the cover layer serving as the laser light incident surface, or mixed between the signal recording layer and the disk substrate or cover layer. It has the collar part 65 formed with foreign materials, such as a dust. FIG. 4 is an enlarged view of the main part showing the encircled part indicated by arrow A in FIG.
[0054]
As shown in FIG. 4, the adjustment optical disc 60 has a plurality of recording tracks 66 formed on the signal recording layer, and information signals are recorded along these recording tracks. Since the reflected light amount of the laser beam greatly fluctuates in the recording track at the existing part, recording / reproduction at this part is not possible.
[0055]
Further, in the peripheral region of the collar portion 65 indicated by the arrow B in FIG. 4, although the reflected light quantity of the laser beam does not vary, stress is generated on the incident surface of the laser beam due to the influence of the collar portion 65. This causes an optical phase abnormality. For this reason, in the peripheral region of the collar portion 65, the RF signal obtained at the time of reproduction varies. Hereinafter, the peripheral region of the collar portion 65 indicated by the arrow B in FIG. 4 is referred to as a “phase abnormality region” for convenience.
[0056]
Here, FIG. 5 shows an example of the output waveform of the RF signal obtained when the recording track (recording tracks 66a, 66b, 66c in FIG. 4) existing at the position of the collar 65 is reproduced by the optical disc apparatus 10. Show. In this recording track, the amount of the return light greatly fluctuates at the position of the collar 65, so that the waveform of the RF signal changes to a trapezoid as shown by an arrow C in FIG. That is, a section indicated by an arrow C in FIG. 5 corresponds to a section where the flange portion 65 exists in this recording track.
[0057]
Therefore, normal recording / reproduction cannot be performed at the position of the flange 65 in the recording track. Such a recording track is excluded from the target of recording / reproducing by the defect management mechanism provided in the optical disc apparatus 10 in advance, so that recording / reproducing is not performed. As the defect management mechanism, various methods have been widely used in the past, and are out of the scope of the present invention, so detailed description thereof is omitted here.
[0058]
On the other hand, FIG. 6 shows an example of the output waveform of the RF signal obtained when the recording track (recording tracks 66d to 66h in FIG. 4) existing at the position in the phase abnormal region is reproduced by the optical disc apparatus 10. In this recording track, the waveform of the RF signal changes to a sine wave shape as indicated by an arrow D in FIG. That is, a section indicated by an arrow D in FIG. 6 corresponds to a section covering the phase abnormal region in this recording track.
[0059]
As described above, the cause of the sinusoidal change in the RF signal in the phase abnormal region is that stress is acting in the radial direction around the flange 65 in the phase abnormal region. This is presumably because a phase component obtained by synthesizing the change in the phase and the optical phase (orientation of the disc) that originally exists on the incident surface of the laser beam in the adjustment optical disc 60 acts.
[0060]
For example, when a stepped portion as shown in FIG. 7 (a) is present on the signal recording surface of the adjustment optical disc 60, the RF signal obtained during reproduction at this portion is shown in FIG. 7 (b). The output waveform is as follows. FIG. 7A is a diagram schematically showing a cross section of the adjustment optical disc 60, and is a diagram showing a laminated structure of the disc substrate 67, the signal recording layer 68, and the cover layer or the disc substrate 69. .
[0061]
That is, at the position of the end portion in the stepped portion (stepped portion 67a), the amount of return light changes, so that a large variation is seen in the RF signal as shown in FIG. 7B, but the stepped portion 67a. In the position of the smooth top at, there is no change in the amount of return light, and a normal RF signal waveform is obtained. Therefore, although recording / reproduction is hindered at the end position of the stepped portion 67a, no problem occurs in recording / reproducing at the top position of the stepped portion 67a. Therefore, when the defect management mechanism of the optical disc device 10 functions, the recording track applied to the stepped portion 67a may not be excluded from recording and reproduction.
[0062]
Therefore, when the optical phase of the optical pickup 12 is adjusted using the adjustment optical disc 60, a sinusoidal output waveform as shown in FIG. 6 is obtained from the waveforms of the RF signals as described above. Adjustment work is performed at the position of the correct recording track.
[0063]
In this adjustment operation, any recording track whose RF signal output has a sine wave shape may be selected. However, the recording track (which does not hang on the flange portion 65 and exists at a position closest to the flange portion 65 ( For example, in FIG. 4, it is desirable to select the recording track 66f or the recording track 66g). As a result, the largest change in the RF signal can be obtained, so that it becomes easy to determine the phase position to be adjusted as described below.
[0064]
The optical phase adjustment work in the optical pickup 12 is performed by repeating the reproduction of the recording track selected as described above by the optical disc apparatus 10 at the peripheral position of the phase abnormal region, while the optical pickup 12 is provided with a 1/2 as a phase compensation mechanism. This is done by rotating the wave plate 36 little by little. Then, the rotational position of the half-wave plate 36 is adjusted to a position where the change in the output signal level of the RF signal obtained at this time is minimized.
[0065]
Here, a change in the output waveform of the RF signal obtained when the half-wave plate 36 is rotated will be specifically described.
[0066]
First, an example of the output waveform of the RF signal obtained when the rotational position of the half-wave plate 36 matches the position to be adjusted is shown in FIG. The angle of the half-wave plate 36 at this time is assumed to be α ° from the reference position.
[0067]
Next, FIG. 9 shows an example of an output waveform of an RF signal obtained when the angle of the half-wave plate 36 is rotated by −x ° from the adjustment target. Note that x is a predetermined minute value. FIG. 10 shows an example of the output waveform of the RF signal obtained when the angle of the half-wave plate 36 is rotated by x ° from the adjustment target.
[0068]
As is apparent from FIGS. 8 to 10, when the rotational position of the half-wave plate 36 matches the adjustment target position, the output waveform of the obtained RF signal becomes flat, and the signal level change is minimized. . Further, when the rotational position of the half-wave plate 36 deviates from the adjustment target position, a change in the sine wave shape appears in the output waveform of the obtained RF signal, and the half-wave plate 36 in the positive and negative directions from the adjustment target position. When the angle is displaced, the change in the sine wave shape seen in the output waveform is also reversed.
[0069]
Here, the waveforms shown in FIGS. 8 to 10 show the RF signal output obtained when the adjustment optical disk 60 is played back without any information signal being recorded. Therefore, the fine fluctuations seen in the waveforms shown in FIGS. 8 to 10 are due to noise components contained in the RF signal. Here, comparing FIG. 8, FIG. 9 and FIG. 10, it is clear that the noise component is remarkably reduced when the rotational position of the half-wave plate 36 is matched with the adjustment target position. Therefore, by adjusting the half-wave plate 36 as described above, by adjusting the optical system phase of the optical pickup 12, the noise component contained in the RF signal is remarkably reduced, and the error rate is greatly reduced. Can be reduced.
[0070]
Hereinafter, a case where the above-described optical phase adjustment method is compared with a conventionally used adjustment method based on CNR will be described with reference to FIG.
[0071]
A solid line in FIG. 11 indicates a change in the signal level of the RF signal obtained when the half-wave plate 36 is rotated while performing reproduction at the position of the phase abnormality region described above, and a dotted line in FIG. A change in CNR obtained when the half-wave plate 36 is rotated is shown.
[0072]
As is clear from FIG. 11, the change in CNR is slow with respect to the rotation angle of the half-wave plate 36, and even if the half-wave plate 36 is rotated, no significant change is observed in the CNR. Wide angle range. Therefore, in the conventional adjustment method, the rotation angle of the half-wave plate 36 is set to the maximum. Also hope It is difficult to adjust to an appropriate angle β, and highly accurate phase adjustment cannot be performed.
[0073]
However, in the adjustment method to which the present invention is applied, as shown by the solid line in FIG. 11, the output signal level of the RF signal changes sharply according to the rotation angle of the half-wave plate 36, and the adjustment target The angle α can be easily determined. Therefore, the rotation angle of the half-wave plate 36 can be adjusted with high accuracy, and thereby the phase of the optical system in the optical pickup 12 can be adjusted with high accuracy.
[0074]
Therefore, by adjusting the optical phase of the optical pickup 12 by the technique to which the present invention is applied, it is possible to effectively suppress variations in the optical phase for each optical pickup 12. As a result, even if the laser light output at the time of reproduction is increased in order to cope with, for example, a magneto-optical disk of a magnetic super-resolution system or to improve the transfer rate, it can be reproduced by a specific optical disk device. A situation in which the optical disk cannot be reproduced by another optical disk device does not occur, and high compatibility between the optical disk devices can be ensured.
[0075]
As shown in FIG. 11, the adjustment target angle β of the half-wave plate 36 according to the conventional method does not match the adjustment target angle α of the half-wave plate 36 according to the method to which the present invention is applied. The angle difference between the angle α and the angle β is considered to be generated for the following reason.
[0076]
That is, in the conventional method, the optical phase on the optical disk side is not considered at all when adjusting the rotation angle of the half-wave plate 36 based on the CNR change, whereas the method to which the present invention is applied. , The rotation angle of the half-wave plate 36 is adjusted based on the level change of the RF signal obtained at the position of the phase abnormal region, and the phase of the optical pickup 12 is an optical phase distortion component on the optical disc side. It is adjusted to match the direction of a certain disc. Therefore, the angle difference between the angle α and the angle β is considered to be equal to the amount of phase shift corresponding to the azimuth of the optical disk.
[0077]
In the method to which the present invention is applied, the optical phase in the optical pickup 12 can be matched with the orientation of the optical disk, so that the noise component included in the RF signal is reduced as described with reference to FIG. Can do.
[0078]
Therefore, according to the technique to which the present invention is applied, not only can the BER (Byte Error Rate) in the optical disc apparatus 10 be improved, but also the BER unevenness that occurs in the phase abnormal region existing in the optical disc can be eliminated. Further, since the phase of the optical system in the optical pickup 12 can be adjusted with high accuracy, the output margin of the laser beam can be expanded, and stable recording and reproduction can be performed even when a larger laser beam output is used. It becomes possible.
[0079]
In the above description, as an embodiment of the present invention, the case of adjusting the phase of the optical system in the optical pickup 12 provided in the optical disk apparatus 10 that performs recording / reproduction with respect to the magneto-optical disk 50 by the magnetic super-resolution method. Although specifically described, it is needless to say that the present invention can be widely applied to an optical pickup used when recording / reproducing with respect to various optical disks.
[0080]
In the above description, the half-wave plate 36 is rotated when adjusting the phase of the optical system in the optical pickup 12, but the half-wave plate 36 is particularly targeted for phase adjustment. The phase of the optical system may be adjusted by adjusting another phase compensation mechanism provided in the optical pickup 12.
[0081]
【The invention's effect】
In the present invention, unlike the conventional method of adjusting the phase of the optical system in the optical pickup device while observing the CNR, based on the change of the output signal (RF signal) level obtained at the position of the phase abnormal region of the optical disk for adjustment. The phase of the optical system is adjusted. Since the RF signal changes abruptly in the phase abnormality region of the optical disc, the phase position to be adjusted can be determined with extremely high accuracy by adjusting the phase based on the RF signal. In addition to this point, since the phase is adjusted using a predetermined adjustment optical disk, it is possible to effectively suppress variations in the phase of each optical pickup device.
[0082]
Therefore, even when the output of the laser beam is increased in response to an increase in recording density of the optical disc or an increase in transfer rate of the optical disc apparatus, the optical pickup in which the phase of the optical system is adjusted with high accuracy according to the present invention. If the apparatus is used, the deterioration of the RF signal can be prevented, and stable and reliable recording and reproduction can be realized. In addition, according to the present invention, it is possible to effectively suppress the variation in the phase of each optical pickup device, and therefore, for example, it is possible to prevent a situation in which an optical disc that can be reproduced by a specific optical disc device cannot be reproduced by another optical disc device. Thus, compatibility between optical disk devices can be improved.
[0083]
In the present invention, since the phase is adjusted using the phase abnormality region of the adjustment optical disc, the optical system of the optical pickup apparatus after the adjustment has optical phase distortion generated in the adjustment optical disc. The phase can be adjusted in accordance with the component (the orientation of the disk).
[0084]
Therefore, even when the output of the laser beam is increased, the influence of the disk orientation on the RF signal can be suppressed, and the error rate can be prevented from deteriorating.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing an example of an optical disc apparatus that employs a phase adjustment method according to the present invention.
FIG. 2 is a schematic diagram showing an example of an optical system provided in an optical pickup mounted on the optical disc apparatus.
FIG. 3 is a schematic plan view showing an outline of an adjustment optical disk used in the phase adjustment method according to the present invention.
FIG. 4 is an enlarged view of a main part schematically showing the vicinity of a collar part present in the adjustment optical disc.
FIG. 5 is a schematic diagram showing an example of an output waveform of an RF signal obtained when a recording track existing at a position on the collar of the adjustment optical disc is reproduced.
FIG. 6 is a schematic diagram showing an example of an output waveform of an RF signal obtained when a recording track existing at a position over a phase abnormality region existing around a buttock of the optical disk for adjustment is reproduced.
7 is a diagram for explaining an example of another case of the adjustment optical disc, and FIG. 7A is an enlarged cross-sectional view of a main part showing an outline of the other collar; FIG. FIG. 7B is a schematic diagram illustrating an example of an output waveform of an RF signal obtained when a recording track existing at a position on the flange portion of the cross-sectional shape illustrated in FIG.
FIG. 8 is a schematic diagram showing an example of an output waveform of an RF signal obtained when the half-wave plate is rotated to the adjustment target position (angle α °) in the phase abnormality region of the adjustment optical disc.
FIG. 9 is a schematic diagram showing an example of an output waveform of an RF signal obtained when the half-wave plate is rotated by −x ° from the adjustment target position in the phase abnormality region of the adjustment optical disc.
FIG. 10 is a schematic diagram showing an example of an output waveform of an RF signal obtained when the half-wave plate is rotated by x ° from the adjustment target position in the phase abnormality region of the adjustment optical disc.
FIG. 11 shows changes in the signal level of the RF signal with respect to the angle of the half-wave plate in the phase adjustment method according to the present invention, and changes in the CNR with respect to the angle of the half-wave plate in the conventional phase adjustment method. It is a schematic diagram which shows.
[Explanation of symbols]
10 optical disk device, 11 spindle motor, 12 optical pickup, 30 semiconductor laser, 31 collimator lens, 32 beam splitter, 33 mirror, 34 objective lens, 35 1/4 wavelength plate, 36 1/2 wavelength plate, 37 condenser lens, 38 deflection beam splitter, 39 first optical detector, 40 second optical detector, 50 magneto-optical disk, 60 adjustment optical disk, 65 collar, 66 recording track

Claims (4)

In a phase adjustment method for adjusting the phase of an optical system in an optical pickup device that reads information recorded on the optical disc by irradiating the optical disc with light in a predetermined wavelength range and detecting return light,
The change in the output signal level obtained when a read operation is performed at the position of the phase abnormal region by the optical pickup device with respect to a predetermined adjustment optical disc having a phase abnormal region where the phase abnormality has occurred is minimized. As described above, the phase adjustment mechanism provided in the return optical system of the optical pickup device is adjusted as described above. The phase abnormality region is present in the vicinity of the physical ridge generated on the information reading surface of the adjustment optical disc and in the position closest to the ridge among the recording tracks in which the amount of return light is normal. 2. The phase adjustment method for an optical pickup device according to claim 1, wherein a recording track is selected. 2. The phase adjustment method for an optical pickup device according to claim 1, wherein the phase abnormality region is a region where a change in the output signal level in a sine wave shape is obtained when a reading operation is performed. 2. The phase of an optical pickup device according to claim 1, wherein when the change of the output signal level is minimized, the half-wave plate provided as the phase compensation mechanism is rotated about the optical axis. Adjustment method.

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