JP2004103087A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact optical pickup device having a spherical aberration correction means for easily adjusting an optical axis. <P>SOLUTION: The optical pickup device 10 for recording and/reproducing on an optical disk 24 having a cover layer formed on a signal recording layer is provided with a collimator lens unit 18 which includes a collimator lens and a moving means constituted of a coil and a magnet between a light source 12 and an objective lens 22. When the thickness of the cover layer is deviated from a reference value and spherical aberration is caused, the collimator lens is moved back and forth along the optical axis by the moving means to cancel the caused spherical aberration. Since the collimator lens is moved in the direction of the optical axis by the moving means constituted of the coil and the magnet to cancel the spherical aberration, no new lens is necessary. Thus, the optical pickup device incorporating this moving means is made small-sized, and the adjustment of the optical axis is easy. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical pickup device, and more particularly to an optical pickup for performing recording and / or reproduction capable of correcting spherical aberration caused by a thickness of a cover layer formed on a signal recording layer of an optical disc deviating from a reference value. Equipment related.
[0002]
[Prior art]
In recent years, optical disks have been widely used as media for recording data such as video data, audio data, and computer data, and demands for higher recording densities and higher capacities for optical disks have been increasing.
[0003]
This optical disk has a cover layer that transmits light on the signal recording layer, and recording and / or reproduction is performed by irradiating the signal recording layer with light through the cover layer. The objective lens is designed so that spherical aberration on the signal recording layer is minimized when the thickness of the cover layer is a reference value (standard value of the standard value of the optical disc). Therefore, when the thickness of the cover layer deviates from the reference value, for example, when there are a plurality of signal recording layers on one side, or when there is a manufacturing variation in the thickness of the cover layer, spherical aberration occurs.
[0004]
As a means for correcting the spherical aberration caused by the deviation of the thickness of the cover layer from the reference value, a beam expander comprising two convex lenses or one convex lens and one concave lens is provided with a collimator lens and an objective lens. There is an optical pickup device that is disposed between lenses and adjusts the distance between these two lenses to adjust the degree of parallelism of light (for example, see Patent Document 1).
[0005]
This beam expander generates spherical aberration in advance in the light emitted from the objective lens by converting the light incident on the objective lens into convergent light or diffused light, and changes the thickness of the cover layer from a reference value by a deviation. Correct the generated spherical aberration.
[0006]
That is, when the thickness of the cover layer deviates from the reference value, the emitted light is changed from parallel light to diffused light or convergent light by the beam expander. For example, when the thickness of the cover layer is small, convergent light is incident on the objective lens, thereby canceling the spherical aberration generated by the objective lens by the spherical aberration caused by the thin cover layer, and The recording layer has almost no aberration.
[0007]
[Patent Document 1]
JP-A-2002-170276 (page 3-4, FIG. 2-3)
[0008]
[Problems to be solved by the invention]
However, when the beam expander is arranged in the optical pickup device, there is a problem that the entire optical pickup device becomes very large. Also, by disposing the beam expander, the optical pickup device uses two more lenses, so that there is a problem that the adjustment of the optical axis becomes complicated.
[0009]
SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an optical pickup device which is small and has a spherical aberration correcting means whose optical axis can be easily adjusted.
[0010]
[Means for Solving the Problems]
The present invention relates to an optical pickup device for performing recording and / or reproduction of an optical disk having a cover layer formed on a signal recording layer, wherein the light source transmits light from the light source through the cover layer to the signal recording layer. An optical pickup device comprising: an objective lens for condensing light; a collimator lens disposed between the light source and the objective lens; and moving means for moving the collimator lens along the optical axis.
[0011]
[Action]
The optical pickup device includes a light source, an objective lens for condensing light from the light source on a signal recording layer of the optical disc having a cover layer, a collimator lens disposed between the light source and the objective lens, and a collimator lens. Transportation means. In order to suppress the spherical aberration that occurs when the thickness of the cover layer deviates from the reference value, the moving means moves the collimator lens back and forth in the optical axis direction so that the light incident on the objective lens becomes diffused light or convergent light. I do. Then, spherical aberration is generated in the direction opposite to the spherical aberration caused by the deviation of the thickness of the cover layer from the reference value, and these spherical aberrations cancel each other, thereby suppressing the spherical aberration.
[0012]
Preferably, the moving means includes a first drive coil wound around the collimator lens in a direction orthogonal to the optical axis, and a magnet arranged so that a magnetic field acts on the first drive coil. When a current flows through the first drive coil, the first drive coil receives a force in the optical axis direction from the magnetic field. For this reason, the spherical aberration can be suppressed by moving the collimator lens back and forth along the optical axis to make the light incident on the objective lens diffused light or convergent light.
[0013]
In addition, it is preferable that the optical pickup device further includes a temperature sensor that measures an ambient temperature of the light source, and that the moving unit moves the collimator lens according to the temperature measured by the temperature sensor. The wavelength of the light from the light source fluctuates depending on the ambient temperature of the light source, and the refractive index of the cover layer also changes according to the wavelength, so that spherical aberration occurs. Therefore, the spherical aberration is suppressed by moving the collimator lens along the optical axis based on the ambient temperature of the light source obtained by the temperature sensor.
[0014]
Further, it is preferable that the optical pickup device includes an output sensor that measures the output of the light source. The output of the light source changes the wavelength of the light from the light source, and the refractive index of the cover layer also changes according to the wavelength, so that spherical aberration occurs. Therefore, the spherical aberration is suppressed by moving the collimator lens along the optical axis based on the output of the light source obtained by the output sensor.
[0015]
Further, in the optical pickup device, it is preferable that the collimator lens is moved by the moving means in accordance with the position information of the objective lens in the optical axis direction. If the objective lens is moved in order to focus on the signal recording layer of the optical disc, the distance between the objective lens and the collimator lens changes, and spherical aberration occurs. Therefore, the optical pickup device has a function of calculating position information in the optical axis direction, which is the focus direction of the objective lens, from the focus drive voltage and the voltage sensitivity of the actuator for driving the objective lens, and suppresses spherical aberration.
[0016]
Further, it is preferable that the optical pickup device further includes a radial direction driving unit that tilts the collimator lens in a radial direction of the optical disk. When the collimator lens is tilted in the radial direction of the optical disk, the tilt of the collimator lens is corrected by using the radial direction driving means to prevent coma from occurring.
[0017]
In the radial driving means, two coils wound in opposite directions are arranged to face each other across the optical axis in a direction parallel to the main surface of the optical disc, and a magnetic field acts on these coils. It is preferable that the magnet is arranged as described above. Since these two coils are wound in opposite directions, they flow in opposite directions when current flows. When a magnetic field from a magnet acts on this current, forces opposite to each other act on the two coils in the direction of the optical axis, so that the collimator lenses are also pulled in opposite directions in the radial direction of the optical disk.
[0018]
It is preferable that the optical pickup device further includes a tangential direction drive unit that tilts the collimator lens in the tangential direction of the optical disk. When the collimator lens is inclined in the tangential direction of the optical disk, the inclination of the collimator lens is corrected by using the tangential direction driving means to prevent coma aberration.
[0019]
In the tangential direction driving means, two coils wound in opposite directions are arranged opposite to each other across the optical axis in a direction perpendicular to the main surface of the optical disk, and a magnetic field acts on these coils. It is preferable that the configuration is such that the magnet is arranged so as to perform the operation. Since these two coils are wound in opposite directions, they flow in opposite directions when current flows. When a magnetic field from a magnet acts on this current, forces opposite to each other act on the two coils in the optical axis direction, so that the collimator lenses are also pulled in opposite directions in the tangential direction of the optical disk.
[0020]
【The invention's effect】
According to the present invention, in order to correct the spherical aberration due to the deviation of the cover layer from the reference value, it is only necessary to newly incorporate a moving means for moving the collimator lens along the optical axis. it can. Further, since a new lens for correcting spherical aberration is not required, adjustment of the optical axis can be easily performed.
[0021]
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.
[0022]
【Example】
With reference to FIG. 1, an embodiment of an optical pickup device 10 used for recording and reproduction of an optical disk will be described. FIG. 1 shows a perspective view, a plan view, and a side view of the optical pickup device. Linearly polarized laser light emitted from a semiconductor laser 12 as a light source passes through a polarization beam splitter 14 and is converted into circularly polarized light by a quarter-wave plate 16.
[0023]
The laser light converted into the circularly polarized light is converted into parallel light by a collimator lens incorporated in the collimator lens unit 18. The collimator lens unit 18 can move back and forth along the optical axis of the laser light. Details of the structure will be described later.
[0024]
The collimated laser light is then reflected by the 45-degree reflecting mirror 20 in the direction in which the objective lens 22 is disposed, and is focused on the signal recording layer of the optical disc 24 by the objective lens 22.
[0025]
Then, the circularly polarized laser light reflected by the optical disk 24 is reflected again by the 45-degree reflecting mirror 20, passes through the collimator lens incorporated in the collimator lens unit 18, and is further initially transmitted by the 波長 wavelength plate 16. Is converted into linearly polarized laser light rotated by 90 degrees with respect to the polarization direction. This laser light is reflected by the polarizing beam splitter 14 in a direction making an angle of 90 degrees with the incident direction.
[0026]
The reflected light is incident on a photodetector 30 via a condenser lens 26 and a cylindrical lens 28 that causes astigmatism so that focus servo can be performed. The photodetector 30 includes a photodiode, and outputs an output signal corresponding to the intensity of the incident light.
[0027]
With reference to FIGS. 2 to 4, a relationship between spherical aberration generated when the thickness of the cover layer of the optical disc 24 deviates from the reference value and incident light incident on the objective lens 22 in order to correct the spherical aberration. Will be described.
[0028]
First, referring to FIG. 2A, when parallel light is incident on the objective lens 22, the parallel light passes through the cover layer 32a from the disk surface 24a, and the first signal recording layer 24b close to the disk surface 24a. When the objective lens 24 is designed to focus light on the first signal recording layer 24b, the spherical aberration of the spot light focused on the first signal recording layer 24b is minimized.
[0029]
As shown in FIG. 2B, when the parallel light is condensed on the second signal recording layer 24c located at a position deeper than the first signal recording layer 24b by using the objective lens 22, the value becomes smaller than the reference value. Since the light passes through the thick cover layers 32a and 32b, spherical aberration occurs. Therefore, if the incident light to the objective lens 22 is diffused light, spherical aberration that almost cancels out this spherical aberration occurs, and the spherical aberration of the spot light focused on the second signal recording layer 24c can be suppressed. .
[0030]
Next, referring to FIG. 3A, when parallel light enters the objective lens 22, the parallel light passes through the cover layers 32a and 32b from the disk surface 24a and condenses on the second signal recording layer 24c. In the case where the objective lens 22 is designed to perform the operation, the spherical aberration of the spot light is minimized in the second signal recording layer 24c.
[0031]
When the objective lens 22 is used to focus light on the first signal recording layer 24b as shown in FIG. 3B, spherical aberration occurs because the cover layer 32a through which the parallel light passes is thin. . Therefore, if the incident light on the objective lens 22 is converged light, spherical aberration occurs that almost cancels out the spherical aberration, and the spherical aberration of the spot light focused on the first signal recording layer 24b can be suppressed. .
[0032]
Further, referring to FIG. 4A, when parallel light is made incident on the objective lens 22, the parallel light is applied to the cover layer 32b between the first signal recording layer 24b and the second signal recording layer 24c. When the objective lens 22 is designed to converge light to the intermediate position 24d, the spherical aberration of the spot light becomes minimum at the intermediate thickness position 24d.
[0033]
When the objective lens 22 is used to collect light on the first signal recording layer 24b as shown in FIG. 4B, the incident light passes through the cover layer 32a thinner than the reference value. Therefore, spherical aberration occurs in the first signal recording layer 24b. At this time, if the light incident on the objective lens 22 is converted into convergent light, a spherical aberration that almost cancels out the spherical aberration occurs. Therefore, the spherical aberration of the spot light focused on the first signal recording layer 24b is suppressed. Can be.
[0034]
Further, as shown in FIG. 4C, when the light is focused on the second signal recording layer 24c, the incident light passes through the cover layers 32a and 32b which are thicker than the reference value. Spherical aberration occurs in the layer 24c. At this time, if the light incident on the objective lens 22 is made into diffused light, a spherical aberration that almost cancels out the spherical aberration occurs. Therefore, the spherical aberration of the spot light focused on the second signal recording layer 24c is suppressed. Can be.
[0035]
Thus, by suppressing the spherical aberration by using the incident light to the objective lens 22 as convergent light or diffused light, it is possible to reduce the deterioration of the recording and / or reproducing characteristics.
[0036]
Note that the thickness of the cover layers 32a and 32b of the optical disc 24 may deviate from the reference value due to variations in the film thickness at the time of manufacturing the optical disc 24. In this case as well, the spherical aberration can be suppressed.
[0037]
Further, when the temperature, output, and the like of the semiconductor laser as the light source fluctuate, the wavelength slightly fluctuates accordingly. At this time, since the refractive index of the cover layer of the optical disk 24 corresponding to the wavelength of the laser beam also changes, a spherical aberration occurs. In this case, the spherical aberration can be similarly suppressed.
[0038]
Next, with reference to FIG. 5, it will be described that incident light to the objective lens 22 becomes parallel light, diffused light, and convergent light depending on the position of the collimator lens 34. Here, the position of the light source 12 and the position of the objective lens 22 are fixed, and only the collimator lens 34 can move back and forth in the optical axis direction. Further, a is the focal length on the emission side (rear focal length) of the objective lens 22, and b is the focal length on the incident side (front focal length) of the objective lens 22.
[0039]
The middle part of FIG. 5 shows a case where the thickness of the cover layer of the optical disc is a reference value. At this time, the position of the collimator lens 34 is located on the side of the objective lens 22 away from the light source 12 by the focal length of the collimator lens 34, so that the light emitted from the collimator lens 34 is parallel light.
[0040]
The upper part of FIG. 5 shows a case where the thickness of the cover layer of the optical disk is larger than a reference value. At this time, since the position of the collimator lens 34 has moved toward the light source 12 as compared with the case of the center diagram in FIG. 5, the light emitted from the collimator lens 34 is diffused light.
[0041]
The lower part of FIG. 5 shows a case where the thickness of the cover layer of the optical disc is smaller than a reference value. At this time, since the position of the collimator lens 34 has moved toward the objective lens 22 as compared with the case of the center diagram in FIG. 5, the light emitted from the collimator lens becomes convergent light.
[0042]
Next, with reference to FIG. 6, a description will be given of spherical aberration that occurs when the thickness of the cover layer of the optical disk is in the range of 70 μm to 130 μm, and a simulation result when the above-described correction is performed on the spherical aberration. Here, the reference value of the thickness of the cover layer is 100 μm, the numerical aperture NA of the objective lens is 0.85, the focal length of the objective lens is 2.35 mm, the wavelength of the laser beam is 405 nm, and the focal length of the collimator lens is 14. 1 mm.
[0043]
For example, when the thickness of the cover layer deviates from the reference value of 100 μm by ± 10 μm, that is, when the thickness of the cover layer is 110 μm or 90 μm, as shown in FIG. .1λ (“λ” is the wavelength of light, the same applies hereinafter). Generally, in order to obtain good recording / reproducing characteristics, it is said that good recording / reproducing characteristics cannot be obtained unless the amount of generated spherical aberration is suppressed to 0.07λ or less in the entire optical pickup device. When the amount of occurrence of is 0.1λ, good recording / reproducing characteristics cannot be obtained.
[0044]
Therefore, in this case, when the collimator lens is moved back and forth in the optical axis direction and the light emitted from the collimator lens is corrected to be diffuse light or convergent light, FIG. 005λ or less, it can be seen that it can be greatly suppressed as compared with the case where no correction is performed. As described above, it is considered that the recording / reproducing characteristics are hardly affected if the spherical aberration is 0.005λ or less.
[0045]
For example, when the reference value of the cover layer of the optical disk is 100 μm, the amount of movement of the collimator lens required to correct spherical aberration is obtained. Here, the moving amount is considered based on a position where the collimator lens emits parallel light, that is, a position which is away from the light emitting point toward the objective lens by a focal length of the collimator.
[0046]
As shown in FIG. 6, for example, when the thickness of the cover layer is increased by 10 μm to 110 μm, it is necessary to move the collimator lens by 0.1835 mm, that is, −0.1835 mm to the light emitting point side. When the thickness of the cover layer is reduced by 10 μm to 90 μm, the cover layer may be moved toward the objective lens by 0.1707 mm, that is, +0.1707 mm. As described above, it can be seen that the collimator lens unit should be driven based on the graph of FIG. 6 to cancel out the spherical aberration caused by the deviation of the thickness of the cover layer from the reference value by the correction.
[0047]
Next, the structure of the collimator lens unit 18 and the operation principle thereof will be described with reference to FIG. The collimator lens unit 18 includes a movable portion 44. The movable portion 44 includes a collimator lens holder 36 in which the collimator lens 34 is fitted, a first drive coil 38 disposed around the collimator lens holder 36, and a second It comprises a drive coil 40 and a third drive coil 42.
[0048]
The first drive coil 38 is wound around the outer periphery of the collimator lens holder 36 at a position separated from the second drive coil 40 and the third drive coil 42 so as to be orthogonal to the optical axis.
[0049]
Next, in the second drive coil 40, two coils 40a and 40b are arranged to face each other with the optical axis therebetween in the Y direction which is a direction parallel to the main surface of the optical disc, and are opposite to each other. It is wound and connected.
[0050]
In the third drive coil 42, two coils 42a and 42b are arranged to face each other with the optical axis therebetween in the Z direction which is a direction perpendicular to the main surface of the optical disk, and are wound in opposite directions. Connected. The outer periphery of the collimator lens holder 36 is surrounded by the two coils 40a and 40b of the second drive coil 40 and the two coils 42a and 42b of the third drive coil 42.
[0051]
Further, a magnet 46 is arranged so as to surround the entire outer peripheral portion of the movable portion 44, and the magnet 46 is divided into four parts corresponding to the second drive coil 40 and the third drive coil 42. When the inner peripheral surface of the magnet is, for example, the south pole, the outer peripheral surface is the north pole. At this time, the direction of the magnetic field generated by the magnet is perpendicular to the optical axis and radially from the inner peripheral side toward the outer peripheral side. It is the direction to go out.
[0052]
The yoke 48 includes a cylindrical outer wall and a cylindrical inner wall formed concentrically with the outer wall, and a magnet 46 and a movable portion 44 surrounded by the magnet 46 in the space sandwiched between the outer wall and the inner wall. Is arranged. The yoke 48 forms a magnetic circuit together with the magnet 46, and functions to increase the strength of the magnetic field generated by the magnet 46.
[0053]
Further, connection boards 50 are attached to the outer peripheral portions of the yokes 48 corresponding to the four positions where the end faces of the second drive coil 40 and the third drive coil 42 face each other. Suspension wires 52 supporting the movable part 44 are fixed to each other.
Next, the roles of the first drive coil 38, the second drive coil 40, and the third drive coil 42 will be described with reference to FIG. First, as described above, the first drive coil 38 is wound around the optical axis in a direction perpendicular to the optical axis. When a current is applied to the first drive coil 38, the direction of the current is applied to the first drive coil 38 by the Fleming left-hand rule by a radial magnetic field generated by a magnet 44 surrounding the outer periphery and orthogonal to the optical axis. The force acts in the direction of the optical axis which is a direction perpendicular to both the direction of the magnetic field and the direction of the magnetic field.
[0054]
For example, as shown in FIG. 8A, when the current flowing through the first drive coil 38 is caused to flow clockwise in the direction of the arrow, and the direction of the magnetic field is from the inner circumference to the outer circumference of the magnet 46, A force acts on the first drive coil in a direction that moves the optical axis away from the objective lens (a direction that moves away perpendicularly to the plane of the paper). Therefore, the collimator lens unit moves on the optical axis in a direction away from the objective lens, so that light emitted from the collimator lens becomes diffused light. As described above, the correction of the spherical aberration occurring on the signal recording layer of the optical disc is performed by moving the movable part back and forth on the optical axis by passing a current through the first drive coil 38.
[0055]
Next, the two coils 40a and 40b constituting the second drive coil 40 are also wound in the direction perpendicular to the optical axis, but are wound in opposite directions and connected. Therefore, when a current flows through one coil 40a, a current flows in the other coil 40b in the opposite direction. Therefore, according to Fleming's left-hand rule, pulling forces are generated in directions opposite to each other in a direction parallel to the optical axis. Therefore, since the collimator lens can be tilted in the radial direction of the optical disc, the tilt in this direction can be corrected.
[0056]
Similarly, the two coils 42a and 42b constituting the third drive coil 42 are wound in the direction perpendicular to the optical axis, but are wound in the opposite directions and connected. Therefore, when a current flows through one coil 42a, currents flow in opposite directions in the other coil 42b according to Fleming's left-hand rule, so that pulling forces are generated in directions parallel to the optical axis and in opposite directions. . Therefore, the collimator lens can be tilted in the tangential direction of the optical disc, so that the tilt in this direction can be corrected.
[0057]
The correction of the inclination of the collimator lens in the radial or tangential direction by the second drive coil 40 or the third drive coil 42 is performed when coma aberration occurs. That is, the case where the collimator lens is tilted when the collimator lens is moved by the above-described first drive coil 38, the case where the disc is tilted, or the case where an assembly error of the optical pickup device occurs. By performing this correction, coma can be reduced, so that good recording and / or reproduction can be performed.
[0058]
Next, an optical disk recording and / or reproducing apparatus 54 using the optical pickup device 10 will be described with reference to FIG. The optical disk recording and / or reproducing device 54 includes the optical pickup device 10 and further includes a signal generating circuit 56, a semiconductor laser driving circuit 58, and a computer 60.
[0059]
The optical pickup device 10 further includes a temperature sensor 62 that measures the ambient temperature of the semiconductor laser and a front monitor diode 64 that functions as an output sensor that monitors the output of the semiconductor laser 12. Sent.
[0060]
Further, a signal generation circuit 56 is connected to the photodetector 30, and the signal generation circuit 56 generates signals such as a focus error signal, a tracking error signal, and an RF signal based on an output signal from the photodetector 30, These signals are also transmitted to the computer 60.
[0061]
When the computer 60 knows from the focus error signal that the laser beam is not focused on the signal recording layer of the optical disc 24, it drives the actuator 66 of the objective lens 22 to move the objective lens 22 to the main surface of the optical disc 24. Move vertically to focus. Then, the computer 60 calculates position information of the objective lens 22 in the optical axis direction, which is the focus direction of the objective lens 22 when there is a focus, based on the focus drive voltage of the actuator 66 and the focus voltage sensitivity. Here, the position of the objective lens 22 is calculated because if the position of the objective lens 22 changes, the distance between the objective lens 22 and the collimator lens 34 changes, which affects the occurrence of spherical aberration.
[0062]
Similarly, when the tracking error signal indicates that the laser beam is off the track of the optical disk 24, the actuator 66 of the objective lens 22 is driven to move the objective lens 22 parallel to the main surface of the optical disk 24. It is moved so that the laser beam is always irradiated on the track of the optical disk 24.
[0063]
In addition, the computer 60 calculates the RF signal generated by the signal generation circuit 56, the ambient temperature of the semiconductor laser 12 measured by the temperature sensor 62, the output of the semiconductor laser 12 measured by the front monitor diode 64, and the position of the objective lens 22. The collimator lens unit 18 is controlled based on the information to correct the spherical aberration. Here, the reason why the ambient temperature and the output of the semiconductor laser 12 are necessary is that the wavelength of the laser light changes with the fluctuation of the ambient temperature or the output of the semiconductor laser 12, so that the cover layer of the optical disk 24 corresponding to the wavelength is changed. Is also changed, causing spherical aberration. The reason why the position information of the objective lens 22 is necessary is that, for example, when the optical disk 24 is warped and the objective lens 22 is moved in a direction perpendicular to the main surface of the optical disk 24 and focused, the objective lens 22 and the This is because the distance from the collimator lens in the collimator lens unit 18 changes.
[0064]
Further, the computer 60 feeds back the output of the semiconductor laser 12 from the front monitor diode 64 to the semiconductor laser drive circuit 58, and generates a strong pulsed laser beam for stabilizing the output of the semiconductor laser 12 and for recording on the optical disc 24. For example, a signal is sent to the semiconductor laser drive circuit 58 to drive the semiconductor laser 12.
[0065]
Next, a flow of processing in the collimator lens unit will be described with reference to FIG. First, in step S1, it is determined whether or not the signal recording layer on which recording and / or reproduction is performed is layer 0, which is the first signal recording layer of the disc. As a result, if it is Layer 0, coarse adjustment of the position of the collimator lens is performed as Layer 0 in Step S3. If the layer is not the layer 0, it is the layer 1 which is the second signal recording layer. Therefore, in step S5, the position of the collimator lens as the layer 1 is roughly adjusted. That is, the collimator lens is moved to a temporary position along the optical axis so that spherical aberration can be substantially canceled.
[0066]
Next, in step S7, spherical aberration generated based on temperature information of the semiconductor laser from the temperature sensor, output information of the semiconductor laser, and position information of the objective lens is obtained.
[0067]
That is, based on the temperature information of the semiconductor laser obtained from the temperature sensor, the spherical aberration ΔX is calculated by the following equations (1) and (2). _T Ask for.
[0068]
(Equation 1)
Δλ _T = A _T × ΔT (1)
Where Δλ _T : Wavelength change
ΔT: temperature change
A _T : Coefficient that changes depending on the thickness of the cover layer, the wavelength of laser light
[0069]
(Equation 2)
ΔX _T ≒ B _T × λ _T = A _T B _T × ΔT (2)
Where ΔX _T : Amount of spherical aberration generated
B _T : Coefficient that changes depending on the thickness of the cover layer, the wavelength of the laser beam, etc.
Similarly, based on the output information of the semiconductor laser obtained from the front monitor diode, the spherical aberration ΔX is calculated by the following equations (3) and (4). _p Ask for.
[0070]
[Equation 3]
Δλ _p = A _P × ΔP (3)
Where Δλ _P : Wavelength change
ΔP: output change
A _p : Coefficient that changes depending on the thickness of the cover layer, the wavelength of the laser beam, etc.
[0071]
(Equation 4)
ΔX _p ≒ B _p × λ _p = A _p B _p × ΔP (4)
Where Δ _P : Amount of spherical aberration generated
B _P : Coefficient that changes depending on the thickness of the cover layer, the wavelength of the laser beam, etc.
Further, based on the position information of the objective lens obtained from the position sensor, the spherical aberration ΔX is calculated by the following equations (5) to (9). _s Ask for.
[0072]
(Equation 5)
α = 1 / ((1 / f _CL ) + (1 / (f _CL + ΔCL))) (5)
Where f _CL : Focal length of collimator lens
ΔCL: the amount of movement from the reference position of the collimator lens (the position where the laser light emitted from the collimator lens becomes parallel light), with the objective lens side in the positive direction
[0073]
(Equation 6)
a = L−α + ΔOL (6)
Here, L: distance between the objective lens and the collimator lens
ΔOL: The amount of movement from the reference position of the objective lens (the position of the objective lens at which the laser beam focuses on the signal recording layer when the cover layer is at the reference value), with the optical disk side in the positive direction.
[0074]
(Equation 7)
b = 1 / ((1 / f _OL ) + (1 / a)) (7)
Where f _OL : Focal length of objective lens
Therefore, spherical aberration ΔX when diffused light enters the objective lens _S1 Is
[0075]
(Equation 8)
ΔX _S1 = C × (b / a) + E (8)
Here, C: a negative coefficient that varies depending on the thickness of the cover layer, the wavelength of the laser beam, and the like.
E: Coefficient that changes depending on the thickness of the cover layer, the wavelength of the laser beam, etc.
Further, spherical aberration ΔX when convergent light is incident on the objective lens _S2 Is
[0076]
(Equation 9)
ΔX _S2 = D × (b / a) + E (9)
Here, D: a positive coefficient that changes depending on the thickness of the cover layer, the wavelength of the laser beam, and the like.
Next, in order to correct the spherical aberration obtained in step S7, the collimator lens is further moved from the temporary position in step S3 or step S5 by fine adjustment in step S9. After the position of the collimator lens is determined in this way, recording and / or reproduction of the optical disk is tried in step S11. That is, the spherical aberration is obtained based on the temperature information, output information or the position information of the objective lens of the semiconductor laser obtained by the temperature sensor, the output sensor of the semiconductor laser and the position sensor of the objective lens, respectively. Then, by finely adjusting the position of the collimator lens in accordance with the obtained amount of the generated spherical aberration, the generated spherical aberration is canceled.
[0077]
Then, in step S13, it is determined whether or not the result of the trial performed in step S11 is an optimal condition. This determination is made, for example, by checking whether the reproduction result of the data recorded in step S11 is lower than a predetermined error rate.
[0078]
As a result, when it is determined that the conditions are not the optimum conditions, the position of the collimator lens is slightly shifted in step S15, and then, in step S11, recording and / or reproduction on the optical disk is tried again.
[0079]
If it is determined in step S13 that the optimum condition is satisfied, recording and / or reproduction on the optical disc are performed in step S17.
[0080]
In this processing flow, in step S1, it is determined which of the two signal recording layers is the signal recording layer. However, this processing flow is not limited to the case where the signal recording layer is the two layers. The same applies to the case of three or more layers, and also to the case where the thickness of the cover layer of the optical disc varies.
[Brief description of the drawings]
FIG. 1 is an illustrative view showing one embodiment of an optical pickup device of the present invention;
FIG. 2 is an illustrative view showing a relationship between spherical aberration and incident light of an objective lens;
FIG. 3 is an illustrative view showing a relationship between spherical aberration and incident light of an objective lens;
FIG. 4 is an illustrative view showing a relationship between spherical aberration and incident light of an objective lens;
FIG. 5 is an illustrative view showing a relationship between a position of a collimator lens and incident light of an objective lens;
FIG. 6 is an illustrative view showing a configuration of a collimator lens unit;
FIG. 7 is an illustrative view showing a principle of operation of a first drive coil, a second drive coil, and a third drive coil;
FIG. 8 is a graph showing the effect of the embodiment of FIG. 1;
FIG. 9 is a block diagram showing the overall configuration of an optical disk recording and / or reproducing apparatus including the optical pickup device of FIG. 1;
FIG. 10 is a flowchart showing the operation of the embodiment in FIG. 1;
[Explanation of symbols]
10 Optical pickup device
12 ... Semiconductor laser
18 Collimator lens unit
22 ... Objective lens
24 ... Optical disk
24a: first signal recording layer
24b... Second signal recording layer
30 ... Photodetector
32a, 32b ... cover layer
34 ... Collimator lens
38 first drive lens
40: second driving lens
42: Third drive lens
46… Magnet
60 ... Computer
62 temperature sensor
64 Front diode
66 ... actuator

Claims (9)

An optical pickup device for performing recording and / or reproduction on an optical disc having a cover layer formed on a signal recording layer,
light source,
An objective lens that transmits light from the light source through the cover layer and condenses the light on the signal recording layer;
An optical pickup device comprising: a collimator lens disposed between the light source and the objective lens; and a moving unit that moves the collimator lens along an optical axis. The moving means includes a first drive coil wound around the collimator lens in a direction orthogonal to the optical axis, and a magnet arranged so that a magnetic field acts on the first drive coil. The optical pickup device according to claim 1, wherein the collimator lens is moved along the optical axis by passing a current through one drive coil. The optical pickup device according to claim 1, further comprising a temperature sensor that measures an ambient temperature of the light source, wherein the moving unit moves the collimator lens according to the temperature measured by the temperature sensor. 4. The optical pickup device according to claim 1, further comprising an output sensor that measures an output of the light source, wherein the moving unit moves the collimator lens according to an output measured by the output sensor. 5. The optical pickup device according to claim 1, wherein said collimator lens is moved by said moving means in accordance with positional information of said objective lens in the optical axis direction. 6. The optical pickup device according to claim 1, further comprising a radial direction driving unit that tilts the collimator lens in a radial direction of the optical disc. The radial drive means includes two coils wound in opposite directions, a second drive coil opposed to the main surface of the optical disc across the optical axis, and a magnetic field applied to the second drive coil. And the magnets arranged so as to act on each other, and by causing a current to flow through the second drive coil, two coils constituting the second drive coil generate forces opposite to each other in the radial direction of the optical disc. The optical pickup device according to claim 6, wherein: The optical pickup device according to claim 1, further comprising a tangential direction driving unit that tilts the collimator lens in a tangential direction of the optical disc. The tangential direction driving means includes two coils wound in opposite directions, a third driving coil opposed to the main surface of the optical disc across the optical axis, and a magnetic field applied to the third driving coil. And the magnets arranged so as to act on each other, and by applying a current to the third drive coil, forces opposite to each other in the tangential direction of the optical disk are applied to two coils constituting the third drive coil. The optical pickup device according to claim 8, wherein the optical pickup device generates the following.

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