JP2943375B2 - Optical pickup and optical disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup suitable for application to, for example, detecting a signal from an optical disc, and performing tracking and focusing on the optical disc, and an optical disc apparatus having such an optical pickup.
About the installation .

[0002]

2. Description of the Related Art Hitherto, an optical pickup for detecting a signal from an optical disk and performing tracking and focusing on the optical disk has been proposed. This optical pickup is configured as shown in FIG. That is, the divergent laser light from the laser diode 3 is made incident on the beam splitter 4, the beam light reflected by the beam splitter 4 is focused and irradiated by the objective lens 2, and the beam light is imaged on the disk 1, and the disk 1 The beam light reflected by the optical system is returned to the objective lens 2 and the beam splitter 4.
Incident on the photodiode 5 through which the detection signal from the photodiode 5 is calculated to detect the signal recorded on the disk 1 and to perform tracking and focusing.

[0003] Although not shown, in FIG. 4, the tracking and focusing coils (moving coils) are arranged in the optical pickup body, and the detection signal from the photodiode 5 is calculated. The tracking error signal and the focus error signal obtained as described above are supplied. Accordingly, tracking with respect to the disk 1 is performed by moving the optical pickup body with respect to the disk 1 in the horizontal direction by the electromagnetic force F of the tracking coil as shown by an arrow x in FIG. Focusing is performed by moving the optical pickup main body in the vertical direction with respect to the disk 1 by the electromagnetic force F of the focusing coil as shown by an arrow y in FIG.

[0004]

By the way, in the conventional optical pickup, astigmatism occurs when the tracking field of view is changed. In FIG. 6, when the objective lens 2 is at the position shown by the solid line, the image forming point of the light beam on the disc 1 is denoted by O.
O ″ is the imaging point of the light beam on the disk 1 at the position shown by the broken line, and the point where the optical axis of the objective lens 2 intersects the disk 1 at the position shown by the broken line (hereinafter simply referred to as light O ') and the light beam imaging point O
The distance (field of view) from the light beam to the imaging point O ″ is Δr
The case where the imaging magnification m of the objective lens 2 is “5” is shown. In FIG. 6, when the track of the disk 1 is shifted by 120 μm from the point O to the point O ′, the distance from the image point O of the light beam to the optical axis O ′ of the objective lens is m · Δr
/ (M + 1) , that is, 100 μm, and the distance (image height) from the optical axis O ′ of the objective lens to the image point O ″ of the light beam is Δr / (m + 1) , that is, 20 μm. FIG.
The vertical axis represents the wavefront aberration (WFE: Wave Front E).
rr) (λ), and the horizontal axis shows the image height (mm). As shown by the solid line in the graph of FIG. 5, when the tracking field of view is swung, aberrations such as astigmatism (two-dot chain line), spherical aberration (dashed line), and coma (single-dot chain line) occur according to the image height. . Then, as shown by the one-dot chain line, it can be seen that the ratio of astigmatism to the total aberration shown by the solid line is large. Incidentally, when the image height is 0.1 mm, the total aberration is 0.1 mm.
056λrms. Therefore, as described above, the tracking field of view cannot be expanded due to astigmatism generated when the tracking field of view is swung, and there is a problem that tolerance cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an optical pickup capable of increasing a tracking field by reducing astigmatism generated when the tracking field is shaken and providing a tolerance, and an optical pickup having such an optical pickup.
It is intended to provide a disk device .

[0006]

As shown in FIGS. 1 to 3, for example, an optical pickup according to the present invention comprises a finite objective lens 2 for converging and irradiating light to a disk 1, and a movable fixed fixed finite objective lens 2. Unit 6 and a focusing coil 7 for displacing the movable unit 6 in the optical axis direction of the finite objective lens 2
A tracking coil 8 for displacing the movable section 6 in the radial direction of the disk 1, a correction coil 9 for displacing the movable section 6 so that the optical axis of the finite objective lens 2 is inclined, and a magnetic flux. And a magnetic flux generating means for generating the magnetic flux.
The moving coil 7 and the tracking coil 8 are
6, when placed on a plane parallel to the optical axis of the finite objective lens 2
In both cases, the correction coil 9 is the same as the tracking coil 8.
One side and partly overlaps with the tracking coil 8
And the magnetic flux generating means
Coil 7, tracking coil 8, and correction coil
9 to generate a magnetic flux .
Further, the optical disc apparatus of the present invention includes a finite objective lens 2 for converging and irradiating light toward the disc 1, a movable portion 6 to which the finite objective lens 2 is fixed, and a displacement of the movable portion 6 in the optical axis direction of the finite objective lens 2. A focusing coil 7 for causing
A tracking coil 8 for displacing the movable part 6 in the radial direction of the disk 1 and a correction coil 9 for displacing the movable part 6 so that the optical axis of the finite objective lens 2 is inclined.
Magnetic flux generating means for generating magnetic flux,
Light detecting means 5 for detecting reflected light;
Moving coil 7 and tracking coil 8
Of the finite objective lens 2 in parallel with the optical axis
The correction coil 9 is the same as the tracking coil 8.
And partly overlaps with the tracking coil 8
The magnetic flux generating means is used for focusing.
Coil 7, tracking coil 8, and correction coil 9
The finite objective lens 2 is moved in the optical axis direction and the radial direction by flowing a current based on the detection result of the light detecting means 5 to the focusing coil 7 and the tracking coil 8. And the correction coil 9
The optical axis of the finite objective lens 2 is tilted by applying a current to the finite objective lens 2.

[0007]

According to the optical pickup of the present invention described above, the truck
The movable part 6 is separated from the buckling coil 8 by a finite objective lens.
Correction coil for displacing the optical axis of the lens 2 to be inclined
9 for tracking, this correction coil
Current through the magnetic flux generating means 9
Tilting the optical axis of the finite objective lens 2 with the correction coil 9
As a result, astigmatism generated when the tracking field of view is shaken can be reduced, the tracking field of view can be widened, and tolerance can be taken. In addition, the optical disk device of the present invention described above
According to this, it is also used for correction separately from the tracking coil 8
A coil 9 is provided, and a disk
Tracks the current based on the detection result of the reflected light from 1
In addition to the current flowing through the
By flowing, when tracking, magnetic flux
A finite pair is generated by the correction coil 9 by the magnetic flux from the generating means.
Since the optical axis of the object lens 2 is tilted,
Reduces the astigmatism that occurs when
Can be spread out and tolerated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical pickup of the present invention will be described below in detail with reference to FIG. In FIG. 1A, reference numeral 6 denotes a main body of the movable portion (illustration of magnets, yokes, etc. is omitted). As shown in FIG.
The copper coil is wound to form the focusing coil 7. A current based on a signal obtained by calculating a detection signal from the photodiode 5 shown in FIG. 4 is supplied to the focusing coil 7, thereby moving the main body 6 in the vertical direction. Numeral 8 denotes a tracking coil, two of which are respectively arranged on the front side and on the opposite side of the main body 6 in this figure. The effective magnetic flux of the tracking coil 8 is as indicated by a dashed line. This tracking coil 8
Then, a current based on the signal obtained by calculating the detection signal from the photodiode 5 shown in FIG. 4 is supplied to move the main body 6 in the track direction with respect to the disk 1. Then, the correction coil 9 is arranged in front of the main body 6 and above the surface on the opposite side. This correction coil 9
Then, a predetermined current corresponding to the amount of movement when the main body 6 is moved by flowing a current to the tracking coil 8 is caused to flow. At this time, the effective magnetic flux of the correction coil 9 is as shown by a broken line, and the direction of the electromagnetic force F1 of one correction coil 9 is downward, and the direction of the electromagnetic force F2 of the other correction coil 9 is upward. Therefore, the main body 6 can be tilted (tilted in the vertical direction), that is, the objective lens 2 can be tilted. FIG. 1B shows the arrangement of the coils 7, 8 and 9 when the optical pickup is viewed from the side.

FIG. 2 shows, for example, that the numerical aperture NA of the objective lens 2 is "0.5", the imaging magnification m is "5", the distance v between the issuing point and the imaging point is 18.8 mm, Further, an image forming point on the disk 1 of light passing through the center of the objective lens 2 is O ″, an optical axis of the objective lens 2 is O ′, and an image height is an image forming point O ″ and an optical axis O ′. A case is shown in which the distance between the objective lenses 2 is set to Δθ. FIG. 3 shows a graph of the tilt characteristics of the objective lens 2 with the vertical axis representing the wavefront aberration (λ) and the horizontal axis representing Δθ. Figure 2 above
In the case of (2), as shown in FIG. 3, the case of the solid line will be described. When the image height is 0 mm, the angle Δθ for tilting the objective lens 2 is 0 degree, and the wavefront aberration at this time is 0λ. On the other hand, the case of the broken line will be described.
When tilted by 1 degree, the breaking aberration which was 0.018λ at 0 ° when tilting is not performed becomes 0.015λ, and the wavefront aberration can be reduced by 0.003λ. In the case of the dash-dot line, if the objective lens 2 is tilted by 0.3 degrees when the image height is 0.1 mm, the wavefront aberration that was 0.06λ at 0 degrees when the tilt was not tilted is 0.05λ.
And the wavefront aberration can be reduced by 0.01λ. In the case of the two-dot chain line, when the objective lens 2 is tilted by 0.6 degrees when the image height is 0.15 mm, the wavefront aberration that was 0.135λ at 0 degrees when the tilt is not tilted is 0.1λ. The wavefront aberration can be reduced by 0.035λ. As is clear from FIG. 3, in the present example, the objective lens 2 is tilted at a predetermined angle according to the tracking visual field during tracking, so that the tracking error occurs when the tracking visual field is swung during tracking. Reduces astigmatism and widens the field of view for tracking.

The present invention is not limited to the above-described embodiment, but may take various other configurations without departing from the gist of the present invention.

[0011]

According to the above-described optical pickup of the present invention , the movable portion is provided with a finite objective separately from the tracking coil.
Correction coil to displace the optical axis of the lens so that it tilts
This tracking coil is used for tracking.
By tilting the optical axis of the finite objective lens with the lens, there is an advantage that astigmatism generated when the tracking field is swung is reduced, the tracking field is widened, and the tolerance can be secured. Further, according to the optical disk device of the present invention described above,
For example, a correction coil separate from the tracking coil
And reflection from the disc by the light detection means.
The current based on the light detection result is applied to the tracking coil
Make sure that the current is supplied to the correction coil separately from the
This allows the correction coil to be used during tracking.
Since the optical axis of the objective lens is tilted,
Tracking field of view with reduced astigmatism
Has the benefit of being able to spread and tolerate.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the optical pickup of the present invention.

FIG. 2 is a diagram showing a relationship between an image height and a tilt angle for explaining an embodiment of the optical pickup of the present invention.

FIG. 3 is a graph showing a tilt characteristic of a lens for explaining an embodiment of the optical pickup of the present invention.

FIG. 4 is an explanatory diagram of occurrence of astigmatism.

FIG. 5 is a graph for explaining occurrence of astigmatism.

FIG. 6 is a graph showing a relationship between a tracking visual field and an image height.

[Explanation of symbols]

 1 Disc 2 Objective lens 9 Correction coil

Claims (2)

(57) [Claims] 1. A finite objective lens for converging and irradiating light onto a disk, a movable portion to which the finite objective lens is fixed, and a focus for displacing the movable portion in the optical axis direction of the finite objective lens. A coil, a tracking coil for displacing the movable portion in the radial direction of the disk, a correction coil for displacing the movable portion so that the optical axis of the finite objective lens is inclined, and a magnetic flux A magnetic flux generating means;
The moving coil and the tracking coil
Of the finite objective lens on a plane parallel to the optical axis
In both cases, the correction coil is the same as the tracking coil
Surface and partially overlaps the tracking coil
And the focusing coil,
For the tracking coil and the correction coil
An optical pickup characterized in that the optical pickup is configured to generate a magnetic flux . 2. A finite objective lens for converging and irradiating light onto a disk, a movable part to which the finite objective lens is fixed, and a focus for displacing the movable part in the optical axis direction of the finite objective lens. A coil, a tracking coil for displacing the movable portion in the radial direction of the disk, a correction coil for displacing the movable portion so that the optical axis of the finite objective lens is inclined, and a magnetic flux A magnetic flux generating means, and a light detecting means for detecting light reflected from the disk , wherein the focusing coil and the tracking
For the movable part, the optical axis of the finite objective lens
And the correction coil is the same as the tracking coil.
Surface and partially overlaps the tracking coil
And the focusing coil,
For the tracking coil and the correction coil
Adapted to generate a magnetic flux Te, moves the finite object lens to the optical axis direction and the radial direction by flowing a current based on the detection result of the light detecting means to said focusing coil and said tracking coil An optical disk device characterized in that the optical axis of the finite objective lens is inclined by passing a current through the correction coil.