JPH11273123A - Optical head device - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide an optical pickup having a high frequency response performance with a simple configuration. An optical head device is provided on a track of a recording medium on a disk drive device so as to be movable in a radial direction. The optical head device 15 includes the disc tilt sensor 12, and the beam from the LED 13 is reflected by the recording medium 7 and received by the photo sensor 14. The light emitted from the light source 1 is converted into a parallel beam 5 by the collimator lens 2 and transmitted through the beam splitter 3, and then the traveling direction is changed from the x-axis direction to the y-axis direction by the galvanometer mirror 4. The objective lens 6 has a third-order coma aberration component (Lc) of wavefront aberration in which a light beam incident on the objective lens varies due to off-axis incidence at a unit angle, and a light beam incident on the objective lens varies due to off-axis incidence at a unit angle. For the third-order astigmatism component (La) of the wavefront aberration, | Lc | / | La | <0.3
To be satisfied. The light beam 5 reflected by the recording medium 7 enters a photodetector 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording or reproducing information on or from an optical information recording medium.

[0002]

2. Description of the Related Art In recent years, optical disks have attracted attention as large-capacity information memories. Under such circumstances, it has become necessary for the optical head device to respond to the demand for higher density of the optical disk. For this purpose, it is important to reduce the diameter of the light spot used for recording and reproduction to reduce aberration. For this purpose, it is necessary to set the optical axis of the objective lens of the optical head device to be perpendicular to the optical disk so as to minimize the occurrence of coma.

However, when a tilt of the disk surface due to deformation of the optical disk or so-called disk tilt occurs,
The perpendicularity of the optical head to the recording surface of the optical disk is lost, and coma occurs in the light spot, so that the objective lens cannot exhibit its original performance. Therefore, not only the conventional focus control and tracking control but also control means for reducing coma aberration by some method is required. Various types of objective lens driving devices provided with the control means have been proposed.

Here, a conventional optical disk device having a disk tilt control will be described with reference to FIG.
As shown in FIG. 9, an optical information recording medium 26 is set on a disk drive means 27, and information is recorded and reproduced on tracks of the optical information recording medium 26.
The optical head device 24 is provided so as to be movable in the radial direction of the optical information recording medium 26, and the optical head device 24 is driven by driving means (not shown) of the optical head device 24. Further, the optical disc device 24 is configured such that the movable portion 23 controls the optical information recording medium 26
Can be changed in the radial direction. The optical head device 24 is provided with a disc tilt sensor 29. The beam emitted from the LED 28 is reflected by the optical information recording medium 26 and received by the two-part photo sensor 30. The balance of the amount of light received by the two-divided photo sensor 30 changes due to the tilt of the optical information recording medium 26, and the amount of tilt can be detected (hereinafter referred to as Conventional Example 1).

[0005]

However, Conventional Example 1
The radial tilt servo as shown in (1) is not suitable for obtaining a high-speed response performance because the entire pickup optical system is tilted as described above, but the tilt of the disk in the radial direction is from the inner circumference of the disk to the outer circumference. Is usually a gentle, monotonous surface warp towards
Fast response was not required and was not particularly problematic.

However, in a system that handles a high-density optical disk signal in which a tilt in the tangential direction immediately deteriorates the signal quality, it is necessary to correct the tangential tilt in addition to the radial tilt. The frequency component of the tilt in the tangential direction is higher than the rotation cycle of the disk, and the servo is required to have a much higher frequency response performance than the radial direction.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical pickup having a high frequency response performance with a simple configuration.

[0008]

In order to solve this problem, an optical head device according to the present invention comprises: an optical unit for emitting a light beam for optical recording and reproduction; A condensing means for condensing and irradiating a light spot on a recording medium to perform optical recording and reproduction, and the optical information recording of the light spot by a reflected light beam from the optical information recording medium during the optical recording and reproduction Means for driving and controlling the focusing means in the focusing direction and the tracking direction based on information on the focusing error and the tracking error with respect to the medium. The objective lens used for the focusing means has the following condition: | Lc | / | La | <0.3 (1) where Lc is a third-order coma component of wavefront aberration in which the light beam incident on the objective lens varies due to off-axis incidence at a unit angle. a: the luminous flux incident on the objective lens satisfies the third-order astigmatism component of wavefront aberration that fluctuates due to off-axis incidence at a unit angle, and the tilt of the optical information recording medium detected by the tilt detecting means And a control means for inclining the optical axis incident on the objective lens according to the above.

Preferably, the control means for tilting the optical axis uses a galvanomirror.

[0010] Alternatively, it is preferable that a control means for decentering the optical means for emitting the light beam for optical recording and reproduction is provided as the control means for tilting the optical axis.

Alternatively, it is preferable that a plurality of collimating lenses are provided as control means for tilting the optical axis, and a control means for decentering one of the collimating lenses is provided.

Alternatively, it is preferable that a control unit for tilting a prism provided in the light beam is provided as a control unit for tilting the optical axis.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The objective lens provided in the optical head device of the present invention has the following conditions: | Lc | / | La | <0.3 (1) where Lc is a unit of a light beam incident on the objective lens. A third-order coma aberration component of wavefront aberration that fluctuates due to off-axis incidence of an angle; By decentering the angle of incidence of the light beam incident on the objective lens according to the degree of tilt of the optical disk, the coma aberration is intentionally fluctuated, and the disk aberration is generated by the intentionally generated coma aberration. The correction is performed so as to reduce the coma caused by the tilt.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

Embodiment 1 FIG. 1 is a schematic view of an optical head according to a first embodiment of the present invention.

First, the optical information recording medium 7 is set on the disk drive device 11, and in order to record and reproduce information on the track of the optical information recording medium 7, the optical head device 15 is used. The optical head device 15 is provided so as to be movable in the radial direction of the recording medium 7, and is driven by driving means (not shown) of the optical head device. The optical head device 15 is provided with a disc tilt sensor 12. The beam emitted from the LED 13 is reflected by the optical information recording medium 7,
4 is received.

Next, light emitted from a laser diode 1 (for example, having an oscillation wavelength of 660 nm) as a light source is converted into a parallel light beam 5 by a collimating lens 2. After passing through the beam splitter 3, the traveling direction of the parallel light 5 is changed from the X-axis direction to the Y-axis direction by the galvanometer mirror 4.

An objective lens 6 is provided as a means for condensing the light beam 5, and the light beam 5 condensed by the objective lens 6 is irradiated on the surface of the optical information recording medium 7 as a minute light spot. You. This light spot enables information recording and reproduction.

The light beam 5 reflected by the optical information recording medium 7 is condensed by a detection lens 8 via a galvanomirror 4 and a beam splitter 3, and then condensed by a photodetector 9.
Is incident on. The photodetector 9 detects an information signal recorded on the optical information recording medium 7 from the incident light, and detects a focusing direction control signal and a tracking direction error signal.

The galvanomirror is supported by a biaxial tilt actuator 10, and can change the optical axis of the light beam 5 in the tangential direction and the radial direction of the disk.

Next, the specific objective lens 6 is shown in (Table 1).
Here is a numerical example. The optical information recording medium 7 is a parallel flat plate, the design wavelength is 660 nm, the thickness of the disk is 1.2 mm, and the refractive index is 1.56.

[0022]

[Table 1]

As shown in the aberration diagram of the objective lens 6 in FIG. 2, since the sine condition in FIG. 3A is under as shown in FIG. 3B, the objective lens 6 shown in FIG. It can be seen from the graph of the incident angle of the light beam 5 that coma aberration occurs off-axis. In addition, for an angle shift of about 0.4 degree, the generated aberration is almost coma, and other aberrations (such as astigmatism and spherical aberration) hardly contribute.

FIG. 4 shows a change in each aberration at a light spot when only the optical information recording medium 7 is inclined.
As shown in FIG. 4, when the optical information recording medium 7 is tilted, only the coma aberration fluctuates, and the fluctuation amount is 7 per unit angle.
0 mλ.

From this, the inclination angle direction of the galvanometer mirror 4 is controlled by the amount and direction of the coma aberration generated by the tilt of the optical information recording medium 7, and the coma aberration generated by the inclination of the optical information recording medium 7 is controlled. It can be seen that it is sufficient to cancel.

FIG. 5 shows a specific example. In this optical system, it is assumed that there is no aberration on the spot when the optical information recording medium is installed perpendicular to the optical axis of the objective lens. It is assumed that the optical information recording medium 7 has a tilt of 0.4 ° in the direction shown in FIG. 5 near a point on the spot emitted from the objective lens 6 due to deformation of the optical disk or the like.

At this time, according to the graph of the dependency of the objective lens on the tilt angle of the disk shown in FIG. 4, the coma aberration is 27.5.
mλ occurs. At this time, the disc tilt sensor 12
The light emitted from the LED 13 is reflected by the optical information recording medium 7 and received by the four-divided photodetector 14. However, since the optical information recording medium 7 is tilted, the light reception of each cell of the four-divided photodetector 14 is performed. The amount balance changes, and the direction and magnitude of the tilt of the optical information recording medium 7 are detected. A control signal is sent to the biaxial tilt actuator 10 based on the detection signal.

As can be seen from FIG. 3, since the coma aberration can be canceled by inclining the light beam toward the 0.37 ° objective lens, the biaxial tilt actuator can rotate the 0.19 ° galvanometer mirror 4 in the direction shown in FIG. By sending a control signal to 10,
Coma can be canceled. Incidentally, even if the inclination of the optical information recording medium 7 is not the radial direction but the tangential direction, it is needless to say that the coma aberration can be canceled by the same procedure.

When the tilt control is performed, FIG.
According to the relationship from FIG. 4 and the graph of FIG.
Is less than 0.5 °, even if coma is completely eliminated, astigmatism will be less than 10 mλ and signal quality will not be significantly degraded.

Further, the galvanometer mirror 4 is connected to the objective lens 6.
, It is possible to suppress fluctuations in the intensity distribution of spots coming out of the objective lens 6 due to fluctuations in the optical axis during tilt control.

In the first embodiment, as means for detecting the inclination of the optical information medium 7, the disc tilt sensor 1 is used.
2, the same effect can be obtained even if the inclination is detected from the fluctuation of the signal detected from the optical information medium 7 due to the inclination of the optical information medium 7 (for example, jitter fluctuation of the RF signal). Needless to say.

Embodiment 2 FIG. 6 is a schematic view of an optical head according to a second embodiment of the present invention.

In FIG. 5 described in the first embodiment, a reflection mirror 16 is provided in place of the galvanometer mirror 4, and the laser diode 1 is supported by a biaxial actuator 17 so that a control means for tilting the optical axis is provided. Is provided.

As in the first embodiment, when the optical information recording medium 7 is tilted in the direction shown in FIG. 6 due to deformation of the optical disk or the like, the biaxial actuator 17 is eccentric to the laser diode 1 in the direction shown in FIG. When the control signal is sent to the camera, coma aberration can be eliminated.

(Embodiment 3) FIG. 7 is a schematic view of an optical head according to a third embodiment of the present invention.

Instead of the collimating lens 2 in FIG. 6 described in the second embodiment, two groups of collimating lenses 18 and 1 are used.
The collimating lens 19 is provided with control means for decentering the optical axis by being supported by a biaxial actuator 20.

As in the case of the second embodiment, when the optical information recording medium 7 is tilted in the direction shown in FIG. 6 due to deformation of the optical disk or the like, the biaxial actuator 20 is decentered in the direction shown in FIG. When the control signal is sent to the camera, coma aberration can be eliminated.

(Embodiment 4) FIG. 8 is a schematic view of an optical head according to a fourth embodiment of the present invention.

In FIG. 5 described in the first embodiment, a reflecting mirror 16 is provided instead of the galvanometer mirror 4, a wedge-shaped prism 21 is inserted between the beam splitter 3 and the reflecting mirror 4, and a biaxial tilt actuator 22 is provided. And a control means for decentering the optical axis.

As in the first embodiment, when the optical information recording medium 7 is tilted in the direction shown in FIG. 6 due to deformation of the optical disk or the like, the two-axis actuator eccentrically moves the wedge prism 21 in the direction shown in FIG. If a control signal is sent to 22, the coma aberration can be eliminated.

[0041]

As described above, according to the optical head device of the present invention, it is sufficient that the mirror for decentering the light beam has a structure that can be tilted in two axial directions, and the entire optical head device is tilted for correction. Since the mass of the object to be controlled can be reduced compared to the conventional method, a high frequency response performance, which was impossible in the past, can be obtained, and the tilt servo in the tangential direction can be realized at a low price, light weight and small size. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical head device as one embodiment of the present invention.

FIGS. 2A and 2B are aberration diagrams of an objective lens 6 used in an optical head device as one embodiment of the present invention. FIG. 2A shows a sine condition. FIG. 2B shows astigmatism.

FIG. 3 is a diagram showing a change in each aberration when an incident angle of a light beam of an objective lens 6 is tilted in the optical head device according to one embodiment of the present invention.

FIG. 4 is a diagram showing a change in each aberration when the optical information recording medium 7 is tilted in the optical head device according to one embodiment of the present invention.

FIG. 5 is a schematic diagram of tilt control in the optical head device according to the first embodiment.

FIG. 6 is a schematic diagram of tilt control in the optical head device according to the second embodiment.

FIG. 7 is a schematic diagram of tilt control in the optical head device according to the third embodiment.

FIG. 8 is a schematic diagram of tilt control in an optical head device according to a fourth embodiment.

FIG. 9 is a schematic diagram of an optical head device as Conventional Example 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser diode 2 collimating lens 3 beam splitter 4 galvanometer mirror 4 5 light beam 6 objective lens 7 optical information recording medium 8 detection lens 9 photodetector 10 two-axis tilt actuator 11 disk drive device 12 disk tilt sensor 13 LED 14 quadruple photosensor Reference Signs List 15 optical head device 16 reflection mirror 17 two-axis actuator 18, 19 two-group collimating lens 20 two-axis actuator 21 wedge prism 22 two-axis tilt actuator 23 (optical head device) movable part 24 optical head device 25 (tilt control) motor 26 Optical information recording medium 27 Disk drive means 28 LED 29 Disk tilt sensor 30 Two-part photosensor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuo Hosomi 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] An optical unit for emitting a light beam for optical recording and reproduction, and a light beam emitted from the optical unit is condensed so as to form a light spot on an optical information recording medium and radiated. And a focusing direction based on information on a focusing error and a tracking error of a light spot with respect to the optical information recording medium by a reflected light beam from the optical information recording medium during the optical recording and reproduction. And driving in the tracking direction,
The objective lens used for the condensing means is provided with the following condition: | Lc | / | La | <0.3 (1) where Lc: off-axis incidence of a light beam incident on the objective lens at a unit angle La: a third-order astigmatism component of wavefront aberration that varies due to a unit angle off-axis incidence of a light beam incident on the objective lens, and the tilt detection. An optical head device provided with control means for tilting an optical axis incident on the objective lens according to the tilt of the optical information recording medium detected by the means. 2. The optical head device according to claim 1, wherein a galvanomirror is used as the control unit for tilting the optical axis. 3. The optical head device according to claim 1, wherein the control means for tilting the optical axis is provided with a control means for decentering an optical means for emitting the light beam for optical recording and reproduction. 4. The optical head device according to claim 1, wherein the control means for tilting the optical axis includes a plurality of collimating lenses, and a control means for decentering one of the collimating lenses is provided. 5. The optical head device according to claim 1, wherein a control unit for tilting a prism provided in the light beam is provided as the control unit for tilting the optical axis.