JP2002304764A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device which varies in the thickness of a substrate up to a signal recording surface and is capable of reading the signals of two kinds of disks varying in recording density. SOLUTION: This optical pickup device has an objective lens driving mechanism set in such a manner that the outer peripheral side of the disks is greater in compliance than the inner peripheral side. The light emission point of a laser element 3 corresponding to the disk larger in the thickness of the substrate up to the signal recording surface is arranged to be shifted more to the inner peripheral side of the disk than the optical axis of the objective lens 7 and the objective lens 7 inclines in the displacement central position of the objective lens 7 in correspondence to the disk larger in the thickness of the substrate, by which the comatic aberrations generated on the beam spot on the disk are negated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device capable of reading signals from two types of disks having different recording densities while having different thicknesses of a substrate up to a signal recording surface.

[0002]

2. Description of the Related Art As an optical pickup device, a CD (Co)
laser diode and DVD (Digital Ver.) that emit a laser beam with a wavelength suitable for the recording density of mpact Discs.
(satileDisc) Two types of laser light sources with different wavelengths of a laser diode that emits a laser beam with a wavelength suitable for the recording density are prepared, and the light source to be used is switched according to the recording density of the disc for signal reading. By using an objective lens having substantially two NAs corresponding to a CD and a DVD, respectively, CDs and Ds having different recording densities by a single optical pickup device.
There is one corresponding to VD.

In an optical pickup device using two types of laser light sources having different laser wavelengths as described above,
There are cases where a two-wavelength laser unit capable of generating two types of laser beams having different wavelengths by housing two types of laser elements in the same package is used.

In an optical pickup device using such a two-wavelength laser unit, the laser beam is emitted from each laser element, so that the light emitting points of each laser element are separated. Therefore, it is impossible to make both light emitting points of each laser element coincide with the optical axis of the objective lens at the same time.

[0005] The deviation between the light emitting point of the laser element and the optical axis of the objective lens causes deterioration of the quality of the laser beam applied to the disk, and the degree of the deterioration is determined by the difference between the light emitting point of the laser element and the optical axis. Corresponds to the off-distance.

Therefore, generally, the optical axis of the objective lens is set at the center of the light emitting point of each laser element, the distance between the light emitting point of each laser element and the optical axis is suppressed, and the laser beam applied to the disc is controlled. A design has been made in which quality deterioration is moderately suppressed for both laser beams emitted from each laser element.

Alternatively, the light emitting point of one laser element is made coincident with the optical axis of the objective lens, and the light emitting point of the other laser element is deviated from the optical axis to sacrifice the quality of the laser beam from the other laser element. Thus, the quality of the laser beam from the one laser element is ensured.

When the light emitting point of the laser element deviates from the optical axis of the objective lens, coma aberration occurs due to the thickness of the substrate up to the signal recording surface, and the quality of the laser beam from the laser element deteriorates.

In the objective lens driving mechanism, generally, a lens holder for holding the objective lens is connected to the frame by an elastic supporting member, whereby the lens holder is elastically supported so as to be displaceable with respect to the frame. It has a configuration.

In many cases, a suspension wire is used as the elastic support member. In such an objective lens driving mechanism using the suspension wire, one end of each of four suspension wires installed in parallel with each other is attached to a frame. The lens holder is supported by each suspension wire by fixing the other end of each suspension wire to the lens holder.

By the way, the inclination due to the runout of the disk occurs from the center of the disk mounted on the turntable toward the outer periphery. Therefore, if the objective lens is displaced while being tilted in the same direction as the tilt due to the runout of the disk when the objective lens is driven by the focus control, an objective lens driving mechanism advantageous for the runout of the disk can be obtained. .

As such an objective lens driving mechanism,
As shown in JP-A-64-52233, a wire on the outer peripheral side of the disk has a greater compliance than the wire on the inner peripheral side of the disk, and the objective lens is in the same direction as the inclination due to the runout of the disk. There has been known one that is displaced while being inclined.

[0013]

By the way, CDs and DVs
D, the thickness of the transparent substrate up to the signal recording surface is approximately 1: 2.
Greatly different. Therefore, a single objective lens
And the objective lens drive mechanism compatible with DVD,
The center of displacement of the objective lens differs between CD playback and DVD playback, and the center of displacement of the objective lens during CD playback is closer to the disk than during DVD playback.

Therefore, as described above, in an optical pickup device provided with an objective lens driving mechanism that is advantageous for the deviation of the surface of a disk, if the attitude of the objective lens is set in accordance with the displacement center position of the objective lens during DVD playback, the CD Even when the objective lens is at the displacement center position during reproduction, the objective lens is tilted, and this tilt causes a problem that coma aberration occurs in a beam spot on the disk.

The occurrence of the coma causes deterioration of the jitter characteristic of the reproduction signal obtained from the predetermined light receiving output of the photodetector, and significantly deteriorates the quality of the optical pickup device.

[0016]

According to the present invention, an objective lens driving mechanism is provided such that an elastic support member is set so that the outer peripheral side of a disk has higher compliance than an inner peripheral side, and a two-wavelength laser unit has two types of disks. Of the laser elements respectively corresponding to the above, the light emitting point of the laser element corresponding to the disk with the thicker substrate up to the signal recording surface is shifted toward the inner circumference side of the disk from the optical axis of the objective lens. I do. Accordingly, when the displacement center position of the objective lens approaches the disk corresponding to the disk with a thicker substrate, the objective lens tilts and coma aberration occurs in the beam spot on the disk, and this coma aberration is reduced. The light emitting point of the laser element corresponding to the disk with the thicker substrate is deviated from the optical axis of the objective lens to cancel.

[0017]

FIG. 1 is an optical arrangement diagram showing an optical system of an optical pickup device according to an embodiment of the present invention.

The optical pickup device shown in FIG. 1 has a configuration capable of reading a signal from a CD and a DVD.

Reference numeral 1 denotes a first light emitting a laser beam having a wavelength suitable for DVD, for example, 650 nm, on the same semiconductor substrate.
A laser element 2 is installed, and a second light emitting a laser beam having a wavelength suitable for a CD, for example, 780 nm.
A two-wavelength laser unit in which a laser element 3 is installed and the first laser element 2 and the second laser element 3 are housed in the same package.

The laser beams emitted from the first laser element 2 and the second laser element 3 of the two-wavelength laser unit 1 are formed through the diffraction grating 4 into ± primary light beams used for tracking control. After the three beams are formed, the optical axis is bent by the surface of the obliquely arranged parallel plate type half mirror 5, and the collimator lens 6
The light is then incident on the objective lens 7 and converged by the objective lens 7 to irradiate the signal recording surface of the disk D.

The objective lens 7 is designed so that the diameter of an aperture stop for limiting a laser beam to be incident on the basis of a laser wavelength can be switched, or a bifocal lens can be used for CD reproduction and DVD reproduction, respectively. It is configured to act as a lens with a corresponding NA.

The laser beam modulated and reflected by the signal recording surface of the disk D returns to the objective lens 7, returns to the half mirror 5 via the collimator lens 6, passes through the half mirror 5, and passes to the photodetector 8. The light arrives and is received by the photodetector 8.

The photodetector 8 includes a DVD light receiving section (not shown) used for DVD reproduction and a CD used for CD reproduction.
A light receiving portion (not shown) is formed, and a laser beam emitted by the first laser element 2 is received by each light receiving region of the DVD light receiving portion, so that a DVD recording signal is obtained and the DVD is supported. Each control signal used for the focusing control and the tracking control is obtained.

On the other hand, the laser beam emitted by the second laser element 3 is received by each light receiving area of the CD light receiving section of the photodetector 8, so that a CD recording signal is obtained and the CD is obtained.
Is obtained for each of the control signals used for the focusing control and the tracking control.

Incidentally, in the two-wavelength laser unit 1, the first laser element 2 for DVD is disposed at the center in the direction orthogonal to the emission direction of the laser beam. Then, the two-wavelength laser unit 1 is attached to an optical housing (not shown) in which each optical element is installed so that the light emitting point of the first laser element 2 coincides with the optical axis of the objective lens 7.

That is, the light emitting point of the first laser element 2 is arranged so as to coincide with the optical axis of the objective lens 7, while the light emitting point of the second laser element 3 is deviated from the optical axis of the objective lens 7.

Here, as shown in FIG.
The objective lens driving mechanism that supports the lens holder 9 holding the lens so as to be displaceable with respect to the frame 10 includes four suspension wires 11a, 1
One end of each of the suspension wires 1b, 11c, and 11d is fixed to a mounting plate 12 that is attached to the frame 10, and the other end of each of the suspension wires 11a to 11d is fixed to the lens holder 9.
The lens holder 9 is elastically supported by 1a to 11d.

By the way, the four suspension wires 11a to 11d are separately arranged with the object lens 7 interposed therebetween, and the two suspension wires are arranged at different positions in the radial direction (radial direction) of the disk. Have been.

The suspension wires 11a to 11
d is the same material beryllium copper is used,
One or two of the suspension wires on the outer circumference of the disk are made of a material with a smaller diameter than the other suspension wires, and the objective lens driving mechanism is such that the outer circumference of the disk is more compliant than the inner circumference. Is getting bigger.

Therefore, when the objective lens 7 is displaced in the focus direction, the skew in the radial direction becomes the same direction as the inclination due to the surface deviation of the disk, and the skew characteristic is improved with respect to the surface deviation of the disk.

By the way, the thickness of the transparent substrate up to the signal recording surface differs greatly between CD and DVD, which is approximately 1: 2. For this reason, in the optical pickup device including the objective lens driving mechanism shown in FIG. 2, if the posture of the objective lens 7 is set in accordance with the displacement center position of the objective lens 7 during DVD reproduction, the objective lens 7 will be rotated during CD reproduction. The objective lens 7 is tilted even at the displacement center position.

FIG. 3 shows the optical arrangement shown in FIG.
The optical axis between the wavelength laser unit 1 and the objective lens 7 is schematically shown in a straight line. As shown in FIG. 3, the displacement center position of the objective lens 7 during CD reproduction (shown by a solid line).
Is closer to the disk D than the displacement center position of the objective lens 7 during reproduction of the DVD (indicated by a broken line).
As a result, when the objective lens 7 is displaced to the displacement center position in the CD reproducing state, the objective lens 7 is inclined to be closer to the disk on the outer peripheral side of the disk than on the inner peripheral side.

The inclination of the objective lens 7 causes coma to occur in the beam spot on the disk.

In the two-wavelength laser unit 1, the light emitting point of the first laser element 2 for DVD is arranged to coincide with the optical axis of the objective lens 7, while the light emitting point of the second laser element 3 is It is located off the optical axis of the objective lens 7.

When the laser beam incident on the objective lens 7 is obliquely incident on the optical axis of the objective lens 7, coma is generated in the laser beam passing through the objective lens 7 according to the angle. . Therefore, since the light emitting point of the second laser element 3 is located off the optical axis of the objective lens 7, the laser beam emitted from the second laser element 3 has the light emitting point of the second laser element 3. The coma is generated in accordance with the distance d deviating from the optical axis 7.

Therefore, by appropriately setting the direction in which the light emitting point of the second laser element 3 is deviated from the optical axis of the objective lens 7 and the distance d, the objective lens 7 is displaced to the displacement center position in the CD reproducing state. An effect of canceling coma generated by tilting the objective lens 7 can be expected.

As a result of the simulation, in the target optical pickup device, when the objective lens 7 is displaced to the center of displacement and tilts by 0.4 degrees with respect to the optical axis in the CD reproducing state, It was found that when the light emitting point of the second laser element 3 was shifted by 0.142 mm toward the inner peripheral side of the disk with respect to the optical axis of the objective lens 7, almost coma aberration could be canceled.

Therefore, when the newly designed two-wavelength laser unit 1 is used, the coma aberration is canceled so as to cancel the coma aberration in accordance with the tilt angle when the objective lens 7 is displaced to the displacement center position in the CD reproducing state. 1 laser element 2
The distance d between the first laser element 2 and the second laser element 3 is set, the light emitting point of the first laser element 2 is set on the optical axis of the objective lens, and the light emitting point of the second laser element 3 is set on the disk from the optical axis of the objective lens. In this case, coma aberration is suppressed not only in the DVD reproduction but also in the CD reproduction by shifting the arrangement to the inner peripheral side, thereby improving the quality of the optical pickup device.

When the existing two-wavelength laser unit 1 is used, the distance d between the first laser element 2 and the second laser element 3 is fixed.
0.135 mm), there is no degree of freedom in shifting the emission point of the second laser element 3 with respect to the optical axis of the objective lens 7 with respect to the tilt angle of the objective lens 7, but the emission point of the second laser element 3 is Simply setting the mounting direction of the two-wavelength laser unit 1 so that it is on the inner circumference side of the CD
It is possible to reduce the coma generated when the objective lens 7 is displaced to the displacement center position in the reproducing state.

[0040]

As described above, the present invention relates to an optical pickup device provided with an objective lens driving mechanism in which the outer peripheral side of the disk is set to have a higher compliance than the inner peripheral side, and the optical pickup apparatus including the objective lens driving mechanism is provided with a signal recording surface. The emission point of the laser element corresponding to the disk with the thicker substrate is shifted from the optical axis of the objective lens to the inner circumference side of the disk, so it is compatible with the disk with the thicker substrate Then, when the displacement center position of the objective lens approaches the disk, the objective lens tilts and coma aberration occurs in the beam spot on the disk. This coma aberration can be canceled.

Further, since the light emitting point of the laser element corresponding to the disk having the thinner substrate up to the signal recording surface is arranged on the optical axis of the objective lens, the light emitting point is displaced to the displacement center position of the objective lens. Coma aberration is suppressed even for a disk with a thin substrate whose objective lens is not tilted.

[Brief description of the drawings]

FIG. 1 is an optical layout diagram showing an optical system of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of an objective lens driving mechanism used in the optical pickup device according to the present invention.

FIG. 3 is an explanatory view schematically showing the optical axis between the two-wavelength laser unit 1 and the objective lens 7 in a straight line in the optical arrangement diagram shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2 wavelength laser unit 2 1st laser element 3 2nd laser element 7 Objective lens

Claims (3)

[Claims] 1. A two-wavelength laser unit having two types of laser elements having different laser wavelengths, wherein a laser beam generated from each of the two types of laser elements is selectively incident on a single objective lens and a signal is output. A light source for reading signals from two types of discs having different thicknesses of substrates up to a recording surface, and having an objective lens driving mechanism in which a lens holder holding the objective lens is displaceably supported with respect to a frame by an elastic support member. A pickup device, wherein the objective lens driving mechanism sets an elastic supporting member such that compliance is larger on an outer peripheral side of the disk than on an inner peripheral side thereof, and the two-wavelength laser unit is a laser corresponding to each of two types of disks. Laser element corresponding to the disk with the thickest substrate up to the signal recording surface An optical pickup device, wherein a light emitting point of a child is shifted from an optical axis of an objective lens to an inner peripheral side of a disk. 2. The two-wavelength laser unit according to claim 1, wherein, of the laser elements corresponding to the two types of disks, the light emitting point of the laser element corresponding to the disk having a thinner substrate up to the signal recording surface is the light of the objective lens. The optical pickup device according to claim 1, wherein the optical pickup device is arranged on a shaft. 3. The elastic support member comprises a total of four suspension wires, two on the inner circumference side and the outer circumference side of the disk, and the compliance of the suspension wires on the outer circumference side of the disk is greater than that on the inner circumference side. The optical pickup device according to claim 1, wherein: