JPH09297927A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with plural kinds of recording media which are different in thickness and to suppress upsizing of the device to the utmost in avoiding a collision between an objective lens positioned on the inner circumferential side of a recording medium and a turntable for placing the recording medium even when an innermost circumferential data of the recording medium is recorded or reproduced by using another objective lens positioned on the outer circumferential side of the recording medium. SOLUTION: A lens holder 6 is mounted with two objective lenses 4 and 5 having different specifications respectively to cope with optical disks which are different in thickness. Mounting of the two objective lenses 4 and 5 is different in height respectively, and the objective lens 4 positioned on the inner circumferential side is provided farther separately from the optical disk than the other one. Alternatively, optical distances of the two objective lenses 4 and 5 are different, and the objective lens 4 positioned on the inner circumferential side of the optical disk is provided with its operation distance smaller than the other one.

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 used in an optical disc device for storing information in a recording medium such as an optical disc or reading the recorded information, and more particularly to a plurality of types of optical pickups having different substrate thicknesses. The present invention relates to an optical pickup device applicable to a recording medium.

[0002]

2. Description of the Related Art In recent years, the above-mentioned optical disk device has been generally used as a large-capacity recording / reproducing device. An optical pickup device is mounted on this optical disc device. The optical pickup device usually uses a light source that emits a light beam, an optical system that guides the light beam to an objective lens, and a light beam that is guided by the optical system and converges the optical beam onto an optical recording medium, for example. Objective lens and a mechanism for controlling the movement of the objective lens in the focusing direction and the tracking direction.

FIG. 23 is a perspective view showing the structure of a first conventional optical pickup device. This optical pickup device is used for a magneto-optical recording medium such as an MD (mini disk).
It is used for a device and is configured as follows. Reference numeral 101 is an objective lens driving device, 102 is an objective lens, 103 is a lens holder for housing the objective lens 102, 104 is a substrate attached to both side surfaces of the lens holder 103, and 105 and 106 are central portions of the lens holder 103, respectively. Focusing coil and tracking coil provided in the hole of, 107 is a base,
Reference numeral 108 denotes an elastic body for movably supporting the lens holder 103 with respect to the base 107 in the focusing direction and the tracking direction, and 109 denotes one end 1 of the elastic body 108.
08a is solder for fixing to the substrate 104, 110 is a substrate fixed to the base 107, 111 is solder for fixing the other end 108b of the elastic body 108 to the substrate 110, 11
2 is a damper material, 113 is a permanent magnet, and 114 is a stopper.

In this optical pickup device, one objective lens 102 is mounted on a lens holder 103, and a light beam P from a light source (hologram laser) 115 is set up below the objective lens 102 to bend it toward the objective lens 102. Only one mirror 116 is arranged. 11
Reference numeral 7 is a collimating lens for collimating the light beam. Further, 118 is a polarization beam splitter, and p
The transmittance for polarized light is set to about 80%, and the reflectance for s-polarized light is set to about 100%. Reference numeral 119 denotes a photodetector for receiving a part of the light beam reflected by the polarization beam splitter 118 and monitoring the output of the light source 115. Reference numeral 120 denotes the reflected light from the optical disc in two directions depending on its polarization direction. Wollaston prism for dividing, 121 is a reflecting mirror, 122 is a spot lens,
Reference numeral 123 is a reflection mirror, and 124 is a photodetector for detecting a magneto-optical signal.

By the way, the optical discs are typified by a CD (compact disc), which can only be reproduced, a write-once type which can record only once, a magneto-optical system and a phase change system. There are various things that can be recorded and erased even once. Further, in recent years, in these optical discs, the capacity and the density have been increased, the spot diameter is reduced by shortening the wavelength of the light source, and the skew of the optical disc is affected even if the numerical aperture (NA) of the objective lens is increased. In order to reduce the size of the optical disc, a thin optical disc substrate has also been proposed.

However, the optical pickup device shown in FIG. 23 may be compatible with a magneto-optical disk having the same substrate thickness and a read-only optical disk, but may be compatible with optical disks having different substrate thicknesses and refractive indexes. Can not.
The reason is that, for such an optical disc, the required condensing characteristics cannot be obtained unless an objective lens having a condensing condition suitable for the optical disc is used.

In order to solve this problem, an optical pickup device has been proposed in which two objective lenses are mounted on the movable portion of the objective lens driving device and the objective lens driving device is selectively used according to the type of the optical disc (Japanese Patent Laid-Open No. 6-61). 333255).
In the optical pickup device of the second conventional example, as shown in FIG. 24, a beam separation mirror having two mirror surfaces is arranged below the two objective lenses 130 and 131, and the beam separation mirror is provided. Has a half mirror 132 on the side closer to the light source and a reflection mirror 133 on the other side. With this configuration, the light beam that has entered the beam separation mirror can enter the objective lens 131 by the half mirror 132 and enter the objective lens 130 by the reflection mirror 133.

[0008]

However, the second conventional example has the following problems. This problem will be described with reference to FIGS. 24 and 25. That is, Japanese Patent Laid-Open No. 6-333255, which is the second conventional example, has no description about the height relationship or the working distance relationship between the two objective lenses 130 and 131, and the optical disk 134 is mounted. Of the turntable 136 connected to the spindle motor 135 and the two objective lenses 130, 1
The height relationship with 31 is not described at all.

However, as in this example, the optical disk 13
4 when the two objective lenses 130 and 131 are arranged in the radial direction, when recording and reproducing the data of the innermost circumference of the optical disc 134 using the objective lens 131 located on the outer circumference side, Since the objective lens 130 located at the position must enter further inside than that, there is a risk of colliding with the turntable 136.

Now, assume that the two objective lenses 130 and 13 are
1, the mounting height and working distances W ₁ and W ₂ are almost the same,
It is assumed that the inner peripheral objective lens 130 records and reproduces an optical disc having a thin substrate, and the outer objective lens 131 records and reproduces an optical disc having a thick substrate.
In this case, as shown in FIG. 24, the substrate thickness is thin by using the objective lens 130 on the inner peripheral side (shown by a broken line).
When the data on the innermost circumference of the optical disc 134 is being recorded or reproduced, the objective lens 131 on the outer circumference side is further apart from the turntable 136, so that no particular problem occurs. However, as shown in FIG. 25, when recording and reproducing data on the innermost circumference of an optical disc having a thick substrate by using the objective lens 131 on the outer circumference side, it is not used as shown in FIG. Objective lens 130 on the inner peripheral side
And the turntable 136 are close to each other in the radial direction. Therefore, there is a problem that the gap between the objective lens 130 on the inner peripheral side and the turntable 136 in the focusing direction becomes small, and the possibility of collision between them increases.

As a means for solving this problem, the working distances W ₁ and W ₂ of both objective lenses are set to be sufficiently large in consideration of the thickness of the turntable, and, for example, a portion which interferes with the objective lens is set. Assuming that the thickness of the turntable is D and the conventional required working distance is W ₀ , W ₁ = W ₀ + D, W ₂ = W ₀
A method of setting + D and avoiding a collision is also conceivable. However, if the working distance of the objective lens is increased in this way, the diameter of the objective lens must also be increased, and as a result, the diameter of both objective lenses is also increased and the working distance is increased, thereby increasing the size of the device. However, there is a problem that the movable part also becomes heavy.

The present invention has been made in view of the above-mentioned problems of the prior art, and is applicable to a plurality of types of recording media having different thicknesses, and the objective located on the outer peripheral side of the recording medium. Even when data is recorded or reproduced on the innermost circumference of the recording medium using the lens, collision between the objective lens located on the inner circumference side of the recording medium and the turntable for mounting the recording medium is prevented. It is an object of the present invention to provide an optical pickup device that can be avoided and that the size of the device can be suppressed as much as possible. Another object of the present invention is to provide an optical pickup device capable of reducing the influence of two lights corresponding to two objective lenses.

[0013]

According to a first aspect of the present invention, there is provided an optical pickup device for controlling a movement of an objective lens for converging a light beam and irradiating the recording medium with the converged light in a predetermined direction. An optical pickup device comprising an objective lens driving device, wherein the objective lens driving device comprises two objective lenses arranged side by side substantially in the radial direction of the recording medium. The height of the objective lens located on the inner peripheral side is arranged so as to be more distant from the recording medium than the height of the objective lens located on the outer peripheral side of the recording medium. To be achieved.

An optical pickup device according to a second aspect of the present invention is the optical pickup device according to the first aspect, wherein the two objective lenses correspond to recording media having different substrate thicknesses. The working distance of the objective lens on the peripheral side is larger than the working distance of the objective lens on the outer peripheral side, and the mounting height difference between the two objective lenses is substantially equal to the difference between the two working distances. As a result, the above-mentioned other objects are achieved.

An optical pickup device according to a third aspect of the present invention comprises an objective lens driving device for converging a light beam and controlling movement of an objective lens for irradiating the converged light on a recording medium in a predetermined direction. In an optical pickup device in which two objective lenses are mounted in the objective lens driving device side by side in the radial direction of the recording medium, the optical pickup device is located on the inner peripheral side of the recording medium of the two objective lenses. The working distance of one of the objective lenses is set to be smaller than the working distance of the one of the objective lenses located on the outer peripheral side of the recording medium, thereby achieving the above object.

An optical pickup device according to a fourth aspect of the present invention is the optical pickup device according to the third aspect, wherein the two objective lenses correspond to recording media having different substrate thicknesses. The objective lens located on the inner peripheral side of the one corresponds to the recording medium having the smaller substrate thickness, which achieves the other objects.

In the optical pickup device according to claim 5 of the present invention, at least one of the mounting height and the working distance of the two objective lenses is different between the two objective lenses, and the same recording medium is used. The objective lens is characterized in that both objective lenses are formed so as not to be in focus at the same height with respect to the above, thereby achieving the above-mentioned other object.

The operation of the present invention will be described below.

In the optical pickup device according to the first aspect, the height of the objective lens located on the inner peripheral side of the recording medium is
Since it is lower than the height of the objective lens located on the outer peripheral side, even when recording and reproducing the data of the innermost periphery of the recording medium with the objective lens located on the outer peripheral side, the objective lens located on the inner peripheral side is A wide gap can be secured between the turntable and the turntable, and collision between the objective lens and the turntable can be avoided. Therefore, it is not necessary to increase the diameters of both objective lenses, and it is possible to prevent the apparatus from becoming large.

In the optical pickup device according to the second aspect, since the difference in mounting height is substantially equal to the difference in working distance, the required movable range of the objective lens driving device can be minimized, and the working distance is also as small as possible. Since the two objective lenses are compatible with recording media having different substrate thicknesses, the two objective lenses do not focus at the same height, and both light beams are mixed into the photodetector. The influence of can be reduced.

In the optical pickup device of the third aspect, the working distance of the objective lens located on the inner peripheral side of the recording medium is set to be smaller than the working distance of the objective lens located on the outer peripheral side. Therefore, even when the data on the innermost circumference of the recording medium is recorded and reproduced by the objective lens located on the outer peripheral side, it is possible to widen the gap between the objective lens located on the inner peripheral side and the turntable. And a collision with the turntable can be avoided. Therefore, it is not necessary to increase the diameters of both objective lenses, and it is possible to prevent the apparatus from becoming large.

In the optical pickup device according to the fourth aspect, the objective lens located on the inner peripheral side corresponds to the recording medium having the thinner substrate thickness, and the objective lens located on the outer peripheral side corresponds to the thicker substrate thickness. Since it is adapted to the recording medium of No. 2, it is possible to minimize the required movable range of the objective lens driving device and prevent the two objective lenses from focusing at the same height. It is possible to reduce the effect of mixing both light beams.

In the optical pickup device according to the fifth aspect, the mounting height and working distance of the objective lens are set so as to prevent the two objective lenses from focusing at the same height. It is possible to reduce the effect of mixing both light beams on the light.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIGS. 1 to 16 are configuration diagrams showing an optical pickup device according to the present embodiment. FIG. 1 is an exploded perspective view of the optical pickup device, and FIG. 1 is a plan view showing the configuration of the objective lens driving device in FIG. 1, FIG. 3 is a sectional view taken along the line AA in FIG. 2, and prisms are shown below the objective lens. 4 is a perspective view showing the structure of the hologram laser, FIG. 5 is a view for explaining the positional relationship between the hologram and the photodiode, FIG. 5 (a) is a view showing the hologram pattern, and FIG. 5 (b) is a photo. The pattern of a diode is shown. FIG. 6 and FIG. 7 are views showing the split state of the light beam depending on the polarization direction. 8 to 16
FIG. 6 is a diagram illustrating a positional relationship between a turntable and an objective lens in various cases where the working distance and mounting height of each objective lens are various.

As shown in FIG. 1, the optical pickup device 1 in this embodiment comprises an objective lens driving device 2 and an optical system 3, which are mounted in a housing (not shown).

The objective lens driving device 2 is provided with two objective lenses 4 and 5 for converging a light beam and irradiating the converged light on a recording medium, for example, an optical disc. Two
The two objective lenses 4 and 5 have different specifications so that they can correspond to different types of optical disks.
For example, the objective lens 4 corresponds to an optical disc having a thin substrate, and the objective lens 5 corresponds to an optical disc having a thick substrate. Alternatively, there may be two objective lenses corresponding to the same substrate thickness of the optical disc and having different numerical apertures NA. Although the objective lens 5 is described here as being compatible with an optical disk (magneto-optical disk) having a thick substrate, it can be applied to a recording medium having other specifications, as a matter of course.

1 to 3, the objective lens driving device 2 includes an objective lens 4 and 5, the lens holder 6 for holding the objective lens 4 and 5, and substrates mounted on both side surfaces of the lens holder 6. 7 and a movable portion composed of a focusing coil 8 and a tracking coil 9 fixed to the concave portions at both ends of the lens holder 6. Lens holders 6 are provided on the upper and lower sides of the substrate 7, respectively.
An elastic body 11 for movably supporting the base 10 in the focusing direction and the tracking direction is arranged. One end 11a of the elastic body 11 is fixed to the substrate 7 by the solder 12, and the other end 11b of the elastic body 11 is the solder 1
It is fixed to the substrate 14 by 3. This substrate 14
Is the spacer 1 with respect to the standing portion 10a from the base 10.
It is fixed by a fixing screw 19 via 8. A damper material 15 is fixed to a root portion near the other end 11b side of the elastic body 11, and the damper material 15 has a function of suppressing resonance of the elastic body 11. Two substantially U-shaped yokes 16 are mounted on the base 10, and a permanent magnet 17 is fixed to the inner wall surface at one end of each yoke 16. The focusing coil 8 is provided at the end of each yoke 16 on the side where the permanent magnet 17 is not provided, and the tracking coil 9 is provided between both ends. The terminals of the focusing coil 8 and the tracking coil 9 are electrically connected to the substrate 14 via the substrate 7 and the elastic body 11.

In the above structure, when current is passed through the focusing coil 8 and the tracking coil 9,
The movable portion can be driven independently in each of the focusing direction and the tracking direction. Here, in FIG. 2, Tr is the tracking direction and Ta is the tangential direction.

The optical system 3 includes a reflection mirror 21, a polarization beam splitter 22, a hologram laser 23, a collimator lens 24, a Wollaston prism 25, and a reflection mirror 2.
6, spot lens 27, reflection mirror 28, photodetector 2
It consists of 9 and so on. The reflection mirror 21 and the polarization beam splitter 22 are arranged below the objective lenses 4 and 5, respectively.

As shown in FIGS. 4 to 5, the hologram laser 23 includes a semiconductor laser 30 and a photodiode 31 in one package 32.
A glass substrate 35 having a hologram 33 and a diffraction grating 34 formed on both surfaces is fixed to the surface of the package 32. The light beam emitted from the semiconductor laser 30 is divided into three main beams and two sub beams by the diffraction grating 34, passes through the hologram 33 as zero-order light, and travels toward the optical disc.

A part of the light beam reflected by the optical disk returns to the hologram 33 through the same route, and the first-order diffracted light diffracted here is divided into five-division photodiodes 31.
Guided above. The hologram 33 is composed of two regions 36 and 37 having different grating periods, as shown in FIG.
The five-division photodiode 31 is composed of _five photodetectors D _{1 to} D ₅ as shown in FIG. 5B. The reflected light of the main beam incident on one area 36 of the hologram 33 is collected on the dividing line between the photodetectors D ₂ and D ₃ , and the reflected light of the main beam incident on the other area 37 is collected on the photodetector D _4. Be illuminated. Further, the reflected light of the sub-beams is condensed on the photodetectors D ₁ and D ₅ , respectively.

Therefore, the five-division photodiode 31
The outputs of the photodetectors D _{1 to} D ₅ of S ₁ , S ₂ , S ₃ , S ₄ , S
_If it is set to ₅ , the focus error signal FES is given by FES = S ₂ −S ₃ , and the tracking error signal TES is detected by the so-called three-beam method, and given by TES = S ₁ −S ₅ . As described above, the servo signal can be detected. For optical discs other than magneto-optical discs that detect the intensity of reflected light, the reproduction signal RF is given by RF = S ₂ + S ₃ + S ₄ .

Next, the operation of injecting the light beam into the two objective lenses 4 and 5 and the detection of the magneto-optical signal will be described with reference to FIG.
This will be described with reference to FIG. The s-polarized light beam emitted from the hologram laser 23 is converted into parallel light by the collimator lens 24 and enters the polarization beam splitter 22. The polarization beam splitter 22 is designed to reflect approximately 80% of the s-polarized component and transmit the remaining 20% and approximately 100% of the p-polarized component.
Therefore, s collimated by the collimator lens 24
80% of the polarized light beam is reflected by the polarization beam splitter 22 and enters the objective lens 5, and the remaining 20%
Is transmitted through the polarization beam splitter 22, and is reflected by the reflection mirror 21.
It is reflected by and enters the objective lens 4.

When the optical disk is a magneto-optical disk, the objective lens 5 is used. The light beam applied to the medium surface of the magneto-optical disk by the objective lens 5 undergoes the Kerr effect, its polarization direction changes slightly, that is, it returns to the polarization beam splitter 22 with a slight p-polarized component. come. At this time, the transmittance of the s-polarized component in the polarization beam splitter 22 is about 20% and the transmittance of the p-polarized component is almost 100%.
The s-polarized light component of the light beam passing through is reduced, resulting in an increase in the rotation angle of the polarization direction. The light beam with the increased rotation angle is divided into two light beams having respective polarization components by the Wollaston prism 25, passes through the reflection mirror 26, the spot lens 27, and the like, and a photodetector 29 detects a magneto-optical signal. To be done.

On the other hand, of the light beam reflected by the optical disk, the component (s
The polarized light returns to the hologram laser 23, and the servo signal is detected by the built-in photodiode 31. At the same time that the light beam is incident on the objective lens 5, the remaining 20% of the light beam is incident on the objective lens 4, and the light beam reflected by the optical disk is detected by the photodetector 29 for detecting the magneto-optical signal. Although it is incident on the photodiode 31 built in the hologram laser 23, the working distance and other conditions are set so that the objective lens 4 and the objective lens 5 are not focused at the same height. As a result, the unnecessary light beam is not sufficiently condensed on the medium surface, and is in a blurred state on the photodetector, so that the influence can be almost eliminated.

Next, a case other than the magneto-optical disk in which the substrate thickness of the optical disk is different from the above will be described with reference to FIG. In this case, since the specifications of the objective lens 5 are different, it is not possible to collect light sufficiently.
Is used. The light beam (20% s-polarized component) incident on the objective lens 4 is reflected by the optical disk. In this case, since it is not a magneto-optical disk, it returns to the polarization beam splitter 22 with its polarization direction unchanged, and 20% thereof is transmitted. And enters the hologram laser 23, and the servo signal and the RF signal are detected. Although the light beam is incident on the objective lens 4 at the same time as the light beam is incident on the objective lens 5,
As in the previous case, by properly setting the working distance of the objective lens and other conditions, the unwanted light beam is not sufficiently condensed on the medium surface and is blurred on the photodetector. Therefore, the influence can be almost eliminated.

Next, the relationship between the mounting height difference of the objective lens and the turntable of the optical disk, which is the main part of the present invention, will be described with reference to FIGS. (A) in each of FIGS. 8 to 16 shows a case where data is recorded and reproduced on the innermost circumference of the optical disc by using the objective lens 4 located on the inner circumference side of the optical disc. In (b), the objective lens 5 located on the outer peripheral side of the optical disc is used to record and reproduce data on the innermost periphery of the optical disc. When the objective lens 4 on the inner peripheral side is used as in the case of (a), the turntable 39
There is a radial distance between and the objective lens 4. on the other hand,
Even when the outer objective lens 5 is used as in (b), since the inner objective lens 4 is mounted at a position lowered by one step in the present embodiment, the turntable 39 and the inner objective lens 4 are mounted. It is possible to make a sufficient gap in the optical axis direction between the objective lens 4 and the objective lens 4, and it is possible to avoid a collision between the turntable 39 and the objective lens 4. Alternatively, the probability of collision can be reduced.

The individual cases will be described below.

In FIG. 8, the objective lens 4 on the inner peripheral side corresponds to the optical disc 38 having a thin substrate thickness shown by the broken line, and the objective lens 5 on the outer peripheral side corresponds to the optical disc 38 having a thick substrate thickness shown by the solid line. The case is shown. In the figure, 38 is an optical disk, 39 is a turntable, and 40 is a spindle motor. The working distances of the objective lenses 4 and 5 are W ₁ and W ₂ , respectively, and W ₁ <W _{2 in} FIG. The height difference between the objective lenses 4 and 5 is d.

In this case, in order to avoid the collision between the objective lens and the optical disk, it is necessary to secure a necessary working distance W ₀ , and as shown in FIG. ₁ requires a value obtained by adding d to W ₀ . That is, there is a relationship of W ₀ <W ₁ <W ₂ , and the working distances W ₁ and W ₂ of both objective lenses are W ₁ = W ₀ + d, W _{2 in the} figure.
= W ₀ + d + α ₁ (α ₁ is the difference between W ₁ and W ₂ ). Also,
In FIG. 8B, considering the gap between the objective lens 4 on the inner circumference side and the turntable 39, if W ₂ + d−D = W ₀ , the required working distance can be secured. As a result, d =
It means that (D-α) / 2 is sufficient.

Therefore, the sum of the working distances of both objective lenses is W ₁ + W ₂ = 2W ₀ + D, which is the value (W ₁ in the conventional case of increasing the working distances of both objective lenses).
+ W ₂ = 2W ₀ + 2D).
Therefore, the size of the device can be prevented from increasing. Although standard use heights are different between (a) and (b), the movable range of the objective lens driving device may be increased correspondingly.

FIG. 9 shows a case in which both objective lenses correspond to an optical disc having the same substrate thickness and different specifications such as numerical aperture NA. In this case, as in the case of FIG. 8 described above, the relationship of W ₀ <W _{1 and} W ₂ is set, and similarly, the sum of the working distances can be made smaller than before.

FIG. 10 shows a case where the objective lens 4 on the inner peripheral side corresponds to an optical disc having a thin substrate and the objective lens 5 on the outer peripheral side corresponds to an optical disc having a thick substrate. The relationship between the working distance and the mounting height is W ₁ > W ₂ (= W
₀ ), W ₁ −W ₂ > d, and W ₁ = W ₀ + d + in the figure.
(here, the difference between the alpha ₂ is W ₁ and W ₂ + d, may be considered d + α ₂ = D) of α _2, W ₂ = W ₀ and made so that the sum of the working distance, W ₁ + W ₂ = 2W _It becomes ₀ + D, which can be smaller than the conventional one. However, depending on the relationship between the working distance and the difference in the substrate thickness, for example, in the case of the relationship of W ₁ −W ₂ ≈the difference in the substrate thickness, both objective lenses are focused on the same optical disc. Because of the danger, it is necessary to properly set the working distance of the objective lens and other conditions. In addition,
Although the standard operating height differs between (a) and (b), the movable range of the objective lens driving device may be increased accordingly.

FIG. 11 shows a case where both objective lenses correspond to an optical disc having the same substrate thickness and different specifications such as numerical aperture NA. In this case, as in the case of FIG. 10 described above, the relations W ₁ > W ₂ and W ₁ −W ₂ > d are set, and similarly the sum of the working distances can be made smaller than before. In this case, since the substrate thickness is the same, there is no risk of focusing both objective lenses on the same optical disc. Although the standard operating height differs between (a) and (b), the movable range of the objective lens driving device may be increased accordingly.

FIG. 12 shows a case where the objective lens 4 on the inner peripheral side corresponds to an optical disc having a thin substrate and the objective lens 5 on the outer peripheral side corresponds to an optical disc having a thick substrate. The relationship between the working distance and the mounting height is W ₁ > W ₂ (= W
₀ ), W ₁ −W ₂ ≈d, and in the figure W ₁ ≈W ₀ + d, W ₂
= W ₀ (d = D is sufficient), the sum of the working distances is W ₁ + W ₂ = 2W ₀ + D, which can be made smaller than in the conventional case. Further, since the standard use height is the same, the movable range of the objective lens driving device can be minimized.

FIG. 13 shows a case in which both objective lenses correspond to an optical disc having the same substrate thickness and different specifications such as numerical aperture NA. In this case, W ₁ > W ₂ (= W ₀ ), W ₁ −W ₂ as in the case of FIG. 12 described above.
Since the relationship is set to ≈d, the sum of the working distances can be made smaller than before. However, in this case, W ₁ −W ₂ ≈d
Therefore, there is a risk that both objective lenses will be focused on the same optical disc, and it is necessary to properly set the working distance of the objective lenses and other conditions.

FIG. 14 shows a case where the objective lens 4 on the inner peripheral side corresponds to an optical disc having a thin substrate and the objective lens 5 on the outer peripheral side corresponds to an optical disc having a thick substrate. In this case, the relationship between the working distance and the mounting height is W ₁ > W ₂ (> W ₀ ), W ₁ −W ₂ <d, and in the figure, W ₁ = W ₀ + d, W ₂ = W ₀ + α ₃ (here,
α ₃ is the difference between W ₂ and W ₀ , and d + α ₃ = D).
The sum of the working distances is W ₁ + W ₂ = 2W ₀ + D, which can be made smaller than before. Although the standard operating height differs between (a) and (b), the movable range of the objective lens driving device may be increased accordingly.

FIG. 15 shows a case where both objective lenses correspond to an optical disc having the same substrate thickness and different specifications such as numerical aperture NA. In this case, as in the case of FIG. 14 described above, W ₁ > W ₂ (> W ₀ ), W ₁ −W ₂
The relationship of <d is set, and similarly, the sum of the working distances can be made smaller than before.

Up to this point, for optical discs having different substrate thicknesses, the objective lens 4 on the inner peripheral side corresponds to an optical disc having a thin substrate thickness, and the objective lens 5 on the outer peripheral side corresponds to an optical disc having a thick substrate thickness. I've explained in the case. Contrary to the above, the present invention can be applied even when the inner peripheral side objective lens 4 corresponds to an optical disc having a thick substrate and the outer peripheral side objective lens 5 corresponds to an optical disc having a thin substrate.

FIG. 16 shows such a case.
In this case, similar to FIG. 12 described above, the relationship between the working distance and the mounting height is W ₁ > W ₂ (= W ₀ ), and W ₁ −W ₂ ≈d
It is. In this case as well, the sum of the working distances can be made smaller than in the past, and the standard working height is also the same, so that the movable range of the objective lens driving device can be made the smallest.

As described above, the sum of the working distances of the two objective lenses can be made smaller than before in any case, which can contribute to downsizing of the apparatus. Further, when the substrate thickness is different, it is desirable to set W ₁ -W ₂ ≈d as shown in FIG. 12 or FIG. 16 because the movable range of the objective lens driving device can be minimized. When the substrate thickness is the same,
Alternatively, it is desirable to set W ₁ −W ₂ ≠ d as shown in FIG. 15 because it is possible to prevent both objective lenses from being focused on the same optical disc.

(Second Embodiment) FIGS. 17 to 22 are structural views showing an optical pickup device according to the present embodiment. FIG. 17 shows the structure of an objective lens driving device provided in the optical pickup device. 18 is a plan view shown in FIG.
7 is a sectional view taken along line AA of FIG. 7, and prisms are shown below the objective lens. 19 to 22 are views for explaining the positional relationship between the turntable and the objective lens in various cases where the working distance of each objective lens is various. In this embodiment, the structure of the drive mechanism and the optical system of the objective lens driving device is the same as that of the first embodiment, and the description thereof is omitted. The difference from the first embodiment is that the mounting heights of the two objective lenses are the same and that only the working distance is different.

19 (a) to 22 (a) shows a case where the objective lens located on the inner circumference side of the optical disk is used to record / reproduce data on the innermost circumference of the optical disk. In each drawing, (b) is a case where the recording and reproduction of the data of the innermost circumference of the optical disk is performed by using the objective lens located on the outer circumference side of the optical disk. When the inner peripheral objective lens is used as in the case of (a), there is a radial distance between the turntable and the objective lens. Even when the outer objective lens is used as in (b), in the present embodiment, the working distance of the outer objective lens is set to be larger than the working distance of the inner objective lens. Therefore, when using the objective lens on the outer peripheral side, the distance between the objective lens and the optical disk becomes large, and a sufficient gap in the optical axis direction can be provided between the turntable and the objective lens on the inner peripheral side. Therefore, the collision between the turntable and the objective lens can be avoided. Alternatively, the probability of collision can be reduced.

The individual cases will be described below.

FIG. 19 shows a case where the objective lens 4 on the inner peripheral side corresponds to an optical disc having a thin substrate and the objective lens 5 on the outer peripheral side corresponds to an optical disc having a thick substrate. The working distance relationship is W ₁ <W ₂ . In this case, the working distance can be increased only by the objective lens 5, and the sum of the working distances can be made smaller than in the conventional case. Although the standard operating height differs between (a) and (b), the movable range of the objective lens driving device may be increased accordingly.

FIG. 20 shows a case in which both objective lenses correspond to an optical disc having the same substrate thickness and different specifications such as numerical aperture NA. In this case, as in the case of FIG. 19 described above, the relationship of W ₁ <W ₂ is set, and similarly, the sum of the working distances can be made smaller than before.

In FIG. 19 described above, for optical disks having different substrate thicknesses, the objective lens 4 on the inner peripheral side corresponds to an optical disk having a thin substrate thickness, and the objective lens 5 on the outer peripheral side corresponds to an optical disk having a thick substrate thickness. In contrast to this, the present invention, on the contrary, corresponds to an optical disc having a thick substrate and the objective lens 4 on the inner peripheral side is an optical disc having a thin substrate on the outer peripheral side. It is also applicable to the corresponding cases. The description will be given based on FIGS. 21 and 22.

In FIG. 21, W ₁ <W ₂ , but W ₂ −W ₁
≈ Substrate thickness difference is shown. In this case, there is a risk that both objective lenses will be focused on the same optical disc, and it is necessary to properly set the working distance of the objective lenses and other conditions.

FIG. 22 shows a case where the setting is such that W ₂ −W ₁ > difference in substrate thickness. In this case, although the above problem can be solved, W ₂ must be increased more than necessary, and the movable range of the objective lens driving device must be increased further. Therefore, as shown in FIG. 19, it is preferable that the objective lens 4 on the inner peripheral side corresponds to an optical disc having a thin substrate and the objective lens 5 on the outer peripheral side corresponds to an optical disc having a thick substrate.

As described in the first and second embodiments described above, when both objective lenses are focused on the same optical disc at the same height, both signals are sent to the photodetector. Since the incident light has an adverse effect, it is necessary to set the value of each working distance and the difference in height to appropriate values. The depth of focus of the objective lens is usually on the order of microns, and it is unlikely that both will be in focus, but it should be set to an appropriate value so as not to include the possibility of being in focus due to component tolerances. Is desirable.

In the above description, the case where the objective lens driving device of the type supported by the elastic spring mechanism is used to divide the beam according to the polarization direction of the light beam has been described, but the present invention is not limited to this. Needless to say, the present invention can also be applied to a system in which an objective lens driving device called a shaft sliding type is used and the objective lens is switched by rotation of its movable part.

[0063]

As described above, according to the optical pickup device of the first aspect, the height of the objective lens located on the inner peripheral side of the recording medium is higher than the height of the objective lens located on the outer peripheral side. Since it is on the lower side, even when recording and reproducing the data of the innermost circumference of the recording medium with the objective lens located on the outer circumference side,
A wide gap can be provided between the objective lens located on the inner peripheral side and the turntable, and collision between the objective lens and the turntable can be avoided. Further, for this reason, it is not necessary to increase the diameters of both objective lenses, and it is possible to suppress the size increase of the apparatus.

According to the optical pickup device of the second aspect, since the difference in mounting height is substantially equal to the difference in working distance,
The required movable range of the objective lens driving device can be minimized, the working distance can be minimized, and since the two objective lenses correspond to recording media having different substrate thicknesses, the two objective lenses are It is possible to reduce the influence of mixing of both light beams on the photodetector without focusing at the same height.

According to the optical pickup device of the third aspect, the working distance of the objective lens located on the inner peripheral side of the recording medium is set to be smaller than the working distance of the objective lens located on the outer peripheral side. Therefore, even when recording and reproducing the innermost data of the recording medium with the objective lens located on the outer peripheral side, it is possible to widen the gap between the objective lens located on the inner peripheral side and the turntable, A collision between the objective lens and the turntable can be avoided. Also for this,
It is not necessary to increase the diameters of both objective lenses, and it is possible to prevent the apparatus from becoming large.

According to the optical pickup device of the fourth aspect, the objective lens located on the inner peripheral side corresponds to the recording medium having the smaller substrate thickness, and the objective lens located on the outer peripheral side corresponds to the substrate thickness. Since it is adapted to the thicker recording medium, the required movable range of the objective lens driving device can be made as small as possible to prevent two objective lenses from focusing at the same height. It is possible to reduce the effect of mixing both light beams on the light.

According to the optical pickup device of the fifth aspect, the mounting height and working distance of the objective lens are set so as to prevent the two objective lenses from focusing at the same height. It is possible to reduce the effect of mixing both light beams on the detector.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an optical pickup device of a first embodiment.

FIG. 2 is a plan view showing a configuration of an objective lens driving device provided in the optical pickup device of FIG.

FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, in which prisms and the like are shown below the objective lens.

FIG. 4 is a perspective view showing a structure of a hologram laser provided in the optical pickup device of the first embodiment.

FIG. 5 is a diagram illustrating a positional relationship between a hologram and a photodiode included in the optical pickup device according to the first embodiment.

FIG. 6 is a diagram showing a state of division of a light beam according to a polarization direction in the optical pickup device of the first embodiment, which is a case where an objective lens on the outer peripheral side is used to cope with a magneto-optical disk.

FIG. 7 is a diagram showing a split state of a light beam according to a polarization direction in the optical pickup device of the first embodiment, in which the intensity of reflected light other than the magneto-optical disc is detected by using an objective lens on the inner circumference side. This is the case corresponding to the type of optical disc.

FIG. 8 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, and is a case where W ₁ <W ₂ and it corresponds to an optical disc having a different substrate thickness.

FIG. 9 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, and is a case where W ₁ <W ₂ and it corresponds to an optical disc having the same substrate thickness.

FIG. 10 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ and W ₁ -W ₂ > d and different substrate thicknesses are used. This is a case corresponding to an optical disc.

FIG. 11 is a view for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ and W ₁ −W ₂ > d, and the same substrate thickness. This is a case corresponding to an optical disc.

FIG. 12 is a view for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ , W ₁ −W ₂ ≈d, and different substrate thicknesses. This is a case corresponding to an optical disc.

FIG. 13 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ , W ₁ −W ₂ ≈d, and the same substrate thickness. This is a case corresponding to an optical disc.

FIG. 14 is a diagram illustrating the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ and W ₁ −W ₂ <d and different substrate thicknesses are used. This is a case corresponding to an optical disc.

FIG. 15 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ and W ₁ −W ₂ <d, and the same substrate thickness. This is a case corresponding to an optical disc.

FIG. 16 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the first embodiment, where W ₁ > W ₂ , W ₁ −W ₂ ≈d, and the objective on the inner circumference side. This is a case where the lens corresponds to an optical disc having a thick substrate and the objective lens on the outer peripheral side corresponds to an optical disc having a thin substrate.

FIG. 17 is a plan view showing the configuration of an objective lens driving device provided in the optical pickup device of the second embodiment.

FIG. 18 is a cross-sectional view taken along the line AA of FIG. 17, in which prisms and the like are shown below the objective lens.

FIG. 19 is a view for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the second embodiment, where W ₁ <W ₂ and the objective lens on the inner peripheral side is an optical disc with a thin substrate. In this case, the objective lens on the outer peripheral side corresponds to an optical disc having a thick substrate.

FIG. 20 is a diagram for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the second embodiment, which corresponds to the case where W ₁ <W ₂ and an optical disc having the same substrate thickness is dealt with.

FIG. 21 is a view for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the second embodiment, where W ₁ <W ₂ and the objective lens on the inner peripheral side is an optical disc with a thick substrate. In this case, the objective lens on the outer peripheral side corresponds to an optical disc having a thin substrate.

FIG. 22 is a view for explaining the positional relationship between the turntable and the objective lens in the optical pickup device of the second embodiment, where W ₁ << W ₂ and the objective lens on the inner peripheral side is an optical disc with a thick substrate. In this case, the objective lens on the outer peripheral side corresponds to an optical disc having a thin substrate.

FIG. 23 is a perspective view showing a configuration of a first conventional optical pickup device.

FIG. 24 shows a case where the innermost objective lens is used to record and reproduce data on the innermost periphery of an optical disc having a thin substrate in the second conventional optical pickup device.

FIG. 25 shows a case where data is recorded and reproduced on the innermost periphery of an optical disc having a thick substrate by using an objective lens on the outer periphery side in the second conventional optical pickup device.

[Explanation of symbols]

 1 Optical Pickup Device 2 Objective Lens Driving Device 4, 5 Objective Lens 6 Lens Holder 8 Focus Coil 9 Tracking Coil 10 Base 11 Elastic Body 16 Yoke 17 Permanent Magnet 21 Reflection Mirror 22 Polarization Beam Splitter 23 Hologram Laser 24 Collimating Lens 25 Wollaton Prism 27 Spot lens 29 Photodetector 38 Optical disc 39 Turntable

Claims (5)

[Claims] 1. An objective lens driving device for converging a light beam and controlling movement of an objective lens for irradiating the recording medium with the converged light in a predetermined direction, the objective lens driving device including the objective lens driving device. In the optical pickup device in which two of the two objective lenses are mounted side by side in the radial direction of the recording medium, the height of the objective lens of the two objective lenses located on the inner peripheral side of the recording medium is An optical pickup device, wherein the optical pickup device is arranged so as to be more distant from a recording medium than the height of an objective lens located on the outer peripheral side of the medium. 2. The two objective lenses correspond to recording media having different substrate thicknesses, and the working distance of the inner objective lens is larger than the working distance of the outer objective lens. 2. The optical pickup device according to claim 1, wherein the difference in mounting height of the two objective lenses is substantially equal to the difference in both working distances. 3. An objective lens driving device for converging a light beam and controlling movement of an objective lens for irradiating the converged light to a recording medium in a predetermined direction, the objective lens driving device including the objective lens driving device. In the optical pickup device in which two of the two objective lenses are mounted side by side in the radial direction of the recording medium, the working distance of one of the two objective lenses located on the inner peripheral side of the recording medium is recorded. An optical pickup device, which is set to be smaller than a working distance of an objective lens located on the outer peripheral side of a medium. 4. The two objective lenses correspond to recording media having different substrate thicknesses, and the objective lens located on the inner peripheral side of the recording medium is the one having a smaller substrate thickness. The optical pickup device according to claim 3, wherein the optical pickup device corresponds to a recording medium. 5. The values of at least one of the mounting height and the working distance of the two objective lenses are different between the two objective lenses, and both objectives are the same height for the same recording medium. The optical pickup device according to any one of claims 1 to 4, wherein the lens is configured so as not to be in focus.