JPH1011793A - Optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly reproduce an optical disk, which may be of any type with a different substrate thickness, by providing a variable opening means between a light source and the optical disk. SOLUTION: The optical pickup 20 is an infinite system and is provided with a semiconductor laser element 21 as a light source, beam splitter 22 as a light separating means, collimator lens 23, objective lens 24, photodetector 25, and a variable opening means 26 arranged between the collimator lens 23 and the objective lens 24. Then, the variable opening means 26 is structured as a variable opening diaphragm and supported against the case of the optical pickup 20. In addition, the diaphragm of the variable opening means 26 imparts the maximum opening in the case of 0.6mm disk substrate thickness, while the diaphragm is converged in the case of 1.2mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup and an optical disk apparatus for recording and / or reproducing an information signal by irradiating an optical disk with light and detecting return light.

[0002]

2. Description of the Related Art Conventionally, for example, an optical pickup for reproducing an optical disk on which image data is digitized and compressed and recorded is configured as shown in FIG.
In FIG. 8, the optical pickup 1 has an infinite system configuration and includes a semiconductor laser element 2, a beam splitter 3, a collimator lens 4, an objective lens 5, and a photodetector 6.

The beam splitter 3 has a reflection surface 3
a is disposed at an angle of 45 degrees with respect to the optical axis of the objective lens 5, and separates the light beam emitted from the semiconductor laser element 2 from the return light from the signal recording surface of the optical disk 7. That is, the light beam from the semiconductor laser element 2 is reflected by the reflection surface 3a of the beam splitter 3, and
Is transmitted through the beam splitter 3.

The objective lens 5 is a convex lens, and focuses a parallel light beam from the collimator lens 4 on a desired track on a signal recording surface of an optical disk 7 that is driven to rotate. Further, the objective lens 7 is supported by a biaxial actuator (not shown) so as to be movable in a biaxial direction, that is, a focusing direction indicated by an arrow Fcs and a tracking direction indicated by an arrow Trk in the drawing.

[0005] The photodetector 6 is configured to have a light receiving portion for a return light beam that is transmitted through the beam splitter 3 and enters.

According to the optical pickup 1 having such a configuration, the light beam emitted from the semiconductor laser device 2 is
After being reflected by the reflecting surface 3 a of the beam splitter 3 and converted into parallel light by the collimator lens 4, the light is converged through the objective lens 5 to a certain point on the signal recording surface of the optical disk 7.

The return light beam reflected on the signal recording surface of the optical disk 7 again enters the beam splitter 3 via the objective lens 5 and the collimator lens 4. here,
The return light beam passes through the beam splitter 3 and enters the light receiving unit of the photodetector 6. Thereby, based on the detection signal output from the photodetector 6, the information recorded on the signal recording surface of the optical disk 7 is reproduced.

[0008]

In recent years, the density of optical discs has been increasing as an auxiliary storage device of a computer and a package medium of audio / video information. There is a method in which the numerical aperture NA of the objective lens is made larger than the numerical aperture NA of the objective lens in the conventional optical pickup for a compact disk. However, if the numerical aperture NA is increased, the allowable range for the tilt of the optical disk is reduced. There's a problem.

The optical disk has a predetermined disk substrate thickness (generally, 1.2 mm for a compact disk or the like).
mm), the signal recording surface is provided via the transparent substrate. If the optical disk is inclined with respect to the optical axis of the objective lens of the optical pickup, a wavefront aberration occurs, and the RF
The signal reproduction will be affected. At this time, regarding the wavefront aberration, the third-order coma which occurs in proportion to the cube of the numerical aperture and the first power of the skew angle θ is dominant. Accordingly, an optical disk having a transparent substrate made of polycarbonate or the like mass-produced at low cost has a skew angle θ of, for example, ±
Because there is 0.5 to ± 1 degree, by the above wavefront aberration,
The focused spot from the semiconductor laser element 2 of the optical pickup 1 to the optical disk 6 becomes asymmetric, and the intersymbol interference increases significantly, so that accurate reproduction of the RF signal cannot be performed.

Therefore, paying attention to the fact that the third-order coma is proportional to the disk substrate thickness of the optical disk, the third-order coma is reduced by half by reducing the thickness of the disk substrate by half to 0.6 mm. It is possible to In this case, as an optical disc, two standards having different characteristics,
That is, the disk substrate thickness is relatively thick (for example, 1.2 mm)
And a disk substrate having a relatively small thickness (for example, 0.6
mm) are mixed.

Here, for example, when a parallel flat plate having a thickness t is inserted into the optical path, the thickness t and the numerical aperture NA are t
Since spherical aberration occurs in proportion to × (NA) 4, the objective lens is designed to cancel this spherical aberration. By the way, if the disk substrate thickness is different, the spherical aberration is also different.
Using an objective lens corresponding to a 6 mm optical disc,
When an optical disc such as a compact disc having a disc substrate thickness of 1.2 mm, a write-once optical disc, a magneto-optical disc, or the like is to be reproduced, spherical aberration occurs due to a difference in disc substrate thickness. This greatly exceeds the allowable range of the error in the thickness of the disk substrate. Therefore, there is a problem that a signal cannot be correctly detected from the return light from the optical disk.

Thus, there has been a problem that the conventional optical pickup cannot reproduce both types of optical disks.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an optical pickup and an optical disk apparatus which can reproduce an optical disk correctly regardless of the type of optical disk having a different disk substrate pressure. And

[0014]

According to the present invention, there is provided a light source for emitting a light beam, an objective lens for irradiating light from the light source so as to focus on a signal recording surface of an optical disk, and Light separating means disposed between the light source and the objective lens, and a light detector for receiving a return light beam from the signal recording surface of the optical disc separated by the light separating means, further comprising: This is achieved by an optical pickup provided with a diaphragm blade type variable aperture means disposed in an optical path between a light source and an optical disk.

According to the above configuration, since the variable aperture means is provided between the light source and the optical disk, the diaphragm blade of the variable aperture means is driven and adjusted in accordance with the thickness of the disk substrate of the optical disk to be reproduced. As a result, the aperture defined by the aperture blades is narrowed down, the numerical aperture of the variable aperture means is adjusted, and as a result, spherical aberration is corrected. As a result, the light beam from the light source is correctly focused on the signal recording surface of the optical disk via the variable aperture means, and the return light from the signal recording surface of the optical disk is incident on the photodetector, so that the optimal light is always obtained. Signal reproduction will be performed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. still,
Since the embodiments described below are preferred specific examples of the present invention, various technically preferred limitations are added.
The scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

FIG. 1 shows an embodiment of an optical disk device incorporating an optical pickup according to the present invention.
In FIG. 1, an optical disk device 10 includes an optical disk 11
Spindle motor 1 as a driving means for rotationally driving the motor
2. An optical pickup 20 that irradiates an optical beam onto a signal recording surface of a rotating optical disk 11 to record a signal, and reproduces a recorded signal by a return light beam from the signal recording surface, and controls these components. The control unit 13 is provided. Here, the control unit 13 includes an optical disk drive controller 14, a signal demodulator 15, an error correction circuit 16, an interface 17, a head access control unit 18, and a servo circuit 19.

The optical disk drive controller 14 includes:
The drive control of the spindle motor 12 is performed at a predetermined rotation speed.
The signal demodulator 15 demodulates the recording signal from the optical pickup 20 and sends it to the error correction circuit 16. The error correction circuit 16 corrects the error of the recording signal from the signal demodulator 15 and sends it to an external computer or the like via the interface 17. Thus, an external computer or the like can receive a signal recorded on the optical disk 11 as a reproduction signal.

The head access control unit 18 moves the optical pickup 20 to a predetermined recording track on the optical disk 11, for example, by a track jump or the like. At the moved predetermined position, the servo circuit 19 moves the objective lens held by the biaxial actuator of the optical pickup 13 in the focusing direction and the tracking direction.

FIG. 2 shows an embodiment of the optical pickup according to the present invention, which is incorporated in the above-mentioned optical disk device. In FIG. 2, the optical pickup 20 includes
An infinite optical pickup, comprising a semiconductor laser device 21 as a light source, a beam splitter 22, a collimator lens 23, an objective lens 24, and a photodetector 25 as light sources, a collimator lens 23 and an objective lens 24.
And a variable opening means 26 disposed between them.

The semiconductor laser element 21 is a light emitting element utilizing recombination light emission of a semiconductor, and is used as a light source. The light beam emitted from the semiconductor laser element 21 is
The light is guided to the beam splitter 22.

The beam splitter 22 has a reflection surface 22.
a is disposed at an angle of 45 degrees with respect to the optical axis of the objective lens 24, and separates the light beam emitted from the semiconductor laser element 21 and the return light from the signal recording surface of the optical disk 27. That is, the light beam from the semiconductor laser element 21 is reflected by the reflection surface 22a of the beam splitter 22,
The return light passes through the beam splitter 22.

The collimator lens 23 is a convex lens, and converts the light beam reflected by the beam splitter 22 into a parallel light beam.

The objective lens 23 is a convex lens, and focuses the parallel light beam from the collimator lens 23 on a desired track on the signal recording surface of the optical disk 27 that is driven to rotate. Further, the objective lens 24 is supported by a biaxial actuator (not shown) so as to be movable in biaxial directions, that is, in a tracking direction and a focusing direction.

The photodetector 25 is configured to have a light receiving portion for the return light beam transmitted through the beam splitter 22.

As shown in FIGS. 4 and 5, the variable aperture means 26 is configured as a so-called aperture blade type variable aperture mechanism, and is supported by a case (not shown) of the optical pickup 20. Incidentally, the variable opening means 26 may be attached to a holder for supporting the collimator lens 23. In this case, the variable opening means 26
Since it will be configured integrally with the collimator lens,
The optical pickup 20 can be easily assembled,
Optical adjustment becomes easy.

4 and 5, the variable aperture means 26
Is a flat hollow cylindrical base 30 with an open top,
The aperture blades 31, which are sequentially inserted into the base 30,
It includes a ring 32, a print coil 33, a magnet 34, and a yoke 35.

The base 30 is located at the center of its closed lower surface,
Having the aperture 30a and the aperture 30
A plurality (six in the illustrated case) of bosses 30b are provided at equal angular intervals so as to surround a.

The diaphragm blades 31 are composed of the same number of diaphragm blades (six in the drawing) having the same number as the bosses 30b.
It has a hole 31a that engages with the 0 boss 30b and a cam groove 31b.

The ring 32 is formed in a disk shape and has an opening 32a at the center thereof.
A plurality of (six in the illustrated case) bosses 30b, which are arranged at equal angular intervals around 2a, are provided with cam pins 32b protruding downward.

The printed coil 33 is a printed circuit board 33
It has a plurality (four in the illustrated case) of coils 33 b formed by a conductive pattern on a and is fixed to the ring 32.

The magnet 34 is formed in an annular shape, and is magnetized corresponding to each coil 33b of the print coil 33 so that S poles and N poles are alternately arranged along the circumferential direction. .

The yoke 35 is formed in a disk shape by a magnetic material, and is attached so that the magnet 34 is fixed and the open end of the base 30 is closed.

The variable opening means 26 having such a configuration is configured such that a drive voltage is applied to each coil 33b of the print coil 33, so that the magnetic field generated in each coil 33b and the magnetic field generated by the magnet 34 and the yoke 35 The interaction causes the ring 32 to pivot within the base 30.
In this case, the rotation direction of the ring 32 is
3 is determined by the sign of the drive voltage applied to each coil 33b.

As a result, when the ring 32 rotates counterclockwise in FIG. 4, each of the aperture blades 31 slides in its cam groove 31b, so that the cam pin 32b of the ring 32 slides. Base 3 with which 31a is engaged
Swinging outward around the 0 boss 30b,
As shown in FIG. 6, the base 3
It retracts outside the 0 aperture 30a. On the other hand, when the ring 32 rotates clockwise in FIG. 4, each of the aperture blades 31 moves the ring 3 in its cam groove 31b.
When the second cam pin 32b slides, the hole 31
7a is swung inward about the boss 30b of the base 30 with which it engages, enters the inside of the aperture 30a of the base 30, and narrows the aperture 30a, as shown in FIG.

Here, as shown in FIG. 6, when the aperture blade 31 is driven so as to give the maximum aperture, the variable aperture means 26 has, for example, a numerical aperture NA = 0.6.
As shown in FIG. 7, when the aperture blade 31 is narrowed down, the size of the aperture 30b of the base 30 is selected so that the numerical aperture NA is equal to or less than NA0.
The drive adjustment of the aperture blade 31 is performed. NA0 is 0.45 / of the light source wavelength λ (μm).
It is represented by 0.78 times. Therefore, the light source wavelength λ is 0.6
NA0 = 0.366 when the wavelength is 35 μm, NA0 = 0.37 when the light source wavelength λ is 0.650 μm, and NA0 = 0.392 when the light source wavelength λ is 0.680 μm.
Becomes

Thus, for an optical disk having a relatively thin disk substrate thickness of 0.6 mm, the aperture blade 31 provides the maximum aperture, so that the aperture 30a or the objective lens 24 is provided depending on the size of the aperture 30a.
, The numerical aperture NA of the variable aperture means 15 is
0.6 and relatively thick disk substrate thickness
For an optical disk of 2 mm, the aperture blade 31 is narrowed down so that the numerical aperture NA of the variable aperture means 26 is N = N.
It is set to A0 or less.

The optical pickup 10 according to the present embodiment
Is constructed as described above. First, a description will be given of a case where an optical disk having a relatively thin disk substrate thickness of 0.6 mm is reproduced. In this case, as shown in FIG. 6, the variable aperture means 26 is retracted from the aperture 30a so that the aperture blade 31 provides the maximum aperture. In this state,
As shown in FIG. 2, the light beam from the semiconductor laser element 21 is reflected by the reflection surface 22 a of the beam splitter 22, is converted into parallel light by the collimator lens 23, and passes through the aperture 30 a of the variable aperture means 26. Then, the light is focused on the signal recording surface of the optical disk 27 via the objective lens 24. At this time, since NA is set to 0.6 by the variable aperture means 26, the spherical aberration can be suppressed low, so that the light beam is properly focused on the signal recording surface of the optical disk 27.

The return light from the optical disk 27 returns to the objective lens 24, the variable aperture means 26 and the collimator lens 2 again.
3, and through the beam splitter 22,
Focus on the photodetector 25. Thereby, the recording signal of the optical disk 27 is reproduced based on the detection signal of the photodetector 25.

Next, a relatively thick disk substrate thickness of 1.2 m
When reproducing the optical disk of m, the variable aperture means 26 first causes the aperture blade 31 to swing inside the aperture 30a and narrow the aperture 30a, as shown in FIG. Then, in this state, as shown in FIG. 3, the light beam from the semiconductor laser element 21 is reflected by the reflection surface 22a of the beam splitter 22, and then is made into parallel light by the collimator lens 23, and is changed by the variable aperture means. 26 through the aperture 30a, and further through the objective lens 24,
It is focused on the signal recording surface of the optical disc 27. At this time, NA is set to be equal to or less than NA0 by the variable aperture means 26, but the objective lens 24 has a disk substrate thickness of 1.2 mm.
The optical beam is correctly focused on the signal recording surface of the optical disk 27 because the optical disk is designed so that the spherical aberration can be suppressed most.

The return light from the optical disk 27 is again transmitted to the objective lens 24, the variable aperture means 26 and the collimator lens 2.
3, and through the beam splitter 22,
Focus on the photodetector 25. Thereby, the recording signal of the optical disk 27 is reproduced based on the detection signal of the photodetector 25.

In the above embodiment, the variable aperture means 26 is provided between the collimator lens 23 and the objective lens 24. However, the present invention is not limited to this. What is necessary is just to be arrange | positioned in the optical path between. Here, when the variable aperture means is disposed in the optical path between the optical disk 27 and the beam splitter 22, both the light beam from the light source 21 to the optical disk 27 and the return light beam from the optical disk 27
The aperture is narrowed down by the variable aperture means. On the other hand, when the variable aperture means is disposed in the optical path between the beam splitter 22 and the light source 21, the light source 2
Only the light beam from 1 to the optical disk 27 is narrowed down by the variable aperture means, and the return light beam from the optical disk 27 does not pass through the variable aperture means, so that it is not narrowed down.

In the above embodiment, the optical disk has a disk substrate thickness of 1.2 mm and 0.6 mm.
By opening or narrowing the aperture blades 31 of the variable aperture means 26, the light beam is focused on an optical disk having a relatively small disk substrate thickness and a signal recording surface of an optical disk having a relatively large disk substrate thickness. However, the present invention is not limited to this. For example, the present invention can be applied to a case where a bonded optical disk in which two substrates are bonded and a normal optical disk are reproduced.

In the above embodiment, the optical disk device 10 is a read-only optical disk device.
It is apparent that the present invention is not limited to this, and can be applied to an optical pickup used in an optical disc device for recording and reproduction.

[0045]

As described above, according to the present invention, the numerical aperture of the variable aperture means is adjusted by driving the aperture blade in accordance with the thickness of the optical disk to be recorded and / or reproduced. Thereby, the spherical aberration is corrected. As a result, the light beam from the light source is correctly focused on the signal recording surface of the optical disk via the variable aperture means, and the return light from the signal recording surface of the optical disk is incident on the photodetector, so that the optimal light is always obtained. Signal reproduction will be performed. Therefore, regardless of the type of optical disk, the optical disk can be correctly reproduced.
An optical pickup and an optical disk device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disc device incorporating an embodiment of an optical pickup according to the present invention.

FIG. 2 is a schematic perspective view of an embodiment when an optical pickup incorporated in the optical disk apparatus of FIG. 1 reproduces an optical disk having a relatively thin disk substrate pressure.

FIG. 3 is a schematic perspective view of an embodiment of the optical pickup incorporated in the optical disc apparatus of FIG. 1 when reproducing an optical disc having a relatively thick disc substrate pressure.

FIG. 4 is an exploded perspective view showing a configuration of a variable aperture unit in the optical pickup of FIG.

FIG. 5 is a sectional view of the variable opening means of FIG. 4;

FIG. 6 is a schematic plan view of the variable aperture means of FIG. 4 during reproduction of an optical disk having a relatively thin disk substrate pressure.

7 is a schematic plan view of the variable aperture means of FIG. 4 during reproduction of an optical disk having a relatively thin disk substrate pressure.

FIG. 8 is a schematic perspective view showing an example of a conventional optical pickup.

[Explanation of symbols]

10 optical disk device, 11 optical disk, 1
2 ... Spindle motor, 13 ... Control unit, 14.
..Optical disk drive controller, 15 ... signal demodulator, 16 ... error correction circuit, 17 ... interface, 18 ... head access control unit, 20 ...
-Optical pickup, 21 ... semiconductor laser element, 2
2 ... Beam splitter, 23 ... Collimator lens, 24 ... Objective lens, 25 ... Photodetector, 26
... Variable aperture means, 27 ... Optical disk, 30 ...
・ Base, 31 ・ ・ ・ Aperture blade, 32 ・ ・ ・ Ring, 3
3 print coil, 34 magnet, 35
···yoke.

Claims (10)

[Claims] A light source for emitting a light beam; an objective lens for irradiating the light from the light source so as to be focused on a signal recording surface of an optical disc; and a light separator disposed between the light source and the objective lens. Means, and a photodetector for receiving a return light beam from the signal recording surface of the optical disc separated by the light separating means, and further provided in an optical path between the light source and the optical disc. An optical pickup comprising a diaphragm blade type variable aperture means. 2. The method according to claim 1, wherein said variable aperture means adjusts the numerical aperture of the first and second types of optical disks having different disk substrate thicknesses according to the disk substrate thickness of the optical disk to be reproduced. The optical pickup according to claim 1. 3. The variable opening means, wherein the maximum opening is
3. The optical pickup according to claim 2, wherein the optical pickup is selected so as to have a numerical aperture corresponding to a substrate thickness of the first type disc. 4. The variable opening means has a maximum opening,
3. The optical pickup according to claim 2, wherein the optical pickup is selected so as to have a numerical aperture larger than a numerical aperture corresponding to a substrate thickness of the first type disc. 5. The optical pickup according to claim 1, wherein said opening means is attached to a holder supporting a collimator lens. 6. The optical pickup according to claim 1, wherein said variable aperture means is provided in an optical path between an objective lens and a light source. 7. The optical pickup according to claim 1, wherein said variable aperture means is provided in an optical path between the objective lens and the light separating means. 8. The optical pickup according to claim 1, wherein the variable aperture means is provided in an optical path between the light separating means and the light source. 9. The optical pickup according to claim 1, wherein the variable aperture means is provided in an optical path between the objective lens and the optical disk. 10. A drive means for rotating and driving an optical disk, and irradiating the optical disk with light through an objective lens, and detecting a return light from a signal recording surface from the optical disk by a photodetector through the objective lens. Optical pickup, a biaxial actuator for supporting an objective lens movably in two axial directions, a signal processing circuit for generating a reproduction signal based on a detection signal from the photodetector, and a detection signal from the photodetector A servo circuit for moving an objective lens of an optical pickup in two axial directions based on the optical pickup, wherein the optical pickup focuses light from the light source on a signal recording surface of an optical disc. An objective lens for irradiating the light, a light separating unit disposed between the light source and the objective lens, and a signal recording surface of the optical disc separated by the light separating unit. And a photodetector for receiving the return light beam, further comprising a diaphragm blade type variable aperture means disposed in an optical path between the light source and the optical disk. Optical disk device.