JP3433036B2 - Optical pickup device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for reading signals from both a normal density recording medium and a high density recording medium having different recording densities, and a first light source and a first light source which emit light beams having different wavelengths from each other. The present invention relates to an optical pickup device including two light sources.

[0002]

2. Description of the Related Art As an optical disc in which a signal is optically read using a light beam such as a laser beam,
CDs (Compact Discs) are in widespread use, but in response to the needs for even larger capacities, the capacity is increased by making the discs the same disk diameter as the CDs and ensuring mechanical compatibility, and then recording at a higher density than the CDs. A high density disc (DVD) standardized as a drawing has been proposed.

In this high density disc, a recording signal is read by using an optical pickup device in which a laser element having a short wavelength is used and an optical system has a high resolution. By the way, in order to make the optical pickup device compatible with signal reading of both CD and high-density disc, a laser diode that emits a light beam having a wavelength suitable for a CD and a laser that emits a light beam having a wavelength suitable for a high-density disc are used. Two types of light sources with different diode wavelengths are prepared, the light source to be used is switched according to the recording density of the disc for signal reading, and the aperture for limiting the light beam incident on the objective lens is read and the recording density of the disc is read. The NA value of the objective lens is adapted to the recording density of the disc by switching according to, and the NA value of the objective lens is reduced by reducing the aperture diameter when reading the CD.
On the other hand, when reading a high-density disc, by increasing the aperture diameter and increasing the NA value of the objective lens, it is possible to read signals of two types of discs having different recording densities by a single optical pickup. There is a method to do.

In the optical pickup device of such a system, since two kinds of light sources are used, the signal can be read by the light beam having an appropriate wavelength even if the recording medium has a wavelength dependence in the recording film. It is possible to prevent a situation in which the recording signal cannot be read because the signal strength level obtained by the device is significantly reduced.

[0005]

By the way, as described above, in order to switch the aperture diameter for limiting the light beam incident on the objective lens according to the signal recording density, two apertures are mechanically moved. There is a problem in that a mechanism or a mechanism for opening and closing the shutter is required, or if a liquid crystal shutter is used, electrical wiring is required, which makes the structure difficult to manufacture.

[0006]

SUMMARY OF THE INVENTION The present invention provides a first light source and a second light source that emit light beams having different wavelengths for reading signals from a normal density recording medium and a high density recording medium having different recording densities. The aperture setting member is provided with an aperture for setting the NA value of the objective lens in the light beam of the wavelength of the first light source on the long wavelength side, and the outer periphery of the aperture of the aperture setting member The side is a diffraction grating, and the diffraction grating is set so that the light beam of the wavelength of the first light source is diffracted and the light beam of the wavelength of the second light source on the short wavelength side is not diffracted. In this way, the diffraction grating limits the passage of the light beam of the wavelength of the first light source to set the aperture in the light beam, and the diffraction grating affects the aperture of the light beam of the wavelength of the second light source. I try not to. Then, the second aperture setting means provided on the same optical axis as the aperture setting member sets the aperture in the light beam of the wavelength of the second light source, and sets the NA value of the objective lens in this light beam. .

In this case, the second aperture setting means is formed in the lens holder on which the objective lens is mounted, and the aperture of the light beam of the first light source and the aperture of the light beam of the second light source are independently provided on the optical axis. It is possible to adjust the matching. Alternatively, the second aperture setting means is formed on the surface of the aperture setting member where the diffraction grating is not formed, and the aperture of the light beam of the first light source and the aperture of the light beam of the second light source are formed on the same member. I am trying to form.

[0008]

FIG. 1 is a side view showing an essential part of an optical pickup device showing an embodiment of the present invention, and FIG. 2 is a plan view showing the overall optical system of an optical pickup device including the optical system of FIG. It is a figure.

The optical pickup device shown in the drawing is a normal density recording disk of the CD family and a DVD (digital
Versatile disk) high-density recording disk can read signals.

In the figure, reference numeral 1 is provided with a first laser element 2 for emitting a laser beam having a wavelength suitable for a normal density recording disk, for example, 780 nm in the same package, and the first laser element 2 modulated by the disk is provided. The optical unit includes a photodetector 3 that receives a laser beam.

This optical unit 1 has a diffraction grating 4 of a hologram element for dividing the optical path in the front part of the package, and the optical axis of the laser beam returned from the disk is bent by the diffraction grating 4, The laser beam is applied to a photodetector 3 arranged on an optical axis different from that of the first laser element 2.

The laser beam emitted from the first laser element 2 of the optical unit 1 is emitted from the optical unit 1 through the diffraction grating 4, and the divergence lens 5 adjusts the divergence angle of the laser beam. The prism type reflection mirror 6 bends the optical axis. The laser beam bent by the reflection mirror 6 has its optical axis bent by a prism type beam splitter 7 which is in close contact with the reflection mirror 6 and is integrally formed, and travels toward a rising mirror 8.

The laser beam which is reflected by the rising mirror 8 and whose optical axis is perpendicular to the disk surface is formed in the aperture setting plate 9 and the lens holder 11 in which the objective lens 10 is mounted. The light enters the objective lens 10 through the diaphragm 12 and is converged on the signal surface of the disc D by the objective lens 10.

The laser beam modulated by the signal surface of the disk D and reflected is returned to the objective lens 10, and returned to the beam splitter 7 via the aperture stop 12, the aperture setting plate 9 and the rising mirror 8, and the beam splitter. It is reflected by 7, then reflected by the reflection mirror 6 and returned to the optical unit 1 via the divergent lens 5.

The optical axis of the laser beam returned to the optical unit 1 is bent by the diffraction grating 4 and the photodetector 3 is detected.
Is received by. The laser beam corresponding to the normal density disk emitted from the first laser element 2 arranged in the optical unit 1 in this way is received by the photodetector 3 in the optical unit 1, and is normally detected by the photodetector 3. The recording signal of the density disc is obtained, and each control signal used for focusing control and tracking control corresponding to the normal density disc is obtained.

On the other hand, the first laser element 2 and the second laser element 1 are arranged in the optical path branched by the beam splitter 7.
3 are arranged. The second laser element 13 emits a laser beam having a wavelength suitable for a high density disc, for example, 635 nm.

The laser beam emitted from the second laser element 13 is reflected by the surface of the half mirror 14, is collimated by the collimator lens 15, and is then incident on the beam splitter 7. The laser beam incident on the beam splitter 7 goes straight as it is, and goes to the rising mirror 8.

After that, the laser beam is directed to the raising mirror 8
The optical axis is bent by the aperture setting plate 9 and the aperture stop 12.
Is incident on the objective lens 10 via the
Is converged on the signal surface of the disk D.

The laser beam modulated by the signal surface of the disk D and reflected is returned to the objective lens 10, and is returned to the beam splitter 7 via the aperture stop 12, the aperture setting plate 9 and the raising mirror 8, and the beam splitter. 7 goes straight on, and then returns to the half mirror 14 via the collimator lens 15.

The laser beam returned to the half mirror 14 passes through the half mirror 14, reaches the photodetector 16, and is received by the photodetector 16. The laser beam corresponding to the high-density disc emitted from the second laser element 13 is received by the photodetector 16 and a recording signal of the high-density disc is obtained by the photodetector 16 and the high-density disc is obtained. Each control signal used for the focusing control and the tracking control corresponding to is obtained.

By the way, the aperture setting plate 9 is arranged on the optical path of the laser beam by being bonded to the lower surface of the lens holder 11 on which the objective lens 10 is mounted, as shown in FIG. The opening setting plate 9 is, as shown in the plan view of FIG.
A diffraction grating is formed around the pupil 9a of the pupil 9a, which is a circular transmission region in the center. The diffraction grating is formed by providing a 1: 1 rectangular grating on a flat plate substrate made of a transparent material such as glass, and the grating is the first laser element 2
Is designed to diffract the laser beam having the wavelength of and the property of not diffracting the laser beam having the wavelength of the second laser element 13.

When the diffraction grating is made of titanium dioxide (TiO2), the second laser element 1
The refractive index is 2.349 for the laser beam of wavelength 3 (635 nm), and the grating depth is 941n with a phase difference of 4π.
When m is set, the characteristic of the diffraction efficiency as shown in FIG. 4 can be obtained, and the transmittance is set to 100% without causing diffraction to the laser beam of the wavelength of the second laser element 13, and the first laser is used. Diffraction can be caused to the laser beam of the wavelength (780 nm) of the element 2 so that the transmittance can be about 5%.

Therefore, the aperture setting plate 9 does not limit the luminous flux of the laser beam having the wavelength of the second laser element 13,
The luminous flux of the laser beam having the wavelength of the laser element 2 is limited. By the way, in front of the objective lens 10, an aperture stop 12 which is a second aperture setting means formed in the lens holder 11 is arranged.

The aperture setting plate 9 is bonded to the lens holder 11 so that the pupil 9a in the central portion where the diffraction grating is not formed is coaxial with the pupil of the aperture stop 12, and the pupil of the aperture stop 12 is set for aperture. It has a larger diameter than the pupil 9a of the plate 9.

Therefore, when the laser beam emitted from the first laser element 2 is used, the aperture of the objective lens 10 is set by the pupil 9a of the aperture setting plate 9, and the objective lens is determined by the diameter of the pupil 9a. The NA value of the objective lens 10 is set according to the effective diameter of 10. Therefore, the NA value and the wavelength of the laser beam emitted from the first laser element 2 can determine the diameter of the light spot and the depth of focus that are converged on the signal surface of the disk. The pupil 9 of the aperture setting plate 9 in consideration of the wavelength of the emitted laser beam
By appropriately setting the diameter of a, the light spot for reading the recording signal of the disc can be made to have the light spot diameter and the depth of focus suitable for the normal density recording disc.

On the other hand, the diffraction grating portion of the aperture setting plate 9 has a characteristic of transmitting the laser beam of the wavelength emitted from the second laser element 2. Therefore, the laser beam from the second laser element 2 is not affected by the pupil 9a of the aperture setting plate 9 and the aperture of the objective lens 10 is set by the pupil of the aperture stop 12.

That is, when the laser beam emitted from the second laser element 2 is used, the aperture stop 12
The NA value of the objective lens 10 is set according to the effective diameter of the objective lens 10 which is determined by the pupil diameter of the objective lens 10. Therefore, the NA value and the wavelength of the laser beam emitted from the second laser element 13 can determine the diameter of the light spot and the depth of focus converged on the signal surface of the disk. By appropriately setting the pupil diameter of the aperture stop 12 in consideration of the wavelength of the emitted laser beam, the light spot for reading the recording signal of the disc can be set to the light spot diameter and the depth of focus suitable for the high density recording disc. I can.

As described above, in the case of a normal density recording disk, by appropriately setting the diameter of the pupil 9a of the aperture setting plate 9 in consideration of the wavelength of the laser beam emitted from the first laser element 1, a high density can be obtained. Second for recording discs
By setting the pupil diameter of the aperture stop 12 in consideration of the wavelength of the laser beam emitted from the laser element 2, the light spot diameter and the depth of focus can be set. With respect to, the light spot diameter and the depth of focus can be set independently.

In the above embodiment, the NA value of the objective lens 10 is set for the laser beam emitted from the second laser element 13 by the pupil diameter of the aperture stop 12. Figure 3 without
As shown by the dotted line in FIG. 3, a light-shielding region that is concentric with the pupil 9a and has a large diameter in which the laser beam from the second laser element 13 is transmitted is left in the aperture setting plate 9 and the laser beam is shielded on the outer peripheral side. To form N of the objective lens 10 in the laser beam from the second laser element 2.
The A value may be set.

In this case, the light shielding region can be easily formed by, for example, depositing a metal film on the surface of the aperture setting plate 9 where the diffraction grating is not formed, and the laser beam from the first laser element 2 can be formed. Since the opening in and the opening in the laser beam from the second laser element 13 are formed in the same member, the objective lens 10
On the other hand, if the position of the aperture setting plate 9 is appropriately set, the optical axes of the respective apertures can be aligned with the objective lens 10 at the same time.

[0031]

As described above, the present invention uses the diffraction grating to limit the light beam from the first light source of the aperture setting member that sets the aperture of the objective lens in the light beam of the wavelength of the first light source. Since the diffraction grating is set to a characteristic that does not diffract the light beam of the wavelength of the second light source, the aperture setting member does not affect the aperture of the light beam of the wavelength of the second light source. By providing the second aperture setting means for setting the aperture of the objective lens in the light beam of the wavelength of the second light source on the same optical axis as the member, it is possible to correspond to each light beam from the first and second light sources. The reliability can be improved without switching the aperture diameter, and each aperture of the objective lens in each light beam can be set.

Further, since the second aperture setting means is formed in the lens holder on which the objective lens is mounted, the labor for installing the second aperture setting means can be omitted and the second aperture setting means can be omitted. It is not necessary to provide the aperture setting member on the aperture setting member, and the optical axis alignment of each aperture in each light beam from the first and second light sources can be independently adjusted.

Further, the second aperture setting means is formed on the surface of the aperture setting member where the diffraction grating is not formed so that the aperture of the light beam of the first light source and the aperture of the light beam of the second light source are the same. If it is formed on the member, the optical axes of the respective openings can be aligned with the objective lens at the same time.

[Brief description of drawings]

FIG. 1 is a side view showing a main part of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a plan layout view showing an entire optical system of an optical pickup device including the optical system of FIG.

FIG. 3 is a plan view showing an aperture setting plate 9.

FIG. 4 is a characteristic diagram showing an example of the diffraction efficiency of the aperture setting plate 9.

[Explanation of symbols]

1 Optical unit 2 First laser element 9 Aperture setting plate 9a Hitomi 10 Objective lens 11 lens holder 12 Aperture stop 13 Second laser device

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-50647 (JP, A) JP-A-63-39150 (JP, A) JP-A-8-339567 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B ^7/ 12-7/22

Claims (3)

(57) [Claims] 1. An optical pickup device for reading signals from both a normal density recording medium and a high density recording medium having different recording densities, the first light source emitting a light beam having a wavelength suitable for the normal density recording medium. A second light source that emits a light beam having a wavelength suitable for a high-density recording medium, and a diffraction grating set to a characteristic that diffracts a light beam having a wavelength of the first light source limits the light beam of the light beam, An aperture setting member configured to form a transmission region of a light beam from the first light source by a pupil portion that does not form a diffraction grating and set an aperture of an objective lens in the light beam of the wavelength of the first light source; Is set to a characteristic that does not diffract the light beam of the wavelength of the second light source, and sets the aperture of the objective lens for the light beam of the wavelength of the second light source on the same optical axis as the aperture setting member. An optical pickup device comprising a second aperture setting means. 2. The optical pickup device according to claim 1, wherein the second aperture setting means is formed in a lens holder on which an objective lens is mounted. 3. The optical pickup device according to claim 1, wherein the second aperture setting means is formed on a surface of the aperture setting member where the diffraction grating is not formed.