JPH10302294A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely eliminate a crosstalk from an adjacent track which is included in a returning light to a photodetector, by constituting a light- shielding element which is movable integrally with an objective lens so that it passes a light projected to an optical disk and eliminates the crosstalk from the adjacent track to a track being recorded, reproduced among the returning light from the optical disk. SOLUTION: A light-shielding element 20 includes a 1/4 wave plate 20A and a polarization hologram plate 20B. The 1/4 wave plate 20A is located at the side of an optical disk 10, and the polarization hologram plate 20B is placed at the side of a polarization beam splitter 17. A laser light from a laser light source 11 is turned to parallel light beams by a collimator lens 13, and guided to an objective lens 19 through the polarization beam splitter 17, polarization hologram plate 20B and 1/4 wave plate 20A. The light reduced by the objective lens 19 is projected to the optical disk 10. A returning light from the optical disk 10 is guided to the polarization beam splitter 17 and a crosstalk is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for an optical disk, and more particularly, to a technique for removing crosstalk from a pit row of an adjacent track during recording and reproduction.

[0002]

2. Description of the Related Art An example of a conventional optical pickup will be described with reference to FIG. This optical pickup uses a rewritable optical disk, that is, a digital video disk (hereinafter referred to as a DVD).
Called. A) a pickup for a RAM, comprising a laser light source 11 such as a semiconductor laser, a collimator lens 13 for parallelizing the laser light, and an anamorphic prism 15 and an anamorphic prism 15 for beam shaping the parallelized laser light. A polarizing beam splitter 17 for transmitting the transmitted light and deflecting the return light from the optical disk 10; an objective lens 19 for narrowing the laser light to form a minute beam spot on the optical disk 10;
A converging lens 21 and a photodetector 23 for detecting the returning light passing through the converging lens 21.

The function of the anamorphic prism 15 will be described. Since a semiconductor laser generally used as the laser light source 11 has a non-uniform beam divergence angle, the collimator lens 13
The beam converted into a parallel beam has an elliptical cross section, and forms an elliptical beam spot on the optical disc 10. In particular, in the case of a red laser, the aspect ratio of the beam divergence angle is large. If an elliptical beam is used, sufficient rim intensity or fill conditions cannot be obtained in the elements of the optical system.

On the other hand, in a rewritable optical disk such as a DVD-RAM, it is necessary to effectively guide light onto the optical disk 10 in order to irradiate the optical disk 10 with predetermined light energy at the time of writing, and high coupling efficiency is required. Is done. To meet these requirements, the anamorphic prism 15
, And the parallel light beam emitted from the collimator lens 13 is beam-shaped from an elliptical beam to a circular beam.

Since the optical pickup provided with the anamorphic prism 15 is an infinite optical system, it is difficult to reduce the size of the optical system. If the light transmitted through the anamorphic prism 15 is not completely parallel due to the misalignment of the collimator lens 13, aberration occurs, which affects reading performance.

Optical pickups without the anamorphic prism 15 are often used. If the anamorphic prism 15 is not provided, the beam spot formed on the optical disk 10 will be elliptical. In order to improve recording density, reduce reading errors, etc., the laser beam is usually applied so that the minor axis of the ellipse of the beam spot is along the tangential direction of the track, that is, the major axis of the ellipse of the beam spot is tangential to the track Irradiated so as to be orthogonal to. Therefore, when the beam spot also irradiates the pit train of the adjacent track, crosstalk occurs. In particular, when the aspect ratio is large, it is necessary to eliminate crosstalk.

Japanese Patent Application Laid-Open No. 06-044605 describes a method of removing crosstalk caused by return light from a pit row of an adjacent track when a recording signal is reproduced from an optical disk. In this example, a light shielding plate is provided between the polarizing beam splitter 17 and the converging lens 21. The light blocking plate includes a plurality of parallel light blocking bands spaced apart from each other. Thereby, the crosstalk included in the return light to the photodetector 23 is removed.

The intensity distribution of the crosstalk light from the pit row of the adjacent track has a plurality of periodic peaks that decrease outward from the center. Therefore, a plurality of light-shielding bands may be provided at intervals corresponding to the intervals between these peaks.

[0009]

Problems to be Solved by the Invention Japanese Patent Application Laid-Open No. 06-0446
In the example described in No. 05, a light-shielding plate is provided on the optical path of the return light to the photodetector. Therefore, when the objective lens shakes the field of view and the optical path of the return light to the photodetector is displaced, the relative position between the return light and the light shielding plate shifts, and a function of removing crosstalk from an adjacent track included in the return light is provided. descend.

In view of the foregoing, it is an object of the present invention to completely remove crosstalk from an adjacent track included in return light to a photodetector even when the field of view of an objective lens is changed.

[0011]

According to the present invention, there is provided a light-shielding element which can be displaced integrally with an objective lens, and the light-shielding element transmits light emitted to the optical disk. It is configured to remove crosstalk from a track adjacent to the track being recorded / reproduced.

Since the light-shielding element can be displaced integrally with the objective lens, the relative positional relationship between the objective lens and the light-shielding element does not change even if the field of view of the objective lens is changed, and the return to the photodetector occurs. Crosstalk from adjacent tracks included in light can be completely removed.

The light shielding element includes a quarter-wave plate and a band-shaped polarization hologram. Since the return light from the optical disk has passed through the quarter wavelength plate twice, the phase is shifted by a half wavelength. That is, the 90 ° polarization direction has changed.

The strip-shaped polarization hologram transmits light on the outward path to the optical disk, but diffracts and scatters light on the return path from the optical disk having a polarization plane different from that of the optical disk by 90 °. The band-shaped polarization hologram is arranged at a position matching the optical path of the crosstalk from the pit row of the adjacent track. Therefore, the crosstalk from the pit row of the adjacent track is removed by the band-like polarization hologram.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an optical pickup according to the present invention will be described with reference to FIG. The optical pickup of this example is
A laser light source 11 and a collimator lens 13 for collimating the laser beam, a polarization beam splitter 17 for transmitting the collimated laser beam and deflecting the return light from the optical disk 10, and the laser beam on the optical disk 10. An objective lens 19 for forming a narrow beam spot, a light blocking element 20 mounted on the objective lens 19, and a multi-lens for narrowing return light from the optical disk 10, that is, a converging lens 21 and a return light passing through the converging lens 21 And a photodetector 23 for detection.

The light shielding element 20 includes a quarter wavelength plate 20A and a polarization hologram plate 20B. The quarter-wave plate 20A is arranged on the upper side, that is, on the side of the optical disk 10, and the polarization hologram plate 20B is arranged on the lower side, that is, on the side of the polarization beam splitter 17.

The optical pickup of this embodiment is different from the conventional optical pickup shown in FIG. 3 in that a light-shielding element 20 mounted on an objective lens 19 is provided, and other configurations are the same. May be. Although the anamorphic prism 15 is removed in the example of FIG. 1, the anamorphic prism 15 may be provided if necessary.

The laser light output from the laser light source 11 is collimated by the collimator lens 13, passes through the polarization beam splitter 17, and is polarized by the polarization hologram plate 20B.
And the objective lens 19 via the quarter-wave plate 20A. The light focused by the objective lens 19 is applied to the optical disk 10. The return light from the optical disk 10 passes through the objective lens 19, and is guided to the polarization beam splitter 17 via the quarter-wave plate 20A and the polarization hologram plate 20B.

The return light is deflected by the polarization beam splitter 17 and detected by the photodetector 23 via the converging lens 21.

The function of the light shielding element 20 will be described. First, 1 /
The function of the four-wavelength plate 20A will be described. When the linearly polarized light from the polarizing beam splitter 17 passes through the quarter wave plate 20A, it becomes circularly polarized light having a phase shifted by a quarter wavelength. The optical disk 10 is irradiated with this circularly polarized light, but the return light remains circularly polarized. When this return light passes through the quarter-wave plate 20A again, it becomes linearly polarized light having a phase shifted by a quarter wavelength. Therefore, the phase of the return linearly polarized light is shifted by a half wavelength as compared with the phase of the outwardly polarized light. That is, the polarization directions of the return-side linear polarization and the outward-path linear polarization are orthogonal to each other.

Next, referring to FIG.
The function of B will be described. Polarization hologram plate 20B of this example
Has a band-shaped polarization hologram 20-1 having a width W mounted on a transparent substrate 20-2, as shown in the figure. The polarization hologram 20-1 is configured to completely transmit linearly polarized light in a predetermined direction and diffract and scatter linearly polarized light in a direction orthogonal thereto. Portions other than the polarization hologram 20-1 are transparent, and are configured to transmit light of any polarization state and light from any direction.

If the polarization hologram 20-1 is configured to transmit the return linearly polarized light, the forward linearly polarized light is diffracted and scattered. The width W and the distance S from the center of the polarization hologram 20-1 are set to predetermined values so as to remove crosstalk from an adjacent track. That is, the polarization hologram 20-1 is arranged so as to match the optical path of the crosstalk included in the return light from the optical disk 10 toward the polarization beam splitter 17. In FIG. 2, the radius R indicates the diameter of the beam having a circular cross section. Polarization hologram 2
0-1 is arranged to cross the beam of circular cross section.

The polarization hologram 20-1 may be formed on a transparent glass plate by grating using a material such as lithium niobate.

Referring back to FIG. The beam on the outward path, that is, out of the polarization beam splitter 17,
All upward linearly polarized light passes through the polarization hologram plate 20B. Of the return beam, that is, of the linearly polarized light returning from the optical disk 10 to the polarization beam splitter 17, all of the linearly polarized light passing through the polarization hologram 20-1 is transmitted, but the linearly polarized light passing through the polarization hologram 20-1 is diffracted. And scatter.

As described above, the polarization hologram 20-1
Are arranged on the optical path of the crosstalk included in the return light from the optical disk 10 toward the polarization beam splitter 17. Therefore, the crosstalk from the pitch train of the adjacent track is removed by the polarization hologram plate 20B.

According to this embodiment, the light-shielding element 20 composed of the quarter-wave plate 20A and the polarization hologram plate 20B is mounted on the objective lens 19. The light shielding element 20 may be mounted on the objective lens 19 by a suitable holder 20C as shown. Therefore, even if the objective lens 19 is displaced by the field swing, the light shielding element 20 is displaced together with the objective lens 19.
That is, the light blocking element 20 and the objective lens 19 move integrally,
The light shielding element 20 does not shift with respect to the objective lens 19. Even if the objective lens 19 is displaced by the field swing, crosstalk from an adjacent track can always be removed.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to these examples, and various modifications can be made within the scope of the invention described in the claims. It will be understood by those skilled in the art.

[0028]

According to the present invention, when reading recorded information from an optical disk by an optical pickup, the light shielding element for removing crosstalk can be displaced integrally with the objective lens. Even if it is displaced, there is an advantage that crosstalk from a pit row of an adjacent track can be effectively removed.

According to the present invention, the crosstalk can be effectively removed even if the light blocking element for removing the crosstalk is arranged not only in the parallel light beam but also in a relatively large beam diameter in the convergent light beam. Therefore, there is an advantage that the present invention can be applied to a finite optical system optical pickup that does not include a collimator lens or the like.

According to the present invention, there is an advantage that an anamorphic prism can be eliminated because crosstalk can be effectively eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical pickup according to the present invention.

FIG. 2 is a diagram illustrating an example of a polarization hologram.

FIG. 3 is a diagram illustrating an example of a conventional optical pickup.

[Explanation of symbols]

Reference Signs List 10 optical disk, 11 laser light source, 13 collimator lens, 15 anamorphic prism, 17 polarization beam splitter, 19 objective lens, 20 light shielding element, 20A quarter-wave plate, 20B polarization hologram plate 20C holder, 21 converging lens, 23 light detection Vessel,

Claims (2)

[Claims] 1. A light-shielding element displaceable integrally with an objective lens is provided. The light-shielding element transmits light emitted to an optical disk. An optical pickup configured to remove crosstalk from the optical pickup. 2. The optical pickup according to claim 1, wherein the light shielding element includes a quarter-wave plate and a band-shaped polarization hologram.