JPH1055561A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce surface power fluctuation due to tracking and also to enhance resolution in the track direction. SOLUTION: At the time of forming a laser spot on an information recording medium by an objective lens 6 after laser beams emitted from two 1st and 2nd laser elements 1 (1a and 1b) are passed through the same optical path respectively and are incident upon the objective lens 6, the polarization direction of the laser spot by the laser beam emitted from the 1st laser element 1a and the polarization direction of the laser spot by the laser beam emitted from the 2nd laser element 1b are made to go straight, and also the polarization direction of the laser spot by the laser beam emitted from the 1st laser element 1a is adjusted to coincide with the track direction. Consequently, the resolution in the track direction is enhanced by the laser spot polarized in the straight direction of the track direction so as to perform reproduction of information, and the surface power fluctuation is reduced by the laser spot polarized in the track direction so as to perform recording/erasing detection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device capable of performing recording / reproducing or erasing at a high recording density with a single device while maintaining compatibility with different substrate thicknesses.

[0002]

2. Description of the Related Art In recent years, high-density information is strongly required in an optical pickup device, and the next-generation optical disk has a narrower track pitch (higher track density) than the current-generation optical disk and has the shortest mark. The length is also short (higher mark density).

[0003] Generally, an information recording medium (hereinafter, referred to as a disc) has spirally provided tracks, information (hereinafter, referred to as marks) is recorded between the tracks, and various kinds of recorded information such as marks are recorded on the tracks. Is recorded.

An optical pickup device converges a laser beam on such a disk with an objective lens to form a laser spot on the disk, records a mark with the laser spot, and records the recorded mark. A reproduction process of receiving the reflected light from the mark and reading the contents of the mark is performed.

In order to increase the recording density in such an optical pickup device, it is effective to reduce the shortest mark length and the track density as described above. For this reason, the laser spot diameter is reduced to increase the resolution. It is necessary to increase.

In order to reduce the diameter of the laser spot, there are measures for increasing the numerical aperture of the objective lens and shortening the wavelength of the laser beam. When the numerical aperture of the objective lens is increased, it is necessary to reduce the thickness of the disk substrate in order to reduce the coma caused by the disk tilt.

[0007]

However, in the current generation and the next generation optical disks, since the substrate thickness of the disks, the mark size (the shortest mark length and the groove depth of the mark, etc.), the track pitch, etc. are different, a single There is a problem that it is very difficult to perform reproduction / recording or erasing of the discs of both generations with the optical pickup device.

That is, since the curvature and the shape of the objective lens are optimally designed for a disk having a specific substrate thickness, when used for disks having different substrate thicknesses, the spherical aberration increases. It becomes blurred, making it difficult to perform high-density recording and the like.

Further, for example, if the apparatus is optimally set for a next-generation disk having a high track density, there is a problem that a tracking signal cannot be detected for the current disk.

Further, the allowable variation of the power of the laser spot on the disk surface (hereinafter referred to as surface power) becomes smaller as the information density becomes higher and the mark size becomes smaller. There is a problem that even when recording or the like is performed on a next-generation disc using the device that has been set, the recording or the like is not performed correctly.

Accordingly, the present invention provides an optical pickup which maintains compatibility with disks having different substrate thicknesses, track pitches, and recording densities, reduces fluctuations in surface power due to tracking, and has a high resolution in the track direction. The purpose is to do.

[0012]

According to a first aspect of the present invention, a laser spot is formed by condensing a laser beam by an objective lens on an information recording medium provided with a spiral track. An optical pickup device for recording information on the information recording medium by the laser spot and reproducing or erasing the recorded information;
In order to form at least two laser spots on the information recording medium by the objective lens, the objective lens has two or more laser sources for emitting laser light, and the polarization direction of the laser spot by the laser light from one of the laser sources is The laser beam is set so as to coincide with the spiral track direction, and the polarization direction of the laser spot by the laser beam from the other laser source is set so as to be orthogonal to the track direction.

That is, when the laser beams emitted from the two laser sources pass through the same optical path and enter the objective lens to form a laser spot on the information recording medium by the objective lens, one of the laser sources The direction of polarization of the laser spot of the laser beam emitted from the laser source is perpendicular to the direction of polarization of the laser spot of the laser beam emitted from the other laser source, and the laser spot is emitted by the laser beam emitted from one laser source. Each laser source is arranged so that the polarization direction of the laser beam coincides with the direction of the track. As a result, information is reproduced by a laser spot polarized in a direction perpendicular to the track direction, and recording / erasing is performed by a laser spot polarized in the track direction.

The invention according to claim 2 is characterized in that the laser source is integrally provided with a light receiving element for receiving the reflected light from the information recording medium.

That is, when the laser light emitted from the laser source is reflected by the information recording medium and returns, a light receiving element for receiving the reflected light is provided integrally with the laser source, so that mounting of each component can be performed. Adjustment is facilitated and the overall size is reduced.

According to a third aspect of the present invention, one of the two laser sources is used when recording or erasing information on the information recording medium and the other laser source reproduces information. It is characterized by being set to be used for.

According to a fourth aspect of the present invention, the wavelength of each laser beam emitted from the two laser sources is set according to the information recording density of the information recording medium.

According to a fifth aspect of the present invention, the wavelength of each laser beam emitted from the two laser sources is set to a shorter wavelength when the information recording density of the information recording medium is high. When the density is low, the wavelength is set to the longer wavelength.

According to a sixth aspect of the present invention, the numerical aperture of the objective lens is set according to the information recording density of the information recording medium, and is optimally set for the information recording medium having a high information recording density. It is characterized by having.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an optical pickup device according to the present invention.

The optical pickup device comprises a first and second laser units 1 (1a, 1b) having a laser element for emitting laser light and a light receiving element for receiving incident laser light.
First and second hologram elements 2 (2
a, 2b), a beam splitter for transmitting or reflecting laser light, a coupling lens for converting laser light into substantially parallel light, a deflecting prism for deflecting and reflecting incident laser light, and condensing laser light. A laser beam from the objective lens 6 and the beam splitter 3 to detect the laser power.

Hereinafter, the first and second laser units 1 (1a, 1a,
1b) and the first and second hologram elements 2 (2a, 2b), when individual members are specified and described,
It should be described like the first laser unit 1a, and if it is not necessary to distinguish between them, it is simply described like the laser unit 1.

With the above configuration, the laser light emitted from the laser unit 1 passes through the hologram prism 2 and enters the beam splitter 3.

A part of the laser light incident on the beam splitter 3 is incident on the detecting element 8 and is used as a power monitor for the laser light emitted from the laser unit 1.
The other laser light enters the coupling lens 4, is converted by the coupling lens 4 so that the degree of divergence of the laser light is reduced, becomes substantially parallel light, and enters the deflection prism 5.

The laser beam incident on the deflecting prism 5 is deflected by the deflecting prism 5, reflected by the objective lens 6, condensed by the objective lens 6, and forms a laser spot on the disk 7. Recording, reproducing and erasing of information are performed by such a laser spot.

On the other hand, the laser light reflected from the disk 7 is converted into substantially parallel light by the objective lens 6, reflected by the deflecting prism 5 and incident on the coupling lens 4.

After being converted into convergent light by the coupling lens 4, the light is reflected or transmitted by the beam splitter 3 and enters the hologram prism 2.

Since a hologram is formed on the hologram element 2, the incident laser light is diffracted by the hologram, received by the light receiving element of the laser unit, and converted into an electric signal. This electric signal is used as an information signal, a focus servo signal, and a track servo signal.

Next, the detailed structure and operation of the laser unit 1 and the hologram element 2 will be described with reference to FIGS.

The laser unit 1 comprises a light receiving element 13, a laser element 12, and a can case 11 for accommodating them. The hologram element 2 is provided on the hologram 21 provided on the upper surface of the transparent member 23 and on the lower surface of the transparent member 23. The lower surface side is attached to the can case 11 in close contact.

The laser light emitted from the laser element 12 is separated by the diffraction grating 22 into 0-order light and ± 1st-order laser light and emitted from the hologram element 2.
The zero-order light is used as mark reproduction / recording / erasing and focus signal detection light, and the ± first-order light is used as track signal detection light.

On the other hand, the 0-order reflected light reflected by the disk 7 and incident on the hologram element 2 is
, One of the reflected lights is incident on a two-divided light receiving element, and a focus signal is detected from a differential output by, for example, a knife edge method. The other reflected light (or both lights) is used as an information signal.

The ± 1st-order reflected light is incident on each of the other light receiving elements, and a track signal is detected and detected from a differential output by, for example, a three-beam method.

FIG. 3 is a schematic diagram for explaining the state of the reflected light. The light receiving element 13 is divided into five regions D1 to D5, and a track detection signal is obtained from a difference signal between the regions D1 and D5.

A focus detection signal is obtained from a difference signal between the area D2 and the area D3, and an information signal is obtained from a signal of the area D4 or a sum signal of the areas D2, D3, and D4.

The laser element 12 has a flat active layer as shown in FIG. 4, and the active layer oscillates and emits a laser beam. Therefore, the laser element 12
-Field image (FFP: Far) of laser light emitted from
Field Pattern) is wider in a direction perpendicular to the active layer (θp direction) than in a direction parallel to the active layer (θp direction).

Note that the diameter of the laser spot focused by the objective lens 6 depends on the intensity of the laser light incident on the peripheral portion of the objective lens 6. Therefore, when a laser beam having an elliptical intensity distribution as described above is incident on the objective lens 6,
An elliptical laser spot whose major axis is rotated by 90 degrees with respect to the laser light emission elliptical pattern is formed.

FIG. 5 shows this state.
FIG. 5A shows the FFP of the laser element, and FIG. 5B shows the schematic shape of the laser spot focused by the objective lens 6.

In this embodiment, the direction of polarization of the laser spot by the laser beam emitted from the first laser unit 1a and the direction of polarization of the laser spot by the laser beam emitted from the second laser unit 1b are orthogonal. Is configured.

Accordingly, a laser spot polarized on the spiral track formed on the disk 7 (tangential direction of the circular disk) and a laser spot polarized on the track perpendicular to the track (radial direction of the circular disk). And the resolution in each direction is particularly enhanced.

As is understood from FIG. 5, the setting of the polarization direction is performed by making the direction of the active layer of the laser element coincide with the track direction or the vertical direction.

That is, when the polarization direction of the laser spot is made to coincide with the track direction (in the case of a laser spot having a long axis in the track direction), the resolution in the direction perpendicular to the track can be increased. In contrast, when the polarization direction of the laser spot is perpendicular to the track direction (in the case of a laser spot having a major axis in the direction perpendicular to the track direction), the resolution in the track direction can be increased. Will be possible.

FIGS. 6A and 6B show the intensity distribution of the FFP of the laser device. FIG. 6A shows the θt direction, and FIG.
(B) shows the intensity distribution in the θp direction (the polarization direction of the laser element). In FIG. 6, D indicates the effective diameter of the objective lens 6, and the direction of the arrow is the tracking direction of the objective lens 6.

Depending on which of the tracking direction of the objective lens 6 and the direction of θp or θt of the laser element are matched,
The state of the surface power fluctuation during tracking of the objective lens 6 changes. That is, when the θt direction is made to coincide with the tracking direction, the fluctuation of the surface power is reduced.

For the above reason, in the present embodiment, the polarization direction of the first laser unit 1a is made to coincide with the track direction, surface power fluctuation during tracking is suppressed, and the polarization direction of the second laser unit 1b is orthogonal to the track. By matching the direction, the resolution in the track direction is set to be increased.

Of course, this is only an example, and the setting of the polarization direction of the first laser unit 1a and the second laser unit 1b may be exchanged.

The wavelength of the second laser unit 1b is set to about 780 nm, and the current generation optical disk (for example, CD-
It is used for reproduction / recording or erasing of R, CD-E or the like with a substrate thickness of 1.2 mm, and the wavelength of the first laser unit 1a is about 650 nm.
Compatibility with both generations of optical discs can be maintained by making the disc exclusively for reproduction with a substrate thickness of 0.6 mm such as a D-ROM.

It is desirable that the objective lens 6 is designed to correspond to the substrate thickness of the next-generation optical disc that requires high-density reproduction, and has a numerical aperture of about 650 nm and a numerical aperture of about 650 nm.
Preferably, the thickness is about 0.6 corresponding to a substrate thickness of 0.6 mm.

In this case, the current generation optical disk (substrate thickness 1.
(2 mm, wavelength 780 nm), a spherical aberration occurs, and the laser spot may be blurred.

Therefore, for the laser element set to such a wavelength, the second laser unit 1b is set so that the degree of divergence of the laser light incident on the objective lens 6 is increased.
If the distance between the lens and the coupling lens 4 is set, the above-described problem can be prevented.

As described above, recording and the like are performed on the current generation disk using the objective lens 6 designed so that the substrate thickness of the next generation disk is 0.6 mm and the wavelength of the laser beam is about 650 nm. However, it is possible to obtain the same characteristics as those optimally set for the current world, and to maintain compatibility with both generations of disks.

[0052]

According to the first aspect of the present invention, since two laser elements are arranged so that their polarization directions are orthogonal to the track direction of the optical disc, when one of the laser elements is used, It is possible to increase the resolution in the track direction, and when the other laser element is used, it is possible to suppress surface power fluctuation during tracking of the objective lens.

According to the second aspect of the present invention, since the laser element and the light receiving element are integrated, there is no need to separate the optical path of the laser light emitted from the laser element from the optical path of the laser light reflected by the disk. This simplifies the configuration of the optical pickup device.

Further, since the laser element and the light receiving element function independently, it is not necessary to consider the relative positional accuracy of each laser element, and the light receiving element can be adjusted independently.

According to the third aspect of the present invention, a laser element is used in which the polarization direction of the laser beam used for reproducing information is perpendicular to the track direction, and the polarization direction of the laser beam used for recording / erasing is the same as the track direction. Since two laser elements are selectively used so as to use parallel laser elements, it is possible to obtain a laser spot having a high resolution in the track direction at the time of reproduction, and at the time of recording / erasing.
It is possible to reduce surface power fluctuations with respect to tracking.

According to the fourth aspect of the invention, when recording / reproducing information according to the information recording density of the information recording medium, two laser elements having different wavelengths are switched and used. Information can be recorded / reproduced properly on each information recording medium.

According to the fifth aspect of the invention, when recording / reproducing information according to the information recording density of the information recording medium, two laser elements having different wavelengths are switched and used. Information can be recorded / reproduced properly on each information recording medium.

According to the sixth aspect of the present invention, the objective lens is set corresponding to the high-density disk, and the divergence of the laser light incident on the objective lens is increased corresponding to the low-density disk. Thus, good reproduction / recording / erasing can be performed on information recording media having different substrate thicknesses.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a pickup device applied to the description of an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view showing the configuration of a laser unit.

FIG. 3 is a schematic diagram showing a reciprocating optical path of laser light.

FIG. 4 is a diagram illustrating a polarization state of laser light emitted from a laser element.

FIG. 5 is a diagram illustrating an emission pattern of a laser beam and the like.
(A) is a diagram showing an emission pattern of laser light emitted from the laser element, and (b) is a diagram showing a laser spot shape on a disk surface.

6A and 6B are diagrams showing the intensity distribution of laser light in the tracking direction, wherein FIG. 6A shows the intensity distribution of laser light polarized in the direction perpendicular to the track direction, and FIG. 6B shows the intensity distribution of laser light polarized in the track direction. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser unit 2 Hologram element 3 Beam splitter 4 Coupling lens 5 Deflection prism 6 Objective lens 7 Disk

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Takehide Ohno 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Masahiko Nakayama 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Toshimichi Hagiya 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company

Claims (6)

[Claims] 1. A laser beam is condensed by an objective lens on an information recording medium provided with a spiral track to form a laser spot, and information is recorded on the information recording medium by the laser spot. An optical pickup device for reproducing or erasing the read information, comprising at least two laser sources for emitting laser light so as to form at least two laser spots on the information recording medium by the objective lens, The direction of polarization of the laser spot by the laser light from the source is set to coincide with the spiral track direction, and the direction of polarization of the laser spot by the laser light from the other laser source is perpendicular to the track direction. An optical pickup device characterized by being set to be: 2. The optical pickup device according to claim 1, wherein a light receiving element for receiving reflected light from the information recording medium is provided integrally with the laser source. 3. A setting so that one of the two laser sources is used when recording or erasing information on the information recording medium, and the other laser source is used when reproducing information. 3. The method according to claim 1, wherein
An optical pickup device as described in the above. 4. The apparatus according to claim 1, wherein the wavelength of each laser beam emitted from said two laser sources is set according to the information recording density of said information recording medium. Optical pickup device. 5. The wavelength of each laser beam emitted from the two laser sources is set to a shorter wavelength when the information recording density of the information recording medium is high, and is set to a shorter wavelength when the information recording density is low. 4. The optical pickup device according to claim 1, wherein the wavelength is set to a longer wavelength. 6. The optical pickup device according to claim 4, wherein the objective lens is optimally set for the information recording medium having a high information recording density.