JP3485692B2 - Optical pickup - 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 which reproduces or reproduces and records information recorded on an information recording medium such as an optical disk, an optical card, or a magneto-optical disk.

[0002]

2. Description of the Related Art For example, a compact disc and a digital video disc differ from each other in the distance from the surface of a transparent substrate constituting the disc to the recording layer such that the former is 1.2 mm and the latter is 0.6 mm. . on the other hand,
Thus, there is a demand for compatibility of reproducing two types of discs having different standards with a single optical pickup.

A bifocal optical head has been proposed as a conventional compatible optical pickup of this type (1994).
Of Applied Physics, September 2013: 19p-S-4: 19
p-S-5). This bifocal optical head uses a grating lens to provide a light beam (635 nm to 65 nm) from one light source.
(0 nm) is split into 0th-order diffracted light and 1st-order diffracted light, and two focal points are generated at the same time. Specifically, as shown in FIG. 6, the grating lens 101 has a region through which the light beam emitted from the light source 105 and reflected by the half mirror 106 is directly transmitted, and a region through which the light beam is diffracted in a spreading direction. Are formed, and the above-mentioned 0.
By using the light beam (0th-order diffracted light) that has been transmitted as it is for the 6 mm disc 102 and using the light beam diffracted in the spreading direction (1st-order diffracted light) for the 1.2 mm disc 103. The focal point positions of the light beam that has passed through the objective lens 104 are different. Further, the aperture of the grating lens 101 is limited so that the beam diameter of the first-order diffracted light at the objective lens position becomes smaller than the effective diameter of the objective lens 104. Therefore, 1.2m
With respect to the disk 103 of m, the effective NA is reduced due to the distance of the focal position and the reduction of the beam diameter, and it is possible to prevent the occurrence of spherical aberration due to the increase of the disk thickness. The light reflected by the optical disk passes through the half mirror 106 and enters the light receiving element 107.

[0004]

However, in the above conventional optical pickup, the 0.6 mm disc 1 is used.
02, the light beam diffracted in the spreading direction is not used, and the light beam directly transmitted to the 1.2 mm disk 103 is not used. ineffective. Therefore, there is a drawback that a high-output light source (semiconductor laser) is required only for reproduction. Further, since a semiconductor laser which oscillates in a short wavelength band such as 635 to 650 nm has a short life and becomes shorter particularly when the output is high, the semiconductor laser used in reproducing the 1.2 mm disc 103 is used. The optical pickup has a drawback that sufficient reliability cannot be ensured.

Further, when the 1.2 mm disc 103 is a compact disc, when the reproduction is performed by using a semiconductor laser that oscillates in the 635 nm band, the compact disc has the smallest aberration with respect to the laser beam having the wavelength of 780 nm. Since it is standardized, the refractive index of the transparent substrate changes due to the shorter wavelength, spherical aberration is more likely to occur, and the S / N of RF signals (pit signals) and the reliability of servo also deteriorate. Have

In view of the above circumstances, it is an object of the present invention to provide an optical pickup which has high utilization efficiency of a light beam and high reliability.

[0007]

An optical pickup according to the present invention is a first light source that emits a light beam in a first polarization direction.
And a second light source for emitting a light beam in the second polarization direction
And lens function only for the light beam in one polarization direction
And a polarization-dependent grating lens that exhibits
Focusing hand that focuses the light beam that has passed through the beam on the information recording medium
Selectively driving the stage, the first light source or the second light source.
And a driving selection unit that moves.

As a result, for example, the focus position of the light beam required for an optical disc of 0.6 mm and 1.2 m
Compatibility can be realized because the focal point position of the light beam required by the m optical disc can be selectively formed. This function is obtained even when both light beams have the same wavelength. Also,
Problems that occur when the light source positions themselves are different, that is, that one light source blocks a part of the light beam from the other light source, are avoided.

[0009]

It is not necessary to drive the first light source and the second light source at the same time, and when one light source is in a driving state, the other light source is in a stopped state. Here, the first light source may be a short-wavelength oscillation semiconductor laser having a short life, and the second light source may be a long-wavelength oscillation semiconductor laser. And 1.
When a 2 mm optical disk is used, a long wavelength oscillation semiconductor laser, which is the second light source, can be used to stop the short wavelength oscillation semiconductor laser. As a result, the life of the optical pickup can be relatively lengthened by the relative driving time of the short wavelength oscillation semiconductor laser. Further, the light beam in one polarization direction is not diffracted by the polarization dependent grating lens, and of course, the light beam in the other polarization direction has a grating cross-sectional shape of the polarization dependent grating lens only in the desired direction. Since it can be made to have a sufficient grating depth so that almost all the light incident on the polarization dependent grating lens is diffracted, the light is emitted from the light source to the objective lens. Almost all of the incident light beam can be utilized, that is, the utilization efficiency of the light beam is high, so that a light source with a low output can be used, and the life and cost can be further reduced.

Further, as described above, the wavelengths of the light beams of the two light sources are made different from each other along with the polarization directions, and, for example,
When reproducing a 1.2 mm optical disc, a long-wavelength oscillation semiconductor laser is used, and the polarization-dependent grating lens is designed to exhibit a lens function only for a long-wavelength light beam. The effective numerical aperture (NA) of the condensing means can be reduced by limiting the area of the portion having the grating pattern and making the beam diameter of the long-wavelength diffracted light at the objective lens position smaller than the objective lens effective diameter. Prevents spherical aberration due to increased disc thickness
The S / N of the F signal (pit signal) and the reliability of the servo can be improved. Further, when the 1.2 mm optical disc is a compact disc, laser light (780 nm) having a wavelength according to the standard can be used,
It is possible to suppress an increase in spherical aberration due to different wavelengths, and it is possible to improve the S / N ratio of the RF signal (pit signal) and the reliability of the servo.

The user knows in advance the type of information recording medium to be used, and performs a predetermined operation to selectively drive either the first light source or the second light source by the driving means. Alternatively, or the drive selection means,
Initially when the information recording medium is loaded into the player provided with the optical pickup, both the first light source and the second light source are driven, and after the type of the loaded information recording medium can be discriminated, according to the type. It may be configured to selectively drive either the first light source or the second light source.

If the first light source and the second light source are arranged on the same plane, wiring to each light source can be easily performed.

Further, a first light source for emitting a TE mode light beam, a second light source for emitting a TM mode light beam, and a polarization dependent grating lens exhibiting a lens function for only one light beam. Also in the case of including, since the TE mode light beam and the TM mode light beam have different polarization directions from each other, the focal points of the two light beams can be different from each other, as described above.

The above polarization dependent grating lens can be easily manufactured by using the proton exchange method.

Further , the optical pickup of the present invention is the above-mentioned
The light source of No. 1 is an AlGaAs semiconductor laser.
To collect . The optical pickup of the present invention is the second
Has a quantum well structure with tensile strain in the well layer.
An AlGaInP-based semiconductor laser having an active layer
It is characterized by Further, the optical pickup of the present invention
Is a light beam emitted from the first light source,
Two kinds of light are used by using the light beam emitted from the two light sources.
Characterized by reproducing or reproducing and recording using a beam
To do . In this case, not only the two types of information recording media having different distances to the recording layers, but also the two types of information recording media having the same distances to the recording layers but different pit sizes, for example, the pit diameter For smaller ones, an AlGaInP-based semiconductor laser having an active layer having a quantum well structure having tensile strain in at least the well layer is used, and for large ones, for example, an AlGaAs-based semiconductor laser (active layer is (Including the case of GaAs) can be used. In this case, since the focal positions are the same for the two types of information recording media, the polarization dependent grating lens is not necessary unless the effective numerical aperture needs to be switched.

[0017]

Further , the polarization element and the TE mode light are oscillated.
Semiconductor laser and semiconductor that oscillates TM mode light
In an optical pickup including a laser, a polarization element can cause light in a specific polarization direction to perform a predetermined optical operation. For example, an optical operation such as changing the virtual light source position or changing the substantial numerical aperture of the lens optical system can be given to the light of the specific mode. Therefore, when the information of the specific information recording medium is reproduced or recorded by the light of the specific mode (the light of the specific mode may have a specific wavelength), the virtual light source position matched with the specific information recording medium By obtaining a substantial numerical aperture, it becomes possible to optimally reproduce and record information. That is, it is possible to perform the optimum reproduction and recording of information according to the characteristics of a plurality of types of information recording media with one optical pickup. Of course, by providing two light sources of the semiconductor laser that oscillates the TE mode light and the semiconductor laser that oscillates the TM mode light, the life of the optical pickup as a whole can be lengthened by selectively using these two light sources. However, it is also possible to enhance the utilization efficiency of the light beams by utilizing almost all of the respective light beams when they are used.

[0019]

Further , the polarizing element and at least the well layer are drawn.
Providing an active layer with a quantum well structure with tensile strain
AlGaInP semiconductor laser and AlGaAs semiconductor
In the optical pickup including the body laser, the polarization element can cause light in a specific polarization direction to perform a predetermined optical operation. For example, an optical operation such as changing the virtual light source position or changing the substantial numerical aperture of the lens optical system can be given to the light of the specific mode. An AlGaInP-based semiconductor laser including an active layer having a quantum well structure having a tensile strain in at least a well layer is a semiconductor laser that oscillates light having a relatively short wavelength in a TM mode, and an AlGaAs-based semiconductor laser is a TE mode. Is a semiconductor laser that oscillates light having a relatively long wavelength. Therefore, when reproducing or recording information on a specific information recording medium in a specific mode and with light of a specific wavelength, a virtual light source position or a substantial numerical aperture matched to the specific information recording medium is obtained to obtain the information It becomes possible to perform reproduction and recording optimally. That is, it is possible to perform the optimum reproduction and recording of information according to the characteristics of a plurality of types of information recording media with one optical pickup. Of course, since the two semiconductor lasers are provided, these two semiconductor lasers are selectively used to prolong the life of the optical pickup as a whole, and when the respective light beams are used, almost all of them are utilized. In this way, the light beam utilization efficiency can be improved.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1A and 1B are schematic sectional views of the optical pickup of the present invention. In FIG. 1A, an optical disk 15 in which the distance from the disk surface to the recording layer 15a is 0.6 mm is used. FIG. 2B shows a case where the optical disc 16 having a distance from the disc surface to the recording layer 16a of 1.2 mm is used.

The optical pickup comprises a first light source 11 and a second light source.
The light source 12 includes two light sources. First light source 11
Is a semiconductor laser that oscillates in the 635 nm band,
A semiconductor laser that oscillates at 780 nm is used as the second light source 12. In this embodiment, the semiconductor laser that oscillates in the 635 nm band, which is the first light source 11, has a TM mode (for example, an active layer having a quantum well structure having a tensile strain in at least the well layer A).
1GaInP-based semiconductor laser).
Since the semiconductor laser that oscillates in the 780 nm band that is the second light source 12 oscillates in the TE mode (for example, an AlGaAs semiconductor laser can be cited), the polarization directions of both light beams are different from each other. In addition, both of these light sources 11, 12
Is selectively driven by a drive selecting means (not shown). Furthermore, both light sources 11, 1
In this embodiment, 2 are arranged on the same plane parallel to the optical axis of the light beam so that wiring to each light source can be easily performed.

In FIG. 1, X, Y and Z indicate crystal axes of the X-cut LiNbO ₃ substrate of the polarization dependent grating lens 13. The direction perpendicular to the main surface of the substrate (optical axis direction) is the X axis, and the direction perpendicular to the plane of the drawing is the Y axis, and the X (axis) above.
The direction perpendicular to the direction and the Y (axis) direction is the Z axis.
Here, the TM mode first light source 11 is arranged so that the polarization direction of the light beam thereof coincides with the Y direction, and the TE mode second light source 12 is arranged in the polarization direction of the light beam. Are arranged so as to coincide with the Z direction.

The light beams emitted from the respective light sources 11 and 12 include a diffraction grating 17 for three beams for producing three beams for tracking control, a hologram element 18 for producing astigmatic light for focus control, and After passing through a polarization dependent grating lens (polarizing element) 13 that exhibits a lens function only for a light beam in the polarization direction, and an objective lens (light condensing means) 14 that condenses the light beam, an optical disk 15 or an optical disk 16 is transmitted. The light is focused on the recording layers 15a and 16a. Then, the recording layer 1 of the optical disk 15 or the optical disk 16
The reflected light reflected by 5a and 16a follows the objective lens 14 and the polarization dependent grating lens 13 in the opposite directions, and reaches the hologram element 18. Then, the hologram element 18 diffracts the 635 nm light beam and guides it to the first light receiving element 20, and the 780 nm light beam is further diffracted and guides it to the second light receiving element 21.

The polarization dependent grating lens 13 receives the light beam emitted from the first light source 11 or the second light source 12, and the first TM mode mode in which the polarization direction is the Y direction.
The second mode of the TE mode in which the polarization direction is the Z direction, which functions simply as a transparent plate for the light beam of the light source 11 of
The light beam of the light source 12 has a concave lens function.

Here, as shown in FIG. 2, for example, Li
The NbO ₃ crystal substrate, due to the proton exchange, has a refractive index distribution n _e (n _e
Is the refractive index in the Z-axis direction, and n _o increases only in the direction orthogonal to the Z-axis). Also, light follows the refractive index in the direction of its polarization.

The polarization dependent grating lens 13 is composed of an X-cut LiNbO ₃ crystal substrate as described above. Then, as also shown in FIGS. 3A and 3B, the proton exchange is not performed with the first region 13a in which the refractive index change (increase) is caused only in the Z direction by the above proton exchange method. And a second region 13b. The first area 13a
Have a lattice pattern that exhibits a concave lens function. When the light beam passes through the polarization dependent grating lens 13, the light beam polarized in the direction orthogonal to the Z axis (that is, the TM mode 635 nm light beam) causes the existence of the first region (proton exchange region) 13a. Since it does not feel, it simply passes through the polarization dependent grating lens 13. The first by the proton exchange method
A method of generating the area 13a will be described later.

With the above arrangement, as shown in FIG. 1A, the 635 nm TM mode light beam simply passes through the polarization dependent grating lens 13 and is recorded on the optical disk 15 of 0.6 mm. While focused on layer 15a,
As shown in FIG. 7B, the TE-mode light beam of 780 nm is diffracted by the polarization dependent grating lens 13 in the direction in which it spreads, and the virtual exit position of the light beam is the objective lens by this diffraction. It ’s closer to 14 ’s side,
The focal position of the light beam by the objective lens 14 shifts away from the objective lens 14 and can be focused on the recording layer 16a of the 1.2 mm optical disc 16.
Therefore, an optical pickup compatible with these two types of optical disks 15 and 16 is realized. Then, it is possible to avoid a problem that occurs when the light source positions themselves are different, that is, one light source blocks a part of the light beam from the other light source.

Further, the first light source 11 and the second light source 12
Is selectively driven by a drive selection means (not shown), and when one light source is in a driving state, the other light source is in a stopped state. Therefore, when the 1.2 mm disk 16 is used, the short-wavelength first light source 11 having a short life can be stopped, so that the driving time of the first light source 11 is relatively short. The life of the optical pickup becomes relatively longer accordingly. Further, the light beam of the light source 11 is not diffracted by the polarization dependent grating lens 13, and of course, the light beam of the light source 12 has a grating cross-sectional shape of the polarization dependent grating lens 13 outside in the radial direction about the optical axis. The polarization-dependent grating lens 13 is blazed so that only the first
Since the grating depth is sufficient so that almost all the light incident on the region 13a is diffracted, almost all the light beams emitted from the light sources 11 and 12 and incident on the objective lens can be used, that is, Since the utilization efficiency of the light beam is high, it is possible to use low-power light sources 11 and 12, and it is possible to further prolong the life and reduce the cost.

Further, as in this embodiment, the polarization directions and wavelengths of the light beams of the two light sources 11 and 12 are made different from each other, and for example, when reproducing the 1.2 mm optical disk 16, the second 780 nm oscillation is generated. Of the light source 12 is used so that the polarization dependent grating lens 13 exhibits a lens function only for a light beam of 780 nm, and the area of the first region 13a of the polarization dependent grating lens 13 is limited. Then, by making the beam diameter of the 780 nm diffracted light at the position of the objective lens 14 smaller than the effective diameter of the objective lens 14, the objective lens 14 with respect to the light beam of 780 nm concerned.
The effective numerical aperture (NA) can be reduced, spherical aberration can be prevented from occurring due to an increase in disk thickness, and the S / N of the RF signal (pit signal) and the reliability of the servo can be improved. Further, when the 1.2 mm optical disc 16 is a compact disc, since the laser light (780 nm) having the standard wavelength can be used, it is possible to suppress the increase of the spherical aberration due to the different wavelength, and the RF
The signal / pit signal S / N and servo reliability can be improved. The L of the polarization dependent grating lens 13
The iNbO ₃ substrate may be Y-cut, and in that case, the polarization dependent grating lens 13 may be arranged so that the X axis coincides with the Y direction.

Next, a method of manufacturing the polarization dependent grating lens 13 will be described with reference to FIGS. In FIG. 4, Ta
A method for producing a (tantalum) mask is shown, and FIG. 5 shows the proton exchange performed after the Ta mask is produced. Also,
4 and 5 are enlarged views corresponding to, for example, a portion indicated by an arrow A in FIG.

First, as shown in FIG. 4 (a), T is placed on an X-cut (or Y-cut) LiNbO ₃ crystal substrate 31.
After depositing the a film 32 with a thickness of 300 to 1000 Å,
A photoresist 33 is spin-coated on the a film 32.
Next, as shown in FIG. 3B, the photoresist 33 is patterned by a general photolithography technique, an opening 33a is formed in the photoresist 33, and the Ta film 32 in that portion is exposed. . It should be noted that this patterning is formed concentrically corresponding to the concentric first regions 13a shown in FIG. In the Ta mask of the first stage, the opening 3
3a has a width narrower than the width of the first region 13a shown in FIG. 3B at the portion indicated by the arrow A, and corresponds to the radius of the proton exchange region 31a that spreads in a substantially semicircular shape as described later. It is formed at a position shifted toward the center of the concentric circle by the distance. Next, as shown in FIG. 3C, the exposed portion of the Ta film 32 is removed by dry etching using a fluorine-based gas to form an opening 32a,
The surface of the LiNbO ₃ crystal substrate 31 in that portion is exposed. After that, the photoresist 33 is removed as shown in FIG.

Next, as shown in FIG. 5A, the opening 3
After the pyrophosphate film 34 is applied on the Ta film 32 having 2a, proton exchange is performed at 200 to 300 ° C. for a long time (for example, 90 minutes). Thereby, the opening 3
Proton exchange region 31a extending in a substantially semicircular shape around 2a
Is formed. In addition to pyrophosphoric acid, benzoic acid or the like can be used for the proton exchange.

Then, the Ta film 32 shown in FIG. 4A is removed with a hydrofluoric acid-based aqueous solution, and the procedure shown in FIGS. 4A to 4D is repeated, and the LiNbO ₃ crystal is again formed. A Ta film 32 having an opening 32a is formed on the substrate 31. The opening 32a at this time is formed to be displaced toward the center side of the concentric circle from the opening 32a of the previous time, and is formed to have a somewhat wider width. Then, as shown in FIG. 5B, the proton exchange is performed again. The depth of the proton exchange region 31a at this time is shallower than that of the previous proton exchange region 31a (that is, the proton exchange time is shorter than the previous time). Similarly, the Ta mask is formed again, and the pyrophosphate film 34 is applied as shown in FIG. 5C, and the proton exchange is performed again. The depth of the proton exchange region 31a at this time is the same as the previous proton exchange region 31a.
Shallower than.

As described above, in this embodiment, the three-step proton exchange is performed. Then, as shown in FIG. 5D, the Ta film 32 is removed and annealed at 300 to 400 ° C. for a predetermined time, whereby the proton exchange region 31 is removed.
Smooth the distribution of.

The sectional structure of the polarization dependent grating lens 13 has a blazed shape so that the light beam is diffracted only from the center to the outer side in the radial direction, that is, the shape shown in FIG. 3B. Is ideal. The ideal shape can be approximated by increasing the number of steps of the proton exchange, but increasing the number of steps causes an increase in cost. Therefore, the number of steps is determined by weighing the cost and the performance of the polarization dependent grating lens 13.

Further, in this embodiment, the LiNbO ₃ crystal substrate is used as the polarization dependent grating lens 13, but the present invention is not limited to this, and for example, a LiTaO ₃ crystal plate or the like can be used.

In the optical system shown in FIG. 1, the optical axis is a straight line. However, for example, between the light sources 11 and 12 and the three-beam diffraction grating 17, or between the three-beam diffraction grating 17 and the hologram element 18. It is also possible to provide a reflection mirror between the two and form an optical system that deflects the optical axis of the light source in different directions. In particular,
When the deflection angle is set to about 90 °, the semiconductor laser chip, which is the light source, and the light receiving element can be arranged on a parallel surface, and wire bonding for wiring becomes easy.

[0040]

As described above, according to the present invention, by providing two light sources having different polarization directions and a polarization dependent grating lens, it is possible to utilize the difference in polarization direction to the recording layer. Can be applied to information recording media having different distances, and further, excellent effects such as high utilization efficiency of a light beam and high reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an optical pickup according to an embodiment of the present invention, where FIG. 1A shows a case where a 0.6 mm optical disc is used, and FIG. 1B shows a 1.2 mm optical disc. The cases where they are used are shown.

FIG. 2 is a schematic diagram showing a refractive index distribution of a LiNbO ₃ crystal according to an embodiment of the present invention before and after proton exchange.

FIG. 3A is a plan view of a polarization dependent grating lens according to an embodiment of the present invention, and FIG. 3B is a longitudinal side view of the same.

FIG. 4 is a process drawing showing the procedure for producing a Ta film according to the embodiment of the present invention.

FIG. 5 is a process chart showing a procedure for producing a proton exchange region according to the embodiment of the present invention.

FIG. 6 is a schematic sectional view of a conventional optical pickup.

[Explanation of symbols]

11 First light source 12 Second light source 13 Polarization dependent grating lens 14 Objective lens (condensing means) 15 Optical disc 16 optical disks 17 3 beam diffraction grating 18 Hologram element

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Ibaraki 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Keiichi Yoshinari 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (56) Reference JP-A-61-189504 (JP, A) JP-A-62-219341 (JP, A) JP-A-7-235718 (JP, A) JP-A-8 -55363 (JP, A) JP 59-14146 (JP, A) JP 56-163531 (JP, A) Actual development 59-78532 (JP, U) (58) Fields investigated (Int.Cl . ⁷ , DB name) G11B ^7/ 12-7/22

Claims (8)

(57) [Claims] 1. A first beam for emitting a light beam in a first polarization direction
1 light source and 2nd which emits the light beam of the 2nd polarization direction
Light source and only one light beam in one polarization direction.
Polarization-dependent grating lens exhibiting a zoom function and the polarization-dependent grating
Focus the light beam that passed through the child lens on the information recording medium
Select from light collecting means, first light source or second light source
An optical pickup comprising: a drive selection unit that is driven dynamically. 2. The first light source and the second light source are on the same plane.
The optical pickup according to claim 1, wherein the optical pickup is arranged . 3. A first mode for emitting a TE-mode light beam
Light source and second light source for emitting TM mode light beam
And a polarized light functioning as a lens for only one light beam.
An optical pickup having a wave-dependent grating lens . 4. The polarization dependent grating lens is a proton
Claims characterized by being manufactured by replacement
The optical pickup according to any one of claims 1 to 3 . 5. Two optical beams having different polarization directions from each other.
Claims in which the wavelengths of the lasers are different from each other
The optical pickup according to any one of claims 1 to 4 . 6. The AlGaAs semiconductor as the first light source.
6. A laser according to claim 1, which is a laser.
The optical pickup described in either one . 7. The second light source has tensile strain in a well layer.
With an active layer having a quantum well structure with
2. An nP semiconductor laser, wherein the semiconductor laser is an nP semiconductor laser.
The optical pickup according to claim 6 . 8. A light beam emitted from the first light source.
And a light beam emitted from the second light source
Play or play and record using two types of light beams
The method according to any one of claims 1 to 7, characterized in that
The optical pickup shown.