JPH0896398A - Grating and optical pickup - Google Patents

Abstract

PURPOSE: To produce gratings with high precision and to easily adjust grating angles with high precision by forming a mount reference face to the grating and forming the grating made of a plastic so as to provide a prescribed grating angle with respect to the reference face. CONSTITUTION: The grating 13 divides an optical beam emitted from a laser light source 11 into three light beams and an objective lens 16 projects the light beams so as to be focused on a recording face of an optical disk D. A beam splitter 14 separates the light beam emitted from the laser light source 11 and the return light beam from a recording face of the optical disk D via the objective lens 16 toward the inner circumferential side of the optical disk D. The grating 13 is made of a plastic so as to have a prescribed grating angle with respect to a track of the optical disk D and provided with two mount reference faces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grating as a diffraction element for splitting a light beam from a light source into, for example, three light beams, and an improvement of an optical pickup having such a grating.

[0002]

2. Description of the Related Art Conventionally, such an optical pickup is
For example, it is configured as shown in FIGS. 9 and 10. 9 and 10, the optical pickup 1 includes a laser coupler 2, a prism mirror 3, a grating 4, a beam splitter 5, a prism mirror 6, an objective lens 7,
The beam splitter 5 is composed of a concave lens 8 and a photodetector 9 on which a return light beam separated in a direction perpendicular to the optical axis of the objective lens 7 is incident.

The laser coupler 2 has a light source section and a light receiving section, and this light source section 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 light source section of the laser coupler 2 is guided to the prism mirror 3.

The prism mirror 3 has a reflecting surface for reflecting incident light, is made of glass, plastic or the like, and forms an angle of 45 degrees with respect to the optical axis of the light beam from the laser coupler 2. It is arranged to have. As a result, the light beam reflected by the prism mirror 3 is guided to the grating 4.

The grating 4 is for diffracting the incident light, and in order to separate the laser light beam from the laser coupler 2 into three light beams of 0-order light and plus / minus two primary lights. used.

The beam splitter 5 is arranged such that its half mirror surface is inclined by 45 degrees with respect to the optical axis. The light beam emitted from the laser coupler 2 and the return light beam from the recording surface of the optical disc D are arranged. To separate.

The prism mirror 6 is a beam splitter 5
The light beam from is reflected by its reflection surface and guided to the objective lens 7.

The objective lens 7 focuses the light beam reflected by the prism mirror 6 on a desired track on the recording surface of the rotationally driven optical disc D.

The light beam applied to the recording surface of the optical disc D is again guided to the beam splitter 5 via the objective lens 7 and the prism mirror 6 as a return light beam. Then, the return light beam reflected by the reflecting surface of the beam splitter 5 is focused on the light receiving surface of the photodetector 9 via the concave lens 8.

The photodetector 9 is a grating 4
The zero-order light and the two first-order lights separated by are each provided with a light-receiving surface.

The return light beam transmitted through the beam splitter 5 is again reflected by the grating 4 and the prism mirror 3.
It is incident on the laser coupler 2 via and is focused on the light receiving portion of the laser coupler 2.

According to the optical pickup 1 having such a structure, the laser light beam emitted from the laser coupler 2 is reflected by the prism mirror 3 and then separated into three light beams by the grating 4 and the beam splitter. Through 5. After that, the light beam is reflected by the prism mirror 6 and is converged to a certain point on the recording surface of the optical disc D via the objective lens 7.

The return light beam from the recording surface of the optical disc D is incident on the beam splitter 5 again via the objective lens 7 and the prism mirror 6. Here, a part of the return light beam is reflected by the half mirror surface of the beam splitter 5, and a part thereof passes through the beam splitter 5.

The return light beam reflected by the beam splitter 5 passes through the concave lens 8 and each light beam separated by the grating 4 is converted into a photodetector 9 respectively.
Is incident on the corresponding light receiving surface of. Thereby, based on the detection signal from each light receiving surface of the photodetector, for example, 3
A tracking error signal and a focusing error signal are generated by the spot method or the like.

The return light beam transmitted through the beam splitter 5 is again reflected by the grating 4 and the prism mirror 3.
Then, the light travels into the laser coupler 2 via and enters the light receiving portion of the laser coupler 2. As a result, the reproduction signal of the optical disc D is generated based on the detection signal from the light receiving section of the laser coupler 2.

By the way, in the optical pickup 1, as shown in FIG. 11, the three light beams divided by the grating 4, that is, the main beam and the two side beams, form a groove G (which constitutes a track of the optical disc D). Alternatively, the main beam forms a spot L1 on the center line of the groove G with respect to the land or pit), and the side beam spots L2 at a position laterally separated from the center line of the groove G by a predetermined distance d. L3
Is required to be formed.

Here, since the interval (so-called beam spacing) S between the main beam and the side beam on the recording surface of the optical disc D is determined by the size of the grating of the grating 4, the side beam is separated from the center line of the groove G. In order to separate them by the distance d, the grating angle θ of the grating 4 is selected such that the side beam spots L2 and L3 are inclined with respect to the main beam spot L1 by an angle θ1 with respect to the track direction. . Thus, the grating 4 is mounted and adjusted with respect to the base member (not shown) so as to form the lattice angle θ.

[0018]

However, in the optical pickup 10 configured as described above, since the grating 4 is made of glass,
It was not possible to create a highly accurate grid in terms of the work accuracy of the grid formation. Therefore, the beam spacing S becomes relatively large. This allows
The angle θ inevitably becomes small, and the distance d from the center line of the groove G of the side beam changes greatly even if the angle θ slightly deviates due to the mounting accuracy of the grating 4. I will end up. Therefore, it is necessary to adjust the grating angle after mounting the grating, and there is a problem that the mounting work of this grating is complicated and troublesome and the time required for the mounting work becomes long.

In view of the above points, the present invention provides a grating and an optical pickup in which the grating of the grating is created with high accuracy and the grating angle is easily and accurately adjusted. Has an aim.

[0020]

According to the present invention, the above object is to provide a grating having a grating formed on one surface thereof with a mounting reference surface and at a predetermined grating angle with respect to the mounting reference surface. Is achieved by a grating, which is made of plastic to have

Further, according to the present invention, the above object is to provide a laser light source for emitting a laser light beam, a grating for splitting the light beam emitted from the light source into a plurality of light beams, and an optical disc for these light beams. An objective lens for irradiating the recording surface of the recording surface with focus, a separation optical system for separating a light beam emitted from the light source and a return light beam from the recording surface of the optical disc through the objective lens, and the separation optical system. And a photodetector for receiving the return light beam separated by the optical system, wherein the grating is made of plastic so as to have a predetermined lattice angle with respect to the track of the optical disc, and the mounting reference surface is With the optical pickup provided,
Achieved.

In the optical pickup according to the present invention, preferably, the mounting reference surface is formed only near both ends of the grating.

In the optical pickup according to the present invention, preferably, the grating is attached to one base member together with other optical elements, and its attachment reference surface is brought into contact with the attachment surface of this base member. ,
Mounted at a predetermined grid angle.

[0024]

According to the above construction, since the grating itself is made of plastic, the grating can be easily formed with high precision. Therefore, when the light beam is divided into, for example, three beams by the grating, the so-called beam spacing between the spots of the main beam and the side beam is configured to be relatively small, so that the main beam and the side of the track on the recording surface of the optical disc are The angle formed by the beam spot becomes relatively large. As a result, even if the grating angle of the grating is slightly deviated, the lateral distances of the spots of the main beam and the side beams with respect to the track do not change much.

Further, since the grating has the mounting reference surface, for example, the mounting reference surface of the grating is brought into contact with the mounting surface of the base member of the optical pickup so that the predetermined grating can be easily and accurately formed. Since the angle can be obtained, the work of adjusting the lattice angle after mounting is unnecessary.

When the mounting reference surface is formed only near both ends of the grating, for example, even when the accuracy of the mounting surface of the base member of the optical pickup is not very good, unevenness in the intermediate region of the mounting reference surface is not observed. Since the mounting accuracy of the grating is not affected, the mounting accuracy of the grating is improved.

When the above-mentioned grating is attached to one base member together with other optical elements and is attached at a predetermined lattice angle by bringing its attachment reference surface into contact with the attachment surface of this base member. The optical axis adjustment with other optical elements can be easily performed.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to FIGS. In addition, since the Examples described below are preferred specific examples of the present invention, various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 1 shows an embodiment of an optical pickup having a grating according to the present invention. In FIG. 1, an optical pickup 10 includes a laser coupler 11 including a light source section and a light receiving section each including a semiconductor laser element,
A first prism mirror 12, a grating 13, a beam splitter 14, a second prism mirror 15, an objective lens 16 and a photodetector that converges the return light beam separated by the beam splitter 14 on the inner circumference side of the optical disc D ( (Not shown).

The laser coupler 21 has a light source section and a light receiving section, and the light source section is a light emitting element utilizing recombination light emission of a semiconductor and is used as a light source.
The light beam emitted from this light source unit is guided to the first prism mirror 22.

The first prism mirror 12 reflects the light beam from the light source section of the laser coupler 11 on its reflection surface and guides it to the grating 13. Since the first prism mirror 12 is for reflecting the incident light beam, another reflecting member such as a mirror may be used. It may be omitted if it is not necessary to bend the optical axis.

The grating 13 diffracts incident light, diffracts the light beam emitted from the light source portion of the laser coupler 11, and diffracts the 0th order diffracted light and the plus / minus 1st order light in the direction perpendicular to the tracking direction. It is used to separate at least three light beams.

The beam splitter 14 is arranged with its half mirror surface inclined at 45 degrees with respect to the optical axis, and separates the light beam from the laser coupler 11 and the return light from the recording surface of the optical disc D. .

The second prism mirror 15 reflects the light beam from the beam splitter 14 on its reflection surface,
It is guided to the objective lens 16. Since the second prism mirror 15 is for reflecting the incident light beam, another reflecting member such as a mirror may be used.

The objective lens 16 is supported by a biaxial actuator so as to be movable in the biaxial directions, and the light beam reflected by the second prism mirror 15 is
It is converged on a desired track on the recording surface of the optical disc D which is rotationally driven.

The light beam applied to the recording surface of the optical disc D is again guided to the beam splitter 14 via the objective lens 16 and the second prism mirror 15 as a return light beam. Then, the return light beam transmitted through the reflecting surface of the beam splitter 14 is again returned to the first prism mirror 12
After being reflected by, the light is incident on the light receiving portion of the laser coupler 21. As a result, in the light receiving part of the laser coupler 21,
A focusing error signal is detected. On the other hand, the return light beam reflected by the reflecting surface of the beam splitter 14 is
The light is incident on the light receiving portion of the photo detector.

Further, in the optical pickup 10 according to the present embodiment, the grating 13 has the structure shown in FIGS.
It is configured as shown in.

FIG. 2 is a front view of the grating 13, and FIG.
Are side views, and in these figures, the grating 13 has a grating 13a formed on its upper surface. A surface on one side (upper side in FIG. 2) of the grating 13 is formed as a mounting reference surface 13c, and a lower surface thereof is formed as a mounting reference surface 13b. As a result, this lattice 13a becomes
It has a predetermined lattice angle with respect to the attachment reference surface 13c. Here, the mounting reference surfaces 13b, 13
c is provided only on both sides in the drawing,
The middle part is missing. The grating 13 is entirely made of plastic, so that the grating 13a is formed by the conventional glass grating 4
Since it is formed with high accuracy as compared with, the grid pitch is formed smaller.

The grating 13, together with other optical elements, that is, the first prism mirror 12, the beam splitter 14, and the second prism mirror 15, is attached to one base member 17 and fixedly held. In this case, the grating 13 is fixedly held to the base member 17 as shown in FIG. 4 or 5. In FIG. 4, the mounting reference surface 13 c of the bottom surface of the grating 13 is in contact with the mounting surface 17 a of the bottom surface of the base member 17, and the mounting reference surface 13 b of the side surface of the grating 13 is the grating of the base member 17. By abutting against the mounting surface 17b provided on the side surface of the mounting portion, the positioning is performed, and as shown in the perspective view of FIG. , Is accurately fixed and held at the mounting position of the base member 17.

In this case, since the mounting reference surfaces 13b and 13c of the grating 13 are provided only on both side portions, even if the mounting surfaces 17a and 17b of the base member 17 have irregularities, the mounting reference surfaces 13b and 13c are not provided. Surface 13b, 1
3c is attached to the mounting surfaces 17a and 17b by the mounting surface 1
The positioning and the holding are ensured without being affected by the unevenness of 7a and 17b as much as possible.

Further, the photodetector is configured to have a light receiving section for receiving the return light beam separated by the beam splitter 14. in this case,
The photodetector is adapted to detect a tracking error signal and a reproduction signal, for example, and does not need to have a divided light receiving surface. Therefore, it is possible to increase the magnification of the detection signal by amplifying the detection signal from the light receiving section.

The optical pickup 10 according to the present embodiment is configured as described above, and the laser light beam emitted from the light source section of the laser coupler 11 is reflected by the first prism mirror 12 and three by the grating 13. After being separated into the light beams of, the light beams pass through the beam splitter 14. After that, the light beam is reflected by the second prism mirror 15 and is converged to a certain point on the recording surface of the optical disc D via the objective lens 16.

The return light beam from the recording surface of the optical disc D enters the beam splitter 14 again via the objective lens 16 and the second prism mirror 15. Here, the return light beam is partially transmitted and partially reflected by the half mirror surface of the beam splitter 14.

The return light beam that has passed through the beam splitter 14 is reflected by the first prism mirror 12 again, and then enters the light receiving portion of the laser coupler 11. At this time, the light receiving portion of the laser coupler 11 has a divided light receiving surface corresponding to each light beam divided by the grating 12. Therefore, the focus error signal of the optical disc D is generated based on the detection signal from each divided light receiving surface of the light receiving portion of the laser coupler 11.

The return light beam reflected by the half mirror surface of the beam splitter 14 is incident on the light receiving surface of the photodetector. Thus, the read signal of the optical disc D and the tracking error signal are generated based on the detection signal from the light receiving surface of the photodetector.

In this case, since the grating 13 is made of plastic, its grating 13 is
The pitch of a is formed with high precision and small. As a result, the spots L1, L2, L3 on the recording surface of the optical disc D formed by the main beam and the side beams divided by the grating 13 have a relatively small beam space, as shown in FIG. For this reason,
The angle θ1 formed by the spots L1, L2 and L3 with the track direction of the optical disc D is relatively large. Therefore, depending on the mounting accuracy of the grating 13, for example, the grating 1
Even when the lattice angle θ of 3 is slightly deviated, the lateral distances of the spots L1 and L2 and the spots L1 and L3 are
It does not change much and is within the allowable range.

Further, since the grating 13 has the attachment reference surfaces 13b and 13c, when it is attached to the base member 17 of the optical pickup 10, the attachment reference surfaces 13b and 13c are attached to the base member 17, respectively. The grating 13 can be easily and accurately attached to the base member 17 at a predetermined lattice angle θ by abutting against the side and bottom attachment surfaces 17b and 17a.

7 and 8 show another fixing means of the grating 13 to the base member 17. In FIG. 7, the grating 13 has its mounting reference surface 13b or 13c abutted against the mounting surface 17b or 17a of the base member 17 by a U-shaped bent leaf spring 18 made of, for example, stainless steel. There is. As a result, the grating 13 is positioned and fixedly held at a predetermined mounting position of the base member 17.

Further, in FIG. 8, the grating 1
3, the mounting reference surface 13c, by the leaf spring 19,
It is in contact with the mounting surface 17a of the base member 17. As a result, the grating 13 is positioned and fixedly held at a predetermined mounting position of the base member 17.

As described above, in the above-described embodiment, since the grating of the grating is formed of plastic with high accuracy, the beam spacing is relatively small. Therefore, the angle formed by the spots of the main beam and the side beam with respect to the track on the recording surface of the optical disk becomes relatively large, and even if the grating angle of the grating is slightly deviated, the spot of the main beam and side beam with respect to the track is The distance does not change much, so
This will increase the allowable range of the grating angle of the grating.

Further, since the grating has the mounting reference surface, the predetermined grating angle can be obtained easily and accurately, and the operation of adjusting the grating angle after mounting becomes unnecessary. Thus, the mounting work of the grating is facilitated and the mounting is performed in a short time, so that the assembly cost is reduced.

When the mounting reference surface is formed only near both ends of the grating, for example, even when the accuracy of the mounting surface of the base member of the optical pickup is not very good, the unevenness in the intermediate region of the mounting reference surface is Since the mounting accuracy of the grating is not affected, the mounting accuracy of the grating is improved.

When the above-mentioned grating is attached to one base member together with other optical elements, and the attachment reference surface is brought into contact with the attachment surface of this base member, the grating is attached at a predetermined lattice angle. The optical axis adjustment with other optical elements can be easily performed.

In the above-mentioned embodiment, the laser coupler is used as the laser light source, and the light receiving portion is integrally formed. However, as the laser light source, a semiconductor laser element of a single light source portion or another laser light source is used. It is also possible to use. Further, in the above-described embodiment, the case of the optical pickup for recording / reproducing of the optical disk is explained, but not only the CD and the CD-ROM but also the MO and M.
It is obvious that the present invention can be applied to an optical pickup for an optical disc such as a magneto-optical disc such as D.

[0055]

As described above, according to the present invention, the grating of the grating is created with high accuracy, and the grating angle is adjusted easily and with high accuracy. The optical pickup used will be provided.

[Brief description of drawings]

FIG. 1 is a schematic side view showing the configuration of an embodiment of an optical pickup including a grating according to the present invention.

FIG. 2 is a front view of a grating in the optical pickup of FIG.

FIG. 3 is a side view of a grating in the optical pickup of FIG.

FIG. 4 is a cross-sectional view of the first configuration example showing the mounting state of the grating of FIG. 2 as seen from the optical axis direction.

5 is a cross-sectional view showing a mounting state of the grating of FIG. 2 as seen from the side.

6 is an enlarged view showing spots on a recording surface of an optical disc by the grating of FIG.

FIG. 7 is a cross-sectional view of a second configuration example showing a mounted state of the grating of FIG.

8 is a cross-sectional view of a third configuration example showing a mounting state of the grating of FIG.

FIG. 9 is a schematic side view showing the configuration of an example of a conventional optical pickup.

FIG. 10 is a schematic plan view of the optical pickup of FIG.

11 is an enlarged view showing spots on a recording surface of an optical disc in the optical pickup of FIG.

[Explanation of symbols]

 10 Optical Pickup 11 Laser Coupler 12 First Prism Mirror 13 Grating 13a Grating 13b Mounting Reference Surface 13c Mounting Reference Surface 14 Beam Splitter 15 Second Prism Mirror 16 Objective Lens 17 Base Member 17a Mounting Surface 17b Mounting Surface

Claims (4)

[Claims] 1. A grating having a grating formed on one surface thereof, wherein the grating is provided with a mounting reference surface, and is made of plastic so as to have a predetermined grating angle with respect to the mounting reference surface. And the grating. 2. A laser light source that emits a laser light beam, a grating that divides the light beam emitted from this light source into a plurality of light beams, and these light beams are focused on the recording surface of the optical disc. An objective lens for irradiating, a separation optical system for separating the light beam emitted from the light source and the return light beam from the recording surface of the optical disc through the objective lens, and the return light beam separated by the separation optical system. An optical pickup including a photodetector for receiving light, wherein the grating is formed of plastic so as to have a predetermined lattice angle with respect to a track of an optical disc, and has a mounting reference surface. . 3. The mounting reference surface is formed only near both ends of the grating.
The optical pickup described in. 4. The grating is attached to one base member together with other optical elements, and is attached at a predetermined lattice angle by bringing its attachment reference surface into contact with the attachment surface of this base member. The optical pickup according to claim 3, wherein: