JPH09265654A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a whole optical pickup small in size and light in weight by making an optical system and a detecting system small in size and light in weight even when a beam forming means is provided. SOLUTION: In this optical pickup, a deflection mirror 4 is arranged between a beam splitter 3 and an objective lens 5, when a laser beam from a semiconductor laser travels to a recording medium 6 through a coupling lens, the beam splitter 3 and the objective lens 5, the mirror 4 has the function of an optical path changing means for changing the direction of the laser beam traveling from the beam splitter 3 to the objective lens 5 and the function of a beam forming means changing the diameter of the laser beam at this time in one direction, expanding/forming the shape of the laser beam and making the beam travel toward the objective lens 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reproduces information recorded on an optical recording medium such as an optical disk by utilizing its reflected light, or records or erases information on the recording medium. The present invention relates to an optical pickup device.

[0002]

2. Description of the Related Art Conventionally, there is an optical pickup device for reproducing information recorded on an optical recording medium such as an optical disk by utilizing its reflected light, or recording or erasing information on the recording medium. Are known.

FIG. 8 is a diagram showing an example of a general schematic structure of an optical pickup device of this type. In the optical pickup device of FIG. 8, the laser beam emitted from the semiconductor laser 1 is coupled to the coupling lens 102, the beam splitter 103,
A minute light spot is irradiated onto the recording medium 6 such as an optical disk through the deflection mirror 104 and the objective lens 105, and the reflected light from the recording medium 6 is detected through the objective lens 105, the deflection mirror 104, and the beam splitter 103. 110
The detection system 110 detects the information signal (recording signal) recorded on the recording medium 6 and controls the position of the light spot on the recording medium 6 by a servo error signal (for example, a focus error signal). ) Is detected.

[0004]

By the way, in the optical pickup device of FIG. 8, since the beam shape of the laser beam from the semiconductor laser 1 is elliptical, the coupling lens 102, the beam splitter 103, and the deflecting mirror.
The shape of the beam spot incident on the recording medium 6 via the (or deflecting prism) 104 and the objective lens 105 is also elliptical. Therefore, in order to make a perfect circular beam spot incident on the recording medium 6, it is necessary to shape the elliptical laser beam from the semiconductor laser 1 into a perfect circular shape.

FIG. 9 shows a schematic configuration example in which a beam shaping technique is applied to the optical pickup device as shown in FIG. That is, FIG. 9 applies a general beam shaping technique, and in the example of FIG. 9, the coupling lens 10 is used.
2 and the deflection mirror (or deflection prism) 104,
Beam shaping means 111 is provided.

Here, the beam shaping means 111 applies the elliptical laser beam from the semiconductor laser 1 to the objective lens 1.
The shape is adjusted (generally, enlarged shape) so as to match the diameter of 05. Specifically, the minor axis of the ellipse of the laser beam is enlarged and shaped to match the major axis.

As described above, by enlarging and shaping the ellipse so that the minor axis of the ellipse matches the major axis of the ellipse, the elliptical laser beam can be shaped into a perfect circle, and the focusing of the beam by the objective lens 105 can be increased. The beam spot diameter of the laser beam incident on the recording medium 6 can be reduced.

FIGS. 10A and 10B are views for explaining the size of the beam spot narrowed down by the objective lens. 10A is a diagram showing a beam spot when an objective lens having a small NA (numerical aperture) is used,
FIG. 10B is a diagram showing a beam spot when an objective lens having a large NA (numerical aperture) is used. As can be seen by comparing FIGS. 10 (a) and 10 (b), the size of the beam spot narrowed down by the objective lens is determined by the NA (numerical aperture) of the objective lens. The aperture can be increased and the spot diameter can be reduced as compared with a small lens.
However, even if a lens having a large NA is used, as long as the beam diameter incident on this lens is small, it is substantially the same as when a lens having a small NA is used.

FIGS. 11A and 11B are views for explaining the size of a beam spot narrowed down by an objective lens having a large NA. Even when an objective lens having a large NA is used, FIG. If the beam diameter incident on this objective lens is small, as in FIG. 11B, the narrowing down is small and the spot diameter cannot be made smaller than when the beam diameter incident on the objective lens is large.

From this, when the elliptical laser beam is shaped into a perfect circle, it is preferable to enlarge and shape the beam diameter so that the minor axis of the ellipse matches the major axis. The size of the objective lens is the focal length f of the objective lens.
(Actually, it is determined by the back focus BF) (see FIG. 12), and the focal length f or the back focus BF is mainly determined by the thickness t of the recording medium, the deflection of the recording medium, and the like. When the thickness t of the recording medium is t = 1.2, the focal length f is about f = 3 mm, which is the limit. However, the focal length f of the objective lens is irrelevant to the spot size.

FIGS. 13 and 14 are views showing a concrete example of the beam shaping means 111 shown in FIG. In the example of FIG. 13, the minor axis direction of the elliptical laser beam from the semiconductor laser 1 is the thickness direction (vertical direction) y of the optical pickup device. In this case, the minor axis of the laser beam is In order to expand and shape in the thickness direction (vertical direction) y of the device, the prism 121
The beam shaping is performed twice by the prism 122 and. Further, in the example of FIG. 14, the minor axis direction of the elliptical laser beam from the semiconductor laser 1 is the width direction (lateral direction) x of the optical pickup device. In this case,
In order to expand and shape the minor axis of the laser beam in the width direction x of the apparatus, one prism 123 performs beam shaping.

There is a demand for those skilled in the art to make the optical pickup device thinner and smaller. For this purpose, it is necessary to make the optical system or the detection system of the optical pickup device thin and small. is there.

However, when the beam shaping means 111 as described above is added to the optical pickup device, there is a problem that the entire optical pickup device cannot be made smaller and thinner.

That is, with the configuration shown in FIG. 13, the thickness of the optical pickup device becomes large, and with the configuration shown in FIG. 14, the optical pickup device can be made thin, but the size in the width direction of the optical pickup device. Becomes large, and in both cases, there is a problem in making the device thinner and smaller.

According to the present invention, even when the beam shaping means is provided, the optical system and the detection system can be downsized and thinned.
An object of the present invention is to provide an optical pickup device capable of downsizing and thinning the entire optical pickup device.

[0016]

In order to achieve the above object, in the invention described in claim 1, a laser beam emitted from a semiconductor laser is recorded through a coupling lens, a beam splitter, an optical path changing means and an objective lens. An optical pickup device that irradiates a medium as a minute light spot, guides reflected light from a recording medium to a detection system via an objective lens, an optical path changing means, and a beam splitter, and detects a predetermined signal in the detection system First beam shaping means for enlarging and shaping the cross-sectional shape of the laser beam so as to irradiate the medium with a minute light spot and making it enter the objective lens is formed integrally with the optical path changing means. Thus, even when the beam shaping means is provided, the number of parts can be reduced, the optical system can be made smaller and thinner, and the entire optical pickup device can be made smaller and thinner.

Further, according to the invention described in claim 2, according to claim 1
In the optical pickup device described above, the cross-sectional shape of the laser beam of the reflected light incident on the detection system is reduced and shaped so that a predetermined signal can be detected with high sensitivity in the detection system even when the detection system is downsized. Since the second beam shaping means for that is provided in the optical path position between the beam splitter and the detection system, the detection sensitivity can be increased even when the detection system is downsized.

According to the third aspect of the present invention, there is provided the second aspect.
In the optical pickup device described above, since the second beam shaping means is formed integrally with the beam splitter, even when the beam shaping is performed to enhance the detection sensitivity of the detection system, the optical system and the detection system are not used. Can be kept small.

According to the invention described in claim 4,
The optical pickup device according to any one of claims 1 to 3, wherein the semiconductor laser and the coupling lens have an oval shape in which the upper side and the lower side are cut, and the beam splitter also has a width relative to the width. It has a flat shape with a low height. This makes it possible to reduce the thickness of the outward path of the optical pickup device.

In the invention according to claim 5, the invention according to claim 1
In the optical pickup device according to any one of claims 3 to 4, the light receiving surface of the light receiving element used for the detection system is displaced from the center of the package. As a result, the distance from the recording medium to the lower surface of the optical pickup device can be reduced, and thus the optical pickup can be thinned using a general-purpose package.

According to the invention of claim 6, claim 1
In the optical pickup device according to any one of claims 3 to 4, when the beam shaping magnification of the second beam shaping means is M, the detection lens used in the detection system has a focal length f, A focal length 1 / M times the focal length f ₀ required when there is no beam shaping is used. This makes it possible to obtain M times the focus error detection sensitivity and reduce the detection system length to 1 / M.

According to the invention of claim 7, claim 1
In the optical pickup device according to any one of claims 3 to 4, when the beam shaping magnification of the second beam shaping means is M, the detection lens used in the detection system has a focal length f, A focal length 1 / M ² times the focal length f ₀ required when there is no beam shaping is used. As a result, the detection system length can be shortened to 1 / M ² with the same detection sensitivity.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are diagrams showing a configuration example of an optical pickup device according to the present invention. 1 is a side view and FIG. 2 is a plan view.

Referring to FIGS. 1 and 2, this optical pickup device includes a semiconductor laser 1, a coupling lens 2 for converting an elliptical laser beam from the semiconductor laser 1 into a parallel beam, a beam splitter 3, and a deflector. Mirror 4
It has an objective lens 5, a beam shaping prism 7, and a detection system 10.

Here, the deflection mirror 4 is arranged between the beam splitter 3 and the objective lens 5, and the semiconductor laser 1
Direction of the elliptical laser beam from the beam splitter 3 toward the objective lens 5 when the laser beam from the laser beam goes through the coupling lens 2, the beam splitter 3 and the objective lens 5 to change the optical path. In addition to having a function as a means, the diameter (short diameter) of the elliptical laser beam in one direction at this time is expanded into a perfect circular shape, and the cross-sectional diameter of the laser beam is increased to increase the objective lens 5. It also has a function as a beam shaping means for directing it to That is, in the configuration examples of FIGS. 1 and 2, the deflection mirror 4 is of the type of the prism 4a that also has a beam shaping function.

The beam shaping prism 7 is arranged between the beam splitter 3 and the detection system 10, and the recording medium 6 is provided.
When the reflected light from the head goes to the detection system 10 through the objective lens 5, the deflection mirror 4 and the beam splitter 3, the detection system 10
Has a function as a beam shaping means for beam shaping the laser beam reflected light from the beam splitter 3 so that the diameter of the reflected light of the laser beam incident on the beam is reduced in one direction and the cross-sectional diameter becomes small. ing.

That is, in the configuration examples of FIGS. 1 and 2, since the deflection mirror 4 which also has a function as a beam shaping means is provided, the cross section of the laser beam incident on the recording medium 6 in the outward path of the laser beam. Enlarge and shape the shape from an ellipse to a perfect circle and make it enter the objective lens 5,
As a result, it is possible to narrow down the beam having a perfect circle shape and make a fine light spot having a good perfect circle shape enter the recording medium 6.

As described above, the laser beam is shaped into a perfect circular shape and is incident on the recording medium 6, whereby the recording medium 6
The laser beam reflected light from is also maintaining the cross-sectional shape of a perfect circle, but when this laser beam reflected light returns to the deflection mirror 4 via the objective lens 5, that is, in the return path,
In the deflecting mirror 4, the beam shape conversion reverse to the above is performed, the cross-sectional shape of the reflected light is returned from the perfect circular shape to the original elliptical shape, and in the original elliptical shape, the beam splitter 3 to the detection system 10 is changed. Head towards. The beam shaping prism 7 has an original elliptical laser from the polarizing prism 4 and the beam splitter 3 so that the reflected laser beam incident on the detection system 10 is not an original elliptical shape but a perfect circular shape. It has a function of reducing the diameter (major axis) of the beam reflected light in one direction, and reducing and shaping the cross-sectional shape of the beam from an ellipse to a true circle to increase the detection sensitivity.

Further, in the configuration example of FIGS. 1 and 2, the detection system 1
Reference numeral 0 indicates the light receiving element 12 and the light receiving surface 12 of the light receiving element 12 that reflects the reflected light from the beam splitter 3 and the beam shaping prism 7.
The detecting system 10 detects the information signal (recording signal) recorded on the recording medium 6 and controls the position of the light spot on the recording medium 6 by the detection lens 11 which leads to a. A servo error signal (for example, a focus error signal) is detected. The focus error in the detection system 10 can be detected by, for example, the astigmatism method. Alternatively, another focus error detection method such as a knife edge method or a beam size method can be used.

Next, the operation of the optical pickup device having such a configuration will be described. In this optical pickup device, the laser beam emitted from the semiconductor laser 1 (ellipse in cross section) becomes a parallel beam by the coupling lens 2. FIG. 3A is a diagram showing a cross-sectional shape (light amount distribution) of this parallel beam, and the parallel beam from the coupling lens 2 has an elliptical cross-sectional shape with a minor axis d and a major axis Md. This parallel beam is reflected by the beam splitter 3 and then enters the deflection mirror 4, where the optical path is changed and the beam is shaped.

That is, in the parallel beam, the minor axis d in one direction y in FIG. 3 (a) is magnified M times to become Md at the incident surface (prism surface) 4a of the deflection mirror 4, and FIG. ), The beam has a cross-sectional shape (light amount distribution) close to a perfect circle. Thereafter, this beam is totally reflected by the upper surface 4b of the deflecting mirror 4, and further, the direction of the optical path is changed upward by the reflecting surface 4c of the deflecting mirror 4, passes through the upper surface 4d of the deflecting mirror 4, and goes to the objective lens 5. A spot image is formed on the recording medium 6 by the objective lens 5.

FIGS. 4 (a), (b), (c) and (d) show the comparison of the optical path thickness between the optical pickup device of the present invention and the conventional optical pickup device having the beam shaping function. There is.
Here, FIG. 4A is a schematic diagram of the optical pickup device of the present invention, and FIGS. 4B, 4C, and 4D are schematic diagrams of a conventional optical pickup device having a beam shaping function. 4 (b) is shown in FIG.
Beam shaping means as shown in FIG.
(c) and (d) have a beam shaping means as shown in FIG. For convenience of explanation, FIG.
It is assumed that the same objective lens 5 is used in any of (a), (b), (c), and (d), and the distance between the objective lens 5 and the recording medium 6 is set to be the same (minimum). It has been done.

In the optical pickup device of the present invention (see FIG. 4 (a)), the optical path to the semiconductor laser 1, the coupling lens 2 and the deflection mirror 4 has an elliptical major axis in the width direction of the device.
(Horizontal direction) x, and the minor axis of the ellipse is set in the thickness direction (longitudinal direction) y of the device. The conventional optical pickup device shown in FIG. 4B (corresponding to FIG. 14). The optical path thickness w in the thickness direction (longitudinal direction) y of the device can be made smaller than that in FIG. Further, as described above, the width of the device in the width direction x can be reduced.

On the other hand, in the optical pickup device shown in FIGS. 4 (c) and 4 (d) (corresponding to FIG. 13), the semiconductor laser 1, coupling lens 2,
The optical path to the deflection mirror 4 has an elliptical major axis in the width direction of the device.
(Horizontal direction) x and the minor axis of the ellipse is set in the thickness direction (longitudinal direction) y of the device, so that the thickness direction (longitudinal direction) of the optical path from the semiconductor laser to the beam shaping means 111 is set. The optical path thickness w in the direction y can be reduced. However, in the optical pickup device of FIGS. 4 (c) and 4 (d), the beam shaping unit 111 uses the deflection mirror.
(Optical path changing means) Since it is provided separately from 4,
Since the thickness L from the recording medium 6 to the lower end of the optical path changing means becomes large, the optical pickup device cannot be made thin. On the other hand, the optical pickup device of the present invention (see FIG.
In (a), since the beam shaping means 111 is provided integrally with the deflection mirror (optical path changing means) 4, the thickness L from the recording medium 6 to the lower end of the optical path changing means can be made sufficiently small. .

As described above, in the optical pickup device of the present invention, in the outward path, the cross-sectional shape of the laser beam is enlarged and shaped by the deflecting mirror 4 provided also immediately before the objective lens 5 and having a function as a beam shaping means. Since the light is made incident on the objective lens 5 by means of the objective lens 5, the thickness of the device can be made thin and the width of the device can be kept small.
The laser beam can be sufficiently narrowed down and a fine light spot having a good circular shape can be incident on the recording medium 6.
Therefore, the optical pickup device can be made thin and compact even when it has a good beam shaping function.

The reflected light from the recording medium 6 returns to the beam splitter 3 in the reverse order of the forward path, and the beam splitter 3
And goes to the detection system 10. At this time, when the reflected light from the recording medium 6 passes through the deflection mirror 4 again, its cross-sectional shape returns from the shape shown in FIG. 3 (b) to the elliptical shape shown in FIG. 3 (a).
(That is, the diameter in one direction y is reduced from Md to d by the beam shaping surface 4a of the deflection mirror 4 and returns to the original shape of FIG. 3A).
Head for. However, in the optical pickup device of FIGS. 1 and 2, this reflected light is subjected to beam reduction shaping by the beam shaping prism 7 before entering the detection system 10, and its cross-sectional area is shown in FIG. 3 (a). Also has a cross-sectional shape (light amount distribution) close to a small perfect circle. That is, the reflected light is
The diameter (major diameter) Md in one direction x is reduced from Md to d by the beam shaping prism 7 to form a perfect circle having the minor diameter d of the outward elliptical beam as a diameter and can be incident on the detection system 10. it can.

In the optical pickup device of FIGS. 1 and 2, since the reflected light having a small beam diameter can be made incident on the detection system 10 in the return path, the detection system 10 can be made compact. It will be possible. For example, as described later, the focal length of the detection lens 11 of the detection system 10 can be shortened.

As described above, according to the present invention, the optical pickup device including the optical system and the detection system can be downsized and thinned.

In order to reduce the loss of light when passing through the beam splitter 3, a λ / 4 plate is placed at the position shown by the broken line in FIGS. 1 and 2, that is, between the beam splitter 3 and the objective lens 5. It is also possible to further provide 8 to configure an isolated optical system. In this case, the light utilization efficiency can be further increased.

In the configuration examples of FIGS. 1 and 2, the beam shaping prism 7 is constructed as a separate body from the beam splitter 3, but the beam shaping prism 7 should be constructed integrally with the beam splitter 3. You can also FIG. 5 is a diagram showing a configuration example of an optical pickup device in which the beam shaping prism 7 is integrated with the beam splitter 3, and by configuring the beam shaping prism 7 with the beam splitter 3, the number of parts can be reduced. Further, the size can be further reduced.

Further, in each of the above configuration examples, in order to further reduce the size and the thickness of the optical pickup device, FIG.
As shown in, a semiconductor laser 1 and a coupling lens 2
It is also possible to make and the oval shape with the upper and lower sides cut, and to make the beam splitter 3 a flat shape having a height lower than the width. This makes it possible to reduce the thickness of the optical pickup device, particularly in the forward path.

Further, regarding the detection system 10, as shown in FIG. 7, the light receiving surface 12a of the light receiving element 12, that is, the light receiving position can be arranged so as to be displaced from the center of the light receiving element package 13. In this case, the distance from the recording medium 6 to the lower surface LW of the optical pickup device can be reduced, so that the general-purpose package 13 can be used to reduce the thickness of the optical pickup.

Further, in the optical pickup device, the size of the detection system is a great obstacle to miniaturization. That is, in order to obtain the required sensitivity for focus error detection, it is necessary to lengthen the focal length f ₀ of the lens of the detection system to some extent.
A focal length f ₀ of about 30 to 60 mm is used. Since it is necessary to use a lens having a large focal length as the lens of the detection system, there is a limit to downsizing the detection system.

On the other hand, in the present invention, as the detection lens 11 of the detection system 10, a lens whose focus is shortened by the beam shaping magnification can be used. In other words, the detection lens 11 of the detection system 10 has a focal length f (combined focal length of the detection lenses 11) which is required when there is no beam shaping (focal length f ₀ (detection lens 11 when there is no beam shaping).
1 / M (M is a beam shaping magnification), that is, f ₀ / M can be used. As described above, by shortening the focal length of the detection lens 10 by 1 / M, the focus error detection sensitivity can be increased by M and the length of the detection system 10 can be shortened by 1 / M. it can. Specifically, the length of the detection system is 30 to
In the present invention, when the beam shaping magnification M is 2, the length of about 60 mm can be shortened to about 15 to 30 mm.

Further, the detection lens 11 of the detection system 10 includes
It is also possible to use a beam having a short focus by the square of the beam shaping magnification M, that is, a beam having an extremely short focus. That is,
The focal length f of the detection lens 11 used in the detection system 10 is the focal length f ₀ required when there is no beam shaping.
Of 1 / M ² , that is, f ₀ / M ² can also be used. In this way, the focal length of the detection lens 10 is set to 1
Since the length can be shortened to / M ² times, the length of the detection system 10 can be shortened to 1 / M ² . Specifically, in the present invention, when the length of the detection system is about 30 to 60 mm, the beam shaping magnification M is 7.5 to 15 in the present invention.
It can be as short as mm.

As described above, in the optical pickup device of the present invention, the deflection mirror 4 having the beam shaping function is arranged immediately before the objective lens 5 in the outward path, thereby reducing the thickness of the optical system portion of the optical pickup. Also in this case, the enlarged and shaped beam can be made incident on the objective lens 5, and a good minute light spot can be made incident on the recording medium 6 from the objective lens 5. In the return path, the deflection mirror 4
In order to make the detection system, that is, the detection lens small (small), reduce the diameter of the reflected light whose beam diameter has been restored again by the beam shaping prism and make it enter the detection system as light with a small beam diameter. Further, due to the beam shaping action of the return path (beam diameter reduction, beam angular displacement enlargement), focus error detection sensitivity of M ² times (M is beam shaping magnification) is obtained.

In the above configuration example, the deflection mirror 4 simultaneously performs the optical path change and the beam shaping in the outward path, but any optical path changing / beam shaping means having such an optical path changing / beam shaping function may be used. Deflection mirror 4
However, any one can be used. That is, any optical path changing means can be used as long as it can be integrated with the beam shaping means.

In the return path, beam shaping is performed by the beam shaping prism 7. However, not limited to the beam shaping prism 7, any means can be used as long as it has a beam shaping function in the return path. .

In the above description, the first beam shaping means (deflection mirror) or the second beam shaping means (beam shaping prism) shapes the cross section of the laser beam from an ellipse to a perfect circle. Any beam can be used as long as it enlarges or reduces the cross-sectional diameter of the beam. Therefore, the beam may be shaped into a shape other than a perfect circle (eg, a shape close to a perfect circle).

[0050]

As described above, according to the first aspect of the invention, the laser beam emitted from the semiconductor laser is transferred onto the recording medium via the coupling lens, the beam splitter, the optical path changing means and the objective lens. An optical pickup device that irradiates as a minute light spot, guides reflected light from a recording medium to a detection system via an objective lens, an optical path changing means, and a beam splitter, and detects a predetermined signal in the detection system, A first beam shaping means for enlarging and shaping the cross-sectional shape of the laser beam so that it is irradiated by a minute light spot and making it enter the objective lens is formed integrally with the optical path changing means. Thus, even when the beam shaping means is provided, the number of parts can be reduced, the optical system can be made smaller and thinner, and the entire optical pickup device can be made smaller and thinner.

According to the second aspect of the invention, the first aspect is
In the optical pickup device described above, the cross-sectional shape of the laser beam of the reflected light incident on the detection system is reduced and shaped so that a predetermined signal can be detected with high sensitivity in the detection system even when the detection system is downsized. Since the second beam shaping means for that is provided in the optical path position between the beam splitter and the detection system, the detection sensitivity can be enhanced even when the detection system is downsized.

According to the invention of claim 3, claim 2
In the optical pickup device described above, since the second beam shaping means is formed integrally with the beam splitter, even when the beam shaping is performed to enhance the detection sensitivity of the detection system, the optical system and the detection system are not used. Can be kept small.

In the invention according to claim 4, the invention according to claim 1
The optical pickup device according to any one of claims 1 to 3, wherein the semiconductor laser and the coupling lens have an oval shape in which the upper side and the lower side are cut, and the beam splitter also has a width relative to the width. It has a flat shape with a low height. This makes it possible to reduce the thickness of the outward path of the optical pickup device.

According to the invention of claim 5, claim 1
In the optical pickup device according to any one of claims 3 to 4, the light receiving surface of the light receiving element used for the detection system is displaced from the center of the package. As a result, the distance from the recording medium to the lower surface of the optical pickup device can be reduced, and thus the optical pickup can be thinned using a general-purpose package.

According to the invention of claim 6, claim 1
In the optical pickup device according to any one of claims 3 to 4, when the beam shaping magnification of the second beam shaping means is M, the detection lens used in the detection system has a focal length f, A focal length 1 / M times the focal length f ₀ required when there is no beam shaping is used. This makes it possible to obtain M times the focus error detection sensitivity and reduce the detection system length to 1 / M.

According to the invention of claim 7, claim 1
In the optical pickup device according to any one of claims 3 to 4, when the beam shaping magnification of the second beam shaping means is M, the detection lens used in the detection system has a focal length f, A focal length 1 / M ² times the focal length f ₀ required when there is no beam shaping is used. As a result, the detection system length can be shortened to 1 / M ² with the same detection sensitivity.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration example of an optical pickup device according to the present invention.

FIG. 3 is a diagram showing a sectional shape of a laser beam.

FIG. 4 is a diagram showing a comparison of optical path thickness between an optical pickup device of the present invention and a conventional optical pickup device having a beam shaping function.

FIG. 5 is a diagram showing a configuration example of an optical pickup device in which a beam shaping prism and a beam splitter are integrally formed.

FIG. 6 is a diagram showing a configuration example of an optical pickup device according to the present invention.

FIG. 7 is a diagram showing a configuration example of an optical pickup device according to the present invention.

FIG. 8 is a diagram showing a schematic configuration example of a conventional optical pickup device.

9 is a diagram showing a schematic configuration example in which a beam shaping technique is applied to the optical pickup device as shown in FIG.

FIG. 10 is a diagram for explaining the size of a beam spot narrowed down by an objective lens.

FIG. 11 is a diagram for explaining the size of a beam spot narrowed down by an objective lens having a large NA.

FIG. 12 is a diagram for explaining characteristics of an objective lens.

FIG. 13 is a diagram showing a specific example of beam shaping means.

FIG. 14 is a diagram showing a specific example of beam shaping means.

[Explanation of symbols]

1 semiconductor laser 2 coupling lens 3 beam splitter 4 deflection mirror 5 objective lens 6 recording medium 7 beam shaping prism 8 λ / 4 plate 10 detection system 12 light receiving element 11 detection lens 13 package

Claims (7)

[Claims] 1. A laser beam emitted from a semiconductor laser is irradiated as a minute light spot on a recording medium through a coupling lens, a beam splitter, an optical path changing means, and an objective lens, and reflected light from the recording medium is an objective lens, In an optical pickup device that guides a beam to a detection system via an optical path changing means and a beam splitter, and detects a predetermined signal in the detection system, the cross-sectional shape of a laser beam is enlarged and shaped so that a minute light spot irradiates a recording medium. An optical pickup device, wherein a first beam shaping means for making the light incident on the objective lens are integrally formed with the optical path changing means. 2. The optical pickup device according to claim 1, further comprising a laser of reflected light which is incident on the detection system so that a predetermined signal can be detected with high sensitivity in the detection system even when the detection system is downsized. An optical pickup device characterized in that a second beam shaping means for reducing and shaping the cross-sectional shape of the beam is provided at an optical path position between the beam splitter and the detection system. 3. The optical pickup device according to claim 2, wherein the second beam shaping means is formed integrally with a beam splitter. 4. The optical pickup device according to claim 1, wherein the semiconductor laser and the coupling lens are cut at an upper side and a lower side in order to reduce the thickness of the optical pickup device. The optical pickup device is characterized in that it has an oval shape and the beam splitter has a flat shape whose height is low relative to the width. 5. The optical pickup device according to claim 1, wherein the light receiving element used for the detection system has a light receiving surface displaced from the center of the light receiving element package. Characteristic optical pickup device. 6. The optical pickup device according to claim 1, wherein when the beam shaping magnification of the second beam shaping means is M, a detection lens used in a detection system is provided. Is an optical pickup device characterized in that its focal length f is 1 / M times the focal length f ₀ required when there is no beam shaping. 7. The optical pickup device according to claim 1, wherein when a beam shaping magnification of the second beam shaping means is M, a detection lens used in a detection system is provided. Is an optical pickup device characterized in that its focal length f is 1 / M ² times the focal length f ₀ required when there is no beam shaping.