JP3354360B2 - Optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup for reproducing or reproducing and recording 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 FIGS. 7A and 7B show a conventional optical pickup. FIG. 7A is a vertical sectional front view, and FIG. 7B is a vertical sectional side view. This optical pickup uses an astigmatism method as a focus control method and a three-beam method as a tracking control method. The light beam emitted from the semiconductor laser 51 is a three-beam diffraction grating 5.
The light beam is divided into three light beams by 2. The hologram element 53 is a kind of diffraction element.
And is focused on the recording layer of the optical disk 55 by the objective lens 54. The light beam reflected by the recording layer reaches the hologram element 53 via the objective lens 54,
Due to the diffraction effect, the light is guided to a six-division photodiode 56 provided substantially on the side of the diffraction grating 52. An optical pickup using such a hologram element has attracted attention in recent years because it is possible to reduce the size, improve the performance, and reduce the price of the optical pickup.

FIG. 8 shows the above-described six-segment photodiode 5.
6, four-divided element portions 56a, 56b, 56c, 5
It is the top view which showed 6d. Quadrant elements 56a-5
The beam spot (shown by a solid line) formed on 6d has a circular shape so as to evenly straddle the four-division element portions 56a to 56d as shown in FIG. When the optical disk 55 is located at a position close to the objective lens 54, the major axis is formed in an elliptical shape located on the four-divided element portions 56a and 56c, as shown in FIG. When the optical disc 55 is located far from the objective lens 54, as shown in FIG. 3C, the major axis is formed in an elliptical shape located on the four-divided element portions 56b and 56d.

As described above, since the outputs Pa to Pd of the four-divided element portions 56a to 56d change depending on the in-focus state, the in-focus state is obtained by calculating (Pa + Pc)-(Pb + Pd). It can be determined whether the position of the optical disk 55 is near or far from the objective lens 54.

[0005]

However, the conventional optical pickup has a disadvantage that it is not easy to reduce the thickness of the optical pickup because it is provided with four divided light receiving elements for focus control. FIG. 10 is a perspective view of a case where a thin optical pickup is configured using a unit 81 in which an optical system other than an objective lens of an optical pickup using a hologram element is integrated. Unit 8
The light emitted in the horizontal direction from 1 is bent vertically upward by the rising mirror 89, and is focused on the signal recording surface of the optical disk 85 by the objective lens 84. Then, the reflected light having read the signal goes through the reverse process, is again incident on the unit 81, and the signal is detected. Here, in order to further reduce the thickness of the optical pickup, it is necessary to reduce the width W of the unit 81. However, as described above, since the light receiving element is divided into four, the number of lead wires 88. As a result, it is difficult to reduce the thickness of the optical pickup.

FIG. 9 shows the positional relationship of the disk 55 with respect to the objective lens 54 on the horizontal axis, and the vertical axis shows the output Pa
It is a figure showing the calculation result about -Pd. Hereinafter, the curve shown in this figure is called an S curve. In order to enhance the reliability of the focus control, the S curve passes through the intersection of the horizontal axis and the vertical axis in the in-focus state, and the difference (amplitude) between the far position and the near position in the out-of-focus state in the out-of-focus state. ) Is required to be large.

However, the wavelength of the light beam emitted from the semiconductor laser fluctuates due to a change in the ambient temperature where the semiconductor laser is placed, and the fluctuation in the wavelength changes the beam diffraction angle in the hologram element 53. When the diffraction angle of the beam changes, as shown by the dotted lines in FIGS.
A position shift occurs in the light beam spot formed on d. As shown by the dotted S-curve in FIG. 9, the displacement can be reduced in amplitude as compared with the solid S-curve, or offset (the intersection of the horizontal axis and the vertical axis in the focused state). ), There is a problem that the reliability of focus control is reduced.

The present invention has been made in view of the above circumstances, and provides an optical pickup which can realize a reduction in thickness by using a light receiving element with a small number of divisions and which does not reduce the reliability of focus control even when the environmental temperature changes. With the goal.

Japanese Patent Application Laid-Open No. 4-117635 (IPC: G11B 7/135) discloses an optical head assembly in which a hologram element is arranged at an angle to the optical axis of a light beam. However, in this optical head assembly, the transparent plate on which the hologram element is formed is tilted for the purpose of correcting the aberration of the laser beam emitted from the semiconductor laser.
The present invention is different from the present invention in that focus control is not performed using a positional shift of a light beam spot based on a focused / unfocused state generated by a hologram element arranged at an angle.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an optical pickup according to the present invention has a diffraction element for guiding a light beam reflected by an information recording medium to a light receiving element by a diffraction effect. At the optical axis of the light beam
Is the Z axis, and the diffraction element is arranged perpendicular to the Z axis.
Diffraction direction of the light beam reflected by the information recording medium
And in the plane including the Z-axis direction and perpendicular to the Z-axis.
When the axis is the X axis, the diffraction element is at least
Around the plane perpendicular to the Z axis, with the X axis as the rotation axis
The light receiving element is arranged to be inclined and parallel to the X axis.
It has a formed region dividing line .

When the light beam spot is in a focused state, the light beam spot is positioned so as to evenly straddle the divided element portion formed by the area dividing line of the light receiving element, and when the information recording medium is at a close position, When the information recording medium is located at a position distant from the division element portion on one side in the direction orthogonal to the region division line, the division element portion on the other side in the direction orthogonal to the region division line is located. It is located shifted.

When the environmental temperature changes, the wavelength of the light beam changes, and the beam diffraction angle at the diffraction element changes. The displacement of the light beam spot due to the change in the diffraction angle is caused by the area division line. Therefore, the displacement of the spot does not change the light reception amount of each divided element portion. Therefore, a change in the environmental temperature does not affect the amplitude of the S-curve and does not cause an offset.

[0013]

In order for a change in the position of the light beam spot at the boundary of the area dividing line based on the distance of the information recording medium to appear, the diffraction element only needs to have at least the angular component in the direction around the X axis. It is. Of course, in order to make the position change of the light beam spot at the boundary of the area dividing line based on the distance of the information recording medium appear best, the diffraction element may be arranged to be inclined around the X axis. Further, when the region dividing line is substantially parallel to the X axis, the light source and the light receiving element can be arranged on a plane, so that assembly and wire bonding are facilitated.

Further, since the focus error detection can be performed by the two-divided light receiving element, it is possible to avoid an increase in the cost of the light receiving element by dividing the light receiving element into three or four parts and an increase in size due to an increase in the number of wirings.

Further, the divided element portion of the light receiving element divided by the region dividing line may be formed in a substantially rectangular shape with the region dividing line as a longitudinal direction. According to this,
Since the permissible range for the displacement of the light beam spot along the region dividing line is increased, it is possible to cope with a larger change in the environmental temperature.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an optical pickup of the present invention, wherein FIG. 1 (a) is a longitudinal sectional front view and FIG. 1 (b) is a longitudinal sectional side view. The light beam emitted from the semiconductor laser 1 is divided into three light beams by the three-beam diffraction grating 2. Then, the light beam passes through the hologram element 3 which is a kind of diffraction element, and is focused on the recording layer of the optical disk 5 by the objective lens 4. The light beam reflected by the recording layer reaches the hologram element 3 via the objective lens 4, and is guided to the four-division photodiode 6 provided substantially on the side of the diffraction grating 2 by the diffraction and light condensing. It is supposed to be.

The hologram element 2 is arranged to be inclined with respect to the optical axis of the light beam as described below. That is, the hologram element 2
Is set in the plane including the diffraction direction and the Z axis when the X axis is arranged perpendicular to the Z axis, and the axis perpendicular to the Z axis is defined as the X axis, and the axis perpendicular to the Z axis and the X axis is defined as the Y axis. At this time, the hologram element 2 is tilted around the X axis. Further, the photodiode 6 is provided as shown by a solid line or a dotted line in the figure, and has an area dividing line substantially including a front X axis and being substantially perpendicular to the diffraction plane of the tilted hologram element 3. . As shown by the solid line, when the semiconductor laser 1 and the photodiode 6 are arranged parallel to the X axis, the semiconductor laser 1 and the photodiode 6 can be arranged on a plane, so that assembly and wire bonding can be easily performed.

FIG. 2 shows the four-division photodiode 6 described above.
FIG. 5 is a plan view showing two divided element portions 6a and 6b for receiving a light beam related to a central light beam of the three light beams and performing information detection and focus control. FIG. 3 is a plan view showing the two divided element portions 6a and 6b, and showing the relationship between the hologram element 2 and the semiconductor laser 1. The two divided element portions 6a and 6b are provided with a region dividing line 7 parallel to the X axis.
Formed by The divided element portions 6a and 6b divided by the area dividing line 7
Is formed in a substantially rectangular shape having a longitudinal direction. In addition,
Two element parts for receiving the other two beams (not shown)
Are provided at an upper position of the dividing element portion 6a and a lower position of the dividing element portion 6b. It is desirable that these two element portions also have a rectangular shape and the longitudinal direction thereof is aligned with the direction of the region dividing line 7.

When the beam spot (shown by a solid line) formed on the two divided element portions 6a and 6b is in a focused state, as shown in FIG. 6b is formed so as to evenly straddle the optical disc 5 when the optical disc 5 is far from the objective lens 4.
As shown in FIG. 7A, the optical element 5 is formed so as to be shifted toward the splitting element portion 6a, and conversely, when the optical disk 5 is close to the objective lens 4, as shown in FIG. It is formed shifted toward the portion 6b.

FIG. 4 shows a spot of a light beam (a light beam transmitted through a part of the hologram element 3) at the boundary of the area dividing line 7 based on the distance of the optical disk 5 by arranging the hologram element 3 at an angle. FIG. 2 is an explanatory diagram showing a state in which a forming position changes in the Y-axis direction, and is a diagram viewed from the same direction as FIG. 1B.

In FIG. 4, reference numeral 8 denotes a path of light reflected from the optical disk which is not diffracted by the hologram element 3. Reference numeral 8a denotes a case where the optical disk is far away; Is the case where the optical disk is close. Thus, the convergence point of the reflected light 8 moves along the Z axis.

Now, with respect to the movement of the convergence point of the reflected light 8,
The movement of the convergence point of the diffracted light 9 by the hologram element 3 depends on the optical axis 10 of the diffracted light 9b when the optical disc is at the in-focus position.
The hologram element 3 can be designed so as not to move along, so that, for example, the convergence point moves on the two-dot chain line in the figure. That is, for 8a, like 9a, 8b
For 9c, and 9c for 8c. Therefore, the spot on the light receiving element surface of the diffracted light is located on the light receiving element portion 6b side when the optical disk is far,
When the optical disk is near, it moves to the light receiving element portion 6a side.

As described above, the in-focus state and the out-of-focus state can be detected by the displacement of the light receiving element 6 at the boundary of the area dividing line 7, and the light receiving element 6 can be constituted by the two-part light receiving element. By dividing the light receiving element into three or four parts, it is possible to avoid an increase in cost of the light receiving element and an increase in size due to an increase in the number of wirings. Such an optical pickup is used, for example, in a compact disc player mounted on a car. When the ambient temperature of the optical pickup changes, for example, when the car is left in the hot sun, the light is emitted from the semiconductor laser 1. The wavelength of the light beam fluctuates, and the beam diffraction angle at the hologram element 2 changes. However, the positional deviation of the light beam spot due to the change of the diffraction angle is along the region dividing line 7 as shown by the dotted line in FIG. , 6b received light amount (or received light amount ratio)
Has little effect on Therefore, a change in the environmental temperature does not affect the amplitude of the S curve in the optical pickup and does not cause an offset, thereby preventing a reduction in the reliability of the focus control.

In this embodiment, the divided element portions 6a and 6a of the light receiving element 6 divided by the area dividing line 7 are used.
Since b is formed in a substantially rectangular shape with the region dividing line 7 as a longitudinal direction, the allowable range for the displacement of the light beam spot along the region dividing line 7 becomes large, and a larger environmental temperature change Can be handled. Further, by making the two light receiving element portions for tracking control into a rectangular shape and aligning the longitudinal direction thereof with the direction of the region dividing line 7, the reliability of the tracking control with respect to the environmental temperature change can be enhanced.

The hologram element 2 is arranged to be inclined so as to have at least the angle component around the X axis, and the position of the light beam spot at the boundary of the area dividing line 7 based on the distance of the optical disk 5 This is because the hologram element 2 only needs to have a component in the X-axis direction as an axis around the axis in order for a change to appear. Of course, in order to make the position change of the light beam spot at the boundary of the area dividing line 7 based on the distance of the optical disk 5 appear best (that is, to obtain an S-curve with small distortion and large amplitude), this embodiment is used. As shown in the above, the hologram element 2 may be arranged to be inclined around the X axis.

Further, even if the hologram element 53 used in the conventional example shown in FIG. 7 and used is inclined, the above-described effects can be obtained. In other words, when the hologram element 53, which is not assumed to be used at an angle as described above, is used at an angle, aberration occurs in the light beam transmitted through the hologram element. Alternatively, even when the hologram element itself has an astigmatism effect, the above-described effect can be obtained. However, since the spot shape of the light beam is distorted, there is a possibility that the shape of the S-curve is asymmetric between the upper side and the lower side. It is preferable to use a hologram pattern in which all aberrations are corrected so that the spot in the focused state has no distortion (becomes a clean circle). FIG. 5 is an explanatory diagram showing an example of a schematic pattern of a hologram element for obtaining a diffraction effect in a predetermined direction. However, the hologram pattern in which all the aberrations are corrected is the same as the pattern shown in FIG. No big difference.

The inclination angle of the hologram element 2 is determined based on the S curve required for the optical pickup. That is, the inclination angle of the hologram element 2 is set in a range necessary to obtain an S-curve in a range satisfying a shape with small amplitude and distortion required for performing focus control properly.

In this embodiment, the case where the distance between the hologram element 3 and the light receiving element 6 is shorter than the distance between the hologram element 3 and the semiconductor laser 1 has been described. Needless to say, the distance may be longer than the distance between the element 3 and the semiconductor laser 1. In such a reverse case, the direction of movement of the diffracted light spot with respect to the distance from the optical disk is opposite to that in the above embodiment. Further, an optical system in which the optical axis is bent as shown in FIG. 6 may be used.

[0031]

As described above, according to the present invention, since the number of divisions of the light receiving element can be reduced, the number of wirings to the divided light receiving element portion can be reduced and the thickness of the optical pickup can be reduced. Further, even when the environmental temperature changes, excellent effects such as not reducing the reliability of focus control can be obtained.

[Brief description of the drawings]

FIG. 1A is a vertical sectional front view schematically showing an optical pickup according to an embodiment of the present invention, and FIG. 1B is a vertical sectional side view of the same.

FIGS. 2A and 2C are plan views of the light receiving element according to the embodiment of the present invention, in which FIGS.
FIG. 2B is a diagram showing a focused state.

FIG. 3 is a plan view showing two divided element portions according to the embodiment of the present invention and showing an arrangement relationship with a hologram element and a semiconductor laser.

FIG. 4 is an explanatory diagram showing a state in which a spot forming position changes in the Y-axis direction based on the distance of the optical disk by the hologram element arranged at an angle according to the embodiment of the present invention.

FIG. 5 is a pattern diagram of the hologram element according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a case where the distance between the hologram element and the light receiving element is longer than the distance between the hologram element and the semiconductor laser according to another embodiment of the present invention.

7A and 7B are diagrams schematically showing a conventional optical pickup, in which FIG. 7A is a vertical sectional front view, and FIG. 7B is a vertical sectional side view.

8A and 8B are plan views of a conventional light receiving element, wherein FIGS. 8A and 8C show an out-of-focus state, and FIG. 8B shows an in-focus state.

FIG. 9 is a graph showing an S curve.

FIG. 10 shows a unit in which an optical system other than an objective lens of an optical pickup using a hologram element is integrated.
FIG. 3 is a perspective view when a thin optical pickup is configured.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser 2 3 beam diffraction grating 3 hologram element 4 objective lens 5 optical disk 6 light receiving element 6 a division element part 6 b division element part 7 area division line

Continuation of front page (56) References JP-A-61-208637 (JP, A) JP-A-3-147527 (JP, A) JP-A-9-120575 (JP, A) JP-A-57-167146 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B ^7/ 09-7/22

Claims (3)

(57) [Claims] 1. An optical pickup having a diffraction element for guiding a light beam reflected by an information recording medium to a light receiving element by a diffraction effect , wherein the optical axis of the light beam is a Z-axis,
The information recording medium when the folding element is arranged perpendicular to the Z axis
The diffraction direction of the light beam reflected by
When the axis in the plane including the axis and perpendicular to the Z axis is the X axis
The diffraction element is at least on a plane perpendicular to the Z axis.
On the other hand, with the X axis being a rotation axis.
Where the light receiving element is formed in parallel with the X axis.
An optical pickup having a score line . 2. The method according to claim 1, wherein the region dividing line is caused by a wavelength variation of a light source.
It is formed substantially along the direction in which the light guided to the light-receiving element moves.
The optical pickup according to claim 1, characterized in that they are. 3. A light receiving element divided by said area dividing line.
Of the divided element portion is substantially the same as the region dividing line in the longitudinal direction.
3. The device according to claim 1, wherein the device is formed in a rectangular shape.
An optical pickup according to any one of the above.