JPH05307760A - Optical pickup - Google Patents

Abstract

PURPOSE:To adjust the offset of a focus error signal and to reduce an offset amt. by providing a unit integrating a semiconductor substrate and a hologram in the direction nearly perpendicular to a diffractional direction by the hologram movably. CONSTITUTION:After a beam outgoing from a semiconductor laser 9 is reflected by a mirror surface 6b, is separated to three beams by a grating 8a and respective beams irradiate a recording medium through a diaphragm 2 and an objective lens 3. The return beams of three beams from the recording medium 4 are made incident on a hologram pattern 8b passing through a reverse path and diffracted and the + or -1-order diffracted beams of the main beam are made incident on central photodetectors 12, 15 respectively and the + or -1st-order diffracted beams of one side sub beam are made incident on e.g. the photodetectors 11, 14 and the + or -1st-order diffracted beams of the other side sub beam are made incident on the photodetectors 13, 16 respectively. Since the hologram pattern 8b is constituted so as to impart reverse dirrectional power each other to the + or -1st-order diffracted beams, e.g. the + or -1st-order diffracted beam among respective beams focuses backward the substrate 6 and the -1st-order diffracted beam focuses forward the substrate 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in a recording / reproducing apparatus for recording and / or reproducing information on an optical information recording medium such as an optical disk.

[0002]

2. Description of the Related Art As conventional optical pickups, for example, Sharp Technical Report (September 1989) and Japanese Patent Laid-Open No. 1-22.
A hologram pickup using a hologram is disclosed in Japanese Patent Application No. 0133, and the applicant of the present invention also discloses Japanese Patent Application No. 2-23.
No. 7236 proposes a hologram pickup in which a semiconductor substrate having a semiconductor laser and a photodetector and a hologram are integrated.

[0003]

However, in the hologram pickup disclosed in the above-mentioned Sharp Technical Report, the semiconductor laser and the photodetector are mounted on a single stem, and then the cap is attached and then the cap is mounted on the cap. The hologram is bonded and fixed to the semiconductor laser,
The photodetector and the hologram are integrated, but when positioning the hologram, the CD is actually reproduced by mounting it on a pickup that serves as a reference, and the intensity, balance, etc. of the signal generated from the output of the photodetector and the CD. While monitoring the jitter value of the reproduction signal, the hologram is moved and adjusted so that the offsets of the focus error signal and the tracking error signal become zero when the jitter value of the CD reproduction signal becomes minimum. For this reason, when they are integrated, there is a problem that the number of man-hours for attaching and detaching to the standard pickup is increased and the cost is increased.

The hologram pickup disclosed in Japanese Unexamined Patent Publication No. 1-220133 and Japanese Patent Application No. 2-2372.
In the hologram pickup proposed in No. 36, even if the hologram is mounted with high accuracy, the mounting accuracy is limited, so that there is a problem that a focus offset occurs when the focus error signal is obtained by the beam size method.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an optical pickup properly configured so that the offset of a focus error signal can be sufficiently reduced and the cost can be reduced. And

[0006]

In order to achieve the above object, in the first invention of this application, a semiconductor laser provided on the same semiconductor substrate and a plurality of photodetectors each having a plurality of light receiving regions, and The converging optical system for irradiating the optical information recording medium with the light emitted from the semiconductor laser, and the reflected light from the optical information recording medium are diffracted into two light fluxes by applying powers in mutually opposite directions to each other. An optical pickup having a hologram to be incident on a detector, wherein a focus error signal for the optical information recording medium of the converging optical system is obtained based on outputs of the plurality of photodetectors. The hologram is integrated as a unit, and this unit is moved to the pickup base in a direction substantially orthogonal to the diffraction direction of the hologram. Capable provided, constituting as capable of adjusting the offset of the focus error signal.

Further, in the second invention, a semiconductor laser provided on the same semiconductor substrate and a plurality of photodetectors each having a plurality of light receiving regions, and light emitted from the semiconductor laser are applied to the optical information recording medium. A converging optical system, and a hologram for diffracting reflected light from the optical information recording medium into two light beams by applying powers in mutually opposite directions and making the light beams enter the plurality of photodetectors. In an optical pickup in which a focusing error signal for the optical information recording medium of the converging optical system is obtained based on the output of a photodetector, the semiconductor substrate and the hologram are integrated as a unit, and the unit is a pickup base. On the other hand, it is rotatably provided around an axis in the diffraction direction of the hologram with the light emitting point of the semiconductor laser as the center. It is configured to be adjusted to offset of the focus error signal.

[0008]

In the first aspect of the invention, when the unit is moved in the direction substantially orthogonal to the diffraction direction of the hologram, the spots on the plurality of photodetectors are displaced in the dividing direction of the light receiving area. This makes it possible to adjust the offset of the focus error signal.

Further, in the second invention, when the unit is rotated around the axis of the diffraction direction by the hologram having the light emitting point of the semiconductor laser as the center, the spots on the plurality of photodetectors are spotted on the first detector. In the same manner as in the invention of, since each of them is displaced in the dividing direction of the light receiving region,
This makes it possible to adjust the offset of the focus error signal.

[0010]

1 shows a first embodiment of the present invention. In this embodiment, the semiconductor laser, the photodetector and the hologram are unitized, the light emitted from this unit 1 is applied to the recording medium 4 through the diaphragm 2 and the objective lens 3, and the reflected light (return light) is reversed. A unit 1 is made to follow the path.

In the unit 1, as shown in the sectional view of FIG. 2, a semiconductor substrate 6 is provided on a substrate 5 and a spacer 7 is provided.
An HOE (Hologram Optical Element) 8 is provided via the above. As shown in the plan view of FIG. 3, a semiconductor laser 9 is mounted on the semiconductor substrate 6, and three photodetectors 11 and 12 are arranged on both sides of the semiconductor laser 9 in the x direction in the y direction. , 13 and 14, 15, 1
6 is formed. The central photodetectors 12 and 15
Are light receiving regions 12a, 12 divided into three in the y direction, respectively.
b, 12c and 15a, 15b, 15c. As shown in the partial sectional view of FIG. 4, the semiconductor laser 9 is mounted in a recess 6a formed by etching the semiconductor substrate 6, and the slope 6b formed by etching the recess 6a is used as a mirror surface. A light flux emitted in a direction parallel to the plane of the semiconductor substrate 6 is reflected by the mirror surface 6b in a direction substantially normal to the semiconductor substrate 6.

Further, as shown in FIG. 2, the HOE 8 has a grating for separating the light beam from the semiconductor laser 9 into three beams of one main beam and two sub-beams on the surface of the semiconductor substrate 6 side. 8a is formed, and the hologram pattern 8b is formed on the opposite surface. The hologram pattern 8b is formed so that the ± 1st-order diffracted lights of the return light from the recording medium 4 are given powers in opposite directions. In the x, y, z coordinates, the optical axis direction is the z axis, and the hologram diffraction direction is the x axis.

In the above structure, the light emitted from the semiconductor laser 9 is reflected by the mirror surface 6b, then separated into three beams by the grating 8a, and irradiated onto the recording medium 4 via the diaphragm 2 and the objective lens 3, respectively. To be done. The return lights of these three beams from the recording medium 4 follow the opposite paths, enter the hologram pattern 8b, and are diffracted respectively, and the ± first-order diffracted lights of the main beam are guided to the photodetectors 12 and 15 at the center. The ± 1st-order diffracted lights of one of the sub-beams are incident on the photodetectors 11 and 14, respectively.
The ± first-order diffracted lights of the other sub-beam enter the photodetectors 13 and 16, respectively. Since the hologram pattern 8b is configured to give powers in the opposite directions to the ± 1st order diffracted light, for example, the + 1st order diffracted light of each beam is focused behind the semiconductor substrate 6, and the −1st order diffracted light is forward. The focus will be on.

Here, the objective lens 3 is attached to the recording medium 4.
Is in the in-focus position, as shown in FIG. 5B, the spots 17 and 18 of the respective beams incident on the photodetectors 12 and 15 have the same size, and the centers of these spots 17 and 18 are the light receiving areas. 12a and 15a
5A and 5B when the objective lens 3 is closer to the recording medium 4 side than the in-focus position, and as shown in FIG. 5C when the objective lens 3 is farther away. , The sizes of the spots 17 and 18 are reversed depending on the direction of non-focus.
Therefore, the light receiving regions 12a, 12b of the photodetector 12,
If the outputs of 12c are A1, A2, A3 and the outputs of the light receiving regions 15a, 15b, 15c of the photodetector 15 are A4, A5, A6, the focus error signal FES can be obtained by the following formula 1. it can.

FES = (A1 + A5 + A6)-(A2 + A3 + A4)

The tracking error signal TES is
The outputs of the photodetectors 11, 13, 14, 16 are respectively B
1, B2, B3, B4 can be obtained from the following Equation 2 by the so-called three-beam method.

[Equation 2] TES = (B1 + B3)-(B2 + B4)

In this embodiment, as described above, the semiconductor substrate 6 on which the semiconductor laser 9 and the photodetectors 11 to 16 are mounted and the HOE 8 on which the grating 8a and the hologram pattern 8b are formed are integrated to form the unit 1. However, this unit 1 can be assembled while adjusting the position with a measuring microscope. When a sticking error occurs on the HOE 8 when assembling this unit 1,
The error is x, y of spots 17 and 18 in FIG.
Appears as a deviation in direction. Here, spots 17 and 18
The x-direction, that is, the deviation in the diffraction direction due to the hologram pattern 8b is the deviation along the direction of the dividing line of the photodetectors 12 and 15, and therefore does not have any adverse effect on the focus error signal, but the hologram pattern 8b The shift in the y direction orthogonal to the diffraction direction due to causes an offset in the focus error signal.

Therefore, in this embodiment, FIG. 1 and FIG.
As shown in, the unit 1 is attached to the pickup base 21 to which it is actually attached so as to be movable in the y direction. For example, as shown in FIG.
Is attached to the pickup base 21 by moving it by Δy in the y direction, the principal ray 31 passing through the center of the diaphragm 2 has a center P (x ′, y ′) = (0,
It goes through a point A (0, Δy ′) which is deviated from 0) in the y direction. Here, considering where the principal ray 31 is diffracted by the hologram pattern 8b on the outward path, generally, the equation f (x, y) of the hologram pattern used in the beam size method is expressed by the terms x ² and y ² . Since it can be expressed by the following formula 3 that contains,

F (x, y) = Fx + Gx ² + Hy ² −nλ = 0 where n is an integer, λ is a wavelength, and F, G, and H are constants. The relationship between the direction cosine (l, m, n) of the incident light on the hologram 8 and the direction cosine (l ', m', n ') of the diffracted light can be expressed by the following formula 4.

Equation 4] l '= l ± (F + 2Gx) m' = m ± 2Hy n '= (1-l' 2 -m '2) 1/2

From m '= m ± 2Hy in the above equation 4, it can be seen that the ray incident on y = 0 is not diffracted in the y direction but is diffracted only in the x direction. Therefore, if the unit 1 is not moved and mounted in the y direction, the chief ray 31 is incident on y = 0, and is thus diffracted only in the x direction, and the diffracted light goes on the x axis (x
Axial = center of photodetectors 12, 15.) On the other hand, if the unit 1 is moved in the y direction and attached, the chief ray 31
Will pass through y = Δy ′, and will also be diffracted in the y direction, and will go to a position deviated from the center of the photodetectors 12, 15 in the y direction.

As described above, when the unit 1 is moved and mounted in the substantially y direction, the chief ray shifts from the center of the photodetectors 12 and 15 in the y direction, so that the spots 17 and 18 are formed.
Also shifts substantially in the y direction, so that the deviation of the spots 17 and 18 caused by the above assembly error can be corrected and the offset of the focus error signal can be adjusted.

According to this embodiment, the semiconductor substrate 6 having the semiconductor laser 9 and the photodetectors 11 to 16 and the HOE 8 are provided.
It is possible to easily adjust the offset of the focus error signal with a simple configuration in which the unit 1 in which the and is integrated is simply attached to the pickup base 21 so as to be movable in a direction substantially orthogonal to the diffraction direction of the hologram pattern 8b. it can.

FIG. 7 shows a second embodiment of the present invention. In this embodiment, as shown in FIG. 4, the pickup base 2 is configured such that the unit 1 is rotatable about the x-axis about the apparent light emitting point 35 of the semiconductor laser 9 as a center.
It is attached to No. 1 and the other structures are similar to those of the first embodiment.

In such a configuration, the unit 1 is approximately x
When rotated about the axis, the chief ray of the return light passing through the center of the diaphragm 2 is the hologram pattern 8b, as in the first embodiment.
Since the light is incident on a portion deviated from the center of the optical axis in the y direction, the offset of the focus error signal can be easily adjusted with a simple configuration as in the first embodiment.

[0023]

As described above, according to the present invention, a semiconductor laser, a plurality of photodetectors each having a plurality of light receiving regions, and a hologram are integrated as a unit, and the unit is actually mounted on a pickup base. Since it is possible to adjust the offset of the focus error signal with a simple configuration that can be moved or rotated by
The offset of the focus error signal can be made small enough,
Moreover, it can be made inexpensive.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of the unit shown in FIG.

FIG. 3 is a plan view of the semiconductor substrate shown in FIG.

FIG. 4 is a partial cross-sectional view of the same semiconductor substrate.

FIG. 5 is a diagram for explaining a focus error signal detection operation in the first embodiment.

FIG. 6 is a diagram for explaining the adjustment operation of the offset of the focus error signal in the first embodiment.

FIG. 7 is a diagram showing a second embodiment of the present invention.

[Explanation of symbols]

 1 unit 2 diaphragm 3 objective lens 4 recording medium 5 substrate 6 semiconductor substrate 6a concave portion 6b mirror surface 7 spacer 8 HOE 8a grating 8b hologram pattern 9 semiconductor laser 11-16 photodetector 12a-12c, 15a-15c light-receiving area 17,18 Spot 21 pickup base

Claims (2)

[Claims] 1. A semiconductor laser provided on the same semiconductor substrate and a plurality of photodetectors each having a plurality of light receiving regions,
The converging optical system for irradiating the optical information recording medium with the light emitted from the semiconductor laser and the reflected light from the optical information recording medium are diffracted into two light fluxes by applying powers in opposite directions to each other. A hologram for entering a photodetector, wherein the focus error signal for the optical information recording medium of the converging optical system is obtained based on the outputs of the plurality of photodetectors. Also, the hologram is integrated as a unit, and the unit is provided so as to be movable with respect to the pickup base in a direction substantially orthogonal to the diffraction direction of the hologram so that the offset of the focus error signal can be adjusted. Characteristic optical pickup. 2. A semiconductor laser provided on the same semiconductor substrate and a plurality of photodetectors each having a plurality of light receiving regions,
The converging optical system for irradiating the optical information recording medium with the light emitted from the semiconductor laser and the reflected light from the optical information recording medium are diffracted into two light fluxes by applying powers in opposite directions to each other. A hologram for entering a photodetector, wherein the focus error signal for the optical information recording medium of the converging optical system is obtained based on the outputs of the plurality of photodetectors. The hologram is integrated as a unit, and the unit is provided rotatably around the axis of the diffraction direction of the hologram with the light emitting point of the semiconductor laser substantially at the center with respect to the pickup base.
An optical pickup having a structure capable of adjusting an offset of a focus error signal.