JPH04238121A - Focus detector - Google Patents

Abstract

PURPOSE:To allow high-accuracy registration by executing the registration of a reflection mirror in common use as photodetectors and a semiconductor laser element by the output of the photodetectors. CONSTITUTION:A semiconductor substrate 50 formed with the photodetectors 51 divided to >=2 parts for registration and the photodetectors 51, 53 for signal detection and the semiconductor laser element 61 are disposed on the same substrate 62. The exit light from a semiconductor laser chip 61 is detected and reflected in the region of the photodetectors 51. The registration of the semiconductor laser and the photodetectors is executed while the difference between the outputs of the photodetectors 51 are detected. The high-accuracy registration is thus possible.

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 A conventional technique disclosed in Japanese Unexamined Patent Publication No. 62-236152 is shown in FIG. 11 and will be described below.

A part of the light emitted from the laser diode 1 is monitored by a light receiving element 2 on the optical path, and based on the output of the light receiving element 2, an automatic output control device (hereinafter referred to as APC) is used.
), the amount of light irradiated onto the recording medium 3 can be maintained at an appropriate level.

[0004] Furthermore, a conventional technique disclosed in Japanese Patent Application Laid-Open No. 1-220133 is shown in FIGS. 12, 13, and 14, and will be described below.

In FIGS. 12 and 13, light emitted from a laser diode 11 passes through a collimator lens 12, a beam splitter 16, a λ/4 plate 19, a mirror 18, and an objective lens 13, and is focused on a disk 14, where optical information is transmitted. The reflected light containing the .lamda. In the hologram element 20, ±1st-order light that causes astigmatism in mutually opposite directions is generated, and spots 28 and 3 are formed on the photodetector.
form 0. Further, the zero-order light becomes a spot 29. The spots 28 and 30 have astigmatism in opposite directions, and when defocused, the spots 28 and 30 are as shown in FIG. 13(a).
, the shape is an ellipse as shown in (c). Here, the outputs of the photodetectors 21, 22, 23, 24, 25, 26 are A
1, A2, A3, A4, A5, A6, the focus error signal FES is: FES=(A1+A5+A6)-(A2+A3+A4)
It can be obtained by In this technique, focus error detection is performed using both the +1st-order light and the -1st-order light generated by the hologram element, so the amount of light can be used effectively and detection with high sensitivity is possible. Further, as shown in FIG. 14, a surface emitting laser 94 and photodetectors 21 to 26 are arranged on the same substrate 95. This eliminates the need for adjusting the photodetector when assembling the optical pickup, thereby reducing assembly man-hours and achieving low costs.

The technique disclosed in Japanese Patent Application Laid-Open No. 1-229437 is shown in FIGS. 15 and 16 and will be described below.

[0007] The focus error signal is
Similar to the one shown in Japanese Patent No.-220133, the hologram element 32 has a ±
It is obtained by generating primary light and receiving each light with a photodetector.

In this case, the light emitting section and the light receiving section are formed on the same semiconductor, and the active layer is subjected to forward bias and
This is achieved by applying a reverse bias. This makes it possible to arrange the photodetector and light source with high precision without any adjustment.

[0009] Japanese Unexamined Patent Application Publication No. 1-237939 includes FIG.
7 shows an element used in an optical pickup. The above element will be explained below using FIG. 17.

The above element includes a semiconductor substrate 43, a semiconductor laser 41, a prism 42 with a semi-transparent film, and photodetectors 45 and 46.
, a semiconductor protective layer 44 , and a semi-transparent film 47 attached in front of a photodetector 45 . Light 49a emitted from the semiconductor laser 41 is reflected by the semi-transparent surface 42a and heads toward the optical disk. The semi-radiated light 49b from the optical disk is
The light that passes through the semi-transparent surface 42a and enters the semi-transparent film 47 is received by the photodetector 45, and the light that is reflected from this film is reflected by the reflective surface 42c of the prism 42. , the light is received by the photodetector 46.

As described above, by providing the semi-transparent film 47 on the photodetector 45, the light incident on the photodetector 45 can not only be received but also reflected and guided to another photodetector 46. can. That is, the photodetector 45 plays the role of a light receiving element and a mirror, thereby realizing multiple functions and miniaturization of the element.

0012

[Problem to be solved by the invention] JP-A-1-22013
In the technique disclosed in Publication No. 3, the light source and the photodetector are separate bodies, resulting in an increase in the size of the device. Furthermore, in the technique shown in FIG. 14, the semiconductor laser must be mounted on the X-axis (FIG. 14) of the photodetector with very strict precision, and the method is quite cumbersome.

On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. 1-229437, the light receiving area of the photodetector is limited to the active layer, and light can only be received in a very narrow range. Therefore, it is difficult to perform focus detection with high sensitivity.

Furthermore, the technique disclosed in Japanese Patent Laid-Open No. 62-236152 does not disclose any means for using the output of the light receiving element on the optical path for adjusting the optical system.

Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 1-237939 does not disclose any means for using a light-receiving element having reflection and light-receiving functions for adjusting an optical system.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an optical pickup that can be easily adjusted and therefore inexpensive, and that can detect focus error signals with high sensitivity. purpose.

[0017]

[Means for Solving the Problems] In order to facilitate adjustment, the present invention includes a light-receiving element for focus error detection and a light-receiving element that reflects a light beam from a light source and functions as a light-receiving section on the same semiconductor substrate. A reflection/light receiving element is formed, and the semiconductor substrate on which the light source and the light receiving element are formed is mounted on the same substrate. The reflection/light receiving element is divided into two parts in at least one direction of the plane. When mounting the semiconductor substrate with a light-receiving section and the light source on the substrate, positioning is performed by differentially detecting the light flux from the light source using a reflection/light-receiving element.

[0018]

[Operation] In order to obtain a focus error signal with high sensitivity, an optical system is composed of a light source, the semiconductor substrate with the light receiving section, an optical element that generates a focus error detection beam, and an objective lens, and the beam generated by the optical element is By receiving the light with the focus error detection light receiving element, it is possible to capture a large amount of light and obtain a highly sensitive focus error signal.

[0019]

Embodiment FIGS. 1, 2, 3, and 4 are schematic diagrams showing a first embodiment of the present invention. In this embodiment, the same substrate 62
The light beam 54 emitted from the LD 61 is reflected by the reflection/light-receiving element 51 on the semiconductor substrate, passes through the hologram element 63, passes through the objective lens 64, and is directed to the disk. 65. The reflected light from the disk 65 is reflected by the objective lens 64.
The ±1st-order light enters the hologram element 63 and is received by the light-receiving elements 52 and 53, and the hologram element 63 imparts astigmatism to the ±1st-order light to transmit it to the light-receiving element 5.
2 and 53, the beam shapes of the ±1st-order lights are made to change in opposite directions. Here, the light receiving elements 52 and 53 are each divided into three parts. Moreover, the spot shapes on the light receiving elements 52 and 53 at the time of defocusing are as shown in (a) in FIG.
The shape will look like the schematic diagram shown in (c). Therefore, the focus error signal FES is transmitted to the light receiving elements 52a, 52b, 5
2c, 53a, 53b, 53c outputs A, B, C, D
, E, F, it can be obtained as FES=(A+E+F)-(B+C+D).

On the other hand, when mounting the light source 61 and the semiconductor substrate 50 with a light-receiving section on the substrate 62, the emitted light beam 54 of the LD 61 is monitored by the reflection/light-receiving element 51, and 51a
, 51b, the optical axis of the LD 61 and the light receiving elements 52, 53 are adjusted in the y direction. In the case of this embodiment, since the light receiving elements 52 and 53 are divided only in the y direction, the adjustment in the x direction may be rough.

FIG. 5 shows the light-receiving elements 58, 59 and the reflection/light-receiving element 57 of a second embodiment of the present invention, and the spot shapes (a) and (c) at the time of defocusing. The configuration is the same as that of the first embodiment, except that the light receiving elements 58, 59 and the reflection/light receiving element 57 are each divided into four parts, and the direction of the astigmatism of the ±1st order light generated in the hologram element is rotated by 45°. It has become.

The focus error signal FES is transmitted to the light receiving elements 58a, 58b, 58c, 58d, 59a, 59b, 5
9c, 59d outputs I, II, III, IV, V, V
When I, VII, VIII, FES=(I+III+VI+VIII)-(II+I
V+V+VII).

On the other hand, when mounting the LD 61 and the semiconductor substrate 50 with a light-receiving section on the substrate 62, the emitted light beam 54 of the light source 61 is monitored by the reflection/light-receiving element 57,
LD while looking at the output difference between +57d and 57b+57c
Adjust the optical axis of the light source 61 and the light receiving elements 58, 59 in the y direction, and adjust the optical axis of the light source 61 and the light receiving elements 58, 59 in the x direction while checking the output difference between 57a+57b and 57c+57d. Make adjustments.

FIGS. 6, 7, 8 and 9 show a third embodiment of the present invention. In this embodiment, an LD 71 mounted on the same substrate 72 and a semiconductor substrate 8 with a light receiving section are mounted on the same substrate 72.
0, the light beam 75 emitted from the LD 71 is reflected by the reflection/light receiving element 81 on the semiconductor substrate, passes through the prism 73 and the objective lens 74, and is projected onto the disk 75. The reflected light from the disk 75 passes through the objective lens 74 and enters the prism 7.
3, is reflected by a semi-transparent surface 90 and a reflective surface 91 within the prism, and is guided to a light receiving element 82. Here, disk 7
The reflected light from 5 is within the prism 73, and the surface 9 is inclined to the optical axis.
1.92, causing astigmatism. Therefore, the shape of the spot 83 on the light receiving element 82 at the time of defocusing is as shown in FIGS. 8(a) and (c), and the focus error signal FES is
When the outputs of are G, H, I, and J, it can be obtained as FES=(G+I)-(H+J).

Furthermore, when mounting the LD 71 and the semiconductor substrate 80 with a light receiving section, adjustments are made while monitoring the emitted light beam 76 of the LD 71 with the reflective light receiving element 81, as in the first and second embodiments.

Note that in the above-described embodiments of the present invention, if the reflective/light-receiving element is formed on silicon, it can be used as is, but a large reflectance cannot be obtained. Therefore, as shown in FIG. 10, for example, it is more effective to apply a metal or dielectric coating layer 93 on the reflective/light-receiving element to increase the reflectance.

Furthermore, the present invention is not limited to the above-described embodiments; for example, the imaging position of the ±1st-order light may be changed using a hologram element, and the focus error may be detected using the beam size method. You can also do that.

[0028]

[Effect of the invention] A reflection/light-receiving element is placed between the light-receiving elements for focus error detection, and the light beam from the light source is received and
Adjustments can be made easily by mounting the semiconductor substrate with a light receiving section and the light source on the same substrate while monitoring, and therefore the number of adjustment steps can be significantly reduced and costs can be reduced.

Furthermore, the +1st order light of the hologram element and -
By receiving both primary lights with a pair of focus error detection light receiving elements, the amount of light can be used effectively.
A highly sensitive focus error signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of a device according to a first embodiment of the present invention.

[Figure 2
] Schematic diagram of the structure of the light receiving element section in the first embodiment of the present invention

FIG. 3: Light emitting element in the first embodiment device of the present invention.
Schematic diagram of the structure of the light receiving element

[Figure 4] (a), (b), and (c) are schematic diagrams of spot shapes on the light receiving element in the same example device.

[Fig. 5] (a), (b), and (c) are schematic diagrams of spot shapes on the light receiving element in the second embodiment of the present invention.

[Figure 6
] Schematic diagram of the configuration of a device according to a third embodiment of the present invention

FIG. 7 is a schematic diagram of the structure of the light-receiving element section in the third embodiment of the present invention.

[Fig. 8] (a), (b), and (c) are schematic diagrams of spot shapes on the light receiving element in the third embodiment of the present invention;

[Figure 9
] Schematic diagram of the structure of the optical element section used in each embodiment of the present invention

FIG. 10 is a cross-sectional schematic diagram of a light-receiving element section that can be used in each example device of the present invention.

FIG. 11: Schematic diagram of the configuration of a conventional optical pickup device

[
FIG. 12: Schematic diagram of the configuration of the optical system part of another conventional optical pickup device

[Fig. 13] (a), (b), and (c) are schematic diagrams of the shape of a focused spot on a light receiving element in another conventional optical pickup device.

[Fig. 14] (a) and (b) are a plan view and a cross-sectional view of a light receiving element in the conventional optical pickup device.

FIG. 15: Schematic diagram of the configuration of another conventional optical pickup device

FIG. 16 is a schematic structural diagram of a light emitting element and a light receiving element used in another conventional optical pickup device.

FIG. 17 is a schematic diagram of the configuration of yet another conventional optical pickup device.

[Explanation of symbols]

1 Laser diode 2 Photo receiving element 3 Recording medium 4 Polarizing prism 5 Shaping prism 6 Critical angle prism 7 Half mirror 8 Information photodetector 9 Control photodetector 10 APC circuit 11 Laser diode 12 Collimator lens 13 Objective lens 14 Disc 15 Photodetector 16 Beam splitter 17 Condensing lens 18 Mirror 19　λ/4 plate 20 Hologram element 21-26 Photodetector 27 Photo receiving element 28-30 Light focus spot 31 Semiconductor laser 32 Hologram diffraction grating 33 Condensing lens 34 Optical disc 35 Semiconductor substrate 36-39 Photo-receiving element 40a Cap layer 40b p cladding layer 40c active layer 40d N cladding layer 40e n-type GaAs substrate 41 Semiconductor laser 42 Semi-transparent membrane prism 42a-42c Prism surface 43 Semiconductor substrate 44 Semiconductor protective layer 45, 46 Photodetector 47 Semi-transparent membrane 48 Resin 49a, 49b Optical path 50 Semiconductor substrate 51 Reflection/light receiving element 52, 53 Photo receiving element 54 Luminous flux 55, 56 Focused beam shape 57 Reflection/light receiving element 58, 59 Photo receiving element 61 Semiconductor laser 62 Base board 71 Semiconductor laser 72 Base board 73 Prism 74 Objective lens 75 Disc 76 Output luminous flux 80 Semiconductor substrate 81 Reflection/light receiving element 82 Photo receiving element 83 Light focus spot 90 Semi-transparent surface of prism 73 91 Reflection surface of prism 73 92 Transparent surface of prism 73 93 Coating film 94 Surface emitting laser 95 Semiconductor substrate

Claims (2)

[Claims] 1. At least a light source, a mirror surface that reflects the emitted light, an optical element that generates at least a focus error detection beam, a converging optical system that projects the reflected light onto an optical recording medium, and the optical recording medium. Consists of a focus error beam photodetector that receives reflected light from the medium.
The mirror surface and the photodetector are arranged on the same semiconductor substrate, and the mirror surface has the function of a photodetector divided into at least two parts, and the differential output of the photodetector allows A focus detection device characterized by adjusting the positions of a light source and a focus error beam photodetector. 2. The focus detection device according to claim 1, wherein the optical element for generating the focus error detection beam is constituted by a hologram element.