JPH07114745A - Optical pickup device - Google Patents

Abstract

PURPOSE:To miniaturize an optical pickup device, to make the device light in weight and to make the assembling of the device easy by using a light receiving element unit provided with a supporting body supporting a light receiving element and a parallel flat plate fixed to the supporting body and provided slantedly with respect to a light receiving plane. CONSTITUTION:The divergent light of a linearly polarized light emitted from a semiconductor laser 1 is collimated by a coupling lens 2 and transmits a polarizing beam splitter 3 and is converged on the recording surface of an optical recording medium 5 by an objective lens 4. A luminous flux (a detection light) reflected at the recording surface is collimated again by the objective lens 4 and is reflected at the polarizing beam splitter 3 and its polarizing direction is rotated by a lambda/2 plate 6 and is given a convergent inclination by a detection lens 7 and then is separated into two polarized components by a polarizing beam splitter 9. Then, one of polarized components is detected by a light receiving element 8 and the other component is made incident on a light receiving element unit 11 via a parallel flat plate 12 on whose incident plane a polarization separating film is provided and then detected by a light receiving element 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device, and more particularly, to a light receiving device including a support for supporting a light receiving element and a parallel plate attached to the support and inclined with respect to a light receiving surface. The present invention relates to an optical pickup device which is designed to be small and lightweight and easy to assemble by using an element unit.

[0002]

9 (a) and 9 (b) are configuration diagrams of a conventional optical pickup device, FIG. 9 (a) is an overall configuration diagram, and FIG. 9 (b) is a partially enlarged view. Incidentally, FIG. 9 is shown in JP-A-4-87041.
It is described in Japanese Patent Publication No. In the figure, 21 is a magneto-optical disk, 21a is a signal recording layer, 22 is a light source, 23 is a collimator lens, 24 is a beam splitter, 25 is an objective lens, 26 is a detection lens, 27 is a photodetector, and 28 is a photodetection element. , 29 is a uniaxial crystal plate, 30 is a housing,
31 is a lead wire.

A light beam is condensed and radiated on the surface of the signal recording layer 21a of the magneto-optical disk 21 to produce the signal recording layer 21a.
The light reflected by is detected by the photodetector 27. Light source 2
The collimator lens 23 collimates the luminous flux emitted from the beam No. 2 into a parallel luminous flux. The light flux transmitted through the collimator lens 23 is transmitted through the beam splitter 24 and is incident on the objective lens 25. The objective lens 25 focuses the incident light flux on the surface of the signal recording layer 21a of the magneto-optical disk 21.

The light flux applied to the surface of the signal recording layer 21a is reflected by the surface and again enters the objective lens 25. The light beam re-incident on the objective lens 25 is made into a parallel light beam and returns to the beam splitter 24. The light flux returning to the beam splitter 24 is reflected by the reflecting surface 24 a of the beam splitter 24, does not return to the collimator lens 23 side, and is detected by the detection lens 26.
Incident on. The detection lens 26 converges the incident light flux and focuses it on the light receiving surface of the photodetector element 28 of the photodetector 27.

The photo-detecting element 28 is mounted and supported on the inner rear surface of the housing 30. The opening on the front side of the housing 30 is formed in a shape inclined with respect to the light receiving surface of the photodetection element 28. A uniaxial crystal plate 9 is attached to the opening. The uniaxial crystal plate 9 is formed of a material such as quartz, rutile, or calcite on a flat plate.

The luminous flux transmitted through the uniaxial crystal plate 29 is
When passing through the uniaxial crystal plate 29, the traveling direction can be deflected according to the difference in the polarization direction. Further, since the uniaxial crystal plate 29 is tilted with respect to the optical axis of the detection lens 26, the signal recording layer 21a of the magneto-optical disk 21 is not affected by the light flux passing through the uniaxial crystal plate 29. Astigmatism is generated according to the defocus of the light beam irradiated on the surface. Therefore, the light receiving surface of the photo-detecting element 28 has a plurality of light receiving surfaces that respectively receive the light beams whose traveling direction is deflected by the uniaxial crystal plate 29.

However, since this conventional example is intended only for magneto-optical detection, a parallel plate is required to have a polarization separation function, and a uniaxial crystal is used as a material for the parallel plate. The uniaxial crystal is more expensive than general optical glass, which is an obstacle to cost reduction. The optical disc includes not only a magneto-optical disc formed by magneto-optical recording, but also a disc obtained by a change in intensity of detection light such as a CD or a disc formed by phase change recording. Therefore,
For such an optical disc, an optical element unit that can be used even if ordinary glass or plastic is used as a parallel plate is required for cost reduction.

FIG. 10 is another block diagram of a conventional optical pickup device, in which 41 is a semiconductor laser (LD) and 42 is a laser diode.
Is a coupling lens (CL), 43 is a beam splitter, 44 is an objective lens, 45 is a recording medium, and 46 is λ / 2.
A plate, 47 is a detection lens, 48 is a parallel plate, 49 is a polarization beam splitter (PBS), and 50 and 51 are light receiving elements. It should be noted that this configuration can also detect a magneto-optical signal.

The linearly polarized divergent light emitted from the semiconductor laser 41 is converted into parallel light by the coupling lens 42, transmitted through the polarization beam splitter 43, and the objective lens 4
The light is focused on the recording surface of the optical recording medium 45 by 4. The light beam reflected on the recording surface is collimated again by the objective lens 44, reflected by the polarization beam splitter 43, and guided to the detection system. The luminous flux guided to the detection system is a λ / 2 plate 46.
The polarization direction is rotated by the detecting lens 47, and the detection lens 47 has a converging tendency.
Since it is inclined with respect to the optical axis of 7, the parallel plate 48 gives astigmatism. The detection light transmitted through the parallel plate 48 is separated into two polarization components by the polarization beam splitter 49 and received by the light receiving elements 50 and 51, respectively. The light receiving element 50 is a four-division light receiving element, and performs focus detection by a so-called astigmatism method.
Reference numeral 1 denotes a two-divided light receiving element, which performs track detection by a so-called push-pull method. The magneto-optical signal is detected from the output difference between the light receiving elements 50 and 51.

As described above, as shown in FIG. 10, in the conventional optical pickup device having the light receiving element and the parallel plate, the light receiving element and the parallel plate are separately arranged and stored. Therefore, the configuration becomes complicated. Further, since it is necessary to maintain the positional relationship between the light receiving element and the parallel plate with high accuracy, the assembly adjustment is delicate,
There is a problem of lack of productivity.

[0011]

[PROBLEMS] The present invention has been made in view of the above circumstances, and a light receiving element, a support for supporting the light receiving element, and a parallel provided on the support and inclined with respect to the light receiving surface. It is an object of the present invention to provide an optical pickup device that uses a light-receiving element unit provided with a flat plate to reduce the size and weight along with the simplification of the configuration and facilitate the assembly.

[0012]

In order to achieve the above object, the present invention provides (1)
In an optical pickup device having a light source, an objective lens that collects a light beam from the light source on an optical information recording medium, and a light receiving element that detects signal light due to reflection from the optical information recording medium, a support for the light receiving element As the window member, a transparent parallel plate having a polarization separation film provided on the incident surface is used, and a light receiving element unit provided with the parallel plate inclined with respect to a plane perpendicular to the optical axis of the signal light is used. (2) use a parallel plate having a diffraction grating formed on at least one surface,
Further, (3) in (2), the surface of the parallel plate on which the diffraction grating is formed is the surface on the light receiving element side, and (4) an antireflection film is formed on the surface of the parallel plate. It is characterized by being provided. Hereinafter, description will be given based on examples of the present invention.

FIG. 1 is a block diagram for explaining an embodiment of an optical pickup device according to the present invention, in which 1 is a semiconductor laser (LD), 2 is a coupling lens (CL),
3 is a polarization beam splitter (PBS), 4 is an objective lens, 5 is an optical recording medium, 6 is a λ / 2 plate, 7 is a detection lens,
8 is a light receiving element, 9 is a polarization beam splitter (PBS),
Reference numeral 10 is a light receiving element, 11 is a light receiving element unit, 12 is a parallel plate, and 13 is a support.

The linearly polarized divergent light emitted from the semiconductor laser 1 is collimated by the coupling lens 2,
The light passes through the polarization beam splitter 3 and is focused on the recording surface of the optical recording medium 5 by the objective lens 4. The light beam (detection light) reflected by the recording surface is collimated again by the objective lens 4 and reflected by the polarization beam splitter 3 to obtain λ / 2.
The plate 6 rotates the polarization direction, the detection lens 7 gives a converging tendency, the polarization beam splitter 9 separates the two polarization components, one polarization component is detected by the light receiving element 8, and the other polarization component is detected. Light receiving element unit 11
And is detected by the light receiving element 10.

FIG. 2 is an enlarged view of the light receiving element unit in FIG. The parallel plate 12 is the support 1 of the light receiving element 10.
3 is attached to the light receiving surface 3 and is inclined with respect to the light receiving surface. The detection light reflected by the recording surface passes through the parallel plate 12 and is detected by the four-division light receiving element 10. in this case,
The material of the parallel plate 12 may be glass or plastic. Since the parallel plate 12 is inclined with respect to the optical axis of the detection lens 7, the detection light is convergent light, and astigmatism is generated. The light beam transmitted through the parallel plate 12 has a focus signal generated by one of the light receiving elements 10 by using the so-called astigmatism method according to the defocus of the light beam on the recording surface of the recording medium 5 due to such astigmatism. Can be detected.
The track signal can be detected by the other light receiving element 8 using the push-pull method. In this way, a magneto-optical signal is obtained from the output difference between the light receiving elements 8 and 10.

FIG. 3 is a diagram showing another embodiment of the optical pickup device according to the present invention. In the figure, 6a is a .lamda. / 4 plate, and other parts having the same functions as those in FIG. I am doing it. This configuration cannot be used for detection of a magneto-optical signal, and is suitable for obtaining a change in intensity of detected light as an information signal, such as CD or phase change recording. The linearly polarized divergent light emitted from the semiconductor laser 1 is collimated by the coupling lens 2 and transmitted through the polarization beam splitter 3.
It is converted into circularly polarized light by the λ / 4 plate 6a, and is condensed on the recording surface of the optical recording medium 5 by the objective lens 4. The light beam (detection light) reflected by the recording surface is again collimated by the objective lens 4 and is converted by the λ / 4 plate 6a into linearly polarized light whose polarization plane is rotated by 90 °. The light is reflected by the splitter 3, is given a converging tendency by the detection lens 7, enters the light receiving element unit 11, and is detected by the light receiving element 10.

As the light receiving element unit in this case, the light receiving element unit shown in FIG. 2 is used. That is, the parallel plate is attached to the support 13 of the light receiving element 10 and is provided so as to be inclined with respect to the light receiving surface, and the detection light passes through the parallel plate (the material may be glass, plastic, etc.) 12. Then, it is detected by the four-division light receiving element 10. Thus, the parallel plate 12 is inclined with respect to the optical axis of the detection lens 7, so that astigmatism occurs. Therefore, the focus error signal is detected by the so-called astigmatism method, the track error signal is detected by the push-pull method, and the Rf signal is obtained by the change in the sum light amount of the 4-division by the 4-division light receiving element.

FIG. 4 is a view showing still another embodiment of the optical pickup device according to the present invention. In the figure, 14 is a polarization separation film, and other parts having the same functions as those in FIG. I am doing it. A polarization separation film 14 is formed on the incident surface of the parallel plate 12 to perform polarization separation, and a magneto-optical signal is obtained from the two separated polarizations. In this case, the light receiving element 8 for detecting the polarized light reflected by the polarization separation film 14 needs to be provided outside. The focus error signal is detected by the four-division light receiving element 10 using the astigmatism method from the polarization component transmitted through the parallel plate 12.

FIG. 5 is a diagram showing still another embodiment (claim 2) of the optical pickup device according to the present invention.
Reference numerals 5 and 16 denote diffraction gratings, and other parts having the same functions as those in FIGS. 1 and 4 are designated by the same reference numerals. A parallel plate equivalent to the parallel plate 12 shown in FIG. 2 on which diffraction gratings 15 and 16 for separating polarized light are formed on both surfaces is used as a window member. The detection light having a convergence tendency by the detection lens 7 is separated into an S-polarized component (first-order light) and a P-polarized component (0-order light) by the first diffraction grating 15, and the S-polarized light of the first-order diffracted light is , Is diffracted by the second diffraction grating 16 in the same direction as the 0th order light, and detected by the light receiving elements 8 and 10, respectively.
A magneto-optical signal is obtained from the output difference between the two light receiving elements. Since the parallel flat plate 12 is inclined with respect to the optical axis like the parallel flat plate shown in FIG. 2, the focus error signal and the track error signal can be obtained by the same detection method as the detection method in FIG. In this case, either of the light receiving elements 8 and 10 may be a four-divided light receiving element. Further, either one may be a two-divided light receiving element, and the track signal may be detected by the two-divided light receiving element. Further, both may be divided into four, and the objective lens may be controlled based on both focus signals.

FIG. 6 is a diagram showing another embodiment of FIG. 5, in which 17 is a diffraction grating, 18 is a light receiving element, and other parts having the same functions as those in FIG. I am doing it. The diffraction grating 17 is provided on the incident surface of the parallel plate 12 and has a function of dividing the beam into a plurality of parts. In this example, the part having the track pattern is separated. A track error signal is obtained from the difference signal of the light receiving elements 10 and 18. A focus error signal can be obtained from the output of the four-division light receiving element 8 by the same detection method as that in FIG.

FIG. 7 is a diagram showing still another embodiment (claim 3) of the optical pickup device according to the present invention.
Is a diffraction grating, and other parts having the same functions as those in FIG. 6 are denoted by the same reference numerals. The diffraction grating 19 is provided not on the incident surface side of the parallel plate but on the emission surface side (the side facing the light receiving element). The light receiving element is configured to be sealed by the support 13 and the parallel plate 12. The signal detection method and the like are the same as in the case of FIG.

FIG. 8 is a view showing still another embodiment (claim 4) of the optical pickup device according to the present invention.
Is an antireflection film, and other parts having the same functions as those in FIG. 4 are denoted by the same reference numerals. By providing the antireflection film 20 on the incident surface of the parallel plate 12, the loss of the detection light is reduced. A film or a diffraction grating having other properties or equivalent properties may exist on the exit surface.

[0023]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: As a light-receiving element unit for receiving the detection light having a converging tendency by the detection lens, the light-receiving element, the support for supporting the light-receiving element, and the support attached to the support, By using a light-receiving element unit that is provided with a parallel plate that is inclined with respect to the light-receiving surface, the structure of the optical pickup device can be simplified and the assembling can be facilitated, resulting in lower cost and smaller size. Is achieved. Furthermore, the positional relationship between the parallel plate and the light receiving element can be maintained with high accuracy, and an optical pickup device that is resistant to changes over time can be provided. Further, it is not necessary to use a birefringent crystal as a material of the parallel plate, and a low cost material such as glass or plastic can be used, which leads to cost reduction. Further, since the polarization separation film is formed on the incident surface of the parallel plate, the polarization beam splitter can be omitted, and the polarization separation can be performed only by the light receiving element unit. (2) Effect corresponding to claim 2: Since the diffraction gratings for polarization separation are formed on both surfaces of the parallel plate, the magneto-optical signal can be detected only by the light receiving element unit. Further, a recording signal of a CD or a phase change medium can be detected. By using a hologram, several functions such as beam splitting can be combined into one element, and the cost can be reduced due to the effect of reducing parts. In addition, the two light receiving elements are divided into four, and the objective lens is controlled based on both focus signals, so that the objective lens can be controlled without being affected by so-called birefringence in the base of the recording medium. Position control can be performed accurately. (3) Effect corresponding to claim 3: Since the diffraction grating is sensitive to dust and dirt, the diffraction grating is provided on the exit side of the parallel plate, that is, the diffraction grating surface is inside the case, and the case is sealed. Therefore, the diffraction grating can be protected from dust and dirt. Further, since the plane of incidence of the parallel plate is a flat surface with nothing provided, the light receiving element unit itself is easier to handle than the case where the diffraction grating surface is exposed, and it can be wiped even if it becomes dirty. (4) Effect corresponding to claim 4: Since the antireflection film is provided on the incident surface of the parallel plate, the loss of detection light can be reduced,
Stable control signals and information signals can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an optical pickup device according to the present invention.

FIG. 2 is an enlarged view of a light receiving element unit in FIG.

FIG. 3 is a diagram showing another embodiment of the optical pickup device according to the present invention.

FIG. 4 is a diagram showing still another embodiment of the optical pickup device according to the present invention.

FIG. 5 is a diagram showing still another embodiment (claim 2) of the optical pickup device according to the present invention.

FIG. 6 is a diagram showing still another embodiment of FIG.

FIG. 7 is a diagram showing yet another embodiment (claim 3) of the optical pickup device according to the present invention.

FIG. 8 is a diagram showing still another embodiment (claim 4) of the optical pickup device according to the present invention.

FIG. 9 is a configuration diagram of a conventional optical pickup device.

FIG. 10 is another configuration diagram of a conventional optical pickup device.

[Explanation of symbols]

1 ... Semiconductor laser (LD), 2 ... Coupling lens (CL), 3 ... Polarization beam splitter (PBS), 4 ...
Objective lens, 5 ... Optical recording medium, 6 ... λ / 2 plate, 7 ... Detection lens, 8 ... Light receiving element, 9 ... Polarization beam splitter (P
BS), 10 ... Light receiving element, 11 ... Light receiving element unit.

Claims (4)

[Claims] 1. An optical pickup device comprising a light source, an objective lens for condensing a light flux from the light source onto an optical information recording medium, and a light receiving element for detecting signal light due to reflection from the optical information recording medium, A light receiving element unit in which a transparent parallel plate having a polarization separation film provided on an incident surface is used as a window member of a support of the light receiving element, and the parallel flat plate is inclined with respect to a plane perpendicular to the optical axis of the signal light. An optical pickup device characterized by using. 2. The optical pickup device according to claim 1, wherein a parallel plate having a diffraction grating formed on at least one surface is used. 3. The optical pickup device according to claim 2, wherein the surface of the parallel plate on which the diffraction grating is formed is the surface on the light receiving element side. 4. The optical pickup device according to claim 1, wherein an antireflection film is provided on the surface of the parallel plate.