JPS62266745A - Optical pickup device - Google Patents

Abstract

PURPOSE:To guide the projection power of a light source efficiently by guiding light projected by the 1st optical system to the 2nd or the 3rd optical system by an optical path changing means and also guiding reflected light beams from both surfaces of a disk to an optical system including a photodetecting element. CONSTITUTION:When the top surface of the disk 12 is reproduced, a lambda/2 plate 4 is moved out of an optical path and light from a semiconductor laser 1 is passed through a diffraction grating 2 and a collimator lens 3 and split into three parallel light beams, which are made incident on a beam splitter 5. Its transmitted light changes from a linear polarized state to a circular polarized state by passing through a lambda/4 plate 6a and is guided to prism mirrors 7 and 8 and an objective lens 10 and focused on the top surface of the disk, and the light is reflected by the disk surface to impinge the lambda/4 plate 6a through the same optical path and change into a 90 deg.-rotated linear polarized state, so that information is outputted as an electric signal. Then when the lambda/2 plate 4 is put on the optical path, on the other hand, the polarizing direction becomes a linear polarized state which is 90 deg. rotated from that at the time of projection and crosses the incidence surface of the beam splitter 5 at right angles, so that the light is made incident on a photodetecting element 14 through a detection lens 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an optical pickup device capable of recording and/or reproducing data on both sides of a disc.

(B) Prior Art Conventionally, as an optical pickup device capable of recording and/or reproducing both sides of a disc, for example, Japanese Patent Laid-Open No. 59-2
The technique disclosed in Japanese Patent No. 21844 is publicly known.

In such a conventional technique, as shown in FIG. 2, light emitted from a semiconductor laser (21) first enters and is transmitted through a beam splitter (22) via an optical system. The transmitted light enters a half mirror (25) through a λ/4 plate (23) and a prism mirror (24) and is split, and each of the split lights passes through an optical system to a disk (26). ) surface is irradiated. The reflected light (information signal) from the disk surface is incident on the half mirror (25) through the same optical system as when it is incident on the disk surface, and is further divided there. Of the light divided by the half mirror (25),
The transmitted light is incident on the beam splitter (22) via the prism mirror (24) and the λ/4 plate (23), is reflected, and is incident on the light receiving element (27) via the optical system.

In the conventional technology mentioned above, a beam splitter is used to prevent the reflected light from the disk from entering the semiconductor laser, and a half mirror is used to split the optical path.
This requires a plurality of prism mirrors, which complicates the optical system, and furthermore, there are problems in that the light is considerably attenuated by the half mirror before it reaches the light receiving element from the semiconductor laser.

(c) Problems to be Solved by the Invention The present invention provides a pickup device that can read information recorded on both sides of a disc using a single light source and a light receiving element. This is an attempt to solve the problem that the use of multiple optical path splitting members complicates the structure of the device and that the light emitted from the light source is considerably attenuated before reaching the disk image or light receiving element. be.

(d) Means for Solving the Problems In order to solve the above problems, the present invention provides a first optical system including a light source, a second optical system that guides light to one side of the disk,
a third optical system that guides light to the other surface of the disk; a selection means that selects light that is guided to the second and third optical systems; and a light receiving element that receives reflected light from the disk surface. and an optical path changing means for changing the optical path in cooperation with the selecting means, the optical path changing means converting the light emitted from the first optical system into the second or third optical system. The light receiving element is arranged so as to guide each reflected light from both surfaces of the disk to an optical system including the light receiving element.

(E) Effect By configuring as described above, the present invention allows the light emitted from the first optical system to be controlled by the selection means and the optical path selection means.
It is guided to the second or third optical system. The light guided to the second or third optical system is incident on the disk surface and reflected there. This reflected light is incident on the optical path changing means through the same optical system as that at the time of incidence, and is guided to an optical system including a light receiving element.

(F) Embodiment FIG. 1 shows an embodiment of the present invention. (1) is a semiconductor laser, (2) is a diffraction grating that classifies the light emitted from the semiconductor laser (1) into three beams, and (3) is a diffraction grating that converts the light split by the diffraction grating (2) into parallel light. Collimator lens to convert,
(4) is a λ/2 plate that is a means of selecting light, and (5) is a λ
A polarizing beam splitter (hereinafter referred to as beam splitter) which together with the /4 plates (6a) and (6b) constitute the optical path changing means, (7), (8) and (9) are prism mirrors used to change the optical path. , (10) and (11) are objective lenses, (12) are disks, (13) are detection lenses, and (14)
) is a light receiving element.

The beam splitter (5) has a unique incident plane, and of the light incident on the beam splitter (5), only the light having a polarization direction parallel to the incident plane is transmitted to the beam splitter (5). can be transmitted through the joint surface (5a) of.

The emitted light from the semiconductor laser (1) is linearly polarized, and when the λ/2 plate (4) is removed from the optical path, the polarization direction of the emitted light is parallel to the incident plane of the beam splitter (5). The semiconductor laser (1) and beam splitter (5) are positioned so that

The operation of this embodiment configured as described above will be explained.

When reproducing the upper surface of the disk, the λ/2 plate (4) is moved out of the optical path and the semiconductor laser (1) is oscillated. )
By passing through the collimator lens (3), the light is split into three parallel beams and is incident on the beam splitter (5). As mentioned above, when the λ/2 plate (4) is moved out of the optical path, the polarization direction of the incident light of the beam splitter (5) is parallel to the plane of incidence, so the collimator lens ( The light emitted from the beam splitter (5)
). When this transmitted light passes through the λ/4 plate (6a), its polarization state is converted from linearly polarized light to circularly polarized light, and is guided to prism mirrors (7), (8) and objective lens (10), and is directed onto the top surface of the disk. focused. The focused light reads information recorded on the disk and is reflected from the disk surface. This reflected light enters the λ/4 plate (6a) through the same optical path as described above, but since the direction of rotation of the circularly polarized light is reversed when reflected from the disk surface, the λ/4 plate After passing through (6a),
The light has a linearly polarized state rotated by 90 degrees compared to when it is output from the semiconductor laser (1).

Therefore, the reflected light from the disk surface passes through the beam splitter (
5), since its polarization direction is perpendicular to the incident plane, it is reflected at the joint surface (5a) of the beam splitter (5) and is received through the detection lens (13). The light is incident on the element (14). Therefore, the light reflected from the disk surface is photoelectrically converted by the light receiving element (14), and the information on the disk is output as a photoelectric signal.

Next, when the λ/2 plate (4) is inserted into the optical path, when the emitted light from the semiconductor laser (1) passes through the λ/2 plate (4), the polarization direction is 90° compared to that at the time of emission. The state of linearly polarized light is rotated by 90 degrees, and since it is perpendicular to the plane of incidence of the beam splitter (5), it is reflected by the polarization plane (5a) and the optical path is 9 degrees.
Can be bent by 0°. The light bent in this way passes through the λ/4 plate (
6b), the polarized light becomes circularly polarized light, is guided to a prism mirror (9) and an objective lens (13), is focused on the lower surface of the disk, and is reflected after reading the information.

This reflected light is in a circularly polarized state in which the direction of rotation is opposite to that at the time of incidence, and as described above, when it passes through the λ/4 plate (6b) and enters the beam splitter (5), it becomes λ/4. 2
Compared to the polarization state of the light that passes through the plate (4) and enters the beam splitter (5), it has a linear polarization state rotated by 90°, which is parallel to the incident plane of the beam splitter (5). Therefore, the reflected light from the disk (12) passes through the beam splitter (5) and enters the light receiving element (14) via the detection lens (13).

As described above, in this embodiment, reflected light having information signals from each surface of the disk can be guided to the light receiving element without attenuating the intensity of the emitted light from the semiconductor laser.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, but can also be applied to disc recording devices and the like.

(G) Effects of the Invention According to the present invention, the light emitted from the light source is irradiated onto the disk surface and the light receiving element without being attenuated, so that the emitted power of the light source can be reduced, which is efficient.

Furthermore, since prism mirrors, half mirrors, etc. can be eliminated, the structure can be simplified and the device can be made more compact.

4. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a perspective view showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional example.

(1)...Semiconductor laser, (4)...λ/2 plate (selection means)
, (5) and (6a) (6b)...beam splitter and λ/4 plate (optical path polarization means), (12)...disk, (1
4)...Photodetector.

Claims (1)

[Claims] (1) a first optical system including a light source; a second optical system that guides light to one side of the disk; a third optical system that guides light to the other side of the disk; a selection means for selecting the light guided to the optical system of No. 3; a light receiving element for receiving the reflected light from the disk surface; and an optical path changing means for changing the optical path in cooperation with the selection means; The optical path changing means guides the light emitted from the first optical system to the second or third optical system, and guides each reflected light from both sides of the disk to the light receiving element. An optical pickup device characterized in that it is arranged so as to be guided into an optical system.