JPS63119025A - Optical pick-up device - Google Patents

Abstract

PURPOSE:To miniaturize light pick-up optical system and to detect a focus without being influenced by an environmental temperature change by unifying and providing a second lambda/4 plate and a convex lens mirror equipped with a reflecting part at a poralizing beam splitter, and providing a knife edge and a photodetecting element at the reflecting side of the convex mirror. CONSTITUTION:At a light path after it is S-poralized and reflected by a reflecting film 14a of a poralizing beam splitter 14, the second lambda/4 plate 17 is fitted in bringing it into close contact with the poralizing beam splitter 14, and a convex lens mirror 18 is provided in the front direction of the light path. The light through the second lambda/4 plate 17 is directed to the convex lens mirror 18, reflected by a reflecting part 18a, comes to be a converged light flux and directed to the second lambda/4 plate 17 side again. By passing through the second lambda/4 plate 17 two times, the light comes to be a P poralization again, is made incident on a poralizing beam splitter 1, and thereafter, transmits a reflecting film 14a, proceeds and is made incident on a two-divided photodetecting element 19 for detecting a focus at an opposite side while a part is enclosed by a knife edge 20.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical pickup device capable of recording and reproducing.

BACKGROUND ART Conventionally, there is an optical pickup device of this type as shown in FIG. First, the light from the semiconductor laser 1 (
(P-polarized light) is converted into parallel light by the coupling lens 2. Thereafter, after passing through a polarizing beam splitter 3 and a λ/4 plate 4 (it becomes circularly polarized light), it is focused by an objective lens 5 and irradiated onto an optical disk 6 as a spot of about 1 μm. Then, the reflected light from the optical disk 6 passes through the objective lens 5 and the λ/4 plate 4 again. This allows the light to
The light becomes polarized light, is reflected by the reflection 113a of the polarizing beam splitter 3, and enters the detection lens 7. In FIG. 2, the knife method is used as the focus detection method, so a part of the light from the detection lens 7 is blocked by the knife 8. The remaining light enters the two-split light receiving element 9 for focus detection. Note that a well-known push-pull method is used for track detection, but its optical system will be omitted.

Here, the detection principle of the Knifezi method will be explained with reference to FIG. First, FIG. 6A shows the optical disc 6 when it is in focus. That is, the optical disc 6 is placed at the focal position of the objective lens 5.
This is the case where In this case, since the optical disc 6 is located at the focal point, the reflected light from the optical disc 6 becomes parallel light when it passes through the objective lens 5 again. The light is then focused through the detection lens 7 onto a two-part light receiving element 9 installed at the focal point of the detection lens 7. P indicates the focal point. In such a state, if the two elements of the two-split light-receiving element 9 are A and B, their output relationship will be A=B.

On the other hand, FIG. 6B shows a case where the optical disc 6 is located at a position further away from the focal position of the objective lens 5. In this case, the reflected light from the optical disk 6 is transmitted to the objective lens 5.
After passing through, it becomes convergent light.

The condensing point P1 is located in front of the two-split light receiving element 9. As a result, in the two-split light receiving element 9, more light is incident on the B element side. In other words, the output relationship is B>A.

Further, FIG. 6C shows a case where the optical disc 6 is located at a position closer than the focal position of the objective lens 5. In this case, since the reflected light from the optical disc 6 passes through the objective lens 5 and becomes diverging light, the focal point P is located at a position further back than the two-split light-receiving element 9. As a result, in the two-split light receiving element 9, more light is incident on the A element side. In other words, the output relationship is B<A.

That is, considering these illustrated states, a focus signal can be obtained by calculating the output difference A-B between elements A and B of the two-split light receiving element 9.

However, in such conventional Naifetsugi method,
In order to improve the sensitivity of focus detection, it is necessary to use a long focal length detection lens 7. As a result, the optical pickup optical system becomes larger. Also, it is easily affected by environmental temperature changes. This point will be further explained. Various optical components in an optical pickup can be displaced due to temperature changes. Among these, the tilt of the polarizing beam splitter 3 has the greatest influence. As shown in FIG. 5, if the polarizing beam splitter 3 is tilted due to a change in environmental temperature, the reflected light from the polarizing beam splitter 3 will be emitted at an angle twice that tilted.

Therefore, even when focusing as shown in Fig. 4(a), if the polarizing beam splitter 3 is tilted as shown in Fig. 5, more light will be incident on one of the light receiving elements, causing an offset in the focus signal. occurs. In other words, focus detection errors are likely to occur due to environmental temperature changes.

OBJECTS The present invention has been made in view of these points, and it is an object of the present invention to provide an optical pickup device that has a small and compact configuration and is capable of detecting a focus without being affected by environmental temperature changes.

Structure In order to achieve the above object, the present invention provides an optical pickup device that records or reproduces information by condensing light emitted from a semiconductor laser onto an optical disk using an objective lens. In between, a polarizing beam splitter, a first λ/4 plate, and the objective lens are arranged in order from the semiconductor laser side to set an incident optical path to the optical disk, and the reflected light from the optical disk is directed to the objective lens and the objective lens. In the optical path after passing through the first λ/4 plate and the polarizing beam splitter, a second λ/4 plate and a convex lens mirror having a reflective section by applying reflection treatment to the curved side are integrated into the polarizing beam splitter. A knife and a light receiving element are arranged in the optical path after the reflected light from the reflection part of the convex lens mirror passes through the second λ/4 plate and the polarizing beam splitter.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 and 2. First, a semiconductor laser 11 that emits P-polarized laser light is provided. Optical discs 12 to be recorded or reproduced are provided facing each other and separated from each other. Between these semiconductor lasers 11 and the optical disk 12, there are coupling lenses 13 that sequentially convert the light beam into parallel light from the semiconductor laser 11 side. A polarizing beam splitter 14 equipped with a reflective film 14a that transmits P-polarized light, and a first λ/4 plate 1
5 and an objective lens 16 for condensing the light circularly polarized by the first λ/4 plate 15 are arranged linearly in order,
An incident optical path to the optical disc 12 is formed.

The reflected light from the optical disk 12 passes through the objective lens 16 and the first λ/4 plate 15 again, becomes S-polarized light, and is reflected by the reflective film 14a of the polarizing beam splitter 14. , first, the second λ゛/4 plate 1
7 is attached closely to this polarizing beam splitter 14. Furthermore, a convex lens mirror 18 is placed in front of the optical path.
is provided. This convex lens mirror 18
This second λ/4 plate 7 is also adhesively fixed to one surface of the polarizing beam splitter 14 to be integrated with the second λ/4 plate 7. These may be integrally fixed using a connecting member). The curved back surface side of the convex lens mirror 18 is coated with a reflective film to form a reflective portion 18a.

Further, the light incident on the reflection part 18a of the convex lens mirror 18 is reflected and passes through the second λ/4 single-plate 7-polarized beam splitter 14, but the subsequent optical path includes a focus detection 2 A divided light receiving element 19 is arranged. Further, a knife 20 is provided in the middle of the second optical path. In other words, these light receiving elements 19 and knife 20
is the second λ/4 plate 1 for the polarizing beam splitter 14.
It is arranged on the opposite side to the seven-convex plate lens mirror 18.

In such a configuration, the P-polarized light from the semiconductor laser 11 is transmitted through the polarization beam splitter 14, and is further transmitted through the first polarization beam splitter 14.
When the light passes through the λ/4 plate 15, it becomes circularly polarized light. The light is then condensed by the objective lens 16 and placed on the optical disk 12.
A spot of about 1 μm is formed on the top. Then, the reflected light from the optical disk 12 passes through the objective lens 16 again, and then passes through the first λ/4 plate 15 again. As a result, the light becomes S-polarized light and enters the polarization beam splitter 14. As a result, the light is reflected by the reflective film 14a without passing through the reflective film 14a, and is emitted separated from the incident light. At this time, since the second λ/4 plate is made of one plate, the light becomes circularly polarized light again. The light from the second λ/4 plate 7 is directed toward the convex lens mirror 18, and is reflected by the reflecting portion 18a to become convergent light, which is then transferred to the second λ/4 plate 1 side 7.
Side view.

Here, by passing through this second λ/4 plate 7 times, the light becomes P-polarized light again. Therefore, after entering the polarizing beam splitter 14, the light passes through the reflective film 14a and enters the two-split light receiving element 19 for focus detection on the opposite side while being partially blocked by the knife 20. This allows for focus detection.

The characteristic points of the method of this embodiment will be explained. First, the lens that functions as a detection lens is the convex lens mirror 18.
Since the light after reflection becomes convergent light and is placed in the polarizing beam splitter 14 on the side opposite to the knife 20 and the light receiving element 19, the focus detection optical path can be folded and miniaturized. , space can be used effectively, and the optical pickup can be made smaller. Also, the second λ/4
Since the plate 17 and the convex lens mirror 18 are integrated into the polarizing beam splitter 14, even if the polarizing beam splitter 14 is tilted due to a change in environmental temperature, the convex lens mirror 18 etc. will also tilt in the same direction. FIG. 2 shows a state in which the polarizing beam splitter 14 is tilted by an angle θ. In this state, the light reflected by the reflective film 14a of the polarizing beam splitter 14 is also tilted by the angle e. However, the convex lens mirror 18 also has an angle θ at the same time.
are tilted in the same direction, and the light reflected by the reflecting portion 18a of the convex lens mirror 18 is partially tilted and cancelled. Therefore, no offset occurs in the focus signal detected by the two-split light receiving element 19, and focus detection errors can be reduced.

Effects In addition to the general configuration of an optical pickup as described above, the present invention integrates a second λ/4 plate and a convex lens mirror with a reflecting section into a polarizing beam splitter, and improves the reflection of the convex lens mirror. Since the knife and light receiving element are provided on the side, it is possible to miniaturize the optical pickup optical system and prevent offset from occurring in the detection signal even if the polarizing beam splitter is tilted due to changes in the environmental temperature. It is possible.

[Brief explanation of the drawing]

Fig. 1 is a side view showing an embodiment of the present invention, Fig. 2 is a side view showing an enlarged part of the incline, Fig. 3 is a side view showing a conventional example, and Fig. 4 is a side view showing the Naifetsu method. FIG. 5 is a side view illustrating the detection principle, and FIG. 5 is a side view illustrating the occurrence of offset. 11... Semiconductor laser, 12... Optical disk, 14
...Polarizing beam splitter, 15...first λ/4
Plate, 16... Objective lens, 17... Second λ/4 plate, 18... Convex lens mirror, 18a... For reflective section
Applicant Ricoh Co., Ltd. 1 zu go 1 J, l Figure 7. 5,3 Figure A~1?

Claims (1)

[Claims] In an optical pickup device that records or reproduces information by condensing light emitted from a semiconductor laser onto an optical disk using an objective lens, a polarizing beam splitter is provided between the semiconductor laser and the optical disk in order from the semiconductor laser side; A first λ/4 plate and the objective lens are arranged in order to set an incident optical path to the optical disc, and the reflected light from the optical disc is transmitted to the objective lens and the first λ/4 plate.
A second λ is added to the optical path after passing through the plate and the polarizing beam splitter.
A λ/4 plate and a convex lens mirror having a reflective portion subjected to reflection treatment on the curved surface side are integrated into the polarizing beam splitter, and the reflected light from the reflective portion of the convex lens mirror is reflected from the second λ/4 plate. and an optical pickup device, characterized in that a knife edge and a light receiving element are arranged in the optical path after passing through the polarizing beam splitter.