JPS6087442A - Polarized beam splitter - Google Patents

Abstract

PURPOSE:To prevent a stray beam from entering a detector by tilting slightly a polarized beam splitter to an optical axis, and therefore changing the traveling directions of a normal laser beam and the stray beam. CONSTITUTION:The solid and broken lines show the traveling routes of the normal laser and stray beams, respectively. A polarized beam splitter is attached in a slight tilted state of an angle DELTAtheta to the optical axis. As a result, the S polarized wave sent back from a disk 2 is reflected on a surface A at an angle 2DELTAtheta to an axis Y and made incident to a detector 4. While the stray beams travel in parallel to the axis Y and are never made incident on the detector 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a polarizing beam splitter used in an optical video disc player.

[Background of the invention]

Figure 1 is a schematic diagram showing an example of the configuration of a conventional pickup in an optical video disc player using a laser beam. 5 is a condenser lens, 6 is a diffraction grating, 7 is a quarter wavelength plate, 8 is a mirror, 9
is an objective lens, and 10 is a cylindrical lens.

Here, the A-plane of the polarizing beam splitter 1 transmits the P-polarized light emitted from the laser diode 6 to the disk 2.
The purpose of the polarizing beam splitter 1 is to separate the going and returning laser beams by reflecting the S-polarized light waves reflected from the disk 2 and guiding them to the detector 4.

Conventionally, the polarizing beam splitter 1 has a regular tetrahedral shape and is arranged so that the A plane is at an angle of 45° with respect to the optical axis to achieve the above purpose.

FIGS. 2 and 6 are explanatory diagrams for explaining the operation of a conventional polarizing beam splitter, respectively.

In such a conventional polarizing beam splitter, most of the incident light from the laser diode 6 passes through the A plane and enters the disk 9, as shown by the solid line in FIGS. The light is A as shown by the broken line in Figure 2.
It is reflected by the surface, further reflected by the B surface, and enters the detector 4.

Also, some of the light is reflected by the zero plane as shown by the broken line in Figure 3,
Further, it is reflected by the A plane and enters the detector 4.

When these two types of stray light (broken lines in the figure) enter the detector 4 in addition to the regular laser light (solid lines in the figure),
This caused problems such as a drop in the S/N ratio of the screen, leading to a decline in performance as a video disc player.

FIG. 4 is a schematic diagram showing another conventional example of a polarizing beam splitter, in which solid lines indicate regular laser light and broken lines indicate stray light.

As shown in Fig. 4, a conventional method to solve this problem is to change the direction of stray light by making the shape of the polarizing beam splitter not a regular tetrahedron, but by making the stray light generating surface angle with respect to the optical axis. However, this method has the disadvantage that the polarizing beam splitter becomes expensive.

[Purpose of the invention]

It is an object of the present invention to provide a polarizing beam splitter that eliminates the drawbacks of the prior art described above and that uses an existing narrow beam splitter to guide only regular laser light to a detector and prevent stray light from entering the detector. Our goal is to provide the following.

[Summary of the invention]

In order to achieve the above object, in the present invention, Ir! .

By tilting the polarizing beam splitter slightly with respect to the optical axis and changing the traveling direction of the regular laser beam and stray light, stray light was prevented from entering the detector.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained with reference to Fig. 5.4 Fig. 5 is a schematic diagram showing one embodiment of the present invention.0 In Fig. 5, the solid line is the normal traveling path of the laser beam, and the broken line is the normal traveling path of the laser beam. Shows the path of stray light.

In this embodiment, the polarizing beam splitter is mounted slightly inclined by an angle Δθ with respect to the optical axis.

Therefore, the S-polarized light returning from the disk 2 is reflected on the A plane in a direction at an angle of 2Δθ with respect to the Y axis, and is detected by the detector 4.
incident on . On the other hand, stray light does not enter the detector 4 because it travels parallel to the Y axis.

Next, the operation of this embodiment will be explained in more detail using FIGS. 6 and 7.

6 and 7 are explanatory diagrams for explaining the operation of the embodiment shown in FIG. 5, respectively.

As shown in FIG. 6, the polarizing beam splitter is slightly inclined at an angle Δθ with respect to the optical axis.

Here, the S-polarized light wave (regular laser light) returned from the disk
is reflected on plane A at an angle of 2Δθ with respect to YI111Jζ, and travels straight in the direction of the arrow.

On the other hand, stray light indicated by a broken line is reflected by surface A, then reflected by surface B, and travels straight in the direction of arrow M1.

Here, θ1=02=45°+Δθ, so,
θ3=Δθ.

Also, since it is 11/m, 03=θ4=Δθ.

Next, θ5=Δθ+θ3:2Δ0 Also, θ6=2×04=2Δθ Therefore, θ5=06.

Therefore, the Y-axis and the traveling direction M1 of stray light become parallel.

Similarly, in FIG. 7, the traveling direction M2 of the stray light generated by reflection at the zero plane is parallel to the Y axis.

As mentioned above, the traveling direction of the regular laser beam and the stray light can be changed by simply tilting the polarizing beam splitter slightly with respect to the optical axis, so by placing the detector only within the traveling path of the regular laser beam, , it is possible to prevent performance deterioration due to stray light entering the detector.

[Effects of the Invention] According to the present invention, since it is possible to prevent stray light from entering the detector, there is an effect of preventing performance deterioration such as a decrease in the S/N ratio of the screen and defective tracking. Furthermore, since an existing polarizing beam splitter can be used, it is possible to suppress the increase in cost due to the use of a special polarizing beam splitter.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of the configuration of a conventional pickup in an optical video disc player, Fig. 6 is an explanatory diagram to explain the operation of a conventional polarizing beam splitter, and Fig. 4 is a schematic diagram showing a configuration example of a conventional pickup in an optical video disc player. FIG. 5 is a schematic diagram showing another conventional example of a splitter, FIG. 5 is a schematic diagram showing an embodiment of the present invention, and FIGS. 6 and 7 are explanatory diagrams for explaining the operation of the embodiment in FIG. 5, respectively. , is. 1...Polarizing beam splitter 2...Disk 6...Laser diode 4...
Detector 5...Condensing lens 6...Diffraction grating 7...1/4 wavelength plate 8...Mirror 9...Objective lens 10-...Cylindrical lens A...Return light from disk Reflective surfaces B, C... Stray light generating surface Diagram 1 Figure 2 Sugar 3 Figure Man 4 [2] Portrait 57

Claims (1)

[Claims] 1) A polarizing beam splitter for a video display player, which consists of a polarizing reflecting surface that transmits incident light from a light source and guides it to a disk, and reflects the returning light from the disk and guides it to a detector, and a wall surface that surrounds the reflecting surface. Polarized light, characterized in that the beam splitter is slightly tilted with respect to the optical axis so that stray light generated by reflection on the wall surface is not transmitted or reflected by the reflective surface and enters the detector. beam splitter.