JPH0651109A - Polarizing prism device - Google Patents

Abstract

PURPOSE:To optionally control the intensity rate of three split light beams, facilitate handling, and efficiently utilize a member by interposing an azimuth rotator between the cemented surfaces of a 1st and a 2nd prism. CONSTITUTION:A rectangular prism 31 is formed in a rectangular outward shape by cutting a Y rod of, for example, artificial crystal to specific width at right angles to a Y axis and cutting this rectangular prism along its diagonal. The oblique surfaces of two crystal bodies of rectangular prisms 31 are cemented having their optical axes at right angles to each other to constitute what is called a Wollaston prism. In this case, the two rectangular prisms 31 are coupled with the azimuth rotator 32 of specific thickness between the oblique surfaces to constitute a polarizing prism 33. This azimuth rotator 32 is obtained by cutting, for example, artificial crystal so that its optical axis is parallel to a light beam made incident on the rectangular prism 31. This prism 33 is used to split the incident light beam 34 into an ordinary light beam 36, an extraordinary light beam 37, and their composite light beam 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing prism device having a simple structure.

[0002]

2. Description of the Related Art Conventionally, a polarization prism has been known as an optical component for separating incident light into linearly polarized light whose polarization planes are orthogonal to each other. There are various types of such polarizing prisms, and one of them is the Wollaston prism. In this way, the Wollaston prism that utilizes the polarization of light rays is made of a uniaxial crystal. One like this
As axial crystals, KDP, ADP, calcite, sapphire,
There are various crystals such as ZnS, ice, and quartz, and artificial quartz is commonly used in industrially produced optical devices. Synthetic quartz is chemically and physically stable, relatively inexpensive, has excellent optical properties, and unlike natural ores, it can be artificially synthesized, so stable supply is possible. . Moreover, since artificial quartz can be obtained in a uniform and constant shape, it has an advantage that the yield in obtaining a product from the crystal is significantly better than that of natural quartz. Such an optical component has been variously studied because it is used in an optical system for reading information recorded on an optical disc in an optical device such as an optical disc, which has recently received attention. When such a Wollaston prism is cut out from an artificial quartz crystal, for example, FIG.
A so-called Y rod 1 grown in the Y-axis (mechanical axis) direction as shown in the side view is cut from a cutting line 2 at a predetermined width d at right angles to the Y-axis direction, and further cut crystal The outer shape is formed into a substantially cubic shape. And
This cube is cut along the diagonal to obtain two right angle prisms. Then, for example, as shown in FIG. 7, the slopes of two right-angle prisms 3 whose Z-axis (optical axis) directions are orthogonal to each other are joined together by using a Canadian balsam or the like, and again shaped into a cube, so-called Wollaston prism. Is completed. In such a Wollaston prism, a ray 4 incident perpendicularly to the incident plane has an angle with respect to the incident ray and its plane of polarization is an ordinary ray 5 and an anomalous ray which are orthogonal to each other as shown in FIG. It can be separated into two components consisting of the ray 6. Thus, in an apparatus for reproducing information recorded on an optical disk, for example, using such a Wollaston prism, a transmitted light ray transmitted through the optical disk is separated into an ordinary ray and an extraordinary ray to reproduce a signal, and The focus of the optical system is adjusted so as to maximize the intensity.

FIG. 9 is a block diagram showing an outline of an example of such an optical device. A laser light source 7 such as a laser diode is shown in FIG.
The laser light 8 from the laser light is transmitted through the polarizer 9 through the optical disc 10 on which information is recorded. Then, the transmitted light of the optical disk 10 is split into two directions by the beam splitter 11, and one split light is measured by the first optical sensor 12. Further, the other split light of the beam splitter 10 has a polarization plane from the optical axis 4
The light is incident on the Wollaston prism 13 which is inclined by 5 ° and is divided into two light beams having different polarization planes, which are applied to the second and third optical sensors 14 and 15 to detect optical information. Then, for example, the above-mentioned first optical sensor 12
Is used to adjust the focus of the optical system with respect to the optical disk 10, and the second and third optical sensors 14 and 15 are adjusted.
The information recorded on the optical disk 10 is reproduced from the detection output of the above. However, such a device requires a relatively expensive beam splitter 11,
In addition, the Wollaston prism 13 must be accurately tilted by a certain angle with respect to the optical axis, so that the assembly is troublesome. Further, the second and third optical sensors 14 and 15
In order to provide sufficient intensity of light, it is necessary to form a special polarizing film on the beam splitter 10, for example, and there is a problem that the manufacturing is troublesome and the cost is high.

For this reason, for example, as shown in FIG. 10, there is also one in which the wave plate 16 is arranged between the beam splitter 11 and the Wollaston prism 13 so that the Wollaston prism 13 is arranged without being tilted. It is considered. However, in this kind of
Since the number of the optical components is increased due to the need for the / 2 wavelength plate 16, and since the optical components must be accurately positioned and arranged, the assembly is troublesome and the apparatus becomes large in size. .

Further, for example, Japanese Patent Laid-Open No. 63-11350.
As shown in No. 3, there is also one in which the optical axes of two crystal bodies constituting a polarizing prism are arranged so as to be non-orthogonal to each other with respect to the light incident surface. In such a polarization prism, for example, as shown in FIG. 11, the plane including the optical axis 17 of the incident light and the optical axis of one crystal prism 18 is the optical axis 17 and the other crystal prism 19 is the optical axis. Is non-perpendicular to the plane containing. According to such a polarization prism 20, the plane of polarization becomes non-perpendicular as shown in FIG. 12, for example. Then, 2 which constitutes the polarization prism
By appropriately selecting the inclination of the optical axis of each crystal, the incident light 21 is divided into a combined ray 22, an ordinary ray 23 having a certain angle with respect to the incident light 21, and a certain angle with respect to the incident light 21. It can be divided into three existing extraordinary rays 24. When such a polarization prism 20 is used, when the information recorded on the optical disc is read, the ordinary ray 23 and the extraordinary ray 24 can be obtained as the emitted light as shown in FIG. 13, and further, without using a beam splitter. A synthetic ray 22 can also be obtained. Then, the combined light beam 22 is detected by the first optical sensor 12, and the focus of the optical system is adjusted, and the ordinary light beam 2 is detected.
3 and the extraordinary ray 24 to the second and third optical sensors 14, 1
It is possible to reproduce the information detected by the method 5 and recorded on the optical disk 10. However, when such a polarizing prism is used, there is a difference in the intensities of the three separated rays. That is, the ordinary ray 23 and the extraordinary ray 24 have substantially the same intensity, whereas the intensity of the synthetic ray 22 is doubled. Therefore, the intensity of the ordinary ray 23 and the extraordinary ray 24 is 25% of that of the rays incident on the polarizing prism 20, respectively.
It will only be used for the reproduction of optical information. Therefore, when such a polarizing prism 20 is used, it is necessary to use a high-power laser diode, and such a laser diode is inevitably expensive. Further, when cutting out such a polarizing prism from artificial quartz, one of the two right angle prisms forming the polarizing prism is cut out at an angle of 45 ° with respect to the Y axis of the crystal, and the other is against the Y axis. It was necessary to cut at a right angle to form a rectangular parallelepiped, cut it along a diagonal line, and combine two types of prisms having different cutting angles. However, it is difficult to distinguish these two types of prisms from the outside. For this reason, there is a trouble such that an identification mark is provided in advance so that the two types of prisms can be easily identified at the time of assembly, and it is necessary to specify the direction of the optical path when using the prism. Mark was also needed.

[0006]

The present invention has been made in view of the above circumstances, and the intensity ratio of the three separated lights can be arbitrarily controlled, and the overall price is low and the handling is easy. It is an object of the present invention to provide a polarizing prism device that is easy and can efficiently use members.

[0007]

According to the present invention, in a polarizing prism in which first and second prisms made of a birefringent crystal are joined, an optical rotator is interposed between the joining surfaces of the first and second prisms. It is characterized by that.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A polarizing prism according to an embodiment of the present invention will be described in detail below with reference to the perspective view shown in FIG. 1 and the side view shown in FIG. In the figure, 31 is a right-angled prism made of a birefringent crystal such as artificial quartz. The rectangular prism 31 is, for example, a Y rod of artificial crystal cut at a right angle with respect to the Y axis to a rectangular parallelepiped shape, and the rectangular parallelepiped is cut along a diagonal line. The right-angled prism 31 can constitute a so-called Wollaston prism as shown in FIG. 7 by joining the slopes so that the optical axes of the two crystals are orthogonal to each other. Therefore, when the crystal body is cut out, for example, as shown in FIG. 5 and FIG. 6, it is sufficient to cut the crystal body at a predetermined width d in the direction perpendicular to the Y axis, and the material can be efficiently used. Then, the polarization prism 33 is configured by bonding the optical rotator 32 having a predetermined thickness to the inclined surfaces of the two right-angled prisms 31 so as to be bonded to each other. This optical rotator 32
Is, for example, an artificial quartz crystal cut so that its optical axis is parallel to the light rays incident on the rectangular prism.
If such a polarizing prism 33 is used, for example, as shown in FIG.
The incident ray 34 can be separated into an ordinary ray 36, an extraordinary ray 37, and a combined ray 35 in which the ordinary ray 36 and the extraordinary ray 37 are combined, as shown in FIG. The intensity ratio of the separated light beams 35, 36, 37 can be controlled according to the thickness of the optical rotator, and for example, the intensity of the three separated output lights can be adjusted to be equal to each other. 3A, 3B, and 3C show the optical axis (solid line) of the crystal and the polarization direction (broken line) of the light in the right-angle prism 31, the optical rotator 32, and the right-angle prism 31 on the rear side of the polarizing prism. FIG. 3 is a diagram of a plane of polarization showing the relationship of FIG. That is, in the right-angled prism 31 on the front side, as shown in FIG. 3A, the Z axis direction of the crystal is vertical and the polarization direction of the light beam is inclined by 45 ° with respect to the Z axis. In the optical rotator 32, as shown in FIG. 3B, the Z axis of the crystal is perpendicular to the incident light beam, and the polarization direction of the light beam rotates by an angle corresponding to the thickness of the optical rotator 32. Further, in the right-angled prism 31 on the rear side, as shown in FIG. 3C, the Z axis of the crystal is in the horizontal direction, and the light rays are two polarizations inclined by ± 45 ° with respect to the horizontal direction and the two polarizations. Yields a synthesized component of.

An outline of an apparatus for reading the information recorded on the optical disk using the polarizing prism 33 will be described with reference to the block diagram shown in FIG. That is, the laser light 42 from the laser light source 41 such as a laser diode is transmitted through the polarizer 43 through the optical disc 44 on which information is recorded. Then, the transmitted light of the optical disc 44 enters the polarization prism 33. The polarizing prism 33 separates the incident laser light 42 into a combined ray 45, an ordinary ray 46 and an extraordinary ray 47, which are a combination of an ordinary ray and an extraordinary ray. Therefore, the combined light beam 45 is transmitted to the first optical sensor 4
8 to adjust the focus of the optical system with respect to the optical disk, for example, and the ordinary ray 46 and the extraordinary ray 47.
To the second and third optical sensors 49 and 50, respectively,
For example, the information recorded on the optical disc 44 can be reproduced.

With such a polarizing prism 33, however, the intensities of the three separated lights can be controlled according to the thickness of the optical rotator. Therefore, if the intensities of the separated lights are made equal, the intensities of the respective output light beams are 33% of the intensities of the incident light. On the other hand, in the conventional polarizing prism as shown in FIG. 13, the intensity of the ordinary ray and the extraordinary ray is 25% of the incident ray, whereas in the case of the above embodiment, the intensity of these output rays is increased by about 33%. can do. Therefore, it is possible to reproduce optical information by using a relatively inexpensive laser diode and reduce the cost of the entire apparatus. Further, it is not necessary to dispose such a polarization prism 33 inclined with respect to the optical axis, and since the optical rotator 32 is integrated with the polarization prism 33 itself, positioning is easy and compact. Further, since the optical rotator 32 itself has a flat shape, it is possible to obtain a desired thickness with high accuracy by using an ordinary polishing apparatus. For example, the optical rotator 32 is cut slightly thicker than the desired thickness and then polished to obtain an accurate parallelism. A high-quality optical rotator having a desired thickness on a plane can be easily obtained. In addition, such a polarization prism 33
Since each of the right-angle prisms 31 may be cut out at the same angle with respect to the crystal axis of the birefringent crystal, it is easy to assemble, and the characteristic of the optical path is symmetrical with respect to the input / output light when used. There is an advantage that the direction is not limited. Therefore, for example, the volume of the optical system in an optical device such as an optical disk device can be made compact, the optical characteristics are good, and moreover, it is suitable for mass production and the cost can be reduced.

[0011]

As described above in detail, according to the present invention, it is possible to provide a polarizing prism having a small volume, good characteristics and suitable for mass production.

[0012]

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a side view illustrating the operation of the polarization prism of the present invention.

3 (a), (b) and (c) are diagrams showing the relationship between the optical axis of the crystal of each polarization plane of the polarization prism of the present invention and the polarization direction of a light beam.

FIG. 4 is a block diagram showing an outline of an optical device using the polarizing prism of the present invention.

FIG. 5 is a plan view for explaining cutting out of a conventional Wollaston prism from an artificial crystal of a Y rod.

FIG. 6 is a side view for explaining cutting out of a conventional Wollaston prism from an artificial quartz crystal of a Y rod.

FIG. 7 is a side view for explaining the operation of the conventional Wollaston prism.

FIG. 8 is a diagram showing a polarization plane of a conventional Wollaston prism.

FIG. 9 is a block diagram showing an example of an outline of an optical device using a conventional Wollaston prism.

FIG. 10 is a block diagram showing another example of the outline of an optical device using a conventional Wollaston prism.

FIG. 11 is a side view showing still another example of a conventional Wollaston prism.

12 is a diagram showing a polarization plane of the Wollaston prism shown in FIG.

13 is a block diagram showing an outline of an optical instrument using the Wollaston prism shown in FIG.

[Explanation of symbols]

 31 Right angle prism 32 Optical rotator 33 Polarizing prism

Claims (2)

[Claims] 1. A birefringent prism in which first and second prisms made of a birefringent crystal are cemented, wherein a polarization rotator is interposed between the cemented surfaces of the first and second prisms. apparatus. 2. A polarizing prism device according to claim 1, wherein the optical axis of the crystal of the optical rotator is arranged parallel to the incident light.